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Bibliography on: Reynolds Number

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ESP: PubMed Auto Bibliography 12 Aug 2022 at 01:32 Created: 

Reynolds Number

It is well known that relative size greatly affects how organisms interact with the world. Less well known, at least among biologists, is that at sufficiently small sizes, mechanical interaction with the environment becomes difficult and then virtually impossible. In fluid dynamics, an important dimensionless parameter is the Reynolds Number (abbreviated Re), which is the ratio of inertial to viscous forces affecting the movement of objects in a fluid medium (or the movement of a fluid in a pipe). Since Re is determined mainly by the size of the object (pipe) and the properties (density and viscosity) of the fluid, organisms of different sizes exhibit significantly different Re values when moving through air or water. A fish, swimming at a high ratio of inertial to viscous forces, gives a flick of its tail and then glides for several body lengths. A bacterium, "swimming" in an environment dominated by viscosity, possesses virtually no inertia. When the bacterium stops moving its flagellum, the bacterium "coasts" for about a half of a microsecond, coming to a stop in a distance less than a tenth the diameter of a hydrogen atom. Similarly, the movement of molecules (nutrients toward, wastes away) in the vicinity of a bacterium is dominated by diffusion. Effective stirring — the generation of bulk flow through mechanical means — is impossible at very low Re. An understanding of the constraints imposed by life at low Reynolds numbers is essentially for understanding the prokaryotic biosphere.

Created with PubMed® Query: "reynolds number" NOT pmcbook NOT ispreviousversion

Citations The Papers (from PubMed®)


RevDate: 2022-08-04

Bhattacharjee A, Jabbarzadeh M, Kararsız G, et al (2022)

Bacteria-Inspired Magnetically Actuated Rod-Like Soft Robot in Viscous Fluids.

Bioinspiration & biomimetics [Epub ahead of print].

This paper seeks to design, develop, and explore the locomotive dynamics and morphological adaptability of a bacteria-inspired rod-like soft robot propelled in highly viscous Newtonian fluids. The soft robots were fabricated as tapered, hollow rod-like soft scaffolds by applying a robust and economic molding technique to a polyacrylamide-based hydrogel polymer. Cylindrical micro-magnets were embedded in both ends of the soft scaffolds, which allowed bending (deformation) and actuation under a uniform rotating magnetic field. We demonstrated that the tapered rod-like soft robot in viscous Newtonian fluids could perform two types of propulsion; boundary rolling was displayed when the soft robot was located near a boundary, and swimming was displayed far away from the boundary. In addition, we performed numerical simulations to understand the swimming propulsion along the rotating axis and the way in which this propulsion is affected by the soft robot's design, rotation frequency, and fluid viscosity. Our results suggested that a simple geometrical asymmetry would enable the rod-like soft robot to perform propulsion in the low Reynolds number (Re<< 1) regime; these promising results provide essential insights into the improvements that must be made to integrate the soft robots into minimally invasivein vivoapplications.

RevDate: 2022-08-02

Xiao L, Liu Q, W Huang (2022)

Experimental research and analysis on the resistance characteristics of simulated ore bin in water.

Scientific reports, 12(1):13211.

In order to research the variation law of the longitudinal resistance coefficient of the ore bin in the marine mining system under different length-diameter ratio, external shape, additional weight and Reynolds number, a set of experimental system for testing the resistance coefficient was designed and built independently. By analyzing the experimental results, it can be seen that under the same conditions, the resistance coefficient decreases gradually with the increase of Reynolds number and finally fluctuates around a certain value. Increasing the excitation displacement will reduce the overall resistance coefficient of the ore bin. The smaller the length-diameter ratio is, the larger the corresponding force value when the vibration acceleration of the ore bin is 0, and the larger the overall resistance coefficient is. The resistance coefficient of the cylindrical section is greater than that of the rectangular shape. In order to reduce the longitudinal vibration and the transverse towing offset, the shape of the ore bin should be cylindrical in actual design and production. At low Reynolds number, the increase of added weight will increase the resistance coefficient, while at high Reynolds number, the change of added weight will not cause the change of resistance coefficient.

RevDate: 2022-08-01

Ram D, Bhandari DS, Tripathi D, et al (2022)

Propagation of H1N1 virus through saliva movement in oesophagus: a mathematical model.

European physical journal plus, 137(7):866.

H1N1 (Swine flu) is caused by the influenza A virus which belongs to the Orthomyxoviridae family. Influenza A is very harmful to the elderly, and people with chronic respiratory disease and cardiovascular disease. Therefore, it is essential to analyse the behaviour of virus transmission through the saliva movement in oesophagus. A mathematical paradigm is developed to study the saliva movement under the applications of transverse magnetic field. Jeffrey fluid model is considered for saliva to show the viscoelastic nature. The flow nature is considered creeping and assumptions of long wavelength and low Reynolds number are adopted for analytical solutions. The Basset-Boussinesq-Oseen equation is employed to understand the propagation of H1N1 virus through saliva under the effect of applicable forces such as gravity, virtual mass, basset force, and drag forces. The suitable data for saliva, oesophagus and H1N1 virus are taken from the existing literature for simulation of the results using MATLAB software. From the graphical results, it is observed that the susceptibility to viral infections is less because the magnetic field reduces the motion of the virus particle. Further, the chances of infections in males are more as compared to females and children due to variation in viscosity of saliva. Such findings provide an understanding of the mechanics of the virus floating through the saliva (viscoelastic fluids) in the oesophagus.

RevDate: 2022-08-01

Strazzullo M, Girfoglio M, Ballarin F, et al (2022)

Consistency of the full and reduced order models for evolve-filter-relax regularization of convection-dominated, marginally-resolved flows.

International journal for numerical methods in engineering, 123(14):3148-3178.

Numerical stabilization is often used to eliminate (alleviate) the spurious oscillations generally produced by full order models (FOMs) in under-resolved or marginally-resolved simulations of convection-dominated flows. In this article, we investigate the role of numerical stabilization in reduced order models (ROMs) of marginally-resolved, convection-dominated incompressible flows. Specifically, we investigate the FOM-ROM consistency, that is, whether the numerical stabilization is beneficial both at the FOM and the ROM level. As a numerical stabilization strategy, we focus on the evolve-filter-relax (EFR) regularization algorithm, which centers around spatial filtering. To investigate the FOM-ROM consistency, we consider two ROM strategies: (i) the EFR-noEFR, in which the EFR stabilization is used at the FOM level, but not at the ROM level; and (ii) the EFR-EFR, in which the EFR stabilization is used both at the FOM and at the ROM level. We compare the EFR-noEFR with the EFR-EFR in the numerical simulation of a 2D incompressible flow past a circular cylinder in the convection-dominated, marginally-resolved regime. We also perform model reduction with respect to both time and Reynolds number. Our numerical investigation shows that the EFR-EFR is more accurate than the EFR-noEFR, which suggests that FOM-ROM consistency is beneficial in convection-dominated, marginally-resolved flows.

RevDate: 2022-07-29

Wang X, Shih HY, N Goldenfeld (2022)

Stochastic Model for Quasi-One-Dimensional Transitional Turbulence with Streamwise Shear Interactions.

Physical review letters, 129(3):034501.

The transition to turbulence in wall-bounded shear flows is typically subcritical, with a poorly understood interplay between spatial fluctuations, pattern formation, and stochasticity near the critical Reynolds number. Here, we present a spatially extended stochastic minimal model for the energy budget in transitional pipe flow, which successfully recapitulates the way localized patches of turbulence (puffs) decay, split, and grow, respectively, as the Reynolds number increases through the laminar-turbulent transition. Our approach takes into account the flow geometry, as we demonstrate by extending the model to quasi-one-dimensional Taylor-Couette flow, reproducing the observed directed percolation pattern of turbulent patches in space and time.

RevDate: 2022-07-28

Godeau AL, Leoni M, Comelles J, et al (2022)

3D single cell migration driven by temporal correlation between oscillating force dipoles.

eLife, 11: pii:71032 [Epub ahead of print].

Directional cell locomotion requires symmetry breaking between the front and rear of the cell. In some cells, symmetry breaking manifests itself in a directional flow of actin from the front to the rear of the cell. Many cells, especially in physiological 3D matrices do not show such coherent actin dynamics and present seemingly competing protrusion/retraction dynamics at their front and back. How symmetry breaking manifests itself for such cells is therefore elusive. We take inspiration from the scallop theorem proposed by Purcell for micro-swimmers in Newtonian fluids: self-propelled objects undergoing persistent motion at low Reynolds number must follow a cycle of shape changes that breaks temporal symmetry. We report similar observations for cells crawling in 3D. We quantified cell motion using a combination of 3D live cell imaging, visualization of the matrix displacement and a minimal model with multipolar expansion. We show that our cells embedded in a 3D matrix form myosin-driven force dipoles at both sides of the nucleus, that locally and periodically pinch the matrix. The existence of a phase shift between the two dipoles is required for directed cell motion which manifests itself as cycles with finite area in the dipole-quadrupole diagram, a formal equivalence to the Purcell cycle. We confirm this mechanism by triggering local dipolar contractions with a laser. This leads to directed motion. Our study reveals that these cells control their motility by synchronizing dipolar forces distributed at front and back. This result opens new strategies to externally control cell motion as well as for the design of micro-crawlers.

RevDate: 2022-07-27

Zhang JD, Sung HJ, WX Huang (2022)

Hydrodynamic interaction of dorsal fin and caudal fin in tuna swimming.

Bioinspiration & biomimetics [Epub ahead of print].

Tuna, which are known for high-performance swimming, possess a large crescent dorsal fin (DF) and caudal fin (CF) that differ from those of other fishes. The hydrodynamic interaction between the DF and CF in tuna, which are represented by two tandem threedimensional (3D) flapping plates, is numerically explored in the present study. Hydrodynamic properties and wake structures of the models with and without a DF are compared to investigate the effects of the DF. The thrust on the CF is substantially enhanced by the DF, whereas the force on the DF is not affected by the CF. The constructive interaction between the leading-edge vortex (LEV) on the CF and the vortices shed from the dorsal fin (DFVs) is identified from 3D wake topology and twodimensional vorticity distributions. The circulation of spanwise vorticity quantitatively reveals that the LEV on the CF is strengthened by the same-signed DFV. The effect of the flapping phase of the CF is examined. The DF-CF interaction is sensitive to the flapping phase at a short spacing, whereas a long spacing between the two fins enables a robust constructive interaction in tuna swimming. A systematic study is carried out to explore the effects of the Strouhal number (St) and the Reynolds number (Re) on the interaction of the fins. The enhancement of thrust due to the DF is diminished at St = 0.63, whereas the Re does not substantially influence the DF-CF constructive interaction.

RevDate: 2022-07-27

Mane NS, Puri DB, Mane S, et al (2022)

Separation of motile human sperms in a T-shaped sealed microchannel.

Biomedical engineering letters, 12(3):331-342 pii:229.

Microfluidic methods act as an effective motile sperm separation technique used in infertility treatments. This work presents a standalone microfluidic device to separate motile sperm cells from non-motile sperm cells and debris. The separation mechanism is based on the centrifugal force acting on sperms and the ability of progressive motile sperms to swim upstream. The separation of motile sperm is carried out using a simple T-shaped microchannel which constitutes three reservoirs: one inlet and two outlets. Herein, one of the outlets is kept sealed. The sealed channel leads to a high-velocity gradient and a rheotaxis zone at the T junction resulting in the separation of motile sperms. Separated sperms are isolated in a sealed channel with a low Reynolds number flow so that sperms cannot have a net displacement, which ensures that the sperms do not re-enter the fluid flow. CFD simulation is conducted to study the flow fields inside the channel and experimental investigation is carried to observe the separation behaviour of sperms. The reported device provides 100% sperm separation efficiency and ensures the entrapment of sperm cells for a longer period. A modified colorimetric nitroblue tetrazolium test conducted on separated sperm cells shows that there is only a marginal increase in superoxide (O2 -) production, proving normal sperm integrity. This device offers an effective and safe alternative to conventional sperm sorting methods.

Supplementary Information: The online version contains supplementary material available at 10.1007/s13534-022-00229-9.

RevDate: 2022-07-27

Ghachem K, Selimefendigil F, Alshammari BM, et al (2022)

Coupled Effects of Using Magnetic Field, Rotation and Wavy Porous Layer on the Forced Convection of Hybrid Nanoliquid Flow over 3D-Backward Facing Step.

Nanomaterials (Basel, Switzerland), 12(14): pii:nano12142466.

In the present study, the effects of using a corrugated porous layer on the forced convection of a hybrid nanofluid flow over a 3D backward facing step are analyzed under the coupled effects of magnetic field and surface rotation. The thermal analysis is conducted for different values of the Reynolds number (Re between 100 and 500), the rotational Reynolds number (Rew between 0 and 2000), the Hartmann number (Ha between 0 and 15), the permeability of the porous layer (the Darcy number, Da between 10-5 and 10-2) and the amplitude (ax between 0.01 ap and 0.7 ap) and wave number (N between 1 and 16) of the porous layer corrugation. When rotations are activated, the average Nusselt number (Nu) and pressure coefficient values rise, while the increment of the latter is less. The increment in the average Nu is higher for the case with a higher permeability of the layer. When the corrugation amplitude and wave number are increased, favorable impacts of the average Nu are observed, but at the same time pressure coefficients are increased. Successful thermal performance estimations are made by using a neural-based modeling approach with a four input-two output system.

RevDate: 2022-07-27

Minea AA, El-Maghlany WM, EZ Massoud (2022)

Heat Transfer Analysis of Nanocolloids Based on Zinc Oxide Nanoparticles Dispersed in PEG 400.

Nanomaterials (Basel, Switzerland), 12(14): pii:nano12142344.

