MAIN OUTCOMES: The amplitude of velocity distribution is increased (decreased) at larger values of non-uniform parameter (cilia length). The non-uniform parameter played a vital role not only in the enhancement of circulation at the upper half of the channel but also the length of bolus increased. Results of straight channel are gained for larger value of the dimensionless radius of curvature parameter as well as cilia length.}, } @article {pmid33449773, year = {2020}, author = {Pan, Z and Nunes, JK and Stone, HA}, title = {Regime Map and Triple Point in Selective Withdrawal.}, journal = {Physical review letters}, volume = {125}, number = {26}, pages = {264502}, doi = {10.1103/PhysRevLett.125.264502}, pmid = {33449773}, issn = {1079-7114}, abstract = {Entrainment in selective withdrawal occurs when both the top and bottom phases are withdrawn through a capillary tube oriented perpendicular to a flat gravitationally separated liquid-liquid interface. The tube introduces two distinct features to the conditions for fluid entrainment. First, the ratio of the two phases being withdrawn is affected by the region of influence of the flow upstream of the tube's orifice. Second, a minimum withdrawal flow rate must be reached for entrainment regardless of the distance between the interface and the tube. We show that these phenomena can be understood based on the Reynolds number that governs the external flow field around the capillary tube and the capillary number that regulates the effect of the viscosity and capillarity.}, } @article {pmid33438620, year = {2020}, author = {Shit, GC and Bera, A}, title = {Mathematical model to verify the role of magnetic field on blood flow and its impact on thermal behavior of biological tissue for tumor treatment.}, journal = {Biomedical physics & engineering express}, volume = {6}, number = {1}, pages = {015032}, doi = {10.1088/2057-1976/ab6e22}, pmid = {33438620}, issn = {2057-1976}, abstract = {The numerical computation has been performed to study the effects of static magnetic field on thermal behavior of tumor surrounded by living biological tissues and blood vessels. A small rectangular shaped tumor enclosing the blood vessel surrounded by healthy tissue is considered. The model consists of two-layer composite system in which the microvessel for blood flow is considered as a fluid layer and the living biological tissue including tumor as a solid layer. The wave bioheat transfer equation in the tissue layer together with energy transport equation for blood flow layer has been used in the cylindrical polar coordinates. The analytical expression for blood velocity in the presence of magnetic field has been used from Gold's solution. The computational work has been performed by employing the Crank-Nicolson finite difference method. A comparison has been made to validate our numerical results with the previous solution by setting some parameters. The temperature profiles have been plotted at different locations of the axial tissue length for various values of the Hartmann number, Prandtl number, Womersley number and Reynolds number. It is observed that the application of magnetic field increases heat transfer rate within tumor tissues which in turn attribute to an enhancement of temperature about 316 K or above for hyperthermic treatment in cancer therapy.}, } @article {pmid33430317, year = {2021}, author = {Gnapowski, E and Pytka, J and Józwik, J and Laskowski, J and Michałowska, J}, title = {Wind Tunnel Testing of Plasma Actuator with Two Mesh Electrodes to Boundary Layer Control at High Angle of Attack.}, journal = {Sensors (Basel, Switzerland)}, volume = {21}, number = {2}, pages = {}, doi = {10.3390/s21020363}, pmid = {33430317}, issn = {1424-8220}, abstract = {The manuscript presents experimental research carried out on the wing model with the SD 7003 profile. A plasma actuator with DBD (Dielectric Barrier Discharge) discharges was placed on the wing surface to control boundary layer. The experimental tests were carried out in the AeroLab wind tunnel where the forces acting on the wing during the tests were measured. The conducted experimental research concerns the analysis of the phenomena that take place on the surface of the wing with the DBD plasma actuator turned off and on. The plasma actuator used during the experimental tests has a different structure compared to the classic plasma actuator. The commonly tested plasma actuator uses solid/impermeable electrodes, while in the research, the plasma actuator uses a new type of electrodes, two mesh electrodes separated by an impermeable Kapton dielectric. The experimental research was carried out for the angle of attack α = 15° and several air velocities V = 5-15 m/s with a step of 5 m/s for the Reynolds number Re = 87,500-262,500. The critical angle of attack at which the SD 7003 profile has the maximum lift coefficient is about 11°; during the experimental research, the angle was 15°. Despite the high angle of attack, it was possible to increase the lift coefficient. The use of a plasma actuator with two mesh electrodes allowed to increase the lift by 5%, even at a high angle of attack. During experimental research used high voltage power supply for powering the DBD plasma actuator in the voltage range from 7.5 to 15 kV.}, } @article {pmid33416336, year = {2020}, author = {Monsalve, E and Brunet, M and Gallet, B and Cortet, PP}, title = {Quantitative Experimental Observation of Weak Inertial-Wave Turbulence.}, journal = {Physical review letters}, volume = {125}, number = {25}, pages = {254502}, doi = {10.1103/PhysRevLett.125.254502}, pmid = {33416336}, issn = {1079-7114}, abstract = {We report the quantitative experimental observation of the weak inertial-wave turbulence regime of rotating turbulence. We produce a statistically steady homogeneous turbulent flow that consists of nonlinearly interacting inertial waves, using rough top and bottom boundaries to prevent the emergence of a geostrophic flow. As the forcing amplitude increases, the temporal spectrum evolves from a discrete set of peaks to a continuous spectrum. Maps of the bicoherence of the velocity field confirm such a gradual transition between discrete wave interactions at weak forcing amplitude and the regime described by weak turbulence theory (WTT) for stronger forcing. In the former regime, the bicoherence maps display a near-zero background level, together with sharp localized peaks associated with discrete resonances. By contrast, in the latter regime, the bicoherence is a smooth function that takes values of the order of the Rossby number in line with the infinite-domain and random-phase assumptions of WTT. The spatial spectra then display a power-law behavior, both the spectral exponent and the spectral level being accurately predicted by WTT at high Reynolds number and low Rossby number.}, } @article {pmid33404675, year = {2021}, author = {Klein, AK and Dietzel, A}, title = {A Primer on Microfluidics: From Basic Principles to Microfabrication.}, journal = {Advances in biochemical engineering/biotechnology}, volume = {}, number = {}, pages = {}, pmid = {33404675}, issn = {0724-6145}, abstract = {Microfluidic systems enable manipulating fluids in different functional units which are integrated on a microchip. This chapter describes the basics of microfluidics, where physical effects have a different impact compared to macroscopic systems. Furthermore, an overwiew is given on the microfabrication of these systems. The focus lies on clean-room fabrication methods based on photolithography and soft lithography. Finally, an outlook on advanced maskless micro- and nanofabrication methods is given. Special attention is paid to laser structuring processes.}, } @article {pmid33398321, year = {2021}, author = {Chen, W and Wen, Y and Fan, X and Sun, M and Tian, C and Yang, M and Xie, H}, title = {Magnetically actuated intelligent hydrogel-based child-parent microrobots for targeted drug delivery.}, journal = {Journal of materials chemistry. B}, volume = {}, number = {}, pages = {}, doi = {10.1039/d0tb02384a}, pmid = {33398321}, issn = {2050-7518}, abstract = {Small intestine-targeted drug delivery by oral administration has aroused the growing interest of researchers. In this work, the child-parent microrobot (CPM) as a vehicle protects the child microrobots (CMs) under a gastric acid environment and releases them in the small intestinal environment. The intelligent hydrogel-based CPMs with sphere, mushroom, red blood cell, and teardrop shapes are fabricated by an extrusion-dripping method. The CPMs package uniform CMs, which are fabricated by designed microfluidic (MF) devices. The fabrication mechanism and tunability of CMs and CPMs with different sizes and shapes are analyzed, modeled, and simulated. The shape of CPM can affect its drug release efficiency and kinetic characteristics. A vision-feedback magnetic driving system (VMDS) actuates and navigates CPM along the predefined path to the destination and continuously releases drug in the simulated intestinal fluid (SIF, a low Reynolds number (Re) regime) using a new motion control method with the tracking-learning-detection (TLD) algorithm. The newly designed CPM combines the advantages of powerful propulsion, good biocompatibility, and remarkable drug loading and release capacity at the intestinal level, which is expected to be competent for oral administration of small intestine-targeted therapy in the future.}, } @article {pmid33396499, year = {2020}, author = {Avila, K and Hof, B}, title = {Second-Order Phase Transition in Counter-Rotating Taylor-Couette Flow Experiment.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {1}, pages = {}, doi = {10.3390/e23010058}, pmid = {33396499}, issn = {1099-4300}, support = {ZF04B /2019/FB04 Avila_Kerstin//Central Reserach Development Fund of the University of Bremen/ ; }, abstract = {In many basic shear flows, such as pipe, Couette, and channel flow, turbulence does not arise from an instability of the laminar state, and both dynamical states co-exist. With decreasing flow speed (i.e., decreasing Reynolds number) the fraction of fluid in laminar motion increases while turbulence recedes and eventually the entire flow relaminarizes. The first step towards understanding the nature of this transition is to determine if the phase change is of either first or second order. In the former case, the turbulent fraction would drop discontinuously to zero as the Reynolds number decreases while in the latter the process would be continuous. For Couette flow, the flow between two parallel plates, earlier studies suggest a discontinuous scenario. In the present study we realize a Couette flow between two concentric cylinders which allows studies to be carried out in large aspect ratios and for extensive observation times. The presented measurements show that the transition in this circular Couette geometry is continuous suggesting that former studies were limited by finite size effects. A further characterization of this transition, in particular its relation to the directed percolation universality class, requires even larger system sizes than presently available.}, } @article {pmid33362423, year = {2020}, author = {Elsinga, GE and Ishihara, T and Hunt, JCR}, title = {Extreme dissipation and intermittency in turbulence at very high Reynolds numbers.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {476}, number = {2243}, pages = {20200591}, doi = {10.1098/rspa.2020.0591}, pmid = {33362423}, issn = {1364-5021}, abstract = {Extreme dissipation events in turbulent flows are rare, but they can be orders of magnitude stronger than the mean dissipation rate. Despite its importance in many small-scale physical processes, there is presently no accurate theory or model for predicting the extrema as a function of the Reynolds number. Here, we introduce a new model for the dissipation probability density function (PDF) based on the concept of significant shear layers, which are thin regions of elevated local mean dissipation. At very high Reynolds numbers, these significant shear layers develop layered substructures. The flow domain is divided into the different layer regions and a background region, each with their own PDF of dissipation. The volume-weighted regional PDFs are combined to obtain the overall PDF, which is subsequently used to determine the dissipation variance and maximum. The model yields Reynolds number scalings for the dissipation maximum and variance, which are in agreement with the available data. Moreover, the power law scaling exponent is found to increase gradually with the Reynolds numbers, which is also consistent with the data. The increasing exponent is shown to have profound implications for turbulence at atmospheric and astrophysical Reynolds numbers. The present results strongly suggest that intermittent significant shear layer structures are key to understanding and quantifying the dissipation extremes, and, more generally, extreme velocity gradients.}, } @article {pmid33362112, year = {2021}, author = {Foo, CT and Unterberger, A and Menser, J and Mohri, K}, title = {Tomographic imaging using multi-simultaneous measurements (TIMes) for flame emission reconstructions.}, journal = {Optics express}, volume = {29}, number = {1}, pages = {244-255}, doi = {10.1364/OE.412048}, pmid = {33362112}, issn = {1094-4087}, abstract = {The method of tomographic imaging using multi-simultaneous measurements (TIMes) for flame emission reconstructions is presented. Measurements of the peak natural CH* chemiluminescence in the flame and luminescence from different vaporised alkali metal salts that were seeded in a multi-annulus burner were used. An array of 29 CCD cameras around the Cambridge-Sandia burner was deployed, with 3 sets of cameras each measuring a different colour channel using bandpass optical filters. The three-dimensional instantaneous and time-averaged fields of the individual measured channels were reconstructed and superimposed for two new operating conditions, with differing cold flow Reynolds numbers. The contour of the reconstructed flame front followed the interface between the burnt side of the flame, where the alkali salt luminescence appears, and the cold gas region. The increased mixing between different reconstructed channels in the downstream direction that is promoted by the higher levels of turbulence in the larger Reynolds number case was clearly demonstrated. The TIMes method enabled combustion zones originating from different streams and the flame front to be distinguished and their overlap regions to be identified, in the entire volume.}, } @article {pmid33361564, year = {2020}, author = {Brum, J and Bernal, M and Barrere, N and Negreira, C and Cabeza, C}, title = {Vortex dynamics and transport phenomena in stenotic aortic models using Echo-PIV.}, journal = {Physics in medicine and biology}, volume = {}, number = {}, pages = {}, doi = {10.1088/1361-6560/abd670}, pmid = {33361564}, issn = {1361-6560}, abstract = {Atherosclerosis is the most fatal cardiovascular disease. As disease progresses, stenoses grow inside the arteries blocking their lumen and altering blood flow. Analysing flow dynamics can provide a deeper insight on the stenosis evolution. In this work we combined Eulerian and Lagrangian descriptors to analyse blood flow dynamics and fluid transport in stenotic aortic models with morphology, mechanical and optical properties close to those of real arteries. To this end, vorticity, particle residence time (PRT), particle's final position (FP) and finite time Lyapunov's exponents (FTLE) were computed from the experimental fluid velocity fields acquired using ultrasonic particle imaging velocimetry (Echo-PIV). For the experiments, CT-images were used to create morphological realistic models of the descending aorta with 0%, 35% and 50% occlusion degree with same mechanical properties as real arteries. Each model was connected to a circuit with a pulsatile programmable pump which mimics physiological flow and pressure conditions. The pulsatile frequency was set to ≈ 0.9 Hz (55 bpm) and the upstream peak Reynolds number (Re) was changed from 1100 to 2000. Flow in the post-stenotic region was composed of two main structures: a high velocity jet over the stenosis throat and a recirculation region behind the stenosis where vortex form and shed. We characterized vortex kinematics showing that vortex propagation velocity increases withRe. Moreover, from the FTLE field we identified Lagrangian Coherent Structures (i.e. material barriers) that dictate transport behind the stenosis. The size and strength of those barriers increased withReand the occlusion degree. Finally, from the PRT and FP maps, we showed that independently ofRe, the same amount of fluid remains on the stenosis over more than a pulsatile period.}, } @article {pmid33352968, year = {2020}, author = {Wu, CY and Lai, BH}, title = {Numerical Study of T-Shaped Micromixers with Vortex-Inducing Obstacles in the Inlet Channels.}, journal = {Micromachines}, volume = {11}, number = {12}, pages = {}, doi = {10.3390/mi11121122}, pmid = {33352968}, issn = {2072-666X}, support = {NSC 101 - 2221 - E - 006 - 108 - MY3//Ministry of Science and Technology of the Republic of China on Taiwan/ ; }, abstract = {To enhance fluid mixing, a new approach for inlet flow modification by adding vortex-inducing obstacles (VIOs) in the inlet channels of a T-shaped micromixer is proposed and investigated in this work. We use a commercial computational fluid dynamics code to calculate the pressure and the velocity vectors and, to reduce the numerical diffusion in high-Peclet-number flows, we employ the particle-tracking simulation with an approximation diffusion model to calculate the concentration distribution in the micromixers. The effects of geometric parameters, including the distance between the obstacles and the angle of attack of the obstacles, on the mixing performance of micromixers are studied. From the results, we can observe the following trends: (i) the stretched contact surface between different fluids caused by antisymmetric VIOs happens for the cases with the Reynolds number (Re) greater than or equal to 27 and the enhancement of mixing increases with the increase of Reynolds number gradually, and (ii) the onset of the engulfment flow happens at Re≈125 in the T-shaped mixer with symmetric VIOs or at Re≈140 in the standard planar T-shaped mixer and results in a sudden increase of the degree of mixing. The results indicate that the early initiation of transversal convection by either symmetric or antisymmetric VIOs can enhance fluid mixing at a relatively lower Re.}, } @article {pmid33252039, year = {2020}, author = {Asadzadeh, SS and Kiørboe, T and Larsen, PS and Leys, SP and Yahel, G and Walther, JH}, title = {Hydrodynamics of sponge pumps and evolution of the sponge body plan.}, journal = {eLife}, volume = {9}, number = {}, pages = {}, doi = {10.7554/eLife.61012}, pmid = {33252039}, issn = {2050-084X}, support = {7014-00033B//Danish council for Independent Research/ ; 9278//Villum Fonden/ ; 2016-05446//NSERC Discovery grant/ ; 2016-05446//NSERC/ ; 7014-00033B//Danish Council for Independent Research Natural Sciences/ ; }, abstract = {Sponges are suspension feeders that filter vast amounts of water. Pumping is carried out by flagellated chambers that are connected to an inhalant and exhalant canal system. In 'leucon' sponges with relatively high-pressure resistance due to a complex and narrow canal system, pumping and filtering are only possible owing to the presence of a gasket-like structure (forming a canopy above the collar filters). Here, we combine numerical and experimental work and demonstrate how sponges that lack such sealing elements are able to efficiently pump and force the flagella-driven flow through their collar filter, thanks to the formation of a 'hydrodynamic gasket' above the collar. Our findings link the architecture of flagellated chambers to that of the canal system, and lend support to the current view that the sponge aquiferous system evolved from an open-type filtration system, and that the first metazoans were filter feeders.}, } @article {pmid33333847, year = {2020}, author = {Li, YH and Chen, SC}, title = {Propulsion Mechanism of Flexible Microbead Swimmers in the Low Reynolds Number Regime.}, journal = {Micromachines}, volume = {11}, number = {12}, pages = {}, doi = {10.3390/mi11121107}, pmid = {33333847}, issn = {2072-666X}, support = {MOST 107-2218-E-606-003-MY2 and MOST 109-2221-E-606-003//Ministry of Science and Technology, Taiwan/ ; }, abstract = {A propulsion mechanism for a flexible microswimmer constructed from superparamagnetic microbeads with different diameters and subjected to an oscillating field was studied experimentally and theoretically herein. Various types of artificial swimmers with different bending patterns were fabricated to determine the flexibility and an effective waveform for a planar beating flagellum. Waveform evolutions for various swimmer configurations were studied to determine the flexible mechanism of the swimmers. A one-armed microswimmer can propel itself only if the friction of its wavelike body is anisotropic. A swimmer with a larger head and a stronger magnetic dipole moment with a flexible tail allows the bending wave to propagate from the head toward the tail to generate forward thrust. The oscillating head and tail do not simultaneously generate positive thrust all the time within a period of oscillation. To increase the propulsion for a bending swimmer, this study proposes a novel configuration for a microbead swimmer that ensures better swimming efficiency. The ratio of the oscillation amplitude of the head to the length of the swimmer (from 0.26 to 0.28) produces a faster swimmer. On the other hand, the swimmer is propelled more effectively if the ratio of the oscillation amplitude of the tail to the length of the swimmer is from 0.29 to 0.33. This study determined the optimal configuration for a flexible microbead swimmer that generates the greatest propulsion in a low Reynolds number environment.}, } @article {pmid33331388, year = {2020}, author = {Dou, Y and Tzelios, PM and Livitz, D and Bishop, KJM}, title = {Programmable topotaxis of magnetic rollers in time-varying fields.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d0sm01443e}, pmid = {33331388}, issn = {1744-6848}, abstract = {We describe how spatially uniform, time-periodic magnetic fields can be designed to power and direct the migration of ferromagnetic spheres up (or down) local gradients in the topography of a solid substrate. Our results are based on a dynamical model that considers the time-varying magnetic torques on the particle and its motion through the fluid at low Reynolds number. We use both analytical theory and numerical simulation to design magnetic fields that maximize the migration velocity up (or down) an inclined plane. We show how "topotaxis" of spherical particles relies on differences in the hydrodynamic resistance to rotation about axes parallel and perpendicular to the plane. Importantly, the designed fields can drive multiple independent particles to move simultaneously in different directions as determined by gradients in their respective environments. Experiments on ferromagnetic spheres provide evidence for topotactic motions up inclined substrates. The ability to program the autonomous navigation of driven particles within anisotropic environments is relevant to the design of colloidal robots.}, } @article {pmid33327683, year = {1981}, author = {Wegener, WA}, title = {Diffusion coefficients for rigid macromolecules with irregular shapes that allow rotational-translational coupling.}, journal = {Biopolymers}, volume = {20}, number = {2}, pages = {303-326}, doi = {10.1002/bip.1981.360200205}, pmid = {33327683}, issn = {1097-0282}, abstract = {We consider six-dimensional diffusion and frictional tensors for a rigid macromolecule immersed in a viscous fluid at low Reynolds number. Our treatment allows for screwlike properties which couple rotational and translational movements. We show that the center of diffusion of a screwlike body can be distinct from its hydrodynamic center of reaction. Symmetry conditions which ensure coincidence are examined. The center of diffusion is found to be the point of a body with the slowest diffusive movements, while rotations about the center of reaction encounter the least average resistance. The macroscopic translational diffusion coefficient is evaluated from a perturbation analysis of the six-dimensional diffusion equation. We show that methodologies which ignore translational-rotational coupling will necessarily underestimate the diffusion rate of screwlike particles. A procedural framework is presented to calculate diffusion coefficients of complicated bodies. As an example we treat a long bent rod.}, } @article {pmid33327115, year = {2020}, author = {Slanina, F}, title = {Colloid particles in microfluidic inertial hydrodynamic ratchet at moderate Reynolds number.}, journal = {Physical review. E}, volume = {102}, number = {5-1}, pages = {052601}, doi = {10.1103/PhysRevE.102.052601}, pmid = {33327115}, issn = {2470-0053}, abstract = {The movement of spherical Brownian particle carried by an alternating fluid flow in a tube of periodically variable diameter is investigated. On the basis of our previous results [Phys. Rev. E 99, 012604 (2019)10.1103/PhysRevE.99.012604] on the hydrodynamics of the problem, we look at the competition of hydrodynamics and diffusion. We use the method of Fick-Jacobs mapping on an effective one-dimensional problem. We calculate the ratchet current and show that is is strictly related to finite size of the particles. The ratchet current grows quadratically with particle radius. We also show that the dominant contribution to the ratchet current is due to inertial hydrodynamic effects. This means that Reynolds number must be at least of order one. We discuss the possible use for separation of particles by size and perspectives of optimization of the tube shape.}, } @article {pmid33325030, year = {2020}, author = {Turon, V and Ollivier, S and Cwicklinski, G and Willison, JC and Anxionnaz-Minvielle, Z}, title = {H2 production by photofermentation in an innovative plate-type photobioreactor with meandering channels.}, journal = {Biotechnology and bioengineering}, volume = {}, number = {}, pages = {}, doi = {10.1002/bit.27656}, pmid = {33325030}, issn = {1097-0290}, abstract = {Hydrogen production by Rhodobacter capsulatus is an anaerobic, photobiological process requiring specific mixing conditions. In this study, an innovative design of photobioreactor is proposed. The design is based on a plate-type photobioreactor with an interconnected meandering channel to allow culture mixing and H2 degassing. The culture flow was characterized as a quasi plug-flow with radial mixing caused by a turbulent-like regime achieved at low Reynolds number. The dissipated volumetric power was decreased ten-fold while maintaining PBR performances (production and yields) when compared with a magnetically stirred tank reactor. To increase hydrogen production flow rate, several bacterial concentrations were tested by increasing the glutamate concentration using fed-batch cultures. The maximum hydrogen production flow rate (157.7 ± 9.3 mL H2 /L/h) achieved is one of the highest values so far reported for H2 production by R. capsulatus. These first results are encouraging for future scale-up of the plate-type reactor. This article is protected by copyright. All rights reserved.}, } @article {pmid33322374, year = {2020}, author = {Liu, J and Xiao, Y and Li, M and Tao, J and Xu, S}, title = {Intermittency, Moments, and Friction Coefficient during the Subcritical Transition of Channel Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {12}, pages = {}, doi = {10.3390/e22121399}, pmid = {33322374}, issn = {1099-4300}, support = {91752203, 11772173, 11490553//National Natural Science Foundation of China/ ; }, abstract = {The intermittent distribution of localized turbulent structures is a key feature of the subcritical transitions in channel flows, which are studied in this paper with a wind channel and theoretical modeling. Entrance disturbances are introduced by small beads, and localized turbulent patches can be triggered at low Reynolds numbers (Re). High turbulence intensity represents strong ability of perturbation spread, and a maximum turbulence intensity is found for every test case as Re ≥ 950, where the turbulence fraction increases abruptly with Re. Skewness can reflect the velocity defects of localized turbulent patches and is revealed to become negative when Re is as low as about 660. It is shown that the third-order moments of the midplane streamwise velocities have minima, while the corresponding forth-order moments have maxima during the transition. These kinematic extremes and different variation scenarios of the friction coefficient during the transition are explained with an intermittent structure model, where the robust localized turbulent structure is simplified as a turbulence unit, a structure whose statistical properties are only weak functions of the Reynolds number.}, } @article {pmid33289747, year = {2020}, author = {Yang, PJ and Lee, AB and Chan, M and Kowalski, M and Qiu, K and Waid, C and Cervantes, G and Magondu, B and Biagioni, M and Vogelnest, L and Martin, A and Edwards, A and Carver, S and Hu, DL}, title = {Intestines of non-uniform stiffness mold the corners of wombat feces.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d0sm01230k}, pmid = {33289747}, issn = {1744-6848}, abstract = {The bare-nosed wombat (Vombatus ursinus) is a fossorial, herbivorous, Australian marsupial, renowned for its cubic feces. However, the ability of the wombat's soft intestine to sculpt flat faces and sharp corners in feces is poorly understood. In this combined experimental and numerical study, we show one mechanism for the formation of corners in a highly damped environment. Wombat dissections show that cubes are formed within the last 17 percent of the intestine. Using histology and tensile testing, we discover that the cross-section of the intestine exhibits regions with a two-fold increase in thickness and a four-fold increase in stiffness, which we hypothesize facilitates the formation of corners by contractions of the intestine. Using a mathematical model, we simulate a series of azimuthal contractions of a damped elastic ring composed of alternating stiff and soft regions. Increased stiffness ratio and higher Reynolds number yield shapes that are more square. The corners arise from faster contraction in the stiff regions and relatively slower movement in the center of the soft regions. These results may have applications in manufacturing, clinical pathology, and digestive health.}, } @article {pmid33286895, year = {2020}, author = {Agrawal, R and Ng, HC and Davis, EA and Park, JS and Graham, MD and Dennis, DJC and Poole, RJ}, title = {Low- and High-Drag Intermittencies in Turbulent Channel Flows.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {10}, pages = {}, doi = {10.3390/e22101126}, pmid = {33286895}, issn = {1099-4300}, support = {FA9550-16-1-0076//Air Force Office of Scientific Research/ ; FA9550-18-1-0174//Air Force Office of Scientific Research/ ; OIA-1832976//National Science Foundation/ ; }, abstract = {Recent direct numerical simulations (DNS) and experiments in turbulent channel flow have found intermittent low- and high-drag events in Newtonian fluid flows, at Reτ=uτh/ν between 70 and 100, where uτ, h and ν are the friction velocity, channel half-height and kinematic viscosity, respectively. These intervals of low-drag and high-drag have been termed "hibernating" and "hyperactive", respectively, and in this paper, a further investigation of these intermittent events is conducted using experimental and numerical techniques. For experiments, simultaneous measurements of wall shear stress and velocity are carried out in a channel flow facility using hot-film anemometry (HFA) and laser Doppler velocimetry (LDV), respectively, for Reτ between 70 and 250. For numerical simulations, DNS of a channel flow is performed in an extended domain at Reτ = 70 and 85. These intermittent events are selected by carrying out conditional sampling of the wall shear stress data based on a combined threshold magnitude and time-duration criteria. The use of three different scalings (so-called outer, inner and mixed) for the time-duration criterion for the conditional events is explored. It is found that if the time-duration criterion is kept constant in inner units, the frequency of occurrence of these conditional events remain insensitive to Reynolds number. There exists an exponential distribution of frequency of occurrence of the conditional events with respect to their duration, implying a potentially memoryless process. An explanation for the presence of a spike (or dip) in the ensemble-averaged wall shear stress data before and after the low-drag (or high-drag) events is investigated. During the low-drag events, the conditionally-averaged streamwise velocities get closer to Virk's maximum drag reduction (MDR) asymptote, near the wall, for all Reynolds numbers studied. Reynolds shear stress (RSS) characteristics during these conditional events are investigated for Reτ = 70 and 85. Except very close to the wall, the conditionally-averaged RSS is higher than the time-averaged value during the low-drag events.}, } @article {pmid33286770, year = {2020}, author = {Kashyap, PV and Duguet, Y and Dauchot, O}, title = {Flow Statistics in the Transitional Regime of Plane Channel Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {9}, pages = {}, doi = {10.3390/e22091001}, pmid = {33286770}, issn = {1099-4300}, abstract = {The transitional regime of plane channel flow is investigated above the transitional point below which turbulence is not sustained, using direct numerical simulation in large domains. Statistics of laminar-turbulent spatio-temporal intermittency are reported. The geometry of the pattern is first characterized, including statistics for the angles of the laminar-turbulent stripes observed in this regime, with a comparison to experiments. High-order statistics of the local and instantaneous bulk velocity, wall shear stress and turbulent kinetic energy are then provided. The distributions of the two former quantities have non-trivial shapes, characterized by a large kurtosis and/or skewness. Interestingly, we observe a strong linear correlation between their kurtosis and their skewness squared, which is usually reported at much higher Reynolds number in the fully turbulent regime.}, } @article {pmid33286441, year = {2020}, author = {Lee, T}, title = {Lognormality in Turbulence Energy Spectra.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {6}, pages = {}, doi = {10.3390/e22060669}, pmid = {33286441}, issn = {1099-4300}, abstract = {The maximum entropy principle states that the energy distribution will tend toward a state of maximum entropy under the physical constraints, such as the zero energy at the boundaries and a fixed total energy content. For the turbulence energy spectra, a distribution function that maximizes entropy with these physical constraints is a lognormal function due to its asymmetrical descent to zero energy at the boundary lengths scales. This distribution function agrees quite well with the experimental data over a wide range of energy and length scales. For turbulent flows, this approach is effective since the energy and length scales are determined primarily by the Reynolds number. The total turbulence kinetic energy will set the height of the distribution, while the ratio of length scales will determine the width. This makes it possible to reconstruct the power spectra using the Reynolds number as a parameter.}, } @article {pmid33286423, year = {2020}, author = {Wang, R and Xie, Z and Yin, Y and Chen, L}, title = {Constructal Design of Elliptical Cylinders with Heat Generating for Entropy Generation Minimization.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {6}, pages = {}, doi = {10.3390/e22060651}, pmid = {33286423}, issn = {1099-4300}, support = {51579244//National Natural Science Foundation of China/ ; }, abstract = {A heat dissipation model of discrete elliptical cylinders with heat generation on a thermal conduction pedestal cooled by forced convection is established. Constructal design is conducted numerically by taking the distributions of thermal conductivity and heat generating intensity as design variables, the dimensionless entropy generation rate (DEGR) as performance indicator. The optimal designs for discrete elliptical cylinders with heat generating are obtained respectively, i.e., there are optimal distributions of heat generating intensity with its fixed total amount of heat sources, and there are optimal distributions of thermal conductivity with its fixed total amount of heat sources. These optimums for minimum DEGRs are different at different Reynolds numbers of airflow. The heat generating intensity can be decreased one by one appropriately in the fluid flow direction to achieve the best effect. When the Reynolds number of airflow is smaller, the thermal conductivity of heat source can be increased one by one appropriately in the fluid flow direction to achieve the best effect; when the Reynolds number of airflow is larger, the thermal conductivity of each heat source should be equalized to achieve the best effect. The results can give thermal design guidelines for the practical heat generating devices with different materials and heat generating intensities.}, } @article {pmid33285959, year = {2020}, author = {Yu, S and Tang, T and Li, J and Yu, P}, title = {Effect of Prandtl Number on Mixed Convective Heat Transfer from a Porous Cylinder in the Steady Flow Regime.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {2}, pages = {}, doi = {10.3390/e22020184}, pmid = {33285959}, issn = {1099-4300}, support = {11672124//the National Natural Science Foundation of China/ ; ZDSYS201802081843517//Shenzhen Key Laboratory of Complex Aerospace Flows/ ; KQTD2016022620054656//the Shenzhen Peacock Plan/ ; }, abstract = {The effect of the Prandtl number (Pr) on the flow and heat transfer from a porous circular cylinder with internal heat generation in the mixed convection regime is numerically investigated. The steady flow regime is considered over the ranges of the Reynolds number (Re), Darcy number (Da), and Richardson number (Ri), varying from 5 to 40, 10-6 to 10-2, and 0 to 2, respectively. The wake structure, the temperature distribution, and the heat transfer rate are discussed. Besides precipitating the growth of the recirculating wake, the Prandtl number is found to have a significant impact on the thermal characteristics. The concave isotherms, resembling a saddle-shaped structure, occur behind the cylinder at larger Pr, resulting in swells of the isotherms pairing off at the lateral sides. These swells are found to have a negative effect on heat transfer owing to a relatively smaller temperature gradient there. Then, the heat transfer rate in terms of the local Nusselt number (Nu) and enhancement ratio (Er) is calculated, which is closely related to Pr, Re, Da, and Ri. The local minimum heat transfer rate along the cylinder surface is found at the position where the swells of the isotherms form.}, } @article {pmid33285875, year = {2020}, author = {Deriszadeh, A and de Monte, F}, title = {On Heat Transfer Performance of Cooling Systems Using Nanofluid for Electric Motor Applications.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, doi = {10.3390/e22010099}, pmid = {33285875}, issn = {1099-4300}, abstract = {This paper studies the fluid flow and heat transfer characteristics of nanofluids as advance coolants for the cooling system of electric motors. Investigations are carried out using numerical analysis for a cooling system with spiral channels. To solve the governing equations, computational fluid dynamics and 3D fluid motion analysis are used. The base fluid is water with a laminar flow. The fluid Reynolds number and turn-number of spiral channels are evaluation parameters. The effect of nanoparticles volume fraction in the base fluid on the heat transfer performance of the cooling system is studied. Increasing the volume fraction of nanoparticles leads to improving the heat transfer performance of the cooling system. On the other hand, a high-volume fraction of the nanofluid increases the pressure drop of the coolant fluid and increases the required pumping power. This paper aims at finding a trade-off between effective parameters by studying both fluid flow and heat transfer characteristics of the nanofluid.}, } @article {pmid33285793, year = {2019}, author = {Rasool, G and Zhang, T and Chamkha, AJ and Shafiq, A and Tlili, I and Shahzadi, G}, title = {Entropy Generation and Consequences of Binary Chemical Reaction on MHD Darcy-Forchheimer Williamson Nanofluid Flow Over Non-Linearly Stretching Surface.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, doi = {10.3390/e22010018}, pmid = {33285793}, issn = {1099-4300}, support = {11771389 and 11621101//The National Science Foundation of China/ ; }, abstract = {The current article aims to present a numerical analysis of MHD Williamson nanofluid flow maintained to flow through porous medium bounded by a non-linearly stretching flat surface. The second law of thermodynamics was applied to analyze the fluid flow, heat and mass transport as well as the aspects of entropy generation using Buongiorno model. Thermophoresis and Brownian diffusion is considered which appears due to the concentration and random motion of nanoparticles in base fluid, respectively. Uniform magnetic effect is induced but the assumption of tiny magnetic Reynolds number results in zero magnetic induction. The governing equations (PDEs) are transformed into ordinary differential equations (ODEs) using appropriately adjusted transformations. The numerical method is used for solving the so-formulated highly nonlinear problem. The graphical presentation of results highlights that the heat flux receives enhancement for augmented Brownian diffusion. The Bejan number is found to be increasing with a larger Weissenberg number. The tabulated results for skin-friction, Nusselt number and Sherwood number are given. A decent agreement is noted in the results when compared with previously published literature on Williamson nanofluids.}, } @article {pmid33285790, year = {2019}, author = {Xu, L and Xiong, Y and Xi, L and Gao, J and Li, Y and Zhao, Z}, title = {Numerical Simulation of Swirling Impinging Jet Issuing from a Threaded Hole under Inclined Condition.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, doi = {10.3390/e22010015}, pmid = {33285790}, issn = {1099-4300}, support = {51876157//National Natural Science Foundation of China/ ; 2018A030313183//Guangdong Natural Science Foundation/ ; xjj2018044//special fund for basic scientific research business expenses of Central Universities/ ; }, abstract = {There are some inclined jet holes in the cooling structure of the leading edge region of gas turbine blades. In order to improve the cooling effect of traditional round holes, this paper proposes to replace the round holes with threaded holes, and studies the complex flow and heat transfer performance of the swirling impinging jet (SIJ) issuing from the 45° threaded holes in the inclined condition by numerical simulation. The influencing factors include jet inclination angle α (45°-90°), jet-to-plate distance (H/d = 2, 4, 6), and Reynolds number (6000-24,000). The results show that the inclination angle and jet-to-plate distance have a great influence on the size, shape, and position of vortices in the jet space, while the Reynolds number has little effect on the vortices. In the inclined state, the impinging cooling effect of the swirling impinging jet is better than that of the circular impinging jet (CIJ), both heat transfer coefficients will degrade significantly when the inclination angle is 45°. When the inclination angle is greater than 45°, compared with the round hole, the enhanced heat transfer region for the swirling jet is in the region of r/d < 3, while both of the Nusselt numbers in the wall jet region are weak, with a value of just 20. At the same time, with the increasing of the inclination angle (α > 45°), the average Nusselt number on target surface holds a constant value. Under the inclined conditions, the heat transfer coefficient on the target surface for the swirling jet is increased totally with the increasing of the Re, but when the Re is larger than 18,000, the rate of enhanced heat transfer gradually weakens.}, } @article {pmid33285453, year = {2020}, author = {Maurer, L and Villette, C and Reiminger, N and Jurado, X and Laurent, J and Nuel, M and Mosé, R and Wanko, A and Heintz, D}, title = {Distribution and degradation trend of micropollutants in a surface flow treatment wetland revealed by 3D numerical modelling combined with LC-MS/MS.}, journal = {Water research}, volume = {190}, number = {}, pages = {116672}, doi = {10.1016/j.watres.2020.116672}, pmid = {33285453}, issn = {1879-2448}, abstract = {Conventional wastewater treatment plants are not designed to treat micropollutants; thus, for 20 years, several complementary treatment systems, such as surface flow wetlands have been used to address this issue. Previous studies demonstrate that higher residence time and low global velocities promote nutrient removal rates or micropollutant photodegradation. Nevertheless, these studies were restricted to the system limits (inlet/outlet). Therefore, detailed knowledge of water flow is crucial for identifying areas that promote degradation and optimise surface flow wetlands. The present study combines 3D water flow numerical modelling and liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS/MS). Using this numerical model, validated by tracer experimental data, several velocity areas were distinguished in the wetland. Four areas were selected to investigate the waterflow influence and led to the following results: on the one hand, the number and concentration of micropollutants are independent of the waterflow, which could be due to several assumptions, such as the chronic exposure associated with a low Reynolds number; on the other hand, the potential degradation products (metabolites) were also assessed in the sludge to investigate the micropollutant biodegradation processes occurring in the wetland; micropollutant metabolites or degradation products were detected in higher proportions (both number and concentration) in lower flow rate areas. The relation to higher levels of plant and microorganism metabolites suggests higher biological activity that promotes degradation.}, } @article {pmid33268359, year = {2020}, author = {Milana, E and Zhang, R and Vetrano, MR and Peerlinck, S and De Volder, M and Onck, PR and Reynaerts, D and Gorissen, B}, title = {Metachronal patterns in artificial cilia for low Reynolds number fluid propulsion.}, journal = {Science advances}, volume = {6}, number = {49}, pages = {}, doi = {10.1126/sciadv.abd2508}, pmid = {33268359}, issn = {2375-2548}, abstract = {Cilia are hair-like organelles, present in arrays that collectively beat to generate flow. Given their small size and consequent low Reynolds numbers, asymmetric motions are necessary to create a net flow. Here, we developed an array of six soft robotic cilia, which are individually addressable, to both mimic nature's symmetry-breaking mechanisms and control asymmetries to study their influence on fluid propulsion. Our experimental tests are corroborated with fluid dynamics simulations, where we find a good agreement between both and show how the kymographs of the flow are related to the phase shift of the metachronal waves. Compared to synchronous beating, we report a 50% increase of net flow speed when cilia move in an antiplectic wave with phase shift of -π/3 and a decrease for symplectic waves. Furthermore, we observe the formation of traveling vortices in the direction of the wave when metachrony is applied.}, } @article {pmid33267453, year = {2019}, author = {Ma, H and Duan, Z and Su, L and Ning, X and Bai, J and Lv, X}, title = {Fluid Flow and Entropy Generation Analysis of Al2O3-Water Nanofluid in Microchannel Plate Fin Heat Sinks.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {8}, pages = {}, doi = {10.3390/e21080739}, pmid = {33267453}, issn = {1099-4300}, support = {2019YJS155//Fundamental Research Funds for the Central Universities/ ; }, abstract = {The flow in channels of microdevices is usually in the developing regime. Three-dimensional laminar flow characteristics of a nanofluid in microchannel plate fin heat sinks are investigated numerically in this paper. Deionized water and Al2O3-water nanofluid are employed as the cooling fluid in our work. The effects of the Reynolds number (100 < Re < 1000), channel aspect ratio (0 < ε < 1), and nanoparticle volume fraction (0.5% < Φ < 5%) on pressure drop and entropy generation in microchannel plate fin heat sinks are examined in detail. Herein, the general expression of the entropy generation rate considering entrance effects is developed. The results revealed that the frictional entropy generation and pressure drop increase as nanoparticle volume fraction and Reynolds number increase, while decrease as the channel aspect ratio increases. When the nanoparticle volume fraction increases from 0 to 3% at Re = 500, the pressure drop of microchannel plate fin heat sinks with ε = 0.5 increases by 9%. It is demonstrated that the effect of the entrance region is crucial for evaluating the performance of microchannel plate fin heat sinks. The study may shed some light on the design and optimization of microchannel heat sinks.}, } @article {pmid33267389, year = {2019}, author = {Lee, TW}, title = {Maximum Entropy Method for Solving the Turbulent Channel Flow Problem.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {7}, pages = {}, doi = {10.3390/e21070675}, pmid = {33267389}, issn = {1099-4300}, abstract = {There are two components in this work that allow for solutions of the turbulent channel flow problem: One is the Galilean-transformed Navier-Stokes equation which gives a theoretical expression for the Reynolds stress (u'v'); and the second the maximum entropy principle which provides the spatial distribution of turbulent kinetic energy. The first concept transforms the momentum balance for a control volume moving at the local mean velocity, breaking the momentum exchange down to its basic components, u'v', u'2, pressure and viscous forces. The Reynolds stress gradient budget confirms this alternative interpretation of the turbulence momentum balance, as validated with DNS data. The second concept of maximum entropy principle states that turbulent kinetic energy in fully-developed flows will distribute itself until the maximum entropy is attained while conforming to the physical constraints. By equating the maximum entropy state with maximum allowable (viscous) dissipation at a given Reynolds number, along with other constraints, we arrive at function forms (inner and outer) for the turbulent kinetic energy. This allows us to compute the Reynolds stress, then integrate it to obtain the velocity profiles in channel flows. The results agree well with direct numerical simulation (DNS) data at Reτ = 400 and 1000.}, } @article {pmid33267306, year = {2019}, author = {Abd El-Aziz, M and Afify, AA}, title = {MHD Casson Fluid Flow over a Stretching Sheet with Entropy Generation Analysis and Hall Influence.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {6}, pages = {}, doi = {10.3390/e21060592}, pmid = {33267306}, issn = {1099-4300}, abstract = {The impacts of entropy generation and Hall current on MHD Casson fluid over a stretching surface with velocity slip factor have been numerically analyzed. Numerical work for the governing equations is established by using a shooting method with a fourth-order Runge-Kutta integration scheme. The outcomes show that the entropy generation is enhanced with a magnetic parameter, Reynolds number and group parameter. Further, the reverse behavior is observed with the Hall parameter, Eckert number, Casson parameter and slip factor. Also, it is viewed that Bejan number reduces with a group parameter.}, } @article {pmid33267233, year = {2019}, author = {de Divitiis, N}, title = {Statistical Lyapunov Theory Based on Bifurcation Analysis of Energy Cascade in Isotropic Homogeneous Turbulence: A Physical-Mathematical Review.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, doi = {10.3390/e21050520}, pmid = {33267233}, issn = {1099-4300}, abstract = {This work presents a review of previous articles dealing with an original turbulence theory proposed by the author and provides new theoretical insights into some related issues. The new theoretical procedures and methodological approaches confirm and corroborate the previous results. These articles study the regime of homogeneous isotropic turbulence for incompressible fluids and propose theoretical approaches based on a specific Lyapunov theory for determining the closures of the von Kármán-Howarth and Corrsin equations and the statistics of velocity and temperature difference. While numerous works are present in the literature which concern the closures of the autocorrelation equations in the Fourier domain (i.e., Lin equation closure), few articles deal with the closures of the autocorrelation equations in the physical space. These latter, being based on the eddy-viscosity concept, describe diffusive closure models. On the other hand, the proposed Lyapunov theory leads to nondiffusive closures based on the property that, in turbulence, contiguous fluid particles trajectories continuously diverge. Therefore, the main motivation of this review is to present a theoretical formulation which does not adopt the eddy-viscosity paradigm and summarizes the results of the previous works. Next, this analysis assumes that the current fluid placements, together with velocity and temperature fields, are fluid state variables. This leads to the closures of the autocorrelation equations and helps to interpret the mechanism of energy cascade as due to the continuous divergence of the contiguous trajectories. Furthermore, novel theoretical issues are here presented among which we can mention the following ones. The bifurcation rate of the velocity gradient, calculated along fluid particles trajectories, is shown to be much larger than the corresponding maximal Lyapunov exponent. On that basis, an interpretation of the energy cascade phenomenon is given and the statistics of finite time Lyapunov exponent of the velocity gradient is shown to be represented by normal distribution functions. Next, the self-similarity produced by the proposed closures is analyzed and a proper bifurcation analysis of the closed von Kármán-Howarth equation is performed. This latter investigates the route from developed turbulence toward the non-chaotic regimes, leading to an estimate of the critical Taylor scale Reynolds number. A proper statistical decomposition based on extended distribution functions and on the Navier-Stokes equations is presented, which leads to the statistics of velocity and temperature difference.}, } @article {pmid33267198, year = {2019}, author = {Abd El-Aziz, M and Saleem, S}, title = {Numerical Simulation of Entropy Generation for Power-Law Liquid Flow over a Permeable Exponential Stretched Surface with Variable Heat Source and Heat Flux.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, doi = {10.3390/e21050484}, pmid = {33267198}, issn = {1099-4300}, support = {G.R.P-2/16/40//King Khalid University/ ; }, abstract = {This novel work explored the second law analysis and heat transfer in a magneto non-Newtonian power-law fluid model with the presence of an internal non-uniform heat source/sink. In this investigation, the motion of the studied fluid was induced by an exponentially stretching surface. The rheological behavior of the fluid model, including the shear thinning and shear thickening properties, are also considered as special case studies. The physical problem developed meaningfully with the imposed heat flux and the porosity of the stretched surface. Extensive numerical simulations were carried out for the present boundary layer flow, in order to study the influence of each control parameter on the boundary layer flow and heat transfer characteristics via various tabular and graphical illustrations. By employing the Shooting Runge-Kutta-Fehlberg Method (SRKFM), the resulting nonlinear ordinary differential equations were solved accurately. Based on this numerical procedure, the velocity and temperature fields are displayed graphically. By applying the second law of thermodynamics, and characterizing the entropy generation and Bejan number, the present physical problem was examined and discussed thoroughly in different situations. The attained results showed that the entropy generation can be improved significantly by raising the magnetic field strength and the group parameter. From an energetic point of view, it was found that the Reynolds number boosts the entropy generation of the fluidic medium and reduces the Bejan number. Also, it was observed that an amplification of the power-law index diminished the entropy generation near the stretched surface. As main results, it was proven that the heat transfer rate can be reduced with both the internal heat source intensity and the magnetic field strength.}, } @article {pmid33267194, year = {2019}, author = {Hussien, AA and Abdullah, MZ and Yusop, NM and Al-Kouz, W and Mahmoudi, E and Mehrali, M}, title = {Heat Transfer and Entropy Generation Abilities of MWCNTs/GNPs Hybrid Nanofluids in Microtubes.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, doi = {10.3390/e21050480}, pmid = {33267194}, issn = {1099-4300}, abstract = {Massive improvements in the thermophysical properties of nanofluids over conventional fluids have led to the rapid evolution of using multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) in the field of heat transfer. In this study, the heat transfer and entropy generation abilities of MWCNTs/GNPs hybrid nanofluids were explored. Experiments on forced convective flow through a brass microtube with 300 µm inner diameter and 0.27 m in length were performed under uniform heat flux. MWCNTs/GNPs hybrid nanofluids were developed by adding 0.035 wt.% GNPs to MWCNTs water-based nanofluids with mass fractions of 0.075-0.125 wt.%. The range of the Reynolds number in this experiment was maintained at Re = 200-500. Results showed that the conventional approach for predicting the heat transfer coefficient was applicable for microtubes. The heat transfer coefficient increased markedly with the use of MWCNTs and MWCNTs/GNPs nanofluids, with increased pressure dropping by 12.4%. Results further showed a reduction by 37.5% in the total entropy generation rate in microtubes for hybrid nanofluids. Overall, MWCNTs/GNPs hybrid nanofluids can be used as alternative fluids in cooling systems for thermal applications.}, } @article {pmid33267040, year = {2019}, author = {Geneste, D and Faller, H and Nguyen, F and Shukla, V and Laval, JP and Daviaud, F and Saw, EW and Dubrulle, B}, title = {About Universality and Thermodynamics of Turbulence.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {3}, pages = {}, doi = {10.3390/e21030326}, pmid = {33267040}, issn = {1099-4300}, support = {ANR-16-CE06-0006-01//Agence Nationale de la Recherche/ ; 2A30096//Grand Équipement National De Calcul Intensif/ ; CFR//Commissariat à l'Énergie Atomique et aux Énergies Alternatives/ ; }, abstract = {This paper investigates the universality of the Eulerian velocity structure functions using velocity fields obtained from the stereoscopic particle image velocimetry (SPIV) technique in experiments and direct numerical simulations (DNS) of the Navier-Stokes equations. It shows that the numerical and experimental velocity structure functions up to order 9 follow a log-universality (Castaing et al. Phys. D Nonlinear Phenom. 1993); this leads to a collapse on a universal curve, when units including a logarithmic dependence on the Reynolds number are used. This paper then investigates the meaning and consequences of such log-universality, and shows that it is connected with the properties of a "multifractal free energy", based on an analogy between multifractal and thermodynamics. It shows that in such a framework, the existence of a fluctuating dissipation scale is associated with a phase transition describing the relaminarisation of rough velocity fields with different Hölder exponents. Such a phase transition has been already observed using the Lagrangian velocity structure functions, but was so far believed to be out of reach for the Eulerian data.}, } @article {pmid33266906, year = {2019}, author = {Kurnia, JC and Lim, DC and Chen, L and Jiang, L and Sasmito, AP}, title = {Entropy Generation and Heat Transfer Performance in Microchannel Cooling.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {2}, pages = {}, doi = {10.3390/e21020191}, pmid = {33266906}, issn = {1099-4300}, support = {015LCO-026//Yayasan Universiti Teknologi PETRONAS/ ; }, abstract = {Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most cooling channel studies evaluate the performance in view of the first thermodynamics aspect. This study is conducted to investigate flow behaviour and heat transfer performance of an incompressible fluid in a cooling channel with oblique fins with regards to first law and second law of thermodynamics. The effect of oblique fin angle and inlet Reynolds number are investigated. In addition, the performance of the cooling channels for different heat fluxes is evaluated. The results indicate that the oblique fin channel with 20° angle yields the highest figure of merit, especially at higher Re (250-1000). The entropy generation is found to be lowest for an oblique fin channel with 90° angle, which is about twice than that of a conventional parallel channel. Increasing Re decreases the entropy generation, while increasing heat flux increases the entropy generation.}, } @article {pmid33266845, year = {2019}, author = {Ries, F and Li, Y and Nishad, K and Janicka, J and Sadiki, A}, title = {Entropy Generation Analysis and Thermodynamic Optimization of Jet Impingement Cooling Using Large Eddy Simulation.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {2}, pages = {}, doi = {10.3390/e21020129}, pmid = {33266845}, issn = {1099-4300}, support = {SFB/TRR150//Deutsche Forschungsgemeinschaft/ ; }, abstract = {In this work, entropy generation analysis is applied to characterize and optimize a turbulent impinging jet on a heated solid surface. In particular, the influence of plate inclinations and Reynolds numbers on the turbulent heat and fluid flow properties and its impact on the thermodynamic performance of such flow arrangements are numerically investigated. For this purpose, novel model equations are derived in the frame of Large Eddy Simulation (LES) that allows calculation of local entropy generation rates in a post-processing phase including the effect of unresolved subgrid-scale irreversibilities. From this LES-based study, distinctive features of heat and flow dynamics of the impinging fluid are detected and optimal operating designs for jet impingement cooling are identified. It turned out that (1) the location of the stagnation point and that of the maximal Nusselt number differ in the case of plate inclination; (2) predominantly the impinged wall acts as a strong source of irreversibility; and (3) a flow arrangement with a jet impinging normally on the heated surface allows the most efficient use of energy which is associated with lowest exergy lost. Furthermore, it is found that increasing the Reynolds number intensifies the heat transfer and upgrades the second law efficiency of such thermal systems. Thereby, the thermal efficiency enhancement can overwhelm the frictional exergy loss.}, } @article {pmid33266771, year = {2019}, author = {Zhu, Z and Wang, H and Peng, D and Dou, J}, title = {Modelling the Hindered Settling Velocity of a Falling Particle in a Particle-Fluid Mixture by the Tsallis Entropy Theory.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {1}, pages = {}, doi = {10.3390/e21010055}, pmid = {33266771}, issn = {1099-4300}, support = {51509004//National Natural Science Foundation of China/ ; 2018KJ01//the Open Research Foundation of the Key Laboratory of the Pearl River Estuarine Dynamics and Associated Process Regulation, Ministry of Water Resources, China/ ; }, abstract = {The settling velocity of a sediment particle is an important parameter needed for modelling the vertical flux in rivers, estuaries, deltas and the marine environment. It has been observed that a particle settles more slowly in the presence of other particles in the fluid than in a clear fluid, and this phenomenon has been termed 'hindered settling'. The Richardson and Zaki equation has been a widely used expression for relating the hindered settling velocity of a particle with that in a clear fluid in terms of a concentration function and the power of the concentration function, and the power index is known as the exponent of reduction of the settling velocity. This study attempts to formulate the model for the exponent of reduction of the settling velocity by using the probability method based on the Tsallis entropy theory. The derived expression is a function of the volumetric concentration of the suspended particle, the relative mass density of the particle and the particle's Reynolds number. This model is tested against experimental data collected from the literature and against five existing deterministic models, and this model shows good agreement with the experimental data and gives better prediction accuracy than the other deterministic models. The derived Tsallis entropy-based model is also compared with the existing Shannon entropy-based model for experimental data, and the Tsallis entropy-based model is comparable to the Shannon entropy-based model for predicting the hindered settling velocity of a falling particle in a particle-fluid mixture. This study shows the potential of using the Tsallis entropy together with the principle of maximum entropy to predict the hindered settling velocity of a falling particle in a particle-fluid mixture.}, } @article {pmid33266740, year = {2018}, author = {Wang, W and Pan, C and Wang, J}, title = {Wall-Normal Variation of Spanwise Streak Spacing in Turbulent Boundary Layer With Low-to-Moderate Reynolds Number.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {1}, pages = {}, doi = {10.3390/e21010024}, pmid = {33266740}, issn = {1099-4300}, support = {11672020,11490552//National Natural Science Foundation of China/ ; }, abstract = {Low-speed streaks in wall-bounded turbulence are the dominant structures in the near-wall turbulent self-sustaining cycle. Existing studies have well characterized their spanwise spacing in the buffer layer and below. Recent studies suggested the existence of these small-scale structures in the higher layer where large-scale structures usually receive more attention. The present study is thus devoted to extending the understanding of the streak spacing to the log layer. An analysis is taken on two-dimensional (2D) wall-parallel velocity fields in a smooth-wall turbulent boundary layer with R e τ = 440∼2400, obtained via either 2D Particle Image Velocimetry (PIV) measurement taken here or public Direct Numerical Simulation (DNS). Morphological-based streak identification analysis yields a R e -independent log-normal distribution of the streak spacing till the upper bound of the log layer, based on which an empirical model is proposed to account for its wall-normal growth. The small-scale part of the spanwise spectra of the streamwise fluctuating velocity below y + = 100 is reasonably restored by a synthetic simulation that distributes elementary streak units based on the proposed empirical streak spacing model, which highlights the physical significance of streaks in shaping the small-scale part of the velocity spectra beyond the buffer layer.}, } @article {pmid33266619, year = {2018}, author = {Abdollahzadeh Jamalabadi, MY}, title = {Optimal Design of Nanoparticle Enhanced Phan-Thien-Tanner Flow of a Viscoelastic Fluid in a Microchannel.}, journal = {Entropy (Basel, Switzerland)}, volume = {20}, number = {12}, pages = {}, doi = {10.3390/e20120895}, pmid = {33266619}, issn = {1099-4300}, abstract = {The excellent thermal characteristics of nanoparticles have increased their application in the field of heat transfer. In this paper, a thermophysical and geometrical parameter study is performed to minimize the total entropy generation of the viscoelastic flow of nanofluid. Entropy generation with respect to volume fraction (<0.04), the Reynolds number (20,000-100,000), and the diameter of the microchannel (20-20,000 μm) with the circular cross-section under constant flux are calculated. As is shown, most of the entropy generation owes to heat transfer and by increasing the diameter of the channel, the Bejan number increases. The contribution of heat entropy generation in the microchannel is very poor and the major influence of entropy generation is attributable to friction. The maximum quantity of in-channel entropy generation happens in nanofluids with TiO2, CuO, Cu, and Ag nanoparticles, in turn, despite the fact in the microchannel this behavior is inverted, the minimum entropy generation occurs in nanofluids with CuO, Cu, Ag, and TiO2 nanoparticles, in turn. In the channel and microchannel for all nanofluids except water-TiO2, increasing the volume fraction of nanoparticles decreases entropy generation. In the channel and microchannel the total entropy generation increases by augmentation the Reynolds number.}, } @article {pmid33266252, year = {2020}, author = {Morimatsu, H and Tsukahara, T}, title = {Laminar-Turbulent Intermittency in Annular Couette-Poiseuille Flow: Whether a Puff Splits or Not.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {12}, pages = {}, doi = {10.3390/e22121353}, pmid = {33266252}, issn = {1099-4300}, support = {16H06066, 19H02071//Japan Society for the Promotion of Science/ ; }, abstract = {Direct numerical simulations were carried out with an emphasis on the intermittency and localized turbulence structure occurring within the subcritical transitional regime of a concentric annular Couette-Poiseuille flow. In the annular system, the ratio of the inner to outer cylinder radius is an important geometrical parameter affecting the large-scale nature of the intermittency. We chose a low radius ratio of 0.1 and imposed a constant pressure gradient providing practically zero shear on the inner cylinder such that the base flow was approximated to that of a circular pipe flow. Localized turbulent puffs, that is, axial uni-directional intermittencies similar to those observed in the transitional circular pipe flow, were observed in the annular Couette-Poiseuille flow. Puff splitting events were clearly observed rather far from the global critical Reynolds number, near which given puffs survived without a splitting event throughout the observation period, which was as long as 104 outer time units. The characterization as a directed-percolation universal class was also discussed.}, } @article {pmid33265887, year = {2018}, author = {Qiang, Y and Wei, L and Luo, X and Jian, H and Wang, W and Li, F}, title = {Heat Transfer and Flow Structures of Laminar Confined Slot Impingement Jet with Power-Law Non-Newtonian Fluid.}, journal = {Entropy (Basel, Switzerland)}, volume = {20}, number = {10}, pages = {}, doi = {10.3390/e20100800}, pmid = {33265887}, issn = {1099-4300}, support = {51765033//National Natural Science Foundation of China/ ; }, abstract = {Heat transfer performances and flow structures of laminar impinging slot jets with power-law non-Newtonian fluids and corresponding typical industrial fluids (Carboxyl Methyl Cellulose (CMC) solutions and Xanthangum (XG) solutions) have been studied in this work. Investigations are performed for Reynolds number Re less than 200, power-law index n ranging from 0.5 to 1.5 and consistency index K varying from 0.001 to 0.5 to explore heat transfer and flow structure of shear-thinning fluid and shear-thickening fluid. Results indicate that with the increase of n, K for a given Re, wall Nusselt number increases mainly attributing to the increase of inlet velocity U. For a given inlet velocity, wall Nusselt number decreases with the increase of n and K, which mainly attributes to the increase of apparent viscosity and the reduction of momentum diffusion. For the same Re, U and Pr, wall Nusselt number decreases with the increase of n. Among the study of industrial power-law shear-thinning fluid, CMC solution with 100 ppm shows the best heat transfer performance at a given velocity. Moreover, new correlation of Nusselt number about industrial fluid is proposed. In general, for the heat transfer of laminar confined impinging jet, it is best to use the working fluid with low viscosity.}, } @article {pmid33265465, year = {2018}, author = {Mathur, A and Seddighi, M and He, S}, title = {Transition of Transient Channel Flow with High Reynolds Number Ratios.}, journal = {Entropy (Basel, Switzerland)}, volume = {20}, number = {5}, pages = {}, doi = {10.3390/e20050375}, pmid = {33265465}, issn = {1099-4300}, abstract = {Large-eddy simulations of turbulent channel flow subjected to a step-like acceleration have been performed to investigate the effect of high Reynolds number ratios on the transient behaviour of turbulence. It is shown that the response of the flow exhibits the same fundamental characteristics described in He & Seddighi (J. Fluid Mech., vol. 715, 2013, pp. 60-102 and vol. 764, 2015, pp. 395-427)-a three-stage response resembling that of the bypass transition of boundary layer flows. The features of transition are seen to become more striking as the Re-ratio increases-the elongated streaks become stronger and longer, and the initial turbulent spot sites at the onset of transition become increasingly sparse. The critical Reynolds number of transition and the transition period Reynolds number for those cases are shown to deviate from the trends of He & Seddighi (2015). The high Re-ratio cases show double peaks in the transient response of streamwise fluctuation profiles shortly after the onset of transition. Conditionally-averaged turbulent statistics based on a λ_2-criterion are used to show that the two peaks in the fluctuation profiles are due to separate contributions of the active and inactive regions of turbulence generation. The peak closer to the wall is attributed to the generation of "new" turbulence in the active region, whereas the peak farther away from the wall is attributed to the elongated streaks in the inactive region. In the low Re-ratio cases, the peaks of these two regions are close to each other during the entire transient, resulting in a single peak in the domain-averaged profile.}, } @article {pmid33244217, year = {2020}, author = {Arumuru, V and Pasa, J and Samantaray, SS}, title = {Experimental visualization of sneezing and efficacy of face masks and shields.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {11}, pages = {115129}, doi = {10.1063/5.0030101}, pmid = {33244217}, issn = {1070-6631}, abstract = {In the present work, we propose and demonstrate a simple experimental visualization to simulate sneezing by maintaining dynamic similarity to actual sneezing. A pulsed jet with Reynolds number Re = 30 000 is created using compressed air and a solenoid valve. Tracer particles are introduced in the flow to capture the emulated turbulent jet formed due to a sneeze. The visualization is accomplished using a camera and laser illumination. It is observed that a typical sneeze can travel up to 25 ft in ∼22 s in a quiescent environment. This highlights that the present widely accepted safe distance of 6 ft is highly underestimated, especially under the act of a sneeze. Our study demonstrates that a three-layer homemade mask is just adequate to impede the penetration of fine-sized particles, which may cause the spreading of the infectious pathogen responsible for COVID-19. However, a surgical mask cannot block the sneeze, and the sneeze particle can travel up to 2.5 ft. We strongly recommend using at least a three-layer homemade mask with a social distancing of 6 ft to combat the transmission of COVID-19 virus. In offices, we recommend the use of face masks and shields to prevent the spreading of droplets carrying the infectious pathogen. Interestingly, an N-95 mask blocks the sneeze in the forward direction; however, the leakage from the sides and top spreads the sneeze in the backward direction up to 2 ft. We strongly recommend using the elbow or hands to prevent droplet leakage even after wearing a mask during sneezing and coughing.}, } @article {pmid33244213, year = {2020}, author = {Mallik, AK and Mukherjee, S and Panchagnula, MV}, title = {An experimental study of respiratory aerosol transport in phantom lung bronchioles.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {11}, pages = {111903}, doi = {10.1063/5.0029899}, pmid = {33244213}, issn = {1070-6631}, abstract = {The transport and deposition of micrometer-sized particles in the lung is the primary mechanism for the spread of aerosol borne diseases such as corona virus disease-19 (COVID-19). Considering the current situation, modeling the transport and deposition of drops in human lung bronchioles is of utmost importance to determine their consequences on human health. The current study reports experimental observations on deposition in micro-capillaries, representing distal lung bronchioles, over a wide range of Re that imitates the particle dynamics in the entire lung. The experiment investigated deposition in tubes of diameter ranging from 0.3 mm to 2 mm and over a wide range of Reynolds number (10-2 ⩽ Re ⩽ 103). The range of the tube diameter and Re used in this study is motivated by the dimensions of lung airways and typical breathing flow rates. The aerosol fluid was loaded with boron doped carbon quantum dots as fluorophores. An aerosol plume was generated from this mixture fluid using an ultrasonic nebulizer, producing droplets with 6.5 µm as a mean diameter and over a narrow distribution of sizes. The amount of aerosol deposited on the tube walls was measured using a spectrofluorometer. The experimental results show that dimensionless deposition (δ) varies inversely with the bronchiole aspect ratio (L ¯), with the effect of the Reynolds number (Re) being significant only at low L ¯ . δ also increased with increasing dimensionless bronchiole diameter (D ¯), but it is invariant with the particle size based Reynolds number. We show that δ L ¯ ∼ R e - 2 for 10-2 ⩽ Re ⩽ 1, which is typical of a diffusion dominated regime. For Re ⩾ 1, in the impaction dominated regime, δ L ¯ is shown to be independent of Re. We also show a crossover regime where sedimentation becomes important. The experimental results conclude that lower breathing frequency and higher breath hold time could significantly increase the chances of getting infected with COVID-19 in crowded places.}, } @article {pmid33220061, year = {2020}, author = {Battista, NA}, title = {Diving into a Simple Anguilliform Swimmer's Sensitivity.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1236-1250}, doi = {10.1093/icb/icaa131}, pmid = {33220061}, issn = {1557-7023}, abstract = {Computational models of aquatic locomotion range from modest individual simple swimmers in 2D to sophisticated 3D multi-swimmer models that attempt to parse collective behavioral dynamics. Each of these models contain a multitude of model input parameters to which its outputs are inherently dependent, that is, various performance metrics. In this work, the swimming performance's sensitivity to parameters is investigated for an idealized, simple anguilliform swimming model in 2D. The swimmer considered here propagates forward by dynamically varying its body curvature, similar to motion of a Caenorhabditis elegans. The parameter sensitivities were explored with respect to the fluid scale (Reynolds number), stroke (undulation) frequency, as well as a kinematic parameter controlling the velocity and acceleration of each upstroke and downstroke. The input Reynolds number and stroke frequencies sampled were from [450, 2200] and [1, 3] Hz, respectively. In total, 5000 fluid-structure interaction simulations were performed, each with a unique parameter combination selected via a Sobol sequence, in order to conduct global sensitivity analysis. Results indicate that the swimmer's performance is most sensitive to variations in its stroke frequency. Trends in swimming performance were discovered by projecting the performance data onto particular 2D subspaces. Pareto-like optimal fronts were identified. This work is a natural extension of the parameter explorations of the same model from Battista in 2020.}, } @article {pmid33212661, year = {2020}, author = {Gungor, A and Hemmati, A}, title = {Wake symmetry impacts the performance of tandem hydrofoils during in-phase and out-of-phase oscillations differently.}, journal = {Physical review. E}, volume = {102}, number = {4-1}, pages = {043104}, doi = {10.1103/PhysRevE.102.043104}, pmid = {33212661}, issn = {2470-0053}, abstract = {The hydrodynamics of two oscillating foils in side-by-side configuration is numerically investigated for in-phase and out-of-phase pitching at Reynolds number of 4000 and Strouhal numbers of St=0.25-0.5. The effects of phase difference (in-phase and out-of-phase) and Strouhal number on symmetric attributes of the wake and unsteady propulsive performance of the foils are studied in detail. At lower Strouhal numbers, there is a quasisteady performance in both thrust generation and power consumption, which coincides with persistence of the wake symmetry. As Strouhal number increases, however, in-phase and out-of-phase pitching display unsteady cycle-averaged behavior with very different wake characteristics. The asymmetric wake of in-phase pitching foils at high Strouhal numbers transitions to a quasisymmetric wake, when an extensive interaction between the two vortex streets is observed in the wake. This coincides with an improvement on the propulsive performance of the foils. In contrast, the symmetric wake of the out-of-phase pitching foils at a high Strouhal number transitions to an asymmetric wake. The adverse effect of this transition is only observed on the propulsive performance of one foil while the other exploits the wake towards a better performance. The collective performance of the the out-of-phase pitching system, however, remains unchanged. There is also a strong correlation between the wake symmetric characteristics and total nonzero side-force production.}, } @article {pmid33212599, year = {2020}, author = {Inubushi, M and Goto, S}, title = {Transfer learning for nonlinear dynamics and its application to fluid turbulence.}, journal = {Physical review. E}, volume = {102}, number = {4-1}, pages = {043301}, doi = {10.1103/PhysRevE.102.043301}, pmid = {33212599}, issn = {2470-0053}, abstract = {We introduce transfer learning for nonlinear dynamics, which enables efficient predictions of chaotic dynamics by utilizing a small amount of data. For the Lorenz chaos, by optimizing the transfer rate, we accomplish more accurate inference than the conventional method by an order of magnitude. Moreover, a surprisingly small amount of learning is enough to infer the energy dissipation rate of the Navier-Stokes turbulence because we can, thanks to the small-scale universality of turbulence, transfer a large amount of the knowledge learned from turbulence data at lower Reynolds number.}, } @article {pmid33211148, year = {2020}, author = {Ikoma, T and Suwa, K and Sano, M and Ushio, T and Saotome, M and Ogawa, N and Satoh, H and Maekawa, Y}, title = {Early changes of pulmonary arterial hemodynamics in patients with systemic sclerosis: flow pattern, WSS, and OSI analysis with 4D flow MRI.}, journal = {European radiology}, volume = {}, number = {}, pages = {}, doi = {10.1007/s00330-020-07301-x}, pmid = {33211148}, issn = {1432-1084}, support = {26461065//Ministry of Education, Culture, Sports, Science and Technology/ ; }, abstract = {OBJECTIVES: To study the pulmonary artery (PA) hemodynamics in patients with systemic sclerosis (SSc) using 4D flow MRI (4D-flow).

METHODS: Twenty-three patients with SSc (M/F: 2/21, 57 ± 15 years, 3 manifest PA hypertension (PAH) by right heart catheterization) and 10 control subjects (M/F: 1/9, 55 ± 17 years) underwent 4D-flow for the in vivo measurement of 3D blood flow velocities in the PA. Data analysis included area-averaged flow quantification at the main PA, 3D wall shear stress (WSS), oscillatory shear index (OSI) calculation along the PA surface, and Reynolds number. The composite outcome of all-cause death and major adverse cardiac events was also investigated.

RESULTS: The maximum PA flow at the systole did not differ, but the minimum flow at the diastole was significantly greater in patients with SSc compared with that in control subjects (7.7 ± 16.0 ml/s vs. ‑ 13.0 ± 17.3 ml/s, p < 0.01). The maximum WSS at the peak systole was significantly lower and OSI was significantly greater in patients with SSc compared with those in control subjects (maximum WSS: 1.04 ± 0.20 Pa vs. 1.33 ± 0.34 Pa, p < 0.01, OSI: 0.139 ± 0.031 vs. 0.101 ± 0.037, p < 0.01). The cumulative event-free rate for the composite event was significantly lower in patients with minimum flow in main PA ≤ 9.22 ml/s (p = 0.012) and in patients with Reynolds number ≤ 2560 (p < 0.001).

CONCLUSIONS: 4D-flow has the potential to detect changes of PA hemodynamics noninvasively and predict the outcome in patients with SSc at the stage before manifest PAH.

KEY POINTS: • The WSS at the peak systolic phase was significantly lower (p < 0.05), whereas OSI was greater (p < 0.01) in patients with SSc without manifest PAH than in controls. • The hemodynamic change detected by 4D-flow may help patient management even at the stage before manifest PAH in SSc. • The minimum PA flow and Reynolds number by 4D-flow will serve as a predictive marker for SSc.}, } @article {pmid33201951, year = {2020}, author = {Lochab, V and Prakash, S}, title = {Combined electrokinetic and shear flows control colloidal particle distribution across microchannel cross-sections.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d0sm01646b}, pmid = {33201951}, issn = {1744-6848}, abstract = {Recent experimental observations on combined electrokinetic and shear flows of colloidal suspensions in rectangular cross-section microfluidic channels have shown unusual cross-stream colloidal particle migration and dynamic assembly. Although a new electrophoresis-induced lift force has been postulated to cause the lateral migration of colloidal particles, little is known about how fluid properties and flow conditions impact this force and therefore subsequent colloidal particle migration. Furthermore, no experimental quantification of this electrophoresis-induced lift force is available. We report several key advances by demonstrating that the kinematic viscosity of the fluid can be used to modulate the spatial distribution of particles over the entire microchannel cross-section, with suppression of the colloidal particle migration observed with increase in fluid kinematic viscosity. Colloidal particle migration of ∼10 μm from not only the top and bottom microchannel walls but also from the side walls is shown with the corresponding electrophoresis-induced lift force of up to ∼30 fN. The breadth of flow conditions tested capture the channel Reynolds number in the 0.1-1.1 range, with inertial migration of colloidal particles shown in flow regimes where the migration was previously thought to be ineffective, if not for the electrophoresis-induced lift force. The ability of the electrophoresis-induced lift force to migrate colloidal particles across the entire microchannel cross-section establishes a new paradigm for three-dimensional control of colloidal particles within confined microchannels.}, } @article {pmid33199601, year = {2020}, author = {Omori, T and Ito, H and Ishikawa, T}, title = {Swimming microorganisms acquire optimal efficiency with multiple cilia.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {}, number = {}, pages = {}, doi = {10.1073/pnas.2011146117}, pmid = {33199601}, issn = {1091-6490}, abstract = {Planktonic microorganisms are ubiquitous in water, and their population dynamics are essential for forecasting the behavior of global aquatic ecosystems. Their population dynamics are strongly affected by these organisms' motility, which is generated by their hair-like organelles, called cilia or flagella. However, because of the complexity of ciliary dynamics, the precise role of ciliary flow in microbial life remains unclear. Here, we have used ciliary hydrodynamics to show that ciliates acquire the optimal propulsion efficiency. We found that ciliary flow highly resists an organism's propulsion and that the swimming velocity rapidly decreases with body size, proportional to the power of minus two. Accordingly, the propulsion efficiency decreases as the cube of body length. By increasing the number of cilia, however, efficiency can be significantly improved, up to 100-fold. We found that there exists an optimal number density of cilia, which provides the maximum propulsion efficiency for all ciliates. The propulsion efficiency in this case decreases inversely proportionally to body length. Our estimated optimal density of cilia corresponds to those of actual microorganisms, including species of ciliates and microalgae, which suggests that now-existing motile ciliates and microalgae have survived by acquiring the optimal propulsion efficiency. These conclusions are helpful for better understanding the ecology of microorganisms, such as the energetic costs and benefits of multicellularity in Volvocaceae, as well as for the optimal design of artificial microswimmers.}, } @article {pmid33199599, year = {2020}, author = {Andersen, A and Kiørboe, T}, title = {The effect of tethering on the clearance rate of suspension-feeding plankton.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {}, number = {}, pages = {}, doi = {10.1073/pnas.2017441117}, pmid = {33199599}, issn = {1091-6490}, abstract = {Many planktonic suspension feeders are attached to particles or tethered by gravity when feeding. It is commonly accepted that the feeding flows of tethered suspension feeders are stronger than those of their freely swimming counterparts. However, recent flow simulations indicate the opposite, and the cause of the opposing conclusions is not clear. To explore the effect of tethering on suspension feeding, we use a low-Reynolds-number flow model. We find that it is favorable to be freely swimming instead of tethered since the resulting feeding flow past the cell body is stronger, leading to a higher clearance rate. Our result underscores the significance of the near-field flow in shaping planktonic feeding modes, and it suggests that organisms tether for reasons that are not directly fluid dynamical (e.g., to stay near surfaces where the concentration of bacterial prey is high).}, } @article {pmid33197195, year = {2020}, author = {Hatte, S and Pitchumani, R}, title = {Fractal Model for Drag Reduction on Multiscale Nonwetting Rough Surfaces.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.0c02790}, pmid = {33197195}, issn = {1520-5827}, abstract = {Rough surfaces in contact with a flow of fluid exhibit alternating no-slip and free shear boundary conditions at the solid-liquid and air-liquid interfaces, respectively, thereby potentially offering drag reduction benefits. The balance between the dynamic pressure in the flow and the restoring capillary pressure in the interasperity spaces determines the stability of the Cassie state of wettability and is a function of the relative extent of no-slip and free shear regions per unit surface area. In the present study, using a fractal representation of rough surface topography, an analytical model is developed to quantify the stability of the Cassie state of wettability as well as drag reduction and the friction factor for laminar flow in a rectangular channel between nonwetting multiscale rough surfaces. A systematic study is conducted to quantify the effects of fractal parameters of the surfaces and the flow Reynolds number on drag reduction and the friction factor. The studies are used to develop friction factor curves extending the classical Moody diagram to hydrophobic and superhydrophobic surfaces. On the basis of the studies, regime maps are derived for estimating the extent of drag reduction offered by hydrophobic and superhydrophobic surfaces, revealing that superhydrophobic surfaces do not always offer the best drag reduction performance. The application of the fractal model to practical topographies of nonwetting surfaces of copper, aluminum, and zinc oxide fabricated via electrodeposition and etching is also discussed.}, } @article {pmid33184652, year = {2020}, author = {Rader, JA and Hedrick, TL and He, Y and Waldrop, LD}, title = {Functional Morphology of Gliding Flight II. Morphology Follows Predictions of Gliding Performance.}, journal = {Integrative and comparative biology}, volume = {}, number = {}, pages = {}, doi = {10.1093/icb/icaa126}, pmid = {33184652}, issn = {1557-7023}, abstract = {The evolution of wing morphology among birds, and its functional consequences, remains an open question, despite much attention. This is in part because the connection between form and function is difficult to test directly. To address this deficit, in prior work, we used computational modeling and sensitivity analysis to interrogate the impact of altering wing aspect ratio (AR), camber, and Reynolds number on aerodynamic performance, revealing the performance landscapes that avian evolution has explored. In the present work, we used a dataset of three-dimensionally scanned bird wings coupled with the performance landscapes to test two hypotheses regarding the evolutionary diversification of wing morphology associated with gliding flight behavior: (1) gliding birds would exhibit higher wing AR and greater chordwise camber than their non-gliding counterparts; and (2) that two strategies for gliding flight exist, with divergent morphological conformations. In support of our first hypothesis, we found evidence of morphological divergence in both wing AR and camber between gliders and non-gliders, suggesting that wing morphology of birds that utilize gliding flight is under different selective pressures than the wings of non-gliding taxa. Furthermore, we found that these morphological differences also yielded differences in coefficient of lift measured both at the maximum lift to drag ratio and at minimum sinking speed, with gliding taxa exhibiting higher coefficient of lift in both cases. Minimum sinking speed was also lower in gliders than non-gliders. However, contrary to our hypothesis, we found that the maximum ratio of the coefficient of lift to the coefficient of drag differed between gliders and non-gliders. This may point to the need for gliders to maintain high lift capability for takeoff and landing independent of gliding performance or could be due to the divergence in flight styles among gliders, as not all gliders are predicted to optimize either quantity. However, direct evidence for the existence of two morphologically defined gliding flight strategies was equivocal, with only slightly stronger support for an evolutionary model positing separate morphological optima for these strategies than an alternative model positing a single peak. The absence of a clear result may be an artifact of low statistical power owing to a relatively small sample size of gliding flyers expected to follow the "aerial search" strategy.}, } @article {pmid33184554, year = {2020}, author = {Lee, JY and Kottke, PA and Fedorov, AG}, title = {Hydrodynamics of Vortical Gas Jets Coupled to Point-Like Suction.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {10}, pages = {}, pmid = {33184554}, issn = {1070-6631}, support = {R01 GM112662/GM/NIGMS NIH HHS/United States ; }, abstract = {Vortical jet flows in the Reynolds number (Re) range from 1000 to 3425 and swirl number (S) below 0.5, alone and in combination with suction through a small aperture, are experimentally investigated using optical visualization. Schlieren photography is employed to assess the vortical flow structure and establish the fundamental understanding of the source-to-sink gas-dynamic coupling, including the role played by flow rate, jet diameter, and the separation distance between the gas jet source and the suction sink. Compared to vortex-free jets, vortical jets for Re>2700 with swirl number S>0.27 experience earlier laminar-to-turbulent transition, with resulting rapid growth of the jet boundary. The ability to control growth of the jet expansion and mass and momentum dissipation into the surrounding is demonstrated via use of a coaxially aligned flow suction placed in the path of a jet. When a swirling jet is completely coupled with a flow suction, jet expansion is significantly suppressed. The suction/sink flow rate imposes a limit on the maximum input/source flow rate of gas jet to achieve complete coupling. Furthermore, there is a maximum distance over which effective coupling can occur, and for all Reynolds numbers considered this distance is shorter than the distance at which the jet structure breaks up into turbulent eddies in the absence of a sink.}, } @article {pmid33172214, year = {2020}, author = {Astudillo-Castro, C and Cordova, A and Oyanedel-Craver, V and Soto-Maldonado, C and Valencia, P and Henriquez, P and Jimenez-Flores, R}, title = {Prediction of the Limiting Flux and Its Correlation with the Reynolds Number during the Microfiltration of Skim Milk Using an Improved Model.}, journal = {Foods (Basel, Switzerland)}, volume = {9}, number = {11}, pages = {}, doi = {10.3390/foods9111621}, pmid = {33172214}, issn = {2304-8158}, support = {11110402//Fondo Nacional de Desarrollo Científico y Tecnológico/ ; }, abstract = {Limiting flux (JL) determination is a critical issue for membrane processing. This work presents a modified exponential model for JL calculation, based on a previously published version. Our research focused on skim milk microfiltrations. The processing variables studied were the crossflow velocity (CFV), membrane hydraulic diameter (dh), temperature, and concentration factor, totaling 62 experimental runs. Results showed that, by adding a new parameter called minimum transmembrane pressure, the modified model not only improved the fit of the experimental data compared to the former version (R2 > 97.00%), but also revealed the existence of a minimum transmembrane pressure required to obtain flux (J). This result is observed as a small shift to the right on J versus transmembrane pressure curves, and this shift increases with the flow velocity. This fact was reported in other investigations, but so far has gone uninvestigated. The JL predicted values were correlated with the Reynolds number (Re) for each dh tested. Results showed that for a same Re; JL increased as dh decreased; in a wide range of Re within the turbulent regime. Finally, from dimensionless correlations; a unique expression JL = f (Re, dh) was obtained; predicting satisfactorily JL (R2 = 84.11%) for the whole set of experiments.}, } @article {pmid33171451, year = {2020}, author = {Ford, M and Santhanakrishnan, A}, title = {On the role of phase lag in multi-appendage metachronal swimming of euphausiids.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/abc930}, pmid = {33171451}, issn = {1748-3190}, abstract = {Metachronal paddling is a common method of drag-based aquatic propulsion, in which a series of swimming appendages are oscillated, with the motion of each appendage phase-shifted relative to the neighboring appendages. Ecologically and economically important Euphausiid species such as Antarctic krill (E. superba) swim constantly in the pelagic zone by stroking their paddling appendages (pleopods), with locomotion accounting for the bulk of their metabolic expenditure. They tailor their metachronal swimming gaits for behavioral and energetic needs by changing pleopod kinematics. The functional importance of inter-pleopod phase lag (ϕ) to metachronal swimming performance and wake structure is unknown. To examine this relation, we developed a geometrically and dynamically scaled robot ('krillbot') capable of self-propulsion. Krillbot pleopods were prescribed to mimic published kinematics of fast-forward swimming (FFW) and hovering (HOV) gaits of E. superba, and the Reynolds number and Strouhal number of the krillbot matched well with those calculated for freely-swimming E. superba. In addition to examining published kinematics with uneven ϕ between pleopod pairs, we modified E. superba kinematics to uniformly vary ϕ from 0% to 50% of the cycle. Swimming speed and thrust were largest for FFW with ϕ between 15%-25%, coincident with ϕ range observed in FFW gait of E. superba. In contrast to synchronous rowing (ϕ=0%) where distances between hinged joints of adjacent pleopods were nearly constant throughout the cycle, metachronal rowing (ϕ>0%) brought adjacent pleopods closer together and moved them farther apart. This factor minimized body position fluctuation and augmented metachronal swimming speed. Though swimming speed was lowest for HOV, a ventrally angled downward jet was generated that can assist with weight support during feeding. In summary, our findings show that inter-appendage phase lag can drastically alter both metachronal swimming speed and the large-scale wake structure.}, } @article {pmid33159347, year = {2020}, author = {Ichikawa, C and Ishikawa, D and Yang, JM and Fujii, T}, title = {Phenomenological analysis on whipping behavior of rice flour batter.}, journal = {Journal of food science}, volume = {}, number = {}, pages = {}, doi = {10.1111/1750-3841.15452}, pmid = {33159347}, issn = {1750-3841}, abstract = {In this study, the bubbles in rice flour batter were investigated under a constant temperature, because the bubble size distribution is important for the control of food texture. We obtained experimental data using a hand mixer and compared the properties of doughs prepared using six rice flours; each flour was prepared through a different milling process. We also added the size effect of the rice flour particles as the Bond number. Furthermore, we performed a dynamic wettability test to estimate the wettability of the rice flour surface. The results of this test were described well by the Washburn equation, and dc cosθ/dp was calculated as a wettability parameter (where, dc = effective diameter of a capillary in a powder bed, cosθ = the contact angle, dp = mean particle diameter of rice flour). If bubble sizes depend mainly on the inertial force, viscous force, surface tension, and gravity, then the normalized mean bubble diameter should be a function of the Reynolds number, Weber number, and Froude number. The mean bubble diameter (dbm) generated by whipping was expected to be affected by the thickness (d) of the rod of the mixer, its movement speed, and physical properties of the material. Therefore, dimensionless mean diameter (dbm /d) was expressed based on a dimensionless equation. In the three-phase dispersion, different empirical equations were obtained depending on the amount of rice flour added, and the bubble diameter could be predicted using dimensionless parameters. In addition, the equations were generally applicable to the various materials selected for this study. PRACTICAL APPLICATION: The powder properties of rice flour were investigated, and dimensionless parameters were analyzed to construct an appropriate process control system for rice flour-based food products. Although the process method optimized for flour products is also used for rice flour products in practical situations, the comprehensive evaluation based on dimensionless parameters leads to optimization of the process for rice-flour based products. Moreover, this optimization might strongly support the creation of a new texture, and thus, the potential for market expansion of rice-flour based products is considerable.}, } @article {pmid33158219, year = {2020}, author = {Sana, S and Zivkovic, V and Boodhoo, K}, title = {Empirical Modelling of Hydrodynamic Effects on Starch Nanoparticles Precipitation in a Spinning Disc Reactor.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {11}, pages = {}, doi = {10.3390/nano10112202}, pmid = {33158219}, issn = {2079-4991}, abstract = {Empirical correlations have been developed to relate experimentally determined starch nanoparticle size obtained in a solvent-antisolvent precipitation process with key hydrodynamic parameters of a spinning disc reactor (SDR). Three different combinations of dimensionless groups including a conventional Reynolds number (Re), rotational Reynolds number (Reω) and Rossby number (Ro) have been applied in individual models for two disc surfaces (smooth and grooved) to represent operating variables affecting film flow such as liquid flowrate and disc rotational speed, whilst initial supersaturation (S) has been included to represent varying antisolvent concentrations. Model 1 featuring a combination of Re, Reω and S shows good agreement with the experimental data for both the grooved and smooth discs. For the grooved disc, Re has a greater impact on particle size, whereas Reω is more influential on the smooth disc surface, the difference likely being due to the passive mixing induced by the grooves irrespective of the magnitude of the disc speed. Supersaturation has little impact on particle size within the limited initial supersaturation range studied. Model 2 which characterises both flow rate and disc rotational speed through Ro alone and combined with Re was less accurate in predicting particle size due to several inherent limitations.}, } @article {pmid33157545, year = {2020}, author = {Harvey, C and Inman, DJ}, title = {Aerodynamic efficiency of gliding birds vs. comparable UAVs: a review.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/abc86a}, pmid = {33157545}, issn = {1748-3190}, abstract = {Here, we reviewed published aerodynamic efficiencies of gliding birds and similar sized unmanned aerial vehicles (UAVs) motivated by a fundamental question: are gliding birds more efficient than comparable UAVs? Despite a multitude of studies that have quantified the aerodynamic efficiency of gliding birds, there is no comprehensive summary of these results. This lack of consolidated information inhibits a true comparison between birds and UAVs. Such a comparison is complicated by variable uncertainty levels between the different techniques used to predict avian efficiency. To support our comparative approach, we began by surveying theoretical and experimental estimates of avian aerodynamic efficiency and investigating the uncertainty associated with each estimation method. We found that the methodology used by a study affects the estimated efficiency and can lead to incongruent conclusions on gliding bird aerodynamic efficiency. Our survey showed that studies on live birds gliding in wind tunnels provide a reliable minimum estimate of a birds' aerodynamic efficiency while simultaneously quantifying the wing configurations used in flight. Next, we surveyed the aeronautical literature to collect the published aerodynamic efficiencies of similar-sized, non-copter UAVs. The compiled information allowed a direct comparison of UAVs and gliding birds. Contrary to our expectation, we found that there is no definitive evidence that any gliding bird species is either more or less efficient than a comparable UAV. This non-result highlights a critical need for new technology and analytical advances that can reduce the uncertainty associated with estimating a gliding bird's aerodynamic efficiency. Nevertheless, our survey indicated that species flying within subcritical Reynolds number regimes may inspire UAV designs that can extend their operational range to efficiently operate in subcritical regimes. The survey results provided here point the way forward for research into avian gliding flight and enable informed UAV designs.}, } @article {pmid33156686, year = {2020}, author = {Friedrich, J and Gallon, S and Pumir, A and Grauer, R}, title = {Stochastic Interpolation of Sparsely Sampled Time Series via Multipoint Fractional Brownian Bridges.}, journal = {Physical review letters}, volume = {125}, number = {17}, pages = {170602}, doi = {10.1103/PhysRevLett.125.170602}, pmid = {33156686}, issn = {1079-7114}, abstract = {We propose and test a method to interpolate sparsely sampled signals by a stochastic process with a broad range of spatial and/or temporal scales. To this end, we extend the notion of a fractional Brownian bridge, defined as fractional Brownian motion with a given scaling (Hurst) exponent H and with prescribed start and end points, to a bridge process with an arbitrary number of intermediate and nonequidistant points. Determining the optimal value of the Hurst exponent H_{opt}, appropriate to interpolate the sparse signal, is a very important step of our method. We demonstrate the validity of our method on a signal from fluid turbulence in a high Reynolds number flow and discuss the implications of the non-self-similar character of the signal. The method introduced here could be instrumental in several physical problems, including astrophysics, particle tracking, and specific tailoring of surrogate data, as well as in domains of natural and social sciences.}, } @article {pmid33153075, year = {2020}, author = {Coclite, A and Coclite, GM and De Tommasi, D}, title = {Capsules Rheology in Carreau-Yasuda Fluids.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {11}, pages = {}, doi = {10.3390/nano10112190}, pmid = {33153075}, issn = {2079-4991}, support = {Prin 2017, 267 project code 2017J4EAYB//Ministero dell'Istruzione, dell'Università e della Ricerca/ ; CUP - D94I18000260001//Ministero dell'Istruzione, dell'Università e della Ricerca/ ; }, abstract = {In this paper, a Multi Relaxation Time Lattice Boltzmann scheme is used to describe the evolution of a non-Newtonian fluid. Such method is coupled with an Immersed-Boundary technique for the transport of arbitrarily shaped objects navigating the flow. The no-slip boundary conditions on immersed bodies are imposed through a convenient forcing term accounting for the hydrodynamic force generated by the presence of immersed geometries added to momentum equation. Moreover, such forcing term accounts also for the force induced by the shear-dependent viscosity model characterizing the non-Newtonian behavior of the considered fluid. Firstly, the present model is validated against well-known benchmarks, namely the parabolic velocity profile obtained for the flow within two infinite laminae for five values of the viscosity model exponent, n = 0.25, 0.50, 0.75, 1.0, and 1.5. Then, the flow within a squared lid-driven cavity for Re = 1000 and 5000 (being Re the Reynolds number) is computed as a function of n for a shear-thinning (n < 1) fluid. Indeed, the local decrements in the viscosity field achieved in high-shear zones implies the increment in the local Reynolds number, thus moving the position of near-walls minima towards lateral walls. Moreover, the revolution under shear of neutrally buoyant plain elliptical capsules with different Aspect Ratio (AR = 2 and 3) is analyzed for shear-thinning (n < 1), Newtonian (n = 1), and shear-thickening (n > 1) surrounding fluids. Interestingly, the power law by Huang et al. describing the revolution period of such capsules as a function of the Reynolds number and the existence of a critical value, Rec, after which the tumbling is inhibited in confirmed also for non-Newtonian fluids. Analogously, the equilibrium lateral position yeq of such neutrally buoyant capsules when transported in a plane-Couette flow is studied detailing the variation of yeq as a function of the Reynolds number as well as of the exponent n.}, } @article {pmid33152635, year = {2020}, author = {Kim, J and Jin, D and Choi, H and Kweon, J and Yang, DH and Kim, YH}, title = {A zero-dimensional predictive model for the pressure drop in the stenotic coronary artery based on its geometric characteristics.}, journal = {Journal of biomechanics}, volume = {113}, number = {}, pages = {110076}, doi = {10.1016/j.jbiomech.2020.110076}, pmid = {33152635}, issn = {1873-2380}, abstract = {The diameter- or area-reduction ratio measured from coronary angiography, commonly used in clinical practice, is not accurate enough to represent the functional significance of the stenosis, i.e., the pressure drop across the stenosis. We propose a new zero-dimensional model for the pressure drop across the stenosis considering its geometric characteristics and flow rate. To identify the geometric parameters affecting the pressure drop, we perform three-dimensional numerical simulations for thirty-three patient-specific coronary stenoses. From these numerical simulations, we show that the pressure drop is mostly determined by the curvature as well as the area-reduction ratio of the stenosis before the minimal luminal area (MLA), but heavily depends on the area-expansion ratio after the MLA due to flow separation. Based on this result, we divide the stenosis into the converging and diverging parts in the present zero-dimensional model. The converging part is segmented into a series of straight and curved pipes with curvatures, and the loss of each pipe is estimated by an empirical relation between the total pressure drop, flow rate, and pipe geometric parameters (length, diameter, and curvature). The loss in the diverging part is predicted by a relation among the total pressure drop, Reynolds number, and area expansion ratio with the coefficients determined by a machine learning method. The pressure drops across the stenoses predicted by the present zero-dimensional model agree very well with those obtained from three-dimensional numerical simulations.}, } @article {pmid33147949, year = {2020}, author = {Wang, Y and Zhou, G and Yan, Y and Shao, B and Hou, J}, title = {Construction of Natural Loofah/Poly(vinylidene fluoride) Core-Shell Electrospun Nanofibers via a Controllable Janus Nozzle for Switchable Oil-Water Separation.}, journal = {ACS applied materials & interfaces}, volume = {}, number = {}, pages = {}, doi = {10.1021/acsami.0c12912}, pmid = {33147949}, issn = {1944-8252}, abstract = {Developing microstructure and multifunctional membranes toward switchable oil-water separation has been highly desired in oily wastewater treatment. Herein, a controllable Janus nozzle was employed to innovatively electrospin natural loofah/poly(vinylidene fluoride) (PVDF) nanofibers with a core-shell structure for gravity-driven water purification. By adjusting flow rates of the PVDF component, a core-shell structure of the composite fibers was obtained caused by the lower viscosity and surface tension of PVDF. In addition, a steady laminar motion of fluids was constructed based on the Reynolds number of flow fields being less than 2300. In order to investigate the formation mechanism of the microstructure, a series of Janus nozzles with different lengths were controlled to study the blending of the two immiscible components. The gravity difference between the two components might cause disturbance of the jet motion, and the PVDF component unidirectionally encapsulated the loofah to form the shell layer. Most importantly, the dry loofah/PVDF membranes could separate oil from an oil-water mixture, while the water-wetted membrane exhibited switchable separation that could separate water from the mixtures because of the hydroxyl groups of the hydrophilic loofah hydrogen-bonding with water molecules and forming a hydration layer. The composite fibers can be applied in water remediation in practice, and the method to produce core-shell structures seems attractive for technological applications involving macroscopic core-shell nano- or microfibers.}, } @article {pmid33136360, year = {2020}, author = {Jeon, W and Ahn, J and Kim, T and Kim, SM and Baik, S}, title = {Intertube Aggregation-Dependent Convective Heat Transfer in Vertically Aligned Carbon Nanotube Channels.}, journal = {ACS applied materials & interfaces}, volume = {12}, number = {45}, pages = {50355-50364}, doi = {10.1021/acsami.0c13361}, pmid = {33136360}, issn = {1944-8252}, abstract = {The heat transfer of carbon nanotube fin geometry has received considerable attention. However, the flow typically occurred over or around the pillars of nanotubes due to the greater flow resistance between the tubes. Here, we investigated the forced convective heat transfer of water through the interstitial space of vertically aligned multiwalled carbon nanotubes (VAMWNTs, intertube distance = 69 nm). The water flow provided significantly a greater Reynolds number (Re) and Nusselt number (Nu) than air flow due to the greater density, heat capacity, and thermal conductivity. However, it resulted in surface tension-induced nanotube aggregation after the flow and drying process, generating random voids in the nanotube channel. This increased permeability (1.27 × 10-11 m2) and Re (2.83 × 10-1) but decreased the heat transfer coefficient (h, 9900 W m-2 K-1) and Nu (53.77), demonstrating a trade-off relationship. The h (25,927 W m-2 K-1) and Nu (153.49) could be further increased, at an equivalent permeability or Re, by increasing nanotube areal density from 2.08 × 1010 to 1.04 × 1011 cm-2. The area-normalized thermal resistance of the densified and aggregated VAMWNTs was smaller than those of the Ni foam, Si microchannel, and carbon nanotube fin array, demonstrating excellent heat transfer characteristics.}, } @article {pmid33119653, year = {2020}, author = {Lyons, K and Murphy, CT and Franck, JA}, title = {Flow over seal whiskers: Importance of geometric features for force and frequency response.}, journal = {PloS one}, volume = {15}, number = {10}, pages = {e0241142}, pmid = {33119653}, issn = {1932-6203}, abstract = {The complex undulated geometry of seal whiskers has been shown to substantially modify the turbulent structures directly downstream, resulting in a reduction of hydrodynamic forces as well as modified vortex-induced-vibration response when compared with smooth whiskers. Although the unique hydrodynamic response has been well documented, an understanding of the fluid flow effects from each geometric feature remains incomplete. In this computational investigation, nondimensional geometric parameters of the seal whisker morphology are defined in terms of their hydrodynamic relevance, such that wavelength, aspect ratio, undulation amplitudes, symmetry and undulation off-set can be varied independently of one another. A two-factor fractional factorial design of experiments procedure is used to create 16 unique geometries, each of which dramatically amplifies or attenuates the geometric parameters compared with the baseline model. The flow over each unique topography is computed with a large-eddy simulation at a Reynolds number of 500 with respect to the mean whisker thickness and the effects on force and frequency are recorded. The results determine the specific fluid flow impact of each geometric feature which will inform both biologists and engineers who seek to understand the impact of whisker morphology or lay out a framework for biomimetic design of undulated structures.}, } @article {pmid33095615, year = {2020}, author = {Neuhaus, L and Hölling, M and Bos, WJT and Peinke, J}, title = {Generation of Atmospheric Turbulence with Unprecedentedly Large Reynolds Number in a Wind Tunnel.}, journal = {Physical review letters}, volume = {125}, number = {15}, pages = {154503}, doi = {10.1103/PhysRevLett.125.154503}, pmid = {33095615}, issn = {1079-7114}, abstract = {Generating laboratory flows resembling atmospheric turbulence is of prime importance to study the effect of wind fluctuations on objects such as buildings, vehicles, or wind turbines. A novel driving of an active grid following a stochastic process is used to generate velocity fluctuations with correlation lengths, and, thus, integral scales, much larger than the transverse dimension of the wind tunnel. The combined action of the active grid and a modulation of the fan speed allows one to generate a flow characterized by a four-decade inertial range and an integral scale Reynolds number of 2×10^{7}.}, } @article {pmid33092016, year = {2020}, author = {Domínguez-Pumar, M and Kowalski, L and Jiménez, V and Rodríguez, I and Soria, M and Bermejo, S and Pons-Nin, J}, title = {Analyzing the Performance of a Miniature 3D Wind Sensor for Mars.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {20}, pages = {}, pmid = {33092016}, issn = {1424-8220}, support = {RTI2018-098728-B-C33//Ministerio de Economía y Competitividad/ ; }, abstract = {This paper analyzes the behavior of a miniature 3D wind sensor designed for Mars atmosphere. The sensor is a spherical structure of 10 mm diameter divided in four sectors. By setting all the sectors to constant temperature, above that of the air, the 3D wind velocity vector can be measured. Two sets of experiments have been performed. First, an experimental campaign made under typical Mars conditions at the Aarhus Wind Tunnel Simulator is presented. The results demonstrate that both wind speed and angle can be efficiently measured, using a simple inverse algorithm. The effect of sudden wind changes is also analyzed and fast response times in the range of 0.7 s are obtained. The second set of experiments is focused on analyzing the performance of the sensor under extreme Martian wind conditions, reaching and going beyond the Dust Devil scale. To this purpose, both high-fidelity numerical simulations of fluid dynamics and heat transfer and experiments with the sensor have been performed. The results of the experiments, made for winds in the Reynolds number 1000-2000 range, which represent 65-130 m/s of wind speed under typical Mars conditions, further confirm the simulation predictions and show that it will be possible to successfully measure wind speed and direction even under these extreme regimes.}, } @article {pmid33076024, year = {2020}, author = {Czelusniak, LE and Mapelli, VP and Guzella, MS and Cabezas-Gómez, L and Wagner, AJ}, title = {Force approach for the pseudopotential lattice Boltzmann method.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {033307}, doi = {10.1103/PhysRevE.102.033307}, pmid = {33076024}, issn = {2470-0053}, abstract = {One attractive feature of the original pseudopotential method consists on its simplicity of adding a force dependent on a nearest-neighbor potential function. In order to improve the method, regarding thermodynamic consistency and control of surface tension, different approaches were developed in the literature, such as multirange interactions potential and modified forcing schemes. In this work, a strategy to combine these enhancements with an appropriate interaction force field using only nearest-neighbor interactions is devised, starting from the desired pressure tensor. The final step of our procedure is implementing this external force by using the classical Guo forcing scheme. Numerical tests regarding static and dynamic flow conditions were performed. Static tests showed that current procedure is suitable to control the surface tension and phase densities. Based on thermodynamic principles, it is devised a solution for phase densities in a droplet, which states explicitly dependence on the surface tension and interface curvature. A comparison with numerical results suggest a physical inconsistency in the pseudopotential method. This fact is not commonly discussed in the literature, since most of studies are limited to the Maxwell equal area rule. However, this inconsistency is shown to be dependent on the equation of state (EOS), and its effects can be mitigated by an appropriate choice of Carnahan-Starling EOS parameters. Also, a droplet oscillation test was performed, and the most divergent solution under certain flow conditions deviated 7.5% from the expected analytical result. At the end, a droplet impact test against a solid wall was performed to verify the method stability, and it was possible to reach stable simulation results with density ratio of almost 2400 and Reynolds number of Re=373. The observed results corroborate that the proposed method is able to replicate the desired macroscopic multiphase behavior.}, } @article {pmid33076003, year = {2020}, author = {Rana, N and Perlekar, P}, title = {Coarsening in the two-dimensional incompressible Toner-Tu equation: Signatures of turbulence.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {032617}, doi = {10.1103/PhysRevE.102.032617}, pmid = {33076003}, issn = {2470-0053}, abstract = {We investigate coarsening dynamics in the two-dimensional, incompressible Toner-Tu equation. We show that coarsening proceeds via vortex merger events, and the dynamics crucially depend on the Reynolds number Re. For low Re, the coarsening process has similarities to Ginzburg-Landau dynamics. On the other hand, for high Re, coarsening shows signatures of turbulence. In particular, we show the presence of an enstrophy cascade from the intervortex separation scale to the dissipation scale.}, } @article {pmid33075904, year = {2020}, author = {Bos, WJT and Laadhari, F and Agoua, W}, title = {Linearly forced isotropic turbulence at low Reynolds numbers.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {033105}, doi = {10.1103/PhysRevE.102.033105}, pmid = {33075904}, issn = {2470-0053}, abstract = {We investigate the forcing strength needed to sustain a flow using linear forcing. A critical Reynolds number R_{c} is determined, based on the longest wavelength allowed by the system, the forcing strength and the viscosity. A simple model is proposed for the dissipation rate, leading to a closed expression for the kinetic energy of the flow as a function of the Reynolds number. The dissipation model and the prediction for the kinetic energy are assessed using direct numerical simulations and two-point closure integrations. An analysis of the dissipation-rate equation and the triadic structure of the nonlinear transfer allows to refine the model in order to reproduce the low-Reynolds-number asymptotic behavior, where the kinetic energy is proportional to R-R_{c}.}, } @article {pmid33075884, year = {2020}, author = {Rinoshika, H and Rinoshika, A and Wang, JJ}, title = {Three-dimensional multiscale flow structures behind a wall-mounted short cylinder based on tomographic particle image velocimetry and three-dimensional orthogonal wavelet transform.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {033101}, doi = {10.1103/PhysRevE.102.033101}, pmid = {33075884}, issn = {2470-0053}, abstract = {Three-dimensional (3D) flow structures around a wall-mounted short cylinder of height-to-diameter ratio 1 were instantaneously measured by a high-resolution tomographic particle image velocimetry (Tomo-PIV) at Reynolds number of 10 720 in a water tunnel. 3D velocity fields, 3D vorticity, the Q criterion, the rear separation region, and the characteristic of arch type vortex and tip vortices were first discussed. We found a strong 3D W-type arch vortex behind the short cylinder, which was originated by the interaction between upwash and downwash flows. This W-type arch vortex was reshaped to the M-shaped arch vortex downstream. It indicated that the head shape of the arch vortex structure depended on the aspect ratio of the cylinder. The large-scale streamwise vortices were originated by the downwash and upwash flows near the center location of W-type arch vortex. Then the 3D orthogonal wavelet multiresolution technique was developed to analyze instantaneous 3D velocity fields of Tomo-PIV in order to clarify 3D multiscale wake flow structures. The W-type shape arch vortex was extracted in the time-averaged intermediate-scale structure, while an M-shaped arch vortex was identified in the time-averaged large-scale structure. The tip vortices distributed in the time-averaged large- and intermediate-scale structures. The instantaneous intermediate-scale upwash vortices played an essential role in producing W-type head of arch structure. It was also observed that strong small-scale vortices appeared in the shear layer or near the bottom plate and most of them were contained in the intermediate-scale structures.}, } @article {pmid33057044, year = {2020}, author = {Riasat, S and Ramzan, M and Kadry, S and Chu, YM}, title = {Significance of magnetic Reynolds number in a three-dimensional squeezing Darcy-Forchheimer hydromagnetic nanofluid thin-film flow between two rotating disks.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {17208}, pmid = {33057044}, issn = {2045-2322}, support = {11971142//National Natural Science Foundation of China/ ; 11871202//National Natural Science Foundation of China/ ; 61673169//National Natural Science Foundation of China/ ; 11701176//National Natural Science Foundation of China/ ; 11626101//National Natural Science Foundation of China/ ; 11601485//National Natural Science Foundation of China/ ; }, abstract = {The remarkable aspects of carbon nanotubes like featherweight, durability, exceptional electrical and thermal conduction capabilities, and physicochemical stability make them desirous materials for electrochemical devices. Having such astonishing characteristics of nanotubes in mind our aspiration is to examine the squeezing three dimensional Darcy-Forchheimer hydromagnetic nanofluid thin-film flow amid two rotating disks with suspended multiwalled carbon nanotubes (MWCNTs) submerged into the base fluid water. The analysis is done by invoking partial slip effect at the boundary in attendance of autocatalytic reactions. The mathematical model consists of axial and azimuthal momentum and magnetic fields respectively. The tangential and axial velocity profiles and components of the magnetic field are examined numerically by employing the bvp4c method for varying magnetic, rotational, and squeezing Reynolds number. The torque effect near the upper and lower disks are studied critically using their graphical depiction. The values of the torque at the upper and lower disks are obtained for rotational and squeezed Reynolds numbers and are found in an excellent concurrence when compared with the existing literature. Numerically it is computed that the torque at the lower disk is higher in comparison to the upper disk for mounting estimates of the squeezed Reynolds number and the dimensionless parameter for magnetic force in an axial direction. From the graphical illustrations, it is learned that thermal profile declines for increasing values of the squeezed Reynolds number.}, } @article {pmid33049170, year = {2020}, author = {Wong, JY and Chan, BKK and Chan, KYK}, title = {Swimming kinematics and hydrodynamics of barnacle larvae throughout development.}, journal = {Proceedings. Biological sciences}, volume = {287}, number = {1936}, pages = {20201360}, doi = {10.1098/rspb.2020.1360}, pmid = {33049170}, issn = {1471-2954}, abstract = {Changes in size strongly influence organisms' ecological performances. For aquatic organisms, they can transition from viscosity- to inertia-dominated fluid regimes as they grow. Such transitions are often associated with changes in morphology, swimming speed and kinematics. Barnacles do not fit into this norm as they have two morphologically distinct planktonic larval phases that swim differently but are of comparable sizes and operate in the same fluid regime (Reynolds number 100-101). We quantified the hydrodynamics of the rocky intertidal stalked barnacle Capitulum mitella from the nauplius II to cyprid stage and examined how kinematics and size increases affect its swimming performance. Cyprids beat their appendages in a metachronal wave to swim faster, more smoothly, and with less backwards slip per beat cycle than did all naupliar stages. Micro-particle image velocimetry showed that cyprids generated trailing viscous vortex rings that pushed water backwards for propulsion, contrary to the nauplii's forward suction current for particle capture. Our observations highlight that zooplankton swimming performance can shift via morphological and kinematic modifications without a significant size increase. The divergence in ecological functions through ontogeny in barnacles and the removal of feeding requirement likely contributed to the evolution of the specialized, taxonomically unique cyprid phase.}, } @article {pmid33026993, year = {2020}, author = {Jakob, J and Gross, M and Gunther, T}, title = {A Fluid Flow Data Set for Machine Learning and its Application to Neural Flow Map Interpolation.}, journal = {IEEE transactions on visualization and computer graphics}, volume = {PP}, number = {}, pages = {}, doi = {10.1109/TVCG.2020.3028947}, pmid = {33026993}, issn = {1941-0506}, abstract = {In recent years, deep learning has opened countless research opportunities across many different disciplines. At present, visualization is mainly applied to explore and explain neural networks. Its counterpart-the application of deep learning to visualization problems-requires us to share data more openly in order to enable more scientists to engage in data-driven research. In this paper, we construct a large fluid flow data set and apply it to a deep learning problem in scientific visualization. Parameterized by the Reynolds number, the data set contains a wide spectrum of laminar and turbulent fluid flow regimes. The full data set was simulated on a high-performance compute cluster and contains 8000 time-dependent 2D vector fields, accumulating to more than 16 TB in size. Using our public fluid data set, we trained deep convolutional neural networks in order to set a benchmark for an improved post-hoc Lagrangian fluid flow analysis. In in-situ settings, flow maps are exported and interpolated in order to assess the transport characteristics of time-dependent fluids. Using deep learning, we improve the accuracy of flow map interpolations, allowing a more precise flow analysis at a reduced memory IO footprint.}, } @article {pmid33022594, year = {2020}, author = {Di Luca, M and Mintchev, S and Su, Y and Shaw, E and Breuer, K}, title = {A bioinspired Separated Flow wing provides turbulence resilience and aerodynamic efficiency for miniature drones.}, journal = {Science robotics}, volume = {5}, number = {38}, pages = {}, doi = {10.1126/scirobotics.aay8533}, pmid = {33022594}, issn = {2470-9476}, abstract = {Small-scale drones have enough sensing and computing power to find use across a growing number of applications. However, flying in the low-Reynolds number regime remains challenging. High sensitivity to atmospheric turbulence compromises vehicle stability and control, and low aerodynamic efficiency limits flight duration. Conventional wing designs have thus far failed to address these two deficiencies simultaneously. Here, we draw inspiration from nature's small flyers to design a wing with lift generation robust to gusts and freestream turbulence without sacrificing aerodynamic efficiency. This performance is achieved by forcing flow separation at the airfoil leading edge. Water and wind tunnel measurements are used to demonstrate the working principle and aerodynamic performance of the wing, showing a substantial reduction in the sensitivity of lift force production to freestream turbulence, as compared with the performance of an Eppler E423 low-Reynolds number wing. The minimum cruise power of a custom-built 104-gram fixed-wing drone equipped with the Separated Flow wing was measured in the wind tunnel indicating an upper limit for the flight time of 170 minutes, which is about four times higher than comparable existing fixed-wing drones. In addition, we present scaling guidelines and outline future design and manufacturing challenges.}, } @article {pmid33020499, year = {2020}, author = {Phelps, PR and Lee, CA and Morton, DM}, title = {Episodes of fast crystal growth in pegmatites.}, journal = {Nature communications}, volume = {11}, number = {1}, pages = {4986}, pmid = {33020499}, issn = {2041-1723}, abstract = {Pegmatites are shallow, coarse-grained magmatic intrusions with crystals occasionally approaching meters in length. Compared to their plutonic hosts, pegmatites are thought to have cooled rapidly, suggesting that these large crystals must have grown fast. Growth rates and conditions, however, remain poorly constrained. Here we investigate quartz crystals and their trace element compositions from miarolitic cavities in the Stewart pegmatite in southern California, USA, to quantify crystal growth rates. Trace element concentrations deviate considerably from equilibrium and are best explained by kinetic effects associated with rapid crystal growth. Kinetic crystal growth theory is used to show that crystals accelerated from an initial growth rate of 10-6-10-7 m s-1 to 10-5-10-4 m s-1 (10-100 mm day-1 to 1-10 m day-1), indicating meter sized crystals could have formed within days, if these rates are sustained throughout pegmatite formation. The rapid growth rates require that quartz crystals grew from thin (micron scale) chemical boundary layers at the fluid-crystal interfaces. A strong advective component is required to sustain such thin boundary layers. Turbulent conditions (high Reynolds number) in these miarolitic cavities are shown to exist during crystallization, suggesting that volatile exsolution, crystallization, and cavity generation occur together.}, } @article {pmid32992553, year = {2020}, author = {Qiu, Y and Hu, W and Wu, C and Chen, W}, title = {An Experimental Study of Microchannel and Micro-Pin-Fin Based On-Chip Cooling Systems with Silicon-to-Silicon Direct Bonding.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {19}, pages = {}, pmid = {32992553}, issn = {1424-8220}, support = {51575487//National Natural Science Foundation of China/ ; 6162790014//National Natural Science Foundation of China/ ; }, abstract = {This paper describes an experimental study of the cooling capabilities of microchannel and micro-pin-fin based on-chip cooling systems. The on-chip cooling systems integrated with a micro heat sink, simulated power IC (integrated circuit) and temperature sensors are fabricated by micromachining and silicon-to-silicon direct bonding. Three micro heat sink structures: a microchannel heat sink (MCHS), an inline micro-pin-fin heat sink (I-MPFHS) and a staggered micro-pin-fin heat sink (S-MPFHS) are tested in the Reynolds number range of 79.2 to 882.3. The results show that S-MPFHS is preferred if the water pump can provide enough pressure drop. However, S-MPFHS has the worst performance when the rated pressure drop of the pump is lower than 1.5 kPa because the endwall effect under a low Reynolds number suppresses the disturbance generated by the staggered micro pin fins but S-MPFHS is still preferred when the rated pressure drop of the pump is in the range of 1.5 to 20 kPa. When the rated pressure drop of the pump is higher than 20 kPa, I-MPFHS will be the best choice because of high heat transfer enhancement and low pressure drop price brought by the unsteady vortex street.}, } @article {pmid32992113, year = {2020}, author = {Chen, Y and Chen, Y and Hu, S and Ni, Z}, title = {Continuous ultrasonic flow measurement for aerospace small pipelines.}, journal = {Ultrasonics}, volume = {109}, number = {}, pages = {106260}, doi = {10.1016/j.ultras.2020.106260}, pmid = {32992113}, issn = {1874-9968}, abstract = {Aerospace explorations stimulate extensive research on innovative propellant flow measurement technologies in microgravity conditions. Ultrasonic-based measurements have advantages of non-invasive and non-moving-component constructions as well as fast responses to bi-directional flow detection, its applications in aerospace explorations have already been reported. To avoid the shortages of pulse ultrasonic measurement configurations, flow measurement of continuous ultrasonic wave propagation is presented to match the requirements of large measurement range and high precision. Fabrication process and laboratory validations using water flow are presented. Ground experiments show that the linearity of the proposed ultrasonic flow meter is obtained in the measurement range [0, 80 ml/s] which is typical requirement in aerospace applications. Meanwhile, the fitted linear feature from the experimental data matches well the theoretical prediction except the flow prediction of stationary fluid. Under specific configurations, the absolute measurement error is significantly affected by the corresponding Reynolds number. Furthermore, the absolute measurement error is smaller when excitation signals with higher frequency are used if the phase tracking performance for different frequencies is identical.}, } @article {pmid32984706, year = {2020}, author = {Ye, Y and Luo, X and Dong, C and Xu, Y and Zhang, Z}, title = {Numerical and Experimental Investigation of Soot Suppression by Acoustic Oscillated Combustion.}, journal = {ACS omega}, volume = {5}, number = {37}, pages = {23866-23875}, pmid = {32984706}, issn = {2470-1343}, abstract = {The soot suppression by acoustic oscillations for acetylene diffusion flames was investigated combining numerical and experimental studies. The combustion and soot formation were predicted by the finite-rate detailed chemistry model and modified Moss-Brookes model, respectively, while the turbulence was predicted by the detached eddy simulation (DES) with a low Reynolds number correction. Experimental results showed that the soot rate almost decreased linearly with the amplitude of acoustic oscillation, and the pinch-off of the flame occurred at a large acoustic oscillation. Numerical results showed that the flame structure was well predicted, while the soot rate was over-predicted at large acoustic oscillations; the consumption of O2 increased obviously with the acoustic oscillation. The soot suppression was mainly caused by the decrease of the surface growth rate when the air was pushed toward the flame.}, } @article {pmid32982135, year = {2020}, author = {Dbouk, T and Drikakis, D}, title = {Weather impact on airborne coronavirus survival.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {9}, pages = {093312}, pmid = {32982135}, issn = {1070-6631}, abstract = {The contribution of this paper toward understanding of airborne coronavirus survival is twofold: We develop new theoretical correlations for the unsteady evaporation of coronavirus (CoV) contaminated saliva droplets. Furthermore, we implement the new correlations in a three-dimensional multiphase Eulerian-Lagrangian computational fluid dynamics solver to study the effects of weather conditions on airborne virus transmission. The new theory introduces a thermal history kernel and provides transient Nusselt (Nu) and Sherwood (Sh) numbers as a function of the Reynolds (Re), Prandtl (Pr), and Schmidt numbers (Sc). For the first time, these new correlations take into account the mixture properties due to the concentration of CoV particles in a saliva droplet. We show that the steady-state relationships induce significant errors and must not be applied in unsteady saliva droplet evaporation. The classical theory introduces substantial deviations in Nu and Sh values when increasing the Reynolds number defined at the droplet scale. The effects of relative humidity, temperature, and wind speed on the transport and viability of CoV in a cloud of airborne saliva droplets are also examined. The results reveal that a significant reduction of virus viability occurs when both high temperature and low relative humidity occur. The droplet cloud's traveled distance and concentration remain significant at any temperature if the relative humidity is high, which is in contradiction with what was previously believed by many epidemiologists. The above could explain the increase in CoV cases in many crowded cities around the middle of July (e.g., Delhi), where both high temperature and high relative humidity values were recorded one month earlier (during June). Moreover, it creates a crucial alert for the possibility of a second wave of the pandemic in the coming autumn and winter seasons when low temperatures and high wind speeds will increase airborne virus survival and transmission.}, } @article {pmid32973078, year = {2020}, author = {York, CA and Bartol, IK and Krueger, PS and Thompson, JT}, title = {Squids use multiple escape jet patterns throughout ontogeny.}, journal = {Biology open}, volume = {9}, number = {11}, pages = {}, doi = {10.1242/bio.054585}, pmid = {32973078}, issn = {2046-6390}, abstract = {Throughout their lives, squids are both predators and prey for a multitude of animals, many of which are at the top of ocean food webs, making them an integral component of the trophic structure of marine ecosystems. The escape jet, which is produced by the rapid expulsion of water from the mantle cavity through a funnel, is central to a cephalopod's ability to avoid predation throughout its life. Although squid undergo morphological and behavioral changes and experience remarkably different Reynolds number regimes throughout their development, little is known about the dynamics and propulsive efficiency of escape jets throughout ontogeny. We examine the hydrodynamics and kinematics of escape jets in squid throughout ontogeny using 2D/3D velocimetry and high-speed videography. All life stages of squid produced two escape jet patterns: (1) 'escape jet I' characterized by short rapid pulses resulting in vortex ring formation and (2) 'escape jet II' characterized by long high-volume jets, often with a leading-edge vortex ring. Paralarvae exhibited higher propulsive efficiency than adult squid during escape jet ejection, and propulsive efficiency was higher for escape jet I than escape jet II in juveniles and adults. These results indicate that although squid undergo major ecological transitions and morphology changes from paralarvae to adults, all life stages demonstrate flexibility in escape jet responses and produce escape jets of surprisingly high propulsive efficiency.This article has an associated First Person interview with the first author of the paper.}, } @article {pmid32968087, year = {2020}, author = {Saqr, KM and Tupin, S and Rashad, S and Endo, T and Niizuma, K and Tominaga, T and Ohta, M}, title = {Physiologic blood flow is turbulent.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {15492}, pmid = {32968087}, issn = {2045-2322}, abstract = {Contemporary paradigm of peripheral and intracranial vascular hemodynamics considers physiologic blood flow to be laminar. Transition to turbulence is considered as a driving factor for numerous diseases such as atherosclerosis, stenosis and aneurysm. Recently, turbulent flow patterns were detected in intracranial aneurysm at Reynolds number below 400 both in vitro and in silico. Blood flow is multiharmonic with considerable frequency spectra and its transition to turbulence cannot be characterized by the current transition theory of monoharmonic pulsatile flow. Thus, we decided to explore the origins of such long-standing assumption of physiologic blood flow laminarity. Here, we hypothesize that the inherited dynamics of blood flow in main arteries dictate the existence of turbulence in physiologic conditions. To illustrate our hypothesis, we have used methods and tools from chaos theory, hydrodynamic stability theory and fluid dynamics to explore the existence of turbulence in physiologic blood flow. Our investigation shows that blood flow, both as described by the Navier-Stokes equation and in vivo, exhibits three major characteristics of turbulence. Womersley's exact solution of the Navier-Stokes equation has been used with the flow waveforms from HaeMod database, to offer reproducible evidence for our findings, as well as evidence from Doppler ultrasound measurements from healthy volunteers who are some of the authors. We evidently show that physiologic blood flow is: (1) sensitive to initial conditions, (2) in global hydrodynamic instability and (3) undergoes kinetic energy cascade of non-Kolmogorov type. We propose a novel modification of the theory of vascular hemodynamics that calls for rethinking the hemodynamic-biologic links that govern physiologic and pathologic processes.}, } @article {pmid32959981, year = {2020}, author = {Gibson, BM and Furbish, DJ and Rahman, IA and Schmeeckle, MW and Laflamme, M and Darroch, SAF}, title = {Ancient life and moving fluids.}, journal = {Biological reviews of the Cambridge Philosophical Society}, volume = {}, number = {}, pages = {}, doi = {10.1111/brv.12649}, pmid = {32959981}, issn = {1469-185X}, support = {9968-16//National Geographic Society/ ; EAR-1735992//National Science Foundation/ ; Arthur Boucot Award//Paleontological Society/ ; Alberstadt-Reesman-Stearns Research Grant//Vanderbilt University/ ; }, abstract = {Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft-bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in-depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life.}, } @article {pmid32959135, year = {2020}, author = {Sonnenberg, AH and Taylor, E and Mondoñedo, JR and Jawde, SB and Amin, SD and Song, J and Grinstaff, MW and Suki, B}, title = {Breath Hold Facilitates Targeted Deposition of Aerosolized Droplets in a 3D Printed Bifurcating Airway Tree.}, journal = {Annals of biomedical engineering}, volume = {}, number = {}, pages = {}, doi = {10.1007/s10439-020-02623-9}, pmid = {32959135}, issn = {1573-9686}, support = {U01 HL-139466/HL/NHLBI NIH HHS/United States ; HU0001810012//Defense Health Agency/ ; }, abstract = {The lungs have long been considered a desired route for drug delivery but, there is still a lack of strategies to rationally target delivery sites especially in the presence of heterogeneous airway disease. Furthermore, no standardized system has been proposed to rapidly test different ventilation strategies and how they alter the overall and regional deposition pattern in the airways. In this study, a 3D printed symmetric bifurcating tree model mimicking part of the human airway tree was developed that can be used to quantify the regional deposition patterns of different delivery methodologies. The model is constructed in a novel way that allows for repeated measurements of regional deposition using reusable parts. During ventilation, nebulized ~3-micron-sized fluid droplets were delivered into the model. Regional delivery, quantified by precision weighing individual airways, was highly reproducible. A successful strategy to control regional deposition was achieved by combining an inspiratory wave form with a "breath hold" pause after each inspiration. Specifically, the second generation of the tree was successfully targeted, and deposition was increased by up to four times in generation 2 when compared to a ventilation without the breath hold (p < 0.0001). Breath hold was also demonstrated to facilitate deposition into blocked regions of the model, which mimic airway closure during an asthma that receive no flow during inhalation. Additionally, visualization experiments demonstrated that in the absence of fluid flow, the deposition of 3-micron water droplets is dominated by gravity, which, to our knowledge, has not been confirmed under standard laboratory conditions.}, } @article {pmid32952737, year = {2020}, author = {Bortot, M and Sharifi, A and Ashworth, K and Walker, F and Cox, A and Ruegg, K and Clendenen, N and Neeves, KB and Bark, D and Di Paola, J}, title = {Pathologic Shear and Elongation Rates Do Not Cause Cleavage of Von Willebrand Factor by ADAMTS13 in a Purified System.}, journal = {Cellular and molecular bioengineering}, volume = {13}, number = {4}, pages = {379-390}, pmid = {32952737}, issn = {1865-5025}, abstract = {Introduction: Pathological flows in patients with severe aortic stenosis are associated with acquired von Willebrand syndrome. This syndrome is characterized by excessive cleavage of von Willebrand factor by its main protease, A Disintegrin and Metalloproteinase with a Thrombospondin Type 1 Motif, Member 13 (ADAMTS13) leading to decreased VWF function and mucocutaneous bleeding. Aortic valve replacement and correction of the flow behavior to physiological levels reverses the syndrome, supporting the association between pathological flow and acquired von Willebrand syndrome. We investigated the effects of shear and elongational rates on von Willebrand factor cleavage in the presence of ADAMTS13.

Methods: We identified acquired von Willebrand syndrome in five patients with severe aortic stenosis. Doppler echography values from these patients were used to develop three computational fluid dynamic (CFD) aortic valve models (normal, mild and severe stenosis). Shear, elongational rates and exposure times identified in the CFD simulations were used as parameters for the design of microfluidic devices to test the effects of pathologic shear and elongational rates on the structure and function of von Willebrand factor.

Results: The shear rates (0-10,000s-1), elongational rates (0-1000 s-1) and exposure times (1-180 ms) tested in our microfluidic designs mimicked the flow features identified in patients with aortic stenosis. The shear and elongational rates tested in vitro did not lead to excessive cleavage or decreased function of von Willebrand factor in the presence of the protease.

Conclusions: High shear and elongational rates in the presence of ADAMTS13 are not sufficient for excessive cleavage of von Willebrand Factor.}, } @article {pmid32946425, year = {2020}, author = {Gao, D and Bai, M and Hu, C and Lv, J and Wang, C and Zhang, X}, title = {Investigating control of convective heat transfer and flow resistance of Fe3O4/deionized water nanofluid in magnetic field in laminar flow.}, journal = {Nanotechnology}, volume = {31}, number = {49}, pages = {495402}, doi = {10.1088/1361-6528/abb15c}, pmid = {32946425}, issn = {1361-6528}, abstract = {This paper studies the convective heat transfer and flow resistance of Fe3O4/deionized water nanofluids in laminar flow under the control of an external magnetic field. The basic thermophysical parameters including viscosity, specific heat capacity and thermal conductivity are investigated to describe the fundamental performance of heat transfer and flow resistance. In the absence of the magnetic field, the heat transfer coefficients and flow friction could not change significantly at nanoparticle volume concentration of 0.05%. In the presence of the magnetic field, it can enhance heat transfer and flow resistance by 6% and 3.5% when the magnets interlace on both sides of the tube. The dynamic magnetic experiments discussed the heat transfer increase process in detail. The heat transfer and the flow resistance increase by 11.7% and 5.4% when magnetic field strength is 600 Gs, nanoparticle volume concentration is 2% and Reynolds number is 2000. The radial shuttle movement of magnetic nanoparticles in the cross-section, micro convection in base fluid and the slip velocity between the nanoparticles and the base fluid are considered the main reasons for heat transfer enhancement.}, } @article {pmid32942486, year = {2020}, author = {Mukhopadhyay, S and Mukhopadhyay, A}, title = {Waves and instabilities of viscoelastic fluid film flowing down an inclined wavy bottom.}, journal = {Physical review. E}, volume = {102}, number = {2-1}, pages = {023117}, doi = {10.1103/PhysRevE.102.023117}, pmid = {32942486}, issn = {2470-0053}, abstract = {Evolution of waves and hydrodynamic instabilities of a thin viscoelastic fluid film flowing down an inclined wavy bottom of moderate steepness have been analyzed analytically and numerically. The classical long-wave expansion method has been used to formulate a nonlinear evolution equation for the development of the free surface. A normal-mode approach has been adopted to discuss the linear stability analysis from the viewpoint of the spatial and temporal study. The method of multiple scales is used to derive a Ginzburg-Landau-type nonlinear equation for studying the weakly nonlinear stability solutions. Two significant wave families, viz., γ_{1} and γ_{2}, are found and discussed in detail along with the traveling wave solution of the evolution system. A time-dependent numerical study is performed with Scikit-FDif. The entire investigation is conducted primarily for a general periodic bottom, and the detailed results of a particular case study of sinusoidal topography are then discussed. The case study reveals that the bottom steepness ζ plays a dual role in the linear regime. Increasing ζ has a stabilizing effect in the uphill region, and the opposite occurs in the downhill region. While the viscoelastic parameter Γ has a destabilizing effect throughout the domain in both the linear and the nonlinear regime. Both supercritical and subcritical solutions are possible through a weakly nonlinear analysis. It is interesting to note that the unconditional zone decreases and the explosive zone increases in the downhill region rather than the uphill region for a fixed Γ and ζ. The same phenomena occur in a particular region if we increase Γ and keep ζ fixed. The traveling wave solution reveals the fact that to get the γ_{1} family of waves we need to increase the Reynolds number a bit more than the value at which the γ_{2} family of waves is found. The spatiotemporal evolution of the nonlinear surface equation indicates that different kinds of finite-amplitude permanent waves exist.}, } @article {pmid32942407, year = {2020}, author = {Hassan, MR and Wang, C}, title = {Lateral migration of a ferrofluid droplet in a plane Poiseuille flow under uniform magnetic fields.}, journal = {Physical review. E}, volume = {102}, number = {2-1}, pages = {022611}, doi = {10.1103/PhysRevE.102.022611}, pmid = {32942407}, issn = {2470-0053}, abstract = {The lateral migration of a two-dimensional (2D) viscous ferrofluid droplet in a plane Poiseuille flow under a uniform magnetic field is studied numerically by using the level set method. Focusing on low droplet Reynolds number flows (Re_{d}≤0.05), several numerical simulations are carried out to analyze the effects of magnetic field direction and strength, droplet size, and viscosity ratio on the lateral migration behavior of the droplet. The results indicate that the magnetic field direction plays a pivotal role in the trajectory of lateral migration of the droplet and the final equilibrium position in the channel. When the magnetic field is parallel to the channel, i.e., α=0^{∘} (the direction of magnetic field), the droplet is found to settle closer to the wall with an increase in magnetic Bond number Bo_{m}, while at α=45^{∘}, the droplet settles closer to the channel center. Varying the initial droplet sizes at a fixed magnetic Bond number Bo_{m} and viscosity ratio λ results in different final equilibrium positions within the channel. Additionally, the effect of different viscosity ratios on the migration behavior of the droplet is examined at variable magnetic Bond numbers Bo_{m}. At α=45^{∘}, a critical steady state of deformation is found for λ=0.5 and 1 where the droplet changes its migration direction and shifts toward the center of the channel, while at λ=0.05, the droplet crosses the center. At α=90^{∘}, the droplet is found to settle exactly at the center of the flow domain irrespective of different magnetic Bond numbers, droplet sizes, and viscosity ratios.}, } @article {pmid32926106, year = {2020}, author = {Beratlis, N and Capuano, F and Krishnan, K and Gurka, R and Squires, K and Balaras, E}, title = {Direct numerical simulations of a great horn owl in flapping flight.}, journal = {Integrative and comparative biology}, volume = {}, number = {}, pages = {}, doi = {10.1093/icb/icaa127}, pmid = {32926106}, issn = {1557-7023}, abstract = {The fluid dynamics of owls in flapping flight is studied by coordinated experiments and computations. The great horned owl was selected, which is nocturnal, stealthy, and relatively large sized raptor. On the experimental side, perch-to-perch flight was considered in an open wind tunnel. The owl kinematics were captured with multiple cameras from different view angles. The kinematic extraction was central in driving the computations, which were designed to resolve all significant spatio-temporal scales in the flow with an unprecedented level of resolution. The wing geometry was extracted from the planform image of the owl wing and a three-dimensional model, the reference configuration, was reconstructed. This configuration was then deformed in time to best match the kinematics recorded during flights utilizing an image-registration technique based on the large deformation diffeomorphic metric mapping framework. All simulations were conducted using an eddy-resolving, high-fidelity, solver, where the large displacements/deformations of the flapping owl model were introduced with an immersed boundary formulation. We report detailed information on the spatio-temporal flow dynamics in the near wake including variables that are challenging to measure with sufficient accuracy, such as aerodynamic forces. At the same time our results indicate that high-fidelity computations over smooth wings may have limitations in capturing the full range of flow phenomena in owl flight. The growth and subsequent separation of the laminar boundary layers developing over the wings in this Reynolds number regime is sensitive to the surface micro-features that are unique to each specie.}, } @article {pmid32920676, year = {2020}, author = {Sprenger, AR and Shaik, VA and Ardekani, AM and Lisicki, M and Mathijssen, AJTM and Guzmán-Lastra, F and Löwen, H and Menzel, AM and Daddi-Moussa-Ider, A}, title = {Towards an analytical description of active microswimmers in clean and in surfactant-covered drops.}, journal = {The European physical journal. E, Soft matter}, volume = {43}, number = {9}, pages = {58}, doi = {10.1140/epje/i2020-11980-9}, pmid = {32920676}, issn = {1292-895X}, abstract = {Geometric confinements are frequently encountered in the biological world and strongly affect the stability, topology, and transport properties of active suspensions in viscous flow. Based on a far-field analytical model, the low-Reynolds-number locomotion of a self-propelled microswimmer moving inside a clean viscous drop or a drop covered with a homogeneously distributed surfactant, is theoretically examined. The interfacial viscous stresses induced by the surfactant are described by the well-established Boussinesq-Scriven constitutive rheological model. Moreover, the active agent is represented by a force dipole and the resulting fluid-mediated hydrodynamic couplings between the swimmer and the confining drop are investigated. We find that the presence of the surfactant significantly alters the dynamics of the encapsulated swimmer by enhancing its reorientation. Exact solutions for the velocity images for the Stokeslet and dipolar flow singularities inside the drop are introduced and expressed in terms of infinite series of harmonic components. Our results offer useful insights into guiding principles for the control of confined active matter systems and support the objective of utilizing synthetic microswimmers to drive drops for targeted drug delivery applications.}, } @article {pmid32916991, year = {2020}, author = {Khan, MZU and Uddin, E and Akbar, B and Akram, N and Naqvi, AA and Sajid, M and Ali, Z and Younis, MY and García Márquez, FP}, title = {Investigation of Heat Transfer and Pressure Drop in Microchannel Heat Sink Using Al2O3 and ZrO2 Nanofluids.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {9}, pages = {}, pmid = {32916991}, issn = {2079-4991}, support = {01110G0137//Universidad de Castilla-La Mancha/ ; }, abstract = {A new micro heat exchanger was analyzed using numerical formulation of conjugate heat transfer for single-phase fluid flow across copper microchannels. The flow across bent channels harnesses asymmetric laminar flow and dean vortices phenomena for heat transfer enhancement. The single-channel analysis was performed to select the bent channel aspect ratio by varying width and height between 35-300 μm for Reynolds number and base temperature magnitude range of 100-1000 and 320-370 K, respectively. The bent channel results demonstrate dean vortices phenomenon at the bend for Reynolds number of 500 and above. Thermal performance factor analysis shows an increase of 18% in comparison to straight channels of 200 μm width and height. Alumina nanoparticles at 1% and 3% concentration enhance the Nusselt number by an average of 10.4% and 23.7%, respectively, whereas zirconia enhances Nusselt number by 16% and 33.9% for same concentrations. On the other hand, thermal performance factor analysis shows a significant increase in pressure drop at high Reynolds number with 3% particle concentration. Using zirconia for nanofluid, Nusselt number of the bent multi-channel model is improved by an average of 18% for a 3% particle concentration as compared to bent channel with deionized water.}, } @article {pmid32910129, year = {2020}, author = {Tang, W and Zhu, S and Jiang, D and Zhu, L and Yang, J and Xiang, N}, title = {Channel innovations for inertial microfluidics.}, journal = {Lab on a chip}, volume = {20}, number = {19}, pages = {3485-3502}, doi = {10.1039/d0lc00714e}, pmid = {32910129}, issn = {1473-0189}, abstract = {Inertial microfluidics has gained significant attention since first being proposed in 2007 owing to the advantages of simplicity, high throughput, precise manipulation, and freedom from an external field. Superior performance in particle focusing, filtering, concentrating, and separating has been demonstrated. As a passive technology, inertial microfluidics technology relies on the unconventional use of fluid inertia in an intermediate Reynolds number range to induce inertial migration and secondary flow, which depend directly on the channel structure, leading to particle migration to the lateral equilibrium position or trapping in a specific cavity. With the advances in micromachining technology, many channel structures have been designed and fabricated in the past decade to explore the fundamentals and applications of inertial microfluidics. However, the channel innovations for inertial microfluidics have not been discussed comprehensively. In this review, the inertial particle manipulations and underlying physics in conventional channels, including straight, spiral, sinusoidal, and expansion-contraction channels, are briefly described. Then, recent innovations in channel structure for inertial microfluidics, especially channel pattern modification and unconventional cross-sectional shape, are reviewed. Finally, the prospects for future channel innovations in inertial microfluidic chips are also discussed. The purpose of this review is to provide guidance for the continued study of innovative channel designs to improve further the accuracy and throughput of inertial microfluidics.}, } @article {pmid32901617, year = {2020}, author = {O'Neill, G and Tolley, NS}, title = {Modelling nasal airflow coefficients: an insight into the nature of airflow.}, journal = {Rhinology}, volume = {}, number = {}, pages = {}, doi = {10.4193/Rhin19.440}, pmid = {32901617}, issn = {0300-0729}, abstract = {BACKGROUND: There has been considerable discussion and conflicting views regarding the presence of laminar or turbulent flow within the nose. The aim of this study was to investigate how the modelling of variable flow coefficients can assist in the evalua- tion of the characteristics of flow in the resistive segments of the nose.

METHODOLOGY: A comparison was made between the flow coefficient for the nasal valve, obtained from a mathematical model, and resistive flow components such as a Venturi meter and orifice tube. Also, a variable loss coefficient was formulated for the whole (unilateral) nose which, by utilising the intersection of the laminar and turbulent asymptotes, provided an estimation for the critical Reynolds number (Rcrit).

RESULTS: The results show that the flow resistance of the nasal valve is considerably greater than that for both a Venturi meter and an orifice tube implying turbulent or turbulent-like flow for much of nasal inspiration. Regarding the loss coefficient for the whole (unilateral) nose, normal respiration flowrates are displaced well away from the laminar asymptote. The critical Reynolds number was estimated to be 450.

CONCLUSIONS: A novel method of determining the flow characteristics of the nose, particularly the critical Reynolds number, is presented. The analysis indicates a higher degree of turbulence than is assumed from a simple traditional calculation using a hy- draulic diameter and flow through straight tubes. There are implications for computational fluid dynamics (CFD) modelling where either the entire nasal airflow is assumed to be laminar or a low turbulence model implemented.}, } @article {pmid32895674, year = {2020}, author = {Tegze, G and Podmaniczky, F and Somfai, E and Börzsönyi, T and Gránásy, L}, title = {Orientational order in dense suspensions of elliptical particles in the non-Stokesian regime.}, journal = {Soft matter}, volume = {16}, number = {38}, pages = {8925-8932}, doi = {10.1039/d0sm00370k}, pmid = {32895674}, issn = {1744-6848}, abstract = {Suspensions of neutrally buoyant elliptic particles are modeled in 2D using fully resolved simulations that provide two-way interaction between the particle and the fluid medium. Forces due to particle collisions are represented by a diffuse interface approach that allows the investigation of dense suspensions (up to 47% packing fraction). We focus on the role inertial forces play at low and high particle Reynolds numbers termed low Reynolds number and inertial regimes, respectively. The suspensions are characterized by the orientation distribution function (ODF) that reflects shear induced rotation of the particles at low Reynolds numbers, and nearly stationary (swaying) particles at high Reynolds numbers. In both cases, orientational ordering differs qualitatively from the behavior observed in the Stokesian-regime. The ODF becomes flatter with increasing packing fraction, as opposed to the sharpening previous work predicted in the Stokesian regime. The ODF at low particle concentrations differs significantly for the low Reynolds number and inertial regimes, whereas with increasing packing fraction convergence is observed. For dense suspensions, the particle-particle interactions dominate the particle motion.}, } @article {pmid32881533, year = {2020}, author = {Cui, G and Jacobi, I}, title = {Magnetic Control of Ferrofluid Droplet Adhesion in Shear Flow and on Inclined Surfaces.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {36}, pages = {10885-10891}, doi = {10.1021/acs.langmuir.0c02369}, pmid = {32881533}, issn = {1520-5827}, abstract = {The manipulation of ferrofluidic droplets by magnetic fields is a popular technique for controlling fluid transport in open microfluidic systems. We examine the effect of gravity and shear flow external forces on the adhesion properties of sessile ferrofluidic droplets in the presence of a uniform magnetic field. The magnetic field was found to enhance the critical Bond number at which sliding begins on a tilting substrate but suppress the critical Weber number at which sliding begins in a moderate Reynolds number channel flow. The divergent adhesion trends are explained in terms of the shape deformation induced in the ferrofluidic droplet, the substrate wettability, and the apparent contact angle variation induced by the droplet deformation.}, } @article {pmid32879943, year = {2020}, author = {Xu, H and Baroli, D and Veneziani, A}, title = {Global Sensitivity Analysis for Patient-Specific Aortic Simulations: the Role of Geometry, Boundary Condition and LES Modeling Parameters.}, journal = {Journal of biomechanical engineering}, volume = {}, number = {}, pages = {}, doi = {10.1115/1.4048336}, pmid = {32879943}, issn = {1528-8951}, abstract = {Uncertainties affect the reliability of the numerical simulation of hemodynamics in patient-specific settings and rigorous Uncertainty Quantification (UQ) is in order. This work presents a UQ study on the aorta flow, for assessing the sensitivity of the clinical relevant quantities to the morphology and imprecise knowledge of the inflow boundary condition using the Polynomial Chaos Expansion based Sobol' indices. The geometrical uncertainty is modeled based on a set of longitudinal imaging data of a patient with the abdominal aortic aneurysm. The images of the patient's aorta at different stages of the disease are used to create a map that drives the realistic variation of the reconstructed morphology. The aorta is a peculiar site for hemodynamics, since the flow is highly disturbed due to the high Reynolds number during systole, and the modeling of turbulence helps to avoid the high computational costs. The deconvolution-based Leray model was considered in the past for these simulations. The LES model features problem-dependent numerical parameters to tune. We borrow the same UQ tools used for physical uncertain quantities to assess the sensitivity of the simulations to one of these numerical parameters, the filter radius. The sensitivity of the total kinetic energy, the time average wall shear stress, and the oscillatory shear index are analyzed. The results show that the geometry has the most dominant contribution to the uncertainty of all the quantities of interest. The sensitivity analysis provides confidence intervals for the simulations that quantify the reliability of the numerical predictions.}, } @article {pmid32879533, year = {2019}, author = {Battista, F and Mollicone, JP and Gualtieri, P and Messina, R and Casciola, CM}, title = {Exact regularized point particle (ERPP) method for particle-laden wall-bounded flows in the two-way coupling regime.}, journal = {Journal of fluid mechanics}, volume = {878}, number = {}, pages = {420-444}, pmid = {32879533}, issn = {0022-1120}, abstract = {The Exact Regularized Point Particle (ERPP) method is extended to treat the interphase momentum coupling between particles and fluid in the presence of walls by accounting for the vorticity generation due to the particles close to solid boundaries. The ERPP method overcomes the limitations of other methods by allowing the simulation of an extensive parameter space (Stokes number, mass loading, particle-to-fluid density ratio and Reynolds number) and of particle spatial distributions that are uneven (few particles per computational cell). The enhanced ERPP method is explained in detail and validated by considering the global impulse balance. In conditions when particles are located close to the wall, a common scenario in wall-bounded turbulent flows, the main contribution to the total impulse arises from the particle-induced vorticity at the solid boundary. The method is applied to direct numerical simulations of particle-laden turbulent pipe flow in the two-way coupling regime to address the turbulence modulation. The effects of the mass loading, the Stokes number and the particle-to-fluid density ratio are investigated. The drag is either unaltered or increased by the particles with respect to the uncoupled case. No drag reduction is found in the parameter space considered. The momentum stress budget, which includes an extra stress contribution by the particles, provides the rationale behind the drag behaviour. The extra stress produces a momentum flux towards the wall that strongly modifies the viscous stress, the culprit of drag at solid boundaries.}, } @article {pmid32876861, year = {2020}, author = {Mottaghi, S and Nazari, M and Fattahi, SM and Nazari, M and Babamohammadi, S}, title = {Droplet size prediction in a microfluidic flow focusing device using an adaptive network based fuzzy inference system.}, journal = {Biomedical microdevices}, volume = {22}, number = {3}, pages = {61}, doi = {10.1007/s10544-020-00513-4}, pmid = {32876861}, issn = {1572-8781}, abstract = {Microfluidics has wide applications in different technologies such as biomedical engineering, chemistry engineering, and medicine. Generating droplets with desired size for special applications needs costly and time-consuming iterations due to the nonlinear behavior of multiphase flow in a microfluidic device and the effect of several parameters on it. Hence, designing a flexible way to predict the droplet size is necessary. In this paper, we use the Adaptive Neural Fuzzy Inference System (ANFIS), by mixing the artificial neural network (ANN) and fuzzy inference system (FIS), to study the parameters which have effects on droplet size. The four main dimensionless parameters, i.e. the Capillary number, the Reynolds number, the flow ratio and the viscosity ratio are regarded as the inputs and the droplet diameter as the output of the ANFIS. Using dimensionless groups cause to extract more comprehensive results and avoiding more experimental tests. With the ANFIS, droplet sizes could be predicted with the coefficient of determination of 0.92.}, } @article {pmid32873833, year = {2020}, author = {McGurk, KA and Owen, B and Watson, WD and Nethononda, RM and Cordell, HJ and Farrall, M and Rider, OJ and Watkins, H and Revell, A and Keavney, BD}, title = {Heritability of haemodynamics in the ascending aorta.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {14356}, pmid = {32873833}, issn = {2045-2322}, support = {MR/K501311/1/MRC_/Medical Research Council/United Kingdom ; /BHF_/British Heart Foundation/United Kingdom ; }, abstract = {Blood flow in the vasculature can be characterised by dimensionless numbers commonly used to define the level of instabilities in the flow, for example the Reynolds number, Re. Haemodynamics play a key role in cardiovascular disease (CVD) progression. Genetic studies have identified mechanosensitive genes with causal roles in CVD. Given that CVD is highly heritable and abnormal blood flow may increase risk, we investigated the heritability of fluid metrics in the ascending aorta calculated using patient-specific data from cardiac magnetic resonance (CMR) imaging. 341 participants from 108 British Caucasian families were phenotyped by CMR and genotyped for 557,124 SNPs. Flow metrics were derived from the CMR images to provide some local information about blood flow in the ascending aorta, based on maximum values at systole at a single location, denoted max, and a 'peak mean' value averaged over the area of the cross section, denoted pm. Heritability was estimated using pedigree-based (QTDT) and SNP-based (GCTA-GREML) methods. Estimates of Reynolds number based on spatially averaged local flow during systole showed substantial heritability ([Formula: see text], [Formula: see text]), while the estimated heritability for Reynolds number calculated using the absolute local maximum velocity was not statistically significant (12-13%; [Formula: see text]). Heritability estimates of the geometric quantities alone; e.g. aortic diameter ([Formula: see text], [Formula: see text]), were also substantially heritable, as described previously. These findings indicate the potential for the discovery of genetic factors influencing haemodynamic traits in large-scale genotyped and phenotyped cohorts where local spatial averaging is used, rather than instantaneous values. Future Mendelian randomisation studies of aortic haemodynamic estimates, which are swift to derive in a clinical setting, will allow for the investigation of causality of abnormal blood flow in CVD.}, } @article {pmid32859015, year = {2020}, author = {Nichka, VS and Geoffroy, TR and Nikonenko, V and Bazinet, L}, title = {Impacts of Flow Rate and Pulsed Electric Field Current Mode on Protein Fouling Formation during Bipolar Membrane Electroacidification of Skim Milk.}, journal = {Membranes}, volume = {10}, number = {9}, pages = {}, pmid = {32859015}, issn = {2077-0375}, support = {SD-210829409//Natural Sciences and Engineering Research Council of Canada/ ; 19-38-90256//Russian Foundation for Basic Research/ ; }, abstract = {Fouling is one of the major problems in electrodialysis. The aim of the present work was to investigate the effect of five different solution flow rates (corresponding to Reynolds numbers of 162, 242, 323, 404 and 485) combined with the use of pulsed electric field (PEF) current mode on protein fouling of bipolar membrane (BPM) during electrodialysis with bipolar membranes (EDBM) of skim milk. The application of PEF prevented the fouling formation by proteins on the cationic interface of the BPM almost completely, regardless of the flow rate or Reynolds number. Indeed, under PEF mode of current the weight of protein fouling was negligible in comparison with CC current mode (0.07 ± 0.08 mg/cm2 versus 5.56 ± 2.40 mg/cm2). When a continuous current (CC) mode was applied, Reynolds number equals or higher than 323 corresponded to a minimal value of protein fouling of BPM. This positive effect of both increasing the flow rate and using PEF is due to the facts that during pauses, the solution flow flushes the accumulated protein from the membrane while in the same time there is a decrease in concentration polarization (CP) and consequently decrease in H+ generation at the cationic interface of the BPM, minimizing fouling formation and accumulation.}, } @article {pmid32858042, year = {2020}, author = {Tripathi, D and Prakash, J and Tiwari, AK and Ellahi, R}, title = {Thermal, microrotation, electromagnetic field and nanoparticle shape effects on Cu-CuO/blood flow in microvascular vessels.}, journal = {Microvascular research}, volume = {132}, number = {}, pages = {104065}, doi = {10.1016/j.mvr.2020.104065}, pmid = {32858042}, issn = {1095-9319}, abstract = {A thermal analysis of Cu-CuO/ blood nanofluids flow in asymmetric microchannel propagating with wave velocity is presented in this study. For the blood, a micropolar fluid model is considered to investigate the microrotation effects of blood flow. Thermal radiation effects and the influence of nanoparticle shape, electric double layer thickness, and electromagnetic fields on the flow are studied. Three types of nanoparticles shapes namely cylinder, bricks and platelets are taken into account. Governing equations are solved under the approximations of long wavelength, low Reynolds number, and Debye-Hückel linearization. Numerical computations are performed for the axial pressure gradient, axial velocity, spin velocity and temperature distribution. The effects of various physical parameters on flow and thermal characteristics are computed and their physical interpretation is also discussed. The outcomes indicate that the axial velocity of Cu-CuO/blood nanoparticles strongly depends on applied electromagnetic field and microrotation. The model's finding will be applicable in designing the smart electromagnetic micro pumps for the hemodialysis and lungs-on-chip devices for the pumping of the blood.}, } @article {pmid32850285, year = {2020}, author = {Zhu, L and Xu, B and Wu, X and Lei, J and Hacker, DL and Liang, X and Wurm, FM}, title = {Analysis of volumetric mass transfer coefficient (kLa) in small- (250 mL) to large-scale (2500 L) orbitally shaken bioreactors.}, journal = {3 Biotech}, volume = {10}, number = {9}, pages = {397}, pmid = {32850285}, issn = {2190-572X}, abstract = {In this study, the combination of dimensional analysis (DA) and analysis of variance (ANOVA) was used to predict the volumetric mass transfer coefficient (kLa) values under different operating conditions for orbitally shaken bioreactors (OSRs) with different filling volumes. It was found that Reynolds number and the interaction between Froude number and geometric number have the largest impact on kLa with impact indexes of 7.41 and 7.50, respectively. Moreover, the volume number has the largest negative impact on kLa, with an impact index of - 5.34. Thus, an effective way to increase the oxygen supply is by increasing the shaking speed and shaking diameter or decreasing the vessel diameter. However, cell cultivation with a higher filling volume will have an increased risk of oxygen scarcity. Therefore, with the help of the kLa prediction model, a suitable operating condition can be determined effectively and easily.}, } @article {pmid32846914, year = {2020}, author = {Ghalambaz, M and Arasteh, H and Mashayekhi, R and Keshmiri, A and Talebizadehsardari, P and Yaïci, W}, title = {Investigation of Overlapped Twisted Tapes Inserted in a Double-Pipe Heat Exchanger Using Two-Phase Nanofluid.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {9}, pages = {}, doi = {10.3390/nano10091656}, pmid = {32846914}, issn = {2079-4991}, abstract = {This study investigated the laminar convective heat transfer and fluid flow of Al2O3 nanofluid in a counter flow double-pipe heat exchanger equipped with overlapped twisted tape inserts in both inner and outer tubes. Two models of the same (co-swirling twisted tapes) and opposite (counter-swirling twisted tapes) angular directions for the stationary twisted tapes were considered. The computational fluid dynamic simulations were conducted through varying the design parameters, including the angular direction of twisted tape inserts, nanofluid volume concentration, and Reynolds number. It was found that inserting the overlapped twisted tapes in the heat exchanger significantly increases the thermal performance as well as the friction factor compared with the plain heat exchanger. The results indicate that models of co-swirling twisted tapes and counter-swirling twisted tapes increase the average Nusselt number by almost 35.2-66.2% and 42.1-68.7% over the Reynolds number ranging 250-1000, respectively. To assess the interplay between heat transfer enhancement and pressure loss penalty, the dimensionless number of performance evaluation criterion was calculated for all the captured configurations. Ultimately, the highest value of performance evaluation criterion is equal to 1.40 and 1.26 at inner and outer tubes at the Reynolds number of 1000 and the volume fraction of 3% in the case of counter-swirling twisted tapes model.}, } @article {pmid32845950, year = {2020}, author = {Zhang, S and Cui, Z and Wang, Y and den Toonder, JMJ}, title = {Metachronal actuation of microscopic magnetic artificial cilia generates strong microfluidic pumping.}, journal = {Lab on a chip}, volume = {20}, number = {19}, pages = {3569-3581}, doi = {10.1039/d0lc00610f}, pmid = {32845950}, issn = {1473-0189}, abstract = {Biological cilia that generate fluid flow or propulsion are often found to exhibit a collective wavelike metachronal motion, i.e. neighboring cilia beat slightly out-of-phase rather than synchronously. Inspired by this observation, this article experimentally demonstrates that microscopic magnetic artificial cilia (μMAC) performing a metachronal motion can generate strong microfluidic flows, though, interestingly, the mechanism is different from that in biological cilia, as is found through a systematic experimental study. The μMAC are actuated by a facile magnetic setup, consisting of an array of rod-shaped magnets. This arrangement imposes a time-dependent non-uniform magnetic field on the μMAC array, resulting in a phase difference between the beatings of adjacent μMAC, while each cilium exhibits a two-dimensional whip-like motion. By performing the metachronal 2D motion, the μMAC are able to generate a strong flow in a microfluidic chip, with velocities of up to 3000 μm s-1 in water, which, different from biological cilia, is found to be a result of combined metachronal and inertial effects, in addition to the effect of asymmetric beating. The pumping performance of the metachronal μMAC outperforms all previously reported microscopic artificial cilia, and is competitive with that of most of the existing microfluidic pumping methods, while the proposed platform requires no physical connection to peripheral equipment, reduces the usage of reagents by minimizing "dead volumes", avoids undesirable electrical effects, and accommodates a wide range of different fluids. The 2D metachronal motion can also generate a flow with velocities up to 60 μm s-1 in pure glycerol, where Reynolds number is less than 0.05 and the flow is primarily caused by the metachronal motion of the μMAC. These findings offer a novel solution to not only create on-chip integrated micropumps, but also design swimming and walking microrobots, as well as self-cleaning and antifouling surfaces.}, } @article {pmid32833583, year = {2020}, author = {Latt, J and Coreixas, C and Beny, J and Parmigiani, A}, title = {Efficient supersonic flow simulations using lattice Boltzmann methods based on numerical equilibria.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {378}, number = {2175}, pages = {20190559}, pmid = {32833583}, issn = {1471-2962}, abstract = {A double-distribution-function based lattice Boltzmann method (DDF-LBM) is proposed for the simulation of polyatomic gases in the supersonic regime. The model relies on a numerical equilibrium that has been extensively used by discrete velocity methods since the late 1990s. Here, it is extended to reproduce an arbitrary number of moments of the Maxwell-Boltzmann distribution. These extensions to the standard 5-constraint (mass, momentum and energy) approach lead to the correct simulation of thermal, compressible flows with only 39 discrete velocities in 3D. The stability of this BGK-LBM is reinforced by relying on Knudsen-number-dependent relaxation times that are computed analytically. Hence, high Reynolds-number, supersonic flows can be simulated in an efficient and elegant manner. While the 1D Riemann problem shows the ability of the proposed approach to handle discontinuities in the zero-viscosity limit, the simulation of the supersonic flow past a NACA0012 aerofoil confirms the excellent behaviour of this model in a low-viscosity and supersonic regime. The flow past a sphere is further simulated to investigate the 3D behaviour of our model in the low-viscosity supersonic regime. The proposed model is shown to be substantially more efficient than the previous 5-moment D3Q343 DDF-LBM for both CPU and GPU architectures. It then opens up a whole new world of compressible flow applications that can be realistically tackled with a purely LB approach. This article is part of the theme issue 'Fluid dynamics, soft matter and complex systems: recent results and new methods'.}, } @article {pmid32828761, year = {2020}, author = {Akram, J and Akbar, NS and Tripathi, D}, title = {Blood-based graphene oxide nanofluid flow through capillary in the presence of electromagnetic fields: A Sutterby fluid model.}, journal = {Microvascular research}, volume = {132}, number = {}, pages = {104062}, doi = {10.1016/j.mvr.2020.104062}, pmid = {32828761}, issn = {1095-9319}, abstract = {Pumping devices with the electrokinetics phenomena are important in many microscale transport phenomena in physiology. This study presents a theoretical and numerical investigation on the peristaltic pumping of non-Newtonian Sutterby nanofluid through capillary in presence of electromagnetohydrodynamics. Here blood (Sutterby fluid) is taken as a base fluid and nanofluid is prepared by the suspension of graphene oxide nanoparticle in blood. Graphene oxide is extremely useful in the medical domain for drug delivery and cancer treatment. The modified Buongiorno model for nanofluids and Poisson-Boltzmann ionic distribution is adopted for the formulation of the present problem. Constitutive flow equations are linearized by the implementation of approximations low Reynolds number, large wavelength, and the Debye-Hückel linearization. The numerical solution of reduced coupled and nonlinear set of equations is computed through Mathematica and graphical illustration is presented. Further, the impacts of buoyancy forces, thermal radiation, and mixed convection are also studied. It is revealed in this investigation that the inclusion of a large number of nanoparticles alters the flow characteristics significantly and boosts the heat transfer mechanism. Moreover, the pumping power of the peristaltic pump can be enhanced by the reduction in the width of the electric double layer which can be done by altering the electrolyte concentration.}, } @article {pmid32810744, year = {2020}, author = {Moruzzi, RB and Campos, LC and Sharifi, S and da Silva, PG and Gregory, J}, title = {Nonintrusive investigation of large Al-kaolin fractal aggregates with slow settling velocities.}, journal = {Water research}, volume = {185}, number = {}, pages = {116287}, doi = {10.1016/j.watres.2020.116287}, pmid = {32810744}, issn = {1879-2448}, mesh = {Flocculation ; *Fractals ; *Kaolin ; Particle Size ; Rheology ; }, abstract = {Although a combination of aggregate characteristics dictate particle settling, it is commonly assumed that large particles have higher terminal velocities. This simplifying assumption often leads to overprediction of large aggregate settling velocities which in turn negatively impacts on estimates of sedimentation clarification efficiency. Despite its importance, little attention has been given to large aggregates with slow-settling velocities. This paper addresses this gap by investigating slow-settling velocities of large, heterodisperse and multi-shape Al-kaolin aggregates using non-intrusive methods. A particle image velocimetry technique (PIV) was applied to track aggregate velocity and a non-intrusive image technique was used to determine aggregate characteristics, including size (df), three-dimensional fractal dimension (Df), density (ρf), aggregate velocity (Vexp) and Reynolds number (Re). Results showed no strict dependence of settling velocity on large aggregate size, shape and density, as Al-kaolin aggregates with the same size exhibited different settling velocities. A comparison of the results with the well-known Stokes' law for velocity modified by a shape factor showed that the settling velocities measured here can vary from 2 to 14 fold lower than the predicted values for perfect sphere-shape aggregates with the same density and size. Furthermore, results have also shown large Al-kaolin aggregate's drag coefficient (Cd) to be around 56/Re, for average fractal aggregate sphericity of around 0.58.}, } @article {pmid32809129, year = {2020}, author = {Cui, J and Liu, Y and Xiao, L and Chen, S and Fu, BM}, title = {Numerical study on the adhesion of a circulating tumor cell in a curved microvessel.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {}, number = {}, pages = {}, doi = {10.1007/s10237-020-01380-x}, pmid = {32809129}, issn = {1617-7940}, support = {G-UAHL//Hong Kong Polytechnic University/ ; G-UACM//Hong Kong Polytechnic University/ ; 19YF1417400//Science and Technology Commission of Shanghai Municipality/ ; 11902188//National Natural Science Foundation of China/ ; }, abstract = {The adhesion of a circulating tumor cell (CTC) in a three-dimensional curved microvessel was numerically investigated. Simulations were first performed to characterize the differences in the dynamics and adhesion of a CTC in the straight and curved vessels. After that, a parametric study was performed to investigate the effects of the applied driven force density f (or the flow Reynolds number Re) and the CTC membrane bending modulus Kb on the CTC adhesion. Our simulation results show that the CTC prefers to adhere to the curved vessel as more bonds are formed around the transition region of the curved part due to the increased cell-wall contact by the centrifugal force. The parametric study also indicates that when the flow driven force f (or Re) increases or when the CTC becomes softer (Kb decreases), the bond formation probability increases and the bonds will be formed at more sites of a curved vessel. The increased f (or Re) brings a larger centrifugal force, while the decreased Kb generates more contact areas at the cell-wall interface, both of which are beneficial to the bond formation. In the curved vessel, it is found that the site where bonds are formed the most (hotspot) varies with the applied f and the Kb. For our vessel geometry, when f is small, the hotspot tends to be within the first bend of the vessel, while as f increases or Kb decreases, the hotspot may shift to the second bend of the vessel.}, } @article {pmid32805051, year = {2020}, author = {Rao, C and Liu, H}, title = {Effects of Reynolds number and distribution on passive flow control in owl-inspired leading-edge serrations.}, journal = {Integrative and comparative biology}, volume = {}, number = {}, pages = {}, doi = {10.1093/icb/icaa119}, pmid = {32805051}, issn = {1557-7023}, abstract = {As a sophisticated micro device for noise reduction, the owl-inspired leading-edge (LE) serrations have been confirmed capable of achieving passive control of laminar-turbulent transition while normally paying a cost of lowering the aerodynamic performance in low Reynolds number (Re∼O(103)) regime. In order to explore potential applications of the owl-inspired serrated airfoils or blades in developing low noise wind turbines or multi-copters normally operating at higher Res, we conducted a large-eddy simulation (LES)-based study of Re effects on the aerodynamic performance of 2D clean and serrated models. Our results show that the LE serrations keep working effectively in mitigating turbulent fluctuations over a broad range of Re (O(103) ∼ O(105)), capable of achieving marked improvement in lift-to-drag ratio with increasing Res. As the aeroacoustic fields are in close association with the propagation of the turbulence sources, it is observed that the tradeoff between passive mitigation of turbulent fluctuations (hence aeroacoustic noise suppression) and aerodynamic performance can be noticeably mitigated at large angles of attack (AoA) and at high Res. This indicates that the LE serrations present an alternative passive flow control mechanism at high Res through a straightforward local excitation of the flow transition while capable of mitigating the turbulent intensity passively. We further developed a 3D LES model of clean and partially serrated rectangular wings to investigate the effects of the LE serrations' distribution on aerodynamic features, on the basis of the observation that longer serrations are often distributed intensively in the mid-span of real owl's feathers. We find that the mid-span distributed LE serrations can facilitate the break-up of leading-edge vortices and the turbulent transition passively and effectively while achieving a low level of turbulence kinetic energy over the upper suction surface of the wing.}, } @article {pmid32801384, year = {2020}, author = {Ardeshiri, H and Cassiani, M and Park, SY and Stohl, A and Pisso, I and Dinger, AS}, title = {On the Convergence and Capability of the Large-Eddy Simulation of Concentration Fluctuations in Passive Plumes for a Neutral Boundary Layer at Infinite Reynolds Number.}, journal = {Boundary-layer meteorology}, volume = {176}, number = {3}, pages = {291-327}, pmid = {32801384}, issn = {0006-8314}, abstract = {Large-eddy simulation (LES) experiments have been performed using the Parallelized LES Model (PALM). A methodology for validating and understanding LES results for plume dispersion and concentration fluctuations in an atmospheric-like flow is presented. A wide range of grid resolutions is shown to be necessary for investigating the convergence of statistical characteristics of velocity and scalar fields. For the scalar, the statistical moments up to the fourth order and the shape of the concentration probability density function (p.d.f.) are examined. The mean concentration is influenced by grid resolution, with the highest resolution simulation showing a lower mean concentration, linked to larger turbulent structures. However, a clear tendency to convergence of the concentration variance is observed at the two higher resolutions. This behaviour is explained by showing that the mechanisms driving the mean and the variance are differently influenced by the grid resolution. The analysis of skewness and kurtosis allows also the obtaining of general results on plume concentration fluctuations. Irrespective of grid resolution, a family of Gamma p.d.f.s well represents the shape of the concentration p.d.f. but only beyond the peak of the concentration fluctuation intensity. In the early plume dispersion phases, the moments of the p.d.f. are in good agreement with those generated by a fluctuating plume model. To the best of our knowledge, our study demonstrates for the first time that, if resolution and averaging time are adequate, atmospheric LES provides a trustworthy representation of the high order moments of the concentration field, up to the fourth order, for a dispersing plume.}, } @article {pmid32796948, year = {2020}, author = {Ryan, DP and Chen, Y and Nguyen, P and Goodwin, PM and Carey, JW and Kang, Q and Werner, JH and Viswanathan, HS}, title = {3D particle transport in multichannel microfluidic networks with rough surfaces.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {13848}, pmid = {32796948}, issn = {2045-2322}, support = {20180151ER//Laboratory Directed Research and Development,United States/ ; ACI-1548562//National Science Foundation/ ; FWP LANLE3W1//Basic Energy Sciences/ ; }, abstract = {The transport of particles and fluids through multichannel microfluidic networks is influenced by details of the channels. Because channels have micro-scale textures and macro-scale geometries, this transport can differ from the case of ideally smooth channels. Surfaces of real channels have irregular boundary conditions to which streamlines adapt and with which particle interact. In low-Reynolds number flows, particles may experience inertial forces that result in trans-streamline movement and the reorganization of particle distributions. Such transport is intrinsically 3D and an accurate measurement must capture movement in all directions. To measure the effects of non-ideal surface textures on particle transport through complex networks, we developed an extended field-of-view 3D macroscope for high-resolution tracking across large volumes ([Formula: see text]) and investigated a model multichannel microfluidic network. A topographical profile of the microfluidic surfaces provided lattice Boltzmann simulations with a detailed feature map to precisely reconstruct the experimental environment. Particle distributions from simulations closely reproduced those observed experimentally and both measurements were sensitive to the effects of surface roughness. Under the conditions studied, inertial focusing organized large particles into an annular distribution that limited their transport throughout the network while small particles were transported uniformly to all regions.}, } @article {pmid32783851, year = {2020}, author = {Deng, D and Pan, Y and Liu, G and Liu, W and Ma, L}, title = {Seeking the hotspots of nitrogen removal: A comparison of sediment denitrification rate and denitrifier abundance among wetland types with different hydrological conditions.}, journal = {The Science of the total environment}, volume = {737}, number = {}, pages = {140253}, doi = {10.1016/j.scitotenv.2020.140253}, pmid = {32783851}, issn = {1879-1026}, mesh = {China ; Denitrification ; Hydrology ; *Nitrogen ; *Wetlands ; }, abstract = {Wetlands play a vital role in removing nitrogen (N) from aquatic environments via the denitrification process, which is regulated by multiple environmental and biological factors. Until now, the mechanisms by which environmental factors and microbial abundance regulate denitrification rates in wetlands under different hydrological conditions remain poorly understood. Here, we investigated sediment potential denitrification rate (PDR) and unamended denitrification rate (UDR), and quantified denitrifier abundance (nirS, nirK, and nosZ genes) in 36 stream, river, pond, and ditch wetland sites along the Dan River, a nitrogen-rich river in central China. The result indicated that ditches had the highest denitrification rates and denitrifier abundance. Both PDR and UDR showed strong seasonality, and were observed to be negatively correlated with water velocity in streams and rivers. Moreover, denitrification rates were significantly related to denitrifier abundance and many water quality parameters and sediment properties. Interestingly, PDR and UDR were generally positively associated with N and carbon (C) availability in streams and rivers, but such correlations were not found in ponds and ditches. Using a scaling analysis, we found that environmental parameters, including Reynolds number, sediment total C ratio, and interstitial space, coupled with relative nirS gene abundance could predict the hotspots of denitrification rates in wetlands with varying hydrologic regimes. Our findings highlight that hydrological conditions, especially water velocity and hydrologic pulsing, play a nonnegligible role in determining N biogeochemical processes in wetlands.}, } @article {pmid32770358, year = {2020}, author = {Patterson, LHC and Walker, JL and Naivar, MA and Rodriguez-Mesa, E and Hoonejani, MR and Shields, K and Foster, JS and Doyle, AM and Valentine, MT and Foster, KL}, title = {Inertial flow focusing: a case study in optimizing cellular trajectory through a microfluidic MEMS device for timing-critical applications.}, journal = {Biomedical microdevices}, volume = {22}, number = {3}, pages = {52}, doi = {10.1007/s10544-020-00508-1}, pmid = {32770358}, issn = {1572-8781}, support = {1631656//Division of Chemical, Bioengineering, Environmental, and Transport Systems/International ; 1254893//Division of Civil, Mechanical and Manufacturing Innovation/International ; }, abstract = {Although microfluidic micro-electromechanical systems (MEMS) are well suited to investigate the effects of mechanical force on large populations of cells, their high-throughput capabilities cannot be fully leveraged without optimizing the experimental conditions of the fluid and particles flowing through them. Parameters such as flow velocity and particle size are known to affect the trajectories of particles in microfluidic systems and have been studied extensively, but the effects of temperature and buffer viscosity are not as well understood. In this paper, we explored the effects of these parameters on the timing of our own cell-impact device, the μHammer, by first tracking the velocity of polystyrene beads through the device and then visualizing the impact of these beads. Through these assays, we find that the timing of our device is sensitive to changes in the ratio of inertial forces to viscous forces that particles experience while traveling through the device. This sensitivity provides a set of parameters that can serve as a robust framework for optimizing device performance under various experimental conditions, without requiring extensive geometric redesigns. Using these tools, we were able to achieve an effective throughput over 360 beads/s with our device, demonstrating the potential of this framework to improve the consistency of microfluidic systems that rely on precise particle trajectories and timing.}, } @article {pmid32766844, year = {2020}, author = {Waldrop, LD and He, Y and Hedrick, TL and Rader, J}, title = {Functional morphology of gliding flight I. Modeling reveals distinct performance landscapes based on soaring strategies.}, journal = {Integrative and comparative biology}, volume = {}, number = {}, pages = {}, doi = {10.1093/icb/icaa114}, pmid = {32766844}, issn = {1557-7023}, abstract = {The physics of flight influences the morphology of bird wings through natural selection on flight performance. The connection between wing morphology and performance is unclear due to the complex relationships between various parameters of flight. In order to better understand this connection, we present a holistic analysis of gliding flight that preserves complex relationships between parameters. We use a computational model of gliding flight, along with analysis by uncertainty quantification, to 1) create performance landscapes of gliding based on output metrics (maximum lift-to-drag ratio, minimum gliding angle, minimum sinking speed, lift coefficient at minimum sinking speed); and 2) predict what parameters of flight (chordwise camber, wing aspect ratio, Reynolds number) would differ between gliding and non-gliding species of birds. We also examine performance based on soaring strategy for possible differences in morphology within gliding birds. Gliding birds likely have greater aspect ratios than non-gliding birds, due the high sensitivity of aspect ratio on most metrics of gliding performance. Furthermore, gliding birds can use two distinct soaring strategies based on performance landscapes. First, maximizing distance traveled (maximizing lift-to-drag ratio and minimizing gliding angle) should result in wings with high aspect ratios and middling-to-low wing chordwise camber. Second, maximizing lift extracted from updrafts should result in wings with middling aspect ratios and high wing chordwise camber. Following studies can test these hypotheses using morphological measurements.}, } @article {pmid32762434, year = {2020}, author = {Arrieta, J and Cartwright, JHE and Gouillart, E and Piro, N and Piro, O and Tuval, I}, title = {Geometric mixing.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {378}, number = {2179}, pages = {20200168}, pmid = {32762434}, issn = {1471-2962}, abstract = {Mixing fluids often involves a periodic action, like stirring one's tea. But reciprocating motions in fluids at low Reynolds number, in Stokes flows where inertia is negligible, lead to periodic cycles of mixing and unmixing, because the physics, molecular diffusion excepted, is time reversible. So how can fluid be mixed in such circumstances? The answer involves a geometric phase. Geometric phases are found everywhere in physics as anholonomies, where after a closed circuit in the parameters, some system variables do not return to their original values. We discuss the geometric phase in fluid mixing: geometric mixing. This article is part of the theme issue 'Stokes at 200 (part 2)'.}, } @article {pmid32752686, year = {2020}, author = {Seyler, SL and Pressé, S}, title = {Surmounting potential barriers: Hydrodynamic memory hedges against thermal fluctuations in particle transport.}, journal = {The Journal of chemical physics}, volume = {153}, number = {4}, pages = {041102}, doi = {10.1063/5.0013722}, pmid = {32752686}, issn = {1089-7690}, abstract = {Recently, trapped-particle experiments have probed the instantaneous velocity of Brownian motion revealing that, at early times, hydrodynamic history forces dominate Stokes damping. In these experiments, nonuniform particle motion is well described by the Basset-Boussinesq-Oseen (BBO) equation, which captures the unsteady Basset history force at a low Reynolds number. Building off of these results, earlier we showed that, at low temperature, BBO particles could exploit fluid inertia in order to overcome potential barriers (generically modeled as a tilted washboard), while its Langevin counter-part could not. Here, we explore the behavior of neutrally buoyant BBO particles at finite temperature for moderate Stokes damping. Remarkably, we find that the transport of particles injected into a bumpy potential with sufficiently high barriers can be completely quenched at intermediate temperatures, whereas itinerancy may be possible above and below that temperature window. This effect is present for both Langevin and BBO dynamics, though these occur over drastically different temperature ranges. Furthermore, hydrodynamic memory mitigates these effects by sustaining initial particle momentum, even in the difficult intermediate temperature regime.}, } @article {pmid32752632, year = {2020}, author = {Romanò, F and Türkbay, T and Kuhlmann, HC}, title = {Lagrangian chaos in steady three-dimensional lid-driven cavity flow.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {7}, pages = {073121}, doi = {10.1063/5.0005792}, pmid = {32752632}, issn = {1089-7682}, abstract = {Steady three-dimensional flows in lid-driven cavities are investigated numerically using a high-order spectral-element solver for the incompressible Navier-Stokes equations. The focus is placed on critical points in the flow field, critical limit cycles, their heteroclinic connections, and on the existence, shape, and dependence on the Reynolds number of Kolmogorov-Arnold-Moser (KAM) tori. In finite-length cuboidal cavities at small Reynolds numbers, a thin layer of chaotic streamlines covers all walls. As the Reynolds number is increased, the chaotic layer widens and the complementary KAM tori shrink, eventually undergoing resonances, until they vanish. Accurate data for the location of closed streamlines and of KAM tori are provided, both of which reach very close to the moving lid. For steady periodic Taylor-Görtler vortices in spanwise infinitely extended cavities with a square cross section, chaotic streamlines occupy a large part of the flow domain immediately after the onset of Taylor-Görtler vortices. As the Reynolds number increases, the remaining KAM tori vanish from the Taylor-Görtler vortices, while KAM tori grow in the central region further away from the solid walls.}, } @article {pmid32752610, year = {2020}, author = {Chatterjee, S and Verma, MK}, title = {Kolmogorov flow: Linear stability and energy transfers in a minimal low-dimensional model.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {7}, pages = {073110}, doi = {10.1063/5.0002751}, pmid = {32752610}, issn = {1089-7682}, abstract = {In this paper, we derive a four-mode model for the Kolmogorov flow by employing Galerkin truncation and the Craya-Herring basis for the decomposition of velocity field. After this, we perform a bifurcation analysis of the model. Though our low-dimensional model has fewer modes than past models, it captures the essential features of the primary bifurcation of the Kolmogorov flow. For example, it reproduces the critical Reynolds number for the supercritical pitchfork bifurcation and the flow structures of past works. We also demonstrate energy transfers from intermediate scales to large scales. We perform direct numerical simulations of the Kolmogorov flow and show that our model predictions match the numerical simulations very well.}, } @article {pmid32752609, year = {2020}, author = {Josserand, C and Le Berre, M and Pomeau, Y}, title = {Scaling laws in turbulence.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {7}, pages = {073137}, doi = {10.1063/1.5144147}, pmid = {32752609}, issn = {1089-7682}, abstract = {Following the idea that dissipation in turbulence at high Reynolds number is dominated by singular events in space-time and described by solutions of the inviscid Euler equations, we draw the conclusion that in such flows, scaling laws should depend only on quantities appearing in the Euler equations. This excludes viscosity or a turbulent length as scaling parameters and constrains drastically possible analytical pictures of this limit. We focus on the drag law deduced by Newton for a projectile moving quickly in a fluid at rest. Inspired by this Newton's drag force law (proportional to the square of the speed of the moving object in the limit of large Reynolds numbers), which is well verified in experiments when the location of the detachment of the boundary layer is defined, we propose an explicit relationship between the Reynolds stress in the turbulent wake and quantities depending on the velocity field (averaged in time but depending on space). This model takes the form of an integrodifferential equation for the velocity which is eventually solved for a Poiseuille flow in a circular pipe.}, } @article {pmid32751881, year = {2020}, author = {Voglhuber-Brunnmaier, T and Jakoby, B}, title = {Higher-Order Models for Resonant Viscosity and Mass-Density Sensors.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {15}, pages = {}, pmid = {32751881}, issn = {1424-8220}, support = {LCM (COMET-K2)//Österreichische Forschungsförderungsgesellschaft/ ; }, abstract = {Advanced fluid models relating viscosity and density to resonance frequency and quality factor of vibrating structures immersed in fluids are presented. The numerous established models which are ultimately all based on the same approximation are refined, such that the measurement range for viscosity can be extended. Based on the simple case of a vibrating cylinder and dimensional analysis, general models for arbitrary order of approximation are derived. Furthermore, methods for model parameter calibration and the inversion of the models to determine viscosity and/or density from measured resonance parameters are shown. One of the two presented fluid models is a viscosity-only model, where the parameters of it can be calibrated without knowledge of the fluid density. The models are demonstrated for a tuning fork-based commercial instrument, where maximum deviations between measured and reference viscosities of approximately ±0.5% in the viscosity range from 1.3 to 243 mPas could be achieved. It is demonstrated that these results show a clear improvement over the existing models.}, } @article {pmid32738822, year = {2020}, author = {Manchester, EL and Xu, XY}, title = {The effect of turbulence on transitional flow in the FDA's benchmark nozzle model using large-eddy simulation.}, journal = {International journal for numerical methods in biomedical engineering}, volume = {36}, number = {10}, pages = {e3389}, doi = {10.1002/cnm.3389}, pmid = {32738822}, issn = {2040-7947}, support = {EP/P020267/1//University of Edinburgh/ ; //Imperial College London: EPSRC DTP studentship/ ; }, abstract = {The Food and Drug Administration's (FDA) benchmark nozzle model has been studied extensively both experimentally and computationally. Although considerable efforts have been made on validations of a variety of numerical models against available experimental data, the transitional flow cases are still not fully resolved, especially with regards to detailed comparison of predicted turbulence quantities with experimental measurements. This study aims to fill this gap by conducting large-eddy simulations (LES) of flow through the FDA's benchmark model, at a transitional Reynolds number of 2000. Numerical results are compared to previous interlaboratory experimental results, with an emphasis on turbulence characteristics. Our results show that the LES methodology can accurately capture laminar quantities throughout the model. In the pre-jet breakdown region, predicted turbulence quantities are generally larger than high resolution experimental data acquired with laser Doppler velocimetry. In the jet breakdown regions, where maximum Reynolds stresses occur, Reynolds shear stresses show excellent agreement. Differences of up to 4% and 20% are observed near the jet core in the axial and radial normal Reynolds stresses, respectively. Comparisons between viscous and Reynolds shear stresses show that peak viscous shear stresses occur in the nozzle throat reaching a value of 18 Pa in the boundary layer, whilst peak Reynolds shear stresses occur in the jet breakdown region reaching a maximum value of 87 Pa. Our results highlight the importance in considering both laminar and turbulent contributions towards shear stresses and that neglecting the turbulence effect can significantly underestimate the total shear force exerted on the fluid.}, } @article {pmid32731122, year = {2020}, author = {Ahmed, R and Ali, N and Al-Khaled, K and Khan, SU and Tlili, I}, title = {Finite difference simulations for non-isothermal hydromagnetic peristaltic flow of a bio-fluid in a curved channel: Applications to physiological systems.}, journal = {Computer methods and programs in biomedicine}, volume = {195}, number = {}, pages = {105672}, doi = {10.1016/j.cmpb.2020.105672}, pmid = {32731122}, issn = {1872-7565}, abstract = {Owing to the fundamental significances of peristalsis phenomenon in various biological systems like circulation of blood in vessels, lungs devices, pumping of blood in heart and movement of chyme in the gastrointestinal tract, variety of research by scientist on this topic has been presented in recently years. The peristaltic pumping plays a novel role in various industrial processes like transfer of sanitary materials, the pumping equipment design of roller pumps and many more. The present article investigates numerically the theoretical aspects of heat and mass transportation in peristaltic pattern of Carreau fluid through a curved channel. The computations for axial velocity, pressure rise, temperature field, mass concentration, and stream function are carried out under low Reynolds number and long wavelength approximation in the wave frame of reference by utilizing appropriate numerical implicit finite difference technique (FDM). The implementation of numerical procedure and graphical representation of the computations are accomplished using MATLAB language. The impacts of rheological parameters of Carreau fluid, Brinkmann number, curvature parameter and Hartmann number are shown and discussed briefly. The study shows that for shear thinning of bio-materials, the velocity exhibits the boundary layer character near the boundary walls for greater Hartmann number. The interesting observations based on numerical simulations are graphically elaborated. The results show that the curvature of channel with larger value allows more heat transportation within the flow domain. On the contrary, inside the channel wall, the solutal mass concentration follows an increasing trend with decreasing the channel curvature. The temperature profile enhanced with increment of power-law index and curvature parameter. Moreover, the concentration profile increases with Brinkmann number and Hartmann number.}, } @article {pmid32728231, year = {2020}, author = {Boukharfane, R and Parsani, M and Bodart, J}, title = {Characterization of pressure fluctuations within a controlled-diffusion blade boundary layer using the equilibrium wall-modelled LES.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {12735}, doi = {10.1038/s41598-020-69671-y}, pmid = {32728231}, issn = {2045-2322}, abstract = {In this study, the generation of airfoil trailing edge broadband noise that arises from the interaction of turbulent boundary layer with the airfoil trailing edge is investigated. The primary objectives of this work are: (i) to apply a wall-modelled large-eddy simulation (WMLES) approach to predict the flow of air passing a controlled-diffusion blade, and (ii) to study the blade broadband noise that is generated from the interaction of a turbulent boundary layer with a lifting surface trailing edge. This study is carried out for two values of the Mach number, [Formula: see text] and 0.5, two values of the chord Reynolds number, [Formula: see text] and [Formula: see text], and two angles of attack, AoA [Formula: see text] and [Formula: see text]. To examine the influence of the grid resolution on aerodynamic and aeroacoustic quantities, we compare our results with experimental data available in the literature. We also compare our results with two in-house numerical solutions generated from two wall-resolved LES (WRLES) calculations, one of which has a DNS-like resolution. We show that WMLES accurately predicts the mean pressure coefficient distribution, velocity statistics (including the mean velocity), and the traces of Reynolds tensor components. Furthermore, we observe that the instantaneous flow structures computed by the WMLES resemble those found in the reference WMLES database, except near the leading edge region. Some of the differences observed in these structures are associated with tripping and the transition to a turbulence mechanism near the leading edge, which are significantly affected by the grid resolution. The aeroacoustic noise calculations indicate that the power spectral density profiles obtained using the WMLES compare well with the experimental data.}, } @article {pmid32709009, year = {2020}, author = {Wang, Y and Zhang, Y and Qiao, Z and Wang, W}, title = {A 3D Printed Jet Mixer for Centrifugal Microfluidic Platforms.}, journal = {Micromachines}, volume = {11}, number = {7}, pages = {}, pmid = {32709009}, issn = {2072-666X}, support = {G-231823//The Gulf of Mexico Research Initiative/ ; }, abstract = {Homogeneous mixing of microscopic volume fluids at low Reynolds number is of great significance for a wide range of chemical, biological, and medical applications. An efficient jet mixer with arrays of micronozzles was designed and fabricated using additive manufacturing (three-dimensional (3D) printing) technology for applications in centrifugal microfluidic platforms. The contact surface of miscible liquids was enhanced significantly by impinging plumes from two opposite arrays of micronozzles to improve mixing performance. The mixing efficiency was evaluated and compared with the commonly used Y-shaped micromixer. Effective mixing in the jet mixer was achieved within a very short timescale (3s). This 3D printed jet mixer has great potential to be implemented in applications by being incorporated into multifarious 3D printing devices in microfluidic platforms.}, } @article {pmid32702453, year = {2020}, author = {Emami, MS and Haghshenasfard, M and Zarghami, R and Sadeghi, R and Esfahany, MN}, title = {Experimental study on the reduction of loratadine particle size through confined liquid impinging jets.}, journal = {International journal of pharmaceutics}, volume = {587}, number = {}, pages = {119668}, doi = {10.1016/j.ijpharm.2020.119668}, pmid = {32702453}, issn = {1873-3476}, abstract = {The confined liquid impinging jets (CLIJ) technique was applied as a simple and effective approach to reducing the particle size of loratadine to enhance its solubility. The effect of anti-solvent (AS) to solution (S) flow rate ratio, organic phase concentration, Reynolds number (Re), and stabilizer concentration was investigated in this reduction process. After the synthesis, the chemical and physical properties of loratadine nanoparticles were determined through different characterization and analytical techniques. The results indicated that the particle size of loratadine decreases from 320 nm to 80 nm by increasing the AS/S ratio from 1 to 25. It was found that the particle size of loratadine was unchanged at the higher AS/S ratios. The loratadine nanoparticle size was optimized by changing the solution concentration, Re, and Tween 80 as a stabilizer. The finest loratadine nanoparticle size of about 53 nm was obtained with a narrow size distribution, which corresponds to solution concentration of 35 mg/mL, Re of 5687, and 0.1% (w/v) stabilizer concentration. It was revealed that the optimized loratadine nanoparticles completely dissolved after 11 min, indicating the loratadine nanoparticle dissolution rate 50 times faster than raw loratadine.}, } @article {pmid32688541, year = {2020}, author = {Fouxon, I and Lee, C}, title = {Large deviations, singularity, and lognormality of energy dissipation in turbulence.}, journal = {Physical review. E}, volume = {101}, number = {6-1}, pages = {061101}, doi = {10.1103/PhysRevE.101.061101}, pmid = {32688541}, issn = {2470-0053}, abstract = {We study implications of the assumption of power-law dependence of moments of energy dissipation in turbulence on the Reynolds number Re, holding due to intermittency. We demonstrate that at Re→∞ the dissipation's logarithm divided by lnRe converges with probability one to a negative constant. This implies that the dissipation is singular in the limit, as is known phenomenologically. The proof uses a large deviations function, whose existence is implied by the power-law assumption, and which provides the general asymptotic form of the dissipation's distribution. A similar function exists for vorticity and for velocity differences where it proves the moments representation of the multifractal model (MF). Then we observe that derivative of the scaling exponents of the dissipation, considered as a function of the order of the moment, is small at the origin. Thus the variation with the order is slow and can be described by a quadratic function. Indeed, the quadratic function, which corresponds to log-normal statistics, fits the data. Moreover, combining the lognormal scaling with the MF we derive a formula for the anomalous scaling exponents of turbulence which also fits the data. Thus lognormality, not to be confused with the Kolmogorov (1962) assumption of lognormal dissipation in the inertial range, when used in conjunction with the MF provides a concise way to get all scaling exponents of turbulence available at present.}, } @article {pmid32688510, year = {2020}, author = {Morita, T and Omori, T and Nakayama, Y and Toyabe, S and Ishikawa, T}, title = {Harnessing random low Reynolds number flow for net migration.}, journal = {Physical review. E}, volume = {101}, number = {6-1}, pages = {063101}, doi = {10.1103/PhysRevE.101.063101}, pmid = {32688510}, issn = {2470-0053}, abstract = {Random noise in low Reynolds number flow has rarely been used to obtain net migration of microscale objects. In this study, we numerically show that net migration of a microscale object can be extracted from random directional fluid forces in Stokes flow, by introducing deformability and inhomogeneous density into the object. We also developed a mathematical framework to describe the deformation-induced migration caused by noise. These results provide a basis for understanding the noise-induced migration of a microswimmer and are useful for harnessing energy from low Reynolds number flow.}, } @article {pmid32685735, year = {2020}, author = {Askar, AH and Kadham, SA and Mshehid, SH}, title = {The surfactants effect on the heat transfer enhancement and stability of nanofluid at constant wall temperature.}, journal = {Heliyon}, volume = {6}, number = {7}, pages = {e04419}, doi = {10.1016/j.heliyon.2020.e04419}, pmid = {32685735}, issn = {2405-8440}, abstract = {Surfactants role in the enhancement of the heat transfer and stability of alumina oxide - distilled water nanofluid was introduced in this research, where there are limited studies that conjugate between the stability improvement and its effect on the heat transfer coefficients. Four weight concentrations for the experiment were used (0.1, 0.3, 0.6, and 0.9%) with 20 nm particle size under a constant wall temperature. The selection of appropriate surfactants weight was tested too by implementing three weight concentrations (0.5, 1, 1.5, and 2 %) related to each nanofluid concentration via measuring their effect on the zeta potential value. The heat transfer augmentation was tested through a double horizontal pipe under a constant wall temperature at entrance region with Reynolds number range (4000-11800). The results manifested the use of nanofluid worked on enhancement the heat transfer performance better than water, and the stable nanofluid elucidated better results.}, } @article {pmid32680965, year = {2020}, author = {Yang, T and Sprinkle, B and Guo, Y and Qian, J and Hua, D and Donev, A and Marr, DWM and Wu, N}, title = {Reconfigurable microbots folded from simple colloidal chains.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {31}, pages = {18186-18193}, pmid = {32680965}, issn = {1091-6490}, support = {R21 AI138214/AI/NIAID NIH HHS/United States ; }, mesh = {*Chemical Engineering ; Colloids/*chemistry ; Magnetics ; *Robotics ; }, abstract = {To overcome the reversible nature of low-Reynolds-number flow, a variety of biomimetic microrobotic propulsion schemes and devices capable of rapid transport have been developed. However, these approaches have been typically optimized for a specific function or environment and do not have the flexibility that many real organisms exhibit to thrive in complex microenvironments. Here, inspired by adaptable microbes and using a combination of experiment and simulation, we demonstrate that one-dimensional colloidal chains can fold into geometrically complex morphologies, including helices, plectonemes, lassos, and coils, and translate via multiple mechanisms that can be varied with applied magnetic field. With chains of multiblock asymmetry, the propulsion mode can be switched from bulk to surface-enabled, mimicking the swimming of microorganisms such as flagella-rotating bacteria and tail-whipping sperm and the surface-enabled motion of arching and stretching inchworms and sidewinding snakes. We also demonstrate that reconfigurability enables navigation through three-dimensional and narrow channels simulating capillary blood vessels. Our results show that flexible microdevices based on simple chains can transform both shape and motility under varying magnetic fields, a capability we expect will be particularly beneficial in complex in vivo microenvironments.}, } @article {pmid32680443, year = {2020}, author = {Ma, Y and Zhang, M and Luo, H}, title = {Numerical and experimental studies of gas-liquid flow and pressure drop in multiphase pump valves.}, journal = {Science progress}, volume = {103}, number = {3}, pages = {36850420940885}, doi = {10.1177/0036850420940885}, pmid = {32680443}, issn = {2047-7163}, abstract = {A numerical and experimental study was carried out to investigate the two-phase flow fields of the typical three valves used in the multiphase pumps. Under the gas volume fraction conditions in the range of 0%-100%, the three-dimensional steady and dynamic two-phase flow characteristics, pressure drops, and their multipliers of the ball valve, cone valve, and disk valve were studied, respectively, using Eulerian-Eulerian approach and dynamic grid technique in ANSYS FLUENT. In addition, a valve test system was built to verify the simulated results by the particle image velocimetry and pressure test. The flow coefficient CQ (about 0.989) of the disk valve is greater than those of the other valves (about 0.864) under the steady flow with a high Reynolds number. The two-phase pressure drops of the three valves fluctuate in different forms with the vibration of the cores during the dynamic opening. The two-phase multipliers of the fully opened ball valve are consistent with the predicted values of the Morris model, while those of the cone valve and disk valve had the smallest differences with the predicted values of the Chisholm model. Through the comprehensive analysis of the flow performance, pressure drop, and dynamic stability of the three pump valves, the disk valve is found to be more suitable for the multiphase pumps due to its smaller axial space, resistance loss, and better flow capacity.}, } @article {pmid32679732, year = {2020}, author = {Juraeva, M and Kang, DJ}, title = {Mixing Performance of a Cross-Channel Split-and-Recombine Micro-Mixer Combined with Mixing Cell.}, journal = {Micromachines}, volume = {11}, number = {7}, pages = {}, pmid = {32679732}, issn = {2072-666X}, abstract = {A new cross-channel split-and-recombine (CC-SAR) micro-mixer was proposed, and its performance was demonstrated numerically. A numerical study was carried out over a wide range of volume flow rates from 3.1 μL/min to 826.8 μL/min. The corresponding Reynolds number ranges from 0.3 to 80. The present micro-mixer consists of four mixing units. Each mixing unit is constructed by combining one split-and-recombine (SAR) unit with a mixing cell. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the present micro-mixer performs better than other micro-mixers based on SARs over a wide range of volume flow rate. The mixing enhancement is realized by a particular motion of vortex flow: the Dean vortex in the circular sub-channel and another vortex inside the mixing cell. The two vortex flows are generated on the different planes perpendicular to each other. They cause the two fluids to change their relative position as the fluids flow into the circular sub-channel of the SAR, eventually promoting violent mixing. High vorticity in the mixing cell elongates the flow interface between two fluids, and promotes mixing in the flow regime of molecular diffusion dominance.}, } @article {pmid32675836, year = {2020}, author = {Liu, J and Yang, W and Dong, M and Marsden, AL}, title = {The nested block preconditioning technique for the incompressible Navier-Stokes equations with emphasis on hemodynamic simulations.}, journal = {Computer methods in applied mechanics and engineering}, volume = {367}, number = {}, pages = {}, pmid = {32675836}, issn = {0045-7825}, support = {R01 EB018302/EB/NIBIB NIH HHS/United States ; R01 HL121754/HL/NHLBI NIH HHS/United States ; R01 HL123689/HL/NHLBI NIH HHS/United States ; R01 HL139796/HL/NHLBI NIH HHS/United States ; }, abstract = {We develop a novel iterative solution method for the incompressible Navier-Stokes equations with boundary conditions coupled with reduced models. The iterative algorithm is designed based on the variational multiscale formulation and the generalized-α scheme. The spatiotemporal discretization leads to a block structure of the resulting consistent tangent matrix in the Newton-Raphson procedure. As a generalization of the conventional block preconditioners, a three-level nested block preconditioner is introduced to attain a better representation of the Schur complement, which plays a key role in the overall algorithm robustness and efficiency. This approach provides a flexible, algorithmic way to handle the Schur complement for problems involving multiscale and multiphysics coupling. The solution method is implemented and benchmarked against experimental data from the nozzle challenge problem issued by the US Food and Drug Administration. The robustness, efficiency, and parallel scalability of the proposed technique are then examined in several settings, including moderately high Reynolds number flows and physiological flows with strong resistance effect due to coupled downstream vasculature models. Two patient-specific hemodynamic simulations, covering systemic and pulmonary flows, are performed to further corroborate the efficacy of the proposed methodology.}, } @article {pmid32666327, year = {2020}, author = {Xue, Y and Hellmuth, R and Shin, DH}, title = {Formation of Vortices in Idealised Branching Vessels: A CFD Benchmark Study.}, journal = {Cardiovascular engineering and technology}, volume = {11}, number = {5}, pages = {544-559}, doi = {10.1007/s13239-020-00477-9}, pmid = {32666327}, issn = {1869-4098}, abstract = {PURPOSE: Atherosclerosis preferentially occurs near the junction of branching vessels, where blood recirculation tends to occur (Malek et al. in J Am Med Assoc 282(21):2035-2042, 1999, https://doi.org/10.1001/jama.282.21.2035). For decades, CFD has been used to predict flow patterns such as separation and recirculation zones in hemodynamic models, but those predictions have rarely been validated with experimental data. In the context of verification and validation (V&V), we first conduct a CFD benchmark calculation that reproduces the vortex detection experiments of Karino and Goldsmith (1980) with idealised branching blood vessels (Karino and Goldsmith in Trans. Am. Soc. Artif. Internal Organs 26:500-506, 1980). The critical conditions for the formation of recirculation vortices, the so-called critical Reynolds numbers, are the main parameters for comparison with the experimental data to demonstrate the credibility of the CFD workflow. We then characterise the wall shear stresses and develop a surrogate model for the size of formed vortices.