Cooling and heating are extremely important in many industrial applications, while the thermal performance of these processes generally depends on many factors, such as fluid flow rate, inlet temperature, and many more. Hence, tremendous efforts are dedicated to the investigation of several parameters to reach an efficient cooling or heating process. The interest in adding nanoparticles in regular heat transfer fluids delivered new fluids to the market, the nanofluids. In this paper, a new nanoparticle-enhanced fluid based on polyethylene glycol with ZnO nanoparticles is considered and its hydrothermal performance is investigated for HVAC applications. The thermophysical properties of PEG 400-ZnO and their variation with temperature at different nanoparticle loading are previously determined on experimental bases and here implemented in a numerical application. The numerical results are completed at Reynolds number from 200 to 2000, while the nanoparticle concentration varies from 0.5 to 5%. Results are discussed in terms of Nusselt number, friction factor, and dimensionless pressure drop ratio at different temperatures and ZnO loading in the PEG 400 base fluid. Additionally, the evaluation performance criteria (EC) are calculated and discussed. Concluding, the newly developed fluid enhances the heat transfer up to 16% with a 13% pressure drop penalty, while the performance evaluation criteria are enhanced. Plus, several correlations are developed for both Nusselt number and friction factor as a function of relevant operating conditions.

RevDate: 2022-07-27

Wang Y, Yin Z, Bao F, et al (2022)

CFD-DEM Coupling Model for Deposition Process Analysis of Ultrafine Particles in a Micro Impinging Flow Field.

Micromachines, 13(7): pii:mi13071110.

Gas with ultrafine particle impaction on a solid surface is a unique case of curvilinear motion that can be widely used for the devices of surface coatings or instruments for particle size measurement. In this work, the Eulerian-Lagrangian method was applied to calculate the motion of microparticles in a micro impinging flow field with consideration of the interactions between particle to particle, particle to wall, and particle to fluid. The coupling computational fluid dynamics (CFD) with the discrete element method (DEM) was employed to investigate the different deposition patterns of microparticles. The vortex structure and two types of particle deposits ("halo" and "ring") have been discussed. The particle deposition characteristics are affected both by the flow Reynolds number (Re) and Stokes number (stk). Moreover, two particle deposition patterns have been categorized in terms of Re and stk. Finally, the characteristics and mechanism of particle deposits have been analyzed using the particle inertia, the process of impinging (particle rebound or no rebound), vortical structures, and the kinetic energy conversion in two-phase flow, etc.

RevDate: 2022-07-27

Zhou Y, Dai L, N Jiao (2022)

Review of Bubble Applications in Microrobotics: Propulsion, Manipulation, and Assembly.

Micromachines, 13(7): pii:mi13071068.

In recent years, microbubbles have been widely used in the field of microrobots due to their unique properties. Microbubbles can be easily produced and used as power sources or tools of microrobots, and the bubbles can even serve as microrobots themselves. As a power source, bubbles can propel microrobots to swim in liquid under low-Reynolds-number conditions. As a manipulation tool, microbubbles can act as the micromanipulators of microrobots, allowing them to operate upon particles, cells, and organisms. As a microrobot, microbubbles can operate and assemble complex microparts in two- or three-dimensional spaces. This review provides a comprehensive overview of bubble applications in microrobotics including propulsion, micromanipulation, and microassembly. First, we introduce the diverse bubble generation and control methods. Then, we review and discuss how bubbles can play a role in microrobotics via three functions: propulsion, manipulation, and assembly. Finally, by highlighting the advantages and current challenges of this progress, we discuss the prospects of microbubbles in microrobotics.

RevDate: 2022-07-27

Juraeva M, DJ Kang (2022)

Mixing Enhancement of a Passive Micromixer with Submerged Structures.

Micromachines, 13(7): pii:mi13071050.

A passive micromixer combined with two different mixing units was designed by submerging planar structures, and its mixing performance was simulated over a wider range of the Reynolds numbers from 0.1 to 80. The two submerged structures are a Norman window and rectangular baffles. The mixing performance was evaluated in terms of the degree of mixing (DOM) at the outlet and the required pressure load between inlet and outlet. The amount of submergence was varied from 30 μm to 70 μm, corresponding to 25% to 58% of the micromixer depth. The enhancement of mixing performance is noticeable over a wide range of the Reynolds numbers. When the Reynolds number is 10, the DOM is improved by 182% from that of no submergence case, and the required pressure load is reduced by 44%. The amount of submergence is shown to be optimized in terms of the DOM, and the optimum value is about 40 μm. This corresponds to a third of the micromixer depth. The effects of the submerged structure are most significant in the mixing regime of convection dominance from Re = 5 to 80. In a circular passage along the Norman window, one of the two Dean vortices burst into the submerged space, promoting mixing in the cross-flow direction. The submerged baffles in the semi-circular mixing units generate a vortex behind the baffles that contributes to the mixing enhancement as well as reducing the required pressure load.

RevDate: 2022-07-27

Vatsa A, Alam T, Siddiqui MIH, et al (2022)

Performance of Microchannel Heat Sink Made of Silicon Material with the Two-Sided Wedge.

Materials (Basel, Switzerland), 15(14): pii:ma15144740.

New designs of the microchannel with a two-sided wedge shape at the base were studied numerically. Five different wedge angles ranging from 3° to 15° were incorporated into the microchannel design. Simulation of this novel microchannel was carried out using Computational Fluid Dynamics (CFD). Three-dimensional models of the microchannel heat sink were created, discretized, and based on Navier-Stokes and energy equations; laminar numerical solutions were obtained for heat transfer and pressure drop. Flow characteristics of water as coolant in a microchannel were studied. It was observed that numerical results are in good agreement with experimental results. It was found that the Nusselt number and friction factor are significantly varied with the increase in Reynolds number. The Nusselt number varies in the following ranges of 5.963-8.521, 5.986-8.550, 6.009-8.568, 6.040-8.609, and 6.078-8.644 at 3°, 6°, 9°, 12°, and 15°, respectively. The microchannel with a wedge angle of 15° was found to be better in terms of Nusselt number and thermo-hydraulic performance. The enhancement in the Nusselt number is found as 1.017-1.036 for a wedge angle of 15°; however, friction factors do not show the perceptible values at distinct values of wedge angle. Moreover, the thermo-hydraulic performance parameters (THPP) were evaluated and found to be maximum in the range of 1.027-1.045 for a wedge angle of 15°. However, minimum THPP was found in the range of 1.005-1.0185 for a wedge angle of 3°.

RevDate: 2022-07-27

Qi T, Lin J, Z Ouyang (2022)

Hydrodynamic Behavior of Self-Propelled Particles in a Simple Shear Flow.

Entropy (Basel, Switzerland), 24(7): pii:e24070854.

The hydrodynamic properties of a squirmer type of self-propelled particle in a simple shear flow are investigated using the immersed boundary-lattice Boltzmann method in the range of swimming Reynolds number 0.05 ≤ Res ≤ 2.0, flow Reynolds number 40 ≤ Rep ≤ 160, blocking rate 0.2 ≤ κ ≤ 0.5. Some results are validated by comparing with available other results. The effects of Res, Rep and κ on the hydrodynamic properties of squirmer are discussed. The results show that there exist four distinct motion modes for the squirmer, i.e., horizontal mode, attractive oscillation mode, oscillation mode, and chaotic mode. Increasing Res causes the motion mode of the squirmer to change from a constant tumbling near the centerline to a stable horizontal mode, even an oscillatory or appealing oscillatory mode near the wall. Increasing the swimming intensity of squirmer under the definite Res will induce the squirmer to make periodic and stable motion at a specific distance from the wall. Increasing Rep will cause the squirmer to change from a stable swimming state to a spiral motion or continuous rotation. Increasing κ will strengthen the wall's attraction to the squirmer. Increasing swimming intensity of squirmer will modify the strength and direction of the wall's attraction to the squirmer if κ remains constant.

RevDate: 2022-07-26

Punyaratabandhu N, Dechadilok P, Triampo W, et al (2022)

Hydrodynamic Model for Renal Microvascular Filtration: Effects of Physiological and Hemodynamic Changes on Glomerular Size-selectivity.

Microcirculation (New York, N.Y. : 1994) [Epub ahead of print].

OBJECTIVE: The first step in renal urine formation is ultrafiltration across the glomerular barrier. The change in its nanostructure has been associated with nephrotic syndromes. Effects of physiological and hemodynamic factor alterations associated with diabetic nephropathy (DN) on glomerular permselectivity are examined through a mathematical model employing low-Reynolds-number hydrodynamics and hindered transport theory.

METHODS: Glomerular capillaries are represented as networks of cylindrical tubes with multilayered walls. Glomerular basement membrane (GBM) is a fibrous medium with bimodal fiber sizes. Epithelial slit fiber spacing follows a lognormal distribution based on reported electron micrographs with the highest resolution. Endothelial fenestrae are filled with fibers the size of glycosaminoglycans (GAGs). Effects of fiber-macromolecule steric and hydrodynamic interactions are included. Focusing on diabetic nephropathy, the physiological and hemodynamic factors employed in the computation are those reported for healthy humans and patients with early-but-overt diabetic nephropathy. The macromolecule concentration is obtained as a finite element solution of the convection-diffusion equation.

RESULTS: Computed sieving coefficients averaged along the capillary length agree well with ficoll sieving coefficients from studies in humans for most solute radii. GBM thickening and the loss of the slit diaphragm hardly affect glomerular permselectivity. GAG volume fraction reduction in the endothelial fenestrae, however, significantly increases macromolecule filtration. Increased renal plasma flow rate (RPF), glomerular hypertension and reduction of lumen osmotic pressure cause a slight sieving coefficient decrease. These effects are amplified by an increased macromolecule size.

CONCLUSION: Our results indicate that glomerular hypertension and the reduction in the oncotic pressure decreases glomerular macromolecule filtration. Reduction of RPF and changes in the glomerular barrier structure associated with DN, however, increase the solute sieving. Damage to GAGs caused by hyperglycemia is likely to be the most prominent factor affecting glomerular size-selectivity.

RevDate: 2022-07-25

Skotnicka-Siepsiak A (2022)

Pressure distribution on a flat plate in the context of the phenomenon of the Coanda effect hysteresis.

Scientific reports, 12(1):12687.

As a result of the Coanda effect, a symmetrical free jet will flow as an asymmetrical wall jet. At the same time, at the obstacle along which the flow is observed, the wall jet generates pressure distribution. In this study, the obstacle located at the diffuser outlet is a flat plate with a variable inclination angle. The article presents results of the study on pressure distributions on a flat plate with a variable angle of inclination. In the experiment, the Reynolds number ranged from 16,192 to 42,240. A fixed geometry diffuser (Witoszyński nozzle) with a height of 0.60 m, width of 0.02 m and outlet velocity of 11.33-29.57 m/s was used. A plate with a length of 1.00 m and a variable inclination angle was installed at the diffuser outlet. What is new, however, is that the presented results of the experimental research include the influence of the Coanda effect hysteresis on the pressure distribution on the plate. The article shows how pressure distributions change on the plate depending on whether the initial angle of inclination was 0° and was increased gradually in the course of the experiment until a detachment of the jet flowing from the plate was observed, or the initial angle of inclination was close to 90° in the primal state and as the angle of the plate inclination was decreased, the jet flowing towards the plate reached the state of attachment to the plate surface. The study demonstrated that for a turbulent jet, pressure distribution on a flat plate is determined not only by the plate's inclination angle, but also by the direction of its rotation.

RevDate: 2022-07-21

Hatte S, R Pitchumani (2022)

Novel nonwetting solid-infused surfaces for superior fouling mitigation.

Journal of colloid and interface science, 627:308-319 pii:S0021-9797(22)01145-6 [Epub ahead of print].

Fouling is a ubiquitous issue in several environmental and energy applications. Here we introduce novel nonwetting solid-infused surfaces (SIS) with superior anti-fouling characteristics that are durable than conventional nonwetting surfaces in a dynamic flow environment. A systematic study is presented to elucidate the fouling mitigation performance of SIS in comparison to lubricant-infused surface (LIS) and conventional smooth surface. Copper tubes with SIS, LIS or smooth inner walls are fabricated and subjected to accelerated calcium sulfate fouling in a flow fouling experimental setup. Fouling on the various surface types is quantified in terms of asymptotic fouling resistance, and the fundamental morphological differences in the interactions of the foulant and the various surface types are analyzed. Based on a systematic sweep of the parameter combinations using design of experiments and Taguchi analysis, an analytical dependence of asymptotic fouling resistance on the governing parameters namely, Reynolds number, foulant concentration and temperature is derived. The analytical model is shown to predict the asymptotic fouling resistance to within 20% accuracy with a 95% confidence. In addition, for the first time, the effects of shear durability on the fouling mitigation performance of LIS vis-à-vis SIS are studied. It is shown that the novel nonwetting SIS offers a robust option for superior fouling mitigation over LIS in the long run.

RevDate: 2022-07-21

Pumm AK, Engelen W, Kopperger E, et al (2022)

A DNA origami rotary ratchet motor.

Nature, 607(7919):492-498.

To impart directionality to the motions of a molecular mechanism, one must overcome the random thermal forces that are ubiquitous on such small scales and in liquid solution at ambient temperature. In equilibrium without energy supply, directional motion cannot be sustained without violating the laws of thermodynamics. Under conditions away from thermodynamic equilibrium, directional motion may be achieved within the framework of Brownian ratchets, which are diffusive mechanisms that have broken inversion symmetry1-5. Ratcheting is thought to underpin the function of many natural biological motors, such as the F1F0-ATPase6-8, and it has been demonstrated experimentally in synthetic microscale systems (for example, to our knowledge, first in ref. 3) and also in artificial molecular motors created by organic chemical synthesis9-12. DNA nanotechnology13 has yielded a variety of nanoscale mechanisms, including pivots, hinges, crank sliders and rotary systems14-17, which can adopt different configurations, for example, triggered by strand-displacement reactions18,19 or by changing environmental parameters such as pH, ionic strength, temperature, external fields and by coupling their motions to those of natural motor proteins20-26. This previous work and considering low-Reynolds-number dynamics and inherent stochasticity27,28 led us to develop a nanoscale rotary motor built from DNA origami that is driven by ratcheting and whose mechanical capabilities approach those of biological motors such as F1F0-ATPase.

RevDate: 2022-07-21
CmpDate: 2022-07-21

Shahzad H, Wang X, Ghaffari A, et al (2022)

Fluid structure interaction study of non-Newtonian Casson fluid in a bifurcated channel having stenosis with elastic walls.

Scientific reports, 12(1):12219.