METHODS: An automated parametric study generating more than 12,000 CFD simulations was performed, sweeping the geometries and flow conditions found in the experiments by Karino and Goldsmith. The flow conditions were restricted to steady-state laminar flow, with a range of inflow Reynolds numbers up to 350, with various flow ratios between the main branch outlet and side branch outlet. The side branch diameter was scaled relative to the main branch diameter, ranging from 1.05/3 to 3/3; and the branching angles ranged in size from [Formula: see text] to [Formula: see text]. Recirculation vortices were detected by the inversion of the velocity vector at certain locations, as well as by the inversion of the wall shear stress (WSS) vector.

RESULTS: The CFD simulations demonstrated good agreement with the experimental data on the critical Reynolds numbers. The spatial distributions of WSS on each branch were analysed to identify potential regions of disease. Once a vortex is formed, the size of the vortex increases by the square root of the Reynolds number. The CFD data was fitted to a surrogate model that accurately predicts the vortex size without the need to run computationally more expensive CFD simulations.

CONCLUSIONS: This benchmark study validates the CFD simulation of vortex detection in idealised branching vessels under comprehensive flow conditions. This work also proposes a surrogate model for the size of the vortex, which could reduce the computational requirements in the studies related to branching vessels and complex vascular systems.}, } @article {pmid32664605, year = {2020}, author = {Forte, P and Morais, JE and P Neiva, H and Barbosa, TM and Marinho, DA}, title = {The Drag Crisis Phenomenon on an Elite Road Cyclist-A Preliminary Numerical Simulations Analysis in the Aero Position at Different Speeds.}, journal = {International journal of environmental research and public health}, volume = {17}, number = {14}, pages = {}, pmid = {32664605}, issn = {1660-4601}, mesh = {Arm ; *Bicycling ; Head Protective Devices ; Humans ; *Hydrodynamics ; Male ; *Sports ; }, abstract = {The drag crisis phenomenon is the drop of drag coefficient (Cd) with increasing Reynolds number (Re) or speed. The aim of this study was to assess the hypothetical drag crisis phenomenon in a sports setting, assessing it in a bicycle-cyclist system. A male elite-level cyclist was recruited for this research and his competition bicycle, helmet, suit, and shoes were used. A three-dimensional (3D) geometry was obtained with a 3D scan with the subject in a static aero position. A domain with 7 m of length, 2.5 m of width and 2.5 m of height was created around the cyclist. The domain was meshed with 42 million elements. Numerical simulations by computer fluid dynamics (CFD) fluent numerical code were conducted at speeds between 1 m/s and 22 m/s, with increments of 1 m/s. The drag coefficient ranged between 0.60 and 0.95 across different speeds and Re. The highest value was observed at 2 m/s (Cd = 0.95) and Re of 3.21 × 105, whereas the lower Cd was noted at 9 m/s (Cd = 0.60) and 9.63 × 105. A drag crisis was noted between 3 m/s and 9 m/s. Pressure Cd ranged from 0.35 to 0.52 and the lowest value was observed at 3 m/s and the highest at 2 m/s. The viscous drag coefficient ranged between 0.15 and 0.43 and presented a trend decreasing from 4 m/s to 22 m/s. Coaches, cyclists, researchers, and support staff must consider that Cd varies with speed and Re, and the bicycle-cyclist dimensions, shape, or form may affect drag and performance estimations. As a conclusion, this preliminary work noted a drag crisis between 3 m/s and 9 m/s in a cyclist in the aero position.}, } @article {pmid32660001, year = {2020}, author = {Granados-Ortiz, FJ and Ortega-Casanova, J}, title = {Mechanical Characterisation and Analysis of a Passive Micro Heat Exchanger.}, journal = {Micromachines}, volume = {11}, number = {7}, pages = {}, pmid = {32660001}, issn = {2072-666X}, support = {UMA18-FEDERJA-184//UMA/Junta de Andalucia/European Union/ ; }, abstract = {Heat exchangers are widely used in many mechanical, electronic, and bioengineering applications at macro and microscale. Among these, the use of heat exchangers consisting of a single fluid passing through a set of geometries at different temperatures and two flows in T-shape channels have been extensively studied. However, the application of heat exchangers for thermal mixing over a geometry leading to vortex shedding has not been investigated. This numerical work aims to analyse and characterise a heat exchanger for microscale application, which consists of two laminar fluids at different temperature that impinge orthogonally onto a rectangular structure and generate vortex shedding mechanics that enhance thermal mixing. This work is novel in various aspects. This is the first work of its kind on heat transfer between two fluids (same fluid, different temperature) enhanced by vortex shedding mechanics. Additionally, this research fully characterise the underlying vortex mechanics by accounting all geometry and flow regime parameters (longitudinal aspect ratio, blockage ratio and Reynolds number), opposite to the existing works in the literature, which usually vary and analyse blockage ratio or longitudinal aspect ratio only. A relevant advantage of this heat exchanger is that represents a low-Reynolds passive device, not requiring additional energy nor moving elements to enhance thermal mixing. This allows its use especially at microscale, for instance in biomedical/biomechanical and microelectronic applications.}, } @article {pmid32656413, year = {2020}, author = {Dai, X and Liu, C and Zhao, J and Li, L and Yin, S and Liu, H}, title = {Optimization of Application Conditions of Drag Reduction Agent in Product Oil Pipelines.}, journal = {ACS omega}, volume = {5}, number = {26}, pages = {15931-15935}, pmid = {32656413}, issn = {2470-1343}, abstract = {Drag reduction performance was studied with a rotating disk instrument in the laboratory, and experiments show that there is an initial rapid growth stage and stability stage for drag reduction ratio change. The higher the rotational speed, the larger the initial drag reduction ratio is; the larger the concentration, the shorter the drag reduction stabilization time is. Under high concentration and high speed, the drag reduction onset time is short. Because of the shear degradation, the Reynolds number should be taken into account during use. Through a comparison of diesel properties after adding agents with national standard, it is confirmed that drag reduction agents could be used in this pipeline.}, } @article {pmid32639756, year = {2020}, author = {Pusztai, I and Juno, J and Brandenburg, A and TenBarge, JM and Hakim, A and Francisquez, M and Sundström, A}, title = {Dynamo in Weakly Collisional Nonmagnetized Plasmas Impeded by Landau Damping of Magnetic Fields.}, journal = {Physical review letters}, volume = {124}, number = {25}, pages = {255102}, doi = {10.1103/PhysRevLett.124.255102}, pmid = {32639756}, issn = {1079-7114}, abstract = {We perform fully kinetic simulations of flows known to produce dynamo in magnetohydrodynamics (MHD), considering scenarios with low Reynolds number and high magnetic Prandtl number, relevant for galaxy cluster scale fluctuation dynamos. We find that Landau damping on the electrons leads to a rapid decay of magnetic perturbations, impeding the dynamo. This collisionless damping process operates on spatial scales where electrons are nonmagnetized, reducing the range of scales where the magnetic field grows in high magnetic Prandtl number fluctuation dynamos. When electrons are not magnetized down to the resistive scale, the magnetic energy spectrum is expected to be limited by the scale corresponding to magnetic Landau damping or, if smaller, the electron gyroradius scale, instead of the resistive scale. In simulations we thus observe decaying magnetic fields where resistive MHD would predict a dynamo.}, } @article {pmid32620000, year = {2020}, author = {Silverberg, O and Demir, E and Mishler, G and Hosoume, B and Trivedi, NR and Tisch, C and Plascencia, D and Pak, OS and Araci, IE}, title = {Realization of a Push-Me-Pull-You swimmer at low Reynolds numbers.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/aba2b9}, pmid = {32620000}, issn = {1748-3190}, abstract = {Locomotion at low Reynolds numbers encounters stringent physical constraints due to the dominance of viscous over inertial forces. A variety of swimming microorganisms has demonstrated diverse strategies to generate self-propulsion in the absence of inertia. In particular, ameboid and euglenoid movements exploit shape deformations of the cell body for locomotion. Inspired by these biological organisms, the "Push-Me-Pull-You" (PMPY) swimmer (Avron JE, Kenneth O, Oaknin DH 2005 New J. Phys., 7, 234) represents an elegant artificial swimmer that can escape from the constraints of the scallop theorem and generate self-propulsion in highly viscous fluid environments. In this work, we present the first experimental realization of the PMPY swimmer, which consists of a pair of expandable spheres connected by an extensible link. We designed and constructed robotic PMPY swimmers and characterized their propulsion performance in highly viscous silicone oil in dynamically similar, macroscopic experiments. The proof-of-concept demonstrates the feasibility and robustness of the PMPY mechanism as a viable locomotion strategy at low Reynolds numbers.}, } @article {pmid32618067, year = {2020}, author = {Kashima, Y and Ninomiya, S}, title = {Hemodialysis efficiency management from the viewpoint of blood removal pressure.}, journal = {Therapeutic apheresis and dialysis : official peer-reviewed journal of the International Society for Apheresis, the Japanese Society for Apheresis, the Japanese Society for Dialysis Therapy}, volume = {}, number = {}, pages = {}, doi = {10.1111/1744-9987.13557}, pmid = {32618067}, issn = {1744-9987}, abstract = {Degradation of dialysis efficiency during hemodialysis, caused by incompatible indwelling needle size or increase in hematocrit, is a serious problem that can threaten a patient's life. This study aims to derive a quantitative index for determining the indwelling needle diameter that can maintain an appropriate blood flow rate, and presents an effective method to prevent a decrease in the actual blood flow rate. The relationships between the set flow rate and various parameters such as indwelling needle diameter, blood viscosity, and arterial line pressure are analyzed. A simple and reliable method for estimating the actual blood flow rate is derived from these relationships. A correlation between viscosity and actual blood flow rate is estimated adequately by regression analysis using a least-squares method. The relationship between Reynolds number and the flow rate reduction ratio is also evaluated. A new parameter (simple estimation method for actual blood flow) is derived by measuring the blood removal pressure. A pump control approach that uses blood removal pressure is suggested, which can be a future research direction in the field of hemodialysis.}, } @article {pmid32611152, year = {2020}, author = {Zhou, T and Zhang, X and Zhong, S}, title = {An experimental study of trailing edge noise from a heaving airfoil.}, journal = {The Journal of the Acoustical Society of America}, volume = {147}, number = {6}, pages = {4020}, doi = {10.1121/10.0001419}, pmid = {32611152}, issn = {1520-8524}, abstract = {In this study, the far-field noise and near-field flow properties from a heaving NACA 0012 airfoil at the Reynolds number of 6.6×104 were investigated experimentally in a 0.4 m2 anechoic wind tunnel. The airfoil had an incident angle of 0° and followed a sinusoidal heaving motion. The Strouhal number, controlled by changing the heaving frequency and amplitude, varied from 0.0024 to 0.008. The acoustic properties were measured by a free-field microphone placed at a distance of 1.2 m away from the tunnel central line, and the flow structures near the trailing edge were acquired using the particle image velocimetry. It was found that the heaving motion could reduce the sound pressure level (SPL) of the primary peak in the time-averaged spectra. The spectrograms obtained by the short-time Fourier transform revealed that the discrete tones were produced when the airfoil passed through the maximum heaving position. During the corresponding period, a sequence of large-scaled vortices convected on the airfoil surface was observed, and then was shed from the trailing edge to the wake region at the same frequency as the primary tone of the induced sound. With the increase of Strouhal number, the sound signals tended to be broadband, and the overall SPL was increased in the far field.}, } @article {pmid32609698, year = {2020}, author = {Xu, W and Luo, W and Wang, Y and You, Y}, title = {Data-driven three-dimensional super-resolution imaging of a turbulent jet flame using a generative adversarial network.}, journal = {Applied optics}, volume = {59}, number = {19}, pages = {5729-5736}, doi = {10.1364/AO.392803}, pmid = {32609698}, issn = {1539-4522}, abstract = {Three-dimensional (3D) computed tomography (CT) is becoming a well-established tool for turbulent combustion diagnostics. However, the 3D CT technique suffers from contradictory demands of spatial resolution and domain size. This work therefore reports a data-driven 3D super-resolution approach to enhance the spatial resolution by two times along each spatial direction. The approach, named 3D super-resolution generative adversarial network (3D-SR-GAN), builds a generator and a discriminator network to learn the topographic information and infer high-resolution 3D turbulent flame structure with a given low-resolution counterpart. This work uses numerically simulated 3D turbulent jet flame structures as training data to update model parameters of the GAN network. Extensive performance evaluations are then conducted to show the superiority of the proposed 3D-SR-GAN network, compared with other direct interpolation methods. The results show that a convincing super-resolution (SR) operation with the overall error of ∼4% and the peak signal-to-noise ratio of 37 dB can be reached with an upscaling factor of 2, representing an eight times enhancement of the total voxel number. Moreover, the trained network can predict the SR structure of the jet flame with a different Reynolds number without retraining the network parameters.}, } @article {pmid32600217, year = {2020}, author = {Moum, JN}, title = {Variations in Ocean Mixing from Seconds to Years.}, journal = {Annual review of marine science}, volume = {}, number = {}, pages = {}, doi = {10.1146/annurev-marine-031920-122846}, pmid = {32600217}, issn = {1941-0611}, abstract = {Over the past several decades, there has developed a community-wide appreciation for the importance of mixing at the smallest scales to geophysical fluid dynamics on all scales. This appreciation has spawned greater participation in the investigation of ocean mixing and new ways to measure it. These are welcome developments given the tremendous separation in scales between the basins, 𝒪(107) m, and the turbulence, 𝒪 (10-2) m, and the fact that turbulence that leads to thermodynamically irreversible mixing in high-Reynolds-number geophysical flows varies by at least eight orders of magnitude in both space and time. In many cases, it is difficult to separate the dependencies because measurements are sparse, also in both space and time. Comprehensive shipboard turbulence profiling experiments supplemented by Doppler sonar current measurements provide detailed observations of the evolution of the vertical structure of upper-ocean turbulence on timescales of minutes to weeks. Recent technical developments now permit measurements of turbulence in the ocean, at least at a few locations, for extended periods. This review summarizes recent and classic results in the context of our expanding knowledge of the temporal variability of ocean mixing, beginning with a discussion of the timescales of the turbulence itself (seconds to minutes) and how turbulence-enhanced mixing varies over hours, days, tidal cycles, monsoons, seasons, and El Niño-Southern Oscillation timescales (years). Expected final online publication date for the Annual Review of Marine Science, Volume 13 is January 3, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.}, } @article {pmid32581842, year = {2020}, author = {Campinho, P and Vilfan, A and Vermot, J}, title = {Blood Flow Forces in Shaping the Vascular System: A Focus on Endothelial Cell Behavior.}, journal = {Frontiers in physiology}, volume = {11}, number = {}, pages = {552}, pmid = {32581842}, issn = {1664-042X}, abstract = {The endothelium is the cell monolayer that lines the interior of the blood vessels separating the vessel lumen where blood circulates, from the surrounding tissues. During embryonic development, endothelial cells (ECs) must ensure that a tight barrier function is maintained whilst dynamically adapting to the growing vascular tree that is being formed and remodeled. Blood circulation generates mechanical forces, such as shear stress and circumferential stretch that are directly acting on the endothelium. ECs actively respond to flow-derived mechanical cues by becoming polarized, migrating and changing neighbors, undergoing shape changes, proliferating or even leaving the tissue and changing identity. It is now accepted that coordinated changes at the single cell level drive fundamental processes governing vascular network morphogenesis such as angiogenic sprouting, network pruning, lumen formation, regulation of vessel caliber and stability or cell fate transitions. Here we summarize the cell biology and mechanics of ECs in response to flow-derived forces, discuss the latest advances made at the single cell level with particular emphasis on in vivo studies and highlight potential implications for vascular pathologies.}, } @article {pmid32575895, year = {2020}, author = {Nichols, A and Rubinato, M and Cho, YH and Wu, J}, title = {Optimal Use of Titanium Dioxide Colourant to Enable Water Surfaces to Be Measured by Kinect Sensors.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {12}, pages = {}, pmid = {32575895}, issn = {1424-8220}, support = {EP/L015412/1//Engineering and Physical Sciences Research Council/ ; Singapore attachment scheme//A*STAR UK-IHPC/ ; Early Career Researcher Scheme//The University of Sheffield/ ; }, abstract = {Recent studies have sought to use Microsoft Kinect sensors to measure water surface shape in steady flows or transient flow processes. They have typically employed a white colourant, usually titanium dioxide (TiO2), in order to make the surface opaque and visible to the infrared-based sensors. However, the ability of Kinect Version 1 (KV1) and Kinect Version 2 (KV2) sensors to measure the deformation of ostensibly smooth reflective surfaces has never been compared, with most previous studies using a V1 sensor with no justification. Furthermore, the TiO2 has so far been used liberally and indeterminately, with no consideration as to the type of TiO2 to use, the optimal proportion to use or the effect it may have on the very fluid properties being measured. This paper examines the use of anatase TiO2 with two generations of the Microsoft Kinect sensor. Assessing their performance for an ideal flat surface, it is shown that surface data obtained using the V2 sensor is substantially more reliable. Further, the minimum quantity of colourant to enable reliable surface recognition is discovered (0.01% by mass). A stability test shows that the colourant has a strong tendency to settle over time, meaning the fluid must remain well mixed, having serious implications for studies with low Reynolds number or transient processes such as dam breaks. Furthermore, the effect of TiO2 concentration on fluid properties is examined. It is shown that previous studies using concentrations in excess of 1% may have significantly affected the viscosity and surface tension, and thus the surface behaviour being measured. It is therefore recommended that future studies employ the V2 sensor with an anatase TiO2 concentration of 0.01%, and that the effects of TiO2 on the fluid properties are properly quantified before any TiO2-Kinect-derived dataset can be of practical use, for example, in validation of numerical models or in physical models of hydrodynamic processes.}, } @article {pmid32574537, year = {2020}, author = {Rhodeland, B and Hoeger, K and Ursell, T}, title = {Bacterial surface motility is modulated by colony-scale flow and granular jamming.}, journal = {Journal of the Royal Society, Interface}, volume = {17}, number = {167}, pages = {20200147}, pmid = {32574537}, issn = {1742-5662}, abstract = {Microbes routinely face the challenge of acquiring territory and resources on wet surfaces. Cells move in large groups inside thin, surface-bound water layers, often achieving speeds of 30 µm s-1 within this environment, where viscous forces dominate over inertial forces (low Reynolds number). The canonical Gram-positive bacterium Bacillus subtilis is a model organism for the study of collective migration over surfaces with groups exhibiting motility on length-scales three orders of magnitude larger than themselves within a few doubling times. Genetic and chemical studies clearly show that the secretion of endogenous surfactants and availability of free surface water are required for this fast group motility. Here, we show that: (i) water availability is a sensitive control parameter modulating an abiotic jamming-like transition that determines whether the group remains fluidized and therefore collectively motile, (ii) groups self-organize into discrete layers as they travel, (iii) group motility does not require proliferation, rather groups are pulled from the front, and (iv) flow within expanding groups is capable of moving material from the parent colony into the expanding tip of a cellular dendrite with implications for expansion into regions of varying nutrient content. Together, these findings illuminate the physical structure of surface-motile groups and demonstrate that physical properties, like cellular packing fraction and flow, regulate motion from the scale of individual cells up to length scales of centimetres.}, } @article {pmid32564722, year = {2020}, author = {Coreixas, C and Wissocq, G and Chopard, B and Latt, J}, title = {Impact of collision models on the physical properties and the stability of lattice Boltzmann methods.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {378}, number = {2175}, pages = {20190397}, doi = {10.1098/rsta.2019.0397}, pmid = {32564722}, issn = {1471-2962}, abstract = {The lattice Boltzmann method (LBM) is known to suffer from stability issues when the collision model relies on the BGK approximation, especially in the zero viscosity limit and for non-vanishing Mach numbers. To tackle this problem, two kinds of solutions were proposed in the literature. They consist in changing either the numerical discretization (finite-volume, finite-difference, spectral-element, etc.) of the discrete velocity Boltzmann equation (DVBE), or the collision model. In this work, the latter solution is investigated in detail. More precisely, we propose a comprehensive comparison of (static relaxation time based) collision models, in terms of stability, and with preliminary results on their accuracy, for the simulation of isothermal high-Reynolds number flows in the (weakly) compressible regime. It starts by investigating the possible impact of collision models on the macroscopic behaviour of stream-and-collide based D2Q9-LBMs, which clarifies the exact physical properties of collision models on LBMs. It is followed by extensive linear and numerical stability analyses, supplemented with an accuracy study based on the transport of vortical structures over long distances. In order to draw conclusions as generally as possible, the most common moment spaces (raw, central, Hermite, central Hermite and cumulant), as well as regularized approaches, are considered for the comparative studies. LBMs based on dynamic collision mechanisms (entropic collision, subgrid-scale models, explicit filtering, etc.) are also briefly discussed. This article is part of the theme issue 'Fluid dynamics, soft matter and complex systems: recent results and new methods'.}, } @article {pmid32563162, year = {2020}, author = {Sonwani, RK and Giri, BS and Jaiswal, RP and Singh, RS and Rai, BN}, title = {Performance evaluation of a continuous packed bed bioreactor: Bio-kinetics and external mass transfer study.}, journal = {Ecotoxicology and environmental safety}, volume = {201}, number = {}, pages = {110860}, doi = {10.1016/j.ecoenv.2020.110860}, pmid = {32563162}, issn = {1090-2414}, mesh = {Bacillales/growth & development/metabolism ; Biodegradation, Environmental ; Bioreactors/*microbiology ; Cells, Immobilized/microbiology ; Kinetics ; Naphthalenes/*analysis ; Polyethylene/chemistry ; Water Pollutants, Chemical/*analysis ; Water Purification/*methods ; }, abstract = {The biodegradation of naphthalene using low-density polyethylene (LDPE) immobilized Exiguobacterium sp. RKS3 (MG696729) in a packed bed bioreactor (PBBR) was studied. The performance of a continuous PBBR was evaluated at different inlet flow rates (IFRs) (20-100 mL/h) under 64 days of operation. The maximum naphthalene removal efficiency (RE) was found at low IFR, and it further decreased with increasing IFRs. In a continuous PBBR, the external mass transfer (EMT) aspect was analysed at various IFRs, and experimental data were interrelated between Colburn factor (JD) and Reynolds number (NRe) as [Formula: see text] . A new correlation [Formula: see text] was obtained to predict the EMT aspect of naphthalene biodegradation. Andrew-Haldane model was used to evaluate the bio-kinetic parameters of naphthalene degradation, and kinetic constant νmax, Js, and Ji were found as 0.386 per day, 13.6 mg/L, and 20.54 mg/L, respectively.}, } @article {pmid32557795, year = {2020}, author = {Dial, TR and Lauder, GV}, title = {Longer development provides first-feeding fish time to escape hydrodynamic constraints.}, journal = {Journal of morphology}, volume = {281}, number = {8}, pages = {956-969}, doi = {10.1002/jmor.21224}, pmid = {32557795}, issn = {1097-4687}, abstract = {What is the functional effect of prolonged development? By controlling for size, we quantify first-feeding performance and hydrodynamics of zebrafish and guppy offspring (5 ± 0.5 mm in length), which differ fivefold in developmental time and twofold in ontogenetic state. By manipulating water viscosity, we control the hydrodynamic regime, measured as Reynolds number. We predicted that if feeding performance were strictly the result of hydrodynamics, and not development, feeding performance would scale with Reynolds number. We find that guppy offspring successfully feed at much greater distances to prey (1.0 vs. 0.2 mm) and with higher capture success (90 vs. 20%) compared with zebrafish larvae, and that feeding performance was not a result of Reynolds number alone. Flow visualization shows that zebrafish larvae produce a bow wave ~0.2 mm in length, and that the flow field produced during suction does not extend beyond this bow wave. Due to well-developed oral jaw protrusion, the similar-sized suction field generated by guppy offspring extends beyond the horizon of their bow wave, leading to successful prey capture from greater distances. These findings suggest that prolonged development and increased ontogenetic state provides first-feeding fish time to escape the pervasive hydrodynamic constraints (bow wave) of being small.}, } @article {pmid32555272, year = {2020}, author = {Gangfu, L and Haiwang, L and Ruquan, Y and Huijie, W and Zhi, T and Shuangzhi, X}, title = {Experimental Investigation on Velocity and Temperature Field in a Rotating Non-isothermal Turbulent Boundary Layer using Hot-wire.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9892}, pmid = {32555272}, issn = {2045-2322}, support = {51906008//National Natural Science Foundation of China (National Science Foundation of China)/ ; 51822602//National Natural Science Foundation of China (National Science Foundation of China)/ ; 51906008//National Natural Science Foundation of China (National Science Foundation of China)/ ; }, abstract = {This experiment measured the instantaneous temperature and velocity field synchronously in non-isothermal turbulent boundary layer in a rotating straight channel with a parallel-array hot-wire probe. The Reynolds number based on the bulk mean velocity (U) and hydraulic diameter (D) is 19000, and the rotation numbers are 0, 0.07, 0.14, 0.21 and 0.28. The mean velocity u and mean temperature T as well as their fluctuating quantity u' and T' were measured at three streamwise locations (x/D = 4.06, 5.31, 6.56). A method for temperature-changing calibration with constant temperature hot-wire anemometers was proposed. It achieved the calibration in operational temperature range (15.5 °C-50 °C) of the hot-wire via a home-made heating section. The measurement system can obtain the velocity and temperature in a non-isothermal turbulent boundary layer at rotating conditions. The result analysis mainly contains the dimensionless mean temperature, temperature fluctuation as well as its skewness and flatness and streamwise turbulent heat flux. For the trailing side, the rotation effect is more obvious, and makes the dimensionless temperature profiles lower than that under static conditions. The dimensionless streamwise heat flux shows a linear decrease trend in the boundary layer. It is hoped that this research can improve our understanding of the flow and heat transfer mechanism in the internal cooling passages of turbine rotor blades.}, } @article {pmid32555239, year = {2020}, author = {Gepner, SW and Floryan, JM}, title = {Use of Surface Corrugations for Energy-Efficient Chaotic Stirring in Low Reynolds Number Flows.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9865}, pmid = {32555239}, issn = {2045-2322}, abstract = {We demonstrate that an intensive stirring can be achieved in laminar channel flows in a passive manner by utilizing the recently discovered instability waves which lead to chaotic particle movements. The stirring is suitable for mixtures made of delicate constituents prone to mechanical damage, such as bacteria and DNA samples, as collisions between the stream and both the bounding walls as well as mechanical mixing devices are avoided. Debris accumulation is prevented as no stagnant fluid zones are formed. Groove symmetries can be used to limit stirring to selected parts of the flow domain. The energy cost of flows with such stirring is either smaller or marginally larger than the energy cost of flows through smooth channels.}, } @article {pmid32543084, year = {2020}, author = {Xu, K and Wang, M and Tang, W and Ding, Y and Hu, A}, title = {Flash nanoprecipitation with Gd(III)-based metallosurfactants to fabricate polylactic acid nanoparticles as highly efficient contrast agents for magnetic resonance imaging.}, journal = {Chemistry, an Asian journal}, volume = {15}, number = {16}, pages = {2475-2479}, doi = {10.1002/asia.202000624}, pmid = {32543084}, issn = {1861-471X}, support = {21274042//National Natural Science Foundation of China/ ; 21503078//National Natural Science Foundation of China/ ; 22221818014//Fundamental Research Funds for the Central Universities/ ; B502//Shanghai Leading Academic Discipline Project/ ; //Eastern Scholar Professorship/ ; //Shanghai local government/ ; }, abstract = {Polylactic acid (PLA) nanoparticles coated with Gd(III)-based metallosurfactants (MS) are prepared using a simple and rapid one-step method, flash nanoprecipitation (FNP), for magnetic resonance imaging (MRI) applications. By co-assembling the Gd(III)-based MS and an amphiphilic polymer, methoxy poly(ethylene glycol)-b-poly(ϵ-caprolactone) (mPEG-b-PCL), PLA cores were rapidly encapsulated to form biocompatible T1 contrast agents with tunable particle size and narrow size distribution. The hydrophobic property of Gd(III)-based MS were finely tuned to achieve their high loading efficiency. The size of the nanoparticles was easily controlled by tuning the stream velocity, Reynolds number and the amount of the amphiphilic block copolymer during the FNP process. Under the optimized condition, the relaxivity of the nanoparticles was achieved up to 35.39 mM-1 s-1 (at 1.5 T), which is over 8 times of clinically used MRI contrast agents, demonstrating the potential application for MR imaging.}, } @article {pmid32537967, year = {2020}, author = {Zhao, M and Yang, XN and Chen, PY and Sun, WY and Mu, XM and Gao, P and Zhao, GJ}, title = {[Effects of shrub patch pattern on runoff and sediment yield].}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {31}, number = {3}, pages = {735-743}, doi = {10.13287/j.1001-9332.202003.017}, pmid = {32537967}, issn = {1001-9332}, mesh = {*Environmental Monitoring ; *Geologic Sediments ; Rivers ; Soil ; }, abstract = {Understanding the changes of runoff, sediment transport, and hydrodynamic parameters of slopes under the influence of landscape patch coverage and connectivity is of great significance for revealing the hydrodynamic mechanism and hydrological connectivity of slope soil erosion process. In this study, the changes of runoff, sediment transport and hydrodynamic parameters of downhill surface in different coverage levels (0%, 20%, 40%, 60%, 90%) and different connectivity modes (vertical path, horizonal path, S-shaped path, random patches) of shrublands were analyzed by field artificial simulated rainfall test. The results showed that, with the increases of shrub cove-rage, runoff yield and sediment yield decreased exponentially. When the coverage increased to more than 60%, the capacity of shrubs to reduce runoff and sediment became stable. With the increases of shrub coverage, flow velocity, flow depth, Reynolds number, Froude number, stream power, and flow shear resistance significantly decreased, while Manning's roughness coefficient and Darcy-Weisbach resistance coefficient increased significantly. When shrub coverage increased to more than 60%, there was no significant difference in the eigenvalues of hydraulic parameters. The runoff rate under the four connectivity modes followed the order of vertical path > S-shaped path > horizonal path > random patches. The sediment rate was the largest in the vertical path, followed by the S-shaped path, and the horizonal path was not significantly different from the random patches. The path with poor connectivity (horizonal path, random patches) exhibited stronger resistance of hydraulic transmission and poor hydraulic sedimentation capacity than the well-connected path (vertical path, S-shaped path). Our results could provide important theoretical basis for soil erosion control on the Loess Plateau and high-quality development of the Yellow River basin.}, } @article {pmid32531594, year = {2020}, author = {Lequette, K and Ait-Mouheb, N and Wéry, N}, title = {Hydrodynamic effect on biofouling of milli-labyrinth channel and bacterial communities in drip irrigation systems fed with reclaimed wastewater.}, journal = {The Science of the total environment}, volume = {738}, number = {}, pages = {139778}, doi = {10.1016/j.scitotenv.2020.139778}, pmid = {32531594}, issn = {1879-1026}, mesh = {Bacteria ; Biofilms ; *Biofouling ; *Ear, Inner ; Hydrodynamics ; Membranes, Artificial ; Waste Water ; *Water Purification ; }, abstract = {The clogging of drippers due to the development of biofilms reduces the benefits and is an obstacle to the implementation of drip irrigation technology in a reclaimed water context. The narrow section and labyrinth geometry of the dripper channel results the development of a heterogeneous flow behaviours with the vortex zones which it enhance the fouling mechanisms. The objective of this study was to analyse the influence of the three dripper types, defined by their geometric and hydraulic parameters, fed with reclaimed wastewater, on the biofouling kinetics and the bacterial communities. Using optical coherence tomography, we demonstrated that the inlet of the drippers (mainly the first baffle) and vortex zones are the most sensitive area for biofouling. Drippers with the lowest Reynolds number and average cross-section velocity v (1 l·h-1) were the most sensible to biofouling, even if detachment events seemed more frequent in this dripper type. Therefore, dripper flow path with larger v should be consider to improve the anti-clogging performance. In addition, the dripper type and the geometry of the flow path influenced the structure of the bacterial communities from dripper biofilms. Relative abundancy of filamentous bacteria belonging to Chloroflexi phylum was higher in 1 l·h-1 drippers, which presented a higher level of biofouling. However, further research on the role of this phylum in dripper biofouling is required.}, } @article {pmid32521517, year = {2020}, author = {Gamble, LL and Harvey, C and Inman, DJ}, title = {Load alleviation of feather-inspired compliant airfoils for instantaneous flow control.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/ab9b6f}, pmid = {32521517}, issn = {1748-3190}, abstract = {Birds morph their wing shape to adjust to changing environments through muscle-activated morphing of the skeletal structure and passive morphing of the flexible skin and feathers. The role of feather morphing has not been well studied and its impact on aerodynamics is largely unknown. Here we investigate the aero-structural response of a flexible airfoil, designed with biologically accurate structural and material data from feathers, and compared the results to an equivalent rigid airfoil. Two coupled aero-structural models are developed and validated to simulate the response of a bioinspired flexible airfoil across a range of aerodynamic flight conditions. We found that the bioinspired flexible airfoil maintained lift at Reynolds numbers below 1.5x105, within the avian flight regime, performing similarly to its rigid counterpart. At greater Reynolds numbers, the flexible airfoil alleviated the lift force and experienced trailing edge tip displacement. Principal component analysis identified that the Reynolds number dominated this passive shape change which induced a decambering effect, although the angle of attack was found to effect the location of maximum camber. These results imply that birds or aircraft that have tailored chordwise flexible wings will respond like rigid wings while operating at low speeds, but will passively unload large lift forces while operating at high speeds.}, } @article {pmid32519077, year = {2020}, author = {Wierzchowski, K and Grabowska, I and Pilarek, M}, title = {Efficient propagation of suspended HL-60 cells in a disposable bioreactor supporting wave-induced agitation at various Reynolds number.}, journal = {Bioprocess and biosystems engineering}, volume = {43}, number = {11}, pages = {1973-1985}, pmid = {32519077}, issn = {1615-7605}, support = {DEC-2015/17/B/ST8/00631//Narodowe Centrum Nauki/ ; }, abstract = {Growth of human nonadherent HL-60 cell cultures performed in disposable bioreactor under various hydrodynamic conditions of 2-D wave-assisted agitation has been compared and discussed. Influence of Reynolds number for liquid (ReL) and the kLa coefficient, as key parameters characterized the bioprocessing of HL-60 cells in ReadyToProcess WAVETM 25 system, on reached values of the apparent maximal specific growth rate (μmax) and the specific yield of biomass (Y*X/S) has been identified. The values of ReL (i.e., 510-10,208), as well as kLa coefficient (i.e., 2.83-13.55 h-1), have been estimated for the cultures subjected to wave-induced mixing, based on simplified dimensionless correlation for various presents of WAVE 25 system. The highest values of apparent μmax = 0.038 h-1 and Y*X/S = 25.64 × 108 cells gglc-1 have been noted for cultures independently performed at wave-induced agitation characterized by ReL equaled to 5104 and 510, respectively. The presented results have high applicability potential in scale-up of bioprocesses focused on nonadherent animal cells, or in the case of any application of disposable bioreactors presenting similitude.}, } @article {pmid32518305, year = {2020}, author = {Waini, I and Ishak, A and Pop, I}, title = {Hybrid nanofluid flow towards a stagnation point on a stretching/shrinking cylinder.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9296}, doi = {10.1038/s41598-020-66126-2}, pmid = {32518305}, issn = {2045-2322}, abstract = {This paper examines the stagnation point flow towards a stretching/shrinking cylinder in a hybrid nanofluid. Here, copper (Cu) and alumina (Al2O3) are considered as the hybrid nanoparticles while water as the base fluid. The governing equations are reduced to the similarity equations using a similarity transformation. The resulting equations are solved numerically using the boundary value problem solver, bvp4c, available in the Matlab software. It is found that the heat transfer rate is greater for the hybrid nanofluid compared to the regular nanofluid as well as the regular fluid. Besides, the non-uniqueness of the solutions is observed for certain physical parameters. It is also noticed that the bifurcation of the solutions occurs in the shrinking regions. In addition, the heat transfer rate and the skin friction coefficients increase in the presence of nanoparticles and for larger Reynolds number. It is found that between the two solutions, only one of them is stable as time evolves.}, } @article {pmid32516363, year = {2020}, author = {Cho, M and Koref, IS}, title = {The Importance of a Filament-like Structure in Aerial Dispersal and the Rarefaction Effect of Air Molecules on a Nanoscale Fiber: Detailed Physics in Spiders' Ballooning.}, journal = {Integrative and comparative biology}, volume = {60}, number = {4}, pages = {864-875}, doi = {10.1093/icb/icaa063}, pmid = {32516363}, issn = {1557-7023}, abstract = {Many flying insects utilize a membranous structure for flight, which is known as a "wing." However, some spiders use silk fibers for their aerial dispersal. It is well known that spiders can disperse over hundreds of kilometers and rise several kilometers above the ground in this way. However, little is known about the ballooning mechanisms of spiders, owing to the lack of quantitative data. Recently, Cho et al. discovered previously unknown information on the types and physical properties of spiders' ballooning silks. According to the data, a crab spider weighing 20 mg spins 50-60 ballooning silks simultaneously, which are about 200 nm thick and 3.22 m long for their flight. Based on these physical dimensions of ballooning silks, the significance of these filament-like structures is explained by a theoretical analysis reviewing the fluid-dynamics of an anisotropic particle (like a filament or a high-slender body). (1) The filament-like structure is materially efficient geometry to produce (or harvest, in the case of passive flight) fluid-dynamic force in a low Reynolds number flow regime. (2) Multiple nanoscale fibers are the result of the physical characteristics of a thin fiber, the drag of which is proportional to its length but not to its diameter. Because of this nonlinear characteristic of a fiber, spinning multiple thin ballooning fibers is, for spiders, a better way to produce drag forces than spinning a single thick spider silk, because spiders can maximize their drag on the ballooning fibers using the same amount of silk dope. (3) The mean thickness of fibers, 200 nm, is constrained by the mechanical strength of the ballooning fibers and the rarefaction effect of air molecules on a nanoscale fiber, because the slip condition on a fiber could predominate if the thickness of the fiber becomes thinner than 100 nm.}, } @article {pmid32508348, year = {2020}, author = {van Hooft, JA}, title = {A Note on Scalar-Gradient Sharpening in the Stable Atmospheric Boundary Layer.}, journal = {Boundary-layer meteorology}, volume = {176}, number = {1}, pages = {149-156}, pmid = {32508348}, issn = {0006-8314}, abstract = {The scalar front generated by the horizontal self advection of a dipolar vortex through a modest scalar gradient is investigated. This physical scenario is an idealization of the emergence of strong temperature ramps in the stable atmospheric boundary layer. The proposed mechanism is discussed and a two-dimensional analogy is studied in depth using direct numerical simulation. More specifically, the scalar-gradient sharpening is investigated as a function of the Reynolds number. It appears that the process of gradient sharpening at large-eddy scales may be challenging for turbulence-resolving methods applied to the stable-boundary-layer regime.}, } @article {pmid32507933, year = {2020}, author = {Jain, K}, title = {Efficacy of the FDA nozzle benchmark and the lattice Boltzmann method for the analysis of biomedical flows in transitional regime.}, journal = {Medical & biological engineering & computing}, volume = {58}, number = {8}, pages = {1817-1830}, pmid = {32507933}, issn = {1741-0444}, abstract = {Flows through medical devices as well as in anatomical vessels despite being at moderate Reynolds number may exhibit transitional or even turbulent character. In order to validate numerical methods and codes used for biomedical flow computations, the US Food and Drug Administration (FDA) established an experimental benchmark, which was a pipe with gradual contraction and sudden expansion representing a nozzle. The experimental results for various Reynolds numbers ranging from 500 to 6500 were publicly released. Previous and recent computational investigations of flow in the FDA nozzle found limitations in various CFD approaches and some even questioned the adequacy of the benchmark itself. This communication reports the results of a lattice Boltzmann method (LBM) - based direct numerical simulation (DNS) approach applied to the FDA nozzle benchmark for transitional cases of Reynolds numbers 2000 and 3500. The goal is to evaluate if a simple off the shelf LBM would predict the experimental results without the use of complex models or synthetic turbulence at the inflow. LBM computations with various spatial and temporal resolutions are performed-in the extremities of 45 million to 2.88 billion lattice cells-executed respectively on 32 CPU cores of a desktop to more than 300,000 cores of a modern supercomputer to explore and characterize miniscule flow details and quantify Kolmogorov scales. The LBM simulations transition to turbulence at a Reynolds number 2000 like the FDA's experiments and acceptable agreement in jet breakdown locations, average velocity, shear stress, and pressure is found for both the Reynolds numbers. Graphical Abstract A bisecting plane showing the FDA nozzle and vorticity magnitude at t = 10 s for throat Reynolds numbers of 2000 and 3500.}, } @article {pmid32505518, year = {2020}, author = {Cui, X and Wu, W and Ge, H}, title = {Investigation of airflow field in the upper airway under unsteady respiration pattern using large eddy simulation method.}, journal = {Respiratory physiology & neurobiology}, volume = {279}, number = {}, pages = {103468}, doi = {10.1016/j.resp.2020.103468}, pmid = {32505518}, issn = {1878-1519}, abstract = {In this paper, the airflow field in the upper airway under unsteady respiration process is predicted using large eddy simulation. The geometrical model is created by combining a popular cast-based mouth-throat model with tracheo-bronchial airways modeled with a trumpet-shaped conduit. The respiration process is simulated by sinusoidal displacing the bottom surface of the geometrical model. Large eddy simulation with dynamic sub-grid scale model is adopted for modeling the turbulent flow via a commercial CFD software, Converge. This study has found that (1) the secondary vortices in the mouth cavity are much more complex considering the lung expansion than setting the quasi-steady inspiration flow at the mouth-inlet; (2) the properties of secondary vortices in the trachea are not evidently different at the same Reynolds number at the accelerating and decelerating inspiration phases; (3) the reversed pharynx jet as well as recirculation zone is much unsteadier at the accelerating expiration phase than decelerating expiration phase for the same Reynolds number. We conclude that the properties of airflow structures are highly impacted by the respiration pattern and more investigations should be conducted, particularly, on the airflow structures during expiration phase for further understanding the properties of flow field.}, } @article {pmid32505137, year = {2020}, author = {Howard, MP and Statt, A and Stone, HA and Truskett, TM}, title = {Stability of force-driven shear flows in nonequilibrium molecular simulations with periodic boundaries.}, journal = {The Journal of chemical physics}, volume = {152}, number = {21}, pages = {214113}, doi = {10.1063/5.0010697}, pmid = {32505137}, issn = {1089-7690}, abstract = {We analyze the hydrodynamic stability of force-driven parallel shear flows in nonequilibrium molecular simulations with three-dimensional periodic boundary conditions. We show that flows simulated in this way can be linearly unstable, and we derive an expression for the critical Reynolds number as a function of the geometric aspect ratio of the simulation domain. Approximate periodic extensions of Couette and Poiseuille flows are unstable at Reynolds numbers two orders of magnitude smaller than their aperiodic equivalents because the periodic boundaries impose fundamentally different constraints on the flow. This instability has important implications for simulating shear rheology and for designing nonequilibrium simulation methods that are compatible with periodic boundary conditions.}, } @article {pmid32499595, year = {2020}, author = {Meloni, S and Di Marco, A and Mancinelli, M and Camussi, R}, title = {Experimental investigation of jet-induced wall pressure fluctuations over a tangential flat plate at two Reynolds numbers.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9140}, doi = {10.1038/s41598-020-66037-2}, pmid = {32499595}, issn = {2045-2322}, abstract = {The wall pressure fluctuations induced by a subsonic circular jet on a rigid flat plate have been investigated considering two jets with different exit section diameters at the same Mach number. The analysis is aimed at completing the series of papers presented by the authors on the interaction between a subsonic jet and infinite tangential flat plate where the exit Mach number was the only parameter of the jet flow that was varied. In order to analyse other effects out of the Mach number, two configurations with different nozzle exhaust diameters were explored with the objective of isolating the Reynolds number effect keeping fixed the exit Mach number. The nozzle exhaust diameters are 12 mm and 25.4 mm and the instrumented flat plate, installed parallel to the jet flow, is moved at different radial distances from the jet axis. The pressure footprint on the plate has been measured in the stream-wise direction by means of a pair of flush-mounted pressure transducers, providing point-wise pressure signals. Wall pressure fluctuations have been characterised in terms of spectral and statistical quantities. The effect of Reynolds is evidenced and possible scaling relationships that account for the Reynolds dependence are proposed. Implications for modeling the spectral coherence have been considered by the application of the Corcos' model and the effect of the jet Reynolds number on the model coefficients is analyzed.}, } @article {pmid32498258, year = {2020}, author = {Benedict, F and Kumar, A and Kadirgama, K and Mohammed, HA and Ramasamy, D and Samykano, M and Saidur, R}, title = {Thermal Performance of Hybrid-Inspired Coolant for Radiator Application.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {6}, pages = {}, pmid = {32498258}, issn = {2079-4991}, support = {RDU190323 and RDU1803136//Universiti Malaysia Pahang/ ; FRGS/1/2017/TK03/UMP/02/25//Malaysia higher education ministry/ ; }, abstract = {Due to the increasing demand in industrial application, nanofluids have attracted the considerable attention of researchers in recent decades. The addition of nanocellulose (CNC) with water (W) and ethylene glycol (EG) to a coolant for a radiator application exhibits beneficial properties to improve the efficiency of the radiator. The focus of the present work was to investigate the performance of mono or hybrid metal oxide such as Al2O3 and TiO2 with or without plant base-extracted CNC with varying concentrations as a better heat transfer nanofluid in comparison to distilled water as a radiator coolant. The CNC is dispersed in the base fluid of EG and W with a 60:40 ratio. The highest absorption peak was noticed at 0.9% volume concentration of TiO2, Al2O3, CNC, Al2O3/TiO2, and Al2O3/CNC nanofluids which indicates a better stability of the nanofluids' suspension. Better thermal conductivity improvement was observed for the Al2O3 nanofluids in all mono nanofluids followed by the CNC and TiO2 nanofluids, respectively. The thermal conductivity of the Al2O3/CNC hybrid nanofluids with 0.9% volume concentration was found to be superior than that of the Al2O3/TiO2 hybrid nanofluids. Al2O3/CNC hybrid nanofluid dominates over other mono and hybrid nanofluids in terms of viscosity at all volume concentrations. CNC nanofluids (all volume concentrations) exhibited the highest specific heat capacity than other mono nanofluids. Additionally, in both hybrid nanofluids, Al2O3/CNC showed the lowest specific heat capacity. The optimized volume concentration from the statistical analytical tool was found to be 0.5%. The experimental results show that the heat transfer coefficient, convective heat transfer, Reynolds number and the Nusselt number have a proportional relationship with the volumetric flow rate. Hybrid nanofluids exhibit better thermal conductivity than mono nanofluids. For instance, a better thermal conductivity improvement was shown by the mono Al2O3 nanofluids than the CNC and TiO2 nanofluids. On the other hand, superior thermal conductivity was observed for the Al2O3/CNC hybrid nanofluids compared to the other mono and hybrid ones (Al2O3/TiO2).}, } @article {pmid32495156, year = {2020}, author = {Ahasan, K and Landry, CM and Chen, X and Kim, JH}, title = {Effect of angle-of-attacks on deterministic lateral displacement (DLD) with symmetric airfoil pillars.}, journal = {Biomedical microdevices}, volume = {22}, number = {2}, pages = {42}, doi = {10.1007/s10544-020-00496-2}, pmid = {32495156}, issn = {1572-8781}, support = {1707056//Division of Chemical, Bioengineering, Environmental, and Transport Systems/International ; 1917299//Division of Electrical, Communications and Cyber Systems/International ; }, abstract = {Deterministic lateral displacement (DLD) is a microfluidic technique for size fractionation of particles/cells in continuous flow with a great potential for biological and clinical applications. Growing interest of DLD devices in enabling high-throughput operation for practical applications, such as circulating tumor cell (CTC) separation, necessitates employing higher flow rates, leading to operation at moderate to high Reynolds number (Re) regimes. Recently, it has been shown that symmetric airfoil shaped pillars with neutral angle-of-attack (AoA) can be used for high-throughput design of DLD devices due to their mitigation of vortex effects and preservation of flow symmetry under high Re conditions. While high-Re operation with symmetric airfoil shaped pillars has been established, the effect of AoAs on the DLD performance has not been investigated. In this paper, we have characterized the airfoil DLD device with various AoAs. The transport behavior of microparticles has been observed and analyzed with various AoAs in realistic high-Re. Furthermore, we have modeled the flow fields and anisotropy in a representative airfoil pillar array, for both positive and negative AoA configurations. Unlike the conventional DLD device, lateral displacement has been suppressed with +5° and + 15° AoA configurations regardless of particle sizes. On the other hand, stronger lateral displacement has been seen with -5° and - 15° AoAs. This can be attributed to growing flow anisotropy as Re climbs, and significant expansion or compression of streamlines between airfoils with AoAs. The findings in this study can be utilized for the design and optimization of airfoil DLD microfluidic devices with various AoAs.}, } @article {pmid32488023, year = {2020}, author = {Li, X and Gao, J and Guo, Z and Yin, Y and Zhang, X and Sun, P and Gao, Z}, title = {A Study of Rainfall-Runoff Movement Process on High and Steep Slopes Affected by Double Turbulence Sources.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9001}, pmid = {32488023}, issn = {2045-2322}, support = {41371276//National Natural Science Foundation of China (National Science Foundation of China)/ ; }, abstract = {To increase the available land area, a large-scale land remediation campaign was carried out in the loess hilly and gully area. A large number of high and steep slopes have been produced in the construction of road engineering and water conservancy engineering, and these slopes will cause serious soil erosion under rainfall conditions. Because rainfall runoff is simultaneously affected by slope, bed surface and rainfall, the runoff movement characteristics are complex. It is difficult to consider all influencing factors in the existing models, especially for steep slopes. In this study, artificial rainfall experiments were conducted to study the rainfall-runoff hydraulic processes under different rainfall intensities and slope gradients, and a modified method was proposed to model the key hydraulic parameters (i.e., equilibrium time, water surface line, and runoff processes) on steep slopes. The results showed that (1) For steep slopes (a 70° slope compared to a 5° slope), the runoff generation time, confluence time and equilibrium time of the slope decreased significantly. At the same time, the single width runoff of the steep slope had a power function relationship with the rainfall intensity and gradient. (2) The runoff patterns of steep slopes were different from those on gentle slopes and runoff patterns were more likely to change. The Reynolds number and Froude number for slope flow changed slowly when the slope was less than the critical gradient and increased significantly when the slope exceeded the critical gradient. (3) Based on the analysis of the "double turbulent model theory of thin-layer flow on a high-steep slope", combined with the dispersed motion wave model, a modified method for calculating the hydrodynamic factors of rainfall runoff was proposed. Then, this method was verified with indoor and outdoor experiments. The research results not only have theoretical significance, but also provide a more accurate calculation method for the design of high and steep slopes involved in land treatment engineering, road engineering and water conservancy engineering.}, } @article {pmid32481597, year = {2020}, author = {Robles-Romero, JM and Romero-Martín, M and Conde-Guillén, G and Cruces-Romero, D and Gómez-Salgado, J and Ponce-Blandón, JA}, title = {The Physics of Fluid Dynamics Applied to Vascular Ulcers and Its Impact on Nursing Care.}, journal = {Healthcare (Basel, Switzerland)}, volume = {8}, number = {2}, pages = {}, pmid = {32481597}, issn = {2227-9032}, abstract = {The high incidence of vascular ulcers and the difficulties encountered in their healing process require the understanding of their multiple etiologies to develop effective strategies focused on providing different treatment options. This work provides a description of the principles of the physics of fluid dynamics related to vascular ulcers. The morphological characteristics of the cardiovascular system promote blood flow. The contraction force of the left ventricle is enhanced by its ability to reduce its radius of curvature and by increasing the thickness of the ventricular wall (Laplace's Law). Arterial flow must overcome vascular resistance (Ohm's equation). The elastic nature of the artery and the ability to reduce its diameter as flow rate progresses facilitate blood conduction at high speed up to arteriolar level, and this can be determined by the second equation of continuity. As it is a viscous fluid, we must discuss laminar flow, calculated by the Reynolds number, which favors proper conduction while aiming at the correct net filtration pressure. Any endothelial harmful process that affects the muscle wall of the vessel increases the flow speed, causing a decrease in capillary hydrostatic pressure, thus reducing the exchange of nutrients at the interstitial level. With regard to the return system, the flow direction is anti-gravity and requires endogenous aid to establish the Starling's equilibrium. Knowledge on the physics of vascular fluid dynamics makes it easier to understand the processes of formation of these ulcers so as to choosing the optimal healing and prevention techniques for these chronic wounds.}, } @article {pmid32466224, year = {2020}, author = {Charlton, AJ and Lian, B and Blandin, G and Leslie, G and Le-Clech, P}, title = {Impact of FO Operating Pressure and Membrane Tensile Strength on Draw-Channel Geometry and Resulting Hydrodynamics.}, journal = {Membranes}, volume = {10}, number = {5}, pages = {}, pmid = {32466224}, issn = {2077-0375}, abstract = {In an effort to improve performances of forward osmosis (FO) systems, several innovative draw spacers have been proposed. However, the small pressure generally applied on the feed side of the process is expected to result in the membrane bending towards the draw side, and in the gradual occlusion of the channel. This phenomenon potentially presents detrimental effects on process performance, including pressure drop and external concentration polarization (ECP) in the draw channel. A flat sheet FO system with a dot-spacer draw channel geometry was characterized to determine the degree of draw channel occlusion resulting from feed pressurization, and the resulting implications on flow performance. First, tensile testing was performed on the FO membrane to derive a Young's modulus, used to assess the membrane stretching, and the resulting draw channel characteristics under a range of moderate feed pressures. Membrane apex reached up to 67% of the membrane channel height when transmembrane pressure (TMP) of 1.4 bar was applied. The new FO channels considerations were then processed by computational fluid dynamics model (computational fluid dynamics (CFD) by ANSYS Fluent v19.1) and validated against previously obtained experimental data. Further simulations were conducted to better assess velocity profiles, Reynolds number and shear rate. Reynolds number on the membrane surface (draw side) increased by 20% and shear rate increased by 90% when occlusion changed from 0 to 70%, impacting concentration polarisation (CP) on the membrane surface and therefore FO performance. This paper shows that FO draw channel occlusion is expected to have a significant impact on fluid hydrodynamics when the membrane is not appropriately supported in the draw side.}, } @article {pmid32462438, year = {2020}, author = {Asghar, Z and Ali, N and Waqas, M and Nazeer, M and Khan, WA}, title = {Locomotion of an efficient biomechanical sperm through viscoelastic medium.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {6}, pages = {2271-2284}, doi = {10.1007/s10237-020-01338-z}, pmid = {32462438}, issn = {1617-7940}, abstract = {Every group of microorganism utilizes a diverse mechanical strategy to propel through complex environments. These swimming problems deal with the fluid-organism interaction at micro-scales in which Reynolds number is of the order of 10-3. By adopting the same propulsion mechanism of so-called Taylor's sheet, here we address the biomechanical principle of swimming via different wavy surfaces. The passage (containing micro-swimmers) is considered to be passive two-dimensional channel filled with viscoelastic liquid, i.e., Oldroyd-4 constant fluid. For some initial value of unknowns, i.e., cell speed and flow rate of surrounding liquid, the resulting boundary value problem is solved by robust finite difference scheme. This convergent solution is further employed in the equilibrium conditions which will obviously not be satisfied for such crude values of unknowns. These unknowns are further refined (to satisfy the equilibrium conditions) by modified Newton-Raphson algorithm. These computed pairs are also utilized to compute the energy losses. The speed of swimming sheet its power delivered and flow rate of Oldroyd-4 constant fluid are compared for different kinds of wavy sheets. These results are also useful in the manufacturing of artificial (soft) microbots and the optimization of locomotion strategies.}, } @article {pmid32438546, year = {2020}, author = {Cassineri, S and Cioncolini, A and Smith, L and Curioni, M and Scenini, F}, title = {Experiments on Liquid Flow through Non-Circular Micro-Orifices.}, journal = {Micromachines}, volume = {11}, number = {5}, pages = {}, pmid = {32438546}, issn = {2072-666X}, support = {EP/L01680X/1//Engineering and Physical Sciences Research Council/ ; }, abstract = {Microfluidics is an active research area in modern fluid mechanics, with several applications in science and engineering. Despite their importance in microfluidic systems, micro-orifices with non-circular cross-sections have not been extensively investigated. In this study, micro-orifice discharge with single-phase liquid flow was experimentally investigated for seven square and rectangular cross-section micro-orifices with a hydraulic diameter in the range of 326-510 µm. The discharge measurements were carried out in pressurized water (12 MPa) at ambient temperature (298 K) and high temperature (503 K). During the tests, the Reynolds number varied between 5883 and 212,030, significantly extending the range in which data are currently available in the literature on non-circular micro-orifices. The results indicate that the cross-sectional shape of the micro-orifice has little, if any, effect on the hydrodynamic behavior. Thus, existing methods for the prediction of turbulent flow behavior in circular micro-orifices can be used to predict the flow behavior in non-circular micro-orifices, provided that the flow geometry of the non-circular micro-orifice is described using a hydraulic diameter.}, } @article {pmid32422718, year = {2020}, author = {Moriconi, L}, title = {Magnetic dissipation of near-wall turbulent coherent structures in magnetohydrodynamic pipe flows.}, journal = {Physical review. E}, volume = {101}, number = {4-1}, pages = {043111}, doi = {10.1103/PhysRevE.101.043111}, pmid = {32422718}, issn = {2470-0053}, abstract = {Relaminarization of wall-bounded turbulent flows by means of external static magnetic fields is a long-known phenomenon in the physics of electrically conducting fluids at low magnetic Reynolds numbers. Despite the large literature on the subject, it is not yet completely clear what combination of the Hartmann (M) and the Reynolds number has to be used to predict the laminar-turbulent transition in channel or pipe flows fed by upstream turbulent flows free of magnetic perturbations. Relying upon standard phenomenological approaches related to mixing length and structural concepts, we put forward that M/R_{τ}, where R_{τ} is the friction Reynolds number, is the appropriate controlling parameter for relaminarization, a proposal which finds good support from available experimental data.}, } @article {pmid32422715, year = {2020}, author = {Ekanem, EM and Berg, S and De, S and Fadili, A and Bultreys, T and Rücker, M and Southwick, J and Crawshaw, J and Luckham, PF}, title = {Signature of elastic turbulence of viscoelastic fluid flow in a single pore throat.}, journal = {Physical review. E}, volume = {101}, number = {4-1}, pages = {042605}, doi = {10.1103/PhysRevE.101.042605}, pmid = {32422715}, issn = {2470-0053}, abstract = {When a viscoelastic fluid, such as an aqueous polymer solution, flows through a porous medium, the fluid undergoes a repetitive expansion and contraction as it passes from one pore to the next. Above a critical flow rate, the interaction between the viscoelastic nature of the polymer and the pore configuration results in spatial and temporal flow instabilities reminiscent of turbulentlike behavior, even though the Reynolds number Re≪1. To investigate whether this is caused by many repeated pore body-pore throat sequences, or simply a consequence of the converging (diverging) nature present in a single pore throat, we performed experiments using anionic hydrolyzed polyacrylamide (HPAM) in a microfluidic flow geometry representing a single pore throat. This allows the viscoelastic fluid to be characterized at increasing flow rates using microparticle image velocimetry in combination with pressure drop measurements. The key finding is that the effect, popularly known as "elastic turbulence," occurs already in a single pore throat geometry. The critical Deborah number at which the transition in rheological flow behavior from pseudoplastic (shear thinning) to dilatant (shear thickening) strongly depends on the ionic strength, the type of cation in the anionic HPAM solution, and the nature of pore configuration. The transition towards the elastic turbulence regime was found to directly correlate with an increase in normal stresses. The topology parameter, Q_{f}, computed from the velocity distribution, suggests that the "shear thickening" regime, where much of the elastic turbulence occurs in a single pore throat, is a consequence of viscoelastic normal stresses that cause a complex flow field. This flow field consists of extensional, shear, and rotational features around the constriction, as well as upstream and downstream of the constriction. Furthermore, this elastic turbulence regime, has high-pressure fluctuations, with a power-law decay exponent of up to |-2.1| which is higher than the Kolmogorov value for turbulence of |-5/3|.}, } @article {pmid32388985, year = {2020}, author = {Jain, SK and Banerjee, U and Sen, AK}, title = {Trapping and Coalescence of Diamagnetic Aqueous Droplets Using Negative Magnetophoresis.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {21}, pages = {5960-5966}, doi = {10.1021/acs.langmuir.0c00846}, pmid = {32388985}, issn = {1520-5827}, abstract = {The manipulation of aqueous droplets has a profound significance in biochemical assays. Magnetic field-driven droplet manipulation, offering unique advantages, is consequently gaining attention. However, the phenomenon relating to diamagnetic droplets is not well understood. Here, we report the understanding of trapping and coalescence of flowing diamagnetic aqueous droplets in a paramagnetic (oil-based ferrofluid) medium using negative magnetophoresis. Our study revealed that the trapping phenomenon is underpinned by the interplay of magnetic energy (Em) and frictional (viscous) energy (Ef), in terms of magnetophoretic stability number, Sm = (Em/Ef). The trapping and nontrapping regimes are characterized based on the peak value of magnetophoretic stability number, Smp, and droplet size, D*. The study of coalescence of a trapped droplet with a follower droplet (and a train of droplets) revealed that the film-drainage Reynolds number (Refd) representing the coalescence time depends on the magnetic Bond number, Bom. The coalesced droplet continues to remain trapped or gets self-released obeying the Smp and D* criterion. Our study offers an understanding of the magnetic manipulation of diamagnetic aqueous droplets that can potentially be used for biochemical assays in microfluidics.}, } @article {pmid32357661, year = {2020}, author = {Garcia, F and Seilmayer, M and Giesecke, A and Stefani, F}, title = {Chaotic wave dynamics in weakly magnetized spherical Couette flows.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {4}, pages = {043116}, doi = {10.1063/1.5140577}, pmid = {32357661}, issn = {1089-7682}, abstract = {Direct numerical simulations of a liquid metal filling the gap between two concentric spheres are presented. The flow is governed by the interplay between the rotation of the inner sphere (measured by the Reynolds number Re) and a weak externally applied axial magnetic field (measured by the Hartmann number Ha). By varying the latter, a rich variety of flow features, both in terms of spatial symmetry and temporal dependence, is obtained. Flows with two or three independent frequencies describing their time evolution are found as a result of Hopf bifurcations. They are stable on a sufficiently large interval of Hartmann numbers where regions of multistability of two, three, and even four types of these different flows are detected. The temporal character of the solutions is analyzed by means of an accurate frequency analysis and Poincaré sections. An unstable branch of flows undergoing a period doubling cascade and frequency locking of three-frequency solutions is described as well.}, } @article {pmid32357025, year = {2020}, author = {Kang, S and Kwak, R}, title = {Pattern Formation of Three-Dimensional Electroconvection on a Charge Selective Surface.}, journal = {Physical review letters}, volume = {124}, number = {15}, pages = {154502}, doi = {10.1103/PhysRevLett.124.154502}, pmid = {32357025}, issn = {1079-7114}, abstract = {When a charge selective surface consumes or transports only cations or anions in the electrolyte, biased ion rejection initiates hydrodynamic instability, resulting in vortical fluid motions called electroconvection. In this Letter, we describe the first laboratory observation of three-dimensional electroconvection on a charge selective surface. Combining experiment and scaling analysis, we successfully categorized three distinct patterns of 3D electroconvection according to [(Ra_{E})/(Re^{2}Sc)] [electric Rayleigh number (Ra_{E}), Reynolds number (Re), Schmidt number (Sc)] as (i) polygonal, (ii) transverse, or (iii) longitudinal rolls. If Re increases or Ra_{E} decreases, pure longitudinal rolls are presented. On the other hand, transverse rolls are formed between longitudinal rolls, and two rolls are transformed as polygonal one at higher Ra_{E} or lower Re. In this pattern selection scenario, Sc determines the critical electric Rayleigh number (Ra_{E}^{*}) for the onset of each roll, resulting in Ra_{E}^{*}∼Re^{2}Sc. We also verify that convective ion flux by electroconvection (represented by an electric Nusselt number Nu_{E}) is fitted to a power law, Nu_{E}∼[(Ra_{E}-Ra_{E}^{*})/(Re^{2}Sc)]^{α_{1}}Re^{α_{2}}Pe^{α_{3}} [Péclet number (Pe)], where each term represents the characteristics of electroconvection, shear flow, and ion transport.}, } @article {pmid32349452, year = {2020}, author = {Raza, W and Hossain, S and Kim, KY}, title = {A Review of Passive Micromixers with a Comparative Analysis.}, journal = {Micromachines}, volume = {11}, number = {5}, pages = {}, pmid = {32349452}, issn = {2072-666X}, support = {2019R1A2C1007657//National Research Foundation of Korea/ ; }, abstract = {A wide range of existing passive micromixers are reviewed, and quantitative analyses of ten typical passive micromixers were performed to compare their mixing indices, pressure drops, and mixing costs under the same axial length and flow conditions across a wide Reynolds number range of 0.01-120. The tested micromixers were selected from five types of micromixer designs. The analyses of flow and mixing were performed using continuity, Navier-Stokes and convection-diffusion equations. The results of the comparative analysis were presented for three different Reynolds number ranges: low-Re (Re ≤ 1), intermediate-Re (1 < Re ≤ 40), and high-Re (Re > 40) ranges, where the mixing mechanisms are different. The results show a two-dimensional micromixer of Tesla structure is recommended in the intermediate- and high-Re ranges, while two three-dimensional micromixers with two layers are recommended in the low-Re range due to their excellent mixing performance.}, } @article {pmid32342660, year = {2020}, author = {Storm, TJ and Nolan, KE and Roberts, EM and Sanderson, SL}, title = {Oropharyngeal morphology related to filtration mechanisms in suspension-feeding American shad (Clupeidae).}, journal = {Journal of experimental zoology. Part A, Ecological and integrative physiology}, volume = {333}, number = {7}, pages = {493-510}, doi = {10.1002/jez.2363}, pmid = {32342660}, issn = {2471-5646}, support = {//William & Mary (W&M) Undergraduate Science Education and Research Program, funded by a Howard Hughes Medical Institute grant through the Undergraduate Science Education Program to W&M/ ; }, abstract = {To assess potential filtration mechanisms, scanning electron microscopy was used in a comprehensive quantification and analysis of the morphology and surface ultrastructure for all five branchial arches in the ram suspension-feeding fish, American shad (Alosa sapidissima, Clupeidae). The orientation of the branchial arches and the location of mucus cells on the gill rakers were more consistent with mechanisms of crossflow filtration and cross-step filtration rather than conventional dead-end sieving. The long, thin gill rakers could lead to a large area for the exit of water from the oropharyngeal cavity during suspension feeding (high fluid exit ratio). The substantial elongation of gill rakers along the dorsal-ventral axis formed d-type ribs with a groove aspect ratio of 0.5 and a Reynolds number of approximately 500, consistent with the potential operation of cross-step filtration. Mucus cell abundance differed significantly along the length of the raker and the height of the raker. The mucus cell abundance data and the observed sloughing of denticles along the gill raker margins closest to the interior of the oropharyngeal cavity suggest that gill raker growth may occur primarily at the raker tips, the denticle bases, and the internal raker margins along the length of the raker. These findings will be applied in ongoing experiments with 3D-printed physical models of fish oral cavities in flow tanks, and in future ecological studies on the diet and nutrition of suspension-feeding fishes.}, } @article {pmid32340402, year = {2020}, author = {Singh, AV and Ansari, MHD and Mahajan, M and Srivastava, S and Kashyap, S and Dwivedi, P and Pandit, V and Katha, U}, title = {Sperm Cell Driven Microrobots-Emerging Opportunities and Challenges for Biologically Inspired Robotic Design.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32340402}, issn = {2072-666X}, abstract = {With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are the main challenges. Propulsion at micro-scale where the Reynolds number is very low is difficult. To overcome this, nature has developed flagella which have evolved over millions of years to work as a micromotor. Among the microscopic cells that exhibit this mode of propulsion, sperm cells are considered to be fast paced. Here, we give a brief review of the state-of-the-art of Spermbots - a new class of microrobots created by coupling sperm cells to mechanical loads. Spermbots utilize the flagellar movement of the sperm cells for propulsion and as such do not require any toxic fuel in their environment. They are also naturally biocompatible and show considerable speed of motion thereby giving us an option to overcome the two challenges of propulsion and biocompatibility. The coupling mechanisms of physical load to the sperm cells are discussed along with the advantages and challenges associated with the spermbot. A few most promising applications of spermbots are also discussed in detail. A brief discussion of the future outlook of this extremely promising category of microrobots is given at the end.}, } @article {pmid32325022, year = {2020}, author = {Zhou, Q and Fidalgo, J and Calvi, L and Bernabeu, MO and Hoskins, PR and Oliveira, MSN and Krüger, T}, title = {Spatiotemporal Dynamics of Dilute Red Blood Cell Suspensions in Low-Inertia Microchannel Flow.}, journal = {Biophysical journal}, volume = {118}, number = {10}, pages = {2561-2573}, doi = {10.1016/j.bpj.2020.03.019}, pmid = {32325022}, issn = {1542-0086}, abstract = {Microfluidic technologies are commonly used for the manipulation of red blood cell (RBC) suspensions and analyses of flow-mediated biomechanics. To enhance the performance of microfluidic devices, understanding the dynamics of the suspensions processed within is crucial. We report novel, to our knowledge, aspects of the spatiotemporal dynamics of RBC suspensions flowing through a typical microchannel at low Reynolds number. Through experiments with dilute RBC suspensions, we find an off-center two-peak (OCTP) profile of cells contrary to the centralized distribution commonly reported for low-inertia flows. This is reminiscent of the well-known "tubular pinch effect," which arises from inertial effects. However, given the conditions of negligible inertia in our experiments, an alternative explanation is needed for this OCTP profile. Our massively parallel simulations of RBC flow in real-size microfluidic dimensions using the immersed-boundary-lattice-Boltzmann method confirm the experimental findings and elucidate the underlying mechanism for the counterintuitive RBC pattern. By analyzing the RBC migration and cell-free layer development within a high-aspect-ratio channel, we show that such a distribution is co-determined by the spatial decay of hydrodynamic lift and the global deficiency of cell dispersion in dilute suspensions. We find a cell-free layer development length greater than 46 and 28 hydraulic diameters in the experiment and simulation, respectively, exceeding typical lengths of microfluidic designs. Our work highlights the key role of transient cell distribution in dilute suspensions, which may negatively affect the reliability of experimental results if not taken into account.}, } @article {pmid32317809, year = {2020}, author = {Navah, F and de la Llave Plata, M and Couaillier, V}, title = {A High-Order Multiscale Approach to Turbulence for Compact Nodal Schemes.}, journal = {Computer methods in applied mechanics and engineering}, volume = {363}, number = {}, pages = {}, doi = {10.1016/j.cma.2020.112885}, pmid = {32317809}, issn = {0045-7825}, support = {R01 DC005788/DC/NIDCD NIH HHS/United States ; }, abstract = {This article presents a formulation that extends the multiscale modelling for compressible large-eddy simulation to a vast family of compact nodal numerical methods represented by the high-order flux reconstruction scheme. The theoretical aspects of the proposed formulation are laid down via mathematical derivations which clearly expose the underlying assumptions and approximations and provide sufficient details for accurate reproduction of the methodology. The final form is assessed on a Taylor-Green vortex benchmark with Reynolds number of 5000 and compared to filtered direct numerical simulation data. These numerical experiments exhibit the important role of sufficient de-aliasing, appropriate amount of upwinding from Roe's numerical flux and large/small scale partition, in achieving better agreement with reference data, especially on coarse grids, when compared to the baseline implicit large-eddy simulation.}, } @article {pmid32315915, year = {2020}, author = {Banerjee, A and Sharma, T and Nautiyal, AK and Dasgupta, D and Hazra, S and Bhaskar, T and Ghosh, D}, title = {Scale-up strategy for yeast single cell oil production for Rhodotorula mucilagenosa IIPL32 from corn cob derived pentosan.}, journal = {Bioresource technology}, volume = {309}, number = {}, pages = {123329}, doi = {10.1016/j.biortech.2020.123329}, pmid = {32315915}, issn = {1873-2976}, mesh = {Fermentation ; *Rhodotorula ; Xylose ; Yeasts ; *Zea mays ; }, abstract = {This work was aimed to strategically scale-up the yeast lipid production process using Reynolds number as a standard rheological parameter from 50 mL to 50 L scale. Oleaginous yeast Rhodotorula mucilaginosa IIPL32 was cultivated in xylose rich corncob hydrolysate. The fermentation process for growth and maturation was operated in fed-batch with two different C/N ratios of 40 and 60. The hydrodynamic parameters were used to standardize and represent the effect of rheology on the fermentation process. The growth pattern of the yeast was found similar in both shake flask and fermenter with the maximum growth observed at 48 h. The lipid yield increased from 0.4 g/L and 0.5 g/L to 1.3 g/L and 1.83 g/L for 50 mL to 50 L for C/N ratio 40 and 60 respectively. The increase in productivity during the growth phase and lipid accumulation during the maturation phase showed that the scale-up strategy was successful.}, } @article {pmid32295138, year = {2020}, author = {Erdem, K and Ahmadi, VE and Kosar, A and Kuddusi, L}, title = {Differential Sorting of Microparticles Using Spiral Microchannels with Elliptic Configurations.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32295138}, issn = {2072-666X}, support = {Project Number: MDK-2017-40845//Istanbul Teknik Üniversitesi/ ; }, abstract = {Label-free, size-dependent cell-sorting applications based on inertial focusing phenomena have attracted much interest during the last decade. The separation capability heavily depends on the precision of microparticle focusing. In this study, five-loop spiral microchannels with a height of 90 µm and a width of 500 µm are introduced. Unlike their original spiral counterparts, these channels have elliptic configurations of varying initial aspect ratios, namely major axis to minor axis ratios of 3:2, 11:9, 9:11, and 2:3. Accordingly, the curvature of these configurations increases in a curvilinear manner through the channel. The effects of the alternating curvature and channel Reynolds number on the focusing of fluorescent microparticles with sizes of 10 and 20 µm in the prepared suspensions were investigated. At volumetric flow rates between 0.5 and 3.5 mL/min (allowing separation), each channel was tested to collect samples at the designated outlets. Then, these samples were analyzed by counting the particles. These curved channels were capable of separating 20 and 10 µm particles with total yields up to approximately 95% and 90%, respectively. The results exhibited that the level of enrichment and the focusing behavior of the proposed configurations are promising compared to the existing microfluidic channel configurations.}, } @article {pmid32294955, year = {2020}, author = {Sun, HCM and Liao, P and Wei, T and Zhang, L and Sun, D}, title = {Magnetically Powered Biodegradable Microswimmers.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32294955}, issn = {2072-666X}, abstract = {The propulsive efficiency and biodegradability of wireless microrobots play a significant role in facilitating promising biomedical applications. Mimicking biological matters is a promising way to improve the performance of microrobots. Among diverse locomotion strategies, undulatory propulsion shows remarkable efficiency and agility. This work proposes a novel magnetically powered and hydrogel-based biodegradable microswimmer. The microswimmer is fabricated integrally by 3D laser lithography based on two-photon polymerization from a biodegradable material and has a total length of 200 μm and a diameter of 8 μm. The designed microswimmer incorporates a novel design utilizing four rigid segments, each of which is connected to the succeeding segment by spring to achieve undulation, improving structural integrity as well as simplifying the fabrication process. Under an external oscillating magnetic field, the microswimmer with multiple rigid segments connected by flexible spring can achieve undulatory locomotion and move forward along with the directions guided by the external magnetic field in the low Reynolds number (Re) regime. In addition, experiments demonstrated that the microswimmer can be degraded successfully, which allows it to be safely applied in real-time in vivo environments. This design has great potential in future in vivo applications such as precision medicine, drug delivery, and diagnosis.}, } @article {pmid32290599, year = {2020}, author = {Huang, B and Li, H and Xu, T}, title = {Experimental Investigation of the Flow and Heat Transfer Characteristics in Microchannel Heat Exchangers with Reentrant Cavities.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32290599}, issn = {2072-666X}, support = {No.51906008, No.51822602//National Natural Science Foundation of China/ ; No. YWF-19-BJ-J-293//Fundamental Research Funds for the Central Universities/ ; 2017-Ⅲ-0003-0027//National Major Science and Technology Projects of China/ ; }, abstract = {The application of microchannel heat exchangers is of great significance in industrial fields due to their advantages of miniaturized scale, large surface-area-to-volume ratio, and high heat transfer rate. In this study, microchannel heat exchangers with and without fan-shaped reentrant cavities were designed and manufactured, and experiments were conducted to investigate the flow and heat-transfer characteristics. The impact rising from the radius of reentrant cavities, as well as the Reynolds number on the heat transfer and the pressure drop, is also analyzed. The results indicate that, compared with straight microchannels, microchannels with reentrant cavities could enhance the heat transfer and, more importantly, reduce the pressure drop at the same time. For the ranges of parameters studied, increasing the radius of reentrant cavities could augment the effect of pressure-drop reduction, while the corresponding variation of heat transfer is complicated. It is considered that adding reentrant cavities in microchannel heat exchangers is an ideal approach to improve performance.}, } @article {pmid32290016, year = {2020}, author = {Alboussière, T and Drif, K and Plunian, F}, title = {Dynamo action in sliding plates of anisotropic electrical conductivity.}, journal = {Physical review. E}, volume = {101}, number = {3-1}, pages = {033107}, doi = {10.1103/PhysRevE.101.033107}, pmid = {32290016}, issn = {2470-0053}, abstract = {With materials of anisotropic electrical conductivity, it is possible to generate a dynamo with a simple velocity field, of the type precluded by Cowling's theorems with isotropic materials. Following a previous study by Ruderman and Ruzmaikin [M. S. Ruderman and A. A. Ruzmaikin, Magnetic field generation in an anisotropically conducting fluid, Geophys. Astrophys. Fluid Dyn. 28, 77 (1984)GAFDD30309-192910.1080/03091928408210135], who considered the dynamo effect induced by a uniform shear flow, we determine the conditions for the dynamo threshold when a solid plate is sliding over another one, both with anisotropic electrical conductivity. We obtain numerical solutions for a general class of anisotropy and obtain the conditions for the lowest magnetic Reynolds number, using a collocation Chebyshev method. In a particular geometry of anisotropy and wave number, we also derive an analytical solution, where the eigenvectors are just combinations of four exponential functions. An explicit analytical expression is obtained for the critical magnetic Reynolds number. Above the critical magnetic Reynolds number, we have also derived an analytical expression for the growth rate showing that this is a "very fast" dynamo, extrapolating on the "slow" and "fast" terminology introduced by Vainshtein and Zeldovich [S. I. Vainshtein and Y. B. Zeldovich, Reviews of topical problems: Origin of magnetic fields in astrophysics (turbulent "dynamo" mechanisms), Sov. Phys. Usp. 15, 159 (1972)SOPUAP0038-567010.1070/PU1972v015n02ABEH004960].}, } @article {pmid32289979, year = {2020}, author = {Reyes, F and Torrejón, V and Falcón, C}, title = {Wave damping of a sloshing wave by an interacting turbulent vortex flow.}, journal = {Physical review. E}, volume = {101}, number = {3-1}, pages = {033106}, doi = {10.1103/PhysRevE.101.033106}, pmid = {32289979}, issn = {2470-0053}, abstract = {We report on the enhancement of the hydrodynamic damping of gravity waves at the surface of a fluid layer as they interact with a turbulent vortex flow in a sloshing experiment. Gravity surface waves are excited by oscillating horizontally a square container holding our working fluid (water). At the bottom of the container, four impellers in a quadrupole configuration generate a vortex array at moderate to high Reynolds number, which interact with the wave. We measure the surface fluctuations using different optical nonintrusive methods and the local velocity of the flow. In our experimental range, we show that as we increase the angular velocity of the impellers, the gravity wave amplitude decreases without changing the oscillation frequency or generating transverse modes. This wave dissipation enhancement is contrasted with the increase of the turbulent velocity fluctuations from particle image velocimetry measurements via a turbulent viscosity. To rationalize the damping enhancement a periodically forced shallow water model including viscous terms is presented, which is used to calculate the sloshing wave resonance curve. The enhanced viscous dissipation coefficient is found to scale linearly with the measured turbulent viscosity. Hence, the proposed scheme is a good candidate as an active surface gravity wave dampener via vortex flow reconfiguration.}, } @article {pmid32284987, year = {2020}, author = {Spandan, V and Putt, D and Ostilla-Mónico, R and Lee, AA}, title = {Fluctuation-induced force in homogeneous isotropic turbulence.}, journal = {Science advances}, volume = {6}, number = {14}, pages = {eaba0461}, pmid = {32284987}, issn = {2375-2548}, abstract = {Understanding force generation in nonequilibrium systems is a notable challenge in statistical physics. We uncover a fluctuation-induced force between two plates immersed in homogeneous isotropic turbulence using direct numerical simulations. The force is a nonmonotonic function of plate separation. The mechanism of force generation reveals an intriguing analogy with fluctuation-induced forces: In a fluid, energy and vorticity are localized in regions of defined length scales. When varying the distance between the plates, we exclude energy structures modifying the overall pressure on the plates. At intermediate plate distances, the intense vorticity structures (worms) are forced to interact in close vicinity between the plates. This interaction affects the pressure in the slit and the force between the plates. The combination of these two effects causes a nonmonotonic attractive force with a complex Reynolds number dependence. Our study sheds light on how length scale-dependent distributions of energy and high-intensity vortex structures determine Casimir forces.}, } @article {pmid32260002, year = {2020}, author = {Asakawa, J and Nishii, K and Nakagawa, Y and Koizumi, H and Komurasaki, K}, title = {Direct measurement of 1-mN-class thrust and 100-s-class specific impulse for a CubeSat propulsion system.}, journal = {The Review of scientific instruments}, volume = {91}, number = {3}, pages = {035116}, doi = {10.1063/1.5121411}, pmid = {32260002}, issn = {1089-7623}, abstract = {This paper presents the development of a thrust stand to enable direct measurement of thrust and specific impulse for a CubeSat propulsion system during firing. The thrust stand is an inverted pendulum and incorporates a mass balance for direct in situ mass measurement. The proposed calibration procedure allows precise performance characterization and achieves a resolution of 80 μN thrust and 0.01 g mass loss, by taking into account the drift of the thrust-stand zero caused by propellant consumption. The performance of a water micro-resistojet propulsion system for CubeSats was directly characterized as a proof of concept of the thrust stand. Continuous profiles of thrust, specific impulse, and mass consumption were acquired under various conditions in a single firing test. A thrust from 1 mN to 10 mN and a specific impulse from 45 s to 100 s with a maximum measurement uncertainty of ±15.3% were measured for the throat Reynolds number in the range 100-400.}, } @article {pmid32244961, year = {2020}, author = {Joseph, J and Rehman, D and Delanaye, M and Morini, GL and Nacereddine, R and Korvink, JG and Brandner, JJ}, title = {Numerical and Experimental Study of Microchannel Performance on Flow Maldistribution.}, journal = {Micromachines}, volume = {11}, number = {3}, pages = {}, pmid = {32244961}, issn = {2072-666X}, support = {Grant Agreement No. 643095//European Community H2020 Framework/ ; }, abstract = {Miniaturized heat exchangers are well known for their superior heat transfer capabilities in comparison to macro-scale devices. While in standard microchannel systems the improved performance is provided by miniaturized distances and very small hydraulic diameters, another approach can also be followed, namely, the generation of local turbulences. Localized turbulence enhances the heat exchanger performance in any channel or tube, but also includes an increased pressure loss. Shifting the critical Reynolds number to a lower value by introducing perturbators controls pressure losses and improves thermal efficiency to a considerable extent. The objective of this paper is to investigate in detail collector performance based on reduced-order modelling and validate the numerical model based on experimental observations of flow maldistribution and pressure losses. Two different types of perturbators, Wire-net and S-shape, were analyzed. For the former, a metallic wire mesh was inserted in the flow passages (hot and cold gas flow) to ensure stiffness and enhance microchannel efficiency. The wire-net perturbators were replaced using an S-shaped perturbator model for a comparative study in the second case mentioned above. An optimum mass flow rate could be found when the thermal efficiency reaches a maximum. Investigation of collectors with different microchannel configurations (s-shaped, wire-net and plane channels) showed that mass flow rate deviation decreases with an increase in microchannel resistance. The recirculation zones in the cylindrical collectors also changed the maldistribution pattern. From experiments, it could be observed that microchannels with S-shaped perturbators shifted the onset of turbulent transition to lower Reynolds number values. Experimental studies on pressure losses showed that the pressure losses obtained from numerical studies were in good agreement with the experiments (<4%).}, } @article {pmid32168670, year = {2020}, author = {Thirani, S and Gupta, P and Scalo, C}, title = {Knudsen number effects on the nonlinear acoustic spectral energy cascade.}, journal = {Physical review. E}, volume = {101}, number = {2-1}, pages = {023101}, doi = {10.1103/PhysRevE.101.023101}, pmid = {32168670}, issn = {2470-0053}, abstract = {We present a numerical investigation of the effects of gas rarefaction on the energy dynamics of resonating planar nonlinear acoustic waves. The problem setup is a gas-filled, adiabatic tube, excited from one end by a piston oscillating at the fundamental resonant frequency of the tube and closed at the other end; nonlinear wave steepening occurs until a limit cycle is reached, resulting in shock formation for sufficiently high densities. The Knudsen number, defined here as the ratio of the characteristic molecular collision timescale to the resonance period, is varied in the range Kn=10^{-1}-10^{-5}, from rarefied to dense regime, by changing the base density of the gas. The working fluid is Argon. A numerical solution of the Boltzmann equation, closed with the Bhatnagar-Gross-Krook model, is used to simulate cases for Kn≥0.01. The fully compressible one-dimensional Navier-Stokes equations are used for Kn<0.01 with adaptive mesh refinement to resolve the resonating weak shocks, reaching wave Mach numbers up to 1.01. Nonlinear wave steepening and shock formation are associated with spectral broadening of the acoustic energy in the wavenumber-frequency domain; the latter is defined based on the exact energy corollary for second-order nonlinear acoustics derived by Gupta and Scalo [Phys. Rev. E 98, 033117 (2018)2470-004510.1103/PhysRevE.98.033117], representing the Lyapunov function of the system. At the limit cycle, the acoustic energy spectra exhibit an equilibrium energy cascade with a -2 slope in the inertial range, also observed in freely decaying nonlinear acoustic waves by the same authors. In the present system, energy is introduced externally via a piston at low wavenumbers or frequencies and balanced by thermoviscous dissipation at high wavenumbers or frequencies, responsible for the base temperature increase in the system. The thermoviscous dissipation rate is shown to scale as Kn^{2} for fixed Reynolds number based on the maximum velocity amplitude, i.e., increasing with the degree of flow rarefaction; consistently, the smallest length scale of the steepened waves at the limit cycle, corresponding to the thickness of the shock (when present) also increases with Kn. For a given fixed piston velocity amplitude, the bandwidth of the inertial range of the spectral energy cascade decreases with increasing Knudsen numbers, resulting in a reduced resonant response of the system. By exploiting dimensionless scaling laws borrowed by Kolmogorov's theory of hydrodynamic turbulence, it is shown that an inertial range for spectral energy transfer can be expected for acoustic Reynolds numbers Re_{U_{max}}>100, based on the maximum acoustic velocity amplitude in the domain.}, } @article {pmid32151621, year = {2020}, author = {Krieg, M and Mohseni, K}, title = {Transient pressure modeling in jetting animals.}, journal = {Journal of theoretical biology}, volume = {494}, number = {}, pages = {110237}, doi = {10.1016/j.jtbi.2020.110237}, pmid = {32151621}, issn = {1095-8541}, abstract = {There are many marine animals that employ a form of jet propulsion to move through the water, often creating the jets by expanding and collapsing internal fluid cavities. Due to the unsteady nature of this form of locomotion and complex body/nozzle geometries, standard modeling techniques prove insufficient at capturing internal pressure dynamics, and hence swimming forces. This issue has been resolved with a novel technique for predicting the pressure inside deformable jet producing cavities (M. Krieg and K. Mohseni, J. Fluid Mech., 769, 2015), which is derived from evolution of the surrounding fluid circulation. However, this model was only validated for an engineered jet thruster with simple geometry and relatively high Reynolds number (Re) jets. The purpose of this manuscript is twofold: (i) to demonstrate how the circulation based pressure model can be used to analyze different animal body motions as they relate to propulsive output, for multiple species of jetting animals, (ii) and to quantitatively validate the pressure modeling for biological jetting organisms (typically characterized by complicated cavity geometry and low/intermediate Re flows). Using jellyfish (Sarsia tubulosa) as an example, we show that the pressure model is insensitive to complex cavity geometry, and can be applied to lower Re swimming. By breaking down the swimming behavior of the jellyfish, as well as that of squid and dragonfly larvae, according to circulation generating mechanisms, we demonstrate that the body motions of Sarsia tubulosa are optimized for acceleration at the beginning of pulsation as a survival response. Whereas towards the end of jetting, the velar morphology is adjusted to decrease the energetic cost. Similarly, we show that mantle collapse rates in squid maximize propulsive efficiency. Finally, we observe that the hindgut geometry of dragonfly larvae minimizes the work required to refill the cavity. Date Received: 10-18-2019, Date Accepted: 99-99-9999 *kriegmw@hawaii.edu, UHM Ocean and Res Eng, 2540 Dole St, Honolulu, HI 96822.}, } @article {pmid32125866, year = {2020}, author = {Fang, WZ and Ham, S and Qiao, R and Tao, WQ}, title = {Magnetic Actuation of Surface Walkers: The Effects of Confinement and Inertia.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {25}, pages = {7046-7055}, doi = {10.1021/acs.langmuir.9b03487}, pmid = {32125866}, issn = {1520-5827}, abstract = {Driven by a magnetic field, the rotation of a particle near a wall can be rectified into a net translation. The particles thus actuated, or surface walkers, are a kind of active colloid that finds application in biology and microfluidics. Here, we investigate the motion of spherical surface walkers confined between two walls using simulations based on the immersed-boundary lattice Boltzmann method. The degree of confinement and the nature of the confining walls (slip vs no-slip) significantly affect a particle's translational speed and can even reverse its translational direction. When the rotational Reynolds number Reω is larger than 1, inertia effects reduce the critical frequency of the magnetic field, beyond which the sphere can no longer follow the external rotating field. The reduction of the critical frequency is especially pronounced when the sphere is confined near a no-slip wall. As Reω increases beyond 1, even when the sphere can still rotate in the synchronous regime, its translational Reynolds number ReT no longer increases linearly with Reω and even decreases when Reω exceeds ∼10.}, } @article {pmid32098945, year = {2020}, author = {Stixrude, L and Scipioni, R and Desjarlais, MP}, title = {A silicate dynamo in the early Earth.}, journal = {Nature communications}, volume = {11}, number = {1}, pages = {935}, pmid = {32098945}, issn = {2041-1723}, support = {291432//EC | EC Seventh Framework Programm | FP7 Ideas: European Research Council (FP7-IDEAS-ERC - Specific Programme: "Ideas" Implementing the Seventh Framework Programme of the European Community for Research, Technological Development and Demonstration Activities (2007 to 2013))/ ; EAR-1853388//National Science Foundation (NSF)/ ; }, abstract = {The Earth's magnetic field has operated for at least 3.4 billion years, yet how the ancient field was produced is still unknown. The core in the early Earth was surrounded by a molten silicate layer, a basal magma ocean that may have survived for more than one billion years. Here we use density functional theory-based molecular dynamics simulations to predict the electrical conductivity of silicate liquid at the conditions of the basal magma ocean: 100-140 GPa, and 4000-6000 K. We find that the electrical conductivity exceeds 10,000 S/m, more than 100 times that measured in silicate liquids at low pressure and temperature. The magnetic Reynolds number computed from our results exceeds the threshold for dynamo activity and the magnetic field strength is similar to that observed in the Archean paleomagnetic record. We therefore conclude that the Archean field was produced by the basal magma ocean.}, } @article {pmid32093331, year = {2020}, author = {Rehman, D and Joseph, J and Morini, GL and Delanaye, M and Brandner, J}, title = {A Hybrid Numerical Methodology Based on CFD and Porous Medium for Thermal Performance Evaluation of Gas to Gas Micro Heat Exchanger.}, journal = {Micromachines}, volume = {11}, number = {2}, pages = {}, pmid = {32093331}, issn = {2072-666X}, support = {643095//Horizon 2020 Framework Programme/ ; }, abstract = {In micro heat exchangers, due to the presence of distributing and collecting manifolds as well as hundreds of parallel microchannels, a complete conjugate heat transfer analysis requires a large amount of computational power. Therefore in this study, a novel methodology is developed to model the microchannels as a porous medium where a compressible gas is used as a working fluid. With the help of such a reduced model, a detailed flow analysis through individual microchannels can be avoided by studying the device as a whole at a considerably less computational cost. A micro heat exchanger with 133 parallel microchannels (average hydraulic diameter of 200 μ m) in both cocurrent and counterflow configurations is investigated in the current study. Hot and cold streams are separated by a stainless-steel partition foil having a thickness of 100 μ m. Microchannels have a rectangular cross section of 200 μ m × 200 μ m with a wall thickness of 100 μ m in between. As a first step, a numerical study for conjugate heat transfer analysis of microchannels only, without distributing and collecting manifolds is performed. Mass flow inside hot and cold fluid domains is increased such that inlet Reynolds number for both domains remains within the laminar regime. Inertial and viscous coefficients extracted from this study are then utilized to model pressure and temperature trends within the porous medium model. To cater for the density dependence of inertial and viscous coefficients due to the compressible nature of gas flow in microchannels, a modified formulation of Darcy-Forschheimer law is adopted. A complete model of a double layer micro heat exchanger with collecting and distributing manifolds where microchannels are modeled as the porous medium is finally developed and used to estimate the overall heat exchanger effectiveness of the investigated micro heat exchanger. A comparison of computational results using proposed hybrid methodology with previously published experimental results of the same micro heat exchanger showed that adopted methodology can predict the heat exchanger effectiveness within the experimental uncertainty for both cocurrent and counterflow configurations.}, } @article {pmid32082068, year = {2020}, author = {Luo, J and Chen, L and Li, K and Jackson, A}, title = {Optimal kinematic dynamos in a sphere.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {476}, number = {2233}, pages = {20190675}, pmid = {32082068}, issn = {1364-5021}, abstract = {A variational optimization approach is used to optimize kinematic dynamos in a unit sphere and locate the enstrophy-based critical magnetic Reynolds number for dynamo action. The magnetic boundary condition is chosen to be either pseudo-vacuum or perfectly conducting. Spectra of the optimal flows corresponding to these two magnetic boundary conditions are identical since theory shows that they are relatable by reversing the flow field (Favier & Proctor 2013 Phys. Rev. E88, 031001 (doi:10.1103/physreve.88.031001)). A no-slip boundary for the flow field gives a critical magnetic Reynolds number of 62.06, while a free-slip boundary reduces this number to 57.07. Optimal solutions are found to possess certain rotation symmetries (or anti-symmetries) and optimal flows share certain common features. The flows localize in a small region near the sphere's centre and spiral upwards with very large velocity and vorticity, so that they are locally nearly Beltrami. We also derive a new lower bound on the magnetic Reynolds number for dynamo action, which, for the case of enstrophy normalization, is five times larger than the previous best bound.}, } @article {pmid32082060, year = {2020}, author = {Jose, S and Govindarajan, R}, title = {Non-normal origin of modal instabilities in rotating plane shear flows.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {476}, number = {2233}, pages = {20190550}, pmid = {32082060}, issn = {1364-5021}, abstract = {Small variations introduced in shear flows are known to affect stability dramatically. Rotation of the flow system is one example, where the critical Reynolds number for exponential instabilities falls steeply with a small increase in rotation rate. We ask whether there is a fundamental reason for this sensitivity to rotation. We answer in the affirmative, showing that it is the non-normality of the stability operator in the absence of rotation which triggers this sensitivity. We treat the flow in the presence of rotation as a perturbation on the non-rotating case, and show that the rotating case is a special element of the pseudospectrum of the non-rotating case. Thus, while the non-rotating flow is always modally stable to streamwise-independent perturbations, rotating flows with the smallest rotation are unstable at zero streamwise wavenumber, with the spanwise wavenumbers close to that of disturbances with the highest transient growth in the non-rotating case. The instability critical rotation number scales inversely as the square of the Reynolds number, which we demonstrate is the same as the scaling obeyed by the minimum perturbation amplitude in non-rotating shear flow needed for the pseudospectrum to cross the neutral line. Plane Poiseuille flow and plane Couette flow are shown to behave similarly in this context.}, } @article {pmid32067001, year = {2020}, author = {Razavi Bazaz, S and Mashhadian, A and Ehsani, A and Saha, SC and Krüger, T and Ebrahimi Warkiani, M}, title = {Computational inertial microfluidics: a review.}, journal = {Lab on a chip}, volume = {20}, number = {6}, pages = {1023-1048}, doi = {10.1039/c9lc01022j}, pmid = {32067001}, issn = {1473-0189}, abstract = {Since the discovery of inertial focusing in 1961, numerous theories have been put forward to explain the migration of particles in inertial flows, but a complete understanding is still lacking. Recently, computational approaches have been utilized to obtain better insights into the underlying physics. In particular, fundamental aspects of particle focusing inside straight and curved microchannels have been explored in detail to determine the dependence of focusing behavior on particle size, channel shape, and flow Reynolds number. In this review, we differentiate between the models developed for inertial particle motion on the basis of whether they are semi-analytical, Navier-Stokes-based, or built on the lattice Boltzmann method. This review provides a blueprint for the consideration of numerical solutions for modeling of inertial particle motion, whether deformable or rigid, spherical or non-spherical, and whether suspended in Newtonian or non-Newtonian fluids. In each section, we provide the general equations used to solve particle motion, followed by a tutorial appendix and specified sections to engage the reader with details of the numerical studies. Finally, we address the challenges ahead in the modeling of inertial particle microfluidics for future investigators.}, } @article {pmid32066045, year = {2020}, author = {Tanveer, A and Salahuddin, T and Khan, M and Malik, MY and Alqarni, MS}, title = {Theoretical analysis of non-Newtonian blood flow in a microchannel.}, journal = {Computer methods and programs in biomedicine}, volume = {191}, number = {}, pages = {105280}, doi = {10.1016/j.cmpb.2019.105280}, pmid = {32066045}, issn = {1872-7565}, abstract = {BACKGROUND: In this work the theoretical analysis is presented for a electroosmotic flow of Bingham nanofluid induced by applied electrostatic potential. The linearized Poisson-Boltzmann equation is considered in the presence of Electric double layer (EDL). A Bingham fluid model is employed to describe the rheological behavior of the non-Newtonian fluid. Mathematical formulation is presented under the assumption of long wavelength and small Reynolds number. Flow characteristics are investigated by employing Debye-Huckel linearization principle. Such preferences have not been reported previously for non-Newtonian Bingham nanofluid to the best of author's knowledge.

METHOD: The transformed equations for electroosmotic flow are solved to seek values for the nanofluid velocity, concentration and temperature along the channel length.

RESULTS: The effects of key parameters like Brinkmann number, Prandtl number, Debey Huckel parameter, thermophoresis parameter, Brownian motion parameter are plotted on velocity, temperature and concentration profiles. Graphical results for the flow phenomenon are discussed briefly.

CONCLUSIONS: Non-uniformity in channel as well as yield stress τ0 cause velocity declaration for both positive and negative values of U. Nanofluid temperature is found an increasing function of electro osmotic parameter κ if U is positive while it is a decreasing function if U is negative. A completely reverse response is seen in case of concentration profile. The thermophoresis parameter Nt, the Brow nian motion parameter Nb and Brinkman number Br cause an enhancement in temperature. The results are new in case of U.}, } @article {pmid32062487, year = {2020}, author = {Yan, SR and Sedeh, S and Toghraie, D and Afrand, M and Foong, LK}, title = {Analysis and manegement of laminar blood flow inside a cerebral blood vessel using a finite volume software program for biomedical engineering.}, journal = {Computer methods and programs in biomedicine}, volume = {190}, number = {}, pages = {105384}, doi = {10.1016/j.cmpb.2020.105384}, pmid = {32062487}, issn = {1872-7565}, abstract = {BACKGROUND AND OBJECTIVE: Hemodynamic blood flow analysis in the cerebrovascular is has become one of the important research topics in the bio-mechanic in recent decades. The primary duty of the cerebral blood vessel is supplying Glucose and oxygen for the brain.

METHODS: In this investigation, the non-Newtonian blood flow in the cerebral blood vessels studied. For modeling the geometry of this problem, we used Magnetic Resonance Image (MRI) approach to take Digital Imaging and Communications in Medicine (DICOM) images and using an open-source software package to construct the geometry, which is a complicated one. The power-law indexes, heat flux, and Reynolds number range in the investigation are 0.6 ≤ n ≤ 0.8, 5 ≤ q ≤ 15Wm-2 and 160≤Re≤310. Effects of Reynolds number, power-law indexes and heat fluxes are investigated.

RESULTS: We found that the pressure drop increase with increasing the Reynolds number and power-law index. The maximum Nusselt number in the cerebral blood vessels accrued in the running position of the body in n = 0.8. Also, the highest average wall shear stress occurs in maximum power-law indexes and Reynolds number.

CONCLUSION: By increasing the power-law index and Reynolds number, the wall shear stress increases.}, } @article {pmid32052248, year = {2020}, author = {Waheed, S and Noreen, S and Tripathi, D and Lu, DC}, title = {Electrothermal transport of third-order fluids regulated by peristaltic pumping.}, journal = {Journal of biological physics}, volume = {46}, number = {1}, pages = {45-65}, pmid = {32052248}, issn = {1573-0689}, abstract = {The study of heat and electroosmotic characteristics in the flow of a third-order fluid regulated by peristaltic pumping is examined by using governing equations, i.e., the continuity equation, momentum equation, energy equation, and concentration equation. The wavelength is considered long compared to its height and a low Reynolds number is assumed. The velocity slip condition is employed. Analytical solutions are performed through the perturbation technique. The expressions for the dimensionless velocity components, temperature, concentration, and heat transfer rate are obtained. Pumping features were computed numerically for discussion of results. Trapping and heat transfer coefficient distributions were also studied graphically. The findings of the present study can be applied to design biomicrofluidic devices like tumor-on-a-chip and organ-on-a-chip.}, } @article {pmid32042893, year = {2020}, author = {Cerbus, RT and Liu, CC and Gioia, G and Chakraborty, P}, title = {Small-scale universality in the spectral structure of transitional pipe flows.}, journal = {Science advances}, volume = {6}, number = {4}, pages = {eaaw6256}, pmid = {32042893}, issn = {2375-2548}, abstract = {Turbulent flows are not only everywhere, but every turbulent flow is the same at small scales. The extraordinary simplification engendered by this "small-scale universality" is a hallmark of turbulence theory. However, on the basis of the restrictive assumptions invoked by A. N. Kolmogorov to demonstrate this universality, it is widely thought that only idealized turbulent flows conform to this framework. Using experiments and simulations that span a wide range of Reynolds number, we show that small-scale universality governs the spectral structure of a class of flows with no apparent ties to the idealized flows: transitional pipe flows. Our results not only extend the universality of Kolmogorov's framework beyond expectation but also establish an unexpected link between transitional pipe flows and Kolmogorovian turbulence.}, } @article {pmid32041775, year = {2020}, author = {Usherwood, JR and Cheney, JA and Song, J and Windsor, SP and Stevenson, JPJ and Dierksheide, U and Nila, A and Bomphrey, RJ}, title = {High aerodynamic lift from the tail reduces drag in gliding raptors.}, journal = {The Journal of experimental biology}, volume = {223}, number = {Pt 3}, pages = {}, pmid = {32041775}, issn = {1477-9145}, support = {/WT_/Wellcome Trust/United Kingdom ; 202854/Z/16/Z/WT_/Wellcome Trust/United Kingdom ; }, abstract = {Many functions have been postulated for the aerodynamic role of the avian tail during steady-state flight. By analogy with conventional aircraft, the tail might provide passive pitch stability if it produced very low or negative lift. Alternatively, aeronautical principles might suggest strategies that allow the tail to reduce inviscid, induced drag: if the wings and tail act in different horizontal planes, they might benefit from biplane-like aerodynamics; if they act in the same plane, lift from the tail might compensate for lift lost over the fuselage (body), reducing induced drag with a more even downwash profile. However, textbook aeronautical principles should be applied with caution because birds have highly capable sensing and active control, presumably reducing the demand for passive aerodynamic stability, and, because of their small size and low flight speeds, operate at Reynolds numbers two orders of magnitude below those of light aircraft. Here, by tracking up to 20,000, 0.3 mm neutrally buoyant soap bubbles behind a gliding barn owl, tawny owl and goshawk, we found that downwash velocity due to the body/tail consistently exceeds that due to the wings. The downwash measured behind the centreline is quantitatively consistent with an alternative hypothesis: that of constant lift production per planform area, a requirement for minimizing viscous, profile drag. Gliding raptors use lift distributions that compromise both inviscid induced drag minimization and static pitch stability, instead adopting a strategy that reduces the viscous drag, which is of proportionately greater importance to lower Reynolds number fliers.}, } @article {pmid32024757, year = {2020}, author = {Wu, Z and Zaki, TA and Meneveau, C}, title = {High-Reynolds-number fractal signature of nascent turbulence during transition.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {7}, pages = {3461-3468}, pmid = {32024757}, issn = {1091-6490}, abstract = {Transition from laminar to turbulent flow occurring over a smooth surface is a particularly important route to chaos in fluid dynamics. It often occurs via sporadic inception of spatially localized patches (spots) of turbulence that grow and merge downstream to become the fully turbulent boundary layer. A long-standing question has been whether these incipient spots already contain properties of high-Reynolds-number, developed turbulence. In this study, the question is posed for geometric scaling properties of the interface separating turbulence within the spots from the outer flow. For high-Reynolds-number turbulence, such interfaces are known to display fractal scaling laws with a dimension [Formula: see text], where the 1/3 excess exponent above 2 (smooth surfaces) follows from Kolmogorov scaling of velocity fluctuations. The data used in this study are from a direct numerical simulation, and the spot boundaries (interfaces) are determined by using an unsupervised machine-learning method that can identify such interfaces without setting arbitrary thresholds. Wide separation between small and large scales during transition is provided by the large range of spot volumes, enabling accurate measurements of the volume-area fractal scaling exponent. Measurements show a dimension of [Formula: see text] over almost 5 decades of spot volume, i.e., trends fully consistent with high-Reynolds-number turbulence. Additional observations pertaining to the dependence on height above the surface are also presented. Results provide evidence that turbulent spots exhibit high-Reynolds-number fractal-scaling properties already during early transitional and nonisotropic stages of the flow evolution.}, } @article {pmid32024433, year = {2020}, author = {Xu, Z and Qin, H and Li, P and Liu, R}, title = {Computational fluid dynamics approaches to drag and wake of a long-line mussel dropper under tidal current.}, journal = {Science progress}, volume = {103}, number = {1}, pages = {36850419901235}, doi = {10.1177/0036850419901235}, pmid = {32024433}, issn = {2047-7163}, abstract = {Hydrodynamic effects of mussel farms have attracted increased research attentions in recent years. The understanding of the hydrodynamic impacts is essential for predicting the sustainability of mussel farms. A large mussel farm includes thousands of mussel droppers, and the combined drag on the mussel droppers is sufficient to possibly affect the longevity of the entire long-lines. This article intends to study the drag and wake of an individual long-line mussel dropper using computational fluid dynamics approaches. Two equivalent rough cylinders, namely, Curved-Model and Sharp-Model, have been utilized to simulate the mussel dropper, and each rough cylinder is assigned with surface roughness. The porosity is not considered in this article due to its complexity from inhalant and exhalant of mussels. Two-dimensional laminar simulations are conducted at Reynolds number from 10 to 200, and three-dimensional large eddy simulations are conducted at subcritical Reynolds number ranging from 3900 to 10 5 . The results show that larger drag coefficients and Strouhal numbers are attributed to surface roughness and sharp crowns on the rough cylinder. The obtained drag coefficient ranges from 1.1 to 1.2 with respect to the diameter of the mussel dropper and the peak value of the tidal velocities. Wakes behind rough cylinders fluctuate more actively compared to those of smooth cylinders. This research work provides new insight for further investigations on hydrodynamic interactions between fluid and mussel droppers.}, } @article {pmid32007018, year = {2020}, author = {Ganta, N and Mahato, B and Bhumkar, YG}, title = {Prediction of the aerodynamic sound generated due to flow over a cylinder performing combined steady rotation and rotary oscillations.}, journal = {The Journal of the Acoustical Society of America}, volume = {147}, number = {1}, pages = {325}, doi = {10.1121/10.0000585}, pmid = {32007018}, issn = {1520-8524}, abstract = {Analysis of sound generated due to a laminar flow past a circular cylinder subjected to the mean rotation along with the rotary oscillating motion has been performed for the Reynolds number Re = 150 and the Mach number M = 0.2. The direct numerical simulation approach has been used to study modifications in the generated sound field over a range of forcing parameters using disturbance pressure field information. Flow and sound fields are accurately resolved over a nondimensional radial distance r≤100 from the center of the cylinder. Frequencies, as well as wavelengths of generated sound waves, have been effectively altered by varying the forcing frequency-ratio, whereas the directivity nature of the radiated sound field has been modified by varying the forcing amplitude-ratio. Doak's decomposition technique has been used to understand the reasons behind changes in the radiated sound fields as the forcing parameters are varied.}, } @article {pmid32006194, year = {2020}, author = {Alouges, F and Di Fratta, G}, title = {Parking 3-sphere swimmer: II. The long-arm asymptotic regime.}, journal = {The European physical journal. E, Soft matter}, volume = {43}, number = {2}, pages = {6}, pmid = {32006194}, issn = {1292-895X}, abstract = {The paper carries on our previous investigations on the complementary version of Purcell's rotator (sPr3): a low-Reynolds-number swimmer composed of three balls of equal radii. In the asymptotic regime of very long arms, the Stokes-induced governing dynamics is derived, and then experimented in the context of energy-minimizing self-propulsion characterized in the first part of the paper.}, } @article {pmid31999751, year = {2020}, author = {Liu, P and Liu, H and Yang, Y and Wang, M and Sun, Y}, title = {Comparison of design methods for negative pressure gradient rotary bodies: A CFD study.}, journal = {PloS one}, volume = {15}, number = {1}, pages = {e0228186}, pmid = {31999751}, issn = {1932-6203}, mesh = {Animals ; Computer Simulation ; *Hydrodynamics ; Models, Theoretical ; *Pressure ; Ships ; Stress, Mechanical ; Surface Properties ; }, abstract = {Computational fluid dynamics (CFD) simulation is used to test two body design methods which use negative pressure gradient to suppress laminar flow separation and drag reduction. The steady-state model of the Transition SST model is used to calculate the pressure distribution, wall shear stress, and drag coefficient under zero angle of attack at different velocities. Four bodies designed by two different methods are considered. Our results show the first method is superior to the body of Hansen in drag reduction and the body designed by the first method is more likely to obtain the characteristics of suppressing or eliminating separation, which can effectively improve laminar flow coverage to achieve drag reduction under higher Reynolds number conditions. The results show that the negative pressure gradient method can suppress separation and drag reduction better than the second method. This successful design method is expected to open a promising prospect for its application in the design of small drag, small noise subsonic hydrodynamic hull and underwater weapons.}, } @article {pmid31991147, year = {2020}, author = {Nguyen, KH and Gemmell, BJ and Rohr, JR}, title = {Effects of temperature and viscosity on miracidial and cercarial movement of Schistosoma mansoni: ramifications for disease transmission.}, journal = {International journal for parasitology}, volume = {50}, number = {2}, pages = {153-159}, doi = {10.1016/j.ijpara.2019.12.003}, pmid = {31991147}, issn = {1879-0135}, support = {HHSN272201000005C/AI/NIAID NIH HHS/United States ; HHSN272201000005I/AI/NIAID NIH HHS/United States ; R01 TW010286/TW/FIC NIH HHS/United States ; }, mesh = {Animals ; Biomphalaria/parasitology ; Cercaria/*physiology ; Climate Change ; Host-Parasite Interactions ; Humans ; Larva/physiology ; Life Cycle Stages ; Movement/*physiology ; Schistosoma mansoni/*physiology ; Schistosomiasis mansoni/*transmission ; Temperature ; Viscosity ; }, abstract = {Parasites with complex life cycles can be susceptible to temperature shifts associated with seasonal changes, especially as free-living larvae that depend on a fixed energy reserve to survive outside the host. The life cycle of Schistosoma, a trematode genus containing some species that cause human schistosomiasis, has free-living, aquatic miracidial and cercarial larval stages that swim using cilia or a forked tail, respectively. The small size of these swimmers (150-350 µm) dictates that their propulsion is dominated by viscous forces. Given that viscosity inhibits the swimming ability of small organisms and is inversely correlated with temperature, changes in temperature should affect the ability of free-living larval stages to swim and locate a host. By recording miracidial and cercarial movement of Schistosoma mansoni using a high-speed camera and manipulating temperature and viscosity independently, we assessed the role each factor plays in the swimming mechanics of the parasite. We found a positive effect of temperature and a negative effect of viscosity on miracidial and cercarial speed. Reynolds numbers, which describe the ratio of inertial to viscous forces exerted on an aquatic organism, were <1 across treatments. Q10 values were <2 when comparing viscosity treatments at 20 °C and 30 °C, further supporting the influence of viscosity on miracidial and cercarial speed. Given that both larval stages have limited energy reserves and infection takes considerable energy, successful transmission depends on both speed and lifespan. We coupled our speed data with mortality measurements across temperatures and discovered that the theoretical maximum distance travelled increased with temperature and decreased with viscosity for both larval stages. Thus, our results suggest that S. mansoni transmission is high during warm times of the year, partly due to improved swimming performance of the free-living larval stages, and that increases in temperature variation associated with climate change might further increase transmission.}, } @article {pmid31989130, year = {2020}, author = {Fauzi, FB and Ismail, E and Syed Abu Bakar, SN and Ismail, AF and Mohamed, MA and Md Din, MF and Illias, S and Ani, MH}, title = {The role of gas-phase dynamics in interfacial phenomena during few-layer graphene growth through atmospheric pressure chemical vapour deposition.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {22}, number = {6}, pages = {3481-3489}, doi = {10.1039/c9cp05346h}, pmid = {31989130}, issn = {1463-9084}, abstract = {The complicated chemical vapour deposition (CVD) is currently the most viable method of producing graphene. Most studies have extensively focused on chemical aspects either through experiments or computational studies. However, gas-phase dynamics in CVD reportedly plays an important role in improving graphene quality. Given that mass transport is the rate-limiting step for graphene deposition in atmospheric-pressure CVD (APCVD), the interfacial phenomena at the gas-solid interface (i.e., the boundary layer) are a crucial controlling factor. Accordingly, only by understanding and controlling the boundary-layer thickness can uniform full-coverage graphene deposition be achieved. In this study, a simplified computational fluid dynamics analysis of APCVD was performed to investigate gas-phase dynamics during deposition. Boundary-layer thickness was also estimated through the development of a customised homogeneous gas model. Interfacial phenomena, particularly the boundary layer and mass transport within it, were studied. The effects of Reynolds number on these factors were explored and compared with experimentally obtained results of the characterised graphene deposit. We then discussed and elucidated the important relation of fluid dynamics to graphene growth through APCVD.}, } @article {pmid31982669, year = {2020}, author = {Asghar, Z and Ali, N and Javid, K and Waqas, M and Dogonchi, AS and Khan, WA}, title = {Bio-inspired propulsion of micro-swimmers within a passive cervix filled with couple stress mucus.}, journal = {Computer methods and programs in biomedicine}, volume = {189}, number = {}, pages = {105313}, doi = {10.1016/j.cmpb.2020.105313}, pmid = {31982669}, issn = {1872-7565}, abstract = {BACKGROUND AND OBJECTIVE: The swimming mechanism of self-propelling organisms has been imitated by biomedical engineers to design the mechanical micro bots. The interaction of these swimmers with surrounding environment is another important aspect. The present swimming problem integrates Taylor sheet model with couple stress fluid model. The thin passage containing micro-swimmers and mucus is approximated as a rigid (passive) two-dimensional channel. The spermatozoa forms a pack quite similar as a complex wavy sheet.

METHODS: Swimming problem with couple stress cervical liquid (at low Reynolds number) leads to a linear sixth order differential equation. The boundary value problem (BVP) is solved analytically with two unknowns i.e. speed of complex wavy sheet and flow rate of couple stress mucus. After utilizing this solution into equilibrium conditions these unknowns can be computed via Newton-Raphson algorithm. Furthermore, the pairs of numerically calculated organism speed and flow rate are utilized in the expression of power dissipation.

RESULTS: This work describes that the speed of micro-swimmers can be enhanced by suitable rheology of the surrounding liquid. The usage of couple stress fluid as compared to Newtonian fluid enhances the energy dissipation and reduces the flow rate. On the other hand complex wavy surface also aids the organisms to swim faster.}, } @article {pmid31978919, year = {2020}, author = {Zhu, Y and Yang, G and Zhuang, C and Li, C and Hu, D}, title = {Oral cavity flow distribution and pressure drop in balaenid whales feeding: a theoretical analysis.}, journal = {Bioinspiration & biomimetics}, volume = {15}, number = {3}, pages = {036004}, doi = {10.1088/1748-3190/ab6fb8}, pmid = {31978919}, issn = {1748-3190}, abstract = {Balaenid whales, as continuous ram filter feeders, can efficiently separate prey from water by baleen. The feeding process of balaenid whales is extremely complex, in which the flow distribution and pressure drop in the oral cavity play a significant role. In this paper, a theoretical model coupled with oral cavity velocity and pressure in balaenid whales is established based on mass conservation, momentum conservation and pressure drop equations, considering both the inertial and the friction terms. A discrete method with section-by-section calculation is adopted to solve the theoretical model. The effects of four crucial parameters, i.e. the ratio of filtration area to inlet area (S), the Reynolds number of entrance (Re in), the ratio of thickness to permeability of the porous media formed by the fringe layer (ϕ) and the width ratio of the anteroposterior canal within the mouth along the tongue (APT channel) to that along the lip (APL channel) (H) are discussed. The results show that, for a given case, the flow distribution and the pressure drop both show increasing trends with the flow direction. For different cases, when S is small, Re in is small and ϕ is large, a good flow pattern emerges with a smoother flow speed near the oropharynx, better drainage, better shunting and filtration, and higher energy efficiency. However, for smaller values of H, some energy efficiency is sacrificed to achieve additional average transverse flow in order to produce better shunting and filtration. The research in this paper provides a reference for the design of high-efficiency bionic filters.}, } @article {pmid31978870, year = {2020}, author = {Afrouzi, HH and Ahmadian, M and Hosseini, M and Arasteh, H and Toghraie, D and Rostami, S}, title = {Simulation of blood flow in arteries with aneurysm: Lattice Boltzmann Approach (LBM).}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105312}, doi = {10.1016/j.cmpb.2019.105312}, pmid = {31978870}, issn = {1872-7565}, abstract = {BACKGROUND AND OBJECTIVE: In most countries, the higher death rates are due to cardiovascular disease and stroke. These problems often derive from irregular blood flow and the circulatory system disorder.

METHODS: In this paper, the blood flow is simulated in a created aneurysm in the artery upon using Lattice Boltzmann Method (LBM). Blood is selected as a non-Newtonian fluid which was simulated with power-law model. The lattice Boltzmann results for non-Newtonian fluid flow with power-law model and the curved boundary are compared and validated with previous studies which show a good agreement. In this study, simulations are carried out for two types of aneurysms. For the first aneurysm, three power-law exponents of 0.6, 0.8 and 1.0 at Reynolds number of 100 for three different cases are investigated.

RESULTS: The results show that the wall shear stress increases with increasing the power-law exponent. In addition, in the main duct of artery where the velocity is larger, shear stress is lower due to the smaller velocity gradient. For the second Aneurysm, the simulations are done for three Reynolds numbers of 100, 150 and 200, and three Womersley numbers of 4, 12 and 20. The blood flow is pulsating at the inlet such as the real pulsating wave in the blood. Results show that with increasing the Womersley number, the velocity profiles in the middle of the aneurysm are closer at a constant Reynolds number.

CONCLUSIONS: With increasing the Reynolds number, the range of vortices and values of velocity and tension grow in the aneurysm.}, } @article {pmid31975701, year = {2020}, author = {Porté-Agel, F and Bastankhah, M and Shamsoddin, S}, title = {Wind-Turbine and Wind-Farm Flows: A Review.}, journal = {Boundary-layer meteorology}, volume = {174}, number = {1}, pages = {1-59}, pmid = {31975701}, issn = {0006-8314}, abstract = {Wind energy, together with other renewable energy sources, are expected to grow substantially in the coming decades and play a key role in mitigating climate change and achieving energy sustainability. One of the main challenges in optimizing the design, operation, control, and grid integration of wind farms is the prediction of their performance, owing to the complex multiscale two-way interactions between wind farms and the turbulent atmospheric boundary layer (ABL). From a fluid mechanical perspective, these interactions are complicated by the high Reynolds number of the ABL flow, its inherent unsteadiness due to the diurnal cycle and synoptic-forcing variability, the ubiquitous nature of thermal effects, and the heterogeneity of the terrain. Particularly important is the effect of ABL turbulence on wind-turbine wake flows and their superposition, as they are responsible for considerable turbine power losses and fatigue loads in wind farms. These flow interactions affect, in turn, the structure of the ABL and the turbulent fluxes of momentum and scalars. This review summarizes recent experimental, computational, and theoretical research efforts that have contributed to improving our understanding and ability to predict the interactions of ABL flow with wind turbines and wind farms.}, } @article {pmid31962497, year = {2019}, author = {Kaminsky, J and Klewicki, J and Birnir, B}, title = {Application of the stochastic closure theory to the Townsend-Perry constants.}, journal = {Physical review. E}, volume = {100}, number = {6-1}, pages = {061101}, doi = {10.1103/PhysRevE.100.061101}, pmid = {31962497}, issn = {2470-0053}, abstract = {We compare the stochastic closure theory (SCT) to the Townsend-Perry constants as estimated from measurements in the Flow Physic Facility (FPF) at the University of New Hampshire. First, we explain the derivation of the Townsend-Perry constants, which were originally formulated by Meneveau and Marusic, in analogy with a Gaussian distribution. However, this was not supported by the data. Instead, the data show a sub-Gaussian relation that was explained by Birnir and Chen. We show herein how the SCT can be used to compute the constants, which explains their sub-Gaussian relations. We then compare the SCT theory predictions, including Reynolds-number-dependent corrections, with the data, showing good agreement.}, } @article {pmid31962492, year = {2019}, author = {Jin, Y and Cheng, S and Chamorro, LP}, title = {Active pitching of short splitters past a cylinder: Drag increase and wake.}, journal = {Physical review. E}, volume = {100}, number = {6-1}, pages = {063106}, doi = {10.1103/PhysRevE.100.063106}, pmid = {31962492}, issn = {2470-0053}, abstract = {The flow and drag induced by active pitching of plates in the wake of a cylinder of diameter d were experimentally studied for various plate lengths L as well as pitching frequencies f_{p} and amplitudes A_{0} at Reynolds number Re=1.6×10^{4}. Planar particle image velocimetry and a load cell were used to characterize the flow statistics and mean drag of a variety of cylinder-splitter assemblies. Results show the distinctive effect of active pitching on these quantities. In particular, flow recovery was significantly modulated by L, f_{p}, or A_{0}. Specific pitching settings resulted in a wake with dominant meandering patterns and faster flow recovery. We defined a modified version of the amplitude-based Strouhal number of the system St_{A} to account for the effect of the cylinder in active pitching. It characterizes the drag coefficient C_{d} across all the cases studied, and reveals two regions intersecting at a critical value of St_{A}≈0.035. Below this value, the C_{d} remained nearly constant; however, it exhibited a linear increase with increasing St_{A} past this critical point. Inspection of the integral momentum equation showed the dominant role of velocity fluctuations in modulating C_{d} past the critical St_{A}.}, } @article {pmid31955110, year = {2020}, author = {Rajwa-Kuligiewicz, A and Radecki-Pawlik, A and Skalski, T and Plesiński, K and Rowiński, PM and Manson, JR}, title = {Hydromorphologically-driven variability of thermal and oxygen conditions at the block ramp hydraulic structure: The Porębianka River, Polish Carpathians.}, journal = {The Science of the total environment}, volume = {713}, number = {}, pages = {136661}, doi = {10.1016/j.scitotenv.2020.136661}, pmid = {31955110}, issn = {1879-1026}, abstract = {Growing anthropopressure in mountain streams aimed at limiting erosion and flood protection often caused adverse effects on the natural environment. In recent years, great attention has been paid to the restoration and conservation of natural habitats in mountain streams using environmentally friendly solutions such as the Block Ramp (BR) Hydraulic Structures. In this study we investigated the factors responsible for spatial variability in thermal and oxygen conditions at the single BR structure in the growing season, and the relation between water temperature and dissolved oxygen (DO) concentration. This has been done by measurements of hydraulic characteristics along with physicochemical properties of water, such as water temperature and DO concentration, at two different discharges. The redundancy analysis has been applied in order to describe the relationships among hydraulic parameters and physicochemical variables, and extract potential sources of water temperature and DO variability within the BR hydraulic structure. Results have shown that DO and water temperature distributions within the BR hydraulic structure depend on discharge conditions and are associated with the submergence of the block ramp. The highest heterogeneity in hydraulic, DO and water temperature conditions occurs at low flow and is associated with the presence of crevices between protruding cobbles at the block ramp. The lowest variability, in turn, occurs at high discharge, when the block ramp is completely submerged. The results indicated that thermal and oxygen conditions within the BR hydraulic structure are independent of hydraulic parameters at low flow. Moreover, the relation between DO concentration and water temperature is positive at low flow indicating potential impact of biological processes. On the contrary, at high discharge both, the DO concentrations and water temperature within the BR structure, depend on bed shear velocity and maximum Reynolds number.}, } @article {pmid31948589, year = {2020}, author = {Haghighinia, A and Movahedirad, S}, title = {Mass transfer in a novel passive micro-mixer: Flow tortuosity effects.}, journal = {Analytica chimica acta}, volume = {1098}, number = {}, pages = {75-85}, doi = {10.1016/j.aca.2019.11.028}, pmid = {31948589}, issn = {1873-4324}, abstract = {Hydroynamic fluid tortuosity is a parameter to describe the fluid streamlines average elongation. The motivation of the present study is introducing a new concept for theoretical predictions of dynamic tortuosity effects on mass transfer in a novel three-dimensional passive T-shape micro-mixer both experimentally and by numerical simulation. In the numerical analysis, continuity, motion, and diffusion-convection equations were solved, and the amount of mass transfer and the fluid tortuosity was calculated for different rectangular winglet angles. The Reynolds number is considered in the range of 0.1-93. The results show that when the angle of winglet tends to 22.5°, the fluid tortuosity, lateral velocity, and fluid mass transfer tend to maximum values. Furthermore, the effect of fluid tortuosity on the fluid stretching as a theory of chaotic mixing is investigated.}, } @article {pmid31947897, year = {2020}, author = {Rhoades, T and Kothapalli, CR and Fodor, PS}, title = {Mixing Optimization in Grooved Serpentine Microchannels.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31947897}, issn = {2072-666X}, support = {Undergraduate Summer Research Award 2019 and Graduate Faculty Research Award 2019//Cleveland State University/ ; }, abstract = {Computational fluid dynamics modeling at Reynolds numbers ranging from 10 to 100 was used to characterize the performance of a new type of micromixer employing a serpentine channel with a grooved surface. The new topology exploits the overlap between the typical Dean flows present in curved channels due to the centrifugal forces experienced by the fluids, and the helical flows induced by slanted groove-ridge patterns with respect to the direction of the flow. The resulting flows are complex, with multiple vortices and saddle points, leading to enhanced mixing across the section of the channel. The optimization of the mixers with respect to the inner radius of curvature (Rin) of the serpentine channel identifies the designs in which the mixing index quality is both high (M > 0.95) and independent of the Reynolds number across all the values investigated.}, } @article {pmid31947174, year = {2019}, author = {Oktamuliani, S and Hasegawa, K and Saijo, Y}, title = {Left Ventricular Vortices in Myocardial Infarction Observed with Echodynamography.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2019}, number = {}, pages = {5816-5819}, doi = {10.1109/EMBC.2019.8856394}, pmid = {31947174}, issn = {2694-0604}, mesh = {Blood Flow Velocity ; Case-Control Studies ; Echocardiography, Doppler, Color ; Heart Ventricles ; Hemodynamics ; Humans ; Myocardial Infarction/*diagnostic imaging ; *Ventricular Function, Left ; }, abstract = {Echodynamography (EDG) is a computational method to deduce two-dimensional (2D) blood flow vector from conventional color Doppler ultrasound image by considering that the blood flow is divided into vortex and base flow components. Left ventricular (LV) vortices indicate cardiac flow status influenced by LV wall motion. Thus, quantitative assessment of LV vortices may become new and sensitive parameters for cardiac function. In the present study, quantitative parameters of LV vortices such as vortex index, vortex size, and Reynolds number were calculated and relation between each parameter was assessed. Six healthy volunteers and three patients with myocardial infarction (MI) who underwent color Doppler echocardiography (CDE) were involved in the study. Serial CDE images in apical three-chamber view were recorded and 2D blood flow vector was superimposed on the CDE image. Vortex index, vortex size, and Reynolds number were compared between the normal volunteers and the MI patients. The results showed that vortex index (3.09±2.06 vs. 3.34±2.33, p<; 0.05), vortex size (1.76 0.69 vs. 2.01 ±0.68, p<; 0.05), Reynolds number (1020±603 vs.±1312 1046, p<; ±0.05) were significantly greater in the MI patients than in the healthy volunteers. Vortex equivalent diameter in LV showed significant positive correlation with Reynolds number (R2 = 0.799, y = 0.001x + 0.7098, p <; 0.05) in healthy volunteers and (R2 = 0.6404, y = 0.0005x+1.3185, p<; 0.05) in MI patients. Vortex index showed positive correlation with Reynolds number (R2 = 0.9351, y = 0.002x+0.1397, p<; 0.05) in healthy volunteers and (R2 = 0.758, y = 0.0019x+0.7957, p<; 0.05) in MI patients. In conclusion, EDG provides information on LV hemodynamics by quantitative LV vortices parameters both in healthy volunteers and MI patients.}, } @article {pmid31946085, year = {2019}, author = {Hamad, EM and Sawalmeh, B and Mhawsh, AA and Mansour, M and Awad, M and Al-Halhouli, AT and Al-Gharabli, SI}, title = {Investigation of Bifurcation Effect on Various Microfluidic Designs for Blood Separation.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2019}, number = {}, pages = {1097-1100}, doi = {10.1109/EMBC.2019.8856380}, pmid = {31946085}, issn = {2694-0604}, mesh = {Equipment Design ; *Lab-On-A-Chip Devices ; *Microfluidic Analytical Techniques ; *Microfluidics ; Plasma ; Software ; }, abstract = {In this project, a microfluidic device for blood separation will be designed and tested in order to separate plasma from whole blood for diagnostic purposes. The design will be based on previously implemented designs that will be further discussed in the next sections. When designing microfluidic devices, it is essential to consider the different physical phenomena that arise from switching from the macro scale to the micro scale. Parameters such as the Reynolds number and the forces affecting the fluid must be studied in order to produce a suitable and effective design. Finite element methods have been implemented prior to the production of the microfluidic devices. Various geometries/designs have been tested using Fluent ANSYS software. Later on, the successful design was fabricated using micromachining on an acrylic substrate and was tested using simulated blood through of a syringe pump.}, } @article {pmid31942792, year = {2020}, author = {Martínez-Merino, P and Midgley, SD and Martín, EI and Estellé, P and Alcántara, R and Sánchez-Coronilla, A and Grau-Crespo, R and Navas, J}, title = {Novel WS2-Based Nanofluids for Concentrating Solar Power: Performance Characterization and Molecular-Level Insights.}, journal = {ACS applied materials & interfaces}, volume = {12}, number = {5}, pages = {5793-5804}, doi = {10.1021/acsami.9b18868}, pmid = {31942792}, issn = {1944-8252}, abstract = {Nano-colloidal suspensions of nanomaterials in a fluid, nanofluids, are appealing because of their interesting properties related to heat transfer processes. While nanomaterials based on transition metal chalcogenides (TMCs) have been widely studied in catalysis, sensing, and energy storage applications, there are few studies of nanofluids based on TMCs for heat transfer applications. In this study, the preparation and analysis of nanofluids based on 2D-WS2 in a typical heat transfer fluid (HTF) used in concentrating solar power (CSP) plants are reported. Nanofluids prepared using an exfoliation process exhibited well-defined nanosheets and were highly stable. The nanofluids were characterized in terms of properties related to their application in CSP. The presence of WS2 nanosheets did not modify significantly the surface tension, the viscosity, or the isobaric specific heat, but the thermal conductivity was improved by up to 30%. The Ur factor, which characterizes the thermal efficiency of the fluid in the solar collector, shows an enhancement of up to 22% in the nanofluid, demonstrating great promise for CSP applications. The Reynolds number and friction factor of the fluid were not significantly modified by the addition of the nanomaterial to the HTF, which is also positive for practical applications in CSP plants. Ab initio molecular dynamics simulations of the nanoparticle/fluid interface showed an irreversible dissociative adsorption of diphenyl oxide molecules on the WS2 edge, with very low kinetic barrier. The resulting "decoration" of the WS2 edge dramatically affects the nature of the interface interactions and is therefore expected to affect significantly the rheological and transport properties of the nanofluids.}, } @article {pmid31938721, year = {2020}, author = {Zhang, T and Moreau, D and Geyer, T and Fischer, J and Doolan, C}, title = {Dataset on tip vortex formation noise produced by wall-mounted finite airfoils with flat and rounded tip geometries.}, journal = {Data in brief}, volume = {28}, number = {}, pages = {105058}, pmid = {31938721}, issn = {2352-3409}, abstract = {The vortex generated at the tip of an airfoil such as an aircraft wing, wind turbine blade, submarine fin or propeller blade can dominate its wake and be a significant source of unwanted noise. The data collection presented in this paper consists of measurements of tip vortex formation noise produced by finite length airfoils with flat and rounded tips. These data were obtained using the specialist aeroacoustic test facilities at the Brandenburg University of Technology (BTU) in Cottbus, Germany and a 47-channel planar microphone array. Over 1200 unique test cases with variations in airfoil profile shape, tip geometry, angle of attack and Reynolds number were measured during the experimental campaign. The dataset contains one-third-octave band tip noise spectra that have been processed using Acoular, a Python module for acoustic beamforming.}, } @article {pmid31935152, year = {2020}, author = {Salazar-Magallón, JA and Huerta de la Peña, A}, title = {Production of antifungal saponins in an airlift bioreactor with a cell line transformed from Solanum chrysotrichum and its activity against strawberry phytopathogens.}, journal = {Preparative biochemistry & biotechnology}, volume = {50}, number = {2}, pages = {204-214}, doi = {10.1080/10826068.2019.1676781}, pmid = {31935152}, issn = {1532-2297}, mesh = {Antifungal Agents/*chemical synthesis/pharmacology ; *Bioreactors ; Cell Line, Transformed ; Fragaria/*microbiology ; Saponins/*chemical synthesis/*pharmacology ; Solanum/*chemistry ; }, abstract = {Biotechnology through plant cell cultures in bioreactors is a tool that allows increasing the production of secondary metabolites of commercial interest. The hydrodynamic characterization, in addition to the transfer (OTR) and uptake (OUR) of oxygen through the dynamic method with different aeration rate, were used to see their influence on the production of biomass and saponins. The culture poisoning technique was used to determine the antifungal activity of the SC-2 and SC-3 saponins in vitro. Likewise, the shear or hydrodynamic stress of 273.6 mN/m2 were calculated based on the Reynolds Number. The oxygen supply (OTR) was always greater than the demand (OUR) for all the aeration rate evaluated. Dry weight values of 8.6 gDW/L and a concentration of 2.7 mg/L and 187.3 mg/L of the saponins SC-2 and SC-3 respectively were obtained with an air flow of 0.1 vvm. In addition, it was possible to inhibit the growth of phytopathogenic fungi in vitro by up to 93%, while in vivo it was possible to reduce the infections of strawberry seeds inoculated with phytopathogens, obtaining up to 94% of germinated seeds. This information will facilitate the rational operation of the bioreactor culture system that produces secondary metabolites.}, } @article {pmid31933715, year = {2020}, author = {Hu, X and Lin, J and Chen, D and Ku, X}, title = {Influence of non-Newtonian power law rheology on inertial migration of particles in channel flow.}, journal = {Biomicrofluidics}, volume = {14}, number = {1}, pages = {014105}, pmid = {31933715}, issn = {1932-1058}, abstract = {In this paper, the inertial migration of particles in the channel flow of power-law fluid is numerically investigated. The effects of the power-law index (n), Reynolds number (Re), blockage ratio (k), and channel aspect ratio (AR) on the inertial migration of particles and equilibrium position are explored. The results show that there exist two stages of particle migration and four stable equilibrium positions for particles in the cross section of a square channel. The particle equilibrium positions in a rectangular channel are much different from those in a square channel. In shear-thinning fluids, the long channel face equilibrium position and two kinds of particle trajectories are found at low Re. With increasing Re, the short channel face equilibrium position turns to be stable, multiequilibrium positions, and three kinds of particle trajectories along the long wall start to form. Only two stable equilibrium positions exist in shear-thickening fluids. The equilibrium positions are getting closer to the channel centerline with increasing n and k and with decreasing Re. The inertial focusing length L2 in the second stage of particle migration is much longer than inertial focusing length L1 in the first stage. In the square channel, L2 is decreased with increasing Re and k and with decreasing n. In the rectangular channel, L2 is the shortest in the shear-thinning fluid.}, } @article {pmid31931378, year = {2020}, author = {Feng, Y and Wang, Q and Duan, JL and Li, XY and Ma, JY and Wu, L and Han, Y and Liu, XY and Zhang, YB and Yuan, XZ}, title = {Attachment and adhesion force between biogas bubbles and anaerobic granular sludge in the up-flow anaerobic sludge blanket.}, journal = {Water research}, volume = {171}, number = {}, pages = {115458}, doi = {10.1016/j.watres.2019.115458}, pmid = {31931378}, issn = {1879-2448}, mesh = {Anaerobiosis ; *Biofuels ; Bioreactors ; *Sewage ; Waste Disposal, Fluid ; }, abstract = {The performance of the up-flow anaerobic sludge blanket (UASB) is significantly governed by the hydrodynamics of the reactor. Though the influence of hydrodynamics on mass transfer, granular size distribution, and biogas production was well studied, the interaction between biogas bubbles and anaerobic granular sludge (AGS) is poorly understood. This study used the impinging-jet technique and bubble probe atomic force microscope (AFM) to investigate the attachment and adhesion force between biogas bubbles (CH4 and CO2) and AGS. The fluxes of normalized CH4 or CO2 bubble-attachment on two kinds of AGS were directly affected by gas velocity and decreased with an increase in the Reynolds number ranged from 40 to 140. The bubble-attachment had a positive linear relationship with the contact angles, ratio of exopolymeric protein and polysaccharide, and hydrophilic functional groups of AGS. A bubble probe AFM was used to explore the adhesion force between a single bubble and AGS. The results indicated that the adhesion force between the bubbles and the two kinds of AGS also decreased with increasing approach velocity. Overall, these results contribute to a new insight into the understanding of interaction between biogas bubbles and AGS in UASB reactors.}, } @article {pmid31923819, year = {2020}, author = {Muhammad, R and Khan, MI and Jameel, M and Khan, NB}, title = {Fully developed Darcy-Forchheimer mixed convective flow over a curved surface with activation energy and entropy generation.}, journal = {Computer methods and programs in biomedicine}, volume = {188}, number = {}, pages = {105298}, doi = {10.1016/j.cmpb.2019.105298}, pmid = {31923819}, issn = {1872-7565}, abstract = {BACKGROUND: Mixed convection (forced+natural convection) is frequently observed in exceptionally high output devices where the forced convection isn't sufficient to dissipate all of the heat essential. At this point, consolidating natural convection with forced convection will frequently convey the ideal outcomes. Nuclear reactor technology and a few features of electronic cooling are the examples of these processes. Mixed convection problems are categorized by Richardson number (Ri), which is the ratio of Grashof number (for natural convection) and Reynolds number (for forced convection). For buoyancy or mixed convection the relative effect can be addressed by Richardson number. Typically, the natural convection is negligible when Richardson number is less than 0.1 (Ri < 0.1), forced convection is negligible when Richardson number is greater than 10 (Ri > 10) and neither is negligible when (0.1 < Ri < 10). It might be noticed that generally the forced convection is large comparative with natural convection except in case of remarkably low forced flow velocities. The current work gives significant insights regarding dissipative mixed convective Darcy-Forchheimer flow with entropy generation over a stretched curved surface. The energy equation is developed with respect to nonlinear radiation, dissipation and Ohmic heating (Joule heating). Binary reaction via activation energy is accounted.

METHOD: Curvilinear transformations are utilized to change the nonlinear PDE's into ordinary ones. Computational outcomes are obtained via NDSolve MATHEMATICA. The results are computed and discussed graphically.

RESULTS: Velocity decays for Forchheimer number. Entropy generation enhances for diffusion parameter and chemical reaction parameter. Concentration profile reduces chemical reaction parameter and enhances for activation parameter.}, } @article {pmid31923536, year = {2020}, author = {Rane, YS and Marston, JO}, title = {Computational study of fluid flow in tapered orifices for needle-free injectors.}, journal = {Journal of controlled release : official journal of the Controlled Release Society}, volume = {319}, number = {}, pages = {382-396}, doi = {10.1016/j.jconrel.2020.01.013}, pmid = {31923536}, issn = {1873-4995}, abstract = {Transdermal drug delivery using spring-powered jet injection has been studied for several decades and continues to be highly sought after due to the advent of targeted needle-free techniques, especially for viscous and complex fluids. As such, this paper reports results from numerical simulations to study the role of fluid rheology and cartridge geometry on characteristics such as jet exit velocity, total pressure drop and boundary layer thickness, since these all factor in to jet stability and collimation. The numerical approach involves incompressible steady flow with turbulence modelling based on the system Reynolds number at the orifice (Re = ρdovj/μ). The results are experimentally validated for a given geometry over a wide range of Reynolds numbers (101 < Re < 104), and our results indicate a sharp decrease in dimensionless pressure drop (Eu = 2∆P/ρvj2) for Re < 102) and gradually approaching the inviscid limit at Re ≥ 104. By extending the study to non-Newtonian fluids, whose rheological profile is approximated by the Carreau model, we also elucidated the effect of different rheological parameters. Lastly by studying a range of nozzle geometries such as conical, sigmoid taper and multi-tier tapers, we observe that fluid acceleration suppresses the boundary layer growth, which indicates there may be optimal geometries for creating jets to target specific tissue depths.}, } @article {pmid31907556, year = {2020}, author = {Pan, X and Tang, L and Feng, J and Liang, R and Pu, X and Li, R and Li, K}, title = {Experimental Research on the Degradation Coefficient of Ammonia Nitrogen Under Different Hydrodynamic Conditions.}, journal = {Bulletin of environmental contamination and toxicology}, volume = {104}, number = {2}, pages = {288-292}, doi = {10.1007/s00128-019-02781-0}, pmid = {31907556}, issn = {1432-0800}, support = {2019YFS0505//Major Project for Specialized Science and Technology Fund of Sichuan Province/ ; 2018SZDZX0027//Major Project of Specialized Science and Technology Fund of Sichuan Province/ ; }, mesh = {Ammonia/*analysis/chemistry ; Environmental Monitoring ; Hydrodynamics ; Kinetics ; Nitrogen/*analysis/chemistry ; Rivers/chemistry ; Water Pollutants, Chemical/*analysis/chemistry ; }, abstract = {Degradation coefficients for pollutants in water are important parameters that are significantly influenced by environmental conditions. In controlled experiments, the processes and trends of ammonia nitrogen (NH3-N) degradation in raw waters were studied under different flow conditions using a laboratory annular flume. Analysis of the observed change in NH3-N concentration with time under various flow conditions allowed calculation of a degradation efficiency (concentration change amount/initial concentration) which for NH3-N increased as the flow velocity increased. According to a first-order kinetic equation to fit the experimental data, the range of variation of the degradation coefficient of NH3-N at different flowrates was between 0.047 per day (0.01 m/s) and 0.203 per day (0.30 m/s). Dimensional analysis was used to analyze the relationship between the degradation coefficient and flow velocity (v), water depth (H), Froude number (Fr), and Reynolds number (Re), which was verified through field data collected in the Chishui River.}, } @article {pmid31905597, year = {2019}, author = {Sobecki, C and Zhang, J and Wang, C}, title = {Numerical Study of Paramagnetic Elliptical Microparticles in Curved Channels and Uniform Magnetic Fields.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31905597}, issn = {2072-666X}, abstract = {We numerically investigated the dynamics of a paramagnetic elliptical particle immersed in a low Reynolds number Poiseuille flow in a curved channel and under a uniform magnetic field by direct numerical simulation. A finite element method, based on an arbitrary Lagrangian-Eulerian approach, analyzed how the channel geometry, the strength and direction of the magnetic field, and the particle shape affected the rotation and radial migration of the particle. The net radial migration of the particle was analyzed after executing a π rotation and at the exit of the curved channel with and without a magnetic field. In the absence of a magnetic field, the rotation is symmetric, but the particle-wall distance remains the same. When a magnetic field is applied, the rotation of symmetry is broken, and the particle-wall distance increases as the magnetic field strength increases. The causation of the radial migration is due to the magnetic angular velocity caused by the magnetic torque that constantly changes directions during particle transportation. This research provides a method of magnetically manipulating non-spherical particles on lab-on-a-chip devices for industrial and biological applications.}, } @article {pmid31893769, year = {2019}, author = {Bahrami, A and Hoseinzadeh, S and Heyns, PS and Mirhosseini, SM}, title = {Experimental investigation of co-flow jet's airfoil flow control by hot wire anemometer.}, journal = {The Review of scientific instruments}, volume = {90}, number = {12}, pages = {125107}, doi = {10.1063/1.5113592}, pmid = {31893769}, issn = {1089-7623}, abstract = {An experimental flow control technique is given in this paper to study the jet effect on the coflow jet's airfoil with injection and suction and compared with the jet-off condition. The airfoil is CFJ0025-065-196, and the Reynolds number based on the airfoil's chord length is 105. To measure the turbulence components of flow, a hot wire anemometry apparatus in a wind tunnel has been used. In this paper, the effect of the average velocity and boundary layer thickness on the coflow jet's airfoil is analyzed. The test is done for two different coflow velocities and for different angles of attack. It is also shown that, by increasing the velocity difference between the jet and the main flow, separation is delayed, and this delay can be preserved by raising coflow velocity at higher angles of attack. So, this flow control method has a good efficiency, and it is possible to reach higher numbers of lift and lower numbers of drag coefficients.}, } @article {pmid31890822, year = {2020}, author = {Pendse, V and Mazumdar, B and Kumar, H}, title = {Formulation of experimental data based model for solid-liquid mass transfer enhancement in three phase fluidized bed using nanofluid.}, journal = {Data in brief}, volume = {28}, number = {}, pages = {104990}, pmid = {31890822}, issn = {2352-3409}, abstract = {This experimental data based model in three phase fluidized bed was designed to enhance the solid-liquid mass transfer. This data focuses on mass transfer enhancement using nanomaterial. In present investigation benzoic acid-water-air system was used as three phases ie solid, liquid and gas respectively with Arachitol nano as nanomaterial in different volume percent in three phase fluidized bed. Data from experiment were collected by varying gas velocity, bed height, nanomaterial percentage and time. After a convenient selection various correlation have been derived. The data presented here is the full set of experimental value and coefficients and exponents in correlation were estimated from nonlinear optimization technique in MATLAB.}, } @article {pmid31882681, year = {2019}, author = {Krishnan, SR and Bal, J and Putnam, SA}, title = {A simple analytic model for predicting the wicking velocity in micropillar arrays.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {20074}, pmid = {31882681}, issn = {2045-2322}, support = {N00014-15-1-2481//United States Department of Defense | United States Navy | Office of Naval Research (ONR)/ ; 1653396//National Science Foundation (NSF)/ ; }, abstract = {Hemiwicking is the phenomena where a liquid wets a textured surface beyond its intrinsic wetting length due to capillary action and imbibition. In this work, we derive a simple analytical model for hemiwicking in micropillar arrays. The model is based on the combined effects of capillary action dictated by interfacial and intermolecular pressures gradients within the curved liquid meniscus and fluid drag from the pillars at ultra-low Reynolds numbers [Formula: see text]. Fluid drag is conceptualized via a critical Reynolds number: [Formula: see text], where v0 corresponds to the maximum wetting speed on a flat, dry surface and x0 is the extension length of the liquid meniscus that drives the bulk fluid toward the adsorbed thin-film region. The model is validated with wicking experiments on different hemiwicking surfaces in conjunction with v0 and x0 measurements using Water [Formula: see text], viscous FC-70 [Formula: see text] and lower viscosity Ethanol [Formula: see text].}, } @article {pmid31881751, year = {2019}, author = {Li, H and Li, Y and Huang, B and Xu, T}, title = {Flow Characteristics of the Entrance Region with Roughness Effect within Rectangular Microchannels.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31881751}, issn = {2072-666X}, abstract = {We conducted systematic numerical investigations of the flow characteristics within the entrance region of rectangular microchannels. The effects of the geometrical aspect ratio and roughness on entrance lengths were analyzed. The incompressible laminar Navier-Stokes equations were solved using finite volume method (FVM). In the simulation, hydraulic diameters (Dh) ranging from 50 to 200 µm were studied, and aspect ratios of 1, 1.25, 1.5, 1.75, and 2 were considered as well. The working fluid was set as water, and the Reynolds number ranged from 0.5 to 100. The results showed a good agreement with the conducted experiment. Correlations are proposed to predict the entrance lengths of microchannels with respect to different aspect ratios. Compared with other correlations, these new correlations are more reliable because a more practical inlet condition was considered in our investigations. Instead of considering the influence of the width and height of the microchannels, in our investigation we proved that the critical role is played by the aspect ratio, representing the combination of the aforementioned parameters. Furthermore, the existence of rough elements obviously shortens the entrance region, and this effect became more pronounced with increasing relative roughness and Reynolds number. A similar effect could be seen by shortening the roughness spacing. An asymmetric distribution of rough elements decreased the entrance length compared with a symmetric distribution, which can be extrapolated to other irregularly distributed forms.}, } @article {pmid31878263, year = {2019}, author = {Kang, DJ}, title = {Effects of Channel Wall Twisting on the Mixing in a T-Shaped Micro-Channel.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31878263}, issn = {2072-666X}, support = {2018//Yeungnam University/ ; }, abstract = {A new design scheme is proposed for twisting the walls of a microchannel, and its performance is demonstrated numerically. The numerical study was carried out for a T-shaped microchannel with twist angles in the range of 0 to 34π. The Reynolds number range was 0.15 to 6. The T-shaped microchannel consists of two inlet branches and an outlet branch. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the twisting scheme is an effective way to enhance the mixing in a T-shaped microchannel. The mixing enhancement is realized by the swirling of two fluids in the cross section and is more prominent as the Reynolds number decreases. The twist angle was optimized to maximize the degree of mixing (DOM), which increases with the length of the outlet branch. The twist angle was also optimized in terms of the relative mixing cost (MC). The two optimum twisting angles are generally not coincident. The optimum twist angle shows a dependence on the length of the outlet branch but it is not affected much by the Reynolds number.}, } @article {pmid31875772, year = {2020}, author = {Zhang, L and Zhou, J and Zhang, B and Gong, W}, title = {Numerical investigation on the solid particle erosion in elbow with water-hydrate-solid flow.}, journal = {Science progress}, volume = {103}, number = {1}, pages = {36850419897245}, doi = {10.1177/0036850419897245}, pmid = {31875772}, issn = {2047-7163}, abstract = {Erosion in pipeline caused by solid particles, which may lead to premature failure of the pipe system, is regarded as one of the most important concerns in the field of oil and gas. Therefore, the Euler-Lagrange, erosion model, and discrete phase model are applied for the purpose of simulating the erosion of water-hydrate-solid flow in submarine hydrate transportation pipeline. In this article, the flow and erosion characteristics are well verified on the basis of experiments. Moreover, analysis is conducted to have a good understanding of the effects of hydrate volume, mean curvature radius/pipe diameter (R/D) rate, flow velocity, and particle diameter on elbow erosion. It is finally obtained that the hydrate volume directly affects the Reynolds number through viscosity and the trend of the Reynolds number is consistent with the trend of erosion rate. Taking into account different R/D rates, the same Stokes number reflects different dynamic transforms of the maximum erosion zone. However, the outmost wall (zone D) will be the final erosion zone when the value of the Stokes number increases to a certain degree. In addition, the erosion rate increases sharply along with the increase of flow velocity and particle diameter. The effect of flow velocity on the erosion zone can be ignored in comparison with the particle diameter. Moreover, it is observed that flow velocity is deemed as the most sensitive factor on erosion rate among these factors employed in the orthogonal experiment.}, } @article {pmid31874992, year = {2019}, author = {Liu, X and Fan, D and Yu, X and Liu, Z and Sun, J}, title = {Effects of Simulated Gravel on Hydraulic Characteristics of Overland Flow Under Varying Flow Discharges, Slope Gradients and Gravel Coverage Degrees.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {19781}, doi = {10.1038/s41598-019-56223-2}, pmid = {31874992}, issn = {2045-2322}, abstract = {To quantify the hydraulic characteristics of overland flow on gravel-covered slopes, eight flow discharges (Q) (8.44-122 L/min), five slope gradients (J) (2°-10°) and four gravel coverage degrees (Cr) (0-30%) were examined via a laboratory flume. The results showed that (1) gravel changed flow regime. Gravel increased the Reynolds number (Re) by 2.94-33.03%. Re were less affected by J and positively correlated with Cr and Q. Gravel decreased the Froude number (Fr) by 6.83-77.31%. Fr was positively correlated with Q and J and negatively correlated with Cr. (2) Gravel delayed the flow velocity (u) and increased the flow depth (h) and flow resistance (f). Gravel reduced u by 1.20-58.95%. u was positively correlated with Q and J and negatively correlated with Cr. Gravel increased h by 0.12-2.41 times. h was positively correlated with Q and Cr and negatively correlated with J. Gravel increased f by 0.15-18.42 times. f were less affected by J, positively correlated with Cr and negatively correlated with Q. (3) The relationships between hydraulic parameters and Q, J and Cr identified good power functions. Hydraulic parameters were mainly affected by Cr. These results can guide the ecological construction of soil and water conservation.}, } @article {pmid31868425, year = {2019}, author = {Panickacheril John, J and Donzis, DA and Sreenivasan, KR}, title = {Solenoidal Scaling Laws for Compressible Mixing.}, journal = {Physical review letters}, volume = {123}, number = {22}, pages = {224501}, doi = {10.1103/PhysRevLett.123.224501}, pmid = {31868425}, issn = {1079-7114}, abstract = {Mixing of passive scalars in compressible turbulence does not obey the same classical Reynolds number scaling as its incompressible counterpart. We first show from a large database of direct numerical simulations that even the solenoidal part of the velocity field fails to follow the classical incompressible scaling when the forcing includes a substantial dilatational component. Though the dilatational effects on the flow remain significant, our main results are that both the solenoidal energy spectrum and the passive scalar spectrum assume incompressible forms, and that the scalar gradient essentially aligns with the most compressive eigenvalue of the solenoidal part, provided that only the solenoidal components are consistently used for scaling. A slight refinement of this statement is also pointed out.}, } @article {pmid31862924, year = {2019}, author = {Nath, R and Krishnan, M}, title = {Optimization of double diffusive mixed convection in a BFS channel filled with Alumina nanoparticle using Taguchi method and utility concept.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {19536}, pmid = {31862924}, issn = {2045-2322}, abstract = {This research work focuses on the implementation of Taguchi method and utility concept for optimization of flow, geometrical and thermo-physical parameters for mixed convective heat and mass transfer in a backward facing step (BFS) channel filled with Alumina nanoparticle doped in water-ethylene glycol mixture. Mass, momentum, energy and solutal conservation equations for the flow field are cast in velocity-vorticity form of Navier-Stokes equations, which are solved using Galerkin's weighted residual finite element method through isoparametric formulation. The following six parameters, expansion ratio of the BFS channel (H/h), Reynolds number (Re), buoyancy ratio (N), nanoparticle volume fraction (χ), shape of nanoparticles and thermal Grashof number (GrT) at three levels are considered as controlling parameters for optimization using Taguchi method. An L27 orthogonal array has been chosen to get the levels of the six parameters for the 27 trial runs. Simulation results were obtained for 27 trial runs from which three different sets of optimum levels of the control parameters were obtained for maximum Nu and Sh and minimum wall shear stress during double diffusive mixed convection in the channel. Then, in order to obtain a single set of optimum levels of the control parameters to achieve maximum heat and mass transfer and minimum wall shear stress concurrently, utility concept has been implemented. Taguchi results indicate that expansion ratio and volume fraction of nanoparticles are the significant contributing parameters to achieve maximum heat and mass transfer and minimum wall shear stress. Utility concept predicts the average Nusselt number less by 2% and Sherwood number less by 3% compared to the Taguchi method with equal weightage of 40% assumed for Nusselt and Sherwood numbers and 20% for wall shear stress.}, } @article {pmid31861736, year = {2019}, author = {Maklad, O and Eliasy, A and Chen, KJ and Theofilis, V and Elsheikh, A}, title = {Simulation of Air Puff Tonometry Test Using Arbitrary Lagrangian-Eulerian (ALE) Deforming Mesh for Corneal Material Characterisation.}, journal = {International journal of environmental research and public health}, volume = {17}, number = {1}, pages = {}, pmid = {31861736}, issn = {1660-4601}, mesh = {Cornea/*diagnostic imaging ; Corneal Injuries/*diagnosis ; Humans ; Intraocular Pressure/*physiology ; Manometry/*methods ; *Surgical Mesh ; Tonometry, Ocular/*methods ; }, abstract = {: Purpose: To improve numerical simulation of the non-contact tonometry test by using arbitrary Lagrangian-Eulerian deforming mesh in the coupling between computational fluid dynamics model of an air jet and finite element model of the human eye.

METHODS: Computational fluid dynamics model simulated impingement of the air puff and employed Spallart-Allmaras model to capture turbulence of the air jet. The time span of the jet was 30 ms and maximum Reynolds number was Re=2.3×104, with jet orifice diameter 2.4 mm and impinging distance 11 mm. The model of the human eye was analysed using finite element method with regional hyperelastic material variation and corneal patient-specific topography starting from stress-free configuration. The cornea was free to deform as a response to the air puff using an adaptive deforming mesh at every time step of the solution. Aqueous and vitreous humours were simulated as a fluid cavity filled with incompressible fluid with a density of 1000 kg/m3.

RESULTS: Using the adaptive deforming mesh in numerical simulation of the air puff test improved the traditional understanding of how pressure distribution on cornea changes with time of the test. There was a mean decrease in maximum pressure (at corneal apex) of 6.29 ± 2.2% and a development of negative pressure on a peripheral corneal region 2-4 mm away from cornea centre.

CONCLUSIONS: The study presented an improvement of numerical simulation of the air puff test, which will lead to more accurate intraocular pressure (IOP) and corneal material behaviour estimation. The parametric study showed that pressure of the air puff is different from one model to another, value-wise and distribution-wise, based on cornea biomechanical parameters.}, } @article {pmid31847758, year = {2019}, author = {Sum Wu, K and Nowak, J and Breuer, KS}, title = {Scaling of the performance of insect-inspired passive-pitching flapping wings.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {161}, pages = {20190609}, pmid = {31847758}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; Biomimetics/*methods ; *Computer Simulation ; Flight, Animal/*physiology ; Insecta/*physiology ; Models, Biological ; *Robotics ; Wings, Animal/*physiology ; }, abstract = {Flapping flight using passive pitch regulation is a commonly used mode of thrust and lift generation in insects and has been widely emulated in flying vehicles because it allows for simple implementation of the complex kinematics associated with flapping wing systems. Although robotic flight employing passive pitching to regulate angle of attack has been previously demonstrated, there does not exist a comprehensive understanding of the effectiveness of this mode of aerodynamic force generation, nor a method to accurately predict its performance over a range of relevant scales. Here, we present such scaling laws, incorporating aerodynamic, inertial and structural elements of the flapping-wing system, validating the theoretical considerations using a mechanical model which is tested for a linear elastic hinge and near-sinusoidal stroke kinematics over a range of scales, hinge stiffnesses and flapping frequencies. We find that suitably defined dimensionless parameters, including the Reynolds number, Re, the Cauchy number, Ch, and a newly defined 'inertial-elastic' number, IE, can reliably predict the kinematic and aerodynamic performance of the system. Our results also reveal a consistent dependency of pitching kinematics on these dimensionless parameters, providing a connection between lift coefficient and kinematic features such as angle of attack and wing rotation.}, } @article {pmid31835453, year = {2019}, author = {Tan, L and Ali, J and Cheang, UK and Shi, X and Kim, D and Kim, MJ}, title = {µ-PIV Measurements of Flows Generated by Photolithography-Fabricated Achiral Microswimmers.}, journal = {Micromachines}, volume = {10}, number = {12}, pages = {}, pmid = {31835453}, issn = {2072-666X}, support = {JCYJ20180302174151692//Science, Technology and Innovation Commission of Shenzhen Municipality/ ; 51850410516//National Natural Science Foundation of China/ ; 20181119590C//Shenzhen Peacock Plan/ ; 2017KTSCX167//Department of Education of Guangdong Province/ ; 1735968//National Science Foundation/ ; }, abstract = {Robotic micro/nanoswimmers can potentially be used as tools for medical applications, such as drug delivery and noninvasive surgery. Recently, achiral microswimmers have gained significant attention because of their simple structures, which enables high-throughput fabrication and size scalability. Here, microparticle image velocimetry (µ-PIV) was used to study the hydrodynamics of achiral microswimmers near a boundary. The structures of these microswimmers resemble the letter L and were fabricated using photolithography and thin-film deposition. Through µ-PIV measurements, the velocity flow fields of the microswimmers rotating at different frequencies were observed. The results herein yield an understanding of the hydrodynamics of the L-shaped microswimmers, which will be useful in applications such as fluidic manipulation.}, } @article {pmid31824735, year = {2019}, author = {Ford, MP and Lai, HK and Samaee, M and Santhanakrishnan, A}, title = {Hydrodynamics of metachronal paddling: effects of varying Reynolds number and phase lag.}, journal = {Royal Society open science}, volume = {6}, number = {10}, pages = {191387}, pmid = {31824735}, issn = {2054-5703}, abstract = {Negatively buoyant freely swimming crustaceans such as krill must generate downward momentum in order to maintain their position in the water column. These animals use a drag-based propulsion strategy, where pairs of closely spaced swimming limbs are oscillated rhythmically from the tail to head. Each pair is oscillated with a phase delay relative to the neighbouring pair, resulting in a metachronal wave travelling in the direction of animal motion. It remains unclear how oscillations of limbs in the horizontal plane can generate vertical momentum. Using particle image velocimetry measurements on a robotic model, we observed that metachronal paddling with non-zero phase lag created geometries of adjacent paddles that promote the formation of counter-rotating vortices. The interaction of these vortices resulted in generating large-scale angled downward jets. Increasing phase lag resulted in more vertical orientation of the jet, and phase lags in the range used by Antarctic krill produced the most total momentum. Synchronous paddling produced lower total momentum when compared with metachronal paddling. Lowering Reynolds number by an order of magnitude below the range of adult krill (250-1000) showed diminished downward propagation of the jet and lower vertical momentum. Our findings show that metachronal paddling is capable of producing flows that can generate both lift (vertical) and thrust (horizontal) forces needed for fast forward swimming and hovering.}, } @article {pmid31824223, year = {2019}, author = {Wang, X and Christov, IC}, title = {Theory of the flow-induced deformation of shallow compliant microchannels with thick walls.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2231}, pages = {20190513}, pmid = {31824223}, issn = {1364-5021}, abstract = {Long, shallow microchannels embedded in thick, soft materials are widely used in microfluidic devices for lab-on-a-chip applications. However, the bulging effect caused by fluid-structure interactions between the internal viscous flow and the soft walls has not been completely understood. Previous models either contain a fitting parameter or are specialized to channels with plate-like walls. This work is a theoretical study of the steady-state response of a compliant microchannel with a thick wall. Using lubrication theory for low-Reynolds-number flows and the theory for linearly elastic isotropic solids, we obtain perturbative solutions for the flow and deformation. Specifically, only the channel's top wall deformation is considered, and the ratio between its thickness t and width w is assumed to be (t/w)2≫1. We show that the deformation at each stream-wise cross section can be considered independently, and that the top wall can be regarded as a simply supported rectangle subject to uniform pressure at its bottom. The stress and displacement fields are found using Fourier series, based on which the channel shape and the hydrodynamic resistance are calculated, yielding a new flow rate-pressure drop relation without fitting parameters. Our results agree favourably with, and thus rationalize, previous experiments.}, } @article {pmid31816973, year = {2019}, author = {Raza, W and Kim, KY}, title = {Asymmetrical Split-and-Recombine Micromixer with Baffles.}, journal = {Micromachines}, volume = {10}, number = {12}, pages = {}, pmid = {31816973}, issn = {2072-666X}, support = {2019R1A2C1007657//National Research Foundation of Korea/ ; }, abstract = {The present work proposes a planar micromixer design comprising hybrid mixing modules of split-and-recombine units and curved channels with radial baffles. The mixing performance was evaluated numerically by solving the continuity and momentum equations along with the advection-diffusion equation in a Reynolds number range of 0.1-80. The variance of the concentration of the mixed species was considered to quantify the mixing index. The micromixer showed far better mixing performance over whole Reynolds number range than an earlier split-and-recombine micromixer. The mixer achieved mixing indices greater than 90% at Re ≥ 20 and a mixing index of 99.8% at Re = 80. The response of the mixing quality to the change of three geometrical parameters was also studied. A mixing index over 80% was achieved within 63% of the full length at Re = 20.}, } @article {pmid31808773, year = {2020}, author = {Abay, A and Recktenwald, SM and John, T and Kaestner, L and Wagner, C}, title = {Cross-sectional focusing of red blood cells in a constricted microfluidic channel.}, journal = {Soft matter}, volume = {16}, number = {2}, pages = {534-543}, doi = {10.1039/c9sm01740b}, pmid = {31808773}, issn = {1744-6848}, mesh = {Erythrocytes/*chemistry ; Humans ; Microfluidics/instrumentation ; Rheology ; }, abstract = {Constrictions in blood vessels and microfluidic devices can dramatically change the spatial distribution of passing cells or particles and are commonly used in biomedical cell sorting applications. However, the three-dimensional nature of cell focusing in the channel cross-section remains poorly investigated. Here, we explore the cross-sectional distribution of living and rigid red blood cells passing a constricted microfluidic channel by tracking individual cells in multiple layers across the channel depth and across the channel width. While cells are homogeneously distributed in the channel cross-section pre-contraction, we observe a strong geometry-induced focusing towards the four channel faces post-contraction. The magnitude of this cross-sectional focusing effect increases with increasing Reynolds number for both living and rigid red blood cells. We discuss how this non-uniform cell distribution downstream of the contraction results in an apparent double-peaked velocity profile in particle image velocimetry analysis and show that trapping of red blood cells in the recirculation zones of the abrupt construction depends on cell deformability.}, } @article {pmid31805484, year = {2020}, author = {Shah, Z and Khan, A and Khan, W and Kamran Alam, M and Islam, S and Kumam, P and Thounthong, P}, title = {Micropolar gold blood nanofluid flow and radiative heat transfer between permeable channels.}, journal = {Computer methods and programs in biomedicine}, volume = {186}, number = {}, pages = {105197}, doi = {10.1016/j.cmpb.2019.105197}, pmid = {31805484}, issn = {1872-7565}, abstract = {This article characterizes flow and heat transmission of blood that carries the micropolar nanofluid of gold in a permeable channel. The thermal radiations are also present in the channel while its walls are either moving or stationary. The base-fluid is considered as blood while micro polar nanofluid is taken as gold. By using similarity transformations along with dimensionless quantities the modeled equations of the problem are transmuted into a system of non-linear ODEs with a set of appropriate boundary conditions. The semi-analytical method, HAM is then applied to determine the solution of a set of resultant equations. The results obtained by HAM have also compared with numerical solutions. The influence of non-dimensional parameters like fractional parameter suction/injection β, Reynolds Number Re, Darcys Number Da, micropolar parameter K, Prandtl number Pr and Radiation parameter Rd etc., which provides physical interpretations of temperature, microrotation n and velocity fields are discussed in detail with the help of graphical representations. Nusselt number is calculated and presented through table. This study determined that the temperature of micropolar nanofluid augmented along with augmentation in the volume fraction. Radiation Rd augmented the heat transfer rate at the upper wall and reduce it at the lower wall. The suction/injection parameter 'β' reduces the heat transfer rate in case of β < 0 at the upper wall, where it is augmented at lower wall.}, } @article {pmid31805457, year = {2020}, author = {Pandey, R and Kumar, M and Majdoubi, J and Rahimi-Gorji, M and Srivastav, VK}, title = {A review study on blood in human coronary artery: Numerical approach.}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105243}, doi = {10.1016/j.cmpb.2019.105243}, pmid = {31805457}, issn = {1872-7565}, abstract = {Computational fluid dynamics (CFD) study of blood flow in human coronary artery is one of the emerging fields of Biomed- ical engineering. In present review paper, Finite Volume Method with governing equations and boundary conditions are briefly discussed for different coronary models. Many researchers have come up with astonishing results related to the various factors (blood viscosity, rate of blood flow, shear stress on the arterial wall, Reynolds number, etc.) affecting the hemodynamic of blood in the right/left coronary artery. The aim of this paper is to present an overview of all those work done by the researchers to justify their work related to factors which hampers proper functioning of heart and lead to Coronary Artery Disease (CAD). Governing equations like Navier-stokes equations, continuity equations etc. are widely used and are solved using CFD solver to get a clearer view of coronary artery blockage. Different boundary conditions and blood properties published in the last ten years are summarized in the tabulated form. This table will help new researchers to work on this area.}, } @article {pmid31801127, year = {2020}, author = {Pöhnl, R and Popescu, MN and Uspal, WE}, title = {Axisymmetric spheroidal squirmers and self-diffusiophoretic particles.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {32}, number = {16}, pages = {164001}, doi = {10.1088/1361-648X/ab5edd}, pmid = {31801127}, issn = {1361-648X}, abstract = {We study, by means of an exact analytical solution, the motion of a spheroidal, axisymmetric squirmer in an unbounded fluid, as well as the low Reynolds number hydrodynamic flow associated to it. In contrast to the case of a spherical squirmer-for which, e.g. the velocity of the squirmer and the magnitude of the stresslet associated with the flow induced by the squirmer are respectively determined by the amplitudes of the first two slip ('squirming') modes-for the spheroidal squirmer each squirming mode either contributes to the velocity, or contributes to the stresslet. The results are straightforwardly extended to the self-phoresis of axisymmetric, spheroidal, chemically active particles in the case when the phoretic slip approximation holds.}, } @article {pmid31797965, year = {2019}, author = {Rajappan, A and McKinley, GH}, title = {Epidermal biopolysaccharides from plant seeds enable biodegradable turbulent drag reduction.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {18263}, pmid = {31797965}, issn = {2045-2322}, abstract = {The high cost of synthetic polymers has been a key impediment limiting the widespread adoption of polymer drag reduction techniques in large-scale engineering applications, such as marine drag reduction. To address consumable cost constraints, we investigate the use of high molar mass biopolysaccharides, present in the mucilaginous epidermis of plant seeds, as inexpensive drag reducers in large Reynolds number turbulent flows. Specifically, we study the aqueous mucilage extracted from flax seeds (Linum usitatissimum) and compare its drag reduction efficacy to that of poly(ethylene oxide) or PEO, a common synthetic polymer widely used as a drag reducing agent in aqueous flows. Macromolecular and rheological characterisation confirm the presence of high molar mass (≥2 MDa) polysaccharides in the extracted mucilage, with an acidic fraction comprising negatively charged chains. Frictional drag measurements, performed inside a bespoke Taylor-Couette apparatus, show that the as-extracted mucilage has comparable drag reduction performance under turbulent flow conditions as aqueous PEO solutions, while concurrently offering advantages in terms of raw material cost, availability, and bio-compatibility. Our results indicate that plant-sourced mucilage can potentially serve as a cost-effective and eco-friendly substitute for synthetic drag reducing polymers in large scale turbulent flow applications.}, } @article {pmid31786449, year = {2020}, author = {Ibrahim, M and Ijaz Khan, M}, title = {Mathematical modeling and analysis of SWCNT-Water and MWCNT-Water flow over a stretchable sheet.}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105222}, doi = {10.1016/j.cmpb.2019.105222}, pmid = {31786449}, issn = {1872-7565}, abstract = {In this article we focused on the mixed convection flow of SWCNT-Water and MWCNT-Water over a stretchable permeable sheet. The nanofluid occupied porous medium. Darcy's law is used to characterize porous medium. The impact of viscous dissipation is considered. Transformation procedure is adopted to transform the governing PDE's system into dimensionless form. In order to solve the dimensionless PDE's system we used numerical method known as Finite difference method. Effects of flow variables i.e porosity parameter, suction parameter, Grashof number and Reynolds number on velocity, skin friction, temperature and Nusselt number are described graphically. The obtained results shows that velocity is dominant in SWCNT-Water over MWCNT-Water. Temperature is dominant in MWCNT-Water over SWCNT-Water.}, } @article {pmid31785535, year = {2020}, author = {Turkyilmazoglu, M}, title = {Single phase nanofluids in fluid mechanics and their hydrodynamic linear stability analysis.}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105171}, doi = {10.1016/j.cmpb.2019.105171}, pmid = {31785535}, issn = {1872-7565}, abstract = {BACKGROUND AND OBJECTIVE: The hydrodynamic stability of nanofluids of one phase is investigated in this paper based on linear stability theory. The overall thrust here is that the linear stability features of nanofluids can be estimated from their corresponding working fluid, at least in special circumstances.

METHODS: The approach uses the adjusting parameter to make assertions about stability. This is possible by certain correlations between the resulting eigenvalues.

RESULTS: It is shown that as the nanoparticles are added, the mean flow of nanofluids is slightly modified and the resulting eigen space of nano disturbances is built on the corresponding pure flow eigen space of perturbations. Several fluid dynamics problems are revisited to verify the usefulness of the obtained correlations.

CONCLUSION: The presented approach in this work serves us to understand the stabilizing/destabilizing effects of nanofluids as compared to the standard base fluids in terms of stability of viscous/inviscid and temporal/spatial senses. To illustrate, the critical Reynolds number in a traditional boundary layer flow is shown to be pushed to higher values with the dispersed nanoparticles in a working fluid, clearly implying the delay in transition from laminar to turbulent state.}, } @article {pmid31784839, year = {2019}, author = {Chen, J and He, Y and Wang, J and Huang, M and Guo, C}, title = {Dynamics of nitrogen transformation and bacterial community with different aeration depths in malodorous river.}, journal = {World journal of microbiology & biotechnology}, volume = {35}, number = {12}, pages = {196}, pmid = {31784839}, issn = {1573-0972}, support = {41877477//National Natural Science Foundation of China/ ; 16ZR1408800//Natural Science Foundation of Shanghai/ ; 16PJD023//Shanghai Pujiang Talent Program/ ; 18DZ1203806//Shanghai Science and Technology Development Foundation/ ; 1701K005//Research Funds of The Guangxi Key Laboratory of Theory and Technology for Environmental Pollution Control/ ; }, mesh = {Bacteria/classification/genetics/*metabolism ; China ; Geologic Sediments/microbiology ; Microbiota/*physiology ; Nitrogen/*metabolism ; Oxygen/metabolism ; Phylogeny ; RNA, Ribosomal, 16S ; Rivers/*chemistry/*microbiology ; Sulfur/metabolism ; }, abstract = {In this research, the dynamics of nitrogen transformation and bacterial community in malodorous river were investigated with different aeration depths. Computational flow dynamics (CFD) and Reynolds number (Re) were specially used to characterize the hydrodynamics condition under different aeration depths. The results indicated that aeration depth had vital impact on nitrogen transformation and bacterial community structure. It was found that a range of aeration depth (0.20-0.45 m above sediment-water interface) facilitated the removal of NH4+-N and TN with Re ranging between 6211 and 8930. Proteobacteria took over Firmicutes to become the predominant phylum (36-78%) under aeration, and the main subdivisions of γ-, β- and δ-Proteobacteria also varied greatly with different aeration depths. Interestingly, there was a marked shift of the inferentially identified dominant functional role within Proteobacteria from organic-matter degradation to nitrogen metabolism and then to sulfur metabolism as well as the coupling of nitrogen and sulfur with the increase of disturbance. The redundancy analysis (RDA) further confirmed the importance of aeration disturbance in shaping bacterial community. These findings help to gain improved understanding of endogenous N-behavior and aquatic microbial ecology, and underline the need for integrating the hydrodynamics factors with microbial community.}, } @article {pmid31779425, year = {2019}, author = {Singh, H and Bonnesoeur, A and Besnard, H and Houssin, C and Prigent, A and Crumeyrolle, O and Mutabazi, I}, title = {A large thermal turbulent Taylor-Couette (THETACO) facility for investigation of turbulence induced by simultaneous action of rotation and radial temperature gradient.}, journal = {The Review of scientific instruments}, volume = {90}, number = {11}, pages = {115112}, doi = {10.1063/1.5119811}, pmid = {31779425}, issn = {1089-7623}, abstract = {A thermal turbulent Taylor-Couette facility has been designed to investigate turbulent flows generated by differential rotation and radial temperature gradient. It consists of a cylindrical annulus with a rotating inner cylinder and a fixed outer cylinder. The electric heating system is installed inside the inner cylinder, and the annulus is immersed in a large cylindrical container filled with cooling fluid. Temperature regulators independently control the temperature of the inner surface of the inner cylinder and that of the cooling fluid. The facility allows us to reach values of the Reynolds number (Re ∼ 5 × 105) and of the Rayleigh number (Ra ∼ 3 × 106) for water as the working fluid. The facility provides torque measurements, a full optical access at the side and from the bottom for velocity measurements using particle image velocimetry (2D, stereoscopic, and tomographic). Temperature measurements in the flow can be performed by thermochromic liquid crystals or laser induced fluorescence.}, } @article {pmid31777765, year = {2019}, author = {Zhang, X and Lam, WA and Graham, MD}, title = {Dynamics of deformable straight and curved prolate capsules in simple shear flow.}, journal = {Physical review fluids}, volume = {4}, number = {4}, pages = {}, pmid = {31777765}, issn = {2469-990X}, support = {R21 MD011590/MD/NIMHD NIH HHS/United States ; }, abstract = {This work investigates the motion of neutrally-buoyant, slightly deformable straight and curved prolate fluid-filled capsules in unbounded simple shear flow at zero Reynolds number using direct simulations. The curved capsules serve as a model for the typical crescent-shaped sickle red blood cells in sickle cell disease (SCD). The effects of deformability and curvature on the dynamics are revealed. We show that with low deformability, straight prolate spheroidal capsules exhibit tumbling in the shear plane as their unique asymptotically stable orbit. This result contrasts with that for rigid spheroids, where infinitely many neutrally stable Jeffery orbits exist. The dynamics of curved prolate capsules are more complicated due to a combined effect of deformability and curvature. At short times, depending on the initial orientation, slightly deformable curved prolate capsules exhibit either a Jeffery-like motion such as tumbling or kayaking, or a non-Jeffery-like behavior in which the director (end-to-end vector) of the capsule crosses the shear-gradient plane back and forth. At long times, however, a Jeffery-like quasiperiodic orbit is taken regardless of the initial orientation. We further show that the average of the long-time trajectory can be well approximated using the analytical solution for Jeffery orbits with an effective orbit constant Ceff and aspect ratio ℓeff. These parameters are useful for characterizing the dynamics of curved capsules as a function of given deformability and curvature. As the capsule becomes more deformable or curved, Ceff decreases, indicating a shift of the orbit towards log-rolling motion, while ℓeff increases weakly as the degree of curvature increases but shows negligible dependency on deformability. These features are not changed substantially as the viscosity ratio between the inner and outer fluids is changed from 1 to 5. As cell deformability, cell shape, and cell-cell interactions are all pathologically altered in blood disorders such as SCD, these results will have clear implications on improving our understanding of the pathophysiology of hematologic disease.}, } @article {pmid31771023, year = {2019}, author = {Shan, X}, title = {Central-moment-based Galilean-invariant multiple-relaxation-time collision model.}, journal = {Physical review. E}, volume = {100}, number = {4-1}, pages = {043308}, doi = {10.1103/PhysRevE.100.043308}, pmid = {31771023}, issn = {2470-0053}, abstract = {Aiming at systematically correcting the non-Galilean-invariant thermal diffusivity in the previous multiple-relaxation-time Boltzmann equation collision model [Shan and Chen, Int. J. Mod. Phys. C 18, 635 (2007)IJMPEO0129-183110.1142/S0129183107010887], we show that by separately relaxing the central moments of the distribution function, Chapman-Enskog calculation leads to the correct hydrodynamic equations with mutually independent and Galilean invariant viscosity and thermal diffusivity, provided the velocity-space discretization preserves moments up to the fourth order. By transforming the central moments back to the absolute reference frame and evaluating using fixed discrete velocities, the efficient and accurate streaming-collision time-stepping algorithm is preserved. The lattice Boltzmann model is found to have excellent numerical stability in high-Reynolds-number simulations.}, } @article {pmid31771016, year = {2019}, author = {Berera, A and Clark, D}, title = {Information production in homogeneous isotropic turbulence.}, journal = {Physical review. E}, volume = {100}, number = {4-1}, pages = {041101}, doi = {10.1103/PhysRevE.100.041101}, pmid = {31771016}, issn = {2470-0053}, abstract = {We study the Reynolds number scaling of the Kolmogorov-Sinai entropy and attractor dimension for three-dimensional homogeneous isotropic turbulence through the use of direct numerical simulation. To do so, we obtain Lyapunov spectra for a range of different Reynolds numbers by following the divergence of a large number of orthogonal fluid trajectories. We find that the attractor dimension grows with the Reynolds number as Re^{2.35} with this exponent being larger than predicted by either dimensional arguments or intermittency models. The distribution of Lyapunov exponents is found to be finite around λ≈0 contrary to a possible divergence suggested by Ruelle. The relevance of the Kolmogorov-Sinai entropy and Lyapunov spectra in comparing complex physical systems is discussed.}, } @article {pmid31770976, year = {2019}, author = {Chitsaz, M and Fathali, M}, title = {Impact of an initial random magnetic field on the evolution of two-dimensional shearless mixing layers.}, journal = {Physical review. E}, volume = {100}, number = {4-1}, pages = {043106}, doi = {10.1103/PhysRevE.100.043106}, pmid = {31770976}, issn = {2470-0053}, abstract = {The impact of an initial random magnetic field on the temporal evolution of a two-dimensional incompressible turbulent shearless mixing layer is investigated using direct numerical simulation. Different intensities of the initial random magnetic field are imposed with uniform probability distribution on an identical flow field. The initial flow field condition is the turbulent shearless mixing layer with different kinetic energy ratio (E_{H}/E_{L}=6.7) and identical integral length scale. Simulations are carried out in a moderate magnetic Reynolds number, which causes a two-way interaction between the velocity and magnetic fields. In order to analyze the effect of the initial random magnetic field on the mixing characteristics, the intermittency inside the mixing layer and the mixing evolution parameters are investigated. It is found that with small initial magnetic field intensity, the intermittency in both large and small scales are larger than those values in hydrodynamic flow. However, increasing the intensity of the initial magnetic field reduces the intermittency in the mixing region to lower values compared to the hydrodynamic flow. The mixing layer growth rate and the mixing efficiency both show reduction by increasing the initial magnetic field intensity, which is attributed to the reduction of the averaged Reynolds number of both homogenous isotropic turbulent regions due to the suppressing effect of the Lorentz force on the velocity fields of these regions.}, } @article {pmid31759716, year = {2020}, author = {Ćmiel, AM and Strużyński, A and Wyrębek, M and Lipińska, AM and Zając, K and Zając, T}, title = {Response of freshwater mussel recruitment to hydrological changes in a eutrophic floodplain lake.}, journal = {The Science of the total environment}, volume = {703}, number = {}, pages = {135467}, doi = {10.1016/j.scitotenv.2019.135467}, pmid = {31759716}, issn = {1879-1026}, mesh = {Animals ; Ecosystem ; Endangered Species ; Eutrophication ; Hydrology ; *Lakes ; *Unionidae ; }, abstract = {Although eutrophication of freshwaters is a natural process, the human impact often leads to inland waters becoming overloaded with nutrients, impoverishing many valuable and vanishing habitats, such as floodplain lakes. These changes need to be reversed if the occurrence of endangered aquatic species is to be restored. In this paper we analyse the impact of a change in the water regime of a naturally eutrophic floodplain lake, which harbours a large diversity of Unionidae (large freshwater mussels), a globally threatened taxonomic group that provides important ecosystem functions and services. We found that a slight increase in the discharge from this waterbody, following the construction of an additional outflow pipe, positively influenced recruitment in three of the five mussel species inhabiting the lake. We also found that, after the construction of this additional outflow, the niches of juveniles of Anodonta cygnea and Unio spp. changed, revealing differences in their hydrological requirements. Our results suggest that, as in lotic habitats, complex hydraulic parameters are highly significant to unionid mussels in lentic conditions.}, } @article {pmid31744080, year = {2019}, author = {Taheri, RA and Goodarzi, V and Allahverdi, A}, title = {Mixing Performance of a Cost-effective Split-and-Recombine 3D Micromixer Fabricated by Xurographic Method.}, journal = {Micromachines}, volume = {10}, number = {11}, pages = {}, pmid = {31744080}, issn = {2072-666X}, abstract = {This paper presents experimental and numerical investigations of a novel passive micromixer based on the lamination of fluid layers. Lamination-based mixers benefit from increasing the contact surface between two fluid phases by enhancing molecular diffusion to achieve a faster mixing. Novel three-dimensional split and recombine (SAR) structures are proposed to generate fluid laminations. Numerical simulations were conducted to model the mixer performance. Furthermore, experiments were conducted using dyes to observe fluid laminations and evaluate the proposed mixer's characteristics. Mixing quality was experimentally obtained by means of image-based mixing index (MI) measurement. The multi-layer device was fabricated utilizing the Xurography method, which is a simple and low-cost method to fabricate 3D microfluidic devices. Mixing indexes of 96% and 90% were obtained at Reynolds numbers of 0.1 and 1, respectively. Moreover, the device had an MI value of 67% at a Reynolds number of 10 (flow rate of 116 µL/min for each inlet). The proposed micromixer, with its novel design and fabrication method, is expected to benefit a wide range of lab-on-a-chip applications, due to its high efficiency, low cost, high throughput and ease of fabrication.}, } @article {pmid31737769, year = {2019}, author = {Shaikh, MM and Massan, SU and Wagan, AI}, title = {A sixteen decimal places' accurate Darcy friction factor database using non-linear Colebrook's equation with a million nodes: A way forward to the soft computing techniques.}, journal = {Data in brief}, volume = {27}, number = {}, pages = {104733}, doi = {10.1016/j.dib.2019.104733}, pmid = {31737769}, issn = {2352-3409}, abstract = {The Colebrook's equation is considered as an empirical model to accurately compute the Darcy friction factor in pipes under fully-developed turbulent flow. Due to non-linearity and implicitness of the Colebrook's equation, one needs to use numerical methods to acquire reasonably good approximation to the true friction factor values. However, such idea is not preferred by practitioners as it demands use of computers - also more computational time and effort. To overcome this, explicit equations that can describe Darcy friction factor directly in terms of the Reynolds number and relative roughness are essential. Using Fixed point iteration method in the MATLAB software, we have developed a 16 decimal places' accurate friction factor database for the Darcy friction factor for a 1000 by 1000 mesh of Reynolds number and relative roughness values. The accurate dataset described in this work will serve to be basis for the construction of new and more reliable explicit equations using regression modeling, artificial intelligence techniques and other soft computing methods.}, } @article {pmid31736648, year = {2019}, author = {Papageorgiou, DT and Tanveer, S}, title = {Analysis and computations of a non-local thin-film model for two-fluid shear driven flows.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2230}, pages = {20190367}, doi = {10.1098/rspa.2019.0367}, pmid = {31736648}, issn = {1364-5021}, abstract = {This paper is concerned with analysis and computations of a non-local thin-film model developed in Kalogirou & Papageorgiou (J. Fluid Mech.802, 5-36, 2016) for a perturbed two-layer Couette flow when the thickness of the more viscous fluid layer next to the stationary wall is small compared to the thickness of the less viscous fluid. Travelling wave solutions and their stability are determined numerically, and secondary bifurcation points are identified in the process. We also determine regions in parameter space where bistability is observed with two branches being linearly stable at the same time. The travelling wave solutions are mathematically justified through a quasi-solution analysis in a neighbourhood of an empirically constructed approximate solution. This relies in part on precise asymptotics of integrals of Airy functions for large wave numbers. The primary bifurcation about the trivial state is shown rigorously to be supercritical, and the dependence of bifurcation points, as a function of Reynolds number R and the primary wavelength 2πν-1/2 of the disturbance, is determined analytically.}, } @article {pmid31734470, year = {2020}, author = {Farooq, S and Hayat, T and Khan, MI and Alsaedi, A}, title = {Entropy generation minimization (EGM) in magneto peristalsis with variable properties.}, journal = {Computer methods and programs in biomedicine}, volume = {186}, number = {}, pages = {105045}, doi = {10.1016/j.cmpb.2019.105045}, pmid = {31734470}, issn = {1872-7565}, abstract = {OBJECTIVE AND BACKGROUND: This article featuring the peristaltic transport of viscous material with variable properties (i.e. temperature dependent viscosity and thermal conductivity) through curved configuration. Fluid saturating through porous channel walls of uniform space. Entropy generation consideration here is to analyze irreversibility aspects. Channel boundaries retain the velocity and thermal slip conditions.