Fluid-structure interaction (FSI) gained a huge attention of scientists and researchers due to its applications in biomedical and mechanical engineering. One of the most important applications of FSI is to study the elastic wall behavior of stenotic arteries. Blood is the suspension of various cells characterized by shear thinning, yield stress, and viscoelastic qualities that can be assessed by using non-Newtonian models. In this study we explored non-Newtonian, incompressible Casson fluid flow in a bifurcated artery with a stenosis. The two-dimensional Casson model is used to study the hemodynamics of the flow. The walls of the artery are supposed to be elastic and the stenosis region is constructed in both walls. Suitable scales are used to transform the nonlinear differential equations into a dimensionless form. The problem is formulated and discretized using Arbitrary Lagrangian-Eulerian (ALE) approach. The finite element method (FEM) technique is used to solve the system of equations, together with appropriate boundary conditions. The analysis is carried out for the Bingham number, Hartmann number, and Reynolds number. The graphical results of pressure field, velocity profile, and load on the walls are assessed and used to study the influence of hemodynamic effects on stenotic arteries, bifurcation region, and elastic walls. This study shows that there is an increase in wall shear stresses (WSS) with increasing values of Bingham number and Hartmann number. Also, for different values of the Bingham number, the load on the upper wall is computed against the Hartmann number. The result indicate that load at the walls increases as the values of Bingham number and Hartmann number increase.

RevDate: 2022-07-20

Bandak D, Goldenfeld N, Mailybaev AA, et al (2022)

Dissipation-range fluid turbulence and thermal noise.

Physical review. E, 105(6-2):065113.

We revisit the issue of whether thermal fluctuations are relevant for incompressible fluid turbulence and estimate the scale at which they become important. As anticipated by Betchov in a prescient series of works more than six decades ago, this scale is about equal to the Kolmogorov length, even though that is several orders of magnitude above the mean free path. This result implies that the deterministic version of the incompressible Navier-Stokes equation is inadequate to describe the dissipation range of turbulence in molecular fluids. Within this range, the fluctuating hydrodynamics equation of Landau and Lifschitz is more appropriate. In particular, our analysis implies that both the exponentially decaying energy spectrum and the far-dissipation-range intermittency predicted by Kraichnan for deterministic Navier-Stokes will be generally replaced by Gaussian thermal equipartition at scales just below the Kolmogorov length. Stochastic shell model simulations at high Reynolds numbers verify our theoretical predictions and reveal furthermore that inertial-range intermittency can propagate deep into the dissipation range, leading to large fluctuations in the equipartition length scale. We explain the failure of previous scaling arguments for the validity of deterministic Navier-Stokes equations at any Reynolds number and we provide a mathematical interpretation and physical justification of the fluctuating Navier-Stokes equation as an "effective field theory" valid below some high-wave-number cutoff Λ, rather than as a continuum stochastic partial differential equation. At Reynolds number around a million, comparable to that in Earth's atmospheric boundary layer, the strongest turbulent excitations observed in our simulation penetrate down to a length scale of about eight microns, still two orders of magnitude greater than the mean free path of air. However, for longer observation times or for higher Reynolds numbers, more extreme turbulent events could lead to a local breakdown of fluctuating hydrodynamics.

RevDate: 2022-07-20

Margazoglou G, Biferale L, Cencini M, et al (2022)

Nonequilibrium ensembles for the three-dimensional Navier-Stokes equations.

Physical review. E, 105(6-2):065110.

At the molecular level fluid motions are, by first principles, described by time reversible laws. On the other hand, the coarse grained macroscopic evolution is suitably described by the Navier-Stokes equations, which are inherently irreversible, due to the dissipation term. Here, a reversible version of three-dimensional Navier-Stokes is studied, by introducing a fluctuating viscosity constructed in such a way that enstrophy is conserved, along the lines of the paradigm of microcanonical versus canonical treatment in equilibrium statistical mechanics. Through systematic simulations we attack two important questions: (a) What are the conditions that must be satisfied in order to have a statistical equivalence between the two nonequilibrium ensembles? (b) What is the empirical distribution of the fluctuating viscosity observed by changing the Reynolds number and the number of modes used in the discretization of the evolution equation? The latter point is important also to establish regularity conditions for the reversible equations. We find that the probability to observe negative values of the fluctuating viscosity becomes very quickly extremely small when increasing the effective Reynolds number of the flow in the fully resolved hydrodynamical regime, at difference from what was observed previously.

RevDate: 2022-07-20

Choudhury A, A Samanta (2022)

Linear stability of a falling film over a heated slippery plane.

Physical review. E, 105(6-2):065112.

A detailed parametric study on the linear stability analysis of a three-dimensional thin liquid film flowing down a uniformly heated slippery inclined plane is carried out for disturbances of arbitrary wavenumbers, where the liquid film satisfies Newton's law of cooling at the film surface. A coupled system of boundary value problems is formulated in terms of the amplitudes of perturbation normal velocity and perturbation temperature, respectively. Analytical solution of the boundary value problems demonstrates the existence of three dominant modes, the so-called H mode, S mode, and P mode, where the S mode and P mode emerge due to the thermocapillary effect. It is found that the onset of instabilities for the H mode, S mode, and P mode reduces in the presence of wall slip and leads to a destabilizing influence. Numerical solution based on the Chebyshev spectral collocation method unveils that the finite wavenumber H-mode instability can be stabilized, but the S-mode instability and the finite wavenumber P-mode instability can be destabilized by increasing the value of the Marangoni number. On the other hand, the Biot number shows a dual role in the H-mode and S-mode instabilities. But the P-mode instability can be made stable with the increasing value of the Biot number and the decreasing values of the Marangoni number and the Prandtl number. Furthermore, the H-mode and S-mode instabilities become weaker, but the P-mode instability becomes stronger, with the increasing value of the spanwise wavenumber. In addition, the shear mode emerges in the numerical simulation when the Reynolds number is large, which can be destabilized slightly with the increasing value of the Marangoni number; however, it can be stabilized with the increasing value of the slip length and introducing the spanwise wavenumber to the infinitesimal perturbation.

RevDate: 2022-07-20

Ishimoto K, Moreau C, K Yasuda (2022)

Self-organized swimming with odd elasticity.

Physical review. E, 105(6-1):064603.

We theoretically investigate self-oscillating waves of an active material, which were recently introduced as a nonsymmetric part of the elastic moduli, termed odd elasticity. Using Purcell's three-link swimmer model, we reveal that an odd-elastic filament at low Reynolds number can swim in a self-organized manner and that the time-periodic dynamics are characterized by a stable limit cycle generated by elastohydrodynamic interactions. Also, we consider a noisy shape gait and derive a swimming formula for a general elastic material in the Stokes regime with its elasticity modulus being represented by a nonsymmetric matrix, demonstrating that the odd elasticity produces biased net locomotion from random noise.

RevDate: 2022-07-12

Zhao X, Zuo H, G Jia (2022)

Effects of the continuous pulsation regeneration on the soot combustion in diesel particulate filter for heavy-duty truck.

Chemosphere pii:S0045-6535(22)02144-0 [Epub ahead of print].

Continuous pulsation regeneration combustion of soot is employed for sine and cosine simulation study. Data showed that pressure uniformity of sine condition is better than that of cosine condition with the maximum pressure difference of 4353.5 Pa under the same simulation boundary conditions. The maximum regeneration temperature under cosine pressure is 46.12 K which is higher than that in sine form. Regeneration combustion reaction zone tends to be more stable laminar flow and Reynolds number of sine condition is 435.23 less than that of under cosine condition. The maximum Stanton number of cosine pressure condition is 3.67 and that of sine pressure condition is 5.15, which investigates heat transfer capacity of the sine pressure condition is better than that of the pressure of cosine form. The regeneration efficiency of inlet gradually increased from the minimum regeneration efficiency 74.18%-88.45% of sine and cosine. The soot under both pressure forms has achieved complete regeneration and the regeneration efficiency has exceeded 88% of porous medium filter body section. The soot regeneration combustion efficiency of the porous media filter section and outlet section is more sufficient under sine condition and the heat carried by the fluid can maintain the soot regeneration.

RevDate: 2022-07-11

Sun R, Chen P, Li L, et al (2022)

Experimental Investigation of the Combustion Behavior of Transformer Oil Jet Flame.

ACS omega, 7(26):22969-22976.

Transformer oil jet fire is one of the most dangerous types of fires in substations. The combustion behavior of transformer oil jet fire produces uncontrollable hazards to personnel and equipment and even triggers a domino effect. However, the jet fire combustion behavior of such materials as transformer oil has not been revealed before. Investigation of the combustion behavior of transformer oil jet fire has positive implications for the prevention and control of substation fires. In this paper, KI25X transformer oil was used as fuel. A series of transformer oil jet fire experiments were conducted with variable orifice diameters (5, 10, and 15 mm) with heat release rates ranging from 200 to 659.2 kW. The results showed that the entrainment coefficient of transformer oil jet fire was greater than that of pure gas phase jet fire. The entrainment coefficient of transformer oil jet fire was 0.029. Using dimensionless theory, it was proposed that the imaginary point source was proportional to the 0.317 power of Froude number. Based on the point source model, a dimensional analysis model with Reynolds number was developed. The radiation fraction of transformer oil jet fire was proportional to the -0.133 power of Reynolds number. This study played an important role in improving the jet combustion behavior of transformer oil.

RevDate: 2022-07-05

Jamshed W, Safdar R, Rehman Z, et al (2022)

Computational technique of thermal comparative examination of Cu and Au nanoparticles suspended in sodium alginate as Sutterby nanofluid via extending PTSC surface.

Journal of applied biomaterials & functional materials, 20:22808000221104004.

Current research underscores entropy investigation in an infiltrating mode of Sutterby nanofluid (SNF) stream past a dramatically expanding flat plate that highlights Parabolic Trough Solar Collector (PTSC). Satisfactory likeness factors are utilized to change halfway differential conditions (PDEs) to nonlinear conventional differential conditions (ODEs) along with relating limit requirements. A productive Keller-box system is locked in to achieve approximated arrangement of decreased conventional differential conditions. In the review, two sorts of nanofluids including Copper-sodium alginate (Cu-SA) and Gold-sodium alginate (Au-SA) are dissected. Results are graphically plotted as well as talked about in actual viewpoints. As indicated by key discoveries, an improvement in Brinkmann, as well as Reynolds number, brings about expanding the general framework entropy. Sutterby nanofluid boundary improves heat rate in PTSC. Additionally, Copper-sodium alginate nanofluid is detected as a superior thermal conductor than Gold-sodium alginate nanofluid. Further to that, the reported breakthroughs are beneficial to updating extremely bright lighting bulbs, heating and cooling machinery, fiber required to generate light, power production, numerous boilers, and other similar technologies.

RevDate: 2022-06-30

Saro-Cortes V, Cui Y, Dufficy T, et al (2022)

An Adaptable Flying Fish Robotic Model for Aero- and Hydrodynamic Experimentation.

Integrative and comparative biology pii:6623665 [Epub ahead of print].

Flying fishes (family Exocoetidae) are known for achieving multi-modal locomotion through air and water. Previous work on understanding this animal's aerodynamic and hydrodynamic nature has been based on observations, numerical simulations, or experiments on preserved dead fish, and has focused primarily on flying pectoral fins. The first half of this paper details the design and validation of a modular flying fish inspired robotic model organism (RMO). The second half delves into a parametric aerodynamic study of flying fish pelvic fins, which to date have not been studied in-depth. Using wind tunnel experiments at a Reynolds number of 30,000, we investigated the effect of the pelvic fin geometric parameters on aerodynamic efficiency and longitudinal stability. The pelvic fin parameters investigated in this study include the pelvic fin pitch angle and its location along the body. Results show that the aerodynamic efficiency is maximized for pelvic fins located directly behind the pectoral fins and is higher for more positive pitch angles. In contrast, pitching stability is neither achievable for positive pitching angles nor pelvic fins located directly below the pectoral fin. Thus, there is a clear a trade-off between stability and lift generation, and an optimal pelvic fin configuration depends on the flying fish locomotion stage, be it gliding, taxiing, or taking off. The results garnered from the RMO experiments are insightful for understanding the physics principles governing flying fish locomotion and designing flying fish inspired aerial-aquatic vehicles.

RevDate: 2022-06-28

Wu YK, Liu YP, M Sun (2022)

Aerodynamics of two parallel bristled wings in low Reynolds number flow.

Scientific reports, 12(1):10928.

Most of the smallest flying insects use bristled wings. It was observed that during the second half of their upstroke, the left and right wings become parallel and close to each other at the back, and move upward at zero angle of attack. In this period, the wings may produce drag (negative vertical force) and side forces which tend to push two wings apart. Here we study the aerodynamic forces and flows of two simplified bristled wings experiencing such a motion, compared with the case of membrane wings (flat-plate wings), to see if there is any advantage in using the bristled wings. The method of computational fluid dynamics is used in the study. The results are as follows. In the motion of two bristled wings, the drag acting on each wing is 40% smaller than the case of a single bristled wing conducting the same motion, and only a very small side force is produced. But in the case of the flat-plate wings, although there is similar drag reduction, the side force on each wing is larger than that of the bristled wing by an order of magnitude (the underlying physical reason is discussed in the paper). Thus, if the smallest insects use membrane wings, their flight muscles need to overcome large side forces in order to maintain the intended motion for less negative lift, whereas using bristled wings do not have this problem. Therefore, the adoption of bristled wings can be beneficial during upward movement of the wings near the end of the upstroke, which may be one reason why most of the smallest insects adopt them.

RevDate: 2022-06-27

Huang X, Wang Y, Wang L, et al (2022)

Effect of Structural Optimization of Scrubbing Cooling Rings on Vertical Falling Film Flow Characteristics.

ACS omega, 7(24):21291-21305.

In order to study the influence of the structural optimization of the scrubbing cooling ring in the scrubbing cooling chamber on the flow characteristics of the vertical falling film, the flow characteristics of the turbulent falling film in the rising section of the development region at different internal platform heights of the scrubbing cooling ring and a high Reynolds number were studied by FLUENT software. First, the correctness of the model was verified by the maximum error of simulation and experimental results of no more than 9.836%. Then, the distribution of liquid film thickness (δ), velocity (V), and turbulence intensity (I z) at 0° of the tube in the axial direction x = 0-500 mm were calculated and obtained when the platform height (H) was 0-30 mm and the liquid film Reynolds number (Re l) = 1.1541 × 104-3.4623 × 104. The results showed that δ in the entrance region increased sharply due to the "jet" effect with solid wall constraints formed by the structure of the water inlet pipe and the scrubbing cooling ring. On the contrary, the liquid film in the fully developed region showed a stable fluctuation trend due to the weakening of the "jet" effect. When H = 30 mm, the change of δ was relatively stable and the change of I z was small, indicating that this platform height is conducive to the stable and uniform distribution of the liquid film. In addition, when Re l < 1.1541 × 104, the liquid film was unstable due to the low flow rate and insufficient cohesion of the liquid film, but V increased slightly. In addition, with the increase of Re l, δ did not change significantly along the axial direction, that is, the Plateau-Rayleigh hindered the growth of δ. Finally, the empirical formula for δ applicable to Re l = 1.1541 × 104-3.4623 × 104 at the axial fixed position was fitted for the first time.

RevDate: 2022-06-25

Ducos S, Pugliese S, Demolliens M, et al (2022)

Ontogeny of swimming performance of hatchery-reared post-larvae and juvenile fish: a case of two threatened Mediterranean species.

Journal of fish biology [Epub ahead of print].

Swimming performance is a well-established key physiological parameter of fish that is highly linked to their fitness in the wild. In the context of fish restocking or restauration purposes, it therefore appears crucial to study this specific behaviour. Here, we investigated intra and interspecies differences in the swimming performance of hatchery-reared post-larvae and juveniles belonging to two Mediterranean candidate threatened species, the common dentex, Dentex dentex (Sparidae), and the brown meagre, Sciaena umbra (Sciaenidae), with body sizes ranging from 8 to 37 mm TL (from 24 to 58 days post-hatch). The swimming abilities were estimated through the calculation of their critical swimming speed (Ucrit), their relative Ucrit and their Reynolds number (Re). Two different patterns were observed between D. dentex and S. umbra, showing a different effect of ontogeny on the performance of both species. The relative Ucrit of S. umbra decreased linearly through ontogeny, whereas the relative Ucrit and Ucrit of D. dentex increased linearly through the range of sizes tested. The ontogenetic change in Ucrit of S. umbra occurred in two stages: a first stage of sharp improvement and a second stage of a slow decrease in performance. Both stages were separated by a breakpoint that coincided with the appearance of a refusal to swim behaviour that occurred shortly after the end of metamorphosis and can potentially be associated with the establishment of this species sedentary behaviour. The swimming performance of both species showed ontogenetic differences. Sciaena umbra had the highest relative performance when its body sizes were the smallest, whereas D. dentex showed the highest relative performance as its largest body sizes. These results will be linked to future research on both of these species concerning their escape, exploratory and predatory behaviours, and for restocking purposes to draw a more realistic overview of hatchery-reared juvenile performance. Knowledge of both species' behavioural and swimming performance through ontogeny is important to consider when using hatchery-reared fish juveniles for restocking, as size-at-release can have a large impact on fish survival and thus on restocking success. This article is protected by copyright. All rights reserved.

RevDate: 2022-06-24

Zhang S, Ahmad F, Khan A, et al (2022)

Performance improvement and thermodynamic assessment of microchannel heat sink with different types of ribs and cones.

Scientific reports, 12(1):10802.

The present study aims to investigate the performance of microchannel heat sink via numerical simulations, based on the first and second law of thermodynamics. The heat transfer and flow characteristics of rectangular microchannel heat sinks have been improved by adding six different types of surface enhancers. The cross-sections include rectangular, triangular, and hexagonal-shaped ribs and cones. The cones have been created from the same cross-sections of ribs by drafting them at an angle of 45° orthogonal to the base, which is expected to decrease the pressure drop, dramatically. The performance of ribs and cones has been evaluated using different parameters such as friction factor, wall shear stress, entropy generation rate, augmentation entropy generation number, thermal resistance, and transport efficiency of thermal energy. The results of the present study revealed that the novel effect of coning at an angle of 45° reduces frictional losses (Maximum pressure drop reduced is 85%), however; a compromise on thermal behavior has been shown (Maximum Nusselt number reduced is 25%). Similarly, the application of coning has caused a significant reduction in wall shear stress and friction factor which can lead to reducing the pumping power requirements. Moreover, triangular ribs have more ability to transfer thermal energy than rectangular and hexagonal ribs. Furthermore, it has been examined in the present study that the trend of total entropy generation rate for triangular ribs decreases up to Re = 400 and then increases onwards which means that thermal losses are more significant than frictional losses at lower Reynolds number. However, frictional losses dominate over thermal losses at higher Reynolds numbers, where vortex generation takes place, especially in triangular ribs.

RevDate: 2022-06-24

Buaria D, KR Sreenivasan (2022)

Scaling of Acceleration Statistics in High Reynolds Number Turbulence.

Physical review letters, 128(23):234502.

The scaling of acceleration statistics in turbulence is examined by combining data from the literature with new data from well-resolved direct numerical simulations of isotropic turbulence, significantly extending the Reynolds number range. The acceleration variance at higher Reynolds numbers departs from previous predictions based on multifractal models, which characterize Lagrangian intermittency as an extension of Eulerian intermittency. The disagreement is even more prominent for higher-order moments of the acceleration. Instead, starting from a known exact relation, we relate the scaling of acceleration variance to that of Eulerian fourth-order velocity gradient and velocity increment statistics. This prediction is in excellent agreement with the variance data. Our Letter highlights the need for models that consider Lagrangian intermittency independent of the Eulerian counterpart.

RevDate: 2022-06-24

Chen D, J Lin (2022)

Steady State of Motion of Two Particles in Poiseuille Flow of Power-Law Fluid.

Polymers, 14(12): pii:polym14122368.

The steady state of motion of two particles in Poiseuille flow of power-law fluid is numerically studied using the lattice Boltzmann method in the range of Reynolds number 20 ≤ Re ≤ 60, diameter ratio of two particles 0.125 ≤ β ≤ 2.4, and power-law index of the fluid 0.4 ≤ n ≤ 1.2. Some results are validated by comparing with other available results. The effects of Re, β, and n on the steady state of motion of two particles are discussed. The results show that, for two particles of the same diameter, the particle spacing l in the steady state is independent of n. In shear-thinning fluid, l increases rapidly at first and then slowly, finally approaching a constant for different Re. In shear-thickening fluid, although l tends to be stable in the end, the values of l after stabilization are different. For two particles of different sizes, l does not always reach a stable state, and whether it reaches a stable state depends on n. When the small particle is downstream, l increases rapidly at first and then slowly in shear-thickening fluid, but increases rapidly at first and then decreases slowly, finally approaching a constant in a shear-thinning fluid. In shear-thinning fluid, the larger n is, the smaller l is. In shear-thickening fluid, β has no effect on l in steady-state. When the large particle is downstream, l increases rapidly at first and then slowly in shear-thinning fluid but increases rapidly at first and then decreases in a shear-thickening fluid. The effect of n on l in the steady state is obvious. In shear-thinning fluid, l increases rapidly at first and then slowly, the larger Re is, the smaller l is. In shear- thickening fluid, l will reach a stable state.

RevDate: 2022-06-24

Bui CM, Ho AT, XB Nguyen (2022)

Flow Behaviors of Polymer Solution in a Lid-Driven Cavity.

Polymers, 14(12): pii:polym14122330.

In this work, a numerical study of polymer flow behaviors in a lid-driven cavity, which is inspired by the coating process, at a broad range of Oldroyd numbers (0≤Od≤50), is carried out. The Reynolds number is height-based and kept at Re=0.001. The fluid investigated is of Carbopol gel possessing yield stress and shear-thinning properties. To express rheological characteristics, the Herschel-Bulkley model cooperated with Papanastasiou's regularization scheme is utilized. Results show that the polymer flow characteristics, i.e., velocity, viscosity, and vortex distributions, are considerably influenced by viscoplastic behaviors. Additionally, there exist solid-like regions which can be of either moving rigid or static dead types in the flow patterns; they become greater and tend to merge together to construct larger ones when Od increases. Furthermore, various polymer flow aspects in different cavity configurations are discussed and analyzed; the cavity width/aspect ratio and skewed angle are found to have significant impacts on the vortex structures and the formation of solid-like regions. Moreover, results for the critical aspect ratio at which the static dead zone is broken into two parts and the characteristic height of this zone are also reported in detail.

RevDate: 2022-06-24

Saghir MZ, MM Rahman (2022)

Thermo-Hydraulic Performance of Pin-Fins in Wavy and Straight Configurations.

Micromachines, 13(6): pii:mi13060954.

Pin-fins configurations have been investigated recently for different engineering applications and, in particular, for a cooling turbine. In the present study, we investigated the performance of three different pin-fins configurations: pin-fins forming a wavy mini-channel, pin-fins forming a straight mini-channel, and a mini-channel without pin-fins considering water as the working fluid. The full Navier-Stokes equations and the energy equation are solved numerically using the finite element technique. Different flow rates are studied, represented by the Reynolds number in the laminar flow regime. The thermo-hydraulic performance of the three configurations is determined by examining the Nusselt number, the pressure drop, and the performance evaluation criterion. Results revealed that pin-fins forming a wavy mini-channel exhibited the highest Nusselt number, the lowest pressure drop, and the highest performance evaluation criterion. This finding is valid for any Reynolds number under investigation.

RevDate: 2022-06-24

Tayeb NT, Hossain S, Khan AH, et al (2022)

Evaluation of Hydrodynamic and Thermal Behaviour of Non-Newtonian-Nanofluid Mixing in a Chaotic Micromixer.

Micromachines, 13(6): pii:mi13060933.

Three-dimensional numerical investigations of a novel passive micromixer were carried out to analyze the hydrodynamic and thermal behaviors of Nano-Non-Newtonian fluids. Mass and heat transfer characteristics of two heated fluids have been investigated to understand the quantitative and qualitative fluid faction distributions with temperature homogenization. The effect of fluid behavior and different Al2O3 nanoparticles concentrations on the pressure drop and thermal mixing performances were studied for different Reynolds number (from 0.1 to 25). The performance improvement simulation was conducted in intervals of various Nanoparticles concentrations (φ = 0 to 5%) with Power-law index (n) using CFD. The proposed micromixer displayed a mixing energy cost of 50-60 comparable to that achieved for a recent micromixer (2021y) in terms of fluid homogenization. The analysis exhibited that for high nanofluid concentrations, having a strong chaotic flow enhances significantly the hydrodynamic and thermal performances for all Reynolds numbers. The visualization of vortex core region of mass fraction and path lines presents that the proposed design exhibits a rapid thermal mixing rate that tends to 0.99%, and a mass fraction mixing rate of more than 0.93% with very low pressure losses, thus the proposed micromixer can be utilized to enhance homogenization in different Nano-Non-Newtonian mechanism with minimum energy.

RevDate: 2022-06-23

Abd-Alla AM, Abo-Dahab SM, Thabet EN, et al (2022)

Peristaltic pump with heat and mass transfer of a fractional second grade fluid through porous medium inside a tube.

Scientific reports, 12(1):10608.

In magnetic resonance imaging (MRI), this MRI is used for the diagnosis of the brain. The dynamic of these particles occurs under the action of the peristaltic waves generated on the flexible walls of the brain. Studying such fluid flow of a Fractional Second-Grade under this action is therefore useful in treating tissues of cancer. This paper deals with a theoretical investigation of the interaction of heat and mass transfer in the peristaltic flow of a magnetic field fractional second-grade fluid through a tube, under the assumption of low Reynolds number and long-wavelength. The analytical solution to a problem is obtained by using Caputo's definition. The effect of different physical parameters, the material constant, magnetic field, and fractional parameter on the temperature, concentration, axial velocity, pressure gradient, pressure rise, friction forces, and coefficient of heat and mass transfer are discussed with particular emphasis. The computed results are presented in graphical form. It is because the nature of heat and mass transfer coefficient is oscillatory which is following the physical expectation due to the oscillatory nature of the tube wall. It is perceived that with an increase in Hartmann number, the velocity decreases. A suitable comparison has been made with the prior results in the literature as a limiting case of the considered problem.

RevDate: 2022-06-23

Zubairova US, Kravtsova AY, Romashchenko AV, et al (2022)

Particle-Based Imaging Tools Revealing Water Flows in Maize Nodal Vascular Plexus.

Plants (Basel, Switzerland), 11(12): pii:plants11121533.

In plants, water flows are the major driving force behind growth and play a crucial role in the life cycle. To study hydrodynamics, methods based on tracking small particles inside water flows attend a special place. Thanks to these tools, it is possible to obtain information about the dynamics of the spatial distribution of the flux characteristics. In this paper, using contrast-enhanced magnetic resonance imaging (MRI), we show that gadolinium chelate, used as an MRI contrast agent, marks the structural characteristics of the xylem bundles of maize stem nodes and internodes. Supplementing MRI data, the high-precision visualization of xylem vessels by laser scanning microscopy was used to reveal the structural and dimensional characteristics of the stem vascular system. In addition, we propose the concept of using prototype "Y-type xylem vascular connection" as a model of the elementary connection of vessels within the vascular system. A Reynolds number could match the microchannel model with the real xylem vessels.

RevDate: 2022-06-16
CmpDate: 2022-06-16

Martin AR, WH Finlay (2022)

Empirical Deposition Correlations.

Journal of aerosol medicine and pulmonary drug delivery, 35(3):109-120.

Traditionally, empirical correlations for predicting respiratory tract deposition of inhaled aerosols have been developed using limited available in vivo data. More recently, advances in medical image segmentation and additive manufacturing processes have allowed researchers to conduct extensive in vitro deposition experiments in realistic replicas of the upper and central branching airways. This work has led to a collection of empirical equations for predicting regional aerosol deposition, especially in the upper, nasal and oral airways. The present section reviews empirical correlations based on both in vivo and in vitro data, which may be used to predict total and regional deposition. Equations are presented for predicting total respiratory deposition fraction, mouth-throat fraction, nasal, and nose-throat fractions for a large variety of aerosol sizes, subject age groups, and breathing maneuvers. Use of these correlations to estimate total lung deposition is also described.

RevDate: 2022-06-10

George GR, Bockelmann M, Schmalhorst L, et al (2022)

Influence of Foam Morphology on Flow and Heat Transport in a Random Packed Bed with Metallic Foam Pellets-An Investigation Using CFD.