METHOD: Wave frame of reference is attained with the utilization of long wavelength and small Reynolds number approach. Solution of the simplified coupled system of dimensionless constraints is obtained numerically. Detailed analysis of important quantities of interest has been presented in discussion portion.

RESULTS: Entropy generation variation near center is very small whereas in the vicinity of the channel wall is larger. Bejan number has reverse variation as observed for entropy generation.

CONCLUSION: Variable characteristics of viscosity has opposite impact on velocity and temperature is observed. It is also noticed small irreversibility effects are obtained for higher varying viscosity and thermal conductivity near the vicinity of the channel walls.}, } @article {pmid31719582, year = {2019}, author = {Ying, Y and Lin, Y}, title = {Inertial Focusing and Separation of Particles in Similar Curved Channels.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {16575}, doi = {10.1038/s41598-019-52983-z}, pmid = {31719582}, issn = {2045-2322}, abstract = {Inertial particle focusing in curved channels has enormous potential for lab-on-a-chip applications. This paper compares a zigzag channel, which has not been used previously for inertial focusing studies, with a serpentine channel and a square wave channel to explore their differences in terms of focusing performance and separation possibilities. The particle trajectories and fluid fields in the curved channels are studied by a numerical simulation. The effects of different conditions (structure, Reynolds number, and particle size) on the competition between forces and the focusing performance are studied. The results indicate that the zigzag channel has the best focusing effect at a high Reynolds number and that the serpentine channel is second in terms of performance. Regarding the particle separation potential, the zigzag channel has a good performance in separating 5 μm and 10 μm particles at ReC = 62.5. In addition, the pressure drop of the channel is also considered to evaluate the channel performance, which has not been taken into account in the literature on inertial microfluidics. This result is expected to be instructive for the selection and optimization of inertial microchannel structures.}, } @article {pmid31718189, year = {2019}, author = {Zhang, Z and Zhang, P}, title = {Numerical Interpretation to the Roles of Liquid Viscosity in Droplet Spreading at Small Weber Numbers.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {49}, pages = {16164-16171}, doi = {10.1021/acs.langmuir.9b02736}, pmid = {31718189}, issn = {1520-5827}, abstract = {Droplet impacting a free-slip plane at small Weber numbers (We < 30) was numerically investigated by a front tracking method, with particular emphasis on clarifying the roles of the liquid viscosity and the "left-over" internal kinetic energy in droplet spreading. The most interesting discovery is that there exists a certain range of We in which the maximum diameter rate, D̃m, shows a nonmonotonic variation with the Reynolds number, Re. This non-monotonic variation is owing to the dual role of liquid viscosity in influencing droplet spreading. Specifically, when the initial surface energy is comparable to the initial kinetic energy (the corresponding We is around 10-30), the high strain rates of the droplet internal flow dominate its viscous dissipation at a relatively large Re, while the liquid viscosity dominates the viscous dissipation at a relatively small Re. Furthermore, to unravel the influence of droplet attachment and detachment on droplet spreading, we considered two limiting situations such as full attachment (with no gas film throughout droplet spreading) and full detachment (with a gas film throughout droplet spreading). The results show that the droplet with a gas film tends to generate a stronger vortical motion in its rim, results in a larger left-over kinetic energy, and hence causes a smaller spreading.}, } @article {pmid31718021, year = {2019}, author = {Kottmeier, J and Wullenweber, M and Blahout, S and Hussong, J and Kampen, I and Kwade, A and Dietzel, A}, title = {Accelerated Particle Separation in a DLD Device at Re > 1 Investigated by Means of µPIV.}, journal = {Micromachines}, volume = {10}, number = {11}, pages = {}, pmid = {31718021}, issn = {2072-666X}, abstract = {A pressure resistant and optically accessible deterministic lateral displacement (DLD) device was designed and microfabricated from silicon and glass for high-throughput fractionation of particles between 3.0 and 7.0 µm comprising array segments of varying tilt angles with a post size of 5 µm. The design was supported by computational fluid dynamic (CFD) simulations using OpenFOAM software. Simulations indicated a change in the critical particle diameter for fractionation at higher Reynolds numbers. This was experimentally confirmed by microparticle image velocimetry (µPIV) in the DLD device with tracer particles of 0.86 µm. At Reynolds numbers above 8 an asymmetric flow field pattern between posts could be observed. Furthermore, the new DLD device allowed successful fractionation of 2 µm and 5 µm fluorescent polystyrene particles at Re = 0.5-25.}, } @article {pmid31715344, year = {2019}, author = {Di, D and Qu, X and Liu, C and Fang, L and Quan, P}, title = {Continuous production of celecoxib nanoparticles using a three-dimensional-coaxial-flow microfluidic platform.}, journal = {International journal of pharmaceutics}, volume = {572}, number = {}, pages = {118831}, doi = {10.1016/j.ijpharm.2019.118831}, pmid = {31715344}, issn = {1873-3476}, mesh = {Animals ; Biological Availability ; Celecoxib/*administration & dosage/chemistry/pharmacokinetics ; Glass ; High-Throughput Screening Assays ; Male ; *Microfluidic Analytical Techniques ; *Nanoparticles ; Particle Size ; Rats ; Rats, Wistar ; Solubility ; Water/chemistry ; }, abstract = {Increasing the dissolution rate of water insoluble drugs by decreasing the particle size of the drugs into nano-size is a well-known strategy. However, continuous production of drug nanoparticles with uniform particle size is critical for clinical application of the strategy. Here we report a simple microfluidic mixing method that can achieve continuous production of celecoxib nanoparticles with uniform particle size and high dissolution rate. A three-dimensional (3D) coaxial-flow microfluidic device was fabricated by assembling two coaxial aligned borosilicate glass capillaries on a glass slide, and a tapered glass capillary was inserted into another bigger cylindrical one with coaxial alignment. Celecoxib nanoparticles were prepared by the microfluidic device under the turbulent jet regime. The 3D-coaxial-flow pattern and high Reynolds number ensured the extremely short mixing time, consequently, resulted in the high throughput production of drug nanoparticles with uniform particle size. The obtained nanoparticles were spherical in shape, and showed superior dissolution rate compared with the coarse powder both in sink and non-sink conditions. The bioavailability of the water insoluble drug was also significantly improved by the reduction of particle size into nano-size.}, } @article {pmid31700559, year = {2019}, author = {Herrmann, N and Neubauer, P and Birkholz, M}, title = {Spiral microfluidic devices for cell separation and sorting in bioprocesses.}, journal = {Biomicrofluidics}, volume = {13}, number = {6}, pages = {061501}, pmid = {31700559}, issn = {1932-1058}, abstract = {Inertial microfluidic systems have been arousing interest in medical applications due to their simple and cost-efficient use. However, comparably small sample volumes in the microliter and milliliter ranges have so far prevented efficient applications in continuous bioprocesses. Nevertheless, recent studies suggest that these systems are well suited for cell separation in bioprocesses because of their facile adaptability to various reactor sizes and cell types. This review will discuss potential applications of inertial microfluidic cell separation systems in downstream bioprocesses and depict recent advances in inertial microfluidics for bioprocess intensification. This review thereby focusses on spiral microchannels that separate particles at a moderate Reynolds number in a laminar flow (Re < 2300) according to their size by applying lateral hydrodynamic forces. Spiral microchannels have already been shown to be capable of replacing microfilters, extracting dead cells and debris in perfusion processes, and removing contaminant microalgae species. Recent advances in parallelization made it possible to process media on a liter-scale, which might pave the way toward industrial applications.}, } @article {pmid31674812, year = {2019}, author = {Sharzehee, M and Chang, Y and Song, JP and Han, HC}, title = {Hemodynamic effects of myocardial bridging in patients with hypertrophic cardiomyopathy.}, journal = {American journal of physiology. Heart and circulatory physiology}, volume = {317}, number = {6}, pages = {H1282-H1291}, doi = {10.1152/ajpheart.00466.2019}, pmid = {31674812}, issn = {1522-1539}, mesh = {Adolescent ; Adult ; Aged ; Cardiomyopathy, Hypertrophic/complications/pathology/*physiopathology ; Coronary Circulation ; Female ; *Hemodynamics ; Humans ; Male ; Middle Aged ; *Models, Cardiovascular ; Myocardial Bridging/complications/pathology/*physiopathology ; *Patient-Specific Modeling ; }, abstract = {Myocardial bridging (MB) is linked to angina and myocardial ischemia and may lead to sudden cardiac death in patients with hypertrophic cardiomyopathy (HCM). However, it remains unclear how MB affect the coronary blood flow in HCM patients. The aim of this study was to assess the effects of MB on coronary hemodynamics in HCM patients. Fifteen patients with MB (7 HCM and 8 non-HCM controls) in their left anterior descending (LAD) coronary artery were chosen. Transient computational fluid dynamics (CFD) simulations were conducted in anatomically realistic models of diseased (with MB) and virtually healthy (without MB) LAD from these patients, reconstructed from biplane angiograms. Our CFD simulation results demonstrated that dynamic compression of MB led to diastolic flow disturbances and could significantly reduce the coronary flow in HCM patients as compared with non-HCM group (P < 0.01). The pressure drop coefficient was remarkably higher (P < 0.05) in HCM patients. The flow rate change is strongly correlated with both upstream Reynolds number and MB compression ratio, while the MB length has less impact on coronary flow. The hemodynamic results and clinical outcomes revealed that HCM patients with an MB compression ratio higher than 65% required a surgical intervention. In conclusion, the transient MB compression can significantly alter the diastolic flow pattern and wall shear stress distribution in HCM patients. HCM patients with severe MB may need a surgical intervention.NEW & NOTEWORTHY In this study, the hemodynamic significance of myocardial bridging (MB) in patients with hypertrophic cardiomyopathy (HCM) was investigated to provide valuable information for surgical decision-making. Our results illustrated that the transient MB compression led to complex flow patterns, which can significantly alter the diastolic flow and wall shear stress distribution. The hemodynamic results and clinical outcomes demonstrated that patients with HCM and an MB compression ratio higher than 65% required a surgical intervention.}, } @article {pmid31671753, year = {2019}, author = {Shanko, ES and van de Burgt, Y and Anderson, PD and den Toonder, JMJ}, title = {Microfluidic Magnetic Mixing at Low Reynolds Numbers and in Stagnant Fluids.}, journal = {Micromachines}, volume = {10}, number = {11}, pages = {}, pmid = {31671753}, issn = {2072-666X}, abstract = {Microfluidic mixing becomes a necessity when thorough sample homogenization is required in small volumes of fluid, such as in lab-on-a-chip devices. For example, efficient mixing is extraordinarily challenging in capillary-filling microfluidic devices and in microchambers with stagnant fluids. To address this issue, specifically designed geometrical features can enhance the effect of diffusion and provide efficient mixing by inducing chaotic fluid flow. This scheme is known as "passive" mixing. In addition, when rapid and global mixing is essential, "active" mixing can be applied by exploiting an external source. In particular, magnetic mixing (where a magnetic field acts to stimulate mixing) shows great potential for high mixing efficiency. This method generally involves magnetic beads and external (or integrated) magnets for the creation of chaotic motion in the device. However, there is still plenty of room for exploiting the potential of magnetic beads for mixing applications. Therefore, this review article focuses on the advantages of magnetic bead mixing along with recommendations on improving mixing in low Reynolds number flows (Re ≤ 1) and in stagnant fluids.}, } @article {pmid31671339, year = {2020}, author = {Ijaz Khan, M and Ali, A and Hayat, T and Alsaedi, A}, title = {Entropy optimized dissipative CNTs based flow with probable error and statistical declaration.}, journal = {Computer methods and programs in biomedicine}, volume = {185}, number = {}, pages = {105137}, doi = {10.1016/j.cmpb.2019.105137}, pmid = {31671339}, issn = {1872-7565}, abstract = {BACKGROUND: CNTs are categorized subject to their structures i.e., SWCNTs (single wall nanotubes), DWCNTs (double wall nanotubes) and MWCNTs (multi-wall nanotubes). The various structures have distinct characteristics that make the nanotubes suitable for various physical applications. It is due their unique electrical, mechanical and thermal attributes CNTs present thrilling opportunities for mechanical engineering, industrial, scientific research and commercial applications. There is fruitful potential for carbon nanotubes in the composites business and industry. Today, CNTs find utilization in frequent various products, and analyst continue to explore new applications. Currently applications comprise wind turbines, bicycle components, scanning probe microscopes, flat panel displays, marine paints, sensing devices, electronics, batteries with longer lifetime and electrical circuitry etc. Such applications in mind, entropy optimized dissipative CNTs based flow of nanomaterial by a stretched surface. Flow is caused due to stretching phenomenon and studied in 3D coordinates. Both types of CNTs are studied i.e., SWCNTs and MWCNTs. CNTs are considered for nanoparticles and water for continuous phase fluid. Special consideration is given to the analysis of statistical declaration and probable error for skin friction and Nusselt number. Furthermore, entropy rate is calculated. Entropy rate is discussed in the presence of four main irreversibilities i.e., heat transfer, Joule heating, porosity and dissipation.

METHOD: Homotopy technique is utilized to develop the convergence series solutions.

RESULTS: Impacts of sundry variables subject to both SWCNTs (single) and MWCNTs (multi) are graphically discussed. Statistical analysis and probable error for surface drag force and Nusselt number are numerically calculated subject to various flow variables. Numerical results for such engineering quantities are displayed through tables. In addition, comparative analysis for SWCNTs and MWCNTs are presented for the velocity, concentration and thermal fields.

CONCLUSIONS: Results for entropy rate is calculated in the presence of various sundry variable through implementation of second law of thermodynamics. It is examined from the results that velocity decreases for both CNTs via higher magnetic, inertia coefficient and porosity parameters. Secondary velocity i.e., velocity in g-direction boosts up versus rotation parameter while it declines for larger slip parameter for both CNTs. thermal field intensifies for both CNTs via larger heat generation/absorption parameter. Concentration which shows the mass transfer of species increases subject to higher homogeneous parameter and Schmidt number in case of both CNTs. Entropy rate in more for larger magnetic, Reynolds number and slip parameter. Bejan number boosts up for higher Reynold number and slip parameter while it declines for magnetic parameter.}, } @article {pmid31657131, year = {2020}, author = {Dincau, B and Dressaire, E and Sauret, A}, title = {Pulsatile Flow in Microfluidic Systems.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {16}, number = {9}, pages = {e1904032}, doi = {10.1002/smll.201904032}, pmid = {31657131}, issn = {1613-6829}, abstract = {This review describes the current knowledge and applications of pulsatile flow in microfluidic systems. Elements of fluid dynamics at low Reynolds number are first described in the context of pulsatile flow. Then the practical applications in microfluidic processes are presented: the methods to generate a pulsatile flow, the generation of emulsion droplets through harmonic flow rate perturbation, the applications in mixing and particle separation, and the benefits of pulsatile flow for clog mitigation. The second part of the review is devoted to pulsatile flow in biological applications. Pulsatile flows can be used for mimicking physiological systems, to alter or enhance cell cultures, and for bioassay automation. Pulsatile flows offer unique advantages over a steady flow, especially in microfluidic systems, but also require some new physical insights and more rigorous investigation to fully benefit future applications.}, } @article {pmid31656395, year = {2019}, author = {Folkersma, M and Schmehl, R and Viré, A}, title = {Boundary layer transition modeling on leading edge inflatable kite airfoils.}, journal = {Wind energy (Chichester, England)}, volume = {22}, number = {7}, pages = {908-921}, pmid = {31656395}, issn = {1099-1824}, abstract = {We present a computational fluid dynamic analysis of boundary layer transition on leading edge inflatable kite airfoils used for airborne wind energy generation. Because of the operation in pumping cycles, the airfoil is generally subject to a wide range of Reynolds numbers. The analysis is based on the combination of the shear stress transport turbulence model with the γ - R ˜ e θ t transition model, which can handle the laminar boundary layer and its transition to turbulence. The implementation of both models in OpenFOAM is described. We show a validation of the method for a sailwing (ie, a wing with a membrane) airfoil and an application to a leading edge inflatable kite airfoil. For the sailwing airfoil, the results computed with transition model agree well with the existing low Reynolds number experiment over the whole range of angles of attack. For the leading edge inflatable kite airfoil, the transition modeling has both favorable and unfavorable effects on the aerodynamics. On the one hand, the aerodynamics suffer from the laminar separation. But, on the other hand, the laminar boundary layer thickens slower than the turbulent counterpart, which, in combination with transition, delays the separation. The results also indicate that the aerodynamics of the kite airfoil could be improved by delaying the boundary layer transition during the traction phase and tripping the transition in the retraction phase.}, } @article {pmid31648622, year = {2020}, author = {Ozden, K and Sert, C and Yazicioglu, Y}, title = {Numerical investigation of wall pressure fluctuations downstream of concentric and eccentric blunt stenosis models.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {234}, number = {1}, pages = {48-60}, doi = {10.1177/0954411919884167}, pmid = {31648622}, issn = {2041-3033}, mesh = {Acoustics ; Blood Vessels/*physiopathology ; *Constriction, Pathologic ; *Models, Biological ; *Pressure ; }, abstract = {Pressure fluctuations that cause acoustic radiation from vessel models with concentric and eccentric blunt stenoses are investigated. Large eddy simulations of non-pulsatile flow condition are performed using OpenFOAM. Calculated amplitude and spatial-spectral distribution of acoustic pressures at the post-stenotic region are compared with previous experimental and theoretical results. It is found that increasing the Reynolds number does not change the location of the maximum root mean square wall pressure, but causes a general increase in the spectrum level, although the change in the shape of the spectrum is not significant. On the contrary, compared to the concentric model at the same Reynolds number, eccentricity leads to an increase both at the distance of the location of the maximum root mean square wall pressure from the stenosis exit and the spectrum level. This effect becomes more distinct when radial eccentricity of the stenosis increases. Both the flow rate and the eccentricity of the stenosis shape are evaluated to be clinically important parameters in diagnosing stenosis.}, } @article {pmid31640254, year = {2019}, author = {Su, L and Duan, Z and He, B and Ma, H and Xu, Z}, title = {Thermally Developing Flow and Heat Transfer in Elliptical Minichannels with Constant Wall Temperature.}, journal = {Micromachines}, volume = {10}, number = {10}, pages = {}, pmid = {31640254}, issn = {2072-666X}, support = {2019YJS158//Fundamental Research Funds for the Central Universities/ ; }, abstract = {Laminar convective heat transfer of elliptical minichannels is investigated for hydrodynamically fully developed but thermal developing flow with no-slip condition. A three-dimensional numerical model is developed in different elliptical geometries with the aspect ratio varying from 0.2 to 1. The effect of Reynolds number (25 ≤ Re ≤ 2000) on the local Nusselt number is examined in detail. The results indicate that the local Nusselt number is a decreasing function of Reynolds number and it is sensitive to Reynolds number especially for Re less than 250. The effect of aspect ratio on local Nusselt number is small when compared with the effect of Reynolds number on local Nusselt number. The local Nusselt number is independent of cross-section geometry at the inlet. The maximum effect of aspect ratio on local Nusselt number arises at the transition section rather than the fully developed region. However, the non-dimensional thermal entrance length is a monotonic decreasing concave function of aspect ratio but a weak function of Reynolds number. Correlations for the local Nusselt number and the thermal developing length for elliptical channels are developed with good accuracy, which may provide guidance for design and optimization of elliptical minichannel heat sinks.}, } @article {pmid31640175, year = {2019}, author = {Raza, W and Ma, SB and Kim, KY}, title = {Single and Multi-Objective Optimization of a Three-Dimensional Unbalanced Split-and-Recombine Micromixer.}, journal = {Micromachines}, volume = {10}, number = {10}, pages = {}, pmid = {31640175}, issn = {2072-666X}, support = {No. 2019R1A2C1007657//National Research Foundation of Korea/ ; }, abstract = {The three-dimensional geometry of a micromixer with an asymmetrical split-and-recombine mechanism was optimized to enhance the fluid-mixing capability at a Reynolds number of 20. Single and multi-objective optimizations were carried out by using particle swarm optimization and a genetic algorithm on a modeled surrogate surface. Surrogate modeling was performed using the computational results for the mixing. Mixing and flow analyses were carried out by solving the convection-diffusion equation in combination with the three-dimensional continuity and momentum equations. The optimization was carried out with two design variables related to dimensionless geometric parameters. The mixing effectiveness was chosen as the objective function for the single-objective optimization, and the pressure drop and mixing index at the outlet were chosen for the multi-objective optimization. The sampling points in the design space were determined using a design of experiment technique called Latin hypercube sampling. The surrogates for the objective functions were developed using a Kriging model. The single-objective optimization resulted in 58.9% enhancement of the mixing effectiveness compared to the reference design. The multi-objective optimization provided Pareto-optimal solutions that showed a maximum increase of 48.5% in the mixing index and a maximum decrease of 55.0% in the pressure drop in comparison to the reference design.}, } @article {pmid31639948, year = {2019}, author = {Basu, A and Bhattacharjee, JK}, title = {Kolmogorov or Bolgiano-Obukhov scaling: Universal energy spectra in stably stratified turbulent fluids.}, journal = {Physical review. E}, volume = {100}, number = {3-1}, pages = {033117}, doi = {10.1103/PhysRevE.100.033117}, pmid = {31639948}, issn = {2470-0053}, abstract = {We set up the scaling theory for stably stratified turbulent fluids. For a system having infinite extent in the horizontal directions, but with a finite width in the vertical direction, this theory predicts that the inertial range can display three possible scaling behavior, which are essentially parametrized by the buoyancy frequency N, or dimensionless horizontal Froude number F_{h}, and the vertical length scale l_{v} that sets the scale of variation of the velocity field in the vertical direction for a fixed Reynolds number. For very low N or very high Re_{b} or F_{h}, and with l_{v}≫l_{h}, the typical horizontal length scale, buoyancy forces are irrelevant and hence, unsurprisingly, the kinetic energy spectra show the well-known K41 scaling in the inertial range. In this regime, the local temperature behaves as a passively advected scalar, without any effect on the flow fields. For intermediate ranges of values of N,F_{h}∼O(1), corresponding to moderate stratification, buoyancy forces are important enough to affect the scaling. This leads to the Bolgiano-Obukhov scaling which is isotropic, when l_{v}∼l_{h}. Finally, for very large N, corresponding to strong stratification, together with a very small l_{v}, the inertial-range flow fields effectively two-dimensionalize. The kinetic energy spectra are predicted to be anisotropic with only the horizontal part of the kinetic energy spectra following the K41 scaling. This suggests an intriguing re-entrant K41 scaling, as a function of stratification, for the horizontal components of the velocity field in this regime. The scaling theory further predicts the scaling of the thermal energy in each of these three scaling regimes. Our theory can be tested in large-scale simulations and appropriate laboratory-based experiments.}, } @article {pmid31631905, year = {2019}, author = {Bae, HJ and Lozano-Durán, A and Bose, ST and Moin, P}, title = {Dynamic slip wall model for large-eddy simulation.}, journal = {Journal of fluid mechanics}, volume = {859}, number = {}, pages = {400-432}, pmid = {31631905}, issn = {0022-1120}, support = {NNX15AU93A//NASA/United States ; }, abstract = {Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-slip boundary condition at the wall with a Neumann boundary condition in the wall-parallel directions while maintaining the no-transpiration condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (slip) boundary condition with transpiration (non-zero wall-normal velocity) in the context of wall-modelled LES. The effect of the slip boundary condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and a flat-plate turbulent boundary layer. It is shown that the slip condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting non-zero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models (Jiménez & Moser, AIAA J., vol. 38 (4), 2000, pp. 605-612). Second, we discuss the requirements for the slip condition to be used in conjunction with wall models and derive the equation that connects the slip boundary condition with the stress at the wall. Finally, a dynamic procedure for the slip coefficients is formulated, providing a dynamic slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow and a zero-pressure-gradient flat-plate turbulent boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers and grid resolutions.}, } @article {pmid31631902, year = {2019}, author = {Lozano-Durán, A and Bae, HJ}, title = {Error scaling of large-eddy simulation in the outer region of wall-bounded turbulence.}, journal = {Journal of computational physics}, volume = {392}, number = {}, pages = {532-555}, pmid = {31631902}, issn = {0021-9991}, support = {NNX15AU93A//NASA/United States ; }, abstract = {We study the error scaling properties of large-eddy simulation (LES) in the outer region of wall-bounded turbulence at moderately high Reynolds numbers. In order to avoid the additional complexity of wall-modeling, we perform LES of turbulent channel flows in which the no-slip condition at the wall is replaced by a Neumann condition supplying the exact mean wall-stress. The statistics investigated are the mean velocity profile, turbulence intensities, and kinetic energy spectra. The errors follow (Δ / L) α R e τ γ , where Δ is the characteristic grid resolution, Reτ is the friction Reynolds number, and L is the meaningful length-scale to normalize Δ in order to collapse the errors across the wall-normal distance. We show that Δ can be expressed as the L2-norm of the grid vector and that L is well represented by the ratio of the friction velocity and mean shear. The exponent α is estimated from theoretical arguments for each statistical quantity of interest and shown to roughly match the values computed by numerical simulations. For the mean profile and kinetic energy spectra, α ≈ 1, whereas the turbulence intensities converge at a slower rate α < 1. The exponent γ is approximately 0, i.e. the LES solution is independent of the Reynolds number. The expected behavior of the turbulence intensities at high Reynolds numbers is also derived and shown to agree with the classic log-layer profiles for grid resolutions lying within the inertial range. Further examination of the LES turbulence intensities and spectra reveals that both quantities resemble their filtered counterparts from direct numerical simulation (DNS) data, but that the mechanism responsible for this similarity is related to the balance between the input power and dissipation rather than to filtering.}, } @article {pmid31627151, year = {2020}, author = {Hayat, T and Waqar Ahmad, M and Ijaz Khan, M and Alsaedi, A}, title = {Entropy optimization in CNTs based nanomaterial flow induced by rotating disks: A study on the accuracy of statistical declaration and probable error.}, journal = {Computer methods and programs in biomedicine}, volume = {184}, number = {}, pages = {105105}, doi = {10.1016/j.cmpb.2019.105105}, pmid = {31627151}, issn = {1872-7565}, abstract = {BACKGROUND: CNTs (Carbon nanotubes) being allotropes of carbon, made of graphene and diameters of single and multi-walls carbon nanotubes are typically 0.8 to 2 nm and 5 to 20 mn, although diameter of MWCNTs can exceed 100 nm. Carbon nanotubes lengths range from less than 100 nm to 0.5 m. Their impressive structural, electronic and mechanical attributes subject to their small size and mass, their high electrical and thermal conductivities, and their strong mechanical potency. CNTs based materials are successfully applied in medicine and pharmacy subject to their huge surface area that is proficient of conjugating or adsorbing with a wide variety of genes, drugs, antibodies, vaccines and biosensors etc. Therefore, we have presented a theoretical study about mathematical modeling of CNTs based viscous material flow between two rotating disks. Both types of nanotubes i.e., SWCNTs and MWCNTs are considered. Xue model is used for the mathematical modeling. Fluid flow is due to rotating disks. Main focus here is given to probable error and statistical declaration. Entropy is calculated for both single and multi-walls nanotubes.

METHOD: Nonlinear PDEs are first converted into ODEs and then computed for homotopy convergent solutions.

RESULTS AND CONCLUSION: Statistical declaration and probable error for skin friction and Nusselt number are numerically computed and discussed through Tables. From obtained outcomes it is concluded that magnitude of skin friction increases at both disks surface for higher values of Reynolds number, lower stretching parameter and porosity parameter while it decays for both of disks versus larger rotation parameter. Nusselt number or heat transfer rate also enhances at both disks in the presence of radiation and Reynolds number while it decays against Eckert number.}, } @article {pmid31620754, year = {2019}, author = {Bukowicki, M and Ekiel-Jeżewska, ML}, title = {Sedimenting pairs of elastic microfilaments.}, journal = {Soft matter}, volume = {15}, number = {46}, pages = {9405-9417}, doi = {10.1039/c9sm01373c}, pmid = {31620754}, issn = {1744-6848}, abstract = {The dynamics of two identical elastic filaments settling under gravity in a viscous fluid in the low Reynolds number regime is investigated numerically. A large family of initial configurations symmetric with respect to a vertical plane is considered, as well as their non-symmetric perturbations. The behaviour of the filaments is primarily governed by the elasto-gravitational number, which depends on the filament's length and flexibility, and the strength of the external force. Flexible filaments usually converge toward horizontal and parallel orientation. We explain this phenomenon and show that it occurs also for curved rigid particles of similar shapes. Once aligned, the two fibres either converge toward a stationary, flexibility-dependent distance, or tend to collide or continuously repel each other. Rigid and straight rods perform periodic motions while settling down. Apart from very stiff particles, the dynamics is robust to non-symmetric perturbations.}, } @article {pmid31611726, year = {2019}, author = {Holdenried-Chernoff, D and Chen, L and Jackson, A}, title = {A trio of simple optimized axisymmetric kinematic dynamos in a sphere.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2229}, pages = {20190308}, pmid = {31611726}, issn = {1364-5021}, abstract = {Planetary magnetic fields are generated by the motion of conductive fluid in the planet's interior. Complex flows are not required for dynamo action; simple flows have been shown to act as efficient kinematic dynamos, whose physical characteristics are more straightforward to study. Recently, Chen et al. (2018, J. Fluid Mech.839, 1-32. (doi:10.1017/jfm.2017.924)) found the optimal, unconstrained kinematic dynamo in a sphere, which, despite being of theoretical importance, is of limited practical use. We extend their work by restricting the optimization to three simple two-mode axisymmetric flows based on the kinematic dynamos of Dudley & James (1989, Proc. R. Soc. Lond. A425, 407-429. (doi:10.1098/rspa.1989.0112)). Using a Lagrangian optimization, we find the smallest critical magnetic Reynolds number for each flow type, measured using an enstrophy-based norm. A Galerkin method is used, in which the spectral coefficients of the fluid flow and magnetic field are updated in order to maximize the final magnetic energy. We consider the t01s01, t01s02 and t02s02 flows and find enstrophy-based critical magnetic Reynolds numbers of 107.7, 142.4 and 125.5 (13.7, 19.6 and 16.4, respectively, with the energy-based definition). These are up to four times smaller than the original flows. These simple and efficient flows may be used as benchmarks in future studies.}, } @article {pmid31602809, year = {2020}, author = {Browne, CA and Shih, A and Datta, SS}, title = {Pore-Scale Flow Characterization of Polymer Solutions in Microfluidic Porous Media.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {16}, number = {9}, pages = {e1903944}, doi = {10.1002/smll.201903944}, pmid = {31602809}, issn = {1613-6829}, abstract = {Polymer solutions are frequently used in enhanced oil recovery and groundwater remediation to improve the recovery of trapped nonaqueous fluids. However, applications are limited by an incomplete understanding of the flow in porous media. The tortuous pore structure imposes both shear and extension, which elongates polymers; moreover, the flow is often at large Weissenberg numbers, Wi, at which polymer elasticity in turn strongly alters the flow. This dynamic elongation can even produce flow instabilities with strong spatial and temporal fluctuations despite the low Reynolds number, Re. Unfortunately, macroscopic approaches are limited in their ability to characterize the pore-scale flow. Thus, understanding how polymer conformations, flow dynamics, and pore geometry together determine these nontrivial flow patterns and impact macroscopic transport remains an outstanding challenge. This review describes how microfluidic tools can shed light on the physics underlying the flow of polymer solutions in porous media at high Wi and low Re. Specifically, microfluidic studies elucidate how steady and unsteady flow behavior depends on pore geometry and solution properties, and how polymer-induced effects impact nonaqueous fluid recovery. This work thus provides new insights for polymer dynamics, non-Newtonian fluid mechanics, and applications such as enhanced oil recovery and groundwater remediation.}, } @article {pmid31594959, year = {2019}, author = {Houba, T and Dasgupta, A and Gopalakrishnan, S and Gosse, R and Roy, S}, title = {Supersonic turbulent flow simulation using a scalable parallel modal discontinuous Galerkin numerical method.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {14442}, doi = {10.1038/s41598-019-50546-w}, pmid = {31594959}, issn = {2045-2322}, support = {GS04T09DBC0017//Science Applications International Corporation (SAIC)/ ; GS04T09DBC0017//Science Applications International Corporation (SAIC)/ ; GS04T09DBC0017//Science Applications International Corporation (SAIC)/ ; GS04T09DBC0017//Science Applications International Corporation (SAIC)/ ; ACI-1548562//National Science Foundation (NSF)/ ; ACI-1548562//National Science Foundation (NSF)/ ; ACI-1548562//National Science Foundation (NSF)/ ; ACI-1548562//National Science Foundation (NSF)/ ; ACI-1548562//NSF | National Science Board (NSB)/ ; }, abstract = {The scalability and efficiency of numerical methods on parallel computer architectures is of prime importance as we march towards exascale computing. Classical methods like finite difference schemes and finite volume methods have inherent roadblocks in their mathematical construction to achieve good scalability. These methods are popularly used to solve the Navier-Stokes equations for fluid flow simulations. The discontinuous Galerkin family of methods for solving continuum partial differential equations has shown promise in realizing parallel efficiency and scalability when approaching petascale computations. In this paper an explicit modal discontinuous Galerkin (DG) method utilizing Implicit Large Eddy Simulation (ILES) is proposed for unsteady turbulent flow simulations involving the three-dimensional Navier-Stokes equations. A study of the method was performed for the Taylor-Green vortex case at a Reynolds number ranging from 100 to 1600. The polynomial order P = 2 (third order accurate) was found to closely match the Direct Navier-Stokes (DNS) results for all Reynolds numbers tested outside of Re = 1600, which had a normalized RMS error of 3.43 × 10-4 in the dissipation rate for a 603 element mesh. The scalability and performance study of the method was then conducted for a Reynolds number of 1600 for polynomials orders from P = 2 to P = 6. The highest order polynomial that was tested (P = 6) was found to have the most efficient scalability using both the MPI and OpenMP implementations.}, } @article {pmid31590559, year = {2019}, author = {Porteous, R and Moreau, DJ and Doolan, CJ}, title = {The effect of the incoming boundary layer thickness on the aeroacoustics of finite wall-mounted square cylinders.}, journal = {The Journal of the Acoustical Society of America}, volume = {146}, number = {3}, pages = {1808}, doi = {10.1121/1.5126693}, pmid = {31590559}, issn = {1520-8524}, abstract = {This paper is concerned with the influence of the incoming wall boundary layer thickness on the noise produced by a square finite wall-mounted cylinder in cross-flow. Acoustic and near wake velocity measurements have been taken in an anechoic wind tunnel for a cylinder in two different near-zero-pressure gradient turbulent boundary layers with thicknesses of 130% and 370% of the cylinder width, W. The cylinders have an aspect ratio of 0.29≤L/W≤22.9 (where L is the cylinder span) and were examined at a Reynolds number, based on width, of ReW = 1.4 × 104. The results presented in this paper demonstrate that increasing the height of the boundary layer delays the production of acoustic tones to higher aspect ratios. The height of the boundary layer changes the balance between upwash and downwash across the cylinder span, resulting in a delayed onset of the shedding regimes and correspondingly, the production of acoustic tones.}, } @article {pmid31590317, year = {2019}, author = {Kawaguchi, M and Fukui, T and Funamoto, K and Tanaka, M and Tanaka, M and Murata, S and Miyauchi, S and Hayase, T}, title = {Viscosity Estimation of a Suspension with Rigid Spheres in Circular Microchannels Using Particle Tracking Velocimetry.}, journal = {Micromachines}, volume = {10}, number = {10}, pages = {}, pmid = {31590317}, issn = {2072-666X}, abstract = {Suspension flows are ubiquitous in industry and nature. Therefore, it is important to understand the rheological properties of a suspension. The key to understanding the mechanism of suspension rheology is considering changes in its microstructure. It is difficult to evaluate the influence of change in the microstructure on the rheological properties affected by the macroscopic flow field for non-colloidal particles. In this study, we propose a new method to evaluate the changes in both the microstructure and rheological properties of a suspension using particle tracking velocimetry (PTV) and a power-law fluid model. Dilute suspension (0.38%) flows with fluorescent particles in a microchannel with a circular cross section were measured under low Reynolds number conditions (Re ≈ 10-4). Furthermore, the distribution of suspended particles in the radial direction was obtained from the measured images. Based on the power-law index and dependence of relative viscosity on the shear rate, we observed that the non-Newtonian properties of the suspension showed shear-thinning. This method will be useful in revealing the relationship between microstructural changes in a suspension and its rheology.}, } @article {pmid31574775, year = {2019}, author = {Singh, G and Lakkaraju, R}, title = {Wall-mounted flexible plates in a two-dimensional channel trigger early flow instabilities.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023109}, doi = {10.1103/PhysRevE.100.023109}, pmid = {31574775}, issn = {2470-0053}, abstract = {A high level of mixing by passive means is a desirable feature in microchannels for various applications, and use of flexible obstacles (or plates) is one of the prime choices in that regard. To gain further insight, we carry out two-dimensional numerical simulations for flow past one or two flexible plates anchored to a channel's opposite walls using a fluid-structure interaction framework. For the inlet flow Reynolds number vs the Strouhal number plane, we observe a sudden flow change from a laminar to a time-periodic vortex shedding state when flexible plates are present in the channel. We found the critical Reynolds number to be Re_{cr}≈370 when a single plate is anchored on the channel wall and Re_{cr}≈290 or even lower when two plates are anchored. With an increase in the inlet flow Reynolds number (up to 3200), we found that vortices detach regularly at the plates' tips, which causes the flow to meander in the channel. In a two-plate anchored configuration, primary vortices generated at the first plate are constrained by the second plate and result in an energetic secondary vortex generation in the downstream side. The overall flow features and the energy dissipation in the channel are mainly controlled by the separation gap between the plates. At high-inlet-flow Reynolds numbers (≥1600), the probability density function (F) of the kinetic energy dissipation in a flexible plate configuration shows a stretched exponential shape in the form F(Z)∼1/sqrt[Z]e^{-pZ^{q}}, where Z is the normalized kinetic energy dissipation and the constants p=0.89 and q=0.86. The observed increase in energy dissipation comes at the cost of an increase in pressure loss in the channel, and we found that the loss is inversely related to the plates' separation gap. From our simulations, we found that if high mixing levels are desired, then two flexible plates anchored to the channel walls is a better choice than a channel flow without obstacles or flow past a single plate. The two-plate configuration with zero separation gap between the plates is best suited to achieve a high mixing level.}, } @article {pmid31574747, year = {2019}, author = {Feng, Y and Boivin, P and Jacob, J and Sagaut, P}, title = {Hybrid recursive regularized lattice Boltzmann simulation of humid air with application to meteorological flows.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023304}, doi = {10.1103/PhysRevE.100.023304}, pmid = {31574747}, issn = {2470-0053}, abstract = {An extended version of the hybrid recursive regularized lattice-Boltzmann model which incorporates external force is developed to simulate humid air flows with phase change mechanisms under the Boussinesq approximation. Mass and momentum conservation equations are solved by a regularized lattice Boltzmann approach well suited for high Reynolds number flows, whereas the energy and humidity related equations are solved by a finite volume approach. Two options are investigated to account for cloud formation in atmospheric flow simulations. The first option considers a single conservation equation for total water and an appropriate invariant variable of temperature. In the other approach, liquid and vapor are considered via two separated equations, and phase transition is accounted for via a relaxation procedure. The obtained models are then systematically validated on four well-established benchmark problems including a double diffusive Rayleigh Bénard convection of humid air, two- and three-dimensional thermal moist rising bubble under convective atmospheric environment, as well as a shallow cumulus convection in the framework of large-eddy simulation.}, } @article {pmid31574698, year = {2019}, author = {Topayev, S and Nouar, C and Bernardin, D and Neveu, A and Bahrani, SA}, title = {Taylor-vortex flow in shear-thinning fluids.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023117}, doi = {10.1103/PhysRevE.100.023117}, pmid = {31574698}, issn = {2470-0053}, abstract = {This paper deals with the Taylor-Couette flow of shear-thinning fluids. It focuses on the first principles understanding of the influence of the viscosity stratification and the nonlinear variation of the effective viscosity μ with the shear rate γ[over ̇] on the flow structure in the Taylor-vortex flow regime. A wide gap configuration (η=0.4) is mainly considered. A weakly nonlinear analysis, using the amplitude expansion method at high order, is adopted as a first approach to study nonlinear effects. For the numerical computation, the shear-thinning behavior is described by the Carreau model. The rheological parameters are varied in a wide range. The results indicate that the flow field undergoes a significant change as shear-thinning effects increase. First, vortices are squeezed against the inner wall and the center of the patterns is shifted axially toward the radial outflow boundaries (z=0,z/λ_{z}=1). This axial shift leads to increasing concentration of vorticity at these positions. The outflow becomes stronger than the inflow and the extent of the inflow zone where the vorticity is low increases acoordingly. Nevertheless, the strength of the vortices relative to the velocity of the inner cylinder is weaker. Second, the pseudo-Nusselt number, ratio of the torque to that obtained in the laminar flow, decreases. Third, higher harmonics become more relevant and grow faster with Reynolds number. Finally, the modification of the viscosity field is described.}, } @article {pmid31574640, year = {2019}, author = {Krämer, A and Wilde, D and Küllmer, K and Reith, D and Foysi, H}, title = {Pseudoentropic derivation of the regularized lattice Boltzmann method.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023302}, doi = {10.1103/PhysRevE.100.023302}, pmid = {31574640}, issn = {2470-0053}, abstract = {The lattice Boltzmann method (LBM) facilitates efficient simulations of fluid turbulence based on advection and collision of local particle distribution functions. To ensure stable simulations on underresolved grids, the collision operator must prevent drastic deviations from local equilibrium. This can be achieved by various methods, such as the multirelaxation time, entropic, quasiequilibrium, regularized, and cumulant schemes. Complementing a part of a unified theoretical framework of these schemes, the present work presents a derivation of the regularized lattice Boltzmann method (RLBM), which follows a recently introduced entropic multirelaxation time LBM by Karlin, Bösch, and Chikatamarla (KBC). It is shown that both methods can be derived by locally maximizing a quadratic Taylor expansion of the entropy function. While KBC expands around the local equilibrium distribution, the RLBM is recovered by expanding entropy around a global equilibrium. Numerical tests were performed to elucidate the role of pseudoentropy maximization in these models. Simulations of a two-dimensional shear layer show that the RLBM successfully reproduces the largest eddies even on a 16×16 grid, while the conventional LBM becomes unstable for grid resolutions of 128×128 and lower. The RLBM suppresses spurious vortices more effectively than KBC. In contrast, simulations of the three-dimensional Taylor-Green and Kida vortices show that KBC performs better in resolving small scale vortices, outperforming the RLBM by a factor of 1.8 in terms of the effective Reynolds number.}, } @article {pmid31574614, year = {2019}, author = {Morris, RG and Rao, M}, title = {Active morphogenesis of epithelial monolayers.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {022413}, doi = {10.1103/PhysRevE.100.022413}, pmid = {31574614}, issn = {2470-0053}, mesh = {Epithelium/*growth & development/metabolism ; Hydrodynamics ; *Models, Biological ; *Morphogenesis ; Thermodynamics ; }, abstract = {During typical early-stage embryo development, single-cell-thick tissues of tightly bound epithelial cells autonomously generate profound changes in their shape, forming the basis of organism anatomy. We report on a (covariant) active-hydrodynamic theory of such monolayer morphogenesis that is closed under its shape-changing dynamics-i.e., the degrees of freedom that encode monolayer geometry appear properly as broken-symmetry variables. In our theory, the salient physics of tissue-scale deformations emerges from a balance between the displacement and/or shear of a low-Reynolds-number embedding fluid (the "yolk") and cell-autonomous stresses, themselves a result of combining apical contractile stresses with an elastic-like mechanical response under the constraint of constant cell volume. The leading-order hydrodynamic instabilities include both passive constrained-buckling and active deformation, which can be further categorized by cell shape changes that are either "squamous to columnar" or "regular-prism to truncated-pyramid." The deformations resulting from the latter qualitatively reproduce in vivo observations of the onset of both mesoderm and posterior midgut invaginations, which take place during gastrulation in the model organism Drosophila melanogaster.}, } @article {pmid31546025, year = {2020}, author = {Phuong, NL and Quang, TV and Khoa, ND and Kim, JW and Ito, K}, title = {CFD analysis of the flow structure in a monkey upper airway validated by PIV experiments.}, journal = {Respiratory physiology & neurobiology}, volume = {271}, number = {}, pages = {103304}, doi = {10.1016/j.resp.2019.103304}, pmid = {31546025}, issn = {1878-1519}, mesh = {Animals ; *Computer Simulation ; Haplorhini ; *Hydrodynamics ; Inhalation Exposure ; Macaca fascicularis ; Male ; Mouth/diagnostic imaging/physiology ; Nasal Cavity/diagnostic imaging/*physiology ; *Particle Size ; Respiratory Mechanics/*physiology ; Rheology/*methods ; }, abstract = {Inhalation exposure to airborne contaminants has adverse effects on humans; however, related research is typically conducted using in vivo/in vitro tests on animals. Extrapolating the test results is complicated by anatomical and physiological differences between animals and humans and a lack of understanding of the transport mechanism inside their respective respiratory tracts. This study determined the detailed air-flow structure in the upper airway of a monkey. A steady computational fluid dynamics simulation, which was validated by previous particle image velocimetry measurements, was adopted for flow rates of 4 L/min and 10 L/min to analyze the flow structure from the nasal/oral cavities to the trachea region in a monkey airway model. The low Reynolds number type k-ε model provided a reasonably accurate prediction of the airflow in a monkey upper airway. Furthermore, it was confirmed that large velocity gradients were generated in the nasal vestibule and larynx regions, as well as increased turbulent air kinetic energy and wall sheer stress.}, } @article {pmid31542476, year = {2020}, author = {Shi, L and Wu, J and Krenn, HW and Yang, Y and Yan, S}, title = {Temporal model of fluid-feeding mechanisms in a long proboscid orchid bee compared to the short proboscid honey bee.}, journal = {Journal of theoretical biology}, volume = {484}, number = {}, pages = {110017}, doi = {10.1016/j.jtbi.2019.110017}, pmid = {31542476}, issn = {1095-8541}, abstract = {Bees (Apidae) are flower-visiting insects that possess highly efficient mouthparts for the ingestion of nectar and other sucrose fluids. Their mouthparts are composed of mandibles and a tube-like proboscis. The proboscis forms a food canal, which encompasses a protrusible and hairy tongue to load and imbibe nectar, representing a fluid-feeding technique with a low Reynolds number. The western honey bee, Apis mellifera ligustica, can rhythmically erect the tongue microtrichia to regulate the glossal shape, achieving a tradeoff between nectar intake rate and viscous drag. Neotropical orchid bees (Euglossa imperialis) possess a proboscis longer than the body and combines this lapping-sucking mode of fluid-feeding with suction feeding. This additional technique of nectar uptake may have different biophysics. In order to reveal the effect of special structures of mouthparts in terms of feeding efficiency, we build a temporal model for orchid bees considering fluid transport in multi-states including active suction, tongue protraction and viscous dipping. Our model indicates that the dipping technique employed by honey bees can contribute to more than seven times the volumetric and energetic intake rate at a certain nectar concentration compared with the combined mode used by orchid bees. The high capability of the honey bee's proboscis to ingest nectar may inspire micropumps for transporting viscous liquid with higher efficiency.}, } @article {pmid31538112, year = {2019}, author = {Onyiriuka, EJ and Ighodaro, OO and Adelaja, AO and Ewim, DRE and Bhattacharyya, S}, title = {A numerical investigation of the heat transfer characteristics of water-based mango bark nanofluid flowing in a double-pipe heat exchanger.}, journal = {Heliyon}, volume = {5}, number = {9}, pages = {e02416}, pmid = {31538112}, issn = {2405-8440}, abstract = {In this study, the heat transfer characteristics of a new class of nanofluids made from mango bark was numerically simulated and studied during turbulent flow through a double pipe heat exchanger. A range of volume fractions was considered for a particle size of 100 nm. A two-phase flow was considered using the mixture model. The mixture model governing equations of continuity, momentum, energy and volume fraction were solved using the finite-volume method. The results showed an increase of the Nusselt number by 68% for a Reynolds number of 5,000 and 45% for a Reynolds number of 13 000, and the heat transfer coefficient of the nanofluid was about twice that of the base fluid. In addition, the Nusselt number decreased by an average value of 0.76 with an increase of volume fraction by 1%. It was also found that there was a range of Reynolds numbers in which the trend of the average heat transfer coefficient of the nanofluid was completely reversed, and several plots showing zones of higher heat transfer which if taken advantage of in design will lead to higher heat transfer while avoiding other zones that have low heat transfer. It is hoped that these results will influence the thermal design of new heat exchangers.}, } @article {pmid31534269, year = {2019}, author = {Blumenthal, BT and Elmiligui, AA and Geiselhart, KA and Campbell, RL and Maughmer, MD and Schmitz, S}, title = {Computational Investigation of a Boundary-Layer Ingesting Propulsion System for the Common Research Model.}, journal = {Journal of aircraft}, volume = {55}, number = {3}, pages = {1141-1153}, doi = {10.2514/1.C034454}, pmid = {31534269}, issn = {0021-8669}, support = {//Langley Research Center NASA/United States ; N-999999//Intramural NASA/United States ; }, abstract = {The present paper examines potential propulsive and aerodynamic benefits of integrating a Boundary-Layer Ingestion (BLI) propulsion system into the Common Research Model (CRM) geometry and the NASA Tetrahedral Unstructured Software System (TetrUSS). The Numerical Propulsion System Simulation (NPSS) environment is used to generate engine conditions for Computational Fluid Dynamics (CFD) analyses. Improvements to the BLI geometry are made using the Constrained Direct Iterative Surface Curvature (CDISC) design method. Potential benefits of the BLI system relating to cruise propulsive power are quantified using a power balance method, and a comparison to the baseline case is made. Iterations of the BLI geometric design are shown, and improvements between subsequent BLI designs are presented. Simulations are conducted for a cruise flight condition of Mach 0.85 at an altitude of 38,500 feet, with Reynolds number of 40 million based on mean aerodynamic chord and an angle of attack of 2° for all geometries. Results indicate an 8% reduction in engine power requirements at cruise for the BLI configuration compared to the baseline geometry. Small geometric alterations of the aft portion of the fuselage using CDISC has been shown to marginally increase the benefit from boundary-layer ingestion further, resulting in an 8.7% reduction in power requirements for cruise, as well as a drag reduction of approximately twelve counts over the baseline geometry.}, } @article {pmid31533305, year = {2019}, author = {Wang, R and Wang, J and Yuan, W}, title = {Analysis and Optimization of a Microchannel Heat Sink with V-Ribs Using Nanofluids for Micro Solar Cells.}, journal = {Micromachines}, volume = {10}, number = {9}, pages = {}, pmid = {31533305}, issn = {2072-666X}, support = {11572107, 51376055//National Natural Science Foundation of China/ ; }, abstract = {It is crucial to control the temperature of solar cells for enhancing efficiency with the increasing power intensity of multiple photovoltaic systems. In order to improve the heat transfer efficiency, a microchannel heat sink (MCHS) with V-ribs using a water-based nanofluid as a coolant for micro solar cells was designed. Numerical simulations were carried out to investigate the flows and heat transfers in the MCHS when the Reynolds number ranges from 200 to 1000. The numerical results showed that the periodically arranged V-ribs can interrupt the thermal boundary, induce chaotic convection, increase heat transfer area, and subsequently improve the heat transfer performance of a MCHS. In addition, the preferential values of the geometric parameters of V-ribs and the physical parameters of the nanofluid were obtained on the basis of the Nusselt numbers at identical pump power. For MCHS with V-ribs on both the top and bottom wall, preferential values of V-rib are rib width d / W = 1 , flare angle α = 75 ° , rib height h r / H = 0.3 , and ratio of two slant sides b / a = 0.75 , respectively. This can provide sound foundations for the design of a MCHS in micro solar cells.}, } @article {pmid31533232, year = {2019}, author = {Tang, L and Pan, X and Feng, J and Pu, X and Liang, R and Li, R and Li, K}, title = {Experimental Investigation on the Relationship Between COD Degradation and Hydrodynamic Conditions in Urban Rivers.}, journal = {International journal of environmental research and public health}, volume = {16}, number = {18}, pages = {}, pmid = {31533232}, issn = {1660-4601}, mesh = {*Biological Oxygen Demand Analysis ; China ; Cities ; Hydrodynamics ; Rivers/*chemistry ; Water Pollution, Chemical/*analysis ; *Water Quality ; }, abstract = {Due to extensive pollution and the relatively weak flow replacement in urban rivers, determining how to fully utilize the self-purification abilities of water bodies for water quality protection has been a complex and popular topic of research and social concern. Organic pollution is an important type of urban river pollution, and COD (chemical oxygen demand) is one of the key pollution factors. Currently, there is a lack of research on the relationship between COD degradation and the flow characteristics of urban rivers. In this paper, COD degradation experiments were conducted in an annular flume with Jinjiang River water at controlled flow velocities and the COD degradation coefficients under different hydraulic conditions were analyzed. A good correlation was observed between the degradation coefficient and hydraulic conditions. According to dimensional analysis, the relationship between the COD degradation coefficient and hydraulic conditions such as the flow velocity, water depth, Reynolds number (Re), and Froude number (Fr) was established as K COD = 86400 u h F r 0.8415 R e - 1.2719 + 0.258 . The COD degradation coefficients of the Chishui River in Guizhou Province ranged from 0.175-0.373 1/d based on this formula, and the field-measured values varied from 0.234-0.463 1/d. The error in the formula ranged from 5.4-25.3%. This study provides a scientific basis for the prediction of the COD degradation coefficients of urban rivers.}, } @article {pmid31533091, year = {2019}, author = {Wang, C and Ren, F and Tang, H}, title = {Enhancing propulsion performance of a flexible heaving foil through dynamically adjusting its flexibility.}, journal = {Bioinspiration & biomimetics}, volume = {14}, number = {6}, pages = {064002}, doi = {10.1088/1748-3190/ab45d9}, pmid = {31533091}, issn = {1748-3190}, mesh = {Algorithms ; Animals ; Biomechanical Phenomena ; Biomimetics/instrumentation/*methods ; Fishes/*physiology ; Hydrodynamics ; Models, Biological ; Robotics/instrumentation/methods ; }, abstract = {This study investigates how dynamically adjusting the bending stiffness of a heaving foil affects its propulsion performance in a flow of Reynolds number 200. The foil is forced to oscillate sinusoidally at the leading edge, and its bending stiffness is tuned in a square-wave manner. Such a fluid-structure interaction (FSI) problem is explored using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. The results reveal that when the lower and upper bounds of the foil's time-dependent bending stiffness are moderate, the net thrust can be evidently enhanced compared to those in the corresponding constant-bending-stiffness cases, while the propulsion efficiency is not apparently ameliorated. The most significant enhancement is observed when the bending stiffness has lower and upper bounds of the same duration (i.e. a duty cycle of 1/2) and also it remains at the lower bound during stroke reversals (corresponding to an actuation phase angle of [Formula: see text]). When the two bounds simultaneously increase or decrease, however, dynamically adjusting the bending stiffness fails to improve the net thrust. Through this study, competitions among various forces/moments, including the inertial force, tension force, bending moment and fluid loading, acting on the foil and their influences on the foil's dynamics are also unveiled.}, } @article {pmid31511924, year = {2019}, author = {Acosta-Avalos, D and Rodrigues, E}, title = {On the motion of magnetotactic bacteria: theoretical predictions and experimental observations.}, journal = {European biophysics journal : EBJ}, volume = {48}, number = {8}, pages = {691-700}, pmid = {31511924}, issn = {1432-1017}, mesh = {*Bacteria ; *Bacterial Physiological Phenomena ; Biomechanical Phenomena ; *Magnetic Fields ; *Models, Biological ; *Movement ; }, abstract = {The movement of magnetotactic bacteria is done in a viscous media in the low Reynolds number regime. In the present research, the simple model for magnetotactic bacteria motion, proposed by Nogueira and Lins de Barros (Eur Biophys J 24:13-21, 1995), was used to numerically simulate their trajectory. The model was done considering a spherical bacterium with a single flagellum and a magnetic moment positioned in the sphere center and parallel to the flagella. The numerical solution shows that the trajectory is a cylindrical helix and that the body Euler angles have linear dependencies on time. Using that information, analytical expressions were obtained for the first time for the center-of-mass coordinates, showing that the trajectories are helixes oriented to the magnetic field direction. They also show that the magnetic moment does not align to the magnetic field, but it precesses around it, being fully oriented only for very high magnetic fields. The analytical solution obtained permits to relate for the first time the flagellar force to the axial velocity and helical radius. Trajectories of uncultivated magnetotactic bacteria were registered in video and the coordinates were obtained for several bacteria in different magnetic fields. The trajectories showed to be a complex mixture of two oscillating functions: one with frequency lower than 5 Hz and the other one with frequency higher than 10 Hz. The simple model of Nogueira and Lins de Barros shows to be incomplete, because is unable to explain the trajectories composed of two oscillating functions observed in uncultivated magnetotactic bacteria.}, } @article {pmid31499817, year = {2019}, author = {Falsaperla, P and Giacobbe, A and Mulone, G}, title = {Nonlinear stability results for plane Couette and Poiseuille flows.}, journal = {Physical review. E}, volume = {100}, number = {1-1}, pages = {013113}, doi = {10.1103/PhysRevE.100.013113}, pmid = {31499817}, issn = {2470-0053}, abstract = {We prove that the plane Couette and Poiseuille flows are nonlinearly stable if the Reynolds number is less than Re_{Orr}(2π/(λsinθ))/sinθ when a perturbation is a tilted perturbation in the direction x^{'} which forms an angle θ∈(0,π/2] with the direction i of the basic motion and does not depend on x^{'}. Re_{Orr} is the critical Orr-Reynolds number for spanwise perturbations which is computed for wave number 2π/(λsinθ), with λ being any positive wavelength. By taking the minimum with respect to λ, we obtain the critical energy Reynolds number for a fixed inclination angle and any wavelength: for plane Couette flow, it is Re_{Orr}=44.3/sinθ, and for plane Poiseuille flow, it is Re_{Orr}=87.6/sinθ (in particular, for θ=π/2 we have the classical values Re_{Orr}=44.3 for plane Couette flow and Re_{Orr}=87.6 for plane Poiseuille flow). Here the nondimensional interval between the planes bounding the channel is [-1,1]. In particular, these results improve those obtained by Joseph, who found for streamwise perturbations a critical nonlinear value of 20.65 in the plane Couette case, and those obtained by Joseph and Carmi who found the value 49.55 for plane Poiseuille flow for streamwise perturbations. If we fix some wavelengths from the experimental data and the numerical simulations, the critical Reynolds numbers that we obtain are in a very good agreement both with the the experiments and the numerical simulation. These results partially solve the Couette-Sommerfeld paradox.}, } @article {pmid31499421, year = {2019}, author = {Shah, F and Khan, MI and Hayat, T and Khan, MI and Alsaedi, A and Khan, WA}, title = {Theoretical and mathematical analysis of entropy generation in fluid flow subject to aluminum and ethylene glycol nanoparticles.}, journal = {Computer methods and programs in biomedicine}, volume = {182}, number = {}, pages = {105057}, doi = {10.1016/j.cmpb.2019.105057}, pmid = {31499421}, issn = {1872-7565}, mesh = {Aluminum/*chemistry ; *Entropy ; Ethylene Glycol/*chemistry ; *Hydrodynamics ; *Models, Theoretical ; Nanoparticles/*chemistry ; }, abstract = {BACKGROUND: Here we have conducted a magnetohydrodynamic (MHD) flow of viscous material with alumina water and ethylene glycol over a stretched surface. The flow is discussed with and without effective Prandtl number. MHD liquid is considered. Electric field is absent. Effect of uniform magnetic field is taken in the vertical direction to the surface. Influence of thermal radiation as well as Joule heating are taken into account for both aluminum oxide-water and aluminum oxide-Ethylene glycol nanofluids. Velocity slip and melting heat effects are considered.

METHODS: The nonlinear flow expressions are numerically solved via ND-solve technique (built-in-Shooting).

RESULTS: The physical impacts of flow variables like mixed convection parameter, magnetic parameter, Reynold number, Eckert number, melting parameter and heat source/sink parameter are graphically discussed. Moreover, entropy generation (irreversibility) and Bejan number are discussed graphically through various flow variables. Physical quantities like skin friction coefficient and Sherwood and Nusselt numbers are numerically calculated and discussed through Tables.

CONCLUSIONS: Impact of magnetic and slip parameters on the velocity field show decreasing behavior for both effective and without effective Prandtl number. Temperature field increases for both effective and without effective Prandtl number for higher values of magnetic and radiative parameters. Entropy number is an increasing function of Reynolds number while Bejan number shows opposite impact against Reynolds number. Moreover, heat transfer rate upsurges versus larger melting and radiative parameter.}, } @article {pmid31481279, year = {2019}, author = {DeJonckere, P and Lebacq, J}, title = {Intraglottal Aerodynamics at Vocal Fold Vibration Onset.}, journal = {Journal of voice : official journal of the Voice Foundation}, volume = {}, number = {}, pages = {}, doi = {10.1016/j.jvoice.2019.08.002}, pmid = {31481279}, issn = {1873-4588}, abstract = {The most frequently observed type of voice onset in spontaneous speech in normal subjects is the soft onset, and it may be considered as the "physiological" onset. It starts from an immobile narrow glottal slit crossed by a continuous airflow, and then a few oscillations (even a single one in some cases) precede the first glottal closure. It is a transient event, during which the acting forces, lung pressure, intraglottal pressure, myoelastic tension of the vocal fold (VF) oscillator and inertance of the supraglottal vocal tract, interact to progressively reach the steady state of a sustained oscillation. Combined measurements of flow, area, and pressure provide a detailed qualitative and quantitative analysis of the intraglottal mechanical events at the precise moment of starting oscillation in a physiological (soft or soft/breathy) onset. Our in vivo measurements of airflow and glottal area show that the very first oscillation occurs exactly at the time when turbulence appears at the level of the glottal narrowing, ie, when the Reynolds number reaches its critical value. The turbulence may be assumed to trigger an oscillator consisting in the ensemble of the VFs and the air of the vocal tract, which is known to be weakly damped. Turbulence can act here as an aspecific flick, triggering the oscillator, the frequency of oscillation being determined by its mechanical properties. Furthermore, the first noticeable glottal oscillations are sinusoidal: the VFs are neither steeply sucked together by a negative Bernoulli pressure, nor burst apart by the lung pressure. Our measurements show that, at the critical time, the rising positive lung pressure is balanced by the rising negative Bernoulli pressure generated by the transglottal flow.}, } @article {pmid31480452, year = {2019}, author = {Tsai, CD and Lin, XY}, title = {Experimental Study on Microfluidic Mixing with Different Zigzag Angles.}, journal = {Micromachines}, volume = {10}, number = {9}, pages = {}, pmid = {31480452}, issn = {2072-666X}, support = {108-2321-B-009-004-//Ministry of Science and Technology, Taiwan/ ; 108-2221-E-009-107-//Ministry of Science and Technology, Taiwan/ ; 108-2218-E-009-013-//Ministry of Science and Technology, Taiwan/ ; }, abstract = {This paper presents experimental investigations of passive mixing in a microfluidic channel with different zigzag angles. Zigzag channel is commonly used for microfluidic mixing because it does not need an additional control unit and can be easily implemented in a lab-on-a-chip system. In this work, microfluidic channels with six different zigzag angles, from θ = 0° to θ = 75°, are tested under ten different flow rates corresponding to Reynolds number from 0.309 to 309. Two colored liquids are mixed with the zigzag channels and mixing performance is evaluated based on the color of the pixels on the region of interest from captured images. According to the results, we found that the mixing performance is almost independent of the zigzag angle in the low-speed regime where its Reynolds number is less than 4. The mixing became very much depending on the zigzag angle in the high-speed regime where its Reynolds number is greater than 100. Microfluidic mixing is needed for Lab-on-a-chip applications in both low flow speed, such as medium perfusion for cell culture, and high flow speed, such as high-speed sensing on a point-of-care device. This work is aimed to provide practical information on zigzag mixing for chip design and applications.}, } @article {pmid31473843, year = {2020}, author = {Waheed, W and Alazzam, A and Al-Khateeb, AN and Abu-Nada, E}, title = {Dissipative particle dynamics for modeling micro-objects in microfluidics: application to dielectrophoresis.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {1}, pages = {389-400}, doi = {10.1007/s10237-019-01216-3}, pmid = {31473843}, issn = {1617-7940}, mesh = {*Algorithms ; Animals ; *Electrophoresis ; Erythrocytes/physiology ; Humans ; *Microfluidics ; *Models, Theoretical ; }, abstract = {The dissipative particle dynamics (DPD) technique is employed to model the trajectories of micro-objects in a practical microfluidic device. The simulation approach is first developed using an in-house Fortran code to model Stokes flow at Reynolds number of 0.01. The extremely low Reynolds number is achieved by adjusting the DPD parameters, such as force coefficients, thermal energies of the particles, and time steps. After matching the numerical flow profile with the analytical results, the technique is developed further to simulate the deflection of micro-objects under the effect of a deflecting external force in a rectangular microchannel. A mapping algorithm is introduced to establish the scaling relationship for the deflecting force between the physical device and the DPD domain. Dielectrophoresis is studied as a case study for the deflecting force, and the trajectory of a single red blood cell under the influence of the dielectrophoretic force is simulated. The device is fabricated using standard microfabrication techniques, and the experiments involving a dilute sample of red blood cells are performed at two different cases of the actuation voltage. Good agreement between the numerical and experimental results is achieved.}, } @article {pmid31473190, year = {2019}, author = {Chaput, R and Majoris, JE and Buston, PM and Paris, CB}, title = {Hydrodynamic and biological constraints on group cohesion in plankton.}, journal = {Journal of theoretical biology}, volume = {482}, number = {}, pages = {109987}, doi = {10.1016/j.jtbi.2019.08.018}, pmid = {31473190}, issn = {1095-8541}, mesh = {Animals ; Behavior, Animal/*physiology ; Coral Reefs ; *Ecosystem ; Environment ; Fishes/growth & development/*physiology ; *Hydrodynamics ; Larva ; *Mass Behavior ; Plankton/*physiology ; Social Behavior ; Swimming/physiology ; Viscosity ; }, abstract = {The dynamics of plankton in the ocean are determined by biophysical interactions. Although physics and biotic behaviors are known to influence the observed patchiness of planktonic populations, it is still unclear how much, and if, group behavior contributes to this biophysical interaction. Here, we demonstrate how simple rules of behavior can enhance or inhibit active group cohesion in plankton in a turbulent environment. In this study, we used coral-reef fish larvae as a model to investigate the interaction between microscale turbulence and planktonic organisms. We synthesized available information on the swimming speeds and sizes of reef fish larvae, and developed a set of equations to investigate the effects of viscosity and turbulence on larvae dispersion. We then calculated the critical dispersion rates for three different swimming strategies - cruise, random-walk, and pause-travel - to determine which strategies could facilitate group cohesion during dispersal. Our results indicate that swimming strategies and migration to low-turbulence regions are the key to maintaining group cohesion, suggesting that many reef fish species have the potential to remain together, from hatching to settlement. In addition, larvae might change their swimming strategies to maintain group cohesion, depending on environmental conditions and/or their ontogenic stage. This study provides a better understanding of the hydrodynamic and biological constraints on group formation and cohesion in planktonic organisms, and reveals a wide range of conditions under which group formation may occur.}, } @article {pmid31472558, year = {2019}, author = {Zhang, C and Sanjose, M and Moreau, S}, title = {Aeolian noise of a cylinder in the critical regime.}, journal = {The Journal of the Acoustical Society of America}, volume = {146}, number = {2}, pages = {1404}, doi = {10.1121/1.5122185}, pmid = {31472558}, issn = {1520-8524}, abstract = {The noise from the flow around a circular cylinder in the critical regime is investigated by combining a compressible wall-resolved large eddy simulation and a Ffowcs Williams and Hawkings analogy on solid and porous surfaces. This simulation is validated by comparing several flow parameters with previous experimental and numerical data in the same flow regime. Significantly reduced drag and increased vortex shedding Strouhal number (0.33) are observed. Two slightly asymmetric laminar separation bubbles (LSBs) on the cylinder surface at about 100° are shown to trigger turbulence through Kelvin-Helmholtz (KH) shear-layer instability. The latter contributes to a narrowband hump in the wall-pressure fluctuations with a tone at a Strouhal number of 27, which can be as intense as the dominant vortex shedding tone. The ratio of the corresponding Strouhal numbers is consistent with the proposed variation with the Reynolds number by Prasad and Williamson [(1997). J. Fluid Mech. 333, 375-402]. The dominant far-field noise source is still the vortex shedding dipolar tone radiating mostly at 90°. Yet, two additional broadband noise sources are evidenced in the wake, one at low frequencies caused by the wake oscillation and another one at high frequencies caused by the KH instability mostly directly toward the LSB locations.}, } @article {pmid31462974, year = {2019}, author = {Gholampour, S and Bahmani, M and Shariati, A}, title = {Comparing the Efficiency of Two Treatment Methods of Hydrocephalus: Shunt Implantation and Endoscopic Third Ventriculostomy.}, journal = {Basic and clinical neuroscience}, volume = {10}, number = {3}, pages = {185-198}, pmid = {31462974}, issn = {2008-126X}, abstract = {Introduction: Hydrocephalus is one of the most common diseases in children, and its treatment requires brain operation. However, the pathophysiology of the disease is very complicated and still unknown.

Methods: Endoscopic Third Ventriculostomy (ETV) and Ventriculoperitoneal Shunt (VPS) implantation are among the common treatments of hydrocephalus. In this study, Cerebrospinal Fluid (CSF) hydrodynamic parameters and efficiency of the treatment methods were compared with numerical simulation and clinical follow-up of the treated patients.

Results: Studies have shown that in patients under 19 years of age suffering from hydrocephalus related to a Posterior Fossa Brain Tumor (PFBT), the cumulative failure rate was 21% and 29% in ETV and VPS operation, respectively. At first, the ETV survival curve shows a sharp decrease and after two months it gets fixed while VPS curve makes a gradual decrease and reaches to a level lower than ETV curve after 5.7 months. Post-operative complications in ETV and VPS methods are 17% and 31%, respectively. In infants younger than 12 months with hydrocephalus due to congenital Aqueduct Stenosis (AS), and also in the elderly patients suffering from Normal Pressure Hydrocephalus (NPH), ETV is a better treatment option. Computer simulations show that the maximum CSF pressure is the most reliable hydrodynamic index for the evaluation of the treatment efficacy in these patients. After treatment by ETV and shunt methods, CSF pressure decreases about 9 and 5.3 times, respectively and 2.5 years after shunt implantation, this number returns to normal range.

Conclusion: In infants with hydrocephalus, initial treatment by ETV was more reasonable than implanting the shunt. In adult with hydrocephalus, the initial failure in ETV occurred sooner compared to shunt therapy; however, ETV was more efficient.}, } @article {pmid31446522, year = {2020}, author = {Foo, YY and Pant, S and Tay, HS and Imangali, N and Chen, N and Winkler, C and Yap, CH}, title = {4D modelling of fluid mechanics in the zebrafish embryonic heart.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {1}, pages = {221-232}, doi = {10.1007/s10237-019-01205-6}, pmid = {31446522}, issn = {1617-7940}, mesh = {Algorithms ; Animals ; Blood Flow Velocity ; Computer Simulation ; Embryo, Nonmammalian/*physiology ; Heart/diagnostic imaging/*embryology/*physiology ; *Hydrodynamics ; *Models, Cardiovascular ; Myocardial Contraction ; Ventricular Function ; Zebrafish/*embryology ; }, abstract = {Abnormal blood flow mechanics can result in pathological heart malformation, underlining the importance of understanding embryonic cardiac fluid mechanics. In the current study, we performed image-based computational fluid dynamics simulation of the zebrafish embryonic heart ventricles and characterized flow mechanics, organ dynamics, and energy dynamics in detail. 4D scans of 5 days post-fertilization embryonic hearts with GFP-labelled myocardium were acquired using line-scan focal modulation microscopy. This revealed that the zebrafish hearts exhibited a wave-like contractile/relaxation motion from the inlet to the outlet during both systole and diastole, which we showed to be an energy efficient configuration. No impedance pumping effects of pressure and velocity waves were observed. Due to its tube-like configuration, inflow velocities were higher near the inlet and smaller at the outlet and vice versa for outflow velocities. This resulted in an interesting spatial wall shear stress (WSS) pattern where WSS waveforms near the inlet and those near the outlet were out of phase. There was large spatial variability in WSS magnitudes. Peak WSS was in the range of 47.5-130 dyne/cm2 at the inflow and outflow tracts, but were much smaller, in the range of 4-11 dyne/cm2, in the mid-ventricular segment. Due to very low Reynolds number and the highly viscous environment, intraventricular pressure gradients were high, suggesting substantial energy losses of flow through the heart.}, } @article {pmid31431815, year = {2019}, author = {Rackus, DG and Riedel-Kruse, IH and Pamme, N}, title = {"Learning on a chip:" Microfluidics for formal and informal science education.}, journal = {Biomicrofluidics}, volume = {13}, number = {4}, pages = {041501}, pmid = {31431815}, issn = {1932-1058}, abstract = {Microfluidics is a technique for the handling of small volumes of liquids on the order of picoliters to nanoliters and has impact for miniaturized biomedical science and fundamental research. Because of its multi- and interdisciplinary nature (i.e., combining the fields of biology, chemistry, physics, and engineering), microfluidics offers much potential for educational applications, both at the university level as well as primary and secondary education. Microfluidics is also an ideal "tool" to enthuse and educate members of the general public about the interdisciplinary aspects of modern sciences, including concepts of science, technology, engineering, and mathematics subjects such as (bio)engineering, chemistry, and biomedical sciences. Here, we provide an overview of approaches that have been taken to make microfluidics accessible for formal and informal learning. We also point out future avenues and desired developments. At the extreme ends, we can distinguish between projects that teach how to build microfluidic devices vs projects that make various microscopic phenomena (e.g., low Reynolds number hydrodynamics, microbiology) accessible to learners and the general public. Microfluidics also enables educators to make experiments low-cost and scalable, and thereby widely accessible. Our goal for this review is to assist academic researchers working in the field of microfluidics and lab-on-a-chip technologies as well as educators with translating research from the laboratory into the lecture hall, teaching laboratory, or public sphere.}, } @article {pmid31421603, year = {2019}, author = {Hayat, T and Aslam, N and Ijaz Khan, M and Imran Khan, M and Alsaedi, A}, title = {MHD peristaltic motion of Johnson-Segalman fluid in an inclined channel subject to radiative flux and convective boundary conditions.}, journal = {Computer methods and programs in biomedicine}, volume = {180}, number = {}, pages = {104999}, doi = {10.1016/j.cmpb.2019.104999}, pmid = {31421603}, issn = {1872-7565}, mesh = {Algorithms ; Body Fluids/physiology ; Elasticity ; Humans ; *Hydrodynamics ; *Models, Biological ; Peristalsis/*physiology ; Rheology ; }, abstract = {BACKGROUND: In abundant of a digestive tract like smooth muscle tissue, human gastrointestinal tract contracts in sequence to generate a peristaltic wave, which pushes a food along the tract. The peristaltic motion contains circular relaxation smooth muscles, then their shrinkage (contraction) behind the chewed material to keep it from moving backward, then longitudinal contraction to shove it ahead. Therefore, we have conducted a theoretical investigation on peristaltic transport in flow of Johnson-Segalman liquid subject to inclined magnetic field. The energy equation is developed with extra heat transport assumptions like thermal radiative flux and dissipation. The channel walls are heated convectively.

METHODS: Dimensionless problems subject to small Reynolds number and long wavelength are tackled. Perturbation technique is implemented for small Weissenberg number.

RESULTS: The physical importance of involved parameters that directly affect the heat transfer rate temperature and velocity. The pertinent variables are amplitude ratio, wave number, Reynolds number, Hartman number, Prandtl number, Weissenberg number, thermal radiative heat flux, Biot number, elasticity variables and Froude number are graphically discussed. The obtained outcome shows that the velocity field increases against higher values of elasticity variables but velocity the material decays through higher fluid parameter. Temperature field declines through higher Hartman number. Furthermore, it is also examined that the heat transfer rate decays against rising Hartman number.