Materials (Basel, Switzerland), 15(11): pii:ma15113754.

Open-cell metallic foams used as catalyst supports exhibit excellent transport properties. In this work, a unique application of metallic foam, as pelletized catalyst in a packed bed reactor, is examined. By using a wall-segment Computational Fluid Dynamics (CFD) setup, parametric analyses are carried out to investigate the influence of foam morphologies (cell size ϕ=0.45-3&nbsp;mm and porosity ε=0.55-0.95) and intrinsic conductivity on flow and heat transport characteristics in a slender packed bed (N=D/dp=6.78) made of cylindrical metallic foam pellets. The transport processes have been modeled using an extended version of conventional particle-resolved CFD, i.e., flow and energy in inter-particle spaces are fully resolved, whereas the porous-media model is used for the effective transport processes inside highly-porous foam pellets. Simulation inputs include the processing parameters relevant to Steam Methane Reforming (SMR), analyzed for low (Rep~100) and high (Rep~5000) flow regimes. The effect of foam morphologies on packed beds has shown that the desired requirements contradict each other, i.e., an increase in cell size and porosity favors the reduction in pressure drop, but, it reduces the heat transfer efficiency. A design study is also conducted to find the optimum foam morphology of a cylindrical foam pellet at a higher Rep~5000, which yields ϕ = 0.45, ε = 0.8. Suitable correlations to predict the friction factor and the overall heat transfer coefficient in a foam-packed bed have been presented, which consider the effect of different foam morphologies over a range of particle Reynolds number, 100≤Rep≤5000.

RevDate: 2022-06-08

Castro JM, Y Feisel (2022)

Eruption of ultralow-viscosity basanite magma at Cumbre Vieja, La Palma, Canary Islands.

Nature communications, 13(1):3174.

The viscosity of magma exerts control on all aspects of its migration through the crust to eruption. This was particularly true for the 2021 eruption of Cumbre Vieja (La Palma), which produced exceptionally fast and fluid lava at high discharge rates. We have performed concentric cylinder experiments to determine the effective viscosities of the Cumbre Vieja magma, while accounting for its chemistry, crystallinity, and temperature. Here we show that this event produced a nepheline-normative basanite with the lowest viscosity of historical basaltic eruptions, exhibiting values of less than 10 to about 160 Pa s within eruption temperatures of ~1200 to ~1150 °C. The magma's low viscosity was responsible for many eruptive phenomena that lead to particularly impactful events, including high-Reynolds number turbulent flow and supercritical states. Increases in viscosity due to crystallization-induced melt differentiation were subdued in this eruption, due in part to subtle degrees of silica enrichment in alkaline magma.

RevDate: 2022-06-06

Ruszczyk M, Webster DR, J Yen (2022)

Trends in Stroke Kinematics, Reynolds Number, and Swimming Mode in Shrimp-Like Organisms.

Integrative and comparative biology pii:6602354 [Epub ahead of print].

Metachronal propulsion is commonly seen in organisms with the caridoid facies body plan, i.e. shrimp-like organisms, as they beat their pleopods in an adlocomotory sequence. These organisms exist across length scales ranging several orders of Reynolds number magnitude, from 10 to 104, during locomotion. Further, by altering their stroke kinematics, these organisms achieve three distinct swimming modes. To better understand the relationship between Reynolds number, stroke kinematics, and resulting swimming mode, Euphausia pacifica stroke kinematics were quantified using high-speed digital recordings and compared to the results for the larger E. superba. Euphausia pacifica consistently operate with a greater beat frequency and smaller stroke amplitude than E. superba for each swimming mode, suggesting that length scale may affect the kinematics needed to achieve similar swimming modes. To expand on this observation, these euphausiid data are used in combination with previously-published stroke kinematics from mysids and stomatopods to identify broad trends across swimming mode and length scale in metachrony. Principal component analysis (PCA) reveals trends in stroke kinematics and Reynolds number as well as the variation among taxonomic order. Overall, larger beat frequencies, stroke amplitudes, between-cycle phase lags, and Reynolds numbers are more representative of the fast forward swimming mode compared to the slower hovering mode. Additionally, each species has a unique combination of kinematics that result in metachrony, indicating that there are other factors, perhaps morphological, which affect the overall metachronal characteristics of an organism. Finally, uniform phase lag, in which the timing between power strokes of all pleopods is equal, in 5-paddle systems is achieved at different Reynolds numbers for different swimming modes, highlighting the importance of taking into consideration stroke kinematics, length scale, and the resulting swimming mode.

RevDate: 2022-06-02
CmpDate: 2022-06-02

Broadley P, Nabawy MRA, Quinn MK, et al (2022)

Dynamic experimental rigs for investigation of insect wing aerodynamics.

Journal of the Royal Society, Interface, 19(191):20210909.

This paper provides a systematic and critical review of dynamic experimental rigs used for insect wing aerodynamics research. The goal is to facilitate meaningful comparison of data from existing rigs and provide insights for designers of new rigs. The scope extends from simple one degree of freedom rotary rigs to multi degrees of freedom rigs allowing various rotation and translation motions. Experimental methods are characterized using a consistent set of parameters that allows objective comparison of different approaches. A comprehensive catalogue is presented for the tested flow conditions (assessed through Reynolds number, Rossby number and advance ratio), wing morphologies (assessed through aspect ratio, planform shape and thickness to mean chord ratio) and kinematics (assessed through motion degrees of freedom). Links are made between the type of aerodynamic characteristics being studied and the type of experimental set-up used. Rig mechanical design considerations are assessed, and the aerodynamic measurements obtained from these rigs are discussed.

RevDate: 2022-05-31

Semenov AP, Mendgaziev RI, Stoporev AS, et al (2022)

Dataset for the dimethyl sulfoxide as a novel thermodynamic inhibitor of carbon dioxide hydrate formation.

Data in brief, 42:108289 pii:S2352-3409(22)00491-7.

The temperatures and pressures of the three-phase equilibrium V-Lw-H (gas - aqueous solution - gas hydrate) were measured in the CO2 - H2O - dimethyl sulfoxide (DMSO) system at concentrations of organic solute in the aqueous phase up to 50 mass%. Measurements of CO2 hydrate equilibrium conditions were carried out using a constant volume autoclave by continuous heating at a rate of 0.1 K/h with simultaneous stirring of fluids by a four-blade agitator at 600 rpm. The equilibrium temperature and pressure of CO2 hydrate were determined for the endpoint of the hydrate dissociation in each experiment. The CO2 gas fugacity was calculated by the equation of state for carbon dioxide for the measured points. The flow regime in the autoclave during the operation of the stirring system was characterized by calculating the Reynolds number using literature data on the viscosity and density of water and DMSO aqueous solutions. We employed regression analysis to approximate the dependences of equilibrium pressure (CO2 gas fugacity) on temperature by two- and three-parameter equations. For each measured point, the value of CO2 hydrate equilibrium temperature suppression ΔTh was computed. The dependences of this quantity on CO2 gas fugacity are considered for all DMSO concentrations. The coefficients of empirical correlation describing ΔTh as a function of the DMSO mass fraction in solution and the equilibrium gas pressure are determined. This article is a co-submission with a paper [1].

RevDate: 2022-05-31

Eldesoukey A, H Hassan (2022)

Study of the performance of thermoelectric generator for waste heat recovery from chimney: impact of nanofluid-microchannel cooling system.

Environmental science and pollution research international [Epub ahead of print].

A huge number of chimneys all over the world utilized in many industrial applications and applications like restaurants, homes, etc. contribute badly on the global warming and climate change due to their waste heat. So, in this paper, the performance of thermoelectric generator (TEG) cooled by microchannel heat spreader having nanofluid and used for waste heat recovery from vertical chimney is investigated. Using heat spreader with microchannel cooling system increases the output TEG power compared to natural convection cooling system. In this paper, the impact of microchannel sizes, using nanofluid and heat spreader with different sizes on the TEG performance and cooling, is considered. Three-dimensional mathematical models including TEG, microchannel, nanofluid, and heat spreader are presented and solved by Ansys Fluent software utilizing user-defined memory, user-defined function, and user-defined scalar. All TEG effects (Joule, Seebeck, and Thomson) are considered in TEG model. Results indicate that TEG power rises with increasing the heat spreader and microchannel sizes together. Increasing microchannel and heat spreader sizes four times of TEG size raises the TEG output power by 10%. This also achieves the maximum cooling system efficiency of 88.9% and the maximum net output power. Microchannel heat spreader cooling system raises the system (TEG power-pumping power) net power by 125.2% compared to the normal channel and decreases the required cooling fluid flow rate. Utilizing copper-water and Al2O3-water nanofluids rises maximally the TEG output power by 14% and 4%, respectively; however, it increases the pumping power. Moreover, using nanofluids increases the net output power at low Reynolds number and decreases it at higher Reynolds number.

RevDate: 2022-05-30

Souayeh B, Ramesh K, Hdhiri N, et al (2022)

Heat Transfer Attributes of Gold-Silver-Blood Hybrid Nanomaterial Flow in an EMHD Peristaltic Channel with Activation Energy.

Nanomaterials (Basel, Switzerland), 12(10): pii:nano12101615.

The heat enhancement in hybrid nanofluid flow through the peristaltic mechanism has received great attention due to its occurrence in many engineering and biomedical systems, such as flow through canals, the cavity flow model and biomedicine. Therefore, the aim of the current study was to discuss the hybrid nanofluid flow in a symmetric peristaltic channel with diverse effects, such as electromagnetohydrodynamics (EMHD), activation energy, gyrotactic microorganisms and solar radiation. The equations governing this motion were simplified under the approximations of a low Reynolds number (LRN), a long wavelength (LWL) and Debye-Hückel linearization (DHL). The numerical solutions for the non-dimensional system of equations were tackled using the computational software Mathematica. The influences of diverse physical parameters on the flow and thermal characteristics were computed through pictorial interpretations. It was concluded from the results that the thermophoresis parameter and Grashof number increased the hybrid nanofluid velocity near the right wall. The nanoparticle temperature decreased with the radiation parameter and Schmidt number. The activation energy and radiation enhanced the nanoparticle volume fraction, and motile microorganisms decreased with an increase in the Peclet number and Schmidt number. The applications of the current investigation include chyme flow in the gastrointestinal tract, the control of blood flow during surgery by altering the magnetic field and novel drug delivery systems in pharmacological engineering.

RevDate: 2022-05-30

Soares A, Gomes LC, Monteiro GA, et al (2022)

Hydrodynamic Effects on Biofilm Development and Recombinant Protein Expression.

Microorganisms, 10(5): pii:microorganisms10050931.

Hydrodynamics play an important role in the rate of cell attachment and nutrient and oxygen transfer, which can affect biofilm development and the level of recombinant protein production. In the present study, the effects of different flow conditions on the development of Escherichia coli biofilms and the expression of a model recombinant protein (enhanced green fluorescent protein, eGFP) were examined. Planktonic and biofilm cells were grown at two different flow rates in a recirculating flow cell system for 7 days: 255 and 128 L h-1 (corresponding to a Reynolds number of 4600 and 2300, respectively). The fluorometric analysis showed that the specific eGFP production was higher in biofilms than in planktonic cells under both hydrodynamic conditions (3-fold higher for 255 L h-1 and 2-fold higher for 128 L h-1). In the biofilm cells, the percentage of eGFP-expressing cells was on average 52% higher at a flow rate of 255 L h-1. Furthermore, a higher plasmid copy number (PCN) was obtained for the highest flow rate for both planktonic (244 PCN/cell versus 118 PCN/cell) and biofilm cells (43 PCN/cell versus 29 PCN/cell). The results suggested that higher flow velocities promoted eGFP expression in E. coli biofilms.

RevDate: 2022-05-30

Alenezi A, Almutairi A, Alhajeri H, et al (2022)

Impact of Surface Roughness on Flow Physics and Entropy Generation in Jet Impingement Applications.

Entropy (Basel, Switzerland), 24(5): pii:e24050661.

In this paper, a numerical investigation was performed of an air jet incident that normally occurs on a horizontal heated plane. Analysis of flow physics and entropy generation due to heat and friction is included using a simple easy-to-manufacture, surface roughening element: a circular rib concentric with the air jet. This study shows how varying the locations and dimensions of the rib can deliver a favorable trade-off between entropy generation and flow parameters, such as vortex generation and heat transfer. The performance of the roughness element was tested at three different radii; R/D = 1, 1.5 and 2, where D was the jet hydraulic diameter and R was the radial distance from the geometric center. At each location, the normalized rib height (e/D) was increased from 0.019 to 0.074 based on an increment of (e/D) = 0.019. The jet-to-target distance was H/D = 6 and the jet Reynolds number (Re) ranged from 10,000 to 50,000 Re, which was obtained from the jet hydraulic diameter (D), and the jet exit velocity (U). All results are presented in the form of entropy generation due to friction and heat exchange, as well as the total entropy generated. A detailed comparison of flow physics is presented for all ribs and compared with the baseline case of a smooth surface. The results show that at higher Reynolds numbers, adding a rib of a suitable height reduced the total entropy (St) by 31% compared to the no rib case. In addition, with ribs of heights 0.019, 0.037 and 0.054, respectively, the entropy generated by friction (Sf) was greater than that due to heat exchange (Sh) by about 42%, 26% and 4%, respectively. The rib of height e/D = 0.074 produced the minimum St at R/D = 1. As for varying R/D, varying rib location and Re values had a noticeable impact on Sh, Sf and (St). Placing the rib at R/D = 1 gave the highest total entropy generation (St) followed by R/D = 1.5 for all Re. Finally, the Bejan number increased as both rib height and rib location increased.

RevDate: 2022-05-30

Dressler L, Nicolai H, Agrebi S, et al (2022)

Computation of Entropy Production in Stratified Flames Based on Chemistry Tabulation and an Eulerian Transported Probability Density Function Approach.

Entropy (Basel, Switzerland), 24(5): pii:e24050615.