CONCLUSIONS: The impact of complaint walls on radiative peristaltic transport of Johnson-Segalman liquid in symmetric channel subject to inclined angle. The influence of Johnson-Segalman variable on the velocity field shows decreasing behavior. Velocity also declines against larger Hartman number. Temperature and heat transfer rate boosts through rising values of E1 E2 while decays versus larger E3. Furthermore, reduction in heat transfer coefficient is observed when the values of α and Br are increased.}, } @article {pmid31421600, year = {2019}, author = {Tanveer, A and Khan, M and Salahuddin, T and Malik, MY}, title = {Numerical simulation of electroosmosis regulated peristaltic transport of Bingham nanofluid.}, journal = {Computer methods and programs in biomedicine}, volume = {180}, number = {}, pages = {105005}, doi = {10.1016/j.cmpb.2019.105005}, pmid = {31421600}, issn = {1872-7565}, mesh = {*Electroosmosis ; Hydrodynamics ; Models, Statistical ; *Nanoparticles ; Peristalsis/*physiology ; Rheology ; Solutions/chemistry ; Thermal Conductivity ; }, abstract = {The effects of slip condition and Joule heating on the peristaltic flow of Bingham nanofluid are investigated. The flow is taken in a porous channel with elastic walls. Mathematical formulation is presented under the assumption of long wavelength and small Reynolds number. The transformed equations for the flow are solved to seek values for the nanoparticles velocity, concentration and temperature along the channel length. Graphs are plotted to evaluate the behavior of various physical parameters on flow quantities in both slip and no-slip cases. The main features of the physical parameters are highlighted on the inclined non uniform channel. The results show an increment in velocity with rise in inclination and porosity while it reduces with magnetic field. Moreover, nanofluid favors the heat transfer and decline the concentration.}, } @article {pmid31417749, year = {2019}, author = {Lambert, WB and Stanek, MJ and Gurka, R and Hackett, EE}, title = {Leading-edge vortices over swept-back wings with varying sweep geometries.}, journal = {Royal Society open science}, volume = {6}, number = {7}, pages = {190514}, pmid = {31417749}, issn = {2054-5703}, abstract = {Micro air vehicles are used in a myriad of applications, such as transportation and surveying. Their performance can be improved through the study of wing designs and lift generation techniques including leading-edge vortices (LEVs). Observation of natural fliers, e.g. birds and bats, has shown that LEVs are a major contributor to lift during flapping flight, and the common swift (Apus apus) has been observed to generate LEVs during gliding flight. We hypothesize that nonlinear swept-back wings generate a vortex in the leading-edge region, which can augment the lift in a similar manner to linear swept-back wings (i.e. delta wing) during gliding flight. Particle image velocimetry experiments were performed in a water flume to compare flow over two wing geometries: one with a nonlinear sweep (swift-like wing) and one with a linear sweep (delta wing). Experiments were performed at three spanwise planes and three angles of attack at a chord-based Reynolds number of 26 000. Streamlines, vorticity, swirling strength, and Q-criterion were used to identify LEVs. The results show similar LEV characteristics for delta and swift-like wing geometries. These similarities suggest that sweep geometries other than a linear sweep (i.e. delta wing) are capable of creating LEVs during gliding flight.}, } @article {pmid31411455, year = {2020}, author = {Brown, AI and Sivak, DA}, title = {Theory of Nonequilibrium Free Energy Transduction by Molecular Machines.}, journal = {Chemical reviews}, volume = {120}, number = {1}, pages = {434-459}, doi = {10.1021/acs.chemrev.9b00254}, pmid = {31411455}, issn = {1520-6890}, abstract = {Biomolecular machines are protein complexes that convert between different forms of free energy. They are utilized in nature to accomplish many cellular tasks. As isothermal nonequilibrium stochastic objects at low Reynolds number, they face a distinct set of challenges compared with more familiar human-engineered macroscopic machines. Here we review central questions in their performance as free energy transducers, outline theoretical and modeling approaches to understand these questions, identify both physical limits on their operational characteristics and design principles for improving performance, and discuss emerging areas of research.}, } @article {pmid31406979, year = {2019}, author = {Berg, O and Singh, K and Hall, MR and Schwaner, MJ and Müller, UK}, title = {Thermodynamics of the Bladderwort Feeding Strike-Suction Power from Elastic Energy Storage.}, journal = {Integrative and comparative biology}, volume = {59}, number = {6}, pages = {1597-1608}, doi = {10.1093/icb/icz144}, pmid = {31406979}, issn = {1557-7023}, mesh = {Biomechanical Phenomena ; Energy Transfer/*physiology ; *Food Chain ; Lamiales/*physiology ; Thermodynamics ; }, abstract = {The carnivorous plant bladderwort exemplifies the use of accumulated elastic energy to power motion: respiration-driven pumps slowly load the walls of its suction traps with elastic energy (∼1 h). During a feeding strike, this energy is released suddenly to accelerate water (∼1 ms). However, due to the traps' small size and concomitant low Reynolds number, a significant fraction of the stored energy may be dissipated as viscous friction. Such losses and the mechanical reversibility of Stokes flow are thought to degrade the feeding success of other suction feeders in this size range, such as larval fish. In contrast, triggered bladderwort traps are generally successful. By mapping the energy budget of a bladderwort feeding strike, we illustrate how this smallest of suction feeders can perform like an adult fish.}, } @article {pmid31394810, year = {2019}, author = {Alazzam, A and Al-Khaleel, M and Riahi, MK and Mathew, B and Gawanmeh, A and Nerguizian, V}, title = {Dielectrophoresis Multipath Focusing of Microparticles through Perforated Electrodes in Microfluidic Channels.}, journal = {Biosensors}, volume = {9}, number = {3}, pages = {}, pmid = {31394810}, issn = {2079-6374}, support = {CIRA-2019-014//Khalifa University of Science, Technology and Research/ ; }, mesh = {Biosensing Techniques ; Electrodes ; Electrophoresis/methods ; Microfluidics/instrumentation/*methods ; *Models, Theoretical ; Particle Size ; Polystyrenes/analysis ; Silicon Dioxide/analysis ; }, abstract = {This paper presents focusing of microparticles in multiple paths within the direction of the flow using dielectrophoresis. The focusing of microparticles is realized through partially perforated electrodes within the microchannel. A continuous electrode on the top surface of the microchannel is considered, while the bottom side is made of a circular meshed perforated electrode. For the mathematical model of this microfluidic channel, inertia, buoyancy, drag and dielectrophoretic forces are brought up in the motion equation of the microparticles. The dielectrophoretic force is accounted for through a finite element discretization taking into account the perforated 3D geometry within the microchannel. An ordinary differential equation is solved to track the trajectories of the microparticles. For the case of continuous electrodes using the same mathematical model, the numerical simulation shows a very good agreement with the experiments, and this confirms the validation of focusing of microparticles within the proposed perforated electrode microchannel. Microparticles of silicon dioxide and polystyrene are used for this analysis. Their initial positions and radius, the Reynolds number, and the radius of the pore in perforated electrodes mainly conduct microparticles trajectories. Moreover, the radius of the pore of perforated electrode is the dominant factor in the steady state levitation height.}, } @article {pmid31386484, year = {2019}, author = {Samanta, T and Tian, H and Nakariakov, VM}, title = {Evidence for Vortex Shedding in the Sun's Hot Corona.}, journal = {Physical review letters}, volume = {123}, number = {3}, pages = {035102}, doi = {10.1103/PhysRevLett.123.035102}, pmid = {31386484}, issn = {1079-7114}, abstract = {Vortex shedding is an oscillating flow that is commonly observed in fluids due to the presence of a blunt body in a flowing medium. Numerical simulations have shown that the phenomenon of vortex shedding could also develop in the magnetohydrodynamic (MHD) domain. The dimensionless Strouhal number, the ratio of the blunt body diameter to the product of the period of vortex shedding and the speed of a flowing medium, is a robust indicator for vortex shedding, and, generally of the order of 0.2 for a wide range of Reynolds number. Using an observation from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we report a wavelike or oscillating plasma flow propagating upward against the Sun's gravitational force. A newly formed shrinking loop in the postflare region possibly generates the oscillation of the upflow in the wake of the hot and dense loop through vortex shedding. The computed Strouhal number is consistent with the prediction from previous MHD simulations. Our observation suggests the possibility of vortex shedding in the solar corona.}, } @article {pmid31382385, year = {2019}, author = {Yu, X and Li, Y and Liu, Y and Yang, Y and Wu, Y}, title = {Flow Patterns of Viscoelastic Fracture Fluids in Porous Media: Influence of Pore-Throat Structures.}, journal = {Polymers}, volume = {11}, number = {8}, pages = {}, pmid = {31382385}, issn = {2073-4360}, support = {U1663206, 51704313, 51425406, 21706284//National Natural Science Foundation of China/ ; 18CX02028A, 24720182146A//Fundamental Research Funds for the Central Universities/ ; }, abstract = {Viscoelastic surfactant (VES) fluid and hydrolyzed polyacryamide (HPAM) solution are two of the most common fracturing fluids used in the hydraulic fracturing development of unconventional reservoirs. The filtration of fracturing fluids in porous media is mainly determined by the flow patterns in pore-throat structures. In this paper, three different microdevices analogue of porous media allow access to a large range of Deborah number (De) and concomitantly low Reynolds number (Re). Continuous pore-throat structures were applied to study the feedback effect of downstream structure on upstream flow of VES fluid and HPAM solution with Deborah (De) number from 1.11 to 146.4. In the infinite straight channel, flow patterns between VES fluids and HPAM solution were similar. However, as pore length shortened to 800 μm, flow field of VES fluid exhibited the triangle shape with double-peaks velocity patterns. The flow field of HPAM solution presented stable and centralized streamlines when Re was larger than 4.29 × 10-2. Additionally, when the pore length was further shortened to 400 μm, double-peaks velocity patterns were vanished for VES fluid and the stable convergent flow characteristic of HPAM solution was observed with all flow rates.}, } @article {pmid31380864, year = {2019}, author = {Feng, X and Ren, Y and Hou, L and Tao, Y and Jiang, T and Li, W and Jiang, H}, title = {Tri-fluid mixing in a microchannel for nanoparticle synthesis.}, journal = {Lab on a chip}, volume = {19}, number = {17}, pages = {2936-2946}, doi = {10.1039/c9lc00425d}, pmid = {31380864}, issn = {1473-0189}, abstract = {It is becoming more difficult to use bulk mixing and bi-fluid micromixing in multi-step continuous-flow reactions, multicomponent reactions, and nanoparticle synthesis because they typically involve multiple reactants. To date, most micromixing studies, both passive and active, have focused on how to efficiently mix two fluids, while micromixing of three or more fluids together (multi-fluid mixing) has been rarely explored. This study is the first on tri-fluid mixing in microchannels. We investigated tri-fluid mixing in three microchannel models: a straight channel, a classical staggered herringbone mixing (SHM) channel, and a three-dimensional (3D) X-crossing microchannel. Numerical simulations and experiments were jointly conducted. A two-step experimental process was performed to determine the tri-fluid mixing efficiencies of these microchannels. We found that the SHM cannot significantly enhance mixing of three streams especially for a Reynolds number (Re) higher than 10. However, the 3D X-crossing channel based on splitting-and-recombination (SAR) showed effective tri-mixing performance over a wide Re range up to 275 (with a corresponding flow rate of 1972.5 μL min-1), thereby enabling high microchannel throughput. Furthermore, this tri-fluid micromixing process was used to synthesize a kind of Si-based nanoparticle. This achieved a narrower particle size distribution than traditional bulk mixing. Therefore, SAR-based tri-fluid mixing is an alternative for chemical and biochemical reactions where three reactants need to be mixed.}, } @article {pmid31374925, year = {2019}, author = {Henein, C and Awwad, S and Ibeanu, N and Vlatakis, S and Brocchini, S and Tee Khaw, P and Bouremel, Y}, title = {Hydrodynamics of Intravitreal Injections into Liquid Vitreous Substitutes.}, journal = {Pharmaceutics}, volume = {11}, number = {8}, pages = {}, pmid = {31374925}, issn = {1999-4923}, support = {513211//NIHR Biomedical Research Centre/ ; }, abstract = {Intravitreal injections have become the cornerstone of retinal care and one of the most commonly performed procedures across all medical specialties. The impact of hydrodynamic forces of intravitreal solutions when injected into vitreous or vitreous substitutes has not been well described. While computational models do exist, they tend to underestimate the starting surface area of an injected bolus of a drug. Here, we report the dispersion profile of a dye bolus (50 µL) injected into different vitreous substitutes of varying viscosities, surface tensions, and volumetric densities. A novel 3D printed in vitro model of the vitreous cavity of the eye was designed to visualize the dispersion profile of solutions when injected into the following vitreous substitutes-balanced salt solution (BSS), sodium hyaluronate (HA), and silicone oils (SO)-using a 30G needle with a Reynolds number (Re) for injection ranging from approximately 189 to 677. Larger bolus surface areas were associated with faster injection speeds, lower viscosity of vitreous substitutes, and smaller difference in interfacial surface tensions. Boluses exhibited buoyancy when injected into standard S1000. The hydrodynamic properties of liquid vitreous substitutes influence the initial injected bolus dispersion profile and should be taken into account when simulating drug dispersion following intravitreal injection at a preclinical stage of development, to better inform formulations and performance.}, } @article {pmid31370481, year = {2019}, author = {Gvozdić, B and Dung, OY and van Gils, DPM and Bruggert, GH and Alméras, E and Sun, C and Lohse, D and Huisman, SG}, title = {Twente mass and heat transfer water tunnel: Temperature controlled turbulent multiphase channel flow with heat and mass transfer.}, journal = {The Review of scientific instruments}, volume = {90}, number = {7}, pages = {075117}, doi = {10.1063/1.5092967}, pmid = {31370481}, issn = {1089-7623}, abstract = {A new vertical water tunnel with global temperature control and the possibility for bubble and local heat and mass injection has been designed and constructed. The new facility offers the possibility to accurately study heat and mass transfer in turbulent multiphase flow (gas volume fraction up to 8%) with a Reynolds-number range from 1.5 × 104 to 3 × 105 in the case of water at room temperature. The tunnel is made of high-grade stainless steel permitting the use of salt solutions in excess of 15% mass fraction. The tunnel has a volume of 300 l. The tunnel has three interchangeable measurement sections of 1 m height but with different cross sections (0.3 × 0.04 m2, 0.3 × 0.06 m2, and 0.3 × 0.08 m2). The glass vertical measurement sections allow for optical access to the flow, enabling techniques such as laser Doppler anemometry, particle image velocimetry, particle tracking velocimetry, and laser-induced fluorescent imaging. Local sensors can be introduced from the top and can be traversed using a built-in traverse system, allowing, for example, local temperature, hot-wire, or local phase measurements. Combined with simultaneous velocity measurements, the local heat flux in single phase and two phase turbulent flows can thus be studied quantitatively and precisely.}, } @article {pmid31369336, year = {2019}, author = {O'Neill, G and Tolley, NS}, title = {The complexities of nasal airflow: theory and practice.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {127}, number = {5}, pages = {1215-1223}, doi = {10.1152/japplphysiol.01118.2018}, pmid = {31369336}, issn = {1522-1601}, mesh = {Humans ; *Inhalation ; *Models, Biological ; Turbinates/*physiology ; }, abstract = {The objective of this study was to investigate the effects of nasal valve area, valve stiffness, and turbinate region cross-sectional area on airflow rate, nasal resistance, flow limitation, and inspiratory "hysteresis" by the use of a mathematical model of nasal airflow. The model of O'Neill and Tolley (Clin Otolaryngol Allied Sci 13: 273-277, 1988) describing the effects of valve area and stiffness on the nasal pressure-flow relationship was improved by the incorporation of additional terms involving 1) airflow through the turbinate region, 2) the dependence of the flow coefficients for the valve and turbinate region on the Reynolds number, and 3) effects of unsteady flow. The model was found to provide a good fit for normal values for nasal resistance and for pressure-flow curves reported in the literature for both congested and decongested states. Also, by showing the relative contribution of the nasal valve and turbinate region to nasal resistance, the model sheds light in explaining the generally poor correlation between nasal resistance measurements and the results from acoustic rhinometry. Furthermore, by proposing different flow conditions for the acceleration and deceleration phases of inspiration, the model produces an inspiratory loop (commonly referred to as hysteresis) consistent with those reported in the literature. With simulation of nasal flaring, the magnitude of the loop, the nasal resistance, and flow limitation all show change similar to that observed in the experimental results.NEW & NOTEWORTHY The present model provides considerable insight into some difficult conundrums in both clinical and technical aspects of nasal airflow. Also, the description of nasal airflow mechanics based on the Hagen-Poiseuille equation and Reynolds laminar-turbulent transition in long straight tubes, which has figured prominently in medical textbooks and journal articles for many years, is shown to be seriously in error at a fundamental level.}, } @article {pmid31363000, year = {2019}, author = {R Ferreira, R and Fukui, H and Chow, R and Vilfan, A and Vermot, J}, title = {The cilium as a force sensor-myth versus reality.}, journal = {Journal of cell science}, volume = {132}, number = {14}, pages = {}, doi = {10.1242/jcs.213496}, pmid = {31363000}, issn = {1477-9137}, mesh = {Animals ; Biomechanical Phenomena ; Cilia/*physiology ; Humans ; Mechanotransduction, Cellular ; Organ Specificity ; Rheology ; }, abstract = {Cells need to sense their mechanical environment during the growth of developing tissues and maintenance of adult tissues. The concept of force-sensing mechanisms that act through cell-cell and cell-matrix adhesions is now well established and accepted. Additionally, it is widely believed that force sensing can be mediated through cilia. Yet, this hypothesis is still debated. By using primary cilia sensing as a paradigm, we describe the physical requirements for cilium-mediated mechanical sensing and discuss the different hypotheses of how this could work. We review the different mechanosensitive channels within the cilium, their potential mode of action and their biological implications. In addition, we describe the biological contexts in which cilia are acting - in particular, the left-right organizer - and discuss the challenges to discriminate between cilium-mediated chemosensitivity and mechanosensitivity. Throughout, we provide perspectives on how quantitative analysis and physics-based arguments might help to better understand the biological mechanisms by which cells use cilia to probe their mechanical environment.}, } @article {pmid31359287, year = {2020}, author = {Jain, K}, title = {Transition to turbulence in an oscillatory flow through stenosis.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {1}, pages = {113-131}, doi = {10.1007/s10237-019-01199-1}, pmid = {31359287}, issn = {1617-7940}, mesh = {Blood Flow Velocity ; Computer Simulation ; Constriction, Pathologic ; Numerical Analysis, Computer-Assisted ; Pressure ; *Rheology ; }, abstract = {Onset of flow transition in a sinusoidally oscillating flow through a rigid, constant area circular pipe with a smooth sinusoidal obstruction in the center of the pipe is studied by performing direct numerical simulations, with resolutions close to the Kolmogorov microscales. The studied pipe is stenosed in the center with a 75% reduction in area in two distinct configurations-one that is symmetric to the axis of the parent pipe and the other that is offset by 0.05 diameters to introduce an eccentricity, which disturbs the flow thereby triggering the onset of flow transition. The critical Reynolds number at which the flow transitions to turbulence for a zero-mean oscillatory flow through a stenosis is shown to be nearly tripled in comparison with studies of pulsating unidirectional flow through the same stenosis. The onset of transition is further explored with three different flow pulsation frequencies resulting in a total of 90 simulations conducted on a supercomputer. It is found that the critical Reynolds number at which the oscillatory flow transitions is not affected by the pulsation frequencies. The locations of flow breakdown and re-stabilization post-stenosis are, however, respectively shifted closer to the stenosis throat with increasing pulsation frequencies. The results show that oscillatory physiological flows, while more stable, exhibit fluctuations due to geometric complexity and have implications in studies of dispersion and solute transport in the cerebrospinal fluid flow and understanding of pathological conditions.}, } @article {pmid31345119, year = {2020}, author = {Krishnam, U and Sharma, V and Jha, PK}, title = {The Reynolds number modulated low frequency dynamical modes of aqueous medium embedded spherical virus and implications to detecting and killing viruses.}, journal = {Journal of biomolecular structure & dynamics}, volume = {38}, number = {10}, pages = {3123-3129}, doi = {10.1080/07391102.2019.1648320}, pmid = {31345119}, issn = {1538-0254}, } @article {pmid31342935, year = {2019}, author = {Liu, G and Xue, Q and Zheng, X}, title = {Phase-difference on seal whisker surface induces hairpin vortices in the wake to suppress force oscillation.}, journal = {Bioinspiration & biomimetics}, volume = {14}, number = {6}, pages = {066001}, doi = {10.1088/1748-3190/ab34fe}, pmid = {31342935}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Biomimetics/*instrumentation ; Hydrodynamics ; Models, Biological ; Phoca/*physiology ; Vibrissae/*physiology ; }, abstract = {Seals are able to use their uniquely shaped whiskers to track hydrodynamic trails generated 30 s ago and detect hydrodynamic velocities as low as 245 [Formula: see text]m s-1. The high sensibility has long thought to be related to the wavy shape of the whiskers. This work revisited the hydrodynamics of a seal whisker model in a uniform flow, and discovered a new mechanism of seal whiskers in reducing self-induced noises, which is different from the long thought-of effect of the wavy shape. It was reported that the major and minor axes of the elliptical cross-sections of seal whisker are out of phase by approximately 180 degrees. Three-dimensional numerical simulations of laminar flow (Reynolds number range: 150-500) around seal-whisker-like cylinders were performed to examine the effect of the phase-difference on hydrodynamic forces and wake structures. It was found that the phase-difference induced hairpin vortices in the wake over a wide range of geometric and flow parameters (wavelength, wavy amplitude and Reynolds number), therefore substantially reducing lift-oscillations and self-induced noises. The formation mechanism of the hairpin vortices was analyzed and is discussed in details. The results provide valuable insights into an innovative vibration reduction and hydrodynamic sensing mechanism.}, } @article {pmid31330717, year = {2019}, author = {Jian, X and Zhang, W and Deng, Q and Huang, Y}, title = {Turbulent lithosphere deformation in the Tibetan Plateau.}, journal = {Physical review. E}, volume = {99}, number = {6-1}, pages = {062122}, doi = {10.1103/PhysRevE.99.062122}, pmid = {31330717}, issn = {2470-0053}, abstract = {In this work, we show that the Tibetan Plateau deformation demonstrates turbulence-like statistics, e.g., spatial invariance across continuous scales. A dual-power-law behavior is evident to show the existence of two possible conservation laws for the enstrophy-like cascade in the range 500≲r≲2000km and kinetic-energy-like cascade in the range 50≲r≲500km. The measured second-order structure-function scaling exponents ζ(2) are similar to their counterparts in the Fourier scaling exponents observed in the atmosphere, where in the latter case the earth's rotation is relevant. The turbulent statistics observed here for nearly zero-Reynolds-number flow can be interpreted by the geostrophic turbulence theory. Moreover, the intermittency correction is recognized with an intensity close to that of the hydrodynamic turbulence of high-Reynolds-number turbulent flows, implying a universal scaling feature of very different turbulent flows. Our results not only shed new light on the debate regarding the mechanism of the Tibetan Plateau deformation but also lead to new challenges for the geodynamic modeling using Newton or non-Newtonian models because the observed turbulence-like features have to be taken into account.}, } @article {pmid31318280, year = {2019}, author = {Dölger, J and Kiørboe, T and Andersen, A}, title = {Dense Dwarfs versus Gelatinous Giants: The Trade-Offs and Physiological Limits Determining the Body Plan of Planktonic Filter Feeders.}, journal = {The American naturalist}, volume = {194}, number = {2}, pages = {E30-E40}, doi = {10.1086/703656}, pmid = {31318280}, issn = {1537-5323}, mesh = {Animals ; Body Composition/*physiology ; Body Size ; Energy Metabolism ; Feeding Behavior/*physiology ; Models, Theoretical ; Predatory Behavior ; Zooplankton/*physiology ; }, abstract = {Most marine plankton have a high energy (carbon) density, but some are gelatinous with approximately 100 times more watery bodies. How do those distinctly different body plans emerge, and what are the trade-offs? We address this question by modeling the energy budget of planktonic filter feeders across life-forms, from micron-sized unicellular microbes such as choanoflagellates to centimeter-sized gelatinous tunicates such as salps. We find two equally successful strategies, one being small with high energy density (dense dwarf) and the other being large with low energy density (gelatinous giant). The constraint that forces large-but not small-filter feeders to be gelatinous is identified as a lower limit to the size-specific filter area, below which the energy costs lead to starvation. A further limit is found from the maximum size-specific motor force that restricts the access to optimum strategies. The quantified constraints are discussed in the context of other resource-acquisition strategies. We argue that interception feeding strategies can be accessed by large organisms only if they are gelatinous. On the other hand, organisms that use remote prey sensing do not need to be gelatinous, even if they are large.}, } @article {pmid31315935, year = {2019}, author = {Samson, JE and Miller, LA and Ray, D and Holzman, R and Shavit, U and Khatri, S}, title = {A novel mechanism of mixing by pulsing corals.}, journal = {The Journal of experimental biology}, volume = {222}, number = {Pt 15}, pages = {}, doi = {10.1242/jeb.192518}, pmid = {31315935}, issn = {1477-9145}, mesh = {Animals ; Anthozoa/*physiology ; *Hydrodynamics ; Models, Theoretical ; Rheology ; Video Recording ; Water Movements ; }, abstract = {The dynamic pulsation of xeniid corals is one of the most fascinating phenomena observed in coral reefs. We quantify for the first time the flow near the tentacles of these soft corals, the active pulsations of which are thought to enhance their symbionts' photosynthetic rates by up to an order of magnitude. These polyps are approximately 1 cm in diameter and pulse at frequencies between approximately 0.5 and 1 Hz. As a result, the frequency-based Reynolds number calculated using the tentacle length and pulse frequency is on the order of 10 and rapidly decays as with distance from the polyp. This introduces the question of how these corals minimize the reversibility of the flow and bring in new volumes of fluid during each pulse. We estimate the Péclet number of the bulk flow generated by the coral as being on the order of 100-1000 whereas the flow between the bristles of the tentacles is on the order of 10. This illustrates the importance of advective transport in removing oxygen waste. Flow measurements using particle image velocimetry reveal that the individual polyps generate a jet of water with positive vertical velocities that do not go below 0.1 cm s-1 and with average volumetric flow rates of approximately 0.71 cm3 s-1 Our results show that there is nearly continual flow in the radial direction towards the polyp with only approximately 3.3% back flow. 3D numerical simulations uncover a region of slow mixing between the tentacles during expansion. We estimate that the average flow that moves through the bristles of the tentacles is approximately 0.03 cm s-1 The combination of nearly continual flow towards the polyp, slow mixing between the bristles, and the subsequent ejection of this fluid volume into an upward jet ensures the polyp continually samples new water with sufficient time for exchange to occur.}, } @article {pmid31314164, year = {2019}, author = {Liao, P and Xing, L and Zhang, S and Sun, D}, title = {Magnetically Driven Undulatory Microswimmers Integrating Multiple Rigid Segments.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {15}, number = {36}, pages = {e1901197}, doi = {10.1002/smll.201901197}, pmid = {31314164}, issn = {1613-6829}, mesh = {Biosensing Techniques/methods ; Holography/methods ; Lasers ; Locomotion ; Microtechnology/*methods ; *Robotics ; }, abstract = {Mimicking biological locomotion strategies offers important possibilities and motivations for robot design and control methods. Among bioinspired microrobots, flexible microrobots exhibit remarkable efficiency and agility. These microrobots traditionally rely on soft material components to achieve undulatory propulsion, which may encounter challenges in design and manufacture including the complex fabrication processes and the interfacing of rigid and soft components. Herein, a bioinspired magnetically driven microswimmer that mimics the undulatory propulsive mechanism is proposed. The designed microswimmer consists of four rigid segments, and each segment is connected to the succeeding segment by joints. The microswimmer is fabricated integrally by 3D laser lithography without further assembly, thereby simplifying microrobot fabrication while enhancing structural integrity. Experimental results show that the microswimmer can successfully swim forward along guided directions via undulatory locomotion in the low Reynolds number (Re) regime. This work demonstrates for the first time that the flexible characteristic of microswimmers can be emulated by 3D structures with multiple rigid segments, which broadens possibilities in microrobot design. The proposed magnetically driven microswimmer can potentially be used in biomedical applications, such as medical diagnosis and treatment in precision medicine.}, } @article {pmid31300927, year = {2019}, author = {Hoell, C and Löwen, H and Menzel, AM and Daddi-Moussa-Ider, A}, title = {Creeping motion of a solid particle inside a spherical elastic cavity: II. Asymmetric motion.}, journal = {The European physical journal. E, Soft matter}, volume = {42}, number = {7}, pages = {89}, pmid = {31300927}, issn = {1292-895X}, abstract = {An analytical method is proposed for computing the low-Reynolds-number hydrodynamic mobility function of a small colloidal particle asymmetrically moving inside a large spherical elastic cavity, the membrane of which is endowed with resistance toward shear and bending. In conjunction with the results obtained in the first part (A. Daddi-Moussa-Ider, H. Löwen, S. Gekle, Eur. Phys. J. E 41, 104 (2018)), in which the axisymmetric motion normal to the surface of an elastic cavity is investigated, the general motion for an arbitrary force direction can now be addressed. The elastohydrodynamic problem is formulated and solved using the classic method of images through expressing the hydrodynamic flow fields as a multipole expansion involving higher-order derivatives of the free-space Green's function. In the quasi-steady limit, we demonstrate that the particle self-mobility function of a particle moving tangent to the surface of the cavity is larger than that predicted inside a rigid stationary cavity of equal size. This difference is justified by the fact that a stationary rigid cavity introduces additional hindrance to the translational motion of the encapsulated particle, resulting in a reduction of its hydrodynamic mobility. Furthermore, the motion of the cavity is investigated, revealing that the translational pair (composite) mobility, which linearly couples the velocity of the elastic cavity to the force exerted on the solid particle, is solely determined by membrane shear properties. Our analytical predictions are favorably compared with fully-resolved computer simulations based on a completed-double-layer boundary integral method.}, } @article {pmid31299253, year = {2019}, author = {Novelli, GL and Ferrari, LA and Vargas, GG and Loureiro, BV}, title = {A synergistic analysis of drag reduction on binary polymer mixtures containing guar gum.}, journal = {International journal of biological macromolecules}, volume = {137}, number = {}, pages = {1121-1129}, doi = {10.1016/j.ijbiomac.2019.07.042}, pmid = {31299253}, issn = {1879-0003}, mesh = {Acrylic Resins/*chemistry ; Feasibility Studies ; Galactans/*chemistry ; Mannans/*chemistry ; Molecular Weight ; *Motion ; Plant Gums/*chemistry ; Polyethylene Glycols/*chemistry ; Polysaccharides, Bacterial/chemistry ; Rheology ; Rotation ; Shear Strength ; }, abstract = {Drag reduction by the addition of polymer additives has been widely studied. However, there are only a few studies on binary polymer mixtures, here named blends. In this work, xanthan gum, polyacrylamide and poly(ethylene oxide) were associated with guar gum and drag reduction was used as a parameter to determine the synergistic interaction between polymers. The aim was to verify the relation of the synergy with the rigidity of the polymeric chains, the molecular weights and the magnitude of the molecular interactions between the studied polymers. To that end, several ratios of mixtures were tested at different Reynolds numbers in a rotational rheometer with double-gap concentric cylinders geometry. Finally, experiments were done to verify the behaviour of the blends over time at a fixed Reynolds number. From all these tests, it was documented that blends containing rigid chain polymers show positive synergism in the interaction in at least one of the ratios and that this interaction is more pronounced when the molecular weights are closer and intermolecular forces are stronger. It was also noted that, in general, blends are great substitutes for solutions containing only one type of polymer.}, } @article {pmid31294955, year = {2019}, author = {Mazinani, S and Al-Shimmery, A and Chew, YMJ and Mattia, D}, title = {3D Printed Fouling-Resistant Composite Membranes.}, journal = {ACS applied materials & interfaces}, volume = {11}, number = {29}, pages = {26373-26383}, doi = {10.1021/acsami.9b07764}, pmid = {31294955}, issn = {1944-8252}, abstract = {Fouling remains a long-standing unsolved problem that hinders the widespread use of membrane applications in industry. This article reports the use of numerical simulations coupled with extensive material synthesis and characterization to fabricate fouling-resistant 3D printed composite membranes. The membranes consist of a thin polyethersulfone selective layer deposited onto a 3D printed flat and double sinusoidal (wavy) support. Fouling and cleaning of the composite membranes were tested by using bovine serum albumin solution in a cross-flow ultrafiltration setup. The transmembrane pressure was regulated at 1 bar and the cross-flow Reynolds number (Re) varied between 400 and 1000. In comparison to the flat membrane, the wavy membrane showed superior performance in terms of pure water permeance (PWP) (10% higher) and permeance recovery ratio (87% vs 53%) after the first filtration cycle at Re = 1000. Prolong testing showed that the wavy membrane could retain approximately 87% of its initial PWP after 10 complete filtration cycles. This impressive fouling-resistant behavior is attributed to the localized fluid turbulence induced by the 3D printed wavy structure. These results show that not only the lifetime of membrane operations could be favorably extended but also the operational costs and environmental damage of membrane-based processes could also be significantly reduced.}, } @article {pmid31283274, year = {2019}, author = {Chajwa, R and Menon, N and Ramaswamy, S}, title = {Kepler Orbits in Pairs of Disks Settling in a Viscous Fluid.}, journal = {Physical review letters}, volume = {122}, number = {22}, pages = {224501}, doi = {10.1103/PhysRevLett.122.224501}, pmid = {31283274}, issn = {1079-7114}, abstract = {We show experimentally that a pair of disks settling at negligible Reynolds number (∼10^{-4}) displays two classes of bound periodic orbits, each with transitions to scattering states. We account for these dynamics, at leading far-field order, through an effective Hamiltonian in which gravitational driving endows orientation with the properties of momentum. This treatment is successfully compared against the measured properties of orbits and critical parameters of transitions between types of orbits. We demonstrate a precise correspondence with the Kepler problem of planetary motion for a wide range of initial conditions, find and account for a family of orbits with no Keplerian analog, and highlight the role of orientation as momentum in the many-disk problem.}, } @article {pmid31266939, year = {2019}, author = {Ren, Z and Hu, W and Dong, X and Sitti, M}, title = {Multi-functional soft-bodied jellyfish-like swimming.}, journal = {Nature communications}, volume = {10}, number = {1}, pages = {2703}, doi = {10.1038/s41467-019-10549-7}, pmid = {31266939}, issn = {2041-1723}, mesh = {Animals ; Biomechanical Phenomena ; Elastomers/chemistry ; *Equipment Design ; Locomotion ; Magnetics/instrumentation ; Robotics/*instrumentation ; Scyphozoa/*physiology ; Swimming ; }, abstract = {The functionalities of the untethered miniature swimming robots significantly decrease as the robot size becomes smaller, due to limitations of feasible miniaturized on-board components. Here we propose an untethered jellyfish-inspired soft millirobot that could realize multiple functionalities in moderate Reynolds number by producing diverse controlled fluidic flows around its body using its magnetic composite elastomer lappets, which are actuated by an external oscillating magnetic field. We particularly investigate the interaction between the robot's soft body and incurred fluidic flows due to the robot's body motion, and utilize such physical interaction to achieve different predation-inspired object manipulation tasks. The proposed lappet kinematics can inspire other existing jellyfish-like robots to achieve similar functionalities at the same length and time scale. Moreover, the robotic platform could be used to study the impacts of the morphology and kinematics changing in ephyra jellyfish.}, } @article {pmid31236828, year = {2019}, author = {Klusak, E and Quinlan, NJ}, title = {High-Resolution Measurements of Leakage Flow Inside the Hinge of a Large-scale Bileaflet Mechanical Heart Valve Hinge Model.}, journal = {Cardiovascular engineering and technology}, volume = {10}, number = {3}, pages = {469-481}, doi = {10.1007/s13239-019-00423-4}, pmid = {31236828}, issn = {1869-4098}, mesh = {Blood Flow Velocity ; *Heart Valve Prosthesis ; Heart Valve Prosthesis Implantation/adverse effects/*instrumentation ; *Hemodynamics ; Humans ; Materials Testing ; Prosthesis Design ; Stress, Mechanical ; Thrombosis/etiology/physiopathology ; }, abstract = {PURPOSE: It is believed that non-physiological leakage flow through hinge gaps during diastole contributes to thrombus formation in Bileaflet Mechanical Heart Valves (BMHVs). Because of the small scale and difficulty of experimental access, fluid dynamics inside the hinge cavity has not yet been characterised in detail. The objective is to investigate small-scale structure inside the hinge experimentally, and gain insight into its role in stimulating cellular responses.

METHODS: An optically accessible scaled-up model of a BMHV hinge was designed and built, preserving dynamic similarity to a clinical BMHV. Particle Image Velocimetry (PIV) was used to visualize and quantify the flow fields inside the hinge at physiological Reynolds number and dimensionless pressure drop. The flow was measured at in-plane and out-of-plane spatial resolution of 32 and 86 μm, respectively, and temporal resolution of [Formula: see text] RESULTS: Likely flow separation on the ventricular surface of the cavity has been observed for the first time, and is a source of unsteadiness and perhaps turbulence. The shear stress found in all planes exceeds the threshold of platelet activation, ranging up to 168 Pa.

CONCLUSIONS: The scale-up approach provided new insight into the nature of the hinge flow and enhanced understanding of its complexity. This study revealed flow features that may induce blood element damage.}, } @article {pmid31236057, year = {2019}, author = {Cafiero, G and Vassilicos, JC}, title = {Non-equilibrium turbulence scalings and self-similarity in turbulent planar jets.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2225}, pages = {20190038}, pmid = {31236057}, issn = {1364-5021}, abstract = {We study the self-similarity and dissipation scalings of a turbulent planar jet and the theoretically implied mean flow scalings. Unlike turbulent wakes where such studies have already been carried out (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493); Obligado et al. 2016 Phys. Rev. Fluids1, 044409. (doi:10.1103/PhysRevFluids.1.044409)), this is a boundary-free turbulent shear flow where the local Reynolds number increases with distance from inlet. The Townsend-George theory revised by (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493)) is applied to turbulent planar jets. Only a few profiles need to be self-similar in this theory. The self-similarity of mean flow, turbulence dissipation, turbulent kinetic energy and Reynolds stress profiles is supported by our experimental results from 18 to at least 54 nozzle sizes, the furthermost location investigated in this work. Furthermore, the non-equilibrium dissipation scaling found in turbulent wakes, decaying grid-generated turbulence, various instances of periodic turbulence and turbulent boundary layers (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493); Vassilicos 2015 Annu. Rev. Fluid Mech. 95, 114. (doi:10.1146/annurev-fluid-010814-014637); Goto & Vassilicos 2015 Phys. Lett. A3790, 1144-1148. (doi:10.1016/j.physleta.2015.02.025); Nedic et al. 2017 Phys. Rev. Fluids2, 032601. (doi:10.1103/PhysRevFluids.2.032601)) is also observed in the present turbulent planar jet and in the turbulent planar jet of (Antonia et al. 1980 Phys. Fluids23, 863055. (doi:10.1063/1.863055)). Given these observations, the theory implies new mean flow and jet width scalings which are found to be consistent with our data and the data of (Antonia et al. 1980 Phys. Fluids23, 863055. (doi:10.1063/1.863055)). In particular, it implies a hitherto unknown entrainment behaviour: the ratio of characteristic cross-stream to centreline streamwise mean flow velocities decays as the -1/3 power of streamwise distance in the region, where the non-equilibrium dissipation scaling holds.}, } @article {pmid31229600, year = {2019}, author = {Garwood, RJ and Behnsen, J and Haysom, HK and Hunt, JN and Dalby, LJ and Quilter, SK and Maclaine, JS and Cox, JPL}, title = {Olfactory flow in the sturgeon is externally driven.}, journal = {Comparative biochemistry and physiology. Part A, Molecular & integrative physiology}, volume = {235}, number = {}, pages = {211-225}, doi = {10.1016/j.cbpa.2019.06.013}, pmid = {31229600}, issn = {1531-4332}, mesh = {Animals ; Computer Simulation ; Fishes/*physiology ; Models, Anatomic ; Nasal Cavity/physiology ; Nose/*physiology ; *Odorants ; Smell/*physiology ; Swimming/physiology ; }, abstract = {Fluid dynamics plays an important part in olfaction. Using the complementary techniques of dye visualisation and computational fluid dynamics (CFD), we investigated the hydrodynamics of the nasal region of the sturgeon Huso dauricus. H. dauricus offers several experimental advantages, including a well-developed, well-supported, radial array (rosette) of visible-by-eye olfactory sensory channels. We represented these features in an anatomically accurate rigid model derived from an X-ray scan of the head of a preserved museum specimen. We validated the results from the CFD simulation by comparing them with data from the dye visualisation experiments. We found that flow through both the nasal chamber and, crucially, the sensory channels could be induced by an external flow (caused by swimming in vivo) at a physiologically relevant Reynolds number. Flow through the nasal chamber arises from the anatomical arrangement of the incurrent and excurrent nostrils, and is assisted by the broad, cartilage-supported, inner wall of the incurrent nostril. Flow through the sensory channels arises when relatively high speed flow passing through the incurrent nostril encounters the circular central support of the olfactory rosette, decelerates, and is dispersed amongst the sensory channels. Vortices within the olfactory flow may assist odorant transport to the sensory surfaces. We conclude that swimming alone is sufficient to drive olfactory flow in H. dauricus, and consider the implications of our results for the three other extant genera of sturgeons (Acipenser, Pseudoscaphirhynchus and Scaphirhynchus), and for other fishes with olfactory rosettes.}, } @article {pmid31215548, year = {2019}, author = {Man, Y and Kanso, E}, title = {Morphological transitions of axially-driven microfilaments.}, journal = {Soft matter}, volume = {15}, number = {25}, pages = {5163-5173}, doi = {10.1039/c8sm02397b}, pmid = {31215548}, issn = {1744-6848}, mesh = {Actin Cytoskeleton/*metabolism ; Biomechanical Phenomena ; Elasticity ; *Models, Molecular ; }, abstract = {The interactions of microtubules with motor proteins are ubiquitous in cellular and sub-cellular processes that involve motility and cargo transport. In vitro motility assays have demonstrated that motor-driven microtubules exhibit rich dynamical behaviors from straight to curved configurations. Here, we theoretically investigate the dynamic instabilities of elastic filaments, with free-ends, driven by single follower forces that emulate the action of molecular motors. Using the resistive force theory at low Reynolds number, and a combination of numerical techniques with linear stability analysis, we show the existence of four distinct regimes of filament behavior, including a novel buckled state with locked curvature. These successive instabilities recapitulate the full range of experimentally-observed microtubule behavior, implying that neither structural nor actuation asymmetry are needed to elicit this rich repertoire of motion.}, } @article {pmid31212518, year = {2019}, author = {He, G and Wang, J and Rinoshika, A}, title = {Orthogonal wavelet multiresolution analysis of the turbulent boundary layer measured with two-dimensional time-resolved particle image velocimetry.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053105}, doi = {10.1103/PhysRevE.99.053105}, pmid = {31212518}, issn = {2470-0053}, abstract = {The turbulent boundary layer flow measured by two-dimensional time-resolved particle image velocimetry is analyzed using the discrete orthogonal wavelet method. The Reynolds number of the turbulent boundary layer based on the friction velocity is Re_{τ}=235. The flow field is decomposed into a number of wavelet levels which have different characteristic scales. The velocity statistics and coherent structures at different wavelet levels are investigated. It is found that the fluctuation intensities and their peak locations differ for varying scales. The proper orthogonal decomposition (POD) of different wavelet components reveals a cascade of scales of coherent structures, especially the small-scale ones that are usually difficult to be identified in POD modes of the undecomposed flow field. The interactions among the scales are investigated in terms of large-scale amplitude modulations of the small-scale structures. In previous studies the velocity fluctuations are separated into two parts, the large scale and the small scale, divided usually by the boundary layer thickness. In the present study, however, the scales smaller than the boundary layer thickness are further separated. Therefore, the modulation analysis is a refined investigation that differentiates the modulation effects on separated small scales. The results reveal that the modulation effects vary among the small scales.}, } @article {pmid31212497, year = {2019}, author = {Puljiz, M and Menzel, AM}, title = {Displacement field around a rigid sphere in a compressible elastic environment, corresponding higher-order Faxén relations, as well as higher-order displaceability and rotateability matrices.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053002}, doi = {10.1103/PhysRevE.99.053002}, pmid = {31212497}, issn = {2470-0053}, abstract = {An efficient route to the displacement field around a rigid spherical inclusion in an infinitely extended homogeneous elastic medium is presented in a slightly alternative way when compared to some common textbook methods. Moreover, two Faxén relations of next-higher order beyond the stresslet are calculated explicitly for compressible media. They quantify higher-order moments involving the force distribution on a rigid spherical particle in a deformed elastic medium. As a consequence, additional contributions to the distortions of the deformed elastic medium are identified that are absent to lower order. Furthermore, the displaceability and rotateability matrices for an ensemble of rigid spheres are calculated up to (including) sixth order in inverse particle separation distance. These matrices describe the interactions mediated between the rigid embedded particles by the elastic environment. In this way, additional coupling effects are identified that are absent to lower order, particularly when rotations and torques are involved. All methods and results can formally be transferred to the corresponding case of incompressible hydrodynamic low-Reynolds-number Stokes flow by considering the limit of an incompressible environment. The roles of compressibility of the embedding medium and of the here additionally derived higher-order contributions are highlighted by some selected example configurations.}, } @article {pmid31212461, year = {2019}, author = {Nie, D and Lin, J}, title = {Discontinuity in the sedimentation system with two particles having different densities in a vertical channel.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053112}, doi = {10.1103/PhysRevE.99.053112}, pmid = {31212461}, issn = {2470-0053}, abstract = {The two-dimensional lattice Boltzmann method was used to numerically study a sedimentation system with two particles having different densities in a vertical channel for Galileo numbers in the range of 5≤Ga≤15 (resulting in a Reynolds number, based on the settling velocity, approximately ranging between 0.6 and 7). Two types of periodic motion, differing from each other in terms of the size of the limit cycle, the magnitude of the time period, and their changes upon increasing the density difference between particles, are identified depending on whether there is a wake effect. The most prominent features of this system are discontinuous changes in the settling velocity (6.7≤Ga<9.7) and time period of oscillation (10.5≤Ga≤15) at a critical value of the density difference between particles. The first discontinuity results in an abrupt increase in the Reynolds number, associated with a Hopf bifurcation without the presence of vortex shedding. The second discontinuity is accompanied by the disappearance of "abnormal rotation" (referring to the situation in which a particle appears to roll up a wall when settling) of the heavy particle, which directly results from a sharp increase in the amplitude of oscillation induced by the enhanced wake effect at another critical density difference between particles. The wall effects on these discontinuous changes were also examined.}, } @article {pmid31212451, year = {2019}, author = {Wang, L and Tian, FB}, title = {Numerical simulation of flow over a parallel cantilevered flag in the vicinity of a rigid wall.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053111}, doi = {10.1103/PhysRevE.99.053111}, pmid = {31212451}, issn = {2470-0053}, abstract = {Flow over a parallel cantilevered flag in the vicinity of a rigid wall is numerically studied using an immersed boundary-lattice Boltzmann method (IB-LBM) in two-dimensional domain, where the dynamics of the fluid and structure are, respectively, solved by the LBM and a finite-element method (FEM), with a penalty IB to handle the fluid-structure interaction (FSI). Specifically, a benchmark case considering a plate attached to the downstream of a stationary cylinder is first conducted to validate the current solver. Then, the wall effects on the flag are systemically studied, considering the effects of off-wall distance, structure-to-fluid mass ratio, bending rigidity, and Reynolds number. Three flapping modes, including symmetrical flapping, asymmetrical flapping, and chaotic flapping, along with a steady state are observed in the simulations. It is found that the flag is vibrating or stable with a mean angle inclined in the fluid when it is mounted in the vicinity of a rigid wall. The mean inclined angle first increases in the steady state and then decreases in the unsteady state with the off-wall distance. In the unsteady regime, the dependency of the inclined angle on the off-wall distance is similar to that of the gradient of the fluid velocity. In addition, the rigid wall near the flag decreases the lift and drag generation and further stabilizes the flag-fluid system. Contrarily, the flag inertia destabilizes the flag, and large flag inertia induces chaotic vibrating modes.}, } @article {pmid31207995, year = {2019}, author = {Zhang, H and Li, X and Chuai, R and Zhang, Y}, title = {Chaotic Micromixer Based on 3D Horseshoe Transformation.}, journal = {Micromachines}, volume = {10}, number = {6}, pages = {}, pmid = {31207995}, issn = {2072-666X}, support = {20180550950//Natural Science Foundation of Liaoning/ ; }, abstract = {To improve the efficiency of mixing under laminar flow with a low Reynolds number (Re), a novel three-dimensional Horseshoe Transformation (3D HT) was proposed as the basis for the design of a micromixer. Compared with the classical HT, the Lyapunov exponent of the 3D HT, which was calculated based on a symbolic dynamic system, proved the chaotic enhancement. Based on the 3D HT, a micromixer with a mixing length of 12 mm containing six mixing units was obtained by sequentially applying "squeeze", "stretch", "twice fold", "inverse transformation", and "intersection" operations. Numerical simulation and Peclet Number (Pe) calculations indicated that when the squeeze amplitude 0 < α < 1/2, 0 < β < 1/2, the stretch amplitude γ > 4, and Re ≥ 1, the mass transfer in the mixer was dominated by convective diffusion induced by chaotic flow. When Re = 10, at the outlet of the mixing chamber, the simulated mixing index was 96.4%, which was far less than the value at Re = 0.1 (σ = 0.041). Microscope images of the mixing chamber and the curve trend of pH buffer solutions obtained from a mixing experiment were both consistent with the results of the simulation. When Re = 10, the average mixing index of the pH buffer solutions was 91.75%, which proved the excellent mixing efficiency of the mixer based on the 3D HT.}, } @article {pmid31206776, year = {2019}, author = {Belut, E and Sánchez Jiménez, A and Meyer-Plath, A and Koivisto, AJ and Koponen, IK and Jensen, ACØ and MacCalman, L and Tuinman, I and Fransman, W and Domat, M and Bivolarova, M and van Tongeren, M}, title = {Indoor dispersion of airborne nano and fine particles: Main factors affecting spatial and temporal distribution in the frame of exposure modeling.}, journal = {Indoor air}, volume = {29}, number = {5}, pages = {803-816}, doi = {10.1111/ina.12579}, pmid = {31206776}, issn = {1600-0668}, mesh = {Aerosols/*analysis ; Air Pollutants/*analysis ; Air Pollution, Indoor/*analysis ; Environmental Monitoring ; Humans ; Models, Theoretical ; Nanoparticles ; Particle Size ; Spatio-Temporal Analysis ; Ventilation ; }, abstract = {A particle exposure experiment inside a large climate-controlled chamber was conducted. Data on spatial and temporal distribution of nanoscale and fine aerosols in the range of mobility diameters 8-600 nm were collected with high resolution, for sodium chloride, fluorescein sodium, and silica particles. Exposure scenarios studied included constant and intermittent source emissions, different aggregation conditions, high (10 h-1) and low (3.5 h-1) air exchange rates (AERs) corresponding to chamber Reynolds number, respectively, equal to 1 × 105 and 3 × 104 . Results are presented and analyzed to highlight the main determinants of exposure and to determine whether the assumptions underlying two-box models hold under various scenarios. The main determinants of exposure found were the source generation rate and the ventilation rate. The effect of particles nature was indiscernible, and the decrease of airborne total number concentrations attributable to surface deposition was estimated lower than 2% when the source was active. A near-field/far-field structure of aerosol concentration was always observed for the AER = 10 h-1 but for AER = 3.5 h-1 , a single-field structure was found. The particle size distribution was always homogeneous in space but a general shift of particle diameter (-8% to +16%) was observed between scenarios in correlation with the AER and with the source position, presumably largely attributable to aggregation.}, } @article {pmid31186821, year = {2019}, author = {Aghilinejad, A and Aghaamoo, M and Chen, X}, title = {On the transport of particles/cells in high-throughput deterministic lateral displacement devices: Implications for circulating tumor cell separation.}, journal = {Biomicrofluidics}, volume = {13}, number = {3}, pages = {034112}, pmid = {31186821}, issn = {1932-1058}, abstract = {Deterministic lateral displacement (DLD), which takes advantage of the asymmetric bifurcation of laminar flow around the embedded microposts, has shown promising capabilities in separating cells and particles of different sizes. Growing interest in utilizing high-throughput DLD devices for practical applications, such as circulating tumor cell separation, necessitates employing higher flow rates in these devices, leading to operating in moderate to high Reynolds number (Re) regimes. Despite extensive research on DLD devices in the creeping regime, limited research has focused on the physics of flow, critical size of the device, and deformable cell behavior in DLD devices at moderate to high Re. In this study, the transport behavior of particles/cells is investigated in realistic high-throughput DLD devices with hundreds of microposts by utilizing multiphysics modeling. A practical formula is proposed for the prediction of the device critical size, which could serve as a design guideline for high-throughput DLD devices. Then, the complex hydrodynamic interactions between a deformable cell and DLD post arrays are investigated. A dimensionless index is utilized for comparing different post designs to quantify the cell-post interaction. It is shown that the separation performances in high-throughput devices are highly affected by Re as well as the micropost shapes. These findings can be utilized for the design and optimization of high-throughput DLD microfluidic devices.}, } @article {pmid31185351, year = {2019}, author = {Tshumah-Mutingwende, RRMS and Takahashi, F}, title = {Physio-chemical effects of freshwaters on the dissolution of elementary mercury.}, journal = {Environmental pollution (Barking, Essex : 1987)}, volume = {252}, number = {Pt A}, pages = {627-636}, doi = {10.1016/j.envpol.2019.05.130}, pmid = {31185351}, issn = {1873-6424}, mesh = {Ecosystem ; Environmental Monitoring/methods ; Fresh Water/*chemistry ; Gold/analysis ; Humans ; Mercury/*analysis/chemistry ; Methylmercury Compounds/analysis ; Solubility ; Water Pollutants, Chemical/*analysis/chemistry ; }, abstract = {Elemental mercury (Hg0) is widely used by Artisanal and small-scale gold miners (ASGMs) to extract gold from ore. Due to the unavailability of appropriate waste disposal facilities, Hg0-rich amalgamation tailings are often discharged into nearby aquatic systems where the Hg0 droplets settle in bottom sediment and sediment-water interfaces. Hg0 dissolution and following biogeochemical transformations to methylmercury (MeHg) have been concerned owing to its potential risk to human health and the ecosystem. For reliable estimates of Hg exposure to human bodies using pollutant environmental fate and transport models, knowledge of the Hg0 dissolution rate is important. However, only limited literature is available. Therefore, it was investigated in this study. Dissolution tests in a 'dark chamber' revealed that an increase in medium pH resulted in a decrease in the dissolution rate, whereas, a large Hg0 droplet surface area (SA) and high Reynolds number (Re) resulted in a faster dissolution. A multivariate first order dissolution model of the form:kˆ=-7.9×10-5[pH]+7.0×10-4[logRe]+7.9×10-4[SA]-2.5×10-3 was proposed (adjusted R2 = 0.99). The Breusch-Pagan and White heteroscedasticity tests revealed that the model residuals are homoscedastic (p-value = 0.05) at the 5% significance level. Parameter sensitivity analysis suggests that slow mercury dissolution from the Hg0 droplets to aquatic systems might mask emerging environmental risk of mercury. Even after mercury usage in ASGM is banned, mercury dissolution and following contamination will continue for about 40 years or longer owing to previously discharged Hg0 droplets.}, } @article {pmid31176976, year = {2019}, author = {Almohammadi, H and Amirfazli, A}, title = {Droplet impact: Viscosity and wettability effects on splashing.}, journal = {Journal of colloid and interface science}, volume = {553}, number = {}, pages = {22-30}, doi = {10.1016/j.jcis.2019.05.101}, pmid = {31176976}, issn = {1095-7103}, abstract = {HYPOTHESES: The wettability of a surface affects the splashing behavior of a droplet upon impact onto a surface only when surface exhibits either a very high or a very low contact angle. Viscosity affects the splashing threshold in a non-monotony way.

EXPERIMENTS: To examine the roles of drop viscosity and surface wettability on splashing, a wide range of liquid viscosities (1-100 cSt), surface wettabilities (from hydrophilic to hydrophobic), drop velocities (0.5-3.3 m/s), and liquid surface tensions (∼20 and 70 mN/m) were examined. High speed imaging was used.

FINDINGS: Wettability affects the splashing threshold at very extreme limits of the wettability i.e. at very high or very low contact angle values; however, the wettability effect is less prominent on spreading-splashing regime map. For drops of any surface tension impacting surfaces with any wettability, an increase in viscosity (up to ∼5 cSt or Reynolds number of 2000) promotes splashing; whereas using liquids with viscosities larger than 5 cSt, suppress splashing. We explained such behaviors using evolution of the lamella rim, dynamic contact angle, and velocity of the expanding lamella. Finally, to predict the splashing, we developed a general empirical relationship which explains all of ours, and previously reported data.}, } @article {pmid31167483, year = {2019}, author = {Siddiqui, AA and Turkyilmazoglu, M}, title = {A New Theoretical Approach of Wall Transpiration in the Cavity Flow of the Ferrofluids.}, journal = {Micromachines}, volume = {10}, number = {6}, pages = {}, pmid = {31167483}, issn = {2072-666X}, abstract = {An idea of permeable (suction/injection) chamber is proposed in the current work to control the secondary vortices appearing in the well-known lid-driven cavity flow by means of the water based ferrofluids. The Rosensweig model is conveniently adopted for the mathematical analysis of the physical problem. The governing equation of model is first transformed into the vorticity transport equation. A special finite difference method in association with the successive over-relaxation method (SOR) is then employed to numerically simulate the flow behavior. The effects of intensity of magnetic source (controlled by the Stuart number), aspect ratio of the cavity, rate of permeability (i.e., α p = V 0 U), ratio of speed of suction/injection V 0 to the sliding-speed U of the upper wall of a cavity, and Reynolds number on the ferrofluid in the cavity are fully examined. It is found that the secondary vortices residing on the lower wall of the cavity are dissolved by the implementation of the suction/injection chamber. Their character is dependent on the rate of permeability. The intensity of magnetic source affects the system in such a way to alter the flow and to transport the fluid away from the magnetic source location. It also reduces the loading effects on the walls of the cavity. If the depth of cavity (or the aspect ratio) is increased, the secondary vortices join together to form a single secondary vortex. The number of secondary vortices is shown to increase if the Reynolds number is increased for both the clear fluid as well as the ferrofluids. The suction and injection create resistance in settlement of solid ferroparticles on the bottom. The results obtained are validated with the existing data in the literature and satisfactory agreement is observed. The presented problem may find applications in biomedical, pharmaceutical, and engineering industries.}, } @article {pmid31165744, year = {2019}, author = {Arumuru, V and Dash, JN and Dora, D and Jha, R}, title = {Vortex Shedding Optical Flowmeter based on Photonic Crystal Fiber.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {8313}, doi = {10.1038/s41598-019-40464-2}, pmid = {31165744}, issn = {2045-2322}, abstract = {In the present work we propose a PCF (photonic crystal fiber) based Modal interferometer detector for sensing low flow velocity by detecting the frequency of vortices shed from a bluff body. The proposed novel design encapsulates the interferometric arm inside a metal casing to protect the sensor from harsh process fluids. The characterization of the developed probe is conducted under no flow conditions using a piezo actuator to evaluate the sensor response over wide frequency range (0-500 Hz). The developed sensors shows a reasonably flat response in the tested frequency range. Experiments are conducted by employing the developed sensor behind a bluff body of a vortex flowmeter to measure the frequency of the shed vortices and hence, the fluid flow rate. The low flow rate sensitivity of the vortex flowmeter is improved many folds by using the present sensor and the minimum Reynolds number detected is Re = 5000. A linear trend is observed between the frequency of the vortices and the flow velocity which is desirable for fluid flow measurement. The PCF based interferometric sensor with metal encapsulation makes the vortex flowmeter, sensitive at low flow rates, robust and economical to be used in industrial application.}, } @article {pmid31153354, year = {2019}, author = {Farouk, B and Antao, DS and Hasan, N}, title = {Acoustically driven oscillatory flow fields in a cylindrical resonator at resonance.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {5}, pages = {2932}, doi = {10.1121/1.5097594}, pmid = {31153354}, issn = {1520-8524}, abstract = {Generation and development of acoustic waves in an air-filled cylindrical resonator driven by a conical electro-mechanical speaker are studied experimentally and simulated numerically. The driving frequencies of the speaker are chosen such that a standing wave field is produced at each chosen frequency in the resonator. The amplitude of the generated acoustic (pressure) waves is measured along the axis of the resonator by a fast response piezo-resistive pressure transducer, while the radial distribution of the oscillatory axial velocities is measured at the corresponding velocity anti-node locations by a constant temperature hot-film anemometer. For the cases studied, the acoustic Reynolds number ranged between 20.0 and 60.0 and the flow fields were always found to be in the laminar regime. The flow field in the resonator is also simulated by a high-fidelity numerical scheme with low numerical diffusion. Formation of the standing wave and quasi-steady acoustic streaming are numerically simulated by solving the fully compressible form of the Navier-Stokes equations. The effects of the sound field intensity (i.e., input power to the speaker) and driving frequency on the standing wave field and the resultant formation process of the streaming structures are also investigated.}, } @article {pmid31144946, year = {2019}, author = {Kaneda, Y and Yamamoto, Y and Tsuji, Y}, title = {Linear Response Theory for One-Point Statistics in the Inertial Sublayer of Wall-Bounded Turbulence.}, journal = {Physical review letters}, volume = {122}, number = {19}, pages = {194502}, doi = {10.1103/PhysRevLett.122.194502}, pmid = {31144946}, issn = {1079-7114}, abstract = {The idea of linear response theory well known in the statistical mechanics for thermal equilibrium systems is applied to one-point statistics in the inertial sublayer of wall-bounded turbulence (WBT). A close analogy between the energy transfer from large to small scales in isotropic turbulence and the momentum transfer in the wall normal direction in WBT plays a key role in the application. The application gives estimates of the influence of the finite Reynolds number on the statistics. The estimates are consistent with data by high-resolution direct numerical simulations of turbulent channel flow.}, } @article {pmid31140495, year = {2019}, author = {Fadel, M and Daurelle, JV and Fourmond, V and Vicente, J}, title = {A new electrochemical cell with a uniformly accessible electrode to study fast catalytic reactions.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {21}, number = {23}, pages = {12360-12371}, doi = {10.1039/c9cp01487j}, pmid = {31140495}, issn = {1463-9084}, abstract = {The electrochemical study of fast catalytic reactions is limited by mass transport when using the conventional electrochemical cell with a rotating disk electrode (RDE). To overcome this issue, it is important to find a new device with improved transport properties that respects electrochemical constraints. We used numerical simulations of computational fluid dynamics to design a new electrochemical cell based on the so-called "jet flow" design for the kinetic studies of catalytic chemical reactions at the surface of an electrode. The new cell is characterized by a high, reliable and uniform mass transport over the electroactive part of its surface. We investigated the effects of the nozzle and the electrode diameters, the nozzle-electrode distance and the Reynolds number on the performance of the jet-electrode in the flow system. Through the optimization of the geometry of this jet electrode cell, we achieved a factor of 3 enhancement in transport compared to the rotating disk electrode. We succeeded in constructing the designed electrode, characterized it with electrochemical techniques, and found an excellent agreement between the transport properties deduced from the numerical simulations and those from the measurements.}, } @article {pmid31123743, year = {2019}, author = {Wang, P and Zhang, Q and Wang, M and Yin, B and Hou, D and Zhang, Y}, title = {Atomistic insights into cesium chloride solution transport through the ultra-confined calcium-silicate-hydrate channel.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {21}, number = {22}, pages = {11892-11902}, doi = {10.1039/c8cp07676f}, pmid = {31123743}, issn = {1463-9084}, abstract = {The transport of water and ions in the gel pores of calcium silicate hydrate (C-S-H) determines the durability of cement material. In this study, molecular dynamics was employed to investigate the capillary imbibition process of CsCl solution in the C-S-H channel. The advanced frontier of CsCl solution flow inside the C-S-H capillary shows a concave meniscus shape, which reflects the hydrophilic properties of the C-S-H substrate. Reynolds number calculations show that the transport process is laminar flow and dominated by viscous forces. The invading depth of the CsCl solution deviates from the theoretical prediction of the classic Lucas-Washburn (L-W) equation, but the modified theoretical equation, by incorporating the effect of slip length, dynamic contact angle, and effective viscosity into the L-W equation, can describe the penetration curve of the solution very well. The validity of our developed theoretical equation was confirmed by additional systems with different ion concentrations. In addition, the local structure of ions was analyzed to elucidate the effect of ion concentration on the transport process. The adsorption and accumulation of ions retard the transport process of water. With an increase in the ionic concentration, the effects of immobilization and cluster accumulation became more pronounced, further reducing the transport rate of water. This study provides fundamental insight into the transport behavior of liquid in the gel pores of cement-based material.}, } @article {pmid31120757, year = {2019}, author = {Zhang, J and Liu, H and Ba, Y}, title = {Numerical Study of Droplet Dynamics on a Solid Surface with Insoluble Surfactants.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {24}, pages = {7858-7870}, doi = {10.1021/acs.langmuir.9b00495}, pmid = {31120757}, issn = {1520-5827}, abstract = {Surfactants are widely used in many industrial processes, where the presence of surfactants not only reduces the interfacial tension between fluids but also alters the wetting properties of solid surfaces. To understand how the surfactants influence the droplet motion on a solid surface, a hybrid method for interfacial flows with insoluble surfactants and contact-line dynamics is developed. This method solves immiscible two-phase flows through a lattice Boltzmann color-gradient model and simultaneously solves the convection-diffusion equation for surfactant concentration through a finite difference method. In addition, a dynamic contact angle formulation that describes the dependence of the local contact angle on the surfactant concentration is derived, and the resulting contact angle is enforced by a geometrical wetting condition. Our method is first used to simulate static contact angles for a droplet resting on a solid surface, and the results show that the presence of surfactants can significantly modify surface wettability, especially when the surface is more hydrophilic or more hydrophobic. This is then applied to simulate a surfactant-laden droplet moving on a substrate subject to a linear shear flow for varying effective capillary number (Cae), Reynolds number (Re), and surface wettability, where the results are often compared with those of a clean droplet. For varying Cae, the simulations are conducted by considering a neutral surface. At low values of Cae, the droplet eventually reaches a steady deformation and moves at a constant velocity. In either a clean or surfactant-laden case, the moving velocity of the droplet linearly increases with the moving wall velocity, but the slope is always higher (i.e., the droplet moves faster) in the surfactant-laden case where the droplet exhibits a bigger deformation. When Cae is increased beyond a critical value (Cae,c), the droplet breakup would happen. The presence of surfactants is found to decrease the value of Cae,c, but it shows a non-monotonic effect on the droplet breakup. An increase in Re is able to increase not only droplet deformation but also surfactant dilution. The role of surfactants in the droplet behavior is found to greatly depend upon the surface wettability. For a hydrophilic surface, the presence of surfactants can decrease the wetting length and enables the droplet to reach a steady state faster; while for a hydrophobic surface, it increases the wetting length and delays the departure of the droplet from the solid surface.}, } @article {pmid31083953, year = {2019}, author = {Tian, C and Wang, X and Liu, Y and Yang, W and Hu, H and Pei, X and Zhou, F}, title = {In Situ Grafting Hydrophilic Polymeric Layer for Stable Drag Reduction.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {22}, pages = {7205-7211}, doi = {10.1021/acs.langmuir.9b00321}, pmid = {31083953}, issn = {1520-5827}, abstract = {Developing drag reduction techniques has attracted great attention because of their need in practical applications. However, many of the proposed strategies exhibit some inevitable limitations, especially for long period of adhibition. In this work, the dynamic but stable drag reduction effect of superhydrophilic hydrogel-coated iron sphere falling freely in a cylindrical water tank was investigated. The absolute instantaneous velocities and displacements of either the hydrogel-encapsulated or unmodified iron sphere falling freely in water were monitored via a high-speed video. It was revealed that, in the range of Reynolds number from 104 to 106, the optimized hydrogel-coated iron sphere with uniform stability could reduce the resistance by up to 40%, which was mainly due to the boundary slip of water and the delayed boundary separation that resulted from the coated hydrogel. Besides, the deliberate experiments and analysis further indicated that the superhydrophilic hydrogel layer accompanied by the emergence of the drag crisis has largely effected the distribution of flow field at the boundary around the sphere. More importantly, the drag reduction behavior based on the proposed method was thermodynamically stable and resistant to external stimulus, including fluidic oscillator and hydrodynamic pressure. The effective long-term drag reduction performance of the hydrophilic substrate can be expected, correspondingly, and also provides a novel preliminary protocol and avenues for the development of durable drag reduction technologies.}, } @article {pmid31083496, year = {2019}, author = {Li, H and Huang, B and Wu, M}, title = {Experimental and Numerical Investigations on the Flow Characteristics within Hydrodynamic Entrance Regions in Microchannels.}, journal = {Micromachines}, volume = {10}, number = {5}, pages = {}, pmid = {31083496}, issn = {2072-666X}, abstract = {Flow characteristics within entrance regions in microchannels are important due to their effect on heat and mass transfer. However, relevant research is limited and some conclusions are controversial. In order to reveal flow characteristics within entrance regions and to provide empiric correlation estimating hydrodynamic entrance length, experimental and numerical investigations were conducted in microchannels with square cross-sections. The inlet configuration was elaborately designed in a more common pattern for microdevices to diminish errors caused by separation flow near the inlet and fabrication faults so that conclusions which were more applicable to microchannels could be drawn. Three different microchannels with hydraulic diameters of 100 μm, 150 μm, and 200 μm were investigated with Reynolds (Re) number ranging from 0.5 to 50. For the experiment, deionized water was chosen as the working fluid and microscopic particle image velocimetry (micro-PIV) was adopted to record and analyze velocity profiles. For numerical simulation, the test-sections were modeled and incompressible laminar Navier-Stokes equations were solved with commercial software. Strong agreement was achieved between the experimental data and the simulated data. According to the results of both the experiments and the simulations, new correlations were proposed to estimate entrance length. Re numbers ranging from 12.5 to 15 was considered as the transition region where the relationship between entrance length and Re number converted. For the microchannels and the Reynolds number range investigated compared with correlations for conventional channels, noticeable deviation was observed for lower Re numbers (Re < 12.5) and strong agreement was found for higher Re numbers (Re > 15).}, } @article {pmid31074118, year = {2019}, author = {Xin, C and Yang, L and Li, J and Hu, Y and Qian, D and Fan, S and Hu, K and Cai, Z and Wu, H and Wang, D and Wu, D and Chu, J}, title = {Conical Hollow Microhelices with Superior Swimming Capabilities for Targeted Cargo Delivery.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {31}, number = {25}, pages = {e1808226}, doi = {10.1002/adma.201808226}, pmid = {31074118}, issn = {1521-4095}, support = {51875544//National Science Foundation of China/ ; 51675503//National Science Foundation of China/ ; 61805230//National Science Foundation of China/ ; 51805508//National Science Foundation of China/ ; 51805509//National Science Foundation of China/ ; WK2090000011//Fundamental Research Funds for the Central Universities/ ; WK2090090012//Fundamental Research Funds for the Central Universities/ ; WK2090000013//Fundamental Research Funds for the Central Universities/ ; WK2480000002//Fundamental Research Funds for the Central Universities/ ; WK2090090021//Fundamental Research Funds for the Central Universities/ ; 2017495//Youth Innovation Promotion Association CAS/ ; YZ201566//Chinese Academy of Sciences Instrument/ ; 2017YFB1104303//National Key R&D Program of China/ ; 2018YFB1105400//National Key R&D Program of China/ ; }, abstract = {Inspired by flagellate microorganisms in nature, the microhelix is considered as an ideal model for transportation in fluid environment with low Reynolds number. However, how to promote the swimming and loading capabilities of microhelices with controllable geometries remains challenging. In this study, a novel kind of conical hollow microhelices is proposed and a method is developed to rapidly fabricate these microhelices with controllable parameters by femtosecond vortex beams generated from spatial light modulation along helical scanning. Conical hollow microhelices with designable heights (H = 45-75 µm), diameters (D = 6-18 µm), pitch numbers (Pi = 2-4), taper angles (T = 0.1-0.6 rad), and pitch periods (ΔP = 10-30 µm) are efficiently fabricated. In addition, compared with straight microhelices, the forward swimming capability of conical microhelices increases by 50% and the lateral drift of the conical hollow microhelices is reduced by 70%. Finally, the capabilities of these conical hollow microhelices for nanocargo loading and release by the inner hollow core, as well as transportation of neural stem cells by the outer surface are demonstrated. This work provides new insights into faster and simultaneous transportation of multicargoes for hybrid drug delivery, targeted therapy, and noninvasive surgery in vivo.}, } @article {pmid31067939, year = {2019}, author = {Feng, Y and Gao, Y and Tang, K and Jin, T}, title = {Numerical investigation on turbulent oscillatory flow through a jet pump.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {3}, pages = {1417}, doi = {10.1121/1.5094346}, pmid = {31067939}, issn = {1520-8524}, abstract = {A jet pump with an asymmetrical channel can induce a time-averaged pressure drop in oscillatory flow, which can effectively suppress Gedeon streaming in looped thermoacoustic engines. In this work, the flow characteristics and time-averaged pressure drop caused by a jet pump in turbulent oscillatory flow are investigated through numerical simulation. Through the analysis of the dimensionless governing equations, the emphasis is put on the effects of Womersley number and maximum acoustic Reynolds number on the performance of the jet pump. Meanwhile, the steady flow resistance coefficients are also measured numerically. The results indicate that the oscillatory flow resistance coefficients are relatively insensitive to Womersley number when it is less than 46. Moreover, the oscillatory flow resistance coefficients agree well with the steady state flow results, which validate the quasi-static assumption in turbulent oscillatory flow. However, further increasing Womersley number will lead to a reduction in the time-averaged pressure drop. The simulation method and results, as well as the hydrodynamic mechanism beneath the results, are presented and discussed in detail.}, } @article {pmid31067919, year = {2019}, author = {Ramadan, AB and Abd El-Rahman, AI and Sabry, AS}, title = {Assessment of the transition k-k-ω model application to transitional oscillatory pipe flows.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {3}, pages = {1195}, doi = {10.1121/1.5092605}, pmid = {31067919}, issn = {1520-8524}, abstract = {The flow transition from laminar to turbulent inside of typical thermoacoustic devices influences the heat-exchange capacities of these devices and dramatically impacts overall performances as well. A few measurements [Eckmann and Grotberg (1991), J. Fluid Mech. 222, 329-350; Hino, Sawamoto, and Takasu (1976). J. Fluid Mech. 75, 193-207] and direct simulations [Feldmann and Wagner (2012). J. Turbul. 13(32), 1-28; Feldmann and Wagner (2016a). New Results in Numerical and Experimental Fluid Mechanics X, pp. 113-122] were reported that describe the transitional oscillatory flows; however, almost no turbulence model has been developed that enables accurate detection and characterization of the reported intermittent turbulent fluctuations. The present work aims to assess the applicability of the k-kL-ω transition model to transitional oscillatory pipe flows. A sinusoidal pressure gradient is introduced into ANSYS finite-volume solver for flow field simulation at different acoustic frequencies, while a friction Reynolds number of 1440 is retained. The stationary turbulent and the laminar oscillatory pipe flows are first considered for validation and model calibration against published LDA measurements [Durst, Kikura, Lekakis, Jovanovic, and Ye (1996). Exp. Fluids 20, 417-428] and DNS results [Feldmann and Wagner (2012). J. Turbul. 13(32), 1-28] in addition to the Sexl's laminar-flow theory [Sexl (1930). Zeitschrift Phys. 61(5), 349-362]. Investigation of the total fluctuation kinetic energy of transitional oscillations reveals the appearance of intermittent fluctuations within the near-wall region at Wo = 13 during deceleration, while fully turbulent oscillations are predicted in the entire pipe domain at Wo = 5. Although the present results are qualitatively in good agreement with reported experimental [Eckmann and Grotberg (1991). J. Fluid Mech. 222, 329-350] and DNS findings [Feldmann and Wagner (2012). J. Turbul. 13(32), 1-28], the velocity profiles show poor agreement with corresponding DNS data during flow acceleration at Wo = 5.}, } @article {pmid31046340, year = {2019}, author = {Zhou, T and Sun, Y and Fattah, R and Zhang, X and Huang, X}, title = {An experimental study of trailing edge noise from a pitching airfoil.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {4}, pages = {2009}, doi = {10.1121/1.5094898}, pmid = {31046340}, issn = {1520-8524}, abstract = {In this study, the far-field noise from a pitching NACA 0012 airfoil was measured at a Reynolds number of 6.6 × 104. The pitching motion was in sinusoidal functions with a mean incident angle of 0°. Cases with the pitching amplitude varying from 7.5° to 15° and frequency from 3 to 8 Hz were tested, corresponding to the reduced frequency from 0.094 to 0.25. A microphone was placed in the far-field and the particle image velocimetry technique was utilized to study the flow structures near the trailing edge. The short-time Fourier transformation results of the noise signals revealed that a high-level narrow-band noise hump occurred at a specific angle of attack in a pitching cycle. At the corresponding moment, a coherent vortex street convecting on the airfoil surface was observed, and the vortex shedding frequency was in good agreement with the central frequency of the noise hump. The occurrence of the noise humps was attributed to the laminar boundary layer separation. In one pitching period, the moment when the narrow-band noise hump occurs is independent from the pitching amplitude and it is delayed as the pitching frequency increases. Larger pitching frequency or amplitude results in lower peak level of the noise humps.}, } @article {pmid31045081, year = {2019}, author = {Gao, Y and Yang, X and Fu, C and Yang, Y and Li, Z and Zhang, H and Qi, F}, title = {10 kHz simultaneous PIV/PLIF study of the diffusion flame response to periodic acoustic forcing.}, journal = {Applied optics}, volume = {58}, number = {10}, pages = {C112-C120}, doi = {10.1364/AO.58.00C112}, pmid = {31045081}, issn = {1539-4522}, abstract = {Response of a laminar diffusion dimethyl-ether flame forced by an acoustic field is provided. A forcing frequency of 100 Hz, which is chosen based on the typical thermo-acoustic instability frequency in a practical combustor, is applied to the flame at a Reynolds number of 250. The development of the forced vortical structures present in this flame has been investigated utilizing a burst mode laser with a repetition rate of 10 kHz. Flame/vortex interaction is visualized by planar laser-induced fluorescence (PLIF) of formaldehyde, which is used to identify the early-stage fuel decomposition in the flame. The flame structure is also correlated with the velocity field, which is obtained utilizing particle imaging velocimetry (PIV). The resulting phase-resolved and time-averaged velocity and vortex images indicate that the amplitude of excitation has pronounced effects on the flame via modifying the local heat release.}, } @article {pmid31045033, year = {2019}, author = {Wang, S and Liu, X and Wang, G and Xu, L and Li, L and Liu, Y and Huang, Z and Qi, F}, title = {High-repetition-rate burst-mode-laser diagnostics of an unconfined lean premixed swirling flame under external acoustic excitation.}, journal = {Applied optics}, volume = {58}, number = {10}, pages = {C68-C78}, doi = {10.1364/AO.58.000C68}, pmid = {31045033}, issn = {1539-4522}, abstract = {Lean premixed swirling flames are important in practical combustors, but a commonly encountered problem of practical swirl combustors is thermo-acoustic instability, which may cause internal structure damage to combustors. In this research, a high-repetition-rate burst-mode laser is used for simultaneous particle image velocimetry and planar laser-induced fluorescence measurement in an unconfined acoustically excited swirl burner. The time-resolved flow field and transient flame response to the acoustic perturbation are visualized at 20 kHz, offering insight into the heat release rate oscillation. The premixed mixture flow rate and acoustic modulation are varied to study the effects of Reynolds number, Strouhal number, and acoustic modulation amplitude on the swirling flame. The results suggest that the Strouhal number has a notable effect on the periodic movements of the inner recirculation zone and swirling flame configuration.}, } @article {pmid31039316, year = {2019}, author = {Mozhi Devan Padmanathan, A and Sneha Ravi, A and Choudhary, H and Varanakkottu, SN and Dalvi, SV}, title = {Predictive Framework for the Spreading of Liquid Drops and the Formation of Liquid Marbles on Hydrophobic Particle Bed.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {20}, pages = {6657-6668}, doi = {10.1021/acs.langmuir.9b00698}, pmid = {31039316}, issn = {1520-5827}, abstract = {In this work, we have developed a model to describe the behavior of liquid drops upon impaction on hydrophobic particle bed and verified it experimentally. Poly(tetrafluoroethylene) (PTFE) particles were used to coat drops of water, aqueous solutions of glycerol (20, 40, and 60% v/v), and ethanol (5 and 12% v/v). The experiments were conducted for Weber number (We) ranging from 8 to 130 and Reynolds number (Re) ranging from 370 to 4460. The bed porosity was varied from 0.8 to 0.6. The experimental values of βmax (ratio of the diameter at the maximum spreading condition to the initial drop diameter) were estimated from the time-lapsed images captured using a high-speed camera. The theoretical βmax was estimated by making energy balances on the liquid drop. The proposed model accounts for the energy losses due to viscous dissipation and crater formation along with a change in kinetic energy and surface energy. A good agreement was obtained between the experimental βmax and the estimated theoretical βmax. The proposed model yielded a least % absolute average relative deviation (% AARD) of 5.5 ± 4.3 compared to other models available in the literature. Further, it was found that the liquid drops impacting on particle bed are completely coated with PTFE particles with βmax values greater than 2.}, } @article {pmid31037445, year = {2019}, author = {Hatoum, H and Mo, XM and Crestanello, JA and Dasi, LP}, title = {Modeling of the Instantaneous Transvalvular Pressure Gradient in Aortic Stenosis.}, journal = {Annals of biomedical engineering}, volume = {47}, number = {8}, pages = {1748-1763}, pmid = {31037445}, issn = {1573-9686}, support = {R01HL119824//National Institutes of Health/ ; R01 HL119824/HL/NHLBI NIH HHS/United States ; 19POST34380804//American Heart Association/ ; R01 HL135505/HL/NHLBI NIH HHS/United States ; R03 EB014255/EB/NIBIB NIH HHS/United States ; }, mesh = {Aortic Valve/*physiopathology ; Aortic Valve Stenosis/*physiopathology ; Cardiac Output ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Pressure ; }, abstract = {The simplified and modified Bernoulli equations break down in estimating the true pressure gradient across the stenotic aortic valve due to their over simplifying assumptions of steady and inviscid conditions as well as the fundamental nature in which aortic valves are different than idealized orifices. Nevertheless, despite having newer models based on time-dependent momentum balance across an orifice, the simplified and modified Bernoulli continue to be the clinical standard because to date, they remain the only models clinically implementable. The objective of this study is to (1) illustrate the fundamental considerations necessary to accurately model the time-dependent instantaneous pressure gradient across a fixed orifice and (2) propose empirical corrections when applying orifice based models to severely stenotic aortic valves. We introduce a general model to predict the time-dependent instantaneous pressure gradient across an orifice that explicitly model the Reynolds number dependence of both the steady and unsteady terms. The accuracy of this general model is assessed with respect to previous models through pulse duplicator experiments on a round orifice model as well as an explanted stenotic surgical aortic valve both with geometric areas of 0.6 cm2 (less than 1 cm2 which is the threshold for stenosis determination) over cardiac outputs of 3 and 5 L/min and heart rates of 60, 90 and 120 bpm. The model and the raw experimental data corresponding to the orifice showed good agreement over a wide range of cardiac outputs and heart rates (R2 exceeding 0.91). The derived average and peak transvalvular pressure gradients also demonstrated good agreement with no significant differences between the respective peaks (p > 0.09). The new model proposed holds promise with its physical and closed form representation of pressure drop, however accurate modeling of the time-variability of the valve area is necessary for the model to be applied on stenotic valves.}, } @article {pmid31028849, year = {2019}, author = {Heidarinejad, G and Roozbahani, MH and Heidarinejad, M}, title = {Studying airflow structures in periodic cylindrical hills of human tracheal cartilaginous rings.}, journal = {Respiratory physiology & neurobiology}, volume = {266}, number = {}, pages = {103-114}, doi = {10.1016/j.resp.2019.04.012}, pmid = {31028849}, issn = {1878-1519}, mesh = {Cartilage/*anatomy & histology ; Computer Simulation ; Humans ; *Models, Anatomic ; *Models, Biological ; *Respiratory Physiological Phenomena ; Trachea/*anatomy & histology ; }, abstract = {The objective of this study is to assess tracheobronchial flow features with the cartilaginous rings during a light exercising. Tracheobronchial is part of human's body airway system that carries oxygen-rich air to human's lungs as well as takes carbon dioxide out of the human's lungs. Consequently, evaluation of the flow structures in tracheobronchial is important to support diagnosis of tracheal disorders. Computational Fluid Dynamics (CFD) allows evaluating effectiveness of tracheal cartilage rings in human body under different configurations. This study utilizes Large Eddy Simulation (LES) to model an anatomically-based human large conducting airway model with and without cartilaginous rings at the breathing conditions at Reynolds number of 5,176 in trachea region. It is observed that small recirculating areas shaped between rings cavities. While these recirculating areas are decaying, similar to periodic 2D-hills, the cartilaginous rings contribute to the construction of a vortical flow structure in the main flow. The separated vortically-shaped zone creates a wake in the flow and passes inside of the next ring cavity and disturb its boundary layer. At last, the small recirculation flow impinges onto tracheal wall. The outcome of this impinge flow is a latitudinal rotating flow perpendicular to the main flow in a cavity between the two cartilaginous rings crest which appear and disappear within a hundredth of a second. Kelvin-Helmholtz instability is observed in trachea caused by shear flow created behind of interaction between these flow structures near to tracheal wavy wall and main flow. A comparison of the results between a smooth wall model named simplified model and a rough wall model named modified model shows that these structures do not exist in simplified model, which is common in modeling tracheobronchial flow. This study proposes to consider macro surface roughness to account for the separating and rotating instantaneous flow structures. Finally, solving trachea airflow with its cartilages can become one of major issues in measuring the validity and capability of solving flow in developing types of sub-grid scale models as a turbulence studies benchmark.}, } @article {pmid31008408, year = {2019}, author = {Vasilopoulos, K and Sarris, IE and Tsoutsanis, P}, title = {Assessment of air flow distribution and hazardous release dispersion around a single obstacle using Reynolds-averaged Navier-Stokes equations.}, journal = {Heliyon}, volume = {5}, number = {4}, pages = {e01482}, pmid = {31008408}, issn = {2405-8440}, abstract = {The flow around a cubical building, with a pollution source at the central point of the top of the cube, is studied. The Reynolds-averaged Navier-Stokes and species concentration equations are solved for Reynolds number, Re = 40,000, is based on the height of the cube. The predictions obtained with the standard, the Kato-Launder, and the low-Reynolds number k-epsilon models are examined with various wall functions for the near wall treatment of the flow. Results are compared against Martinuzzi and Tropea measurements (J. of Fluids Eng., 115, 85-92, 1993) for the flow field and against Li and Meroney (J. of Wind Eng. and Industrial Aerodynamics, 81, 333-345, 1983) experiments and Gaussian models for the concentration distribution. It is found that the present unstructured mesh model performs similarly to the structured mesh models. Results from the Kato-Launder model are closer to the experimental data for the flow patterns and contaminant distribution on the cube's roof. However, the Kato-Launder model has an over-prediction for the recirculation zone and the contaminant distribution windward of the cube. The standard k-epsilon and the low-Reynolds number k-epsilon models predict similar flow patterns and are closer to the experimental data of the cube's windward and side face.}, } @article {pmid31007546, year = {2019}, author = {Martins Afonso, M and Mitra, D and Vincenzi, D}, title = {Kazantsev dynamo in turbulent compressible flows.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2223}, pages = {20180591}, pmid = {31007546}, issn = {1364-5021}, abstract = {We consider the kinematic fluctuation dynamo problem in a flow that is random, white-in-time, with both solenoidal and potential components. This model is a generalization of the well-studied Kazantsev model. If both the solenoidal and potential parts have the same scaling exponent, then, as the compressibility of the flow increases, the growth rate decreases but remains positive. If the scaling exponents for the solenoidal and potential parts differ, in particular if they correspond to typical Kolmogorov and Burgers values, we again find that an increase in compressibility slows down the growth rate but does not turn it off. The slow down is, however, weaker and the critical magnetic Reynolds number is lower than when both the solenoidal and potential components display the Kolmogorov scaling. Intriguingly, we find that there exist cases, when the potential part is smoother than the solenoidal part, for which an increase in compressibility increases the growth rate. We also find that the critical value of the scaling exponent above which a dynamo is seen is unity irrespective of the compressibility. Finally, we realize that the dimension d = 3 is special, as for all other values of d the critical exponent is higher and depends on the compressibility.}, } @article {pmid31003548, year = {2019}, author = {Zhang, M and Zhang, W and Wu, Z and Shen, Y and Chen, Y and Lan, C and Li, F and Cai, W}, title = {Comparison of Micro-Mixing in Time Pulsed Newtonian Fluid and Viscoelastic Fluid.}, journal = {Micromachines}, volume = {10}, number = {4}, pages = {}, pmid = {31003548}, issn = {2072-666X}, abstract = {Fluid mixing plays an essential role in many microfluidic applications. Here, we compare the mixing in time pulsing flows for both a Newtonian fluid and a viscoelastic fluid at different pulsing frequencies. In general, the mixing degree in the viscoelastic fluid is higher than that in the Newtonian fluid. Particularly, the mixing in Newtonian fluid with time pulsing is decreased when the Reynolds number Re is between 0.002 and 0.01, while it is enhanced when Re is between 0.1 and 0.2 compared with that at a constant flow rate. In the viscoelastic fluid, on the other hand, the time pulsing does not change the mixing degree when the Weissenberg number Wi ≤ 20, while a larger mixing degree is realized at a higher pulsing frequency when Wi = 50.}, } @article {pmid30999540, year = {2019}, author = {Duran-Matute, M and van Gorp, MD and van Heijst, GJF}, title = {Wavelength selection of vortex ripples in an oscillating cylinder: The effect of curvature and background rotation.}, journal = {Physical review. E}, volume = {99}, number = {3-1}, pages = {033105}, doi = {10.1103/PhysRevE.99.033105}, pmid = {30999540}, issn = {2470-0053}, abstract = {We present results of laboratory experiments on the formation, evolution, and wavelength selection of vortex ripples. These ripples formed on a sediment bed at the bottom of a water-filled oscillating cylindrical tank mounted on top of a rotating table. The table is made to oscillate sinusoidally in time, while a constant background rotation was added for some experiments. The changes in bed thickness are measured using a light attenuation technique. It was found that the wavelength normalized with the excursion length depends on both a Reynolds number and the Strouhal number. This differs from straight or annular geometries where the wavelength is proportional to the excursion length. The flow in an oscillating cylinder has the peculiarity that it develops a secondary flow in the radial direction that depends on the excursion length. The effect of this secondary circulation is evident in the radial transport for small values of the Strouhal number or in the orientation of the ripples for strong enough background rotation. Additionally, ripples in an oscillating cylinder present a rich dynamic behavior where the number of ripples can oscillate even with constant forcing parameters.}, } @article {pmid30999463, year = {2019}, author = {Dutta, AK and Ramachandran, G and Chaudhuri, S}, title = {Investigating thermoacoustic instability mitigation dynamics with a Kuramoto model for flamelet oscillators.}, journal = {Physical review. E}, volume = {99}, number = {3-1}, pages = {032215}, doi = {10.1103/PhysRevE.99.032215}, pmid = {30999463}, issn = {2470-0053}, abstract = {In this paper, we present experimental observations and phenomenological modeling of the intermittent dynamics that emerge while mitigating thermoacoustic instability by rotating the otherwise static swirler in a lean premixed, laboratory-scale combustor. Starting with a self-excited thermoacoustically unstable combustor, here we find that a progressive increase in swirler rotation rate does not uniformly decrease amplitudes of coherent, sinusoidal pressure or heat-release-rate oscillations. Instead, these oscillations emerge as high-amplitude bursts separated by low-amplitude noise in the signal. At increased rotational speeds, the high-amplitude coherent oscillations become scarce and their duration in the signal reduces. The velocity field from high-speed particle image velocimetry and simultaneous pressure and chemiluminescence data support these observations. Such an intermittent route to instability mitigation is reminiscent of the opposite transition implemented by changing the Reynolds number from a fully chaotic state to a fully unstable state. To model such dynamics phenomenologically, we discretize the swirling turbulent premixed flame into an ensemble of flamelet oscillators arranged circumferentially around the center body of the swirler. The Kuramoto model is proposed for these flamelet oscillators which is subsequently used to analyze their synchronization dynamics. The order parameter r, which is a measure of the synchronization between the oscillator phases, provides critical insights on the transition from the thermoacoustically unstable to stable states via intermittency. Finally, it is shown that the Kuramoto model for flamelet oscillator can qualitatively reproduce the time-averaged and intermittent dynamics while transitioning from the state of thermoacoustic instability to a state of incoherent noisy oscillations.}, } @article {pmid30999454, year = {2019}, author = {Shaik, VA and Ardekani, AM}, title = {Swimming sheet near a plane surfactant-laden interface.}, journal = {Physical review. E}, volume = {99}, number = {3-1}, pages = {033101}, doi = {10.1103/PhysRevE.99.033101}, pmid = {30999454}, issn = {2470-0053}, abstract = {In this work we analyze the velocity of a swimming sheet near a plane surfactant-laden interface by assuming the Reynolds number and the sheet's deformation to be small. We observe a nonmonotonic dependence of the sheet's velocity on the Marangoni number (Ma) and the surface Péclet number (Pe_{s}). For a sheet passing only transverse waves, the swimming velocity increases with an increase in Ma for any fixed Pe_{s}. When Pe_{s} is increasing, on the other hand, the swimming velocity of the same sheet either increases (at large Ma) or it initially increases and then decreases (at small Ma). This dependence of the swimming velocity on Ma and Pe_{s} is altered if the sheet is passing longitudinal waves in addition to the transverse waves along its surface.}, } @article {pmid30993773, year = {2019}, author = {Cheng, JL and Au, JS and MacDonald, MJ}, title = {Peripheral artery endothelial function responses to altered shear stress patterns in humans.}, journal = {Experimental physiology}, volume = {104}, number = {7}, pages = {1126-1135}, doi = {10.1113/EP087597}, pmid = {30993773}, issn = {1469-445X}, support = {DG #238819-13//Natural Sciences and Engineering Research Council/International ; }, mesh = {Adult ; Blood Flow Velocity/*physiology ; Brachial Artery/*physiology ; Electrocardiography/methods ; Endothelium, Vascular/*physiology ; Hand Strength/physiology ; Hot Temperature ; Humans ; Male ; Regional Blood Flow/*physiology ; Shear Strength/*physiology ; *Stress, Mechanical ; Vasodilation/physiology ; Young Adult ; }, abstract = {NEW FINDINGS: What is the central question of this study? What is the effect of altered shear stress pattern, with or without concurrent neurohumoral and metabolic activation, on the acute endothelial function response assessed via brachial artery flow-mediated dilatation? What is the main finding and its importance? Despite generating distinctive shear stress patterns (i.e. increases in anterograde only, anterograde only with neurohumoral and metabolic activation, and both anterograde and retrograde), similar acute improvements were observed in the brachial artery flow-mediated dilatation response in all conditions, indicating that anterograde and/or turbulent shear stress might be the essential element to induce acute increases in endothelial function.

ABSTRACT: Endothelial function is influenced by both the direction and the magnitude of shear stress. Acute improvements in endothelial function have mostly been attributed to increased anterograde shear, whereas results from many interventional models in humans suggest that enhancing shear stress in an oscillatory manner (anterograde and retrograde) might be optimal. Here, we determined the acute brachial artery shear stress (SS) and flow-mediated dilatation (FMD) responses to three shear-altering interventions [passive heat stress (HEAT), mechanical forearm compression (CUFF) and handgrip exercise (HGEX)] and examined the relationship between changes in oscillatory shear index (OSI) and changes in FMD. During separate visits, 10 young healthy men (22 ± 3 years old) underwent 10 min of HEAT, CUFF or HGEX in their left forearm. Anterograde and retrograde SS, Reynolds number, OSI and FMD were assessed at rest and during/after each intervention. Anterograde SS increased during all interventions in a stepwise manner (P < 0.05 between interventions), with the change in HGEX (∆37.7 ± 12.2 dyn cm-2 , P < 0.05) > CUFF (∆25.1 ± 11.9 dyn cm-2 , P < 0.05) > HEAT (∆14.5 ± 7.9 dyn cm-2 , P < 0.05). Retrograde SS increased during CUFF (∆-19.6 ± 4.3 dyn cm-2 , P < 0.05). Anterograde blood flow was turbulent (i.e. Reynolds number ≥ |2000|) during all interventions (P < 0.05). The relative FMD improved after all interventions (P = 0.01), and there was no relationship between ∆OSI and ∆FMD. We elicited changes in SS profiles including increased anterograde SS (HEAT and HGEX) and both increased anterograde and retrograde SS (CUFF); regardless of the SS pattern, FMD improved to the same extent. These findings suggest that the presence of anterograde and/or turbulent SS might be the key to optimizing endothelial function in acute assessment protocols.}, } @article {pmid30978086, year = {2019}, author = {Wei, D and Dehnavi, PG and Aubin-Tam, ME and Tam, D}, title = {Is the Zero Reynolds Number Approximation Valid for Ciliary Flows?.}, journal = {Physical review letters}, volume = {122}, number = {12}, pages = {124502}, doi = {10.1103/PhysRevLett.122.124502}, pmid = {30978086}, issn = {1079-7114}, abstract = {Stokes equations are commonly used to model the hydrodynamic flow around cilia on the micron scale. The validity of the zero Reynolds number approximation is investigated experimentally with a flow velocimetry approach based on optical tweezers, which allows the measurement of periodic flows with high spatial and temporal resolution. We find that beating cilia generate a flow, which fundamentally differs from the stokeslet field predicted by Stokes equations. In particular, the flow velocity spatially decays at a faster rate and is gradually phase delayed at increasing distances from the cilia. This indicates that the quasisteady approximation and use of Stokes equations for unsteady ciliary flow are not always justified and the finite timescale for vorticity diffusion cannot be neglected. Our results have significant implications in studies of synchronization and collective dynamics of microswimmers.}, } @article {pmid30978052, year = {2019}, author = {Shekar, A and McMullen, RM and Wang, SN and McKeon, BJ and Graham, MD}, title = {Critical-Layer Structures and Mechanisms in Elastoinertial Turbulence.}, journal = {Physical review letters}, volume = {122}, number = {12}, pages = {124503}, doi = {10.1103/PhysRevLett.122.124503}, pmid = {30978052}, issn = {1079-7114}, abstract = {Simulations of elastoinertial turbulence (EIT) of a polymer solution at low Reynolds number are shown to display localized polymer stretch fluctuations. These are very similar to structures arising from linear stability (Tollmien-Schlichting modes) and resolvent analyses, i.e., critical-layer structures localized where the mean fluid velocity equals the wave speed. Computations of self-sustained nonlinear Tollmien-Schlichting waves reveal that the critical layer exhibits stagnation points that generate sheets of large polymer stretch. These kinematics may be the genesis of similar structures in EIT.}, } @article {pmid30976530, year = {2019}, author = {M, AA and V, M}, title = {Demand factor definition-A dimensionless parameter for Vertical Axis Wind Turbines.}, journal = {MethodsX}, volume = {6}, number = {}, pages = {567-581}, pmid = {30976530}, issn = {2215-0161}, abstract = {The use of dimensionless numbers like Reynolds Number, Froude Number and Webber Number has historically simplified the process of comparison of phenomena irrespective of their scales and in their classification into different categories. This paper deals with the derivational aspects of a dimensionless parameter named "Demand Factor" for optimization of Vertical Axis Wind Turbine (VAWT). •The input parameters considered in this derivation are power, wind velocity, the aspect ratio of the turbine, density of air and viscosity of air and the output parameters are length of the blade, number of blades, chord length, aerofoil shape, radius of the turbine and angular velocity at rated speed.•Four rounds of variable definition trials are carried out through the arrangement of the input parameters on the numerator and denominator positions. With the filtering out of unsuitable combinations at different stages of elimination, out of 32 combinations the expression that holds the potential to represent demand factor was identified. The process of carrying out single point optimization based on Demand factor expression is discussed along with the steps involved in numerically calculating output parameters.•The expression of Demand factor developed provides a different perspective on the process of design and optimization of VAWTs.}, } @article {pmid30960580, year = {2019}, author = {Wang, Y and Wang, Y and Cheng, Z}, title = {Direct Numerical Simulation of Gas-Liquid Drag-Reducing Cavity Flow by the VOSET Method.}, journal = {Polymers}, volume = {11}, number = {4}, pages = {}, pmid = {30960580}, issn = {2073-4360}, support = {No.51576210//National Natural Science Foundation of China (NSFC)/ ; }, abstract = {Drag reduction by polymer is an important energy-saving technology, which can reduce pumping pressure or promote the flow rate of the pipelines transporting fluid. It has been widely applied to single-phase pipelines, such as oil pipelining, district heating systems, and firefighting. However, the engineering application of the drag reduction technology in two-phase flow systems has not been reported. The reason is an unrevealed complex mechanism of two-phase drag reduction and lack of numerical tools for mechanism study. Therefore, we aim to propose governing equations and numerical methods of direct numerical simulation (DNS) for two-phase gas-liquid drag-reducing flow and try to explain the reason for the two-phase drag reduction. Efficient interface tracking method-coupled volume-of-fluid and level set (VOSET) and typical polymer constitutive model Giesekus are combined in the momentum equation of the two-phase turbulent flow. Interface smoothing for conformation tensor induced by polymer is used to ensure numerical stability of the DNS. Special features and corresponding explanations of the two-phase gas-liquid drag-reducing flow are found based on DNS results. High shear in a high Reynolds number flow depresses the efficiency of the gas-liquid drag reduction, while a high concentration of polymer promotes the efficiency. To guarantee efficient drag reduction, it is better to use a high concentration of polymer drag-reducing agents (DRAs) for high shear flow.}, } @article {pmid30958231, year = {2018}, author = {Stocking, JB and Laforsch, C and Sigl, R and Reidenbach, MA}, title = {The role of turbulent hydrodynamics and surface morphology on heat and mass transfer in corals.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {149}, pages = {20180448}, pmid = {30958231}, issn = {1742-5662}, mesh = {Animals ; Anthozoa/*physiology ; *Coral Reefs ; *Hot Temperature ; *Hydrodynamics ; *Models, Biological ; }, abstract = {Corals require efficient heat and mass transfer with the overlying water column to support key biological processes, such as nutrient uptake and mitigation of thermal stress. Transfer rates are primarily determined by flow conditions, coral morphology and the physics of the resulting fluid-structure interaction, yet the relationship among these parameters is poorly understood especially for wave-dominated coral habitats. To investigate the interactive effects of these factors on fluxes of heat and mass, we measure hydrodynamic characteristics in situ over three distinct surface morphologies of massive stony corals in a Panamanian reef. Additionally, we implement a numerical model of flow and thermal transport for both current and wave conditions past a natural coral surface, as well as past three simplified coral morphologies with varying ratios of surface roughness spacing-to-height. We find oscillatory flow enhances rates of heat and mass transfer by 1.2-2.0× compared with unidirectional flow. Additionally, increases in Reynolds number and in surface roughness ratio produce up to a 3.3× and a 2.0× enhancement, respectively. However, as waves begin to dominate the flow regime relative to unidirectional currents, the underlying physical mechanisms mediating transfer rates shift from predominantly turbulence-driven to greater control by inertial accelerations, resulting in larger heat and mass transfer for small surface roughness ratios. We show that for rough corals in wave-dominated flows, novel trade-off dynamics for heat and mass transfer exist between broadly spaced roughness that enhances turbulence production versus narrowly spaced roughness that produces greater surface area. These findings have important implications for differential survivorship during heat-induced coral bleaching, particularly as thermal stress events become increasingly common with global climate change.}, } @article {pmid30958200, year = {2019}, author = {Tuttle, LJ and Robinson, HE and Takagi, D and Strickler, JR and Lenz, PH and Hartline, DK}, title = {Going with the flow: hydrodynamic cues trigger directed escapes from a stalking predator.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {151}, pages = {20180776}, pmid = {30958200}, issn = {1742-5662}, mesh = {Animals ; *Biobehavioral Sciences ; Copepoda/*physiology ; Escape Reaction/*physiology ; Fishes/*physiology ; Food Chain ; Predatory Behavior/*physiology ; Zooplankton/*physiology ; }, abstract = {In the coevolution of predator and prey, different and less well-understood rules for threat assessment apply to freely suspended organisms than to substrate-dwelling ones. Particularly vulnerable are small prey carried with the bulk movement of a surrounding fluid and thus deprived of sensory information within the bow waves of approaching predators. Some planktonic prey have solved this apparent problem, however. We quantified cues generated by the slow approach of larval clownfish (Amphiprion ocellaris) that triggered a calanoid copepod (Bestiolina similis) to escape before the fish could strike. To estimate water deformation around the copepod immediately preceding its jump, we represented the body of the fish as a rigid sphere in a hydrodynamic model that we parametrized with measurements of fish size, approach speed and distance to the copepod. Copepods of various developmental stages (CII-CVI) were sensitive to the water flow caused by the live predator, at deformation rates as low as 0.04 s-1. This rate is far lower than that predicted from experiments that used artificial predator-mimics. Additionally, copepods localized the source, with 87% of escapes directed away (greater than or equal to 90°) from the predator. Thus, copepods' survival in life-threatening situations relied on their detection of small nonlinear signals within an environment of locally linear deformation.}, } @article {pmid30958167, year = {2019}, author = {Nguyen, H and Koehl, MAR and Oakes, C and Bustamante, G and Fauci, L}, title = {Effects of cell morphology and attachment to a surface on the hydrodynamic performance of unicellular choanoflagellates.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {150}, pages = {20180736}, pmid = {30958167}, issn = {1742-5662}, mesh = {Cell Adhesion/*physiology ; Choanoflagellata/cytology/*physiology ; *Hydrodynamics ; *Models, Biological ; Surface Properties ; Swimming/*physiology ; }, abstract = {Choanoflagellates, eukaryotes that are important predators on bacteria in aquatic ecosystems, are closely related to animals and are used as a model system to study the evolution of animals from protozoan ancestors. The choanoflagellate Salpingoeca rosetta has a complex life cycle with different morphotypes, some unicellular and some multicellular. Here we use computational fluid dynamics to study the hydrodynamics of swimming and feeding by different unicellular stages of S. rosetta: a swimming cell with a collar of prey-capturing microvilli surrounding a single flagellum, a thecate cell attached to a surface and a dispersal-stage cell with a slender body, long flagellum and short collar. We show that a longer flagellum increases swimming speed, longer microvilli reduce speed and cell shape only affects speed when the collar is very short. The flux of prey-carrying water into the collar capture zone is greater for swimming than sessile cells, but this advantage decreases with collar size. Stalk length has little effect on flux for sessile cells. We show that ignoring the collar, as earlier models have done, overestimates flux and greatly overestimates the benefit to feeding performance of swimming versus being attached, and of a longer stalk for attached cells.}, } @article {pmid30958164, year = {2019}, author = {Asadzadeh, SS and Nielsen, LT and Andersen, A and Dölger, J and Kiørboe, T and Larsen, PS and Walther, JH}, title = {Hydrodynamic functionality of the lorica in choanoflagellates.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {150}, pages = {20180478}, pmid = {30958164}, issn = {1742-5662}, mesh = {*Choanoflagellata/physiology/ultrastructure ; *Hydrodynamics ; *Models, Biological ; Movement/*physiology ; }, abstract = {Choanoflagellates are unicellular eukaryotes that are ubiquitous in aquatic habitats. They have a single flagellum that creates a flow toward a collar filter composed of filter strands that extend from the cell. In one common group, the loricate choanoflagellates, the cell is suspended in an elaborate basket-like structure, the lorica, the function of which remains unknown. Here, we use Computational Fluid Dynamics to explore the possible hydrodynamic function of the lorica. We use the choanoflagellate Diaphaoneca grandis as a model organism. It has been hypothesized that the function of the lorica is to prevent refiltration (flow recirculation) and to increase the drag and, hence, increase the feeding rate and reduce the swimming speed. We find no support for these hypotheses. On the contrary, motile prey are encountered at a much lower rate by the loricate organism. The presence of the lorica does not affect the average swimming speed, but it suppresses the lateral motion and rotation of the cell. Without the lorica, the cell jiggles from side to side while swimming. The unsteady flow generated by the beating flagellum causes reversed flow through the collar filter that may wash away captured prey while it is being transported to the cell body for engulfment. The lorica substantially decreases such flow, hence it potentially increases the capture efficiency. This may be the main adaptive value of the lorica.}, } @article {pmid30958143, year = {2019}, author = {Asadzadeh, SS and Larsen, PS and Riisgård, HU and Walther, JH}, title = {Hydrodynamics of the leucon sponge pump.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {150}, pages = {20180630}, pmid = {30958143}, issn = {1742-5662}, mesh = {Animals ; Flagella/*physiology ; *Hydrodynamics ; *Models, Biological ; Porifera/*anatomy & histology/*physiology ; }, abstract = {Leuconoid sponges are filter-feeders with a complex system of branching inhalant and exhalant canals leading to and from the close-packed choanocyte chambers. Each of these choanocyte chambers holds many choanocytes that act as pumping units delivering the relatively high pressure rise needed to overcome the system pressure losses in canals and constrictions. Here, we test the hypothesis that, in order to deliver the high pressures observed, each choanocyte operates as a leaky, positive displacement-type pump owing to the interaction between its beating flagellar vane and the collar, open at the base for inflow but sealed above. The leaking backflow is caused by small gaps between the vaned flagellum and the collar. The choanocyte pumps act in parallel, each delivering the same high pressure, because low-pressure and high-pressure zones in the choanocyte chamber are separated by a seal (secondary reticulum). A simple analytical model is derived for the pump characteristic, and by imposing an estimated system characteristic we obtain the back-pressure characteristic that shows good agreement with available experimental data. Computational fluid dynamics is used to verify a simple model for the dependence of leak flow through gaps in a conceptual collar-vane-flagellum system and then applied to models of a choanocyte tailored to the parameters of the freshwater demosponge Spongilla lacustris to study its flows in detail. It is found that both the impermeable glycocalyx mesh covering the upper part of the collar and the secondary reticulum are indispensable features for the choanocyte pump to deliver the observed high pressures. Finally, the mechanical pump power expended by the beating flagellum is compared with the useful (reversible) pumping power received by the water flow to arrive at a typical mechanical pump efficiency of about 70%.}, } @article {pmid30940542, year = {2019}, author = {Janke, T and Koullapis, P and Kassinos, SC and Bauer, K}, title = {PIV measurements of the SimInhale benchmark case.}, journal = {European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences}, volume = {133}, number = {}, pages = {183-189}, doi = {10.1016/j.ejps.2019.03.025}, pmid = {30940542}, issn = {1879-0720}, mesh = {Acrylic Resins ; Benchmarking ; Butadienes ; Computer Simulation ; Humans ; Lung/*metabolism ; *Models, Biological ; Polystyrenes ; Printing, Three-Dimensional ; *Rheology ; }, abstract = {Particle Image Velocimetry (PIV) measurements with the aim of providing experimental data for the SimInhale benchmark case are presented within this work. We, therefore, present a refractive index matched, transparent model of the benchmark geometry, in which the velocity and turbulent kinetic energy fields are examined at flow rates comparable to 15, 30 and 60 L/min (Re ≈ 1000-4500) in air. Furthermore, these results are compared with Large Eddy Simulations (LES). The results reveal a Reynolds number independence of the qualitative velocity field in the range covered within this work. Good agreement is found between the PIV and LES data, with a slight over-prediction of turbulent kinetic energies by the simulations. The obtained experimental data will be part of a common, publicly accessible ERCOFTAC database along with additional results published recently.}, } @article {pmid30937853, year = {2019}, author = {Mancini, V and Bergersen, AW and Vierendeels, J and Segers, P and Valen-Sendstad, K}, title = {High-Frequency Fluctuations in Post-stenotic Patient Specific Carotid Stenosis Fluid Dynamics: A Computational Fluid Dynamics Strategy Study.}, journal = {Cardiovascular engineering and technology}, volume = {10}, number = {2}, pages = {277-298}, pmid = {30937853}, issn = {1869-4098}, mesh = {Aged ; Asymptomatic Diseases ; Blood Flow Velocity ; Carotid Artery, Common/*physiopathology ; Carotid Stenosis/*diagnosis/physiopathology ; Computed Tomography Angiography ; Finite Element Analysis ; *Hemodynamics ; Humans ; Hydrodynamics ; Male ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; *Patient-Specific Modeling ; Predictive Value of Tests ; Proof of Concept Study ; Pulsatile Flow ; Regional Blood Flow ; Time Factors ; Vibration ; }, abstract = {PURPOSE: Screening of asymptomatic carotid stenoses is performed by auscultation of the carotid bruit, but the sensitivity is poor. Instead, it has been suggested to detect carotid bruit as neck's skin vibrations. We here take a first step towards a computational fluid dynamics proof-of-concept study, and investigate the robustness of our numerical approach for capturing high-frequent fluctuations in the post-stenotic flow. The aim was to find an ideal solution strategy from a pragmatic point of view, balancing accuracy with computational cost comparing an under-resolved direct numerical simulation (DNS) approach vs. three common large eddy simulation (LES) models (static/dynamic Smagorinsky and Sigma).

METHOD: We found a reference solution by performing a spatial and temporal refinement study of a stenosed carotid bifurcation with constant flow rate. The reference solution [Formula: see text] was compared against LES for both a constant and pulsatile flow.

RESULTS: Only the Sigma and Dynamic Smagorinsky models were able to replicate the flow field of the reference solution for a pulsatile simulation, however the computational cost of the Sigma model was lower. However, none of the sub-grid scale models were able to replicate the high-frequent flow in the peak-systolic constant flow rate simulations, which had a higher mean Reynolds number.

CONCLUSIONS: The Sigma model was the best combination between accuracy and cost for simulating the pulsatile post-stenotic flow field, whereas for the constant flow rate, the under-resolved DNS approach was better. These results can be used as a reference for future studies investigating high-frequent flow features.}, } @article {pmid30934360, year = {2019}, author = {Ma, J and Xu, L and Tian, FB and Young, J and Lai, JCS}, title = {Dynamic characteristics of a deformable capsule in a simple shear flow.}, journal = {Physical review. E}, volume = {99}, number = {2-1}, pages = {023101}, doi = {10.1103/PhysRevE.99.023101}, pmid = {30934360}, issn = {2470-0053}, abstract = {The dynamic characteristics of a two-dimensional deformable capsule in a simple shear flow are studied with an immersed boundary-lattice Boltzmann method. Simulations are conducted by varying the Reynolds number (Re) from 0.0125 to 2000 and the dimensionless shear rate (G) from 0.001 to 0.5. The G-Re plane can be divided into four regions according to the deformation dependence on the parameters considered: viscous dominant, inertia dominant, transitional, and anomalous regions. There are four typical dynamic behaviors over the G-Re plane: steady deformation, prerupture state, quasisteady deformation, and continuous elongation. Analysis indicates that the pressure distribution and its variations due to the interplay of the fluid inertia force, the viscous shear stress, and the membrane elastic force determines the complex behaviors of the capsule. The effects of the bending rigidity and the internal-to-external viscosity ratio on the dynamics of the capsule are further studied. It is found that the capsule experiences smaller deformation when the higher bending rigidity is included, and the low bending rigidity does not have a remarkable influence on the capsule deformation. The capsule normally experiences smaller deformation due to the increase of the internal-to-external viscosity ratio.}, } @article {pmid30934349, year = {2019}, author = {Pereira, M and Gissinger, C and Fauve, S}, title = {1/f noise and long-term memory of coherent structures in a turbulent shear flow.}, journal = {Physical review. E}, volume = {99}, number = {2-1}, pages = {023106}, doi = {10.1103/PhysRevE.99.023106}, pmid = {30934349}, issn = {2470-0053}, abstract = {A shear flow of liquid metal (Galinstan) is driven in an annular channel by counter-rotating traveling magnetic fields imposed at the end caps. When the traveling velocities are large, the flow is turbulent and its azimuthal component displays random reversals. Power spectra of the velocity field exhibit a 1/f^{α} power law on several decades and are related to power-law probability distributions P(τ)∼τ^{-β} of the waiting times between successive reversals. This 1/f type spectrum is observed only when the Reynolds number is large enough. In addition, the exponents α and β are controlled by the symmetry of the system; a continuous transition between two different types of Flicker noise is observed as the equatorial symmetry of the flow is broken, in agreement with theoretical predictions.}, } @article {pmid30899783, year = {2019}, author = {Tang, X and Staack, D}, title = {Bioinspired mechanical device generates plasma in water via cavitation.}, journal = {Science advances}, volume = {5}, number = {3}, pages = {eaau7765}, pmid = {30899783}, issn = {2375-2548}, abstract = {Nature can generate plasma in liquids more efficiently than human-designed devices using electricity, acoustics, or light. In the animal world, snapping shrimp can induce cavitation that collapses to produce high pressures and temperatures, leading to efficient plasma formation with photon and shock wave emission via energy focusing. Here, we report a bioinspired mechanical device that mimics the plasma generation technique of the snapping shrimp. This device was manufactured using additive manufacturing based on micro-x-ray computed tomography of a snapping shrimp claw molt. A spring fixture was designed to reliably actuate the claw with appropriate force and velocity to produce a high-speed water jet that matches the cavitation number and Reynolds number of the shrimp. Light emission and shocks were imaged, which indicate that our device reproduces the shrimp's plasma generation technique and is more efficient than other plasma generation methods.}, } @article {pmid30891517, year = {2019}, author = {Nagaraju, G and Garvandha, M}, title = {Magnetohydrodynamic viscous fluid flow and heat transfer in a circular pipe under an externally applied constant suction.}, journal = {Heliyon}, volume = {5}, number = {2}, pages = {e01281}, pmid = {30891517}, issn = {2405-8440}, abstract = {An analytical investigation of two-dimensional heat transfer behavior of an axisymmetric incompressible dissipative viscous fluid flow in a circular pipe is considered. The flow is subjected to an externally applied uniform suction over the pipe wall in the transverse direction and a constant magnetic field opposite to the wall. The reduced Navier-Stokes equations in the cylindrical system are applied for the velocity and temperature fields. Constant wall temperature is considered as the thermal boundary condition. The velocity components are expressed into stream function and its solution is acquired by the Homotopy analysis method (HAM). The effects of magnetic body force parameter(M), suction Reynolds number (Re), Prandtl number (Pr)and Eckert number (Ec) on velocity and temperature are examined and are presented in a graphical frame. Streamlines, isotherms and pressure contours are likewise pictured. It is observed that with increasing suction Reynold number decelerates axial flow, whereas it enhances the radial flow. The temperature distribution increases with an increase in Prandtl number, whereas it decreases with an increase in Eckert number (viscous dissipation effect).}, } @article {pmid30879156, year = {2019}, author = {El-Sapa, S}, title = {Settling slip velocity of a spherical particle in an unbounded micropolar fluid.}, journal = {The European physical journal. E, Soft matter}, volume = {42}, number = {3}, pages = {32}, pmid = {30879156}, issn = {1292-895X}, abstract = {The gravitational settling of small spherical particles in an unbounded micropolar fluid with slip surfaces is considered. The motion is studied under the assumption of low Reynolds number. The slip boundary conditions on velocity and microrotation at the surface of the spherical particle is used. The solution for the stream function of the fluid flow is obtained analytically. The settling velocity is obtained and is plotted against the Knudsen number for various values of the micropolarity parameter and constants depending on the material of the solid surface. The problem of rotational motion of a particle with slip surface is also solved and the torque coefficient acting on the spherical particle is obtained and is plotted against Knudsen number for different values of micropolarity parameter, spin parameter, and the material constants. The correction to the Basset equation for settling velocity under gravity for slip particle in micropolar fluids is discussed with the range of Knudsen number which has been proven with known results available in the literature.}, } @article {pmid30875616, year = {2019}, author = {Sun, J and Liu, C and Bhushan, B}, title = {A review of beetle hindwings: Structure, mechanical properties, mechanism and bioinspiration.}, journal = {Journal of the mechanical behavior of biomedical materials}, volume = {94}, number = {}, pages = {63-73}, doi = {10.1016/j.jmbbm.2019.02.031}, pmid = {30875616}, issn = {1878-0180}, mesh = {Animals ; Biomechanical Phenomena ; *Biomimetics ; Coleoptera/*anatomy & histology/physiology ; *Mechanical Phenomena ; Movement ; Wings, Animal/*anatomy & histology/physiology ; }, abstract = {Insects have a small mass and size and a low flying Reynolds number. Consequently, they serve as an excellent bionic representation of a micro air vehicle (MAV). Coleoptera (popularly referred to as beetles) have different characteristics from other flying insects. Not only can they fly at a low Reynolds number, but they also have deployable hindwings, which directly leads to a reduction in the size of their bodies. In narrow working spaces or unfavorable environments, a beetle's hindwings can fold automatically under the hard elytron. When the environment becomes conducive to flight, the hindwings can extend and help the beetle take off. This characteristic provides inspiration for the design of a bionic deployable wing system. In this paper, the structures and mechanical properties of hindwings and the mechanism of hindwing movement are reviewed, in addition to research on bioinspired deployable wings.}, } @article {pmid30873209, year = {2019}, author = {Sepehr, H and Nikrityuk, P and Breakey, D and Sanders, RS}, title = {Numerical study of crude oil batch mixing in a long channel.}, journal = {Petroleum science}, volume = {16}, number = {1}, pages = {187-198}, doi = {10.1007/s12182-018-0276-4}, pmid = {30873209}, issn = {1672-5107}, abstract = {The main objective of this work is to predict the mixing of two different miscible oils in a very long channel. The background to this problem relates to the mixing of heavy and light oil in a pipeline. As a first step, a 2D channel with an aspect ratio of 250 is considered. The batch-mixing of two miscible crude oils with different viscosities and densities is modeled using an unsteady laminar model and unsteady RANS model available in the commercial CFD solver ANSYS-Fluent. For a comparison, a LES model was used for a 3D version of the 2D channel. The distinguishing feature of this work is the Lagrangian coordinate system utilized to set no-slip wall boundary conditions. The global CFD model has been validated against classical analytical solutions. Excellent agreement has been achieved. Simulations were carried out for a Reynolds number of 6300 (calculated using light oil properties) and a Schmidt number of 10 4 . The results show that, in contrast to the unsteady RANS model, the LES and unsteady laminar models produce comparable mixing dynamics for two oils in the channel. Analysis of simulations also shows that, for a channel length of 100 m and a height of 0.4 m, the complete mixing of two oils across the channel has not been achieved. We showed that the mixing zone consists of the three different mixing sub-zones, which have been identified using the averaged mass fraction of the heavy oil along the flow direction. The first sub-zone corresponds to the main front propagation area with a length of several heights of the channel. The second and third sub-zones are characterized by so-called shear-flow-driven mixing due to the Kelvin-Helmholtz vortices occurring between oils in the axial direction. It was observed that the third sub-zone has a steeper mass fraction gradient of the heavy oil in the axial direction in comparison with the second sub-zone, which corresponds to the flow-averaged mass fraction of 0.5 for the heavy oil.}, } @article {pmid30867881, year = {2019}, author = {Kawale, D and Jayaraman, J and Boukany, PE}, title = {Microfluidic rectifier for polymer solutions flowing through porous media.}, journal = {Biomicrofluidics}, volume = {13}, number = {1}, pages = {014111}, pmid = {30867881}, issn = {1932-1058}, abstract = {Fluidic rectification refers to anisotropic flow resistance upon changing the flow direction. Polymeric solutions, in contrast to Newtonian fluids, can exhibit an anisotropic flow resistance in microfluidic devices by tuning the channel shape at low Reynolds number. Such a concept has not been investigated in an anisotropic porous medium. We have developed a fluidic rectifier based on an anisotropic porous medium consisting of a periodic array of triangular pillars that can operate at a low Reynolds number. Rectification is achieved, when the type of high Weissenberg number elastic instabilities changes with the flow direction. The flow resistance differs across the two directions of the anisotropic porous medium geometry. We have identified the type of elastic instabilities that appear in both forward and backward directions. Particularly, we found a qualitative relation between the dead-zone instability and the onset of fluidic rectification.}, } @article {pmid30866409, year = {2019}, author = {Faris Abdullah, M and Zulkifli, R and Harun, Z and Abdullah, S and Wan Ghopa, WA and Soheil Najm, A and Humam Sulaiman, N}, title = {Impact of the TiO₂ Nanosolution Concentration on Heat Transfer Enhancement of the Twin Impingement Jet of a Heated Aluminum Plate.}, journal = {Micromachines}, volume = {10}, number = {3}, pages = {}, pmid = {30866409}, issn = {2072-666X}, abstract = {Here, the researchers carried out an experimental analysis of the effect of the TiO₂ nanosolution concentration on the heat transfer of the twin jet impingement on an aluminum plate surface. We used three different heat transfer enhancement processes. We considered the TiO₂ nanosolution coat, aluminum plate heat sink, and a twin jet impingement system. We also analyzed several other parameters like the nozzle spacing, nanosolution concentration, and the nozzle-to-plate distance and noted if these parameters could increase the heat transfer rate of the twin jet impingement system on a hot aluminum surface. The researchers prepared different nanosolutions, which consisted of varying concentrations, and coated them on the metal surface. Thereafter, we carried out an X-ray diffraction (XRD) and a Field Emission Scanning Electron Microscopy (FESEM) analysis for determining the structure and the homogeneous surface coating of the nanosolutions. This article also studied the different positions of the twin jets for determining the maximal Nusselt number (Nu). The researchers analyzed all the results and noted that the flow structure of the twin impingement jets at the interference zone was the major issue affecting the increase in the heat transfer rate. The combined influence of the spacing and nanoparticle concentration affected the flow structure, and therefore the heat transfer properties, wherein the Reynolds number (1% by volume concentration) maximally affected the Nusselt number. This improved the performance of various industrial and engineering applications. Hypothesis: Nusselt number was affected by the ratio of the nanoparticle size to the surface roughness. Heat transfer characteristics could be improved if the researchers selected an appropriate impingement system and selected the optimal levels of other factors. The surface coating with the TiO₂ nanosolution also positively affected the heat transfer rate.}, } @article {pmid30863983, year = {2019}, author = {Hamid, AH and Javed, T and Ali, N}, title = {Numerical study of hydromagnetic axisymmetric peristaltic flow at high Reynolds number and wave number.}, journal = {Biophysical reviews}, volume = {11}, number = {2}, pages = {139-147}, pmid = {30863983}, issn = {1867-2450}, abstract = {The computational study of MHD peristaltic motion is investigated for axisymmetric flow problem. The developed model is present in the form of partial differential equations. Then obtained partial differential equations are transferred into stream-vorticity (ψ - ω) form. Then Galerkin Finite element method is used to find the computational results of governing problem. The current study is compared with the existing well-known results at low Reynolds number and wave number. It is revealed that the present results are in well agreement with existing results in the literature. So, it is effective for higher values of Reynolds number and wave number. The variations of streamline are present graphically against high Reynolds number. It concludes that high Reynolds number and Hartmann number increase pressure rise per unit wavelength in positive pumping region sharply.}, } @article {pmid30861480, year = {2019}, author = {Luo, X and Yin, H and Ren, J and Yan, H and Huang, X and Yang, D and He, L}, title = {Enhanced mixing of binary droplets induced by capillary pressure.}, journal = {Journal of colloid and interface science}, volume = {545}, number = {}, pages = {35-42}, doi = {10.1016/j.jcis.2019.03.016}, pmid = {30861480}, issn = {1095-7103}, abstract = {The mixing of binary droplets is of paramount importance in microfluidic systems. In order to reveal the mixing mechanism of two free droplets suspended in the immiscible phase, we have developed a novel experimental setup to study the internal mixing in coalescing droplets with varying interfacial tension differences and droplet sizes. It is confirmed that the interfacial energy of droplets supports the jet flow and liquid bridge expansion during the coalescence of droplets. The increase of interfacial tension difference can increase the intensity of jet flow accompanied with slower liquid bridge expansion, which enhances the mixing of droplets. The decrease of droplet size can increase the initial velocity of jet flow. However, the intensity of jet flow decreases due to the rapid expansion of the liquid bridge, which results in weaker internal mixing. On this basis, a Reynolds number incorporating the jet velocity and droplet size is proposed to characterize the vortex size, which represents the degree of droplet mixing. This study presents an effective approach for enhancing the mixing of droplets.}, } @article {pmid30845732, year = {2019}, author = {Ye, C and Liu, J and Wu, X and Wang, B and Zhang, L and Zheng, Y and Xu, T}, title = {Hydrophobicity Influence on Swimming Performance of Magnetically Driven Miniature Helical Swimmers.}, journal = {Micromachines}, volume = {10}, number = {3}, pages = {}, pmid = {30845732}, issn = {2072-666X}, support = {61703392//National Natural Science Foundation of China(NSFC) for Young Scholar with 223 the Project/ ; U1713201//the joint Research Fund between the NSFC and Shenzhen/ ; JCYJ20170413152640731//Fundamental Research and 224 Discipline Layout project/ ; 2018YFC0115200//National Key R&D Program of China/ ; }, abstract = {Helical microswimmers have been involved in a wide variety of applications, ranging from in vivo tasks such as targeted drug delivery to in vitro tasks such as transporting micro objects. Over the past decades, a number of studies have been established on the swimming performance of helical microswimmers and geometrical factors influencing their swimming performance. However, limited studies have focused on the influence of the hydrophobicity of swimmers' surface on their swimming performance. In this paper, we first demonstrated through theoretical analysis that the hydrophobicity of swimmer's surface material of the swimmer does affect its swimming performance: the swimmer with more hydrophobic surface is exerted less friction drag torque, and should therefore exhibit a higher step-out frequency, indicating that the swimmer with more hydrophobic surface should have better swimming performance. Then a series of experiments were conducted to verify the theoretical analysis. As a result, the main contribution of this paper is to demonstrate that one potential approach to improve the helical microswimmers' swimming performance could be making its surface more hydrophobic.}, } @article {pmid30845671, year = {2019}, author = {Xia, Z and Xiao, Y and Yang, Z and Li, L and Wang, S and Liu, X and Tian, Y}, title = {Droplet Impact on the Super-Hydrophobic Surface with Micro-Pillar Arrays Fabricated by Hybrid Laser Ablation and Silanization Process.}, journal = {Materials (Basel, Switzerland)}, volume = {12}, number = {5}, pages = {}, pmid = {30845671}, issn = {1996-1944}, support = {51675371//National Natural Science Foundation of China/ ; }, abstract = {A super-hydrophobic aluminum alloy surface with decorated pillar arrays was obtained by hybrid laser ablation and further silanization process. The as-prepared surface showed a high apparent contact angle of 158.2 ± 2.0° and low sliding angle of 3 ± 1°. Surface morphologies and surface chemistry were explored to obtain insights into the generation process of super-hydrophobicity. The main objective of this current work is to investigate the maximum spreading factor of water droplets impacting on the pillar-patterned super-hydrophobic surface based on the energy conservation concept. Although many previous studies have investigated the droplet impacting behavior on flat solid surfaces, the empirical models were proposed based on a few parameters including the Reynolds number (Re), Weber number (We), as well as the Ohnesorge number (Oh). This resulted in limitations for the super-hydrophobic surfaces due to the ignorance of the geometrical parameters of the pillars and viscous energy dissipation for liquid flow within the pillar arrays. In this paper, the maximum spreading factor was deduced from the perspective of energy balance, and the predicted results were in good agreement with our experimental results with a mean error of 4.99% and standard deviation of 0.10.}, } @article {pmid30842437, year = {2019}, author = {Yang, G and Hou, C and Zhao, M and Mao, W}, title = {Comparison of convective heat transfer for Kagome and tetrahedral truss-cored lattice sandwich panels.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {3731}, pmid = {30842437}, issn = {2045-2322}, support = {20160953008//Aeronautical Science Foundation of China (Aeronautic Science Foundation of China)/ ; }, abstract = {The aim of this paper is to make a thorough comparison between Kagome and tetrahedral truss-cored lattices both experimentally and numerically. Two titanium sandwich panels -one cored with the Kagome lattice and the other with the tetrahedral lattice -are manufactured by 3D printing technology. Comparisons of the thermal insulation, the inner flow pattern and the heat transfer between the two sandwich panels are completed subsequently according to the results from forced convective experiments and numerical simulation. Within the Reynolds number range of interest for this study, the Kagome lattice exhibits excellent heat dissipation compared with the tetrahedral lattice. In particular, when the cooling air flows in the direction OB of the two sandwich panels, the Kagome lattice provides an 8~37% higher overall Nusselt number for the sandwich panel compared to the tetrahedral lattice. The superiority of the Kagome lattice comes from a unique configuration in which the centre vertex acting as the vortex generator not only disturbs the primary flow but also induces more serious flow stagnation and separation. The complex fluid flow behaviours enhance heat transfer on both the endwalls and the trusses while causing a pressure drop that is almost two times higher than that of the tetrahedral lattice in the flow direction OB.}, } @article {pmid30830969, year = {2019}, author = {Khair, AS and Balu, B}, title = {The lift force on a charged sphere that translates and rotates in an electrolyte.}, journal = {Electrophoresis}, volume = {40}, number = {18-19}, pages = {2407-2414}, doi = {10.1002/elps.201900029}, pmid = {30830969}, issn = {1522-2683}, support = {CBET-135064//National Science Foundation/International ; }, mesh = {Colloids/*chemistry ; Diffusion ; Electrolytes/*chemistry ; Electrophoresis/*methods ; Ions/*chemistry ; Kinetics ; Rotation ; }, abstract = {The distortion of the charge cloud around a uniformly charged, dielectric, rigid sphere that translates and rotates in an unbounded binary, symmetric electrolyte at zero Reynolds number is examined. The zeta potential of the particle ζ is assumed small relative to the thermal voltage scale. It is assumed that the equilibrium structure of the cloud is slightly distorted, which requires that the Péclet numbers characterizing distortion due to particle translation, Pe t = U a / D , and rotation, Pe r = Ω a 2 / D , are small compared to unity. Here, a is radius of the particle; D is the ionic diffusion coefficient; U = | U | and Ω = | Ω | , where U and Ω are the rectilinear and angular velocities of the particle, respectively. Perturbation expansions for small Pe t and Pe r are employed to calculate the nonequilibrium structure of the cloud, whence the force and torque on the particle are determined. In particular, we predict that the sphere experiences a force orthogonal to its directions of translation and rotation. This "lift" force arises from the nonlinear distortion of the cloud under the combined actions of particle translation and rotation. The lift force is given by F lift = L (κ a) (ε a 3 ζ 2 / D 2) U × Ω [ 1 + O (Pe t , Pe r) ] . Here, ε is the permittivity of the electrolyte; κ - 1 is the Debye length; and L (κ a) is a negative function that decreases in magnitude with increasing κ a . The lift force implies that an unconstrained particle would follow a curved path; an electrokinetic analog of the inertial Magnus effect. Finally, the implication of the lift force on cross-streamline migration of an electrophoretic particle in shear flow is discussed.}, } @article {pmid30823482, year = {2019}, author = {Rehman, D and Morini, GL and Hong, C}, title = {A Comparison of Data Reduction Methods for Average Friction Factor Calculation of Adiabatic Gas Flows in Microchannels.}, journal = {Micromachines}, volume = {10}, number = {2}, pages = {}, doi = {10.3390/mi10030171}, pmid = {30823482}, issn = {2072-666X}, support = {643095//Horizon 2020 Framework Programme/ ; }, abstract = {In this paper, a combined numerical and experimental approach for the estimation of the average friction factor along adiabatic microchannels with compressible gas flows is presented. Pressure-drop experiments are performed for a rectangular microchannel with a hydraulic diameter of 295 μ m by varying Reynolds number up to 17,000. In parallel, the calculation of friction factor has been repeated numerically and results are compared with the experimental work. The validated numerical model was also used to gain an insight of flow physics by varying the aspect ratio and hydraulic diameter of rectangular microchannels with respect to the channel tested experimentally. This was done with an aim of verifying the role of minor loss coefficients for the estimation of the average friction factor. To have laminar, transitional, and turbulent regimes captured, numerical analysis has been performed by varying Reynolds number from 200 to 20,000. Comparison of numerically and experimentally calculated gas flow characteristics has shown that adiabatic wall treatment (Fanno flow) results in better agreement of average friction factor values with conventional theory than the isothermal treatment of gas along the microchannel. The use of a constant value for minor loss coefficients available in the literature is not recommended for microflows as they change from one assembly to the other and their accurate estimation for compressible flows requires a coupling of numerical analysis with experimental data reduction. Results presented in this work demonstrate how an adiabatic wall treatment along the length of the channel coupled with the assumption of an isentropic flow from manifold to microchannel inlet results in a self-sustained experimental data reduction method for the accurate estimation of friction factor values even in presence of significant compressibility effects. Results also demonstrate that both the assumption of perfect expansion and consequently wrong estimation of average temperature between inlet and outlet of a microchannel can be responsible for an apparent increase in experimental average friction factor in choked flow regime.}, } @article {pmid30818010, year = {2019}, author = {Xia, Y and Yuan, M and Chen, M and Li, J and Ci, T and Ke, X}, title = {Liquid jet breakup: A new method for the preparation of poly lactic-co-glycolic acid microspheres.}, journal = {European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V}, volume = {137}, number = {}, pages = {140-147}, doi = {10.1016/j.ejpb.2019.02.021}, pmid = {30818010}, issn = {1873-3441}, mesh = {Chemistry, Pharmaceutical/methods ; Delayed-Action Preparations ; Drug Carriers/*chemistry ; Drug Compounding/methods ; Drug Liberation ; Microspheres ; Particle Size ; Polylactic Acid-Polyglycolic Acid Copolymer/*chemistry ; Risperidone/*administration & dosage/chemistry ; Surface Tension ; Technology, Pharmaceutical/*methods ; Viscosity ; }, abstract = {The purpose of this study was to apply the phenomenon of liquid jet breakup to the preparation of sustained-release microspheres. The mechanisms of liquid jet breakup in different jet states were investigated and the single factor method was used to study the effect of each process parameter on the particle size and size distribution of microspheres. Meantime, the prepared microspheres were characterized by morphology, drug loading, encapsulation efficiency and in vitro release. The results indicated that the process of liquid jet breakup could have 5 different states. The laminar flow state dominated when the Reynolds number (Re) was low, and the prepared microspheres had larger particle sizes. When the Re was high, the turbulent state was dominant and the microspheres had smaller particle sizes. And during the transition state from the laminar flow to the turbulence, the microspheres had a wide particle size distribution. Different process parameters could affect the particle size and distribution of microspheres by changing the Re, surface tension coefficient and viscosity. The microspheres prepared by liquid jet breakup were smooth and round with the drug loading of 35% and the encapsulation efficiency of 88%. In addition, when the polymeric carrier materials were different, the microspheres could have various drug release models such as sustained release with a lag phase, sustained release with no lag phase, pulsed release and so on, which could be applied widespread in the future.}, } @article {pmid30813604, year = {2019}, author = {Kim, J and Davidson, S and Mani, A}, title = {Characterization of Chaotic Electroconvection near Flat Inert Electrodes under Oscillatory Voltages.}, journal = {Micromachines}, volume = {10}, number = {3}, pages = {}, pmid = {30813604}, issn = {2072-666X}, abstract = {The onset of electroconvective instability in an aqueous binary electrolyte under external oscillatory electric fields at a single constant frequency is investigated in a 2D parallel flat electrode setup. Direct numerical simulations (DNS) of the Poisson⁻Nernst⁻Planck equations coupled with the Navier⁻Stokes equations at a low Reynolds number are carried out. Previous studies show that direct current (DC) electric field can create electroconvection near ion-selecting membranes in microfluidic devices. In this study, we show that electroconvection can be generated near flat inert electrodes when the applied electric field is oscillatory in time. A range of applied voltage, the oscillation frequency and the ratio of ionic diffusivities is examined to characterize the regime in which electroconvection takes place. Similar to electroconvection under DC voltages, AC electroconvection occurs at sufficiently high applied voltages in units of thermal volts and is characterized by transverse instabilities, physically manifested by an array of counter-rotating vortices near the electrode surfaces. The oscillating external electric field periodically generate and destroy such unsteady vortical structures. As the oscillation frequency is reduced to O (10 - 1) of the intrinsic resistor⁻capacitor (RC) frequency of electrolyte, electroconvective instability is considerably amplified. This is accompanied by severe depletion of ionic species outside the thin electric double layer and by vigorous convective transport involving a wide range of scales including those comparable to the distance L between the parallel electrodes. The underlying mechanisms are distinctly nonlinear and multi-dimensional. However, at higher frequencies of order of the RC frequency, the electrolyte response becomes linear, and the present DNS prediction closely resembles those explained by 1D asymptotic studies. Electroconvective instability supports increased electric current across the system. Increasing anion diffusivity results in stronger amplification of electroconvection over all oscillation frequencies examined in this study. Such asymmetry in ionic diffusivity, however, does not yield consistent changes in statistics and energy spectrum at all wall-normal locations and frequencies, implying more complex dynamics and different scaling for electrolytes with unequal diffusivities. Electric current is substantially amplified beyond the ohmic current at high oscillation frequencies. Also, it is found that anion diffusivity higher than cation has stronger impact on smaller-scale motions (≲ 0.1 L).}, } @article {pmid30811449, year = {2019}, author = {Khani, M and Lawrence, BJ and Sass, LR and Gibbs, CP and Pluid, JJ and Oshinski, JN and Stewart, GR and Zeller, JR and Martin, BA}, title = {Characterization of intrathecal cerebrospinal fluid geometry and dynamics in cynomolgus monkeys (macaca fascicularis) by magnetic resonance imaging.}, journal = {PloS one}, volume = {14}, number = {2}, pages = {e0212239}, pmid = {30811449}, issn = {1932-6203}, support = {P20 GM103408/GM/NIGMS NIH HHS/United States ; U54 GM104944/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Central Nervous System Diseases/*diagnostic imaging ; Cerebrospinal Fluid/*diagnostic imaging ; Female ; Hydrodynamics ; Macaca fascicularis ; *Magnetic Resonance Imaging ; Male ; Spine/*diagnostic imaging ; }, abstract = {Recent advancements have been made toward understanding the diagnostic and therapeutic potential of cerebrospinal fluid (CSF) and related hydrodynamics. Increased understanding of CSF dynamics may lead to improved detection of central nervous system (CNS) diseases and optimized delivery of CSF based CNS therapeutics, with many proposed therapeutics hoping to successfully treat or cure debilitating neurological conditions. Before significant strides can be made toward the research and development of interventions designed for human use, additional research must be carried out with representative subjects such as non-human primates (NHP). This study presents a geometric and hydrodynamic characterization of CSF in eight cynomolgus monkeys (Macaca fascicularis) at baseline and two-week follow-up. Results showed that CSF flow along the entire spine was laminar with a Reynolds number ranging up to 80 and average Womersley number ranging from 4.1-7.7. Maximum CSF flow rate occurred ~25 mm caudal to the foramen magnum. Peak CSF flow rate ranged from 0.3-0.6 ml/s at the C3-C4 level. Geometric analysis indicated that average intrathecal CSF volume below the foramen magnum was 7.4 ml. The average surface area of the spinal cord and dura was 44.7 and 66.7 cm2 respectively. Subarachnoid space cross-sectional area and hydraulic diameter ranged from 7-75 mm2 and 2-3.7 mm, respectively. Stroke volume had the greatest value of 0.14 ml at an axial location corresponding to C3-C4.}, } @article {pmid30808870, year = {2019}, author = {Mayzel, J and Steinberg, V and Varshney, A}, title = {Stokes flow analogous to viscous electron current in graphene.}, journal = {Nature communications}, volume = {10}, number = {1}, pages = {937}, pmid = {30808870}, issn = {2041-1723}, abstract = {Electron transport in two-dimensional conducting materials such as graphene, with dominant electron-electron interaction, exhibits unusual vortex flow that leads to a nonlocal current-field relation (negative resistance), distinct from the classical Ohm's law. The transport behavior of these materials is best described by low Reynolds number hydrodynamics, where the constitutive pressure-speed relation is Stoke's law. Here we report evidence of such vortices observed in a viscous flow of Newtonian fluid in a microfluidic device consisting of a rectangular cavity-analogous to the electronic system. We extend our experimental observations to elliptic cavities of different eccentricities, and validate them by numerically solving bi-harmonic equation obtained for the viscous flow with no-slip boundary conditions. We verify the existence of a predicted threshold at which vortices appear. Strikingly, we find that a two-dimensional theoretical model captures the essential features of three-dimensional Stokes flow in experiments.}, } @article {pmid30802483, year = {2019}, author = {Tassew, FA and Bergland, WH and Dinamarca, C and Bakke, R}, title = {Settling velocity and size distribution measurement of anaerobic granular sludge using microscopic image analysis.}, journal = {Journal of microbiological methods}, volume = {159}, number = {}, pages = {81-90}, doi = {10.1016/j.mimet.2019.02.013}, pmid = {30802483}, issn = {1872-8359}, mesh = {Anaerobiosis ; Bioreactors/microbiology ; Microscopy/*methods ; Particle Size ; Sewage/*chemistry/microbiology ; }, abstract = {Settling velocity and size distribution of anaerobic granular sludge samples were studied using microscopic image analysis and settling column experiments. Five granule samples were considered in this study. Three samples were collected at the Top, Middle and Bottom sections of a lab scale upflow anaerobic sludge bed reactor (UASB). Two other granule samples were obtained from industries. This paper aims to establish a method that uses microscopic image analysis and shape factor as a tool to determine the size distribution and settling velocity of anaerobic granules. Image analysis technique was used to calculate the shape factor and equivalent diameter of granules. The equivalent diameter was then used to calculate the theoretical settling velocities based on Allen's formula and estimate size distributions. The results showed that there was a good agreement between the theoretical and experimental mean settling velocity values. Both measured and calculated settling velocities increased with increasing Reynolds number (Re). However, the agreement between measured and calculated values was found to be weaker at higher Re values. Size distribution analyses of the granules have revealed that there was significant difference in the size distribution of granule samples collected at different heights of the lab scale reactor. Overall, granules from the bottom section of the reactor had larger diameter, settling velocity and shape factor than those at the middle and top section granules. Whereas granules collected from the top section exhibited the smallest granular diameter, settling velocity and shape factor.}, } @article {pmid30800393, year = {2019}, author = {Marner, F and Scholle, M and Herrmann, D and Gaskell, PH}, title = {Competing Lagrangians for incompressible and compressible viscous flow.}, journal = {Royal Society open science}, volume = {6}, number = {1}, pages = {181595}, pmid = {30800393}, issn = {2054-5703}, abstract = {A recently proposed variational principle with a discontinuous Lagrangian for viscous flow is reinterpreted against the background of stochastic variational descriptions of dissipative systems, underpinning its physical basis from a different viewpoint. It is shown that additional non-classical contributions to the friction force occurring in the momentum balance vanish by time averaging. Accordingly, the discontinuous Lagrangian can alternatively be understood from the standpoint of an analogous deterministic model for irreversible processes of stochastic character. A comparison is made with established stochastic variational descriptions and an alternative deterministic approach based on a first integral of Navier-Stokes equations is undertaken. The applicability of the discontinuous Lagrangian approach for different Reynolds number regimes is discussed considering the Kolmogorov time scale. A generalization for compressible flow is elaborated and its use demonstrated for damped sound waves.}, } @article {pmid30795856, year = {2019}, author = {Medici, G and West, LJ and Banwart, SA}, title = {Groundwater flow velocities in a fractured carbonate aquifer-type: Implications for contaminant transport.}, journal = {Journal of contaminant hydrology}, volume = {222}, number = {}, pages = {1-16}, doi = {10.1016/j.jconhyd.2019.02.001}, pmid = {30795856}, issn = {1873-6009}, mesh = {Carbonates ; England ; *Groundwater ; *Water Movements ; Water Wells ; }, abstract = {Contaminants that are highly soluble in groundwater are rapidly transported via fractures in mechanically resistant sedimentary rock aquifers. Hence, a rigorous methodology is needed to estimate groundwater flow velocities in such fractured aquifers. Here, we propose an approach using borehole hydraulic testing to compute flow velocities in an un-faulted area of a fractured carbonate aquifer by applying the cubic law to a parallel plate model. The Cadeby Formation (Yorkshire, NE England) - a Permian dolostone aquifer present beneath the University of Leeds Farm - is the fractured aquifer selected for this hydraulic experiment. The bedding plane fractures of this dolostone aquifer, which are sub-horizontal, sub-parallel and laterally persistent, largely dominate the flow at shallow (<~40 mBGL) depths. These flowing bedding plane discontinuities are separated by a rock matrix which is relatively impermeable (Kwell-test/Kcore-plug~104) as is common in fractured carbonate aquifers. In the workflow reported here, the number of flowing fractures - mainly bedding plane fractures - intersecting three open monitoring wells are found from temperature/fluid conductivity and acoustic/optical televiewer logging. Following well installation, average fracture hydraulic apertures for screened intervals are found from analysis of slug tests. For the case study aquifer, this workflow predicts hydraulic apertures ranging from 0.10 up to 0.54 mm. However, groundwater flow velocities range within two order of magnitude from 13 up to 242 m/day. Notably, fracture apertures and flow velocities rapidly reduce with increasing depth below the water table; the upper ~10 m shows relatively high values of hydraulic conductivity (0.30-2.85 m/day) and corresponding flow velocity (33-242 m/day). Permeability development around the water table in carbonate aquifer-types is common, and arises where high pCO2 recharge water from the soil zone causes calcite/dolomite dissolution. Hence, agricultural contaminants entering the aquifer with recharge water are laterally transported rapidly within this upper part. Computation of groundwater flow velocities allows determination of the Reynolds number. Values of up ~1, indicating the lower limit of the transition from laminar to turbulent flow, are found at the studied site, which is situated away from major fault traces. Hence, turbulent flow is likely to arise in proximity to tectonic structures, such as normal faults, which localize flow and enhance karstification. The occurrence of turbulent flow in correspondence of such tectonic structures should be represented in regional groundwater flow simulations.}, } @article {pmid30790045, year = {2019}, author = {Hyeon, J and So, H}, title = {Microfabricaton of microfluidic check valves using comb-shaped moving plug for suppression of backflow in microchannel.}, journal = {Biomedical microdevices}, volume = {21}, number = {1}, pages = {19}, doi = {10.1007/s10544-019-0365-1}, pmid = {30790045}, issn = {1572-8781}, mesh = {Equipment Design ; Humans ; *Lab-On-A-Chip Devices ; *Microfluidic Analytical Techniques/instrumentation/methods ; *Microfluidics/instrumentation/methods ; }, abstract = {This study reports on an efficient microscale one-way valve system that combines the physical properties of photopolymerized microstructures and viscoelastic microchannels to rectify flows with low Reynolds numbers. The comb-shaped moving plug in the microchannel prevented backflow in the closed state to ensure that the microchannel remained completely blocked in the closed state, but allowed forward flow in the open state. This microfluidic check valve was microfabricated using the combination of the soft lithography and the releasing methods with the use of a double photoresist layer to create microchannels and free-moving comb-shaped microstructures, respectively. As a result, the microfluidic check valves elicited average high-pressure differences as much as 10.75 kPa between the backward and forward flows at low Reynolds numbers of the order of 0.253, thus demonstrating efficient rectification of microfluids. This study supports the use of rectification systems for the development of biomedical devices, such as drug delivery, micropumps, and lab-on-a-chip, by allowing unidirectional flow.}, } @article {pmid30785756, year = {2019}, author = {Wang, P and Cilliers, JJ and Neethling, SJ and Brito-Parada, PR}, title = {Effect of Particle Size on the Rising Behavior of Particle-Laden Bubbles.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {10}, pages = {3680-3687}, doi = {10.1021/acs.langmuir.8b04112}, pmid = {30785756}, issn = {1520-5827}, abstract = {The rising behavior of bubbles, initially half and fully coated with glass beads of various sizes, was investigated. The bubble velocity, aspect ratio, and oscillation periods were determined using high-speed photography and image analysis. In addition, the acting forces, drag modification factor, and modified drag coefficient were calculated and interpreted. Results show that the aspect ratio oscillation of the rising bubbles is similar, irrespective of the attached particle size. As the particle size is increased, the rising bubbles have a lower velocity and aspect ratio amplitude, with the time from release to each aspect ratio peak increasing. Higher particle coverage is shown to decrease the bubble velocity and dampen the oscillations, reducing the number of aspect ratio peaks observed. The highest rise velocities correspond to the lowest aspect ratios and vice versa, whereas a constant aspect ratio yields a constant rise velocity, independent of the particle size. Force analysis shows that the particle drag modification factor increases with the increased particle size and is greatest for fully laden bubbles. The modified drag coefficient of particle-laden bubbles increases with the increased particle size, although it decreases with the increased Reynolds number independent of the particle size. The drag force exerted by the particles plays a more dominant role in decreasing bubble velocities as the particle size increases. The results and interpretation produced a quantitative description of the behavior of rising particle-laden bubbles and the development of correlations will enhance the modeling of industrial applications.}, } @article {pmid30781378, year = {2019}, author = {Álvarez-Regueiro, E and Vallejo, JP and Fernández-Seara, J and Fernández, J and Lugo, L}, title = {Experimental Convection Heat Transfer Analysis of a Nano-Enhanced Industrial Coolant.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {9}, number = {2}, pages = {}, pmid = {30781378}, issn = {2079-4991}, support = {ENE2014-55489-C2-1/2-R; ENE2017-86425-C2-1/2-R//Ministerio de Economía, Industria y Competitividad, Gobierno de España/ ; }, abstract = {Convection heat transfer coefficients and pressure drops of four functionalized graphene nanoplatelet nanofluids based on the commercial coolant Havoline® XLC Pre-mixed 50/50 were experimentally determined to assess its thermal performance. The potential heat transfer enhancement produced by nanofluids could play an important role in increasing the efficiency of cooling systems. Particularly in wind power, the increasing size of the wind turbines, up to 10 MW nowadays, requires sophisticated liquid cooling systems to keep the nominal temperature conditions and protect the components from temperature degradation and hazardous environment in off-shore wind parks. The effect of nanoadditive loading, temperature and Reynolds number in convection heat transfer coefficients and pressure drops is discussed. A dimensionless analysis of the results is carried out and empirical correlations for the Nusselt number and Darcy friction factor are proposed. A maximum enhancement in the convection heat transfer coefficient of 7% was found for the nanofluid with nanoadditive loading of 0.25 wt %. Contrarily, no enhancement was found for the nanofluids of higher functionalized graphene nanoplatelet mass fraction.}, } @article {pmid30780337, year = {2019}, author = {Lyu, YZ and Zhu, HJ and Sun, M}, title = {Flapping-mode changes and aerodynamic mechanisms in miniature insects.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {012419}, doi = {10.1103/PhysRevE.99.012419}, pmid = {30780337}, issn = {2470-0053}, mesh = {*Air ; Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta/*physiology ; }, abstract = {Miniature insects fly at very low Reynolds number (Re); low Re means large viscous effect. If flapping as larger insects, sufficient vertical force cannot be produced. We measure the wing kinematics for miniature-insect species of different sizes and compute the aerodynamic forces. The planar upstroke commonly used by larger insects changes to a U-shaped upstroke, which becomes deeper as size or Re decreases. For relatively large miniature insects, the U-shaped upstroke produces a larger vertical force than a planar upstroke by having a larger wing velocity and, for very small ones, the deep U-shaped upstroke produces a large transient drag directed upwards, providing the required vertical force.}, } @article {pmid30780316, year = {2019}, author = {Jiang, L and Sun, C and Calzavarini, E}, title = {Robustness of heat transfer in confined inclined convection at high Prandtl number.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {013108}, doi = {10.1103/PhysRevE.99.013108}, pmid = {30780316}, issn = {2470-0053}, abstract = {We investigate the dependency of the magnitude of heat transfer in a convection cell as a function of its inclination by means of experiments and simulations. The study is performed with a working fluid of large Prandtl number, Pr≃480, and at Rayleigh numbers Ra≃10^{8} and Ra≃5×10^{8} in a quasi-two-dimensional rectangular cell with unit aspect ratio. By changing the inclination angle (β) of the convection cell, the character of the flow can be changed from moderately turbulent, for β=0^{∘}, to laminar and steady at β=90^{∘}. The global heat transfer is found to be insensitive to the drastic reduction of turbulent intensity, with maximal relative variations of the order of 20% at Ra≃10^{8} and 10% at Ra≃5×10^{8}, while the Reynolds number, based on the global root-mean-square velocity, is strongly affected with a decay of more than 85% occurring in the laminar regime. We show that the intensity of the heat flux in the turbulent regime can be only weakly enhanced by establishing a large-scale circulation flow by means of small inclinations. However, in the laminar regime the heat is transported solely by a slow large-scale circulation flow which exhibits large correlations between the velocity and temperature fields. For inclination angles close to the transition regime in-between the turbulentlike and laminar state, a quasiperiodic heat-flow bursting phenomenon is observed.}, } @article {pmid30780239, year = {2019}, author = {Suman, VK and Viknesh S, S and Tekriwal, MK and Bhaumik, S and Sengupta, TK}, title = {Grid sensitivity and role of error in computing a lid-driven cavity problem.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {013305}, doi = {10.1103/PhysRevE.99.013305}, pmid = {30780239}, issn = {2470-0053}, abstract = {The investigation on grid sensitivity for the bifurcation problem of the canonical lid-driven cavity (LDC) flow results is reported here with very fine grids. This is motivated by different researchers presenting different first bifurcation critical Reynolds number (Re_{cr1}), which appears to depend on the formulation, numerical method, and choice of grid. By using a very-high-accuracy parallel algorithm, and the same method with which sequential results were presented by Lestandi et al. [Comput. Fluids 166, 86 (2018)CPFLBI0045-793010.1016/j.compfluid.2018.01.038] [for (257 × 257) and (513 × 513) uniformly spaced grid], we present results using (1025×1025) and (2049×2049) grid points. Detailed results presented using these grids help us understand the computational physics of the numerical receptivity of the LDC flow, with and without explicit excitation. The mathematical physics of the investigated problem will become apparent when we identify the roles of numerical errors with the ambient omnipresent disturbances in real physical flows as interchangeable. In physical or in numerical setups, presence of disturbances cannot be ignored. In this context, the need for explicit excitation for the used compact scheme arises for a definitive threshold amplitude, below which the flow relaxes back to quiescent state after the excitation is removed in computations. We also implement the present parallel method to show the physical aspects of primary and secondary instabilities to be maintained for other numerical schemes, and we show the results to reflect the complex physics during multiple subcritical Hopf bifurcation. Also, we relate the various sources of errors during computations that is typical of such shear-driven flow. These results, with near spectral accuracy, constitute universal benchmark results for the solution of Navier-Stokes equation for LDC.}, } @article {pmid30780221, year = {2019}, author = {Takamure, K and Ozono, S}, title = {Relative importance of initial conditions on outflows from multiple fans.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {013112}, doi = {10.1103/PhysRevE.99.013112}, pmid = {30780221}, issn = {2470-0053}, abstract = {Generation of homogeneous isotropic turbulence was attempted using an innovative "multifan wind tunnel" with 99 fans installed. The driving method used is based on a principle that the shear layers generated between outflows from the adjacent ducts lead to turbulent flow downstream. First, a signal composed of two frequency components is set, and then it is fed to all the fans for three kinds of arrangements of phases. Here, parameter N is introduced as the number of phases used for the 99 fans, which represents a variety of emanated shear layers. Furthermore, S is introduced as a measure of shear magnitude at the inlet of the test section. Relative importance of the initial conditions (N and S) in the development of turbulence was investigated. To estimate the contribution from naturally induced turbulence, we numerically decomposed the resulting velocity fluctuations into the periodic and nonperiodic component. Energy spectra for three values of N were calculated using nonperiodic data. The inertial subrange of a gradient of -5/3 widens with increasing N. The value S is the largest for N=2, but the turbulence intensity of the nonperiodic component is the largest for N=99. Hence, it might be suggested that the shear magnitude at the inlet of the test section is not as important as the variety of shear layers for effective generation of high-Reynolds-number turbulence.}, } @article {pmid30771128, year = {2019}, author = {Li, R and Xu, D and Yin, Q}, title = {Effects of channel morphology on nitrate retention in a headwater agricultural stream in Lake Chaohu Basin, China.}, journal = {Environmental science and pollution research international}, volume = {26}, number = {11}, pages = {10651-10661}, pmid = {30771128}, issn = {1614-7499}, support = {Grant No. 51579061//National Natural Science Foundation of China/ ; }, mesh = {Agriculture ; China ; Environmental Monitoring/methods ; Lakes/*chemistry ; Nitrates/*analysis ; Rivers/chemistry ; Water Resources ; }, abstract = {Five field tracer experiments and relevant detailed investigations of physical characterizations were conducted to investigate the effects of channel geomorphic settings on nitrate uptake efficiency on a 310-m long geomorphically distinct stream reach in a headwater agricultural stream in Hefei District, Lake Chaohu Basin. The model-fitted parameters from the one-dimensional transport with inflow and storage model were used to estimate the transient storage metric ([Formula: see text]) and determine the total nitrate uptake coefficient (k) for the study reach. And then, a nutrient spiraling approach was applied to reach-scale nitrate uptake estimates (Sw, Vf, and U). The results showed that the main channel was the major contributor to nitrate uptake retention, and the higher geomorphic complexity might result in better nitrate uptake efficiency. The partial least squares regression (PLSR) analysis showed strong correlations between the independent variables as geomorphic settings, Reynolds number and transient storage, and the dependent variables as nitrate uptake metrics, which further underscored the importance of stream physical characteristics on measurement of stream nitrate uptake.}, } @article {pmid30770644, year = {2019}, author = {Morales-Acuna, F and Ochoa, L and Valencia, C and Gurovich, AN}, title = {Characterization of blood flow patterns and endothelial shear stress during flow-mediated dilation.}, journal = {Clinical physiology and functional imaging}, volume = {39}, number = {4}, pages = {240-245}, doi = {10.1111/cpf.12564}, pmid = {30770644}, issn = {1475-097X}, mesh = {Adolescent ; Adult ; Blood Flow Velocity ; Brachial Artery/diagnostic imaging/*physiology ; Endothelium, Vascular/diagnostic imaging/*physiology ; Female ; Healthy Volunteers ; Humans ; Male ; Models, Cardiovascular ; *Pulsatile Flow ; Regional Blood Flow ; Time Factors ; *Vasodilation ; Young Adult ; }, abstract = {INTRODUCTION: Endothelial dysfunction is considered the first step in the development of atherosclerosis. Flow-mediated dilation (FMD) has been the most common assessment of endothelial function in research but it has failed in obtaining a widespread use in clinical settings due to a lack of standardization and a large inter-subject variability. Normalization of FMD to endothelial shear stress (ESS) has been proposed to solve its technical limitations. However, studies have not considered the characteristic of the blood flow during FMD under pulsatile conditions in their ESS estimations.

METHODS: A total of 26 young healthy subjects (15 females and 11 males) underwent FMD testing. Microhematocrit measurement was used to determine blood viscosity (μ). ESS was calculated by Womersley's approximation, ESS = μ*2K*Velocity/Diameter, where K is a function of Womersley's parameter (α). Blood flow patterns were determined by critical Reynolds number. Statistical analysis included repeated measures ANOVA to detect ESS differences during FMD until peak dilation. Significance was established at P≤0.05.

RESULTS: The mean (SD) FMD% and time to peak dilation were 7·4 (3·1) % and 35 (9·3) seconds, respectively. ESS was significantly reduced during FMD until peak dilation (P<0·001). Turbulent blood flow was the only pattern observed until peak dilation in 96·15% of the sample.

CONCLUSION: Peak FMD dilation in a young healthy population is triggered mostly by high-ESS under turbulent flow conditions. Due to the pulsatile nature of blood flow and the appearance of a turbulent pattern during FMD, ESS should be estimated by Womersley's approximation rather than Poiseuille's law.}, } @article {pmid30760794, year = {2019}, author = {Tang, H and Hu, F and Xu, L and Dong, S and Zhou, C and Wang, X}, title = {Variations in hydrodynamic characteristics of netting panels with various twine materials, knot types, and weave patterns at small attack angles.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {1923}, pmid = {30760794}, issn = {2045-2322}, abstract = {It is essential to conduct hydrodynamic experiments for fishing gear at small attack angles along the flow direction to better understand the hydrodynamic characteristics of netting and application of gear. The hydrodynamic characteristics of netting panels made of different materials at small attack angles were investigated by a self-designed setup; this is essential for the effective use of netting on different types of gears. As confirmed by experiments, the measured drag of designed frame without netting accounted for less than 20% of the total setup drag including experimental netting and remained in a steady state under various current speeds and small attack angles, indicating that the self-designed frame setup is suitable for such trials. The drag coefficient was determined by varying the attack angle, solidity ratio, Reynolds number, knot types, weave pattern, and twine materials at small attack angles. The results indicate that the drag coefficient increased as the attack angle increased, but decreased as the solidity ratio and Reynolds number increased. The drag generated by knot accounted for 21% of the total drag of nylon (PA) netting. For braided knotless netting, the drag coefficient of PA netting was about 8.4% lower than that of polythene netting (PE) and 7% lower than that of polyester netting (PES). Compared with twined netting, the braided netting exhibited a higher resistance to flow, corresponding to higher values of drag coefficient.}, } @article {pmid30759039, year = {2019}, author = {Sera, T and Kuninaga, H and Fukasaku, K and Yokota, H and Tanaka, M}, title = {The Effectiveness of An Averaged Airway Model in Predicting the Airflow and Particle Transport Through the Airway.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {32}, number = {5}, pages = {278-292}, doi = {10.1089/jamp.2018.1500}, pmid = {30759039}, issn = {1941-2703}, mesh = {Administration, Inhalation ; Adult ; Aerosols/*administration & dosage/pharmacokinetics ; Algorithms ; Biological Transport ; Computer Simulation ; Humans ; *Hydrodynamics ; Male ; Middle Aged ; *Models, Anatomic ; Respiratory System/*anatomy & histology ; Tissue Distribution ; }, abstract = {Background: In this study, we proposed an averaged airway model design based on four healthy subjects and numerically evaluated its effectiveness for predicting the airflow and particle transport through an airway. Methods: Direct-averaged models of the conducting airways of four subjects were restored by averaging the three-dimensional (3D) skeletons of four healthy airways, which were calculated using an inverse 3D thinning algorithm. We simulated the airflow and particle transport in the individual and the averaged airway models using computational fluid dynamics. Results: The bifurcation geometry differs even among healthy subjects, but the averaged model retains the typical geometrical characteristics of the airways. The Reynolds number of the averaged model varied within the range found in the individual subject models, and the averaged model had similar inspiratory flow characteristics as the individual subject models. The deposition fractions at almost all individual lobes ranged within the variation observed in the subjects, however, the deposition fraction was higher in only one lobe. The deposition distribution at the main bifurcation point differed among the healthy subjects, but the characteristics of the averaged model fell within the variation observed in the individual subject models. On the contrary, the deposition fraction of the averaged model was higher than that of the average of the individual subject models and deviated from the range observed in the subject models. Conclusion: These results indicate that the direct-averaged model may be useful for predicting the individual airflow and particle transport on a macroscopic scale.}, } @article {pmid30758910, year = {2019}, author = {Amer, M and Feng, Y and Ramsey, JD}, title = {Using CFD simulations and statistical analysis to correlate oxygen mass transfer coefficient to both geometrical parameters and operating conditions in a stirred-tank bioreactor.}, journal = {Biotechnology progress}, volume = {35}, number = {3}, pages = {e2785}, doi = {10.1002/btpr.2785}, pmid = {30758910}, issn = {1520-6033}, mesh = {Bioreactors ; Cell Culture Techniques/*instrumentation ; Gases/chemistry ; Hydrodynamics ; Kinetics ; Mathematical Computing ; Oxygen/*chemistry ; }, abstract = {Optimization of a bioreactor design can be an especially challenging process. For instance, testing different bioreactor vessel geometries and different impeller and sparger types, locations, and dimensions can lead to an exceedingly large number of configurations and necessary experiments. Computational fluid dynamics (CFD), therefore, has been widely used to model multiphase flow in stirred-tank bioreactors to minimize the number of optimization experiments. In this study, a multiphase CFD model with population balance equations are used to model gas-liquid mixing, as well as gas bubble distribution, in a 50 L single-use bioreactor vessel. The vessel is the larger chamber in an early prototype of a multichamber bioreactor for mammalian cell culture. The model results are validated with oxygen mass transfer coefficient (kL a) measurements within the prototype. The validated model is projected to predict the effect of using ring or pipe spargers of different sizes and the effect of varying the impeller diameter on kL a. The simulations show that ring spargers result in a superior kL a compared to pipe spargers, with an optimum sparger-to-impeller diameter ratio of 0.8. In addition, larger impellers are shown to improve kL a. A correlation of kL a is presented as a function of both the reactor geometry (i.e., sparger-to-impeller diameter ratio and impeller-to-vessel diameter ratio) and operating conditions (i.e., Reynolds number and gas flow rate). The resulting correlation can be used to predict kL a in a bioreactor and to optimize its design, geometry, and operating conditions.}, } @article {pmid30746446, year = {2019}, author = {Huang, HW and Uslu, FE and Katsamba, P and Lauga, E and Sakar, MS and Nelson, BJ}, title = {Adaptive locomotion of artificial microswimmers.}, journal = {Science advances}, volume = {5}, number = {1}, pages = {eaau1532}, pmid = {30746446}, issn = {2375-2548}, support = {/ERC_/European Research Council/International ; }, abstract = {Bacteria can exploit mechanics to display remarkable plasticity in response to locally changing physical and chemical conditions. Compliant structures play a notable role in their taxis behavior, specifically for navigation inside complex and structured environments. Bioinspired mechanisms with rationally designed architectures capable of large, nonlinear deformation present opportunities for introducing autonomy into engineered small-scale devices. This work analyzes the effect of hydrodynamic forces and rheology of local surroundings on swimming at low Reynolds number, identifies the challenges and benefits of using elastohydrodynamic coupling in locomotion, and further develops a suite of machinery for building untethered microrobots with self-regulated mobility. We demonstrate that coupling the structural and magnetic properties of artificial microswimmers with the dynamic properties of the fluid leads to adaptive locomotion in the absence of on-board sensors.}, } @article {pmid30736676, year = {2019}, author = {Waheed, W and Alazzam, A and Al-Khateeb, AN and Sung, HJ and Abu-Nada, E}, title = {Investigation of DPD transport properties in modeling bioparticle motion under the effect of external forces: Low Reynolds number and high Schmidt scenarios.}, journal = {The Journal of chemical physics}, volume = {150}, number = {5}, pages = {054901}, doi = {10.1063/1.5079835}, pmid = {30736676}, issn = {1089-7690}, abstract = {We have used a dissipative particle dynamics (DPD) model to study the movement of microparticles in a microfluidic device at extremely low Reynolds number (Re). The particles, immersed in a medium, are transported in the microchannel by a flow force and deflected transversely by an external force along the way. An in-house Fortran code is developed to simulate a two-dimensional fluid flow using DPD at Re ≥ 0.0005, which is two orders of magnitude less than the minimum Re value previously reported in the DPD literature. The DPD flow profile is verified by comparing it with the exact solution of Hagen-Poiseuille flow. A bioparticle based on a rigid spring-bead model is introduced in the DPD fluid, and the employed model is verified via comparing the velocity profile past a stationary infinite cylinder against the profile obtained via the finite element method. Moreover, the drag force and drag coefficient on the stationary cylinder are also computed and compared with the reported literature results. Dielectrophoresis (DEP) is investigated as a case study for the proposed DPD model to compute the trajectories of red blood cells in a microfluidic device. A mapping mechanism to scale the external deflecting force from the physical to DPD domain is performed. We designed and built our own experimental setup with the aim to compare the experimental trajectories of cells in a microfluidic device to validate our DPD model. These experimental results are used to investigate the dependence of the trajectory results on the Reynolds number and the Schmidt number. The numerical results agree well with the experiment results, and it is found that the Schmidt number is not a significant parameter for the current application; Reynolds numbers combined with the DEP-to-drag force ratio are the only important parameters influencing the behavior of particles inside the microchannel.}, } @article {pmid30736476, year = {2019}, author = {Tai, J and Lam, YC}, title = {Elastic Turbulence of Aqueous Polymer Solution in Multi-Stream Micro-Channel Flow.}, journal = {Micromachines}, volume = {10}, number = {2}, pages = {}, pmid = {30736476}, issn = {2072-666X}, abstract = {Viscous liquid flow in micro-channels is typically laminar because of the low Reynolds number constraint. However, by introducing elasticity into the fluids, the flow behavior could change drastically to become turbulent; this elasticity can be realized by dissolving small quantities of polymer molecules into an aqueous solvent. Our recent investigation has directly visualized the extension and relaxation of these polymer molecules in an aqueous solution. This elastic-driven phenomenon is known as 'elastic turbulence'. Hitherto, existing studies on elastic flow instability are mostly limited to single-stream flows, and a comprehensive statistical analysis of a multi-stream elastic turbulent micro-channel flow is needed to provide additional physical understanding. Here, we investigate the flow field characteristics of elastic turbulence in a 3-stream contraction-expansion micro-channel flow. By applying statistical analyses and flow visualization tools, we show that the flow field bares many similarities to that of inertia-driven turbulence. More interestingly, we observed regions with two different types of power-law dependence in the velocity power spectra at high frequencies. This is a typical characteristic of two-dimensional turbulence and has hitherto not been reported for elastic turbulent micro-channel flows.}, } @article {pmid30715051, year = {2018}, author = {Mehrdel, P and Karimi, S and Farré-Lladós, J and Casals-Terré, J}, title = {Novel Variable Radius Spiral⁻Shaped Micromixer: From Numerical Analysis to Experimental Validation.}, journal = {Micromachines}, volume = {9}, number = {11}, pages = {}, pmid = {30715051}, issn = {2072-666X}, abstract = {A novel type of spiral micromixer with expansion and contraction parts is presented in order to enhance the mixing quality in the low Reynolds number regimes for point-of-care tests (POCT). Three classes of micromixers with different numbers of loops and modified geometries were studied. Numerical simulation was performed to study the flow behavior and mixing performance solving the steady-state Navier⁻Stokes and the convection-diffusion equations in the Reynolds range of 0.1⁻10.0. Comparisons between the mixers with and without expansion parts were made to illustrate the effect of disturbing the streamlines on the mixing performance. Image analysis of the mixing results from fabricated micromixers was used to verify the results of the simulations. Since the proposed mixer provides up to 92% of homogeneity at Re 1.0, generating 442 Pa of pressure drop, this mixer makes a suitable candidate for research in the POCT field.}, } @article {pmid30714602, year = {2019}, author = {Schaaf, C and Rühle, F and Stark, H}, title = {A flowing pair of particles in inertial microfluidics.}, journal = {Soft matter}, volume = {15}, number = {9}, pages = {1988-1998}, doi = {10.1039/c8sm02476f}, pmid = {30714602}, issn = {1744-6848}, abstract = {A flowing pair of particles in inertial microfluidics gives important insights into understanding and controlling the collective dynamics of particles like cells or droplets in microfluidic devices. They are applied in medical cell analysis and engineering. We study the dynamics of a pair of solid particles flowing through a rectangular microchannel using lattice Boltzmann simulations. We determine the inertial lift force profiles as a function of the two particle positions, their axial distance, and the Reynolds number. Generally, the profiles strongly differ between particles leading and lagging in flow and the lift forces are enhanced due to the presence of a second particle. At small axial distances, they are determined by viscous forces, while inertial forces dominate at large separations. We identify cross-streamline pairs as stable fixed points in the lift force profiles and argue that same-streamline configurations are only one-sided stable. Depending on the initial conditions, the two-particle lift forces in combination with the Poiseuille flow give rise to three types of unbound particle trajectories, called moving-apart, passing, and swapping, and one type of bound trajectory, where the particles perform damped oscillations towards the cross-stream line configuration. The damping rate scales with Reynolds number squared, since inertial forces are responsible for driving the particles to their steady-state positions.}, } @article {pmid30712849, year = {2019}, author = {Lippert, T and Bandelin, J and Schlederer, F and Drewes, JE and Koch, K}, title = {Impact of ultrasound-induced cavitation on the fluid dynamics of water and sewage sludge in ultrasonic flatbed reactors.}, journal = {Ultrasonics sonochemistry}, volume = {55}, number = {}, pages = {217-222}, doi = {10.1016/j.ultsonch.2019.01.024}, pmid = {30712849}, issn = {1873-2828}, abstract = {The fluid dynamics of water, thickened waste activated sludge (WAS, total solids concentration 4.4%) and digested sludge (DS, total solids concentration 2.5%) within a lab-scale ultrasonic flatbed reactor were experimentally investigated. For a visual observation of the opaque sludge flow, sewage sludges were approximated by transparent xanthan solutions with identical flow behavior. The visualization of the flow was realized by use of an ultrasonic reactor with a transparent panel and dye streams injected into the flow. Without ultrasonic treatment, xanthan solutions showed distinct laminar flow behavior (generalized Reynolds numbers < 1), at a flow rate of 100 L/h. In water, dye streams remained coherent as well, but with slightly unsteady features (Reynolds number ∼ 350). Activation of the ultrasound reactor caused strong fluid dynamic disturbance in the water flow and dye streams were dissolved instantly, thus indicating turbulent mixing. For the xanthan solutions, however, mixing was considerably less pronounced. The dye streams in the DS substitute (0.5% xanthan solution) remained overall in laminar shape, but exhibited an eruption-like branching and an increase in diameter with advancing treatment duration. For the solution resembling WAS (2.0% xanthan solution), only weak dye stream disruption was observed, thus indicating that WAS flow in flatbed reactors is nearly laminar during ultrasonic treatment.}, } @article {pmid30712603, year = {2019}, author = {Ibrahim, MG and Hasona, WM and ElShekhipy, AA}, title = {Concentration-dependent viscosity and thermal radiation effects on MHD peristaltic motion of Synovial Nanofluid: Applications to rheumatoid arthritis treatment.}, journal = {Computer methods and programs in biomedicine}, volume = {170}, number = {}, pages = {39-52}, doi = {10.1016/j.cmpb.2019.01.001}, pmid = {30712603}, issn = {1872-7565}, mesh = {Algorithms ; Arthritis, Rheumatoid/*physiopathology/*radiotherapy ; Humans ; Models, Statistical ; *Nanoparticles ; Peristalsis/*radiation effects ; Synovial Fluid/*radiation effects ; Viscosity/*radiation effects ; }, abstract = {BACKGROUND AND OBJECTIVE: The biomedical fluid which fills the Synovial joint cavity is called Synovial fluid which behaves as in the fluid classifications to Non-Newtonian fluids. Also it's described as a several micrometers thick layer among the interstitial cartilages with very low friction coefficient. Consequently, the present paper opts to investigate the influence of the concentration-dependent viscosity on Magnetohydrodynamic peristaltic flow of Synovial Nanofluid in an asymmetric channel in presence of thermal radiation effect.

METHOD: Our problem is solved for two models, in the first model which referred as Model-(I), viscosity is considered exponentially dependent on the concentration. Model-(2), Shear thinning index is considered as a function of concentration. Those models are introduced for the first time in peristaltic or Nanofluid flows literature. The governing problem is reformulated under the assumption of low Reynolds number and long wavelength. The resulting system of equations is solved numerically with the aid of Parametric ND Solve.

RESULTS: Detailed comparisons have been made between Model-(I) and Model-(2) and found unrealistic results between them. Results for velocity, temperature and nanoparticle concentration distributions as well as pressure gradient and pressure rise are offered graphically for different values of various physical parameters.

CONCLUSIONS: Such models are applicable to rheumatoid arthritis (RA) treatment. Rheumatoid arthritis patients can be treated by applying the magnetic field on an electrically conducting fluid, due to the movement of the ions within the cell which accelerates the metabolism of fluids.}, } @article {pmid30671967, year = {2019}, author = {Tandler, T and Gellman, E and De La Cruz, D and Ellerby, DJ}, title = {Drag coefficient estimates from coasting bluegill sunfish Lepomis macrochirus.}, journal = {Journal of fish biology}, volume = {94}, number = {3}, pages = {532-534}, doi = {10.1111/jfb.13906}, pmid = {30671967}, issn = {1095-8649}, support = {IOS1354274//NSF/ ; IOS1754650//NSF/ ; 1354274//Division of Integrative Organismal Systems/ ; 1754650//Division of Integrative Organismal Systems/ ; }, mesh = {Animals ; Biomechanical Phenomena ; Perciformes/*physiology ; *Swimming ; }, abstract = {The drag coefficient bluegill sunfish Lepomis macrochirus was estimated from coasting deceleration as (mean ± SD) 0.0154 ± 0.0070 at a Reynolds number of 41,000 ± 14,000. This was within the coasting range in other species and lower than values obtained from dead drag measurements in this species and others. Low momentum losses during coasting may allow its use during intermittent propulsion to modulate power output or maximize energy economy.}, } @article {pmid30657156, year = {2019}, author = {Haward, SJ and Kitajima, N and Toda-Peters, K and Takahashi, T and Shen, AQ}, title = {Flow of wormlike micellar solutions around microfluidic cylinders with high aspect ratio and low blockage ratio.}, journal = {Soft matter}, volume = {15}, number = {9}, pages = {1927-1941}, doi = {10.1039/c8sm02099j}, pmid = {30657156}, issn = {1744-6848}, abstract = {We employ time-resolved flow velocimetry and birefringence imaging methods to study the flow of a well-characterized shear-banding wormlike micellar solution around a novel glass-fabricated microfluidic circular cylinder. In contrast with typical microfluidic cylinders, our geometry is characterized by a high aspect ratio α = H/W = 5 and a low blockage ratio β = 2r/W = 0.1, where H and W are the channel height and width, and the cylinder radius r = 20 μm. The small cylinder radius allows access up to very high Weissenberg numbers 1.9 ≤ Wi = λMU/r ≤ 3750 (where λM is the Maxwell relaxation time) while inertial effects remain entirely negligible (Reynolds number, Re < 10-4). At low Wi values, the flow remains steady and symmetric and a birefringent region (indicating micellar alignment and tensile stress) develops downstream of the cylinder. Above a critical value Wic ≈ 60 the flow transitions to a steady asymmetric state, characterized as a supercritical pitchfork bifurcation, in which the fluid takes a preferential path around one side of the cylinder. At a second critical value Wic2 ≈ 130, the flow becomes time-dependent, with a characteristic frequency f0 ≈ 1/λM. This initial transition to time dependence has characteristics of a subcritical Hopf bifurcation. Power spectra of the measured fluctuations become complex as Wi is increased further, showing a gradual slowing down of the dynamics and emergence of harmonics. A final transition at very high Wic3 corresponds to the re-emergence of a single peak in the power spectrum but at much higher frequency. We discuss this in terms of possible flow-induced breakage of micelles into shorter species with a faster relaxation time.}, } @article {pmid30650659, year = {2019}, author = {Luo, L and He, Y}, title = {Magnetically Induced Flow Focusing of Non-Magnetic Microparticles in Ferrofluids under Inclined Magnetic Fields.}, journal = {Micromachines}, volume = {10}, number = {1}, pages = {}, pmid = {30650659}, issn = {2072-666X}, support = {11502102//National Natural Science Foundation of China/ ; }, abstract = {The ability to focus biological particles into a designated position of a microchannel is vital for various biological applications. This paper reports particle focusing under vertical and inclined magnetic fields. We analyzed the effect of the angle of rotation (θ) of the permanent magnets and the critical Reynolds number (Rec) on the particle focusing in depth. We found that a rotation angle of 10° is preferred; a particle loop has formed when Re < Rec and Rec of the inclined magnetic field is larger than that of the vertical magnetic field. We also conducted experiments with polystyrene particles (10.4 μm in diameter) to prove the calculations. Experimental results show that the focusing effectiveness improved with increasing applied magnetic field strength or decreasing inlet flow rate.}, } @article {pmid30636127, year = {2018}, author = {Iyer, KP and Schumacher, J and Sreenivasan, KR and Yeung, PK}, title = {Steep Cliffs and Saturated Exponents in Three-Dimensional Scalar Turbulence.}, journal = {Physical review letters}, volume = {121}, number = {26}, pages = {264501}, doi = {10.1103/PhysRevLett.121.264501}, pmid = {30636127}, issn = {1079-7114}, abstract = {The intermittency of a passive scalar advected by three-dimensional Navier-Stokes turbulence at a Taylor-scale Reynolds number of 650 is studied using direct numerical simulations on a 4096^{3} grid; the Schmidt number is unity. By measuring scalar increment moments of high orders, while ensuring statistical convergence, we provide unambiguous evidence that the scaling exponents saturate to 1.2 for moment orders beyond about 12, indicating that scalar intermittency is dominated by the most singular shocklike cliffs in the scalar field. We show that the fractal dimension of the spatial support of steep cliffs is about 1.8, whose sum with the saturation exponent value of 1.2 adds up to the space dimension of 3, thus demonstrating a deep connection between the geometry and statistics in turbulent scalar mixing. The anomaly for the fourth and sixth order moments is comparable to that in the Kraichnan model for the roughness exponent of 4/3.}, } @article {pmid30624119, year = {2018}, author = {Caracappa, JC and Munroe, DM}, title = {Morphological Variability Among Broods of First-Stage Blue Crab (Callinectes sapidus) Zoeae.}, journal = {The Biological bulletin}, volume = {235}, number = {3}, pages = {123-133}, doi = {10.1086/699922}, pmid = {30624119}, issn = {1939-8697}, mesh = {Animals ; Biological Variation, Population ; Brachyura/*anatomy & histology ; Female ; Larva/anatomy & histology ; Models, Biological ; Swimming ; }, abstract = {External morphology has been shown to influence predation and locomotion of decapod larvae and is, therefore, directly related to their ability to survive and disperse. The first goal of this study was to characterize first-stage blue crab zoeal morphology and its variability across larval broods to test whether inter-brood differences in morphology exist. The second was to identify possible correlations between maternal characteristics and zoeal morphology. The offspring of 21 individuals were hatched in the laboratory, photographed, and measured. Zoeae exhibited substantial variability, with all metrics showing significant inter-brood differences. The greatest variability was seen in the zoeal abdomen, rostrum, and dorsal spine length. A principal component analysis showed no distinct clustering of broods, with variation generally driven by larger zoeae. Using observed morphology, models of drag induced by swimming and sinking also showed significant inter-brood differences, with a maximum twofold difference across broods. In contrast to trends in other decapod taxa, maternal characteristics (female carapace width and mass and egg sponge volume and mass) are not significant predictors of zoeal morphology. These results suggest that brood effects are present across a wide range of morphological characteristics and that future experiments involving Callinectes sapidus morphology or its functionality should explicitly account for inter-brood variation. Additionally, inter-brood morphological differences may result in differential predation mortality and locomotory abilities among broods.}, } @article {pmid30624117, year = {2018}, author = {Lamont, EI and Emlet, RB}, title = {Permanently Fused Setules Create Unusual Folding Fans Used for Swimming in Cyprid Larvae of Barnacles.}, journal = {The Biological bulletin}, volume = {235}, number = {3}, pages = {185-194}, doi = {10.1086/700084}, pmid = {30624117}, issn = {1939-8697}, mesh = {Animals ; Larva/anatomy & histology/ultrastructure ; *Swimming ; Thoracica/*anatomy & histology/ultrastructure ; }, abstract = {Many crustacean swimming appendages carry arrays of plumose setae-exoskeletal, feather-like structures of long bristles (setae) with short branches (setules) distributed along two sides. Although closely spaced, setae are not physically interconnected. Setal arrays function during swimming as drag-based leaky paddles that push the organism through water. Barnacle cyprids, the final, non-feeding larval stage, swim with six pairs of legs (thoracopods) that open and close setal arrays in alternating high-drag power strokes and low-drag recovery strokes. While studying cyprid swimming, we found that their thoracopods contained setae permanently cross-linked by fused setules. These cuticular connections would seem highly unlikely because setae are individually produced exoskeletal secretions, and the connections imply unknown processes for the production or modification of crustacean setae. We describe the morphology and function of plumose setae on cyprids of Balanus glandula and other species across the clade Cirripedia. Setules from adjacent plumose setae are seamlessly joined at their tips and occur in three distinct linkage patterns. Thoracopods lack muscles to open and close the array; interconnected setae are instead pulled apart, producing a paddle-like fan with high drag when appendages spread laterally during power strokes. Setules are spring-like, passively closing setae into tight bundles with low drag during recovery strokes. The linked setules occur in the three main clades of the Cirripedia. This cuticular arrangement is effective in swimming, may eliminate the need for muscles to close the setal array, and may represent a unique swimming structure within the Crustacea.}, } @article {pmid30606096, year = {2019}, author = {Kunze, E}, title = {Biologically Generated Mixing in the Ocean.}, journal = {Annual review of marine science}, volume = {11}, number = {}, pages = {215-226}, doi = {10.1146/annurev-marine-010318-095047}, pmid = {30606096}, issn = {1941-0611}, mesh = {Aquatic Organisms/*physiology ; Diffusion ; Gravitation ; Swimming ; Temperature ; *Water Movements ; Wind ; }, abstract = {This article assesses the contribution to ocean mixing by the marine biosphere at both high and low Reynolds numbers Re= uℓ/ ν. While back-of-the-envelope estimates have suggested that swimming marine organisms might generate as much high-Reynolds-number turbulence as deep-ocean tide- and wind-generated internal waves, and that turbulent dissipation rates of O(10-5 W kg-1) (Re ∼ 105) could be produced by aggregations of organisms ranging from O(0.01 m) krill to O(10 m) cetaceans, comparable to strong wind and buoyancy forcing near the surface, microstructure measurements do not find consistently elevated dissipation associated with diel vertically migrating krill. Elevated dissipation rates are associated with schools of O(0.1- 1 m) fish but with low mixing coefficients (γ ∼ 0.002-0.02, as compared with γ ∼ 0.2 for geophysical turbulence). Likewise, viscously induced drift at low Reynolds numbers produces little mixing of temperature, solutes, dissolved nutrients, and gases when realistic swimmers and molecular scalar diffusion are taken into account. The conclusion is that, while the marine biosphere can generate turbulence, it contributes little ocean mixing compared with breaking internal gravity waves.}, } @article {pmid30605404, year = {2019}, author = {Itzhak, N and Greenblatt, D}, title = {Aerodynamic factors affecting rebreathing in infants.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {126}, number = {4}, pages = {952-964}, doi = {10.1152/japplphysiol.00784.2018}, pmid = {30605404}, issn = {1522-1601}, mesh = {Carbon Dioxide/metabolism ; Humans ; Infant, Newborn ; Oxygen/metabolism ; Prone Position/*physiology ; Respiration ; Risk Factors ; Sleep/*physiology ; Sudden Infant Death/*prevention & control ; Temperature ; Tidal Volume/physiology ; }, abstract = {The rebreathing of expire air, with high carbon dioxide and low oxygen concentrations, has long been implicated in unexplained Sudden Infant Death Syndrome (SIDS) when infants are placed to sleep in a prone (facedown) position. This study elucidates the effect of the aerodynamic parameters Reynolds number, Strouhal number, and Froude number on the percentage of expired air that is reinspired (rebreathed). A nasal module was designed that served as a simplified geometric representation of infant nostrils and placed above a hard, flat surface. Quantitative and flow visualization experiments were performed to measure rebreathing, using water as the working medium, under conditions of dynamic similarity. Different anatomic (e.g., tidal volume, nostril diameter), physiological (e.g., breathing frequency), and environmental (e.g., temperature, distance from the surface) factors were considered. Increases in Strouhal number (simultaneously faster and shallower breathing) always produced higher rebreathed percentages, because rolled-up vortices in the vicinity of the nostrils had less time to move away by self-induction. Positively and negatively buoyant flows resulted in significant rebreathing. In the latter case, consistent with a warm environment and a high percentage of rebreathed CO2, denser gas pooled in the vicinity of the nostrils. Reynolds numbers below 200 also dramatically increased rebreathing because the expired gas pooled much closer to the nostrils. These results clearly elucidated how the prone position dramatically increases rebreathing by a number of different mechanisms. Furthermore, the results offer plausible explanations of why a high-temperature environment and low birthweight are SIDS risk factors. NEW & NOTEWORTHY A fundamentally new aerodynamics-based approach to the study of rebreathing of expired air in infants is presented. Rebreathing is implicated in unexplained Sudden Infant Death Syndrome (SIDS) when infants sleep in a prone position. This is the first time that aerodynamic parameters are systematically varied and their effects on rebreathing quantified. The study provides us with a deeper understanding of the effects of breathing frequency, tidal volume (birthweight) and environmental conditions.}, } @article {pmid30604300, year = {2019}, author = {Wu, P and Gao, Q and Hsu, PL}, title = {On the representation of effective stress for computing hemolysis.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {18}, number = {3}, pages = {665-679}, doi = {10.1007/s10237-018-01108-y}, pmid = {30604300}, issn = {1617-7940}, support = {51406127//National Natural Science Foundation of China/ ; BK20140344//Natural Science Foundation of Jiangsu Province/ ; }, mesh = {Animals ; Capillaries/physiopathology ; Heart-Assist Devices ; *Hemolysis ; Humans ; Hydrodynamics ; *Models, Cardiovascular ; Pressure ; *Stress, Mechanical ; United States ; United States Food and Drug Administration ; }, abstract = {Hemolysis is a major concern in blood-circulating devices, which arises due to hydrodynamic loading on red blood cells from ambient flow environment. Hemolysis estimation models have often been used to aid hemocompatibility design. The preponderance of hemolysis models was formulated on the basis of laminar flows. However, flows in blood-circulating devices are rather complex and can be laminar, transitional or turbulent. It is an extrapolation to apply these models to turbulent flows. For the commonly used power-law models, effective stress has often been represented using Reynolds stresses for estimating hemolysis in turbulent flows. This practice tends to overpredict hemolysis. This study focused on the representation of effective stress in power-law models. Through arithmetic manipulations from Navier-Stokes equation, we showed that effective stress can be represented in terms of energy dissipation, which can be readily obtained from CFD simulations. Three cases were tested, including a capillary tube, the FDA benchmark cases of nozzle model and blood pump. The results showed that the representation of effective stress in terms of energy dissipation greatly improved the prediction of hemolysis for a wide range of flow conditions. The improvement increases as Reynolds number increases; the overprediction of hemolysis was reduced by up to two orders of magnitude.}, } @article {pmid30603681, year = {2018}, author = {Szaszák, N and Roloff, C and Bordás, R and Bencs, P and Szabó, S and Thévenin, D}, title = {A novel type of semi-active jet turbulence grid.}, journal = {Heliyon}, volume = {4}, number = {12}, pages = {e01026}, pmid = {30603681}, issn = {2405-8440}, abstract = {This article describes a novel approach to generate increased turbulence levels in an incoming flow. It relies on a cost-effective and robust semi-active jet grid, equipped with flexible tubes as moving elements attached onto tube connections placed at the intersections of a fixed, regular grid. For the present study, these flexible tubes are oriented in counter-flow direction in a wind tunnel. Tube motion is governed by multiple interactions between the main flow and the jets exiting the tubes, resulting in chaotic velocity fluctuations and high turbulence intensities in the test section. After describing the structure of the turbulence generator, the turbulent properties of the airflow downstream of the grid in both passive and active modes are measured by hot-wire anemometry and compared with one another. When activating the turbulence generator, turbulence intensity, turbulent kinetic energy, and the Taylor Reynolds number are noticeably increased in comparison with the passive mode (corresponding to simple grid turbulence). Furthermore, the inertial subrange of the turbulent energy spectrum becomes wider and closely follows Kolmogorov's -5/3 law. These results show that the semi-active grid, in contrast to passive systems, is capable of producing high turbulence levels, even at low incoming flow velocity. Compared to alternatives based on actuators driven by servo-motors, the production and operation costs of the semi-active grid are very moderate and its robustness is much higher.}, } @article {pmid30602925, year = {2018}, author = {Garcia, F and Stefani, F}, title = {Continuation and stability of rotating waves in the magnetized spherical Couette system: secondary transitions and multistability.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {474}, number = {2220}, pages = {20180281}, pmid = {30602925}, issn = {1364-5021}, abstract = {Rotating waves (RW) bifurcating from the axisymmetric basic magnetized spherical Couette (MSC) flow are computed by means of Newton-Krylov continuation techniques for periodic orbits. In addition, their stability is analysed in the framework of Floquet theory. The inner sphere rotates while the outer is kept at rest and the fluid is subjected to an axial magnetic field. For a moderate Reynolds number Re = 103 (measuring inner rotation), the effect of increasing the magnetic field strength (measured by the Hartmann number Ha) is addressed in the range Ha∈(0, 80) corresponding to the working conditions of the HEDGEHOG experiment at Helmholtz-Zentrum Dresden-Rossendorf. The study reveals several regions of multistability of waves with azimuthal wavenumber m = 2, 3, 4, and several transitions to quasi-periodic flows, i.e modulated rotating waves. These nonlinear flows can be classified as the three different instabilities of the radial jet, the return flow and the shear layer, as found in the previous studies. These two flows are continuously linked, and part of the same branch, as the magnetic forcing is increased. Midway between the two instabilities, at a certain critical Ha, the non-axisymmetric component of the flow is maximum.}, } @article {pmid30602310, year = {2018}, author = {Murphy, EAK and Barros, JM and Schultz, MP and Flack, KA and Steppe, CN and Reidenbach, MA}, title = {Roughness effects of diatomaceous slime fouling on turbulent boundary layer hydrodynamics.}, journal = {Biofouling}, volume = {34}, number = {9}, pages = {976-988}, doi = {10.1080/08927014.2018.1517867}, pmid = {30602310}, issn = {1029-2454}, mesh = {Biofilms/*growth & development ; Biofouling/*prevention & control ; Friction ; *Hydrodynamics ; Rheology ; *Ships ; Stress, Mechanical ; Surface Properties ; }, abstract = {Biofilm fouling significantly impacts ship performance. Here, the impact of biofilm on boundary layer structure at a ship-relevant, low Reynolds number was investigated. Boundary layer measurements were performed over slime-fouled plates using high resolution particle image velocimetry (PIV). The velocity profile over the biofilm showed a downward shift in the log-law region (ΔU+), resulting in an effective roughness height (ks) of 8.8 mm, significantly larger than the physical thickness of the biofilm (1.7 ± 0.5 mm) and generating more than three times as much frictional drag as the smooth-wall. The skin-friction coefficient, Cf, of the biofilm was 9.0 × 10-3 compared with 2.9 × 10-3 for the smooth wall. The biofilm also enhances turbulent kinetic energy (tke) and Reynolds shear stress, which are more heterogeneous in the streamwise direction than smooth-wall flows. This suggests that biofilms increase drag due to high levels of momentum transport, likely resulting from protruding streamers and surface compliance.}, } @article {pmid32625002, year = {2019}, author = {Pérez-Hernández, J and Nicasio-Torres, MDP and Sarmiento-López, LG and Rodríguez-Monroy, M}, title = {Production of anti-inflammatory compounds in Sphaeralcea angustifolia cell suspension cultivated in stirred tank bioreactor.}, journal = {Engineering in life sciences}, volume = {19}, number = {3}, pages = {196-205}, pmid = {32625002}, issn = {1618-0240}, abstract = {Sphaeralcea angustifolia is a plant used for the treatment of inflammatory processes. Scopoletin, tomentin, and sphaeralcic acid were identified as the compounds with anti-inflammatory and immunomodulatory effects. Successful establishment of the cell culture in Erlenmeyer flasks has been reported previously. The aim of this study was to evaluate the ability of cells in suspension from S. angustifolia grown in a stirred tank bioreactor and demonstrate their capacity to produce bioactive compounds. Cells in suspension grown at 200 rpm reached a maximal cell biomass in dry weight at 19.11 g/L and produced 3.47 mg/g of sphaeralcic acid. The mixture of scopoletin and tomentin was only detected at the beginning of the culture (12.13 μg/g). Considering that the profile of dissolved oxygen during the cultures was lesser than 15%, it is possible that the low growth at 100 rpm could be due to oxygen limitations or to cell sedimentation. At 400 rpm, a negative effect on cell viability could be caused by the increase in the hydrodynamic stress, including the impeller tip, average shear rate, and Reynolds number. The sphaeralcic acid content in the cell suspension of S. angustifolia obtained in the bioreactor was two orders of magnitude greater than that reported for the culture grown in Erlenmeyer flasks.}, } @article {pmid32116345, year = {2019}, author = {Mensch, AE and Cleary, TG}, title = {Measurements and predictions of thermophoretic soot deposition.}, journal = {International journal of heat and mass transfer}, volume = {143}, number = {}, pages = {}, doi = {10.1016/j.ijheatmasstransfer.2019.118444}, pmid = {32116345}, issn = {0017-9310}, support = {9999-NIST/ImNIST/Intramural NIST DOC/United States ; }, abstract = {A thin laminar flow channel with a transverse temperature gradient was used to examine thermophoretic deposition of soot aerosol particles in experiments and modeled in Fire Dynamics Simulator (FDS) simulations. Conditions investigated included three flowrates, with nominal Reynolds number based on the hydraulic diameter of 55, 115 and 230, and two applied temperature gradients, nominally 10 °C/mm and 20 °C/mm, with repeats. Soot was generated from a propene diffusion flame. The burner exhaust was mixed with dilution air, and most large agglomerates greater than 1 μm aerodynamic diameter were removed prior to the channel inlet. The expected thermophoretic velocity of the aerosol was calculated from the applied temperature gradient. A calculated deposition velocity was determined from the mass of deposition, the channel inlet soot concentration, and the exposure time. Uniform soot deposition allowed targets to be used to measure the mass of deposition on the cold side of the channel. The mass of deposition was also determined by subtracting the mass of soot exiting the channel from the mass of soot entering the channel during the exposure time. The deposition velocities from these two methods generally agreed with the thermophoretic velocity and with each other. The deposition mass predicted by the FDS model also compared well with the experiments in most cases. The disagreements for the lowest flow rate cases are attributed to buoyant flow effects adding uncertainty to the actual temperature gradients present in the channel. (The opinions, findings, and conclusions expressed in this paper are the authors' and do not represent the views or policies of NIST or the United States Government.).}, } @article {pmid30584714, year = {2018}, author = {Wang, WX and Wang, WL and Kang, HL and Guo, MM and Yang, B and Chen, ZX and Zhao, M}, title = {Effect of naturally restored grassland on the ephemeral gully erosion in the loess hilly and gully region.}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {29}, number = {12}, pages = {3891-3899}, doi = {10.13287/j.1001-9332.201812.016}, pmid = {30584714}, issn = {1001-9332}, mesh = {Agriculture ; China ; *Conservation of Natural Resources ; Environmental Monitoring ; *Grassland ; *Soil ; }, abstract = {Ephemeral gully erosion is an important erosion type in hilly and gully regions of Loess Plateau. While previous studies mainly focused on ephemeral gullies in agricultural land, little is known about the effects of naturally restored grassland on ephemeral gully erosion. In this study, taking the bare ephemeral gullies as the baseline, we conducted in-situ flushing tests to explore runoff and sediment yield characteristics and erosion mechanism of grassland ephemeral gullies under the runoff conditions of 5, 10, 15, 20 and 25 L·min-1. Compared to the bare ephemeral gully, average flow velocity, stable runoff rate, Reynolds number and Froude number of grassland ephe-meral gullies was reduced by 25.4%-67.3%, 8.4%-26.6%, 54.9%-80.5%, 18.6%-65.1%, respectively, whereas resistance coefficient was increased by 0.09-7.18 folds. Compared to the bare ephemeral gully, the maximum sediment yield rate, stable sediment yield rate, average sediment yield rate of grassland ephemeral gullies was decreased by 55.1%-90.9%, 61.8%-95.4%, and 64.8%-92.4%, respectively. The sediment yield reduction benefit of the naturally restored grassland under the discharge flow rate of 5-25 L·min-1 could reach 65.9%-88.8%, which decreased with increasing discharge flow rate. Compared to the bare ephemeral gully, average stream power and average shear stress of grassland ephemeral gullies was reduced by 54.9%-80.5% and 12.4%-51.1%, respectively, whereas the critical stream power and critical shear stress was increased by 1.43 folds and 33.7%, respectively. The average sediment yield of grassland and bare ephemeral gullies was signifi-cantly linearly related to average stream power and shear stress. Naturally restored grassland significantly increased the erosion resistance and reduced runoff erosion potential of ephemeral gullies.}, } @article {pmid30576199, year = {2018}, author = {Gabbana, A and Polini, M and Succi, S and Tripiccione, R and Pellegrino, FMD}, title = {Prospects for the Detection of Electronic Preturbulence in Graphene.}, journal = {Physical review letters}, volume = {121}, number = {23}, pages = {236602}, doi = {10.1103/PhysRevLett.121.236602}, pmid = {30576199}, issn = {1079-7114}, abstract = {Based on extensive numerical simulations, accounting for electrostatic interactions and dissipative electron-phonon scattering, we propose experimentally realizable geometries capable of sustaining electronic preturbulence in graphene samples. In particular, preturbulence is predicted to occur at experimentally attainable values of the Reynolds number between 10 and 50, over a broad spectrum of frequencies between 10 and 100 GHz.}, } @article {pmid30556777, year = {2019}, author = {Bass, K and Boc, S and Hindle, M and Dodson, K and Longest, W}, title = {High-Efficiency Nose-to-Lung Aerosol Delivery in an Infant: Development of a Validated Computational Fluid Dynamics Method.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {32}, number = {3}, pages = {132-148}, pmid = {30556777}, issn = {1941-2703}, support = {R01 HD087339/HD/NICHD NIH HHS/United States ; R01 HL139673/HL/NHLBI NIH HHS/United States ; }, mesh = {Administration, Inhalation ; Administration, Intranasal ; Aerosols/*administration & dosage/pharmacokinetics ; Computer Simulation ; *Drug Delivery Systems ; Equipment Design ; Humans ; *Hydrodynamics ; Infant ; Lung/metabolism ; *Models, Biological ; Particle Size ; }, abstract = {Background: Computational fluid dynamics (CFD) provides a powerful tool for developing new high-efficiency aerosol delivery strategies, such as nose-to-lung (N2L) aerosol administration to infants and children using correctly sized aerosols. The objective of this study was to establish numerically efficient CFD solution methods and guidelines for simulating N2L aerosol administration to an infant based on comparisons with concurrent in vitro experiments. Materials and Methods: N2L administration of a micrometer-sized aerosol (mass median aerodynamic diameter [MMAD] = 1.4 μm) was evaluated using concurrent CFD simulations and in vitro experiments. Aerosol transport and deposition was assessed in a new nasal airway geometry of a 6-month-old infant with a streamlined nasal cannula interface, which was constructed as a CFD mesh and three-dimensionally printed to form an identical physical prototype. CFD meshes explored were a conventional tetrahedral approach with near-wall (NW) prism elements and a new polyhedral mesh style with an equally refined NW layer. The presence of turbulence in the model was evaluated using a highly efficient low-Reynolds number (LRN) k-ω turbulence model, with previously established NW corrections that accounted for anisotropic wall-normal turbulence as well as improved NW velocity interpolations and hydrodynamic particle damping. Results: Use of the new polyhedral mesh was found to improve numerical efficiency by providing more rapid convergence and requiring fewer control volumes. Turbulent flow was found in the nasal geometry, generated by the inlet jets from the nasal cannula interface. However, due to the small particle size, turbulent dispersion was shown to have little effect on deposition. Good agreement was established between the CFD predictions using the numerically efficient LRN k-ω model with appropriate NW corrections and in vitro deposition data. Aerosol transmission efficiencies through the delivery tube, nasal cannula, and infant nasal model, based on experimental and CFD predictions, were 93.0% and 91.5%, respectively. Conclusions: A numerically efficient CFD approach was established to develop transnasal aerosol administration to infants and children. Small particle aerosols with aerodynamic diameters of ∼1.5 μm were confirmed to have low inertial depositional loss, and have low deposition from turbulent dispersion, making them ideal for high-efficiency lung delivery through an infant nasal cannula interface.}, } @article {pmid30548194, year = {2019}, author = {Enders, A and Siller, IG and Urmann, K and Hoffmann, MR and Bahnemann, J}, title = {3D Printed Microfluidic Mixers-A Comparative Study on Mixing Unit Performances.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {15}, number = {2}, pages = {e1804326}, doi = {10.1002/smll.201804326}, pmid = {30548194}, issn = {1613-6829}, abstract = {One of the basic operations in microfluidic systems for biological and chemical applications is the rapid mixing of different fluids. However, flow profiles in microfluidic systems are laminar, which means molecular diffusion is the only mixing effect. Therefore, mixing structures are crucial to enable more efficient mixing in shorter times. Since traditional microfabrication methods remain laborious and expensive, 3D printing has emerged as a potential alternative for the fabrication of microfluidic devices. In this work, five different passive micromixers known from literature are redesigned in comparable dimensions and manufactured using high-definition MultiJet 3D printing. Their mixing performance is evaluated experimentally, using sodium hydroxide and phenolphthalein solutions, and numerically via computational fluid dynamics. Both experimental and numerical analysis results show that HC and Tesla-like mixers achieve complete mixing after 0.99 s and 0.78 s, respectively, at the highest flow rate (Reynolds number (Re) = 37.04). In comparison, Caterpillar mixers exhibit a lower mixing rate with complete mixing after 1.46 s and 1.9 s. Furthermore, the HC mixer achieves very good mixing performances over all flow rates (Re = 3.7 to 37.04), while other mixers show improved mixing only at higher flow rates.}, } @article {pmid30545916, year = {2019}, author = {Sreenivasan, KR}, title = {Turbulent mixing: A perspective.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {116}, number = {37}, pages = {18175-18183}, pmid = {30545916}, issn = {1091-6490}, abstract = {Mixing of initially distinct substances plays an important role in our daily lives as well as in ecological and technological worlds. From the continuum point of view, which we adopt here, mixing is complete when the substances come together across smallest flow scales determined in part by molecular mechanisms, but important stages of the process occur via the advection of substances by an underlying flow. We know how smooth flows enable mixing but less well the manner in which a turbulent flow influences it; but the latter is the more common occurrence on Earth and in the universe. We focus here on turbulent mixing, with more attention paid to the postmixing state than to the transient process of initiation. In particular, we examine turbulent mixing when the substance is a scalar (i.e., characterized only by the scalar property of its concentration), and the mixing process does not influence the flow itself (i.e., the scalar is "passive"). This is the simplest paradigm of turbulent mixing. Within this paradigm, we discuss how a turbulently mixed state depends on the flow Reynolds number and the Schmidt number of the scalar (the ratio of fluid viscosity to the scalar diffusivity), point out some fundamental aspects of turbulent mixing that render it difficult to be addressed quantitatively, and summarize a set of ideas that help us appreciate its physics in diverse circumstances. We consider the so-called universal and anomalous features and summarize a few model studies that help us understand them both.}, } @article {pmid30523914, year = {2018}, author = {Bodling, A and Sharma, A}, title = {Numerical investigation of low-noise airfoils inspired by the down coat of owls.}, journal = {Bioinspiration & biomimetics}, volume = {14}, number = {1}, pages = {016013}, doi = {10.1088/1748-3190/aaf19c}, pmid = {30523914}, issn = {1748-3190}, mesh = {Animals ; Computer Simulation ; Flight, Animal/*physiology ; Models, Biological ; Noise ; Pressure ; Rotation ; Strigiformes/*physiology ; Wings, Animal/physiology ; }, abstract = {Numerical analysis of airfoil geometries inspired by the down coat of the night owl is presented. The bioinspired geometry consists of an array of 'finlet fences', which is placed near the trailing edge of the baseline (NACA 0012) airfoil. Two fences with maximum nondimensional heights, [Formula: see text] and [Formula: see text] are investigated, where [Formula: see text] is the displacement thickness at 2.9% chord upstream of the airfoil trailing edge. Wall-resolved large eddy simulations are performed at chord-based Reynolds number, [Formula: see text], flow Mach number, [Formula: see text], and angle of attack, [Formula: see text]. The simulation results show significant reductions in unsteady surface pressure and farfield radiated noise with the fences, in agreement with the measurements available in the literature. Analysis of the results reveals that the fences increase the distance between the boundary layer turbulence (source) and the airfoil trailing (scattering) edge, which is identified to be the mechanism behind high-frequency noise reduction. These reductions are larger for the taller fence as the source-scattering edge separation is greater. Two-point correlations show that the fences reduce the spanwise coherence at low frequencies for separation distances greater than a fence pitch (distance between two adjacent fences) and increase the coherence for smaller distances, the increase being higher for the taller fence. This increase in coherence and the reduced obliqueness of the leading edge of the fence are hypothesized to be responsible for the small increase in farfield noise at low frequencies observed in the simulations with the taller fence.}, } @article {pmid30522876, year = {2019}, author = {Paxman, T and Noga, M and Finlay, WH and Martin, AR}, title = {Experimental evaluation of pressure drop for flows of air and heliox through upper and central conducting airway replicas of 4- to 8-year-old children.}, journal = {Journal of biomechanics}, volume = {82}, number = {}, pages = {134-141}, doi = {10.1016/j.jbiomech.2018.10.028}, pmid = {30522876}, issn = {1873-2380}, mesh = {*Air ; *Airway Resistance ; Child ; Child, Preschool ; Female ; *Helium ; Humans ; Inhalation ; Male ; Models, Biological ; *Oxygen ; *Pressure ; *Respiratory Physiological Phenomena ; }, abstract = {Airway resistance describes the ratio between pressure drop and flow rate through the conducting respiratory airways. Analytical models of airway resistance for tracheobronchial airways have previously been developed and assessed without upper airways positioned upstream of the trachea. This work investigated pressure drop as a function of flow rate and gas properties for upper and central airway replicas of 10 child subjects, ages 4-8. Replica geometries were built based on computed tomography scan data and included airways from the nose through 3-5 distal branching airway generations. Pressure drop through the replicas was measured for constant inspiratory flows of air and heliox. For both the nose-throat and branching airways, the relationship between non-dimensional coefficient of friction, CF, with Reynolds number, Re, was found to resemble the turbulent Blasius equation for pipe flow, where CF∝Re-0.25. Additionally, pressure drop ratios between heliox and air were consistent with analytical predictions for turbulent flow. The presence of turbulence in the branching airways likely resulted from convection of turbulence produced upstream in the nose and throat. An airway resistance model based on the Blasius pipe friction correlation for turbulent flow was proposed for prediction of pressure drop through the branching bronchial airways downstream from the upper airway.}, } @article {pmid30522286, year = {2018}, author = {Acconcia, CN and Wright, A and Goertz, DE}, title = {Translational dynamics of individual microbubbles with millisecond scale ultrasound pulses.}, journal = {The Journal of the Acoustical Society of America}, volume = {144}, number = {5}, pages = {2859}, doi = {10.1121/1.5063353}, pmid = {30522286}, issn = {1520-8524}, abstract = {It is established that radiation forces can be used to transport ultrasound contrast agents, particularly for molecular imaging applications. However, the ability to model and control this process in the context of therapeutic ultrasound is limited by a paucity of data on the translational dynamics of encapsulated microbubbles under the influence of longer pulses. In this work, the translation of individual microbubbles, isolated with optical tweezers, was experimentally investigated over a range of diameters (1.8-8.8 μm, n = 187) and pressures (25, 50, 100, 150, and 200 kPa) with millisecond pulses. Data were compared with theoretical predictions of the translational dynamics, assessing the role of shell and history force effects. A pronounced feature of the displacement curves was an effective threshold size, below which there was only minimal translation. At higher pressures (≥150 kPa) a noticeable structure emerged where multiple local maxima occurred as a function of bubble size. The ability to accurately capture these salient features depended on the encapsulation model employed. In low Reynolds number conditions (i.e., low pressures, or high pressures, off-resonance) the inclusion of history force more accurately fit the data. After pulse cessation, bubbles exhibited substantial displacements consistent with the influence of history effects.}, } @article {pmid30511712, year = {2018}, author = {Jeon, W and Kim, T and Kim, SM and Baik, S}, title = {Fast mass transport-assisted convective heat transfer through a multi-walled carbon nanotube array.}, journal = {Nanoscale}, volume = {10}, number = {48}, pages = {23103-23112}, doi = {10.1039/c8nr07529h}, pmid = {30511712}, issn = {2040-3372}, abstract = {The recently reported fast mass transport through nanochannels provides a unique opportunity to explore nanoscale energy transport. Here we experimentally investigated the convective heat transport of air through vertically aligned multi-walled carbon nanotubes (VAMWNTs). The flow through the unit cell, defined as an interstitial space among four adjacent nanotubes (hydraulic diameter = 84.9 nm), was in the transition (0.62 ≤ Knudsen number ≤ 0.78) and creeping flow (3.83 × 10-5 ≤ Reynolds number (Re) ≤ 1.55 × 10-4) regime. The constant heat flux (0.102 or 0.286 W m-2) was supplied by a single-mode microwave (2.45 GHz) instantly heating the VAMWNTs. The volume flow rate was two orders of magnitude greater than the Hagen-Poiseuille theory value. The experimentally determined convective heat transfer coefficient (h, 3.70 × 10-4-4.01 × 10-3 W m-2 K-1) and Nusselt number (Nu, 1.17 × 10-9-1.26 × 10-8) were small partly due to the small Re. A further increase in Re (2.12 × 10-3) with the support of a polytetrafluoroethylene mesh significantly increased h (5.48 × 10-2 W m-2 K-1) and Nu (2.37 × 10-7). A large number of nanochannels in a given cross-section of heat sinks may enhance the heat dissipation significantly.}, } @article {pmid30511653, year = {2018}, author = {Wang, C and Tang, H}, title = {Influence of complex driving motion on propulsion performance of a heaving flexible foil.}, journal = {Bioinspiration & biomimetics}, volume = {14}, number = {1}, pages = {016011}, doi = {10.1088/1748-3190/aaf17a}, pmid = {30511653}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Biomimetics/*methods ; Fishes/physiology ; Models, Biological ; Motion ; Movement/*physiology ; Swimming/physiology ; }, abstract = {This study explores the effects of complex driving motion on the propulsion performance of a flexible foil heaving in the flight regimes of natural flyers. Such a fluid-structure interaction problem is numerically studied using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. It is found that, at the Reynolds number 200 and when the foil's bending stiffness and mass ratio are moderate, adding an extra driving motion of doubled frequency to a purely harmonic motion on the foil's leading edge can enhance the thrust and propulsive efficiency by about 860% and 70%, respectively. The improvement in thrust increases with the extra-driving-motion amplitude. When the extra-driving-motion amplitude is fixed, there exists an optimal extra-driving-motion phase angle. As the foil becomes much stiffer or lighter, the improvement in the propulsion performance turns less. On the other hand, as the foil becomes much more flexible or heavier, drag instead of thrust is generated, and extra driving motion brings no improvement. Although the extra driving motion can improve the foil's propulsion performance in flows of different Reynolds numbers, the increasing rate of the thrust reduces with the Reynolds number. Through this study, details about the competitions among various forces exerted on the foil and their roles in the foil's dynamics are also revealed.}, } @article {pmid30487240, year = {2018}, author = {Kamal, A and Keaveny, EE}, title = {Enhanced locomotion, effective diffusion and trapping of undulatory micro-swimmers in heterogeneous environments.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {148}, pages = {}, pmid = {30487240}, issn = {1742-5662}, mesh = {Helicobacter/*physiology ; Locomotion/*physiology ; *Models, Biological ; Plasmodium/*physiology ; }, abstract = {Swimming cells and microorganisms must often move through complex fluids that contain an immersed microstructure such as polymer molecules or filaments. In many important biological processes, such as mammalian reproduction and bacterial infection, the size of the immersed microstructure is comparable to that of the swimming cells. This leads to discrete swimmer-microstructure interactions that alter the swimmer's path and speed. In this paper, we use a combination of detailed simulation and data-driven stochastic models to examine the motion of a planar undulatory swimmer in an environment of spherical obstacles tethered via linear springs to random points in the plane of locomotion. We find that, depending on environmental parameters, the interactions with the obstacles can enhance swimming speeds or prevent the swimmer from moving at all. We also show how the discrete interactions produce translational and angular velocity fluctuations that over time lead to diffusive behaviour primarily due to the coupling of swimming and rotational diffusion. Our results demonstrate that direct swimmer-microstructure interactions can produce changes in swimmer motion that may have important implications for the spreading of cell populations in or the trapping of harmful pathogens by complex fluids.}, } @article {pmid30467607, year = {2018}, author = {Grosjean, G and Hubert, M and Collard, Y and Pillitteri, S and Vandewalle, N}, title = {Surface swimmers, harnessing the interface to self-propel.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {11}, pages = {137}, pmid = {30467607}, issn = {1292-895X}, abstract = {In the study of microscopic flows, self-propulsion has been particularly topical in recent years, with the rise of miniature artificial swimmers as a new tool for flow control, low Reynolds number mixing, micromanipulation or even drug delivery. It is possible to take advantage of interfacial physics to propel these microrobots, as demonstrated by recent experiments using the proximity of an interface, or the interface itself, to generate propulsion at low Reynolds number. This paper discusses how a nearby interface can provide the symmetry breaking necessary for propulsion. An overview of recent experiments illustrates how forces at the interface can be used to generate locomotion. Surface swimmers ranging from the microscopic scale to typically the capillary length are covered. Two systems are then discussed in greater detail. The first is composed of floating ferromagnetic spheres that assemble through capillarity into swimming structures. Two previously studied configurations, triangular and collinear, are discussed and contrasted. A new interpretation for the triangular swimmer is presented. Then, the non-monotonic influence of surface tension and viscosity is evidenced in the collinear case. Finally, a new system is introduced. It is a magnetically powered, centimeter-sized piece that swims similarly to water striders.}, } @article {pmid30465777, year = {2019}, author = {Walker, BJ and Wheeler, RJ and Ishimoto, K and Gaffney, EA}, title = {Boundary behaviours of Leishmania mexicana: A hydrodynamic simulation study.}, journal = {Journal of theoretical biology}, volume = {462}, number = {}, pages = {311-320}, pmid = {30465777}, issn = {1095-8541}, mesh = {Animals ; Biophysical Phenomena ; *Hydrodynamics ; Insect Vectors/parasitology ; Leishmania mexicana/*physiology ; Life Cycle Stages ; Psychodidae/*parasitology ; Swimming ; }, abstract = {It is well established that the parasites of the genus Leishmania exhibit complex surface interactions with the sandfly vector midgut epithelium, but no prior study has considered the details of their hydrodynamics. Here, the boundary behaviours of motile Leishmania mexicana promastigotes are explored in a computational study using the boundary element method, with a model flagellar beating pattern that has been identified from digital videomicroscopy. In particular a simple flagellar kinematics is observed and quantified using image processing and mode identification techniques, suggesting a simple mechanical driver for the Leishmania beat. Phase plane analysis and long-time simulation of a range of Leishmania swimming scenarios demonstrate an absence of stable boundary motility for an idealised model promastigote, with behaviours ranging from boundary capture to deflection into the bulk both with and without surface forces between the swimmer and the boundary. Indeed, the inclusion of a short-range repulsive surface force results in the deflection of all surface-bound promastigotes, suggesting that the documented surface detachment of infective metacyclic promastigotes may be the result of their particular morphology and simple hydrodynamics. Further, simulation elucidates a remarkable morphology-dependent hydrodynamic mechanism of boundary approach, hypothesised to be the cause of the well-established phenomenon of tip-first epithelial attachment of Leishmania promastigotes to the sandfly vector midgut.}, } @article {pmid30464056, year = {2018}, author = {Digumarti, KM and Conn, AT and Rossiter, J}, title = {EuMoBot: replicating euglenoid movement in a soft robot.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {148}, pages = {}, pmid = {30464056}, issn = {1742-5662}, mesh = {Euglenida/*physiology ; *Locomotion ; *Robotics ; }, abstract = {Swimming is employed as a form of locomotion by many organisms in nature across a wide range of scales. Varied strategies of shape change are employed to achieve fluidic propulsion at different scales due to changes in hydrodynamics. In the case of microorganisms, the small mass, low Reynolds number and dominance of viscous forces in the medium, requires a change in shape that is non-invariant under time reversal to achieve movement. The Euglena family of unicellular flagellates evolved a characteristic type of locomotion called euglenoid movement to overcome this challenge, wherein the body undergoes a giant change in shape. It is believed that these large deformations enable the organism to move through viscous fluids and tiny spaces. The ability to drastically change the shape of the body is particularly attractive in robots designed to move through constrained spaces and cluttered environments such as through the human body for invasive medical procedures or through collapsed rubble in search of survivors. Inspired by the euglenoids, we present the design of EuMoBot, a multi-segment soft robot that replicates large body deformations to achieve locomotion. Two robots have been fabricated at different sizes operating with a constant internal volume, which exploit hyperelasticity of fluid-filled elastomeric chambers to replicate the motion of euglenoids. The smaller robot moves at a speed of [Formula: see text] body lengths per cycle (20 mm min-1 or 2.2 cycles min-1) while the larger one attains a speed of [Formula: see text] body lengths per cycle (4.5 mm min-1 or 0.4 cycles min-1). We show the potential for biomimetic soft robots employing shape change to both replicate biological motion and act as a tool for studying it. In addition, we present a quantitative method based on elliptic Fourier descriptors to characterize and compare the shape of the robot with that of its biological counterpart. Our results show a similarity in shape of 85% and indicate that this method can be applied to understand the evolution of shape in other nonlinear, dynamic soft robots where a model for the shape does not exist.}, } @article {pmid30457929, year = {2019}, author = {Huang, HW and Tibbitt, MW and Huang, TY and Nelson, BJ}, title = {Matryoshka-Inspired Micro-Origami Capsules to Enhance Loading, Encapsulation, and Transport of Drugs.}, journal = {Soft robotics}, volume = {6}, number = {1}, pages = {150-159}, doi = {10.1089/soro.2018.0028}, pmid = {30457929}, issn = {2169-5180}, support = {/ERC_/European Research Council/International ; }, mesh = {Capsules/*chemistry ; Drug Delivery Systems/*methods ; Hydrogel, Polyethylene Glycol Dimethacrylate/chemistry ; Hydrogels/chemistry ; Russia ; Technology, Pharmaceutical/*methods ; Temperature ; }, abstract = {Stimuli-responsive hydrogels are promising candidates for use in the targeted delivery of drugs using microrobotics. These devices enable the delivery and sustained release of quantities of drugs several times greater than their dry weight and are responsive to external stimuli. However, existing systems have two major drawbacks: (1) severe drug leakage before reaching the targeted areas within the body and (2) impeded locomotion through liquids due to the inherent hydrophilicity of hydrogels. This article outlines an approach to the assembly of hydrogel-based microcapsules in which one device is assembled within another to prevent drug leakage during transport. Inspired by the famous Russian stacking dolls (Matryoshka), the proposed scheme not only improves drug-loading efficiency but also facilitates the movement of hydrogel-based microcapsules driven by an external magnetic field. At room temperature, drug leakage from the hydrogel matrix is 90%. However, at body temperature the device folds up and assembles to encapsulate the drug, thereby reducing leakage to a mere 6%. The Matryoshka-inspired micro-origami capsule (MIMC) can disassemble autonomously when it arrives at a targeted site, where the temperature is slightly above body temperature. Up to 30% of the encapsulated drug was shown to diffuse from the hydrogel matrix within 1 h when it unfolds and disassembles. The MIMC is also shown to enhance the movement of magnetically driven microcapsules while navigating through media with a low Reynolds number. The translational velocity of the proposed MIMC (four hydrogel-based microcapsules) driven by magnetic gradients is more than three times greater than that of a conventional (single) hydrogel-based microcapsule.}, } @article {pmid30425950, year = {2018}, author = {Rigatelli, G and Zuin, M and Dell'Avvocata, F and Nanjundappa, A and Daggubati, R and Nguyen, T}, title = {Non-invasive Evaluation of Fluid Dynamic of Aortoiliac Atherosclerotic Disease: Impact of Bifurcation Angle and Different Stent Configurations.}, journal = {Journal of translational internal medicine}, volume = {6}, number = {3}, pages = {138-145}, pmid = {30425950}, issn = {2450-131X}, abstract = {Objectives: To non-invasively evaluate by computational fluid dynamic (CFD) analysis the physiology and rheology of aortoiliac bifurcation disease at different angles and different stent configurations.