This contribution presents a straightforward strategy to investigate the entropy production in stratified premixed flames. The modeling approach is grounded on a chemistry tabulation strategy, large eddy simulation, and the Eulerian stochastic field method. This enables a combination of a detailed representation of the chemistry with an advanced model for the turbulence chemistry interaction, which is crucial to compute the various sources of exergy losses in combustion systems. First, using detailed reaction kinetic reference simulations in a simplified laminar stratified premixed flame, it is demonstrated that the tabulated chemistry is a suitable approach to compute the various sources of irreversibilities. Thereafter, the effects of the operating conditions on the entropy production are investigated. For this purpose, two operating conditions of the Darmstadt stratified burner with varying levels of shear have been considered. The investigations reveal that the contribution to the entropy production through mixing emerging from the chemical reaction is much larger than the one caused by the stratification. Moreover, it is shown that a stronger shear, realized through a larger Reynolds number, yields higher entropy production through heat, mixing and viscous dissipation and reduces the share by chemical reaction to the total entropy generated.

RevDate: 2022-05-30

Li H, MRA Nabawy (2022)

Wing Planform Effect on the Aerodynamics of Insect Wings.

Insects, 13(5): pii:insects13050459.

This study investigates the effect of wing planform shape on the aerodynamic performance of insect wings by numerically solving the incompressible Navier-Stokes equations. We define the wing planforms using a beta-function distribution and employ kinematics representative of normal hovering flight. In particular, we use three primary parameters to describe the planform geometry: aspect ratio, radial centroid location, and wing root offset. The force coefficients, flow structures, and aerodynamic efficiency for different wing planforms at a Reynolds number of 100 are evaluated. It is found that the wing with the lowest aspect ratio of 1.5 results in the highest peaks of lift and drag coefficients during stroke reversals, whereas the higher aspect ratio wings produce higher lift and drag coefficients during mid half-stroke translation. For the wings considered, the leading-edge vortex detachment is found to be approximately at a location that is 3.5-5 mean chord lengths from the wing center of rotation for all aspect ratios and root offsets investigated. Consequently, the detachment area increases with the increase of aspect ratio and root offset, resulting in reduced aerodynamic coefficients. The radial centroid location is found to influence the local flow evolution time, and this results in earlier formation/detachment of the leading-edge vortex for wings with a smaller radial centroid location. Overall, the best performance, when considering both average lift coefficient and efficiency, is found at the intermediate aspect ratios of 4.5-6; increasing the centroid location mainly increases efficiency; and increasing the root offset leads to a decreased average lift coefficient whilst leading to relatively small variations in aerodynamic efficiency for most aspect ratios.

RevDate: 2022-06-10

Huang F, Noël R, Berg P, et al (2022)

Simulation of the FDA nozzle benchmark: A lattice Boltzmann study.

Computer methods and programs in biomedicine, 221:106863 pii:S0169-2607(22)00245-0 [Epub ahead of print].

BACKGROUND AND OBJECTIVE: Contrary to flows in small intracranial vessels, many blood flow configurations such as those found in aortic vessels and aneurysms involve larger Reynolds numbers and, therefore, transitional or turbulent conditions. Dealing with such systems require both robust and efficient numerical methods.

METHODS: We assess here the performance of a lattice Boltzmann solver with full Hermite expansion of the equilibrium and central Hermite moments collision operator at higher Reynolds numbers, especially for under-resolved simulations. To that end the food and drug administration's benchmark nozzle is considered at three different Reynolds numbers covering all regimes: (1) laminar at a Reynolds number of 500, (2) transitional at a Reynolds number of 3500, and (3) low-level turbulence at a Reynolds number of 6500.

RESULTS: The lattice Boltzmann results are compared with previously published inter-laboratory experimental data obtained by particle image velocimetry. Our results show good agreement with the experimental measurements throughout the nozzle, demonstrating the good performance of the solver even in under-resolved simulations.

CONCLUSION: In this manner, fast but sufficiently accurate numerical predictions can be achieved for flow configurations of practical interest regarding medical applications.

RevDate: 2022-06-06

Sharma S, Jain S, Saha A, et al (2022)

Evaporation dynamics of a surrogate respiratory droplet in a vortical environment.

Journal of colloid and interface science, 623:541-551 pii:S0021-9797(22)00845-1 [Epub ahead of print].

HYPOTHESIS: Vortex droplet interaction is crucial for understanding the route of disease transmission through expiratory jet where several such embedded droplets continuously interact with vortical structures of different strengths and sizes.

EXPERIMENTS: A train of vortex rings with different vortex strength, quantified with vortex Reynolds number (Re'=0,53,221,297) are made to interact with an isolated levitated droplet, and the evolution dynamics is captured using shadowgraphy, particle image velocimetry (PIV), and backlight imaging technique. NaCl-DI water solution of 0, 1, 10 and 20 wt% concentrations are used as test fluids for the droplet.

FINDINGS: The results show the dependence of evaporation characteristics on vortex strength, while the crystallization dynamics was found to be independent of it. A reduction of 12.23% and 14.6% in evaporation time was seen in case of de-ionized (DI) water and 1% wt NaCl solution respectively in presence of vortex ring train at Re'=221. In contrast to this, a minimal reduction in evaporation time (0.6% and 0.9% for DI water and 1% wt NaCl solution, respectively) is observed when Re' is increased from 221 to 297. The mechanisms for evaporation time reduction due to enhancement of convective heat and mass transfer from the droplet and shearing away of vapor layer by vortex ring interaction are discussed in this work.

RevDate: 2022-05-23

Karmveer , Kumar Gupta N, Siddiqui MIH, et al (2022)

The Effect of Roughness in Absorbing Materials on Solar Air Heater Performance.

Materials (Basel, Switzerland), 15(9): pii:ma15093088.

Artificial roughness on the absorber of the solar air heater (SAH) is considered to be the best passive technology for performance improvement. The roughened SAHs perform better in comparison to conventional SAHs under the same operational conditions, with some penalty of higher pumping power requirements. Thermo-hydraulic performance, based on effective efficiency, is much more appropriate to design roughened SAH, as it considers both the requirement of pumping power and useful heat gain. The shape, size, and arrangement of artificial roughness are the most important factors for the performance optimization of SAHs. The parameters of artificial roughness and operating parameters, such as the Reynolds number (Re), temperature rise parameter (ΔT/I) and insolation (I) show a combined effect on the performance of SAH. In this case study, various performance parameters of SAH have been evaluated to show the effect of distinct artificial roughness, investigated previously. Therefore, thermal efficiency, thermal efficiency improvement factor (TEIF) and the effective efficiency of various roughened absorbers of SAH have been predicted. As a result, thermal and effective efficiencies strongly depend on the roughness parameter, Re and ΔT/I. Staggered, broken arc hybrid-rib roughness shows a higher value of TEIF, thermal and effective efficiencies consistently among all other distinct roughness geometries for the ascending values of ΔT/I. This roughness shows the maximum value of effective efficiency equals 74.63% at a ΔT/I = 0.01 K·m2/W. The unique combination of parameters p/e = 10, e/Dh = 0.043 and α = 60° are observed for best performance at a ΔT/I higher than 0.00789 K·m2/W.

RevDate: 2022-05-23

Salem S, K Fraňa (2022)

A Wind Tunnel Study of the Flow-Induced Vibrations of a Cylindrical Piezoelectric Transducer.

Sensors (Basel, Switzerland), 22(9):.

Piezoelectric transducers are used as a sensing device to study the fluids' motion. Moreover, they are used as a harvester of energy of Flow-Induced Vibration (FIV). The current FIV harvesters in the literature rely on piezoelectric cantilevers coupled with a bluff body that creates flow instabilities. This paper studies the use of piezoelectric cylinders as a novel transducer in the field of fluid mechanics, where the transducer makes use of its bluff geometry to create instability. The study was based on wind tunnel measurements performed on four piezoelectric cylinders of different sizes over a speed range of 1-7 m/s. The paper looks at the variation of the generated voltage across the Reynolds number. It also compares the spectra of the generated open-circuit voltage to the turbulence spectra features known from the literature.

RevDate: 2022-05-23

Funatani S, Tsukamoto Y, K Toriyama (2022)

Temperature Measurement of Hot Airflow Using Ultra-Fine Thermo-Sensitive Fluorescent Wires.

Sensors (Basel, Switzerland), 22(9):.

In this paper, we propose a temperature measurement method that uses ultrafine fluorescent wires to reduce the wire diameter to a much lesser extent than a thermocouple. This is possible because its structure is simple and any material can be used for the wire. Hence, ultrafine wires with a Reynolds number of less than 1.0 can be selected. Ultra-fine wires less than 50 µm in diameter were set in the test volume. The wire surfaces were coated with fluorescent paint. The test volume was illuminated using an ultraviolet light-emitting diode. The paint emits very tiny, orange-colored fluorescent light with an intensity that changes with the temperature of the atmosphere. The experimental results showed that the heating/cooling layers were well visualized and the temperature field was well analyzed.

RevDate: 2022-05-20

Wang G, Fei L, KH Luo (2022)

Unified lattice Boltzmann method with improved schemes for multiphase flow simulation: Application to droplet dynamics under realistic conditions.

Physical review. E, 105(4-2):045314.

As a powerful mesoscale approach, the lattice Boltzmann method (LBM) has been widely used for the numerical study of complex multiphase flows. Recently, Luo et al. [Philos. Trans. R. Soc. A: Math. Phys. Eng. Sci. 379, 20200397 (2021)10.1098/rsta.2020.0397] proposed a unified lattice Boltzmann method (ULBM) to integrate the widely used lattice Boltzmann collision operators into a unified framework. In this study, we incorporate additional features into this ULBM in order to simulate multiphase flow under realistic conditions. A nonorthogonal moment set [Fei et al., Phys. Rev. E 97, 053309 (2018)10.1103/PhysRevE.97.053309] and the entropic-multi-relaxation-time (KBC) lattice Boltzmann model are used to construct the collision operator. An extended combined pseudopotential model is proposed to realize multiphase flow simulation at high-density ratio with tunable surface tension over a wide range. The numerical results indicate that the improved ULBM can significantly decrease the spurious velocities and adjust the surface tension without appreciably changing the density ratio. The ULBM is validated through reproducing various droplet dynamics experiments, such as binary droplet collision and droplet impingement on superhydrophobic surfaces. Finally, the extended ULBM is applied to complex droplet dynamics, including droplet pancake bouncing and droplet splashing. The maximum Weber number and Reynolds number in the simulation reach 800 and 7200, respectively, at a density ratio of 1000. The study demonstrates the generality and versatility of ULBM for incorporating schemes to tackle challenging multiphase problems.

RevDate: 2022-05-20

Verma S, A Hemmati (2022)

Route to transition in propulsive performance of oscillating foil.

Physical review. E, 105(4-2):045102.

Transition in the propulsive performance and vortex synchronization of an oscillating foil in a combined heaving and pitching motion is numerically investigated at a range of reduced frequencies (0.16 ≤f^{*}≤ 0.64), phase offsets (0^{∘} ≤ϕ≤ 315^{∘}), and Reynolds number (1000≤Re≤16000). Focusing on the common case of Re=1000, the drag to thrust transition is identified on a ϕ-f^{*} phase map. Here, the range of 90^{∘} ≤ϕ≤ 225^{∘} depicted a drag-dominated regime for increasing reduced frequency. However, thrust-dominated regimes were observed for ϕ< 90^{∘} and ϕ> 225^{∘}, where increasing the reduced frequency led to an increased thrust production. The isoline-depicting drag-thrust boundary was further observed to coincide with transitions in the characteristic near-wake modes with increasing reduced frequency, which ranged from 2P+2S to 2P and reverse von Kármán modes. However, evaluation of the wake with changing phase offsets at individual reduced frequencies only depicted effects on the spatial configuration of the vortex structures, while the number of vortices shed in one oscillation period was unchanged. The existence of similar wake modes with significantly different propulsive performance clearly suggests that transitions of the wake topology may not always be a reliable tool for understanding propulsive mechanisms of fish swimming or development of underwater propulsion systems. We further assessed a possible route to drag production via investigation into the mean velocity fields at increasing phase offset and at intermediate reduced frequencies ranging from 0.24 to 0.40. This revealed bifurcation of a velocity jet behind the foil on account of the wake topology and dynamics of shed vortex structures. The changes posed by increasing ϕ on wake structure interactions further hints at potential mechanisms that limit the achievement of optimum efficiency in underwater locomotion.

RevDate: 2022-06-01

Ge M, Sun C, Zhang G, et al (2022)

Combined suppression effects on hydrodynamic cavitation performance in Venturi-type reactor for process intensification.

Ultrasonics sonochemistry, 86:106035.

Hydrodynamic cavitation is an emerging intensification technology in water treatment or chemical processing, and Venturi-type cavitation reactors exhibit advantages for industrial-scale production. The effects of temperature on hydrodynamic cavitating flows are investigated to find the optimum reaction conditions enhancing cavitating treatment intensity. Results show that the cavitation performance, including the cavitation intensity and cavitation unsteady behavior, is influenced by (1) cavitation number σ (the pressure difference affecting the vaporization process), (2) Reynolds number Re (the inertial/viscous ratio affecting the bubble size and liquid-vapor interface area), and (3) thermodynamic parameter Σ (the thermal effect affecting the temperature drop). With increasing temperature, the cavitation length first increases and then decreases, with a cavitation intensity peak at the transition temperature of 58 °C. With the growth of cavitation extent, the cavity-shedding regimes tend to transition from the attached sheet cavity to the periodic cloud cavity, and the vapor volume fluctuating frequency decreases accordingly. A combined suppression parameter (CSP) is provided to predict that, with increasing CSP value, the cavitation intensity can be decreased. Recommendations are given that working under the low-CSP range (55-60 °C) could enhance the intensification of the cavitation process.

RevDate: 2022-06-10

Cherkaoui I, Bettaibi S, Barkaoui A, et al (2022)

Magnetohydrodynamic blood flow study in stenotic coronary artery using lattice Boltzmann method.

Computer methods and programs in biomedicine, 221:106850 pii:S0169-2607(22)00232-2 [Epub ahead of print].

BACKGROUND AND OBJECTIVE: Cardiovascular diseases such as atherosclerosis are the first engender of death in the world. The malfunctioning of cardiovascular system is attributed mainly to hemodynamics. However, blood magnetic properties are of major haemodynamic interest, with significant clinical applications. The aim of this work is to study numerically the effect of high magnetic field on blood flow in stenotic artery.

METHODS: In this paper, a double population D2Q9 lattice Boltzmann model is proposed. Velocity and magnetic field are both solved using Lattice Boltzmann method with single relaxation time. Blood is considered homogeneous and Newtonian bio-magnetic fluid. The results of the proposed model are compared and validated by recent numerical and experimental studies in the literature and show good agreement. In this study, simulations are carried out for both hydrodynamics and magneto-hydrodynamics. For the magneto-hydrodynamic case, five values of Hartmann number of 10, 30, 50, 75 and 100 at Reynolds number of 400, 600 and 800 are investigated Results: The results show that velocity and recirculation zone increase with the increase of the degree of stenosis and Reynolds number. In addition, a considerable decrease in velocity, recirculation zones and pressure drop across the stenotic artery is noticed with the increase of Hartmann number.

CONCLUSION: The suggested model is found to be effective and accurate in the treatment of magneto-hydrodynamic blood flow in stenotic artery. The found results can be used by clinicians in the treatment of certain cardiovascular disorders and in regulating blood flow movement, especially during surgical procedures.

RevDate: 2022-05-16

Chew SH, Hoi SM, Tran MV, et al (2022)

Partially-covered fractal induced turbulence on fins thermal dissipation.

Scientific reports, 12(1):7861.

The impacts of partially-covered fractal grids induced turbulence on the forced convective heat transfer across plate-fin heat sink at Reynolds number ReDh = 22.0 × 103 were numerically and experimentally investigated. Results showed that partially covered grids rendered a higher thermal dissipation performance, with partially-covered square fractal grid (PCSFG) registering an outstanding increase of 43% in Nusselt number relative to the no grid configuration. The analyzation via an in-house developed single particle tracking velocimetry (SPTV) system displayed the findings of unique "Turbulence Annulus" formation, which provided a small degree of predictivity in the periodic annulus oscillations. Further assessments on PCSFG revealed the preferred inter-fin flow dynamics of (i) high flow velocity, (ii) strong turbulence intensity, (iii) vigorous flow fluctuations, (iv) small turbulence length scale, and (v) heightened decelerated flow events. These features stemmed from the coupling effects of multilength-scale fractal bar thicknesses in generating a veracity of eddy sizes, and a vertical segmentation producing heightened mass flow rate while inducing favourable wake-flow structures to penetrate inter-fin regions. Teeming effects of such energetic eddies within plate-fin array unveiled a powerful vortex shedding effect, with PCSFG achieving fluctuation frequency f = 18.5 Hz close to an optimal magnitude. The coaction of such traits limits the growth of fin boundary layers, providing superior thermal transfer capabilities which benefits the community in developing for higher efficiency heat transfer systems.

RevDate: 2022-05-16

Qiao Y, Luo K, J Fan (2022)

Computational Prediction of Thrombosis in Food and Drug Administration's Benchmark Nozzle.

Frontiers in physiology, 13:867613.

Thrombosis seriously threatens human cardiovascular health and the safe operation of medical devices. The Food and Drug Administration's (FDA) benchmark nozzle model was designed to include the typical structure of medical devices. However, the thrombosis in the FDA nozzle has yet not been investigated. The objective of this study is to predict the thrombus formation process in the idealized medical device by coupling computational fluid dynamics and a macroscopic hemodynamic-based thrombus model. We developed the hemodynamic-based thrombus model by considering the effect of platelet consumption. The thrombus model was quantitatively validated by referring to the latest thrombosis experiment, which was performed in a backward-facing step with human blood flow. The same setup was applied in the FDA nozzle to simulate the thrombus formation process. The thrombus shaped like a ring was firstly observed in the FDA benchmark nozzle. Subsequently, the accuracy of the shear-stress transport turbulence model was confirmed in different turbulent flow conditions. Five scenarios with different Reynolds numbers were carried out. We found that turbulence could change the shape of centrosymmetric thrombus to axisymmetric and high Reynolds number blood flow would delay or even prevent thrombosis. Overall, the present study reports the thrombosis process in the FDA benchmark nozzle using the numerical simulation method, and the primary findings may shed light on the effect of turbulence on thrombosis.

RevDate: 2022-05-13

Gil A, Navarro R, Quintero P, et al (2022)

CFD analysis of the HVAD's hemodynamic performance and blood damage with insight into gap clearance.

Biomechanics and modeling in mechanobiology [Epub ahead of print].

Mechanical circulatory support using ventricular assist devices has become commonplace in the treatment of patients suffering from advanced stages of heart failure. While blood damage generated by these devices has been evaluated in depth, their hemodynamic performance has been investigated much less. This work presents the analysis of the complete operating map of a left ventricular assist device, in terms of pressure head, power and efficiency. Further investigation into its hemocompatibility is included as well. To achieve these objectives, computational fluid dynamics simulations of a centrifugal blood pump with a wide-blade impeller were performed. Several conditions were considered by varying the rotational speed and volumetric flow rate. Regarding the device's hemocompatibility, blood damage was evaluated by means of the hemolysis index. By relating the hemocompatibility of the device to its hemodynamic performance, the results have demonstrated that the highest hemolysis occurs at low flow rates, corresponding to operating conditions of low efficiency. Both performance and hemocompatibility are affected by the gap clearance. An innovative investigation into the influence of this design parameter has yielded decreased efficiencies and increased hemolysis as the gap clearance is reduced. As a further novelty, pump operating maps were non-dimensionalized to highlight the influence of Reynolds number, which allows their application to any working condition. The pump's operating range places it in the transitional regime between laminar and turbulent, leading to enhanced efficiency for the highest Reynolds number.

RevDate: 2022-06-03
CmpDate: 2022-06-03

Sander A, Petračić A, Zokić I, et al (2022)

Scaling up extractive deacidification of waste cooking oil.

Journal of environmental management, 316:115222.

Biodiesel produced from waste feedstocks can play a significant role in fighting climate change, improperly disposed waste and growing energy demand. Waste feedstocks such as used cooking oil have a great potential for energy production. However, they often have to be purified from free fatty acids prior to biodiesel production. Extractive deacidification with deep eutectic solvents is a promising alternative to conventional purification methods. To evaluate the process of extractive deacidification of waste cooking oil, a full set of physical, hydrodynamic and kinetic data were experimentally determined on a laboratory scale. Hydrodynamic and kinetic experiments were performed in three geometrically similar jacketed agitated vessels. Vessels were equipped with axial flow impeller (four pitched blade impeller). Physical properties (density, viscosity and surface tension) were experimentally determined. Preliminary hydrodynamic experiments involved several model systems without mass transfer. As a result, correlation between power number and Reynolds number as well as scale-up criterion was developed. Obtained dependencies were correlated with the physical properties. Mixing intensity for achieving complete dispersion was determined. Second stage of investigation involved two sets of experiments, hydrodynamic and kinetic, with interphase mass transfer (the extraction of free fatty acids from waste cooking oil with deep eutectic solvent, potassium carbonate:ethylene glycol, 1:10). Obtained results enabled understanding interphase mass transfer and prediction of mass transfer coefficient from the derived dimensionless correlations. The values of volumetric mass transfer coefficients were smaller for the dispersed phase, indicating that the prevailing mass transfer resistance was within the droplets. The working hypothesis was that the same process result should be achieved at the same dispersion rate, and that hypothesis was confirmed - at all scales extraction efficiency was 97.9 ± 0.1%.

RevDate: 2022-05-16

Callaham JL, Rigas G, Loiseau JC, et al (2022)

An empirical mean-field model of symmetry-breaking in a turbulent wake.

Science advances, 8(19):eabm4786.

Improved turbulence modeling remains a major open problem in mathematical physics. Turbulence is notoriously challenging, in part due to its multiscale nature and the fact that large-scale coherent structures cannot be disentangled from small-scale fluctuations. This closure problem is emblematic of a greater challenge in complex systems, where coarse-graining and statistical mechanics descriptions break down. This work demonstrates an alternative data-driven modeling approach to learn nonlinear models of the coherent structures, approximating turbulent fluctuations as state-dependent stochastic forcing. We demonstrate this approach on a high-Reynolds number turbulent wake experiment, showing that our model reproduces empirical power spectra and probability distributions. The model is interpretable, providing insights into the physical mechanisms underlying the symmetry-breaking behavior in the wake. This work suggests a path toward low-dimensional models of globally unstable turbulent flows from experimental measurements, with broad implications for other multiscale systems.

RevDate: 2022-05-26
CmpDate: 2022-05-26

Zhang R, Toonder JD, PR Onck (2022)

Metachronal patterns by magnetically-programmable artificial cilia surfaces for low Reynolds number fluid transport and mixing.

Soft matter, 18(20):3902-3909.

Motile cilia can produce net fluid flows at low Reynolds number because of their asymmetric motion and metachrony of collective beating. Mimicking this with artificial cilia can find application in microfluidic devices for fluid transport and mixing. Here, we study the metachronal beating of nonidentical, magnetically-programmed artificial cilia whose individual non-reciprocal motion and collective metachronal beating pattern can be independently controlled. We use a finite element method that accounts for magnetic forces, cilia deformation and fluid flow in a fully coupled manner. Mimicking biological cilia, we study magnetic cilia subject to a full range of metachronal driving patterns, including antiplectic, symplectic, laeoplectic and diaplectic waves. We analyse the induced primary flow, secondary flow and mixing rate as a function of the phase lag between cilia and explore the underlying physical mechanism. Our results show that shielding effects between neighboring cilia lead to a primary flow that is larger for antiplectic than for symplectic metachronal waves. The secondary flow can be fully explained by the propagation direction of the metachronal wave. Finally, we show that the mixing rate can be strongly enhanced by laeoplectic and diaplectic metachrony resulting in large velocity gradients and vortex-like flow patterns.

RevDate: 2022-05-09

Gomé S, Tuckerman LS, D Barkley (2022)

Extreme events in transitional turbulence.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 380(2226):20210036.

Transitional localized turbulence in shear flows is known to either decay to an absorbing laminar state or to proliferate via splitting. The average passage times from one state to the other depend super-exponentially on the Reynolds number and lead to a crossing Reynolds number above which proliferation is more likely than decay. In this paper, we apply a rare-event algorithm, Adaptative Multilevel Splitting, to the deterministic Navier-Stokes equations to study transition paths and estimate large passage times in channel flow more efficiently than direct simulations. We establish a connection with extreme value distributions and show that transition between states is mediated by a regime that is self-similar with the Reynolds number. The super-exponential variation of the passage times is linked to the Reynolds number dependence of the parameters of the extreme value distribution. Finally, motivated by instantons from Large Deviation theory, we show that decay or splitting events approach a most-probable pathway. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.

RevDate: 2022-05-09

Drivas TD (2022)

Self-regularization in turbulence from the Kolmogorov 4/5-law and alignment.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 380(2226):20210033.

A defining feature of three-dimensional hydrodynamic turbulence is that the rate of energy dissipation is bounded away from zero as viscosity is decreased (Reynolds number increased). This phenomenon-anomalous dissipation-is sometimes called the 'zeroth law of turbulence' as it underpins many celebrated theoretical predictions. Another robust feature observed in turbulence is that velocity structure functions [Formula: see text] exhibit persistent power-law scaling in the inertial range, namely [Formula: see text] for exponents [Formula: see text] over an ever increasing (with Reynolds) range of scales. This behaviour indicates that the velocity field retains some fractional differentiability uniformly in the Reynolds number. The Kolmogorov 1941 theory of turbulence predicts that [Formula: see text] for all [Formula: see text] and Onsager's 1949 theory establishes the requirement that [Formula: see text] for [Formula: see text] for consistency with the zeroth law. Empirically, [Formula: see text] and [Formula: see text], suggesting that turbulent Navier-Stokes solutions approximate dissipative weak solutions of the Euler equations possessing (nearly) the minimal degree of singularity required to sustain anomalous dissipation. In this note, we adopt an experimentally supported hypothesis on the anti-alignment of velocity increments with their separation vectors and demonstrate that the inertial dissipation provides a regularization mechanism via the Kolmogorov 4/5-law. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.

RevDate: 2022-05-09

Parente E, Farano M, Robinet JC, et al (2022)

Continuing invariant solutions towards the turbulent flow.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 380(2226):20210031.

A new mathematical framework is proposed for characterizing the coherent motion of fluctuations around a mean turbulent channel flow. We search for statistically invariant coherent solutions of the unsteady Reynolds-averaged Navier-Stokes equations written in a perturbative form with respect to the turbulent mean flow, using a suitable approximation of the Reynolds stress tensor. This is achieved by setting up a continuation procedure of known solutions of the perturbative Navier-Stokes equations, based on the continuous increase of the turbulent eddy viscosity towards its turbulent value. The recovered solutions, being sustained only in the presence of the Reynolds stress tensor, are representative of the statistically coherent motion of turbulent flows. For small friction Reynolds number and/or domain size, the statistically invariant motion is almost identical to the corresponding invariant solution of the Navier-Stokes equations. Whereas, for sufficiently large friction number and/or domain size, it considerably departs from the starting invariant solution of the Navier-Stokes equations, presenting spatial structures, main wavelengths and scaling very close to those characterizing both large- and small-scale motion of turbulent channel flows. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.

RevDate: 2022-05-10

Tretola G, K Vogiatzaki (2022)

Unveiling the dynamics of ultra high velocity droplet impact on solid surfaces.

Scientific reports, 12(1):7416.

The impact of a liquid droplet onto a solid surface is a phenomenon present in a wide range of natural processes and technological applications. In this study, we focus on impact conditions characterised by ultra high velocities (up to 500 m/s), to investigate-for the first time-how the impact dynamics change when the compressibility of the liquid in the droplet is no longer negligible. A water droplet impacting a dry substrate at four different velocities, from 50 to 500 m/s, is simulated. Such conditions are particularly relevant to aviation as well as industrial gas turbine engine risk management. Thus, numerical investigations as the one we present here provide a powerful tool to analyse the process. We find that increasing the impact velocity changes the flow field within and outside the droplet the moment that the compressibility can no longer be neglected, with the rise of pressure fronts in both regions. Increasing the impact velocity, the compressibility affects also the lamella formed and changes its ejection velocity observed over time (and thus the wetting behaviour) when the region shift from incompressible to compressible. Moreover, it is found that the maximum pressure observed at the wall during the impact is located at the corner of the impact, where the lamella is ejected, not in the centre, and it is influenced by the initial velocity. To predict the maximum pressure experienced by the surface during the high velocity impact, we propose a correlation based on the initial Weber and Reynolds number of the droplet. The complexity and the scales of the dynamics involved in the ultra-high velocity impact is limiting the experimental and analytical studies. To the best of our knowledge there are no experimental data currently available at such conditions. In this study, through numerical simulations, new insights about the impact dynamics at such conditions are provided.