Material and methods: For the analysis, we considered a physiologic model of abdominal aorta with an iliac bifurcation set at 30°, 45° and 70° without stenosis. Subsequently, a bilateral ostial common iliac stenosis of 80% was considered for each type of bifurcation. For the stent simulation, we reconstructed Zilver vascular self-expanding (Zilver; Cook, Bloomington, MN) and Palmaz Genesis Peripheral (Cordis, Miami, FL) stents.

Results: The physiologic model, across the different angles, static pressure, Reynolds number and stream function, were lower for the 30° bifurcation angle with a gradient from 70° to 30° angles, whereas all the other parameters were inversely higher. After stenting, all the fluid parameters decreased homogenously independent of the stent type, maintaining a gradient in favour of 30° compared to 45° and 70° angles. The absolute greater deviation from physiology was observed for low kissing when self-expandable stents were used across all angles; in particular, the wall shear stress was high at at 45° angle.

Conclusion: Bifurcation angle deeply impacts the physiology of aortoiliac bifurcations, which are used to predict the fluid dynamic profile after stenting. CFD, having the potential to be derived both from computed tomography scan or invasive angiography, appears to be an ideal tool to predict fluid dynamic profile before and after stenting in aortoiliac bifurcation.}, } @article {pmid30424640, year = {2018}, author = {Sadri, M and Hejranfar, K and Ebrahimi, M}, title = {Prediction of fluid flow and acoustic field of a supersonic jet using vorticity confinement.}, journal = {The Journal of the Acoustical Society of America}, volume = {144}, number = {3}, pages = {1521}, doi = {10.1121/1.5055215}, pmid = {30424640}, issn = {1520-8524}, abstract = {In this study, the numerical simulation of the fluid flow and acoustic field of a supersonic jet is performed by using high-order discretization and the vorticity confinement (VC) method on coarse grids. The three-dimensional Navier-Stokes equations are considered in the generalized curvilinear coordinate system and the high-order compact finite-difference scheme is applied for the space discretization, and the time integration is performed by the fourth-order Runge-Kutta scheme. A low-pass high-order filter is applied to stabilize the numerical solution. The non-reflecting boundary conditions are adopted for all the free boundaries, and the Kirchhoff surface integration is utilized to obtain the far-field sound pressure levels in a number of observer locations. Comparisons of the jet mean flow and jet aeroacoustics results with the other numerical and experimental data at similar flow conditions are made and show a reasonable agreement. The study shows that the proposed solution methodology based on the high-order compact finite-difference scheme in conjunction with the VC method can reasonably predict the near-field flow and the far-field noise of high Reynolds number jets with a fairly coarser grid than that used in the large eddy simulations and, thus, the computational cost can be significantly decreased.}, } @article {pmid30424188, year = {2018}, author = {Jung, BJ and Kim, J and Kim, JA and Jang, H and Seo, S and Lee, W}, title = {PDMS-Parylene Hybrid, Flexible Microfluidics for Real-Time Modulation of 3D Helical Inertial Microfluidics.}, journal = {Micromachines}, volume = {9}, number = {6}, pages = {}, pmid = {30424188}, issn = {2072-666X}, support = {NRF-2015M2A2A4A02044826//National Research Foundation of Korea/ ; 10054488//Ministry of Trade, Industry & Energy (MOTIE, Korea)/ ; }, abstract = {Inertial microfluidics has drawn much attention for its applications for circulating tumor cell separations from blood. The fluid flows and the inertial particle focusing in inertial microfluidic systems are highly dependent on the channel geometry and structure. Flexible microfluidic systems can have adjustable 3D channel geometries by curving planar 2D channels into 3D structures, which will enable tunable inertial separation. We present a poly(dimethylsiloxane) (PDMS)-parylene hybrid thin-film microfluidic system that can provide high flexibility for 3D channel shaping while maintaining the channel cross-sectional shape. The PDMS-parylene hybrid microfluidic channels were fabricated by a molding and bonding technique using initiated chemical vapor deposition (iCVD) bonding. We constructed 3D helical inertial microfluidic channels by coiling a straight 2D channel and studied the inertial focusing while varying radius of curvature and Reynolds number. This thin film structure allows for high channel curvature and high Dean numbers which leads to faster inertial particle focusing and shorter channel lengths than 2D spiral channels. Most importantly, the focusing positions of particles and cells in the microchannel can be tuned in real time by simply modulating the channel curvature. The simple mechanical modulation of these 3D structure microfluidic systems is expected to provide unique advantages of convenient tuning of cell separation thresholds with a single device.}, } @article {pmid30424137, year = {2018}, author = {Ansari, MA and Kim, KY and Kim, SM}, title = {Numerical and Experimental Study on Mixing Performances of Simple and Vortex Micro T-Mixers.}, journal = {Micromachines}, volume = {9}, number = {5}, pages = {}, pmid = {30424137}, issn = {2072-666X}, support = {NRF- 2016R1A2B4006987//National Research Foundation of Korea/ ; //Inha University/ ; }, abstract = {Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the mixing performance was compared with a simple micro T-mixer. In the vortex micro T-mixer, the height of the inlet channels is half of the height of the main mixing channel. The inlet channel connects to the main mixing channel (micromixer) at the one end at an offset position in a fashion that creates vortex flow. In the simple micro T-mixer, the height of the inlet channels is equal to the height of the channel after connection (main mixing channel). Mixing of fluids and flow field have been analyzed for Reynolds numbers in a range from 1⁻80. The study has been further extended to planar serpentine microchannels, which were combined with a simple and a vortex T-junction, to evaluate and verify their mixing performances. The mixing performance of the vortex T-mixer is higher than the simple T-mixer and significantly increases with the Reynolds number. The design is promising for efficiently increasing mixing simply at the T-junction and can be applied to all micromixers.}, } @article {pmid30424044, year = {2018}, author = {Raza, W and Ma, SB and Kim, KY}, title = {Multi-Objective Optimizations of a Serpentine Micromixer with Crossing Channels at Low and High Reynolds Numbers.}, journal = {Micromachines}, volume = {9}, number = {3}, pages = {}, pmid = {30424044}, issn = {2072-666X}, abstract = {In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the micromixer were performed using three-dimensional Navier-Stokes equations and convection-diffusion equation. Three dimensionless design variables that were related to the geometry of the micromixer were selected as design variables for optimization. Mixing index at the exit and pressure drop through the micromixer were employed as two objective functions. A parametric study was carried out to explore the effects of the design variables on the objective functions. Latin hypercube sampling method as a design-of-experiment technique has been used to select design points in the design space. Surrogate modeling of the objective functions was performed by using radial basis neural network. Concave Pareto-optimal curves comprising of Pareto-optimal solutions that represents the trade-off between the objective functions were obtained using a multi-objective genetic algorithm at Re = 1 and 120. Through the optimizations, maximum enhancements of 18.8% and 6.0% in mixing index were achieved at Re = 1 and 120, respectively.}, } @article {pmid30411937, year = {2018}, author = {Galitski, V and Kargarian, M and Syzranov, S}, title = {Dynamo Effect and Turbulence in Hydrodynamic Weyl Metals.}, journal = {Physical review letters}, volume = {121}, number = {17}, pages = {176603}, doi = {10.1103/PhysRevLett.121.176603}, pmid = {30411937}, issn = {1079-7114}, abstract = {The dynamo effect is a class of macroscopic phenomena responsible for generating and maintaining magnetic fields in astrophysical bodies. It hinges on the hydrodynamic three-dimensional motion of conducting gases and plasmas that achieve high hydrodynamic and/or magnetic Reynolds numbers due to the large length scales involved. The existing laboratory experiments modeling dynamos are challenging and involve large apparatuses containing conducting fluids subject to fast helical flows. Here we propose that electronic solid-state materials-in particular, hydrodynamic metals-may serve as an alternative platform to observe some aspects of the dynamo effect. Motivated by recent experimental developments, this Letter focuses on hydrodynamic Weyl semimetals, where the dominant scattering mechanism is due to interactions. We derive Navier-Stokes equations along with equations of magnetohydrodynamics that describe the transport of a Weyl electron-hole plasma appropriate in this regime. We estimate the hydrodynamic and magnetic Reynolds numbers for this system. The latter is a key figure of merit of the dynamo mechanism. We show that it can be relatively large to enable observation of the dynamo-induced magnetic field bootstrap in an experiment. Finally, we generalize the simplest dynamo instability model-the Ponomarenko dynamo-to the case of a hydrodynamic Weyl semimetal and show that the chiral anomaly term reduces the threshold magnetic Reynolds number for the dynamo instability.}, } @article {pmid30400531, year = {2017}, author = {Guo, X and Qi, H}, title = {Analytical Solution of Electro-Osmotic Peristalsis of Fractional Jeffreys Fluid in a Micro-Channel.}, journal = {Micromachines}, volume = {8}, number = {12}, pages = {}, pmid = {30400531}, issn = {2072-666X}, support = {11402108//National Natural Science Foundation of China/ ; 11672163//National Natural Science Foundation of China/ ; 11571157//National Natural Science Foundation of China/ ; }, abstract = {The electro-osmotic peristaltic flow of a viscoelastic fluid through a cylindrical micro-channel is studied in this paper. The fractional Jeffreys constitutive model, including the relaxation time and retardation time, is utilized to describe the viscoelasticity of the fluid. Under the assumptions of long wavelength, low Reynolds number, and Debye-Hückel linearization, the analytical solutions of pressure gradient, stream function and axial velocity are explored in terms of Mittag-Leffler function by Laplace transform method. The corresponding solutions of fractional Maxwell fluid and generalized second grade fluid are also obtained as special cases. The numerical analysis of the results are depicted graphically, and the effects of electro-osmotic parameter, external electric field, fractional parameters and viscoelastic parameters on the peristaltic flow are discussed.}, } @article {pmid30397239, year = {2018}, author = {Nourazar, SS and Nazari-Golshan, A and Soleymanpour, F}, title = {On the expedient solution of the magneto-hydrodynamic Jeffery-Hamel flow of Casson fluid.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {16358}, doi = {10.1038/s41598-018-34778-w}, pmid = {30397239}, issn = {2045-2322}, abstract = {The equation of magneto-hydrodynamic Jeffery-Hamel flow of non-Newtonian Casson fluid in a stretching/shrinking convergent/divergent channel is derived and solved using a new modified Adomian decomposition method (ADM). So far in all problems where semi-analytical methods are used the boundary conditions are not satisfied completely. In the present research, a hybrid of the Fourier transform and the Adomian decomposition method (FTADM), is presented in order to incorporate all boundary conditions into our solution of magneto-hydrodynamic Jeffery-Hamel flow of non-Newtonian Casson fluid in a stretching/shrinking convergent/divergent channel flow. The effects of various emerging parameters such as channel angle, stretching/shrinking parameter, Casson fluid parameter, Reynolds number and Hartmann number on velocity profile are considered. The results using the FTADM are compared with the results of ADM and numerical Range-Kutta fourth-order method. The comparison reveals that, for the same number of components of the recursive sequences over a wide range of spatial domain, the relative errors associated with the new method, FTADM, are much less than the ADM. The results of the new method show that the method is an accurate and expedient approximate analytic method in solving the third-order nonlinear equation of Jeffery-Hamel flow of non-Newtonian Casson fluid.}, } @article {pmid30393471, year = {2018}, author = {Shahzad, K and Aeken, WV and Mottaghi, M and Kamyab, VK and Kuhn, S}, title = {Aggregation and clogging phenomena of rigid microparticles in microfluidics: Comparison of a discrete element method (DEM) and CFD-DEM coupling method.}, journal = {Microfluidics and nanofluidics}, volume = {22}, number = {9}, pages = {104}, pmid = {30393471}, issn = {1613-4982}, abstract = {We developed a numerical tool to investigate the phenomena of aggregation and clogging of rigid microparticles suspended in a Newtonian fluid transported through a straight microchannel. In a first step, we implement a time-dependent one-way coupling Discrete Element Method (DEM) technique to simulate the movement and effect of adhesion on rigid microparticles in two- and three-dimensional computational domains. The Johnson-Kendall-Roberts (JKR) theory of adhesion is applied to investigate the contact mechanics of particle-particle and particle-wall interactions. Using the one-way coupled solver, the agglomeration, aggregation and deposition behavior of the microparticles is studied by varying the Reynolds number and the particle adhesion. In a second step, we apply a two-way coupling CFD-DEM approach, which solves the equation of motion for each particle, and transfers the force field corresponding to particle-fluid interactions to the CFD toolbox OpenFOAM. Results for the one-way (DEM) and two-way (CFD-DEM) coupling techniques are compared in terms of aggregate size, aggregate percentages, spatial and temporal evaluation of aggregates in 2D and 3D. We conclude that two-way coupling is the more realistic approach, which can accurately capture the particle-fluid dynamics in microfluidic applications.}, } @article {pmid30393363, year = {2018}, author = {Ma, N and Duan, Z and Ma, H and Su, L and Liang, P and Ning, X and He, B and Zhang, X}, title = {Lattice Boltzmann Simulation of the Hydrodynamic Entrance Region of Rectangular Microchannels in the Slip Regime.}, journal = {Micromachines}, volume = {9}, number = {2}, pages = {}, pmid = {30393363}, issn = {2072-666X}, abstract = {Developing a three-dimensional laminar flow in the entrance region of rectangular microchannels has been investigated in this paper. When the hydrodynamic development length is the same magnitude as the microchannel length, entrance effects have to be taken into account, especially in relatively short ducts. Simultaneously, there are a variety of non-continuum or rarefaction effects, such as velocity slip and temperature jump. The available data in the literature appearing on this issue is quite limited, the available study is the semi-theoretical approximate model to predict pressure drop of developing slip flow in rectangular microchannels with different aspect ratios. In this paper, we apply the lattice Boltzmann equation method (LBE) to investigate the developing slip flow through a rectangular microchannel. The effects of the Reynolds number (1 < Re < 1000), channel aspect ratio (0 < ε < 1), and Knudsen number (0.001 < Kn < 0.1) on the dimensionless hydrodynamic entrance length, and the apparent friction factor, and Reynolds number product, are examined in detail. The numerical solution of LBM can recover excellent agreement with the available data in the literature, which proves its accuracy in capturing fundamental fluid characteristics in the slip-flow regime.}, } @article {pmid30393335, year = {2018}, author = {Afzal, MJ and Ashraf, MW and Tayyaba, S and Hossain, MK and Afzulpurkar, N}, title = {Sinusoidal Microchannel with Descending Curves for Varicose Veins Implantation.}, journal = {Micromachines}, volume = {9}, number = {2}, pages = {}, pmid = {30393335}, issn = {2072-666X}, abstract = {Approximately 26% of adult people, mostly females, are affected by varicose veins in old age. It is a common reason for distress, loss of efficiency, and worsening living conditions. Several traditional treatment techniques (sclerotherapy and foam sclerotherapy of large veins, laser surgeries and radiofrequency ablation, vein ligation and stripping, ambulatory phlebectomy, and endoscopic vein surgery) have failed to handle this disease effectively. Herein, authors have presented an alternative varicose vein implant method-the descending sinusoidal microchannel (DSMC). DSMC was simulated by Fuzzy logic MATLAB (The MathWorks, Natick, MA, USA) and ANSYS (ANSYS 18.2, perpetual license purchased by Ibadat Education Trust, The University of Lahore, Pakistan) with real and actual conditions. After simulations of DSMC, fabrication and testing were performed. The silver DSMC was manufactured by utilizing a micromachining procedure. The length, width, and depth of the silver substrate were 51 mm, 25 mm, and 1.1 mm, respectively. The measurements of the DSMC channel in the silver wafer substrate were 0.9 mm in width and 0.9 mm in depth. The three descending curves of the DSMC were 7 mm, 6 mm, and 5 mm in height. For pressure, actual conditions were carefully taken as 1.0 kPa to 1.5 kPa for varicose veins. For velocity, actual conditions were carefully taken as 0.02 m/s to 0.07 m/s for these veins. These are real and standard values used in simulations and experiments. At Reynolds number 323, the flow rate and velocity were determined as 1001.0 (0.1 nL/s), 11.4 cm/s and 1015.3 (0.1 nL/s), 12.19 cm/s by MATLAB (The MathWorks, Natick, MA, USA) and ANSYS simulations, respectively. The flow rate and velocity were determined to be 995.3 (0.1 nL/s) and 12.2 cm/s, respectively, at the same Reynolds number (323) in the experiment. Moreover, the Dean number was also calculated to observe Dean vortices. All simulated and experimental results were in close agreement. Consequently, DSMC can be implanted in varicose veins as a new treatment to preserve excellent blood flow in human legs from the original place to avoid tissue damage and other problems.}, } @article {pmid30389406, year = {2019}, author = {Amiri Delouei, A and Sajjadi, H and Mohebbi, R and Izadi, M}, title = {Experimental study on inlet turbulent flow under ultrasonic vibration: Pressure drop and heat transfer enhancement.}, journal = {Ultrasonics sonochemistry}, volume = {51}, number = {}, pages = {151-159}, doi = {10.1016/j.ultsonch.2018.10.032}, pmid = {30389406}, issn = {1873-2828}, abstract = {This experimental study examines the impact of ultrasonic vibration on pressure drop and heat transfer enhancement of inlet turbulent flows. A stainless steel tube connected to an ultrasonic transducer and immersed in a constant temperature two-phase fluid was considered as the test section. Regarding the designed configuration, the ultrasonic transducer utilized had an acoustic frequency of 28 kHz and two different power levels of 75 W and 100 W. The experiments were conducted for different ultrasonic power levels, inlet temperatures, and flow rates. The accuracy of measurements was successfully validated via the existing empirical correlations. The results indicate that the effect of ultrasonic vibration on pressure drop and heat transfer enhancement diminishes with the growth of both Reynolds number and inlet temperature. Based on previously reported results on inlet flows with a laminar flow regime, the effect of ultrasonic vibration is very trivial in current turbulent inlet flows (up to 7.28% for heat convection enhancement). The results of the present study will be beneficial for future investigations on designing vibrating heat exchangers.}, } @article {pmid30387646, year = {2018}, author = {Falkovich, G and Vladimirova, N}, title = {Turbulence Appearance and Nonappearance in Thin Fluid Layers.}, journal = {Physical review letters}, volume = {121}, number = {16}, pages = {164501}, doi = {10.1103/PhysRevLett.121.164501}, pmid = {30387646}, issn = {1079-7114}, abstract = {Flows in fluid layers are ubiquitous in industry, geophysics, and astrophysics. Large-scale flows in thin layers can be considered two dimensional with bottom friction added. Here we find that the properties of such flows depend dramatically on the way they are driven. We argue that a wall-driven (Couette) flow cannot sustain turbulence, no matter how small the viscosity and friction. Direct numerical simulations (DNSs) up to the Reynolds number Re=10^{6} confirm that all perturbations die in a plane Couette flow. On the contrary, for sufficiently small viscosity and friction, perturbations destroy the pressure-driven laminar (Poiseuille) flow. What appears instead is a traveling wave in the form of a jet slithering between wall vortices. For 5×10^{3}

METHODS: For steady flow the analytical approach has been taken to obtain the exact solution. Regular perturbation expansion method has been used to solve the governing equations for pulsatile flow up to first order of approximation by assuming the pulsatile Reynolds number to be very small (much less than unity).

RESULTS: Flow rate, wall shear stress and velocity profile have been graphically analyzed and compared with constant viscosity model. A noteworthy observation of the present study is that rise in viscosity index leads to decay in velocity, velocity of plug flow region, flow rate while flow resistance increases with rising viscosity index (m). The results for Power-law fluid (PL), Bingham-plastic fluid (BP), Newtonian fluid (NF) are found as special cases from this model. Like the constant viscosity model, it has been also observed that the velocity, flow rate and plug core velocity of two-fluid model are higher than the single-fluid model for variable viscosity.

CONCLUSIONS: The two-phase fluid model is more significant than the single-fluid model. Effect of viscosity parameter on various hemodynamical quantities has been obtained. It is also concluded that a rising viscosity parameter (varying nature of viscosity) significantly distinguishes the single and two-fluid models in terms of changes in blood flow resistance. The outcome of present study may leave a significant impact on analyzing blood flow through small blood vessels with constriction, where correct measurement of flow rate and flow resistance for medical treatment is very important.}, } @article {pmid30297857, year = {2018}, author = {Karathanassis, IK and Trickett, K and Koukouvinis, P and Wang, J and Barbour, R and Gavaises, M}, title = {Illustrating the effect of viscoelastic additives on cavitation and turbulence with X-ray imaging.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {14968}, pmid = {30297857}, issn = {2045-2322}, abstract = {The effect of viscoelastic additives on the topology and dynamics of the two-phase flow arising within an axisymmetric orifice with a flow path constriction along its main axis has been investigated employing high-flux synchrotron radiation. X-ray Phase Contrast Imaging (XPCI) has been conducted to visualise the cavitating flow of different types of diesel fuel within the orifice. An additised blend containing Quaternary Ammonium Salt (QAS) additives with a concentration of 500 ppm has been comparatively examined against a pure (base) diesel compound. A high-flux, 12 keV X-ray beam has been utilised to obtain time resolved radiographs depicting the vapour extent within the orifice from two views (side and top) with reference to its main axis. Different test cases have been examined for both fuel types and for a range of flow conditions characterised by Reynolds number of 35500 and cavitation numbers (CN) lying in the range 3.0-7.7. It has been established that the behaviour of viscoelastic micelles in the regions of shear flow is not consistent depending on the cavitation regimes encountered. Namely, viscoelastic effects enhance vortical (string) cavitation, whereas hinder cloud cavitation. Furthermore, the use of additised fuel has been demonstrated to suppress the level of turbulence within the orifice.}, } @article {pmid30280982, year = {2020}, author = {de Matos, DB and Barbosa, MPR and Leite, OM and Steter, JR and Lima, NS and Torres, NH and Marques, MN and de Alsina, OLS and Cavalcanti, EB}, title = {Characterization of a tubular electrochemical reactor for the degradation of the commercial diuron herbicide.}, journal = {Environmental technology}, volume = {41}, number = {10}, pages = {1307-1321}, doi = {10.1080/09593330.2018.1531941}, pmid = {30280982}, issn = {1479-487X}, mesh = {Diuron ; Electrodes ; *Herbicides ; Hydrogen Peroxide ; Oxidation-Reduction ; *Water Pollutants, Chemical ; }, abstract = {After designing and constructing an electrochemical reactor with concentric electrodes and tangential feed (RECT), it is necessary to characterize it and to study its performance. The experimental study of the residence time distribution (RTD) was conducted for flow rates of 2.78 × 10-6 m3 s-1, 8.33 × 10-6 m3 s-1 and 13.9 × 10-6 m3 s-1. According to the values obtained from the Pe number (0.67-1.52), the RECT fits as tubular with great dispersion. The determined empirical correlation (Sh = 18.16 Re0.50 Sc0.33) showed a laminar flow behavior in the range of Reynolds number (Re) between 23 and 117. In order to use RECT in effluent treatment, an electrochemical oxidation study of the Diuron model molecule (Nortox®) was performed to analyze reactor performance in a closed system with total reflux. A decay kinetics of pseudo-first order was associated with the decay of the concentration of diuron and 30% mineralization in 180 min of process were obtained, having a total volume of 4 × 10-3 m3 and an initial concentration of commercial Diuron in 215.83 mg dm-3. Eleven by-products were identified by HPLC-MS analysis and, from this, it was possible to propose a route of degradation of the diuron. From these observations, it can be inferred that the studied electrochemical reactor had applicability in the degradation of recalcitrant compounds, as is the case of commercial diuron. Make some changes in the electrochemical reactor studied and other advanced oxidative processes, such as electro-Fenton, can be associated with the studied system to achieve a better conversion efficiency.}, } @article {pmid30242545, year = {2018}, author = {Waldrop, LD and He, Y and Khatri, S}, title = {What Can Computational Modeling Tell Us about the Diversity of Odor-Capture Structures in the Pancrustacea?.}, journal = {Journal of chemical ecology}, volume = {44}, number = {12}, pages = {1084-1100}, pmid = {30242545}, issn = {1573-1561}, support = {1505061//Division of Physics/ ; TG-CDA160015//Extreme Science and Engineering Discovery Environment/ ; TG-BIO170090//Extreme Science and Engineering Discovery Environment/ ; }, mesh = {Air ; Animals ; Arthropod Antennae/metabolism ; Biological Evolution ; *Models, Theoretical ; *Odorants/analysis ; Water/chemistry ; }, abstract = {A major transition in the history of the Pancrustacea was the invasion of several lineages of these animals onto land. We investigated the functional performance of odor-capture organs, antennae with olfactory sensilla arrays, through the use of a computational model of advection and diffusion of odorants to olfactory sensilla while varying three parameters thought to be important to odor capture (Reynolds number, gap-width-to-sensillum-diameter ratio, and angle of the sensilla array with respect to oncoming flow). We also performed a sensitivity analysis on these parameters using uncertainty quantification to analyze their relative contributions to odor-capture performance. The results of this analysis indicate that odor capture in water and in air are fundamentally different. Odor capture in water and leakiness of the array are highly sensitive to Reynolds number and moderately sensitive to angle, whereas odor capture in air is highly sensitive to gap widths between sensilla and moderately sensitive to angle. Leakiness is not a good predictor of odor capture in air, likely due to the relative importance of diffusion to odor transport in air compared to water. We also used the sensitivity analysis to make predictions about morphological and kinematic diversity in extant groups of aquatic and terrestrial crustaceans. Aquatic crustaceans will likely exhibit denser arrays and induce flow within the arrays, whereas terrestrial crustaceans will rely on more sparse arrays with wider gaps and little-to-no animal-induced currents.}, } @article {pmid30212772, year = {2018}, author = {Fu, Q and Chen, H and Liao, Q and Huang, Y and Xia, A and Zhu, X and Xiao, C and Reungsang, A and Liu, Z}, title = {Drag reduction and shear-induced cells migration behavior of microalgae slurry in tube flow.}, journal = {Bioresource technology}, volume = {270}, number = {}, pages = {38-45}, doi = {10.1016/j.biortech.2018.08.133}, pmid = {30212772}, issn = {1873-2976}, mesh = {*Chlorella ; Physical Phenomena ; }, abstract = {To optimize the designing of microalgae slurry pumping system and enhance the efficiency of microalgae products production, the flow characteristics of microalgae slurries (Chlorella pyrenoidosa) in tube flow were for the first time investigated combining experiments and numerical simulation. The drag reduction behavior of microalgae slurry in the fully developed laminar flow regime was studied. In addition, the transition Reynolds number of microalgae slurries from laminar flow to turbulent flow was about 1000-1300, which was similar to the expression of two-phase flow. To provide a further understanding of flow feature of microalgae slurries in tube, a two-phase mixture model was proposed by considering the heterogeneity of concentration due to the shear-induced microalgae cells migration behavior. Simulation results revealed that the heterogeneous distribution of concentration was affected by average velocity and volume fraction of microalgae slurries, significantly affecting the flow resistance and flow stability of microalgae slurry in the tube flow.}, } @article {pmid30211982, year = {2019}, author = {Bergersen, AW and Mortensen, M and Valen-Sendstad, K}, title = {The FDA nozzle benchmark: "In theory there is no difference between theory and practice, but in practice there is".}, journal = {International journal for numerical methods in biomedical engineering}, volume = {35}, number = {1}, pages = {e3150}, doi = {10.1002/cnm.3150}, pmid = {30211982}, issn = {2040-7947}, mesh = {*Benchmarking ; Computer Simulation ; *Hydrodynamics ; United States ; United States Food and Drug Administration ; }, abstract = {The utility of flow simulations relies on the robustness of computational fluid dynamics (CFD) solvers and reproducibility of results. The aim of this study was to validate the Oasis CFD solver against in vitro experimental measurements of jet breakdown location from the FDA nozzle benchmark at Reynolds number 3500, which is in the particularly challenging transitional regime. Simulations were performed on meshes consisting of 5, 10, 17, and 28 million (M) tetrahedra, with Δt = 10-5 seconds. The 5M and 10M simulation jets broke down in reasonable agreement with the experiments. However, the 17M and 28M simulation jets broke down further downstream. But which of our simulations are "correct"? From a theoretical point of view, they are all wrong because the jet should not break down in the absence of disturbances. The geometry is axisymmetric with no geometrical features that can generate angular velocities. A stable flow was supported by linear stability analysis. From a physical point of view, a finite amount of "noise" will always be present in experiments, which lowers transition point. To replicate noise numerically, we prescribed minor random angular velocities (approximately 0.31%), much smaller than the reported flow asymmetry (approximately 3%) and model accuracy (approximately 1%), at the inlet of the 17M simulation, which shifted the jet breakdown location closer to the measurements. Hence, the high-resolution simulations and "noise" experiment can potentially explain discrepancies in transition between sometimes "sterile" CFD and inherently noisy "ground truth" experiments. Thus, we have shown that numerical simulations can agree with experiments, but for the wrong reasons.}, } @article {pmid30200611, year = {2018}, author = {Wan, G and Jin, C and Trase, I and Zhao, S and Chen, Z}, title = {Helical Structures Mimicking Chiral Seedpod Opening and Tendril Coiling.}, journal = {Sensors (Basel, Switzerland)}, volume = {18}, number = {9}, pages = {}, pmid = {30200611}, issn = {1424-8220}, support = {Dartmouth College//Startup fund from Thayer School of Engineering at Dartmouth College/ ; Branco Weiss-Society in Science fellowship//Branco Weiss-Society in Science fellowship (administered by ETH Zürich)/ ; }, mesh = {Biomimetic Materials/*chemistry ; *Biomimetics ; Elastomers/chemistry ; Hydrogels/chemistry ; Liquid Crystals/chemistry ; *Plant Physiological Phenomena ; Plants/*anatomy & histology ; Polymers/chemistry ; }, abstract = {Helical structures are ubiquitous in natural and engineered systems across multiple length scales. Examples include DNA molecules, plants' tendrils, sea snails' shells, and spiral nanoribbons. Although this symmetry-breaking shape has shown excellent performance in elastic springs or propulsion generation in a low-Reynolds-number environment, a general principle to produce a helical structure with programmable geometry regardless of length scales is still in demand. In recent years, inspired by the chiral opening of Bauhinia variegata's seedpod and the coiling of plant's tendril, researchers have made significant breakthroughs in synthesizing state-of-the-art 3D helical structures through creating intrinsic curvatures in 2D rod-like or ribbon-like precursors. The intrinsic curvature results from the differential response to a variety of external stimuli of functional materials, such as hydrogels, liquid crystal elastomers, and shape memory polymers. In this review, we give a brief overview of the shape transformation mechanisms of these two plant's structures and then review recent progress in the fabrication of biomimetic helical structures that are categorized by the stimuli-responsive materials involved. By providing this survey on important recent advances along with our perspectives, we hope to solicit new inspirations and insights on the development and fabrication of helical structures, as well as the future development of interdisciplinary research at the interface of physics, engineering, and biology.}, } @article {pmid30194679, year = {2018}, author = {Daddi-Moussa-Ider, A and Löwen, H and Gekle, S}, title = {Creeping motion of a solid particle inside a spherical elastic cavity⋆.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {9}, pages = {104}, pmid = {30194679}, issn = {1292-895X}, abstract = {On the basis of the linear hydrodynamic equations, we present an analytical theory for the low-Reynolds-number motion of a solid particle moving inside a larger spherical elastic cavity which can be seen as a model system for a fluid vesicle. In the particular situation where the particle is concentric with the cavity, we use the stream function technique to find exact analytical solutions of the fluid motion equations on both sides of the elastic cavity. In this particular situation, we find that the solution of the hydrodynamic equations is solely determined by membrane shear properties and that bending does not play a role. For an arbitrary position of the solid particle within the spherical cavity, we employ the image solution technique to compute the axisymmetric flow field induced by a point force (Stokeslet). We then obtain analytical expressions of the leading-order mobility function describing the fluid-mediated hydrodynamic interactions between the particle and the confining elastic cavity. In the quasi-steady limit of vanishing frequency, we find that the particle self-mobility function is higher than that predicted inside a rigid no-slip cavity. Considering the cavity motion, we find that the pair-mobility function is determined only by membrane shear properties. Our analytical predictions are supplemented and validated by fully resolved boundary integral simulations where a very good agreement is obtained over the whole range of applied forcing frequencies.}, } @article {pmid30140921, year = {2018}, author = {Molony, D and Park, J and Zhou, L and Fleischer, C and Sun, HY and Hu, X and Oshinski, J and Samady, H and Giddens, DP and Rezvan, A}, title = {Bulk Flow and Near Wall Hemodynamics of the Rabbit Aortic Arch: A 4D PC-MRI Derived CFD Study.}, journal = {Journal of biomechanical engineering}, volume = {}, number = {}, pages = {}, pmid = {30140921}, issn = {1528-8951}, support = {HHSN268201000043C/HL/NHLBI NIH HHS/United States ; }, abstract = {Animal models offer a flexible experimental environment for studying atherosclerosis. The mouse is the most commonly used animal, however, the underlying hemodynamics in larger animals such as the rabbit are far closer to that of humans. The aortic arch is a vessel with complex helical flow and highly heterogeneous shear stress patterns which may influence where atherosclerotic lesions form. A better understanding of intra-species flow variation and the impact of geometry on flow may improve our understanding of where disease forms. In this work we use Magnetic Resonance Angiography (MRA) and 4D Phase contrast magnetic resonance imaging (PC-MRI) to image and measure blood velocity in the rabbit aortic arch. Measured flow rates from the PC-MRI were used as boundary conditions in computational fluid dynamics models of the arches. Helical flow, cross flow index (CFI) and time-averaged wall shear stress (TAWSS) were determined from the simulated flow field. Both traditional geometric metrics and shape modes derived from statistical shape analysis were analyzed with respect to flow helicity. High CFI and low TAWSS were found to co-localize in the ascending aorta and to a lesser extent on the inner curvature of the aortic arch. The Reynolds number was linearly associated with an increase in helical flow intensity (R=0.85, p<.05). Both traditional and statistical shape analysis correlated with increased helical flow symmetry. However, a stronger correlation was obtained from the statistical shape analysis demonstrating its potential for discerning the role of shape in hemodynamic studies.}, } @article {pmid30136131, year = {2018}, author = {Krastev, VK and Amati, G and Succi, S and Falcucci, G}, title = {On the effects of surface corrugation on the hydrodynamic performance of cylindrical rigid structures.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {8}, pages = {95}, pmid = {30136131}, issn = {1292-895X}, mesh = {Computer Simulation ; *Hydrodynamics ; Kinetics ; Surface Properties ; }, abstract = {In this work, we perform fully three-dimensional numerical simulations of the flow field surrounding cylindrical structures characterized by different types of corrugated surface. The simulations are carried out using the Lattice Boltzmann Method (LBM), considering a flow regime with a Reynolds number [Formula: see text]. The fluid-dynamic wake structure and stability are investigated by means of PSD analyses of the velocity components and by visual inspection of the vortical coherent structure evolution. Moreover, the energy dissipation of the flow is assessed by considering an equivalent discharge coefficient [Formula: see text], which measures the total pressure losses of the flow moving around the various layout under investigation. Outcomes from our study demonstrate that the helical ridges augment energy dissipation, but might also have a role in the passive control of the characteristic frequencies of the unsteady wake flow.}, } @article {pmid30132443, year = {2018}, author = {Lee, YJ and Lua, KB}, title = {Wing-wake interaction: comparison of 2D and 3D flapping wings in hover flight.}, journal = {Bioinspiration & biomimetics}, volume = {13}, number = {6}, pages = {066003}, doi = {10.1088/1748-3190/aadc31}, pmid = {30132443}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Biomimetics/methods ; Flight, Animal/*physiology ; Models, Biological ; Wings, Animal/*physiology ; }, abstract = {The wing-wake interaction of flapping wings while hovering has been investigated, with the focus on the difference in wing-wake interaction between 2D and 3D flapping wings. Numerical simulations are conducted at a Reynolds number of 100, and the flapping configurations are divided into the 2D, quasi-3D and 3D categories. Variations of the aspect ratio and Rossby number allow the flapping configuration to morph gradually between categories. The wing-wake interaction mechanisms are identified and the effect of three-dimensionality on these mechanisms is discussed. Three-dimensionality affects wing-wake interaction through four primary aerodynamic mechanisms, namely, induced jet, downwash/upwash, leading-edge vortex (LEV) shedding due to vortex pairing, and the formation of a closely attached LEV. The first two mechanisms are well-established in the literature. With regard to the LEV shedding mechanism, it is revealed that the interaction between the LEV and the residue vortex from the previous stroke plays an important role in the early vortex shedding of 2D flapping wings. This effect diminishes with increasing three-dimensionality. With regard to the mechanism of the closely attached LEV, the wake encourages the formation of an LEV that is closely attached to the wing's top surface, which is beneficial to lift generation. This closely attached LEV mechanism accounts for most of the lift enhancement that arises from wake effects. Three-dimensionality alters the efficacy of the different aerodynamic mechanisms. Consequently, the dual peak lift coefficient pattern typically seen on 2D flapping wings transforms into the single peak lift coefficient pattern of the 3D flapping wing. It is also demonstrated that the mean lift enhancement due to wing-wake interaction diminishes rapidly when three-dimensionality is introduced. Results suggest that, for wings with parameters close to those of natural flyers, wing-wake interaction yields marginal lift enhancement and a small increase in energy consumption.}, } @article {pmid30132198, year = {2018}, author = {Espeso, DR and Martínez-García, E and Carpio, A and de Lorenzo, V}, title = {Dynamics of Pseudomonas putida biofilms in an upscale experimental framework.}, journal = {Journal of industrial microbiology & biotechnology}, volume = {45}, number = {10}, pages = {899-911}, pmid = {30132198}, issn = {1476-5535}, support = {ERC-2012-ADG-322797//European Research Council/International ; EU-H2020-BIOTEC-2014-2015-6335536//Horizon 2020 Framework Programme/ ; H2020-FET-OPEN-RIA-2017-1-766975//Horizon 2020 Framework Programme/ ; }, mesh = {Algorithms ; Biofilms/*growth & development ; Culture Media ; Equipment Design ; Hydrodynamics ; Image Processing, Computer-Assisted ; Industrial Microbiology/methods ; Polycarboxylate Cement/chemistry ; Pseudomonas putida/*growth & development ; Software ; }, abstract = {Exploitation of biofilms for industrial processes requires them to adopt suitable physical structures for rendering them efficient and predictable. While hydrodynamics could be used to control material features of biofilms of the platform strain Pseudomonas putida KT2440 there is a dearth of experimental data on surface-associated growth behavior in such settings. Millimeter scale biofilm patterns formed by its parental strain P. putida mt-2 under different Reynolds numbers (Re) within laminar regime were analyzed using an upscale experimental continuous cultivation assembly. A tile-scan image acquisition process combined with a customized image analysis revealed patterns of dense heterogeneous structures at Re = 1000, but mostly flattened coverings sparsely patched for Re < 400. These results not only fix the somewhat narrow hydrodynamic regime under which P. putida cells form stable coatings on surfaces destined for large-scale processes, but also provide useful sets of parameters for engineering catalytic biofilms based on this important bacterium as a cell factory.}, } @article {pmid30123895, year = {2018}, author = {Lee, J and Estlack, Z and Somaweera, H and Wang, X and Lacerda, CMR and Kim, J}, title = {A microfluidic cardiac flow profile generator for studying the effect of shear stress on valvular endothelial cells.}, journal = {Lab on a chip}, volume = {18}, number = {19}, pages = {2946-2954}, doi = {10.1039/c8lc00545a}, pmid = {30123895}, issn = {1473-0189}, mesh = {Aortic Valve/*cytology/physiology ; Endothelial Cells/*metabolism ; Equipment Design ; *Lab-On-A-Chip Devices ; *Shear Strength ; *Stress, Mechanical ; }, abstract = {To precisely investigate the mechanobiological responses of valvular endothelial cells, we developed a microfluidic flow profile generator using a pneumatically-actuated micropump consisting of microvalves of various sizes. By controlling the closing pressures and the actuation times of these microvalves, we modulated the magnitude and frequency of the shear stress to mimic mitral and aortic inflow profiles with frequencies in the range of 0.8-2 Hz and shear stresses up to 20 dyn cm-2. To demonstrate this flow profile generator, aortic inflow with an average of 5.9 dyn cm-2 shear stress at a frequency of 1.2 Hz with a Reynolds number of 2.75, a Womersley number of 0.27, and an oscillatory shear index (OSI) value of 0.2 was applied to porcine aortic valvular endothelial cells (PAVECs) for mechanobiological studies. The cell alignment, cell elongation, and alpha-smooth muscle actin (αSMA) expression of PAVECs under perfusion, steady flow, and aortic inflow conditions were analyzed to determine their shear-induced cell migration and trans-differentiation. In this morphological and immunocytochemical study, we found that the PAVECs elongated and aligned themselves perpendicular to the directions of the steady flow and the aortic inflow. In contrast, under perfusion with a fluidic shear stress of 0.47 dyn cm-2, the PAVECs elongated and aligned themselves parallel to the direction of flow. The PAVECs exposed to the aortic inflow upregulated their αSMA-protein expression to a greater degree than those exposed to perfusion and steady flow. By comparing these results to those of previous studies of pulsatile flow, we also found that the ratio of positive to negative shear stress plays an important role in determining PAVECs' trans-differentiation and adaptation to flow. This microfluidic cardiac flow profile generator will enable future valvular mechanobiological studies to determine the roles of magnitude and frequency of shear stresses.}, } @article {pmid30119494, year = {2018}, author = {Gao, J and Katz, J}, title = {Self-calibrated microscopic dual-view tomographic holography for 3D flow measurements.}, journal = {Optics express}, volume = {26}, number = {13}, pages = {16708-16725}, doi = {10.1364/OE.26.016708}, pmid = {30119494}, issn = {1094-4087}, abstract = {This paper introduces the application of microscopic dual-view tomographic holography (M-DTH) to measure the 3D position and motion of micro-particles located in dense suspensions. Pairing of elongated traces of the same particle in the two inclined reconstructed fields requires precise matching of the entire sample volume that accounts for the inherent distortions in each view. It is achieved by an iterative volumetric self-calibration method, consisting of mapping one view onto the next, dividing the sample volume into slabs, and cross-correlating the two views. Testing of the procedures using synthetic particle fields with imposed distortion and realistic errors in particle locations shows that the self-calibration method achieves a 3D uncertainty of about 1µm, a third of the particle diameter. Multiplying the corrected intensity fields is used for truncating the elongated traces, whose centers are located within 1µm of the exact value. Without correction, only a small fraction of the traces even overlap. The distortion correction also increases the number of intersecting traces in experimental data along with their intensity. Application of this method for 3D velocity measurements is based on the centroids of the truncated/shortened particle traces. Matching of these traces in successive fields is guided by several criteria, including results of volumetric cross-correlation of the multiplied intensity fields. The resulting 3D velocity distribution is substantially more divergence-free, i.e., satisfies conservation of mass, compared to analysis performed using single-view data. Sample application of the new method shows the 3D flow structure around a pair of cubic roughness elements embedded in the inner part of a high Reynolds number turbulent boundary layer.}, } @article {pmid30118276, year = {2018}, author = {Mathai, V and Huisman, SG and Sun, C and Lohse, D and Bourgoin, M}, title = {Dispersion of Air Bubbles in Isotropic Turbulence.}, journal = {Physical review letters}, volume = {121}, number = {5}, pages = {054501}, doi = {10.1103/PhysRevLett.121.054501}, pmid = {30118276}, issn = {1079-7114}, abstract = {Bubbles play an important role in the transport of chemicals and nutrients in many natural and industrial flows. Their dispersion is crucial to understanding the mixing processes in these flows. Here we report on the dispersion of millimetric air bubbles in a homogeneous and isotropic turbulent flow with a Taylor Reynolds number from 110 to 310. We find that the mean squared displacement (MSD) of the bubbles far exceeds that of fluid tracers in turbulence. The MSD shows two regimes. At short times, it grows ballistically (∝τ^{2}), while at larger times, it approaches the diffusive regime where the MSD∝τ. Strikingly, for the bubbles, the ballistic-to-diffusive transition occurs one decade earlier than for the fluid. We reveal that both the enhanced dispersion and the early transition to the diffusive regime can be traced back to the unsteady wake-induced motion of the bubbles. Further, the diffusion transition for bubbles is not set by the integral timescale of the turbulence (as it is for fluid tracers and microbubbles), but instead, by a timescale of eddy crossing of the rising bubbles. The present findings provide a Lagrangian perspective towards understanding mixing in turbulent bubbly flows.}, } @article {pmid30118271, year = {2018}, author = {Oettinger, D and Ault, JT and Stone, HA and Haller, G}, title = {Invisible Anchors Trap Particles in Branching Junctions.}, journal = {Physical review letters}, volume = {121}, number = {5}, pages = {054502}, doi = {10.1103/PhysRevLett.121.054502}, pmid = {30118271}, issn = {1079-7114}, abstract = {We combine numerical simulations and an analytic approach to show that the capture of finite, inertial particles during flow in branching junctions is due to invisible, anchor-shaped three-dimensional flow structures. These Reynolds-number-dependent anchors define trapping regions that confine particles to the junction. For a wide range of Stokes numbers, these structures occupy a large part of the flow domain. For flow in a V-shaped junction, at a critical Stokes number, we observe a topological transition due to the merger of two anchors into one. From a stability analysis, we identify the parameter region of particle sizes and densities where capture due to anchors occurs.}, } @article {pmid30117966, year = {2018}, author = {Karaminejad, S and Askari, MH and Ashjaee, M}, title = {Temperature field investigation of hydrogen/air and syngas/air axisymmetric laminar flames using Mach-Zehnder interferometry.}, journal = {Applied optics}, volume = {57}, number = {18}, pages = {5057-5067}, doi = {10.1364/AO.57.005057}, pmid = {30117966}, issn = {1539-4522}, abstract = {In this study, the optical method of Mach-Zehnder interferometry (MZI) is utilized in order to explore the flame structure and temperature field of syngas/air and hydrogen/air flames. Two axisymmetric burners with inner diameters of 4 mm and 6 mm are used for temperature field measurement of hydrogen and syngas, respectively. The effects of fuel composition, equivalence ratio, and Reynolds number (Re) are investigated at ambient condition (P=0.87 bar, T=300 K). Three different H2/CO fuel compositions with hydrogen fractions of 30%, 50%, and 100% are studied. Temperature profiles are reported at four different sections above the burner tip. Measured temperatures using the interferometry method are compared with thermocouple data and good agreement between them is observed. The results obtained in this investigation indicated that the MZI can be applied for accurate determination of flame front and temperature field, especially for high-temperature flames where other methods cannot be properly utilized. Analyses of the data reduction method revealed that the exact determination of the refractive index distribution and reference temperature is critical for accurate determination of the temperature field. The results indicated that by increasing the Re, the maximum flame temperature is enhanced. Increasing the equivalence ratio leads to expansion of the flame radial distribution (at the same distance from the burner tip). At higher distances from the burner tip, temperature increases uniformly from the flame boundary toward the flame axis, while at lower heights it shows reduction at the burner axis. By increasing the CO content of fuel, the maximum flame temperature increases at all equivalence ratios except at the stoichiometric condition, where SH100 illustrates the highest maximum flame temperature.}, } @article {pmid30109056, year = {2018}, author = {Bhat, SS and Zhao, J and Sheridan, J and Hourigan, K and Thompson, MC}, title = {The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size.}, journal = {Royal Society open science}, volume = {5}, number = {7}, pages = {172197}, pmid = {30109056}, issn = {2054-5703}, abstract = {Stable attachment of a leading-edge vortex (LEV) plays a key role in generating the high lift on rotating wings with a central body. The central body size can affect the LEV structure broadly in two ways. First, an overall change in the size changes the Reynolds number, which is known to have an influence on the LEV structure. Second, it may affect the Coriolis acceleration acting across the wing, depending on the wing-offset from the axis of rotation. To investigate this, the effects of Reynolds number and the wing-offset are independently studied for a rotating wing. The three-dimensional LEV structure is mapped using a scanning particle image velocimetry technique. The rapid acquisition of images and their correlation are carefully validated. The results presented in this paper show that the LEV structure changes mainly with the Reynolds number. The LEV-split is found to be only minimally affected by changing the central body radius in the range of small offsets, which interestingly includes the range for most insects. However, beyond this small offset range, the LEV-split is found to change dramatically.}, } @article {pmid30089029, year = {2018}, author = {Gilmer, GG and Deshpande, VG and Chou, CL and Knepper, M}, title = {Flow resistance along the rat renal tubule.}, journal = {American journal of physiology. Renal physiology}, volume = {315}, number = {5}, pages = {F1398-F1405}, pmid = {30089029}, issn = {1522-1466}, support = {ZIA HL001285/HL/NHLBI NIH HHS/United States ; ZIA HL006129/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; *Diuresis ; *Glomerular Filtration Rate ; Hydrostatic Pressure ; Kidney Tubules/anatomy & histology/*physiology ; *Models, Biological ; Rats ; Time Factors ; *Urodynamics ; Viscosity ; }, abstract = {The Reynolds number in the renal tubule is extremely low, consistent with laminar flow. Consequently, luminal flow can be described by the Hagen-Poiseuille laminar flow equation. This equation calculates the volumetric flow rate from the axial pressure gradient and flow resistance, which is dependent on the length and diameter of each renal tubule segment. Our goal was to calculate the pressure drop along each segment of the renal tubule and to determine the points of highest resistance. When the Hagen-Poiseuille equation was used for rat superficial nephrons based on known tubule flow rates, lengths, and diameters, it was found that the maximum pressure drop occurred in two segments: the thin descending limbs of Henle and the inner medullary collecting ducts. The high resistance in the thin descending limbs is due to their small diameters. The steep pressure drop observed in the inner medullary collecting ducts is due to the convergent structure of the tubules, which channels flow into fewer and fewer tubules toward the papillary tip. For short-looped nephrons, the calculated glomerular capsular pressure matched measured values, even with the high collecting duct flow rates seen in water diuresis, provided that tubule compliance was taken into account. In long-looped nephrons, the greater length of thin limb segments is likely compensated for by a larger luminal diameter. Simulation of the effect of proximal diuretics, namely acetazolamide or type 2 sodium-glucose transporter inhibitors, predicts a substantial back pressure in Bowman's capsule, which may contribute to observed decreases in glomerular filtration rate.}, } @article {pmid30088905, year = {2018}, author = {Mateos-Maroto, A and Guerrero-Martínez, A and Rubio, RG and Ortega, F and Martínez-Pedrero, F}, title = {Magnetic Biohybrid Vesicles Transported by an Internal Propulsion Mechanism.}, journal = {ACS applied materials & interfaces}, volume = {10}, number = {35}, pages = {29367-29377}, doi = {10.1021/acsami.8b09862}, pmid = {30088905}, issn = {1944-8252}, mesh = {*Hydrodynamics ; *Lipids ; *Magnetics ; *Models, Biological ; Rotation ; Transport Vesicles/metabolism ; }, abstract = {Some biological microorganisms can crawl or swim due to coordinated motions of their cytoskeleton or the flagella located inside their bodies, which push the cells forward through intracellular forces. To date, there is no demonstration of synthetic systems propelling at low Reynolds number via the precise actuation of the material confined within an enclosing lipid membrane. Here, we report lipid vesicles and other more complex self-assembled biohybrid structures able to propel due to the advection flows generated by the actuated rotation of the superparamagnetic particles they contain. The proposed swimming and release strategies, based on cooperative hydrodynamic mechanisms and near-infrared laser pulse-triggered destabilization of the phospholipid membranes, open new possibilities for the on-command transport of minute quantities of drugs, fluid or nano-objects. The lipid membranes protect the confined substances from the outside environment during transportation, thus enabling them to work in physiological conditions.}, } @article {pmid30083106, year = {2018}, author = {Vidal, EAG and Zeidberg, LD and Buskey, EJ}, title = {Development of Swimming Abilities in Squid Paralarvae: Behavioral and Ecological Implications for Dispersal.}, journal = {Frontiers in physiology}, volume = {9}, number = {}, pages = {954}, pmid = {30083106}, issn = {1664-042X}, abstract = {This study investigates the development of swimming abilities and its relationship with morphology, growth, and nourishment of reared Doryteuthis opalescens paralarvae from hatching to 60 days of age. Paralarvae (2.5-11 mm mantle length - ML) were videotaped, and their behavior quantified throughout development using computerized motion analysis. Hatchlings swim dispersed maintaining large nearest neighbor distances (NND, 8.7 ML), with swimming speeds (SS) of 3-8 mm s-1 and paths with long horizontal displacements, resulting in high net to gross displacement ratios (NGDR). For 15-day-old paralarvae, swimming paths are more consistent between jets, growth of fins, length, and mass increases. The swimming pattern of 18-day-old paralarvae starved for 72 h exhibited a significant reduction in mean SS and inability to perform escape jets. A key morphological, behavioral, and ecological transition occurs at about 6 mm ML (>35-day old), when there is a clear change in body shape, swimming performance, and behavior, paths are more regularly repeated and directional swimming is evident, suggesting that morphological changes incur in swimming performance. These squid are able to perform sustained swimming and hover against a current at significantly closer NND (2.0 ML), as path displacement is reduced and maneuverability increases. As paralarvae reach 6-7 mm ML, they are able to attain speeds up to 562 mm s-1 and to form schools. Social feeding interactions (kleptoparasitism) are often observed prior to the formation of schools. Schools are always formed within areas of high flow gradient in the tanks and are dependent on squid size and current speed. Fin development is a requisite for synchronized and maneuverable swimming of schooling early juveniles. Although average speeds of paralarvae are within intermediate Reynolds numbers (Re < 100), they make the transition to the inertia-dominated realm during escape jets of high propulsion (Re > 3200), transitioning from plankton to nekton after their first month of life. The progressive development of swimming capabilities and social interactions enable juvenile squid to school, while also accelerates learning, orientation and cognition. These observations indicate that modeling of the lifecycle should include competency to exert influence over small currents and dispersal patterns after the first month of life.}, } @article {pmid30072230, year = {2018}, author = {Gritti, F}, title = {High-resolution turbulent flow chromatography.}, journal = {Journal of chromatography. A}, volume = {1570}, number = {}, pages = {135-147}, doi = {10.1016/j.chroma.2018.07.059}, pmid = {30072230}, issn = {1873-3778}, mesh = {Benz(a)Anthracenes/*analysis/chemistry/isolation & purification ; Carbon Dioxide/*chemistry ; Chromatography, High Pressure Liquid/*methods ; Chromatography, Supercritical Fluid/*methods ; Molecular Weight ; Polycyclic Compounds/*analysis/chemistry/isolation & purification ; }, abstract = {The resolution power of turbulent flow chromatography using carbon dioxide as the mobile phase and coated (crosslinked methyl phenyl polysiloxane) open tube columns (OTCs) as the stationary phase was investigated under retentive conditions (0

MATERIALS AND METHODS: This study presents an experimental observation of a simplified Weibel-based model of the human trachea and bronchi with cartilaginous rings. A transparent model and refractive index-matching methods were used to observe the flow, particularly near the wall. The flow was seeded with tracers to perform particle image velocimetry and particle tracking velocimetry to quantify the effect the rings have on the flow near the trachea and bronchi walls. The experiments were carried out with a flow rate comparable with a resting state (trachea-based Reynolds number of ReD = 2650).

RESULTS: The results present a previously unknown phenomenon in the cavities between the cartilaginous rings: a small recirculation is observed in the upstream side of the cavities throughout the trachea. This recirculation is due to the adverse pressure gradient created by the expansion, which traps particles within the ring cavity, thus affecting the treatment of patients suffering from lung disease and other respiratory conditions.

CONCLUSIONS: The detection of recirculation zones in the cartilage ring cavities sheds light on the particle deposition mechanism and helps explain results from previous studies that have observed an enhancement of particle deposition in models with cartilage rings. These results bring to light the importance of including cartilage rings in experimental, numerical, and theoretical models to better understand particle deposition in the trachea and bronchi. In addition, the results provide scientists and medical staff with new insights for improving drug delivery.}, } @article {pmid29786774, year = {2018}, author = {Bordones, AD and Leroux, M and Kheyfets, VO and Wu, YA and Chen, CY and Finol, EA}, title = {Computational Fluid Dynamics Modeling of the Human Pulmonary Arteries with Experimental Validation.}, journal = {Annals of biomedical engineering}, volume = {46}, number = {9}, pages = {1309-1324}, pmid = {29786774}, issn = {1573-9686}, support = {R01 HL121293/HL/NHLBI NIH HHS/United States ; 14GRNT19020017//American Heart Association/ ; R01HL121293//National Institutes of Health/ ; }, mesh = {Computer Simulation ; Humans ; Hydrodynamics ; *Models, Cardiovascular ; Phantoms, Imaging ; Printing, Three-Dimensional ; Pulmonary Artery/*physiology ; Rheology ; }, abstract = {Pulmonary hypertension (PH) is a chronic progressive disease characterized by elevated pulmonary arterial pressure, caused by an increase in pulmonary arterial impedance. Computational fluid dynamics (CFD) can be used to identify metrics representative of the stage of PH disease. However, experimental validation of CFD models is often not pursued due to the geometric complexity of the model or uncertainties in the reproduction of the required flow conditions. The goal of this work is to validate experimentally a CFD model of a pulmonary artery phantom using a particle image velocimetry (PIV) technique. Rapid prototyping was used for the construction of the patient-specific pulmonary geometry, derived from chest computed tomography angiography images. CFD simulations were performed with the pulmonary model with a Reynolds number matching those of the experiments. Flow rates, the velocity field, and shear stress distributions obtained with the CFD simulations were compared to their counterparts from the PIV flow visualization experiments. Computationally predicted flow rates were within 1% of the experimental measurements for three of the four branches of the CFD model. The mean velocities in four transversal planes of study were within 5.9 to 13.1% of the experimental mean velocities. Shear stresses were qualitatively similar between the two methods with some discrepancies in the regions of high velocity gradients. The fluid flow differences between the CFD model and the PIV phantom are attributed to experimental inaccuracies and the relative compliance of the phantom. This comparative analysis yielded valuable information on the accuracy of CFD predicted hemodynamics in pulmonary circulation models.}, } @article {pmid29776113, year = {2018}, author = {Zhu, B and Ji, Z and Lou, Z and Qian, P}, title = {Torque scaling in small-gap Taylor-Couette flow with smooth or grooved wall.}, journal = {Physical review. E}, volume = {97}, number = {3-1}, pages = {033110}, doi = {10.1103/PhysRevE.97.033110}, pmid = {29776113}, issn = {2470-0053}, abstract = {The torque in the Taylor-Couette flow for radius ratios η≥0.97, with smooth or grooved wall static outer cylinders, is studied experimentally, with the Reynolds number of the inner cylinder reaching up to Re_{i}=2×10^{5}, corresponding to the Taylor number up to Ta=5×10^{10}. The grooves are perpendicular to the mean flow, and similar to the structure of a submersible motor stator. It is found that the dimensionless torque G, at a given Re_{i} and η, is significantly greater for grooved cases than smooth cases. We compare our experimental torques for the smooth cases to the fit proposed by Wendt [F. Wendt, Ing.-Arch. 4, 577 (1993)10.1007/BF02084936] and the fit proposed by Bilgen and Boulos [E. Bilgen and R. Boulos, J Fluids Eng. 95, 122 (1973)10.1115/1.3446944], which shows both fits are outside their range for small gaps. Furthermore, an additional dimensionless torque (angular velocity flux) Nu_{ω} in the smooth cases exhibits an effective scaling of Nu_{ω}∼Ta^{0.39} in the ultimate regime, which occurs at a lower Taylor number, Ta≈3.5×10^{7}, than the well-explored η=0.714 case (at Ta≈3×10^{8}). The same effective scaling exponent, 0.39, is also evident in the grooved cases, but for η=0.97 and 0.985, there is a peak before this exponent appears.}, } @article {pmid29776082, year = {2018}, author = {Liang, H and Xu, J and Chen, J and Wang, H and Chai, Z and Shi, B}, title = {Phase-field-based lattice Boltzmann modeling of large-density-ratio two-phase flows.}, journal = {Physical review. E}, volume = {97}, number = {3-1}, pages = {033309}, doi = {10.1103/PhysRevE.97.033309}, pmid = {29776082}, issn = {2470-0053}, abstract = {In this paper, we present a simple and accurate lattice Boltzmann (LB) model for immiscible two-phase flows, which is able to deal with large density contrasts. This model utilizes two LB equations, one of which is used to solve the conservative Allen-Cahn equation, and the other is adopted to solve the incompressible Navier-Stokes equations. A forcing distribution function is elaborately designed in the LB equation for the Navier-Stokes equations, which make it much simpler than the existing LB models. In addition, the proposed model can achieve superior numerical accuracy compared with previous Allen-Cahn type of LB models. Several benchmark two-phase problems, including static droplet, layered Poiseuille flow, and spinodal decomposition are simulated to validate the present LB model. It is found that the present model can achieve relatively small spurious velocity in the LB community, and the obtained numerical results also show good agreement with the analytical solutions or some available results. Lastly, we use the present model to investigate the droplet impact on a thin liquid film with a large density ratio of 1000 and the Reynolds number ranging from 20 to 500. The fascinating phenomena of droplet splashing is successfully reproduced by the present model and the numerically predicted spreading radius exhibits to obey the power law reported in the literature.}, } @article {pmid29776043, year = {2018}, author = {Oyama, N and Teshigawara, K and Molina, JJ and Yamamoto, R and Taniguchi, T}, title = {Reynolds-number-dependent dynamical transitions on hydrodynamic synchronization modes of externally driven colloids.}, journal = {Physical review. E}, volume = {97}, number = {3-1}, pages = {032611}, doi = {10.1103/PhysRevE.97.032611}, pmid = {29776043}, issn = {2470-0053}, abstract = {The collective dynamics of externally driven N_{p}-colloidal systems (1≤N_{p}≤4) in a confined viscous fluid have been investigated using three-dimensional direct numerical simulations with fully resolved hydrodynamics. The dynamical modes of collective particle motion are studied by changing the particle Reynolds number as determined by the strength of the external driving force and the confining wall distance. For a system with N_{p}=3, we found that at a critical Reynolds number a dynamical mode transition occurs from the doublet-singlet mode to the triplet mode, which has not been reported experimentally. The dynamical mode transition was analyzed in detail from the following two viewpoints: (1) spectrum analysis of the time evolution of a tagged particle velocity and (2) the relative acceleration of the doublet cluster with respect to the singlet particle. For a system with N_{p}=4, we found similar dynamical mode transitions from the doublet-singlet-singlet mode to the triplet-singlet mode and further to the quartet mode.}, } @article {pmid29772223, year = {2018}, author = {Markwalter, CE and Prud'homme, RK}, title = {Design of a Small-Scale Multi-Inlet Vortex Mixer for Scalable Nanoparticle Production and Application to the Encapsulation of Biologics by Inverse Flash NanoPrecipitation.}, journal = {Journal of pharmaceutical sciences}, volume = {107}, number = {9}, pages = {2465-2471}, doi = {10.1016/j.xphs.2018.05.003}, pmid = {29772223}, issn = {1520-6017}, mesh = {Biological Products/*chemical synthesis/metabolism ; *Chemical Precipitation ; Chemistry, Pharmaceutical/*instrumentation/methods ; Equipment Design/*instrumentation/methods ; Hydrophobic and Hydrophilic Interactions ; Nanoparticles/*chemistry/metabolism ; Particle Size ; }, abstract = {Flash NanoPrecipitation is a scalable approach to generate polymeric nanoparticles using rapid micromixing in specially designed geometries such as a confined impinging jets mixer or a Multi-Inlet Vortex Mixer (MIVM). A major limitation of formulation screening using the MIVM is that a single run requires tens of milligrams of the therapeutic. To overcome this, we have developed a scaled-down version of the MIVM, requiring as little as 0.2 mg of therapeutic, for formulation screening. The redesigned mixer can then be attached to pumps for scale-up of the identified formulation. It was shown that Reynolds number allowed accurate scaling between the 2 MIVM designs. The utility of the small-scale MIVM for formulation development was demonstrated through the encapsulation of a number of hydrophilic macromolecules using inverse Flash NanoPrecipitation with target loadings as high as 50% by mass.}, } @article {pmid31831915, year = {2018}, author = {Coleman, GN and Rumsey, CL and Spalart, PR}, title = {Numerical study of turbulent separation bubbles with varying pressure gradient and Reynolds number.}, journal = {Journal of fluid mechanics}, volume = {847}, number = {}, pages = {28-70}, doi = {10.1017/jfm.2018.257}, pmid = {31831915}, issn = {0022-1120}, support = {/LaRC/Langley Research Center NASA/United States ; N-999999/ImNASA/Intramural NASA/United States ; }, abstract = {A family of cases each containing a small separation bubble is treated by direct numerical simulation (DNS), varying two parameters: the severity of the pressure gradients, generated by suction and blowing across the opposite boundary, and the Reynolds number. Each flow contains a well-developed entry region with essentially zero pressure gradient, and all are adjusted to have the same value for the momentum thickness, extrapolated from the entry region to the centre of the separation bubble. Combined with fully defined boundary conditions this will make comparisons with other simulations and turbulence models rigorous; we present results for a set of eight Reynolds-averaged Navier-Stokes turbulence models. Even though the largest Reynolds number is approximately 5.5 times higher than in a similar DNS study we presented in 1997, the models have difficulties matching the DNS skin friction very closely even in the zero pressure gradient, which complicates their assessment. In the rest of the domain, the separation location per se is not particularly difficult to predict, and the most definite disagreement between DNS and models is near reattachment. Curiously, the better models tend to cluster together in their predictions of pressure and skin friction even when they deviate from the DNS, although their eddy-viscosity levels are widely different in the outer region near the bubble (or they do not rely on an eddy viscosity). Stratford's square-root law is satisfied by the velocity profiles, both at separation and reattachment. The Reynolds-number range covers a factor of two, with the Reynolds number based on the extrapolated momentum thickness equal to approximately 1500 and 3000. This allows tentative estimates of the improvements that even higher values will bring to the model comparisons. The solutions are used to assess models through pressure, skin friction and other measures; the flow fields are also used to produce effective eddy-viscosity targets for the models, thus guiding turbulence-modelling work in each region of the flow.}, } @article {pmid29758688, year = {2018}, author = {Sanjeevi, SKP and Zarghami, A and Padding, JT}, title = {Choice of no-slip curved boundary condition for lattice Boltzmann simulations of high-Reynolds-number flows.}, journal = {Physical review. E}, volume = {97}, number = {4-1}, pages = {043305}, doi = {10.1103/PhysRevE.97.043305}, pmid = {29758688}, issn = {2470-0053}, abstract = {Various curved no-slip boundary conditions available in literature improve the accuracy of lattice Boltzmann simulations compared to the traditional staircase approximation of curved geometries. Usually, the required unknown distribution functions emerging from the solid nodes are computed based on the known distribution functions using interpolation or extrapolation schemes. On using such curved boundary schemes, there will be mass loss or gain at each time step during the simulations, especially apparent at high Reynolds numbers, which is called mass leakage. Such an issue becomes severe in periodic flows, where the mass leakage accumulation would affect the computed flow fields over time. In this paper, we examine mass leakage of the most well-known curved boundary treatments for high-Reynolds-number flows. Apart from the existing schemes, we also test different forced mass conservation schemes and a constant density scheme. The capability of each scheme is investigated and, finally, recommendations for choosing a proper boundary condition scheme are given for stable and accurate simulations.}, } @article {pmid29758634, year = {2018}, author = {Mahalinkam, R and Gong, F and Khair, AS}, title = {Reduced-order model for inertial locomotion of a slender swimmer.}, journal = {Physical review. E}, volume = {97}, number = {4-1}, pages = {043102}, doi = {10.1103/PhysRevE.97.043102}, pmid = {29758634}, issn = {2470-0053}, abstract = {The inertial locomotion of an elongated model swimmer in a Newtonian fluid is quantified, wherein self-propulsion is achieved via steady tangential surface treadmilling. The swimmer has a length 2l and a circular cross section of longitudinal profile aR(z), where a is the characteristic width of the cross section, R(z) is a dimensionless shape function, and z is a dimensionless coordinate, normalized by l, along the centerline of the body. It is assumed that the swimmer is slender, ε=a/l≪1. Hence, we utilize slender-body theory to analyze the Navier-Stokes equations that describe the flow around the swimmer. Therefrom, we compute an asymptotic approximation to the swimming speed, U, as U/u_{s}=1-β[V(Re)-1/2∫_{-1}^{1}zlnR(z)dz]/ln(1/ε)+O[1/ln^{2}(1/ε)], where u_{s} is the characteristic speed of the surface treadmilling, Re is the Reynolds number based on the body length, and β is a dimensionless parameter that differentiates between "pusher" (propelled from the rear, β<0) and "puller" (propelled from the front, β>0) -type swimmers. The function V(Re) increases monotonically with increasing Re; hence, fluid inertia causes an increase (decrease) in the swimming speed of a pusher (puller). Next, we demonstrate that the power expenditure of the swimmer increases monotonically with increasing Re. Further, the power expenditures of a puller and pusher with the same value of |β| are equal. Therefore, pushers are superior in inertial locomotion as compared to pullers, in that they achieve a faster swimming speed for the same power expended. Finally, it is demonstrated that the flow structure predicted from our reduced-order model is consistent with that from direct numerical simulation of swimmers at intermediate Re.}, } @article {pmid29757157, year = {2018}, author = {Daddi-Moussa-Ider, A and Lisicki, M and Mathijssen, AJTM and Hoell, C and Goh, S and Bławzdziewicz, J and Menzel, AM and Löwen, H}, title = {State diagram of a three-sphere microswimmer in a channel.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {30}, number = {25}, pages = {254004}, doi = {10.1088/1361-648X/aac470}, pmid = {29757157}, issn = {1361-648X}, abstract = {Geometric confinements are frequently encountered in soft matter systems and in particular significantly alter the dynamics of swimming microorganisms in viscous media. Surface-related effects on the motility of microswimmers can lead to important consequences in a large number of biological systems, such as biofilm formation, bacterial adhesion and microbial activity. On the basis of low-Reynolds-number hydrodynamics, we explore the state diagram of a three-sphere microswimmer under channel confinement in a slit geometry and fully characterize the swimming behavior and trajectories for neutral swimmers, puller- and pusher-type swimmers. While pushers always end up trapped at the channel walls, neutral swimmers and pullers may further perform a gliding motion and maintain a stable navigation along the channel. We find that the resulting dynamical system exhibits a supercritical pitchfork bifurcation in which swimming in the mid-plane becomes unstable beyond a transition channel height while two new stable limit cycles or fixed points that are symmetrically disposed with respect to the channel mid-height emerge. Additionally, we show that an accurate description of the averaged swimming velocity and rotation rate in a channel can be captured analytically using the method of hydrodynamic images, provided that the swimmer size is much smaller than the channel height.}, } @article {pmid29749100, year = {2018}, author = {Tottori, S and Nelson, BJ}, title = {Controlled Propulsion of Two-Dimensional Microswimmers in a Precessing Magnetic Field.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {14}, number = {24}, pages = {e1800722}, doi = {10.1002/smll.201800722}, pmid = {29749100}, issn = {1613-6829}, abstract = {Magnetically actuated micro-/nanoswimmers can potentially be used in noninvasive biomedical applications, such as targeted drug delivery and micromanipulation. Herein, two-dimensional (2D) rigid ferromagnetic microstructures are shown to be capable of propelling themselves in three dimensions at low Reynolds numbers in a precessing field. Importantly, the above propulsion relies neither on soft structure deformation nor on the geometrical chirality of swimmers, but is rather driven by the dynamic chirality generated by field precession, which allows an almost unconstrained choice of materials and fabrication methods. Therefore, the swimming performance is systematically investigated as a function of precession angle and geometric design. One disadvantage of the described propulsion method is that the fabricated 2D swimmers are achiral, which means that the forward/backward swimming direction cannot be controlled. However, it has been found that asymmetric 2D swimmers always propel themselves toward their longer arm, which implies that dynamic chirality can be constrained to be either right-handed or left-handed by permanent magnetization. Thus, the simplicity of fabrication and possibility of dynamic chirality control make the developed method ideal for applications and fundamental studies that require a large number of swimmers.}, } @article {pmid29745778, year = {2018}, author = {Perrin, A and Herbelin, P and Jorand, FPA and Skali-Lami, S and Mathieu, L}, title = {Design of a rotating disk reactor to assess the colonization of biofilms by free-living amoebae under high shear rates.}, journal = {Biofouling}, volume = {34}, number = {4}, pages = {368-377}, doi = {10.1080/08927014.2018.1444756}, pmid = {29745778}, issn = {1029-2454}, mesh = {Amoeba/*physiology ; *Bacteria ; Bacterial Physiological Phenomena ; *Biofilms ; Fresh Water ; Hydrodynamics ; Locomotion ; Stainless Steel ; }, abstract = {The present study was aimed at designing and optimizing a rotating disk reactor simulating high hydrodynamic shear rates (γ), which are representative of cooling circuits. The characteristics of the hydrodynamic conditions in the reactor and the complex approach used to engineer it are described. A 60 l tank was filled with freshwater containing free-living amoebae (FLA) and bacteria. Adhesion of the bacteria and formation of a biofilm on the stainless steel coupons were observed. FLA were able to establish in these biofilms under γ as high as 85,000 s-1. Several physical mechanisms (convection, diffusion, sedimentation) could explain the accumulation of amoeboid cells on surfaces, but further research is required to fully understand and model the fine mechanisms governing such transport under γ similar to those encountered in the industrial environment. This technological advance may enable research into these topics.}, } @article {pmid29744606, year = {2018}, author = {Zhang, S and Luo, X and Cai, Z}, title = {Three-dimensional flows in a hyperelastic vessel under external pressure.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {17}, number = {4}, pages = {1187-1207}, doi = {10.1007/s10237-018-1022-y}, pmid = {29744606}, issn = {1617-7940}, support = {EP/N014642/1//Engineering and Physical Sciences Research Council/ ; 11172200//National Natural Science Foundation of China/ ; 2013CB035042//National Basic Research Program of China/ ; RF-2015-510//Leverhulme Trust/ ; }, mesh = {Algorithms ; Arteries/anatomy & histology/*physiology ; Biomechanical Phenomena ; Blood Flow Velocity/*physiology ; Computer Simulation ; Elasticity ; Finite Element Analysis ; Humans ; Models, Anatomic ; Models, Cardiovascular ; Pressure ; Rheology ; Veins/anatomy & histology/*physiology ; Viscosity ; }, abstract = {We study the collapsible behaviour of a vessel conveying viscous flows subject to external pressure, a scenario that could occur in many physiological applications. The vessel is modelled as a three-dimensional cylindrical tube of nonlinear hyperelastic material. To solve the fully coupled fluid-structure interaction, we have developed a novel approach based on the Arbitrary Lagrangian-Eulerian (ALE) method and the frontal solver. The method of rotating spines is used to enable an automatic mesh adaptation. The numerical code is verified extensively with published results and those obtained using the commercial packages in simpler cases, e.g. ANSYS for the structure with the prescribed flow, and FLUENT for the fluid flow with prescribed structure deformation. We examine three different hyperelastic material models for the tube for the first time in this context and show that at the small strain, all three material models give similar results. However, for the large strain, results differ depending on the material model used. We further study the behaviour of the tube under a mode-3 buckling and reveal its complex flow patterns under various external pressures. To understand these flow patterns, we show how energy dissipation is associated with the boundary layers created at the narrowest collapsed section of the tube, and how the transverse flow forms a virtual sink to feed a strong axial jet. We found that the energy dissipation associated with the recirculation does not coincide with the flow separation zone itself, but overlaps with the streamlines that divide the three recirculation zones. Finally, we examine the bifurcation diagrams for both mode-3 and mode-2 collapses and reveal that multiple solutions exist for a range of the Reynolds number. Our work is a step towards modelling more realistic physiological flows in collapsible arteries and veins.}, } @article {pmid31631904, year = {2018}, author = {Yang, XIA and Abkar, M}, title = {A hierarchical random additive model for passive scalars in wall-bounded flows at high Reynolds numbers.}, journal = {Journal of fluid mechanics}, volume = {842}, number = {}, pages = {354-380}, pmid = {31631904}, issn = {0022-1120}, support = {NNX15AU93A//NASA/United States ; }, abstract = {The kinematics of a fully developed passive scalar is modelled using the hierarchical random additive process (HRAP) formalism. Here, 'a fully developed passive scalar' refers to a scalar field whose instantaneous fluctuations are statistically stationary, and the 'HRAP formalism' is a recently proposed interpretation of the Townsend attached eddy hypothesis. The HRAP model was previously used to model the kinematics of velocity fluctuations in wall turbulence: u = ∑ i = 1 N z a i , where the instantaneous streamwise velocity fluctuation at a generic wall-normal location z is modelled as a sum of additive contributions from wall-attached eddies (ai) and the number of addends is Nz ~ log(δ/z). The HRAP model admits generalized logarithmic scalings including 〈ϕ2〉~log(δ/z), 〈ϕ(x)ϕ(x+rx)〉 ~ log(δ/rx), 〈(ϕ(x) - ϕ(x+rx))2〉 ~ log(rx /z), where ϕ is the streamwise velocity fluctuation, δ is an outer length scale, rx is the two-point displacement in the streamwise direction and 〈·〉 denotes ensemble averaging. If the statistical behaviours of the streamwise velocity fluctuation and the fluctuation of a passive scalar are similar, we can expect first that the above mentioned scalings also exist for passive scalars (i.e. for ϕ being fluctuations of scalar concentration) and second that the instantaneous fluctuations of a passive scalar can be modelled using the HRAP model as well. Such expectations are confirmed using large-eddy simulations. Hence the work here presents a framework for modelling scalar turbulence in high Reynolds number wall-bounded flows.}, } @article {pmid29732048, year = {2018}, author = {Zhou, Y and Lee, C and Wang, J}, title = {The Computational Fluid Dynamics Analyses on Hemodynamic Characteristics in Stenosed Arterial Models.}, journal = {Journal of healthcare engineering}, volume = {2018}, number = {}, pages = {4312415}, pmid = {29732048}, issn = {2040-2295}, mesh = {Arterial Occlusive Diseases/*physiopathology ; Computer Simulation ; Hemodynamics/*physiology ; Humans ; *Models, Cardiovascular ; Rheology ; }, abstract = {Arterial stenosis plays an important role in the progressions of thrombosis and stroke. In the present study, a standard axisymmetric tube model of the stenotic artery is introduced and the degree of stenosis η is evaluated by the area ratio of the blockage to the normal vessel. A normal case (η = 0) and four stenotic cases of η = 0.25, 0.5, 0.625, and 0.75 with a constant Reynolds number of 300 are simulated by computational fluid dynamics (CFD), respectively, with the Newtonian and Carreau models for comparison. Results show that for both models, the poststenotic separation vortex length increases exponentially with the growth of stenosis degree. However, the vortex length of the Carreau model is shorter than that of the Newtonian model. The artery narrowing accelerates blood flow, which causes high blood pressure and wall shear stress (WSS). The pressure drop of the η = 0.75 case is nearly 8 times that of the normal value, while the WSS peak at the stenosis region of η = 0.75 case even reaches up to 15 times that of the normal value. The present conclusions are of generality and contribute to the understanding of the dynamic mechanisms of artery stenosis diseases.}, } @article {pmid29729406, year = {2018}, author = {García-Salazar, G and de la Luz Zambrano-Zaragoza, M and Quintanar-Guerrero, D}, title = {Preparation of nanodispersions by solvent displacement using the Venturi tube.}, journal = {International journal of pharmaceutics}, volume = {545}, number = {1-2}, pages = {254-260}, doi = {10.1016/j.ijpharm.2018.05.005}, pmid = {29729406}, issn = {1873-3476}, mesh = {Acetone/*chemistry ; Drug Compounding ; Dynamic Light Scattering ; Equipment and Supplies ; Excipients/chemistry ; *Nanoparticles ; Nanotechnology ; Particle Size ; Polyesters/*chemistry ; Solvents/*chemistry ; Technology, Pharmaceutical/*instrumentation/methods ; }, abstract = {The Venturi tube (VT) is an apparatus that produces turbulence which is taken advantage of to produce nanoparticles (NP) by solvent displacement. The objective of this study was to evaluate the potential of this device for preparing NP of poly-ε-caprolactone. Response Surface Methodology was used to determine the effect of the opera