RevDate: 2022-05-23

D'Adamo J, Collaud M, Sosa R, et al (2022)

Wake and aeroelasticity of a flexible pitching foil.

Bioinspiration & biomimetics, 17(4):.

A flexible foil undergoing pitching oscillations is studied experimentally in a wind tunnel with different imposed free stream velocities. The chord-based Reynolds number is in the range 1600-4000, such that the dynamics of the system is governed by inertial forces and the wake behind the foil exhibits the reverse Bénard-von Kármán vortex street characteristic of flapping-based propulsion. Particle image velocimetry (PIV) measurements are performed to examine the flow around the foil, whilst the deformation of the foil is also tracked. The first natural frequency of vibration of the foil is within the range of flapping frequencies explored, determining a strongly-coupled dynamics between the elastic foil deformation and the vortex shedding. Cluster-based reduced order modelling is applied on the PIV data in order to identify the coherent flow structures. Analysing the foil kinematics and using a control-volume calculation of the average drag forces from the corresponding velocity fields, we determine the optimal flapping configurations for thrust generation. We show that propulsive force peaks occur at dimensionless frequencies shifted with respect to the elastic resonances that are marked by maximum trailing edge oscillation amplitudes. The thrust peaks are better explained by a wake resonance, which we examine using the tools of classic hydrodynamic stability on the mean propulsive jet profiles.

RevDate: 2022-05-09

Schindler F, Eckert S, Zürner T, et al (2022)

Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection.

Physical review letters, 128(16):164501.

The large-scale flow structure and the turbulent transfer of heat and momentum are directly measured in highly turbulent liquid metal convection experiments for Rayleigh numbers varied between 4×10^{5} and ≤5×10^{9} and Prandtl numbers of 0.025≤Pr≤0.033. Our measurements are performed in two cylindrical samples of aspect ratios Γ=diameter/height=0.5 and 1 filled with the eutectic alloy GaInSn. The reconstruction of the three-dimensional flow pattern by 17 ultrasound Doppler velocimetry sensors detecting the velocity profiles along their beam lines in different planes reveals a clear breakdown of coherence of the large-scale circulation for Γ=0.5. As a consequence, the scaling laws for heat and momentum transfer inherit a dependence on the aspect ratio. We show that this breakdown of coherence is accompanied with a reduction of the Reynolds number Re. The scaling exponent β of the power law Nu∝Ra^{β} crosses eventually over from β=0.221 to 0.124 when the liquid metal flow at Γ=0.5 reaches Ra≳2×10^{8} and the coherent large-scale flow is completely collapsed.

RevDate: 2022-05-18

Fei L, Qin F, Zhao J, et al (2022)

Pore-Scale Study on Convective Drying of Porous Media.

Langmuir : the ACS journal of surfaces and colloids, 38(19):6023-6035.

In this work, a numerical model for isothermal liquid-vapor phase change (evaporation) of the two-component air-water system is proposed based on the pseudopotential lattice Boltzmann method. Through the Chapman-Enskog multiscale analysis, we show that the model can correctly recover the macroscopic governing equations of the multicomponent multiphase system with a built-in binary diffusion mechanism. The model is verified based on the two-component Stefan problem where the measured binary diffusivity is consistent with theoretical analysis. The model is then applied to convective drying of a dual-porosity porous medium at the pore scale. The simulation captures a classical transition in the drying process of porous media, from the constant rate period (CRP, first phase) showing significant capillary pumping from large to small pores, to the falling rate period (FRP, second phase) with the liquid front receding in small pores. It is found that, in the CRP, the evaporation rate increases with the inflow Reynolds number (Re), while in the FRP, the evaporation curves almost collapse at different Res. The underlying mechanism is elucidated by introducing an effective Péclet number (Pe). It is shown that convection is dominant in the CRP and diffusion in the FRP, as evidenced by Pe > 1 and Pe < 1, respectively. We also find a log-law dependence of the average evaporation rate on the inflow Re in the CRP regime. The present work provides new insights into the drying physics of porous media and its direct modeling at the pore scale.

RevDate: 2022-05-03

Salari A, Appak-Baskoy S, Coe IR, et al (2021)

An ultrafast enzyme-free acoustic technique for detaching adhered cells in microchannels.

RSC advances, 11(52):32824-32829.

Adherent cultured cells are widely used biological tools for a variety of biochemical and biotechnology applications, including drug screening and gene expression analysis. One critical step in culturing adherent cells is the dissociation of cell monolayers into single-cell suspensions. Different enzymatic and non-enzymatic methods have been proposed for this purpose. Trypsinization, the most common enzymatic method for dislodging adhered cells, can be detrimental to cells, as it can damage cell membranes and ultimately cause cell death. Additionally, all available techniques require a prolonged treatment duration, typically on the order of minutes (5-10 min). Dissociation of cells becomes even more challenging in microfluidic devices, where, due to the nature of low Reynolds number flow and reduced mixing efficiency, multiple washing steps and prolonged trypsinization may be necessary to treat all cells. Here, we report a novel acoustofluidic method for the detachment of cells adhered onto a microchannel surface without exposing the cells to any enzymatic or non-enzymatic chemicals. This method enables a rapid (i.e., on the order of seconds), cost-effective, and easy-to-operate cell detachment strategy, yielding a detachment efficiency of ∼99% and cellular viability similar to that of the conventional trypsinization method. Also, as opposed to biochemical-based techniques (e.g., enzymatic), in our approach, cells are exposed to the dissociating agent (i.e., substrate-mediated acoustic excitation and microstreaming flow) only for as long as they remain attached to the substrate. After dissociation, the effect of acoustic excitation is reduced to microstreaming flow, therefore, minimizing unwanted effects of the dissociating agent on the cell phenotype. Additionally, our results suggest that cell excitation at acoustic powers lower than that required for complete cell detachment can potentially be employed for probing the adhesion strength of cell-substrate attachment. This novel approach can, therefore, be used for a wide range of lab-on-a-chip applications.

RevDate: 2022-05-03
CmpDate: 2022-05-03

Das A, Styslinger M, Harris DM, et al (2022)

Force and torque-free helical tail robot to study low Reynolds number micro-organism swimming.

The Review of scientific instruments, 93(4):044103.

Helical propulsion is used by many micro-organisms to swim in viscous-dominated environments. Their swimming dynamics are relatively well understood, but a detailed study of the flow fields is still needed to understand wall effects and hydrodynamic interactions among swimmers. In this letter, we describe the development of an autonomous swimming robot with a helical tail that operates in the Stokes regime. The device uses a battery-based power system with a miniature motor that imposes a rotational speed on a helical tail. The speed, direction, and activation are controlled electronically using an infrared remote control. Since the robot is about 5 cm long, we use highly viscous fluids to match the Reynolds number, Re, to be less than 0.1. Measurements of swimming speeds are conducted for a range of helical wavelengths, λ, head geometries, and rotation rates, ω. We provide comparisons of the experimental measurements with analytical predictions derived from resistive force theory. This force and torque-free neutrally buoyant swimmer mimics the swimming strategy of bacteria more closely than previously used designs and offers a lot of potential for future applications.

RevDate: 2022-05-02

Prasad V, Kulkarni SS, A Sharma (2022)

Chaotic advection in a recirculating flow: Effect of a fluid-flexible-solid interaction.

Chaos (Woodbury, N.Y.), 32(4):043122.

The present work is on laminar recirculating flow-induced deformation as well as motion of a neutrally buoyant flexible elliptical solid, resulting in Lagrangian chaos in a two-dimensional lid-driven cavity flow. Using a fully Eulerian and monolithic approach-based single-solver for the fluid flow and flexible-solid deformation, a chaotic advection study is presented for various aspect ratios β (=0.5-1.0) and a constant volume fraction Φ=10% of an elliptical solid at a constant Ericksen number Er=0.05 and Reynolds number Re=100. Our initial analysis reveals maximum chaotic advection at β=0.5 for which a comprehensive nonlinear dynamical analysis is presented. The Poincaré map revealed elliptic islands and chaotic sea in the fluid flow. Three large elliptic islands, apart from certain smaller islands, were identified near the solid. Periodic point analysis revealed the lowest order hyperbolic/elliptic periodic points to be three. Adaptive material tracking gave a physical picture of a deforming material blob revealing its exponential stretch along with steep folds and demonstrated unstable/stable manifolds corresponding to lowest order hyperbolic points. Furthermore, adaptive material tracking demonstrates heteroclinic connections and tangles in the system that confirm the existence of chaos. For the transient as compared to the periodic flow, adaptive material tracking demonstrates a larger exponential increase of the blob's interfacial area. The finite-time Lyapunov exponent field revealed attracting/repelling Lagrangian coherent structures and entrapped fluid zones. Our work demonstrates an immersed deformable solid-based onset of chaotic advection, for the first time in the literature, which is relevant to a wide range of applications.

RevDate: 2022-06-21

Akanyeti O, Di Santo V, Goerig E, et al (2022)

Fish-inspired segment models for undulatory steady swimming.

Bioinspiration & biomimetics, 17(4):.

Many aquatic animals swim by undulatory body movements and understanding the diversity of these movements could unlock the potential for designing better underwater robots. Here, we analyzed the steady swimming kinematics of a diverse group of fish species to investigate whether their undulatory movements can be represented using a series of interconnected multi-segment models, and if so, to identify the key factors driving the segment configuration of the models. Our results show that the steady swimming kinematics of fishes can be described successfully using parsimonious models, 83% of which had fewer than five segments. In these models, the anterior segments were significantly longer than the posterior segments, and there was a direct link between segment configuration and swimming kinematics, body shape, and Reynolds number. The models representing eel-like fishes with elongated bodies and fishes swimming at high Reynolds numbers had more segments and less segment length variability along the body than the models representing other fishes. These fishes recruited their anterior bodies to a greater extent, initiating the undulatory wave more anteriorly. Two shape parameters, related to axial and overall body thickness, predicted segment configuration with moderate to high success rate. We found that head morphology was a good predictor of its segment length. While there was a large variation in head segments, the length of tail segments was similar across all models. Given that fishes exhibited variable caudal fin shapes, the consistency of tail segments could be a result of an evolutionary constraint tuned for high propulsive efficiency. The bio-inspired multi-segment models presented in this study highlight the key bending points along the body and can be used to decide on the placement of actuators in fish-inspired robots, to model hydrodynamic forces in theoretical and computational studies, or for predicting muscle activation patterns during swimming.

RevDate: 2022-05-16

Hu S, Zhang J, MJ Shelley (2022)

Enhanced clamshell swimming with asymmetric beating at low Reynolds number.

Soft matter, 18(18):3605-3612.

A single flexible filament can be actuated to escape from the scallop theorem and generate net propulsion at low Reynolds number. In this work, we study the dynamics of a simple boundary-driven multi-filament swimmer, a two-arm clamshell actuated at the hinged point, using a nonlocal slender body approximation with hydrodynamic interactions. We first consider an elastic clamshell consisted of flexible filaments with intrinsic curvature, and then build segmental models consisted of rigid segments connected by different mechanical joints with different forms of response torques. The simplicity of the system allows us to fully explore the effect of various parameters on the swimming performance. Optimal included angles and elastoviscous numbers are identified. The segmental models capture the characteristic dynamics of the elastic clamshell. We further demonstrate how the swimming performance can be significantly enhanced by the asymmetric beating patterns induced by biased torques.

RevDate: 2022-04-28

Kotnurkar A, N Kallolikar (2022)

Effect of Joule heating and entropy generation on multi-slip condition of peristaltic flow of Casson nanofluid in an asymmetric channel.

Journal of biological physics [Epub ahead of print].

In the present investigation, the effect of multi-slip condition on peristaltic flow through asymmetric channel with Joule heating effect is considered. We also considered the incompressible non-Newtonian Casson nanofluid model for blood, which is electrically conducting. Second law of thermodynamics is used to examine the entropy generation. Multi-slip condition is used at the boundary of the wall and the analysis is also restricted under the low Reynolds number and long wavelength assumption. The governing equations were transformed into a non-dimensional form by using suitable terms. The reduced non-dimensional highly nonlinear partial differential equations are solved by using the Homotopy Perturbation Sumudu transformation method (HPSTM). The influence of different physical parameters on dimensionless velocity, pressure gradient, temperature, concentration and nanoparticle is graphically presented. From the results, one can understand that the Joule heating effect controls the heat transfer in the system and as the magnetic parameter is increased, there will be decay in the velocity of fluid. The outcomes of the present investigation can be applicable in examining the chyme motion in the gastrointestinal tract and controlling the blood flow during surgery. Present study shows an excellent agreement with the previously available studies in the limiting case.

RevDate: 2022-05-17
CmpDate: 2022-05-17

Liu J, Yang Z, Li M, et al (2022)

Evaluating the concrete grade-control structures built by modified fish-nest bricks in the river restoration: A lab-based case study.

Journal of environmental management, 314:115056.

Concrete grade-control structures (CGCSs) have broad application prospects in the restoration of large rivers. But there is a lack of indicators to evaluate CGCSs at laboratory study. In this study, we proposed two evaluation indicators from the perspective of the impact of CGCSs on geomorphology change and fish habitat, namely the spatial-averaged occurrence probability of sweep events near the bed and flow diversity. To verify the reasonableness of these indicators, flume experiments were conducted with CGCSs built by modified fish-nest bricks in different Reynolds number and layout condition. Data of the flow field around structures in streamwise, transverse and vertical direction was obtained and analyzed. Results of mean flow field show that large recirculation zones are found in the cavity and behind the element. The mechanism of suspended sediment deposition around CGCSs in the flow can be further clarified by combining sweep and ejection according to quadrant analysis. In the vertical direction, the ratio of sweep to total events near bed after spatial-averaged processing is found to be higher for the staggered array. According to the Shannon's entropy, water flow diversity was calculated to quantify the fish habitat. The water flow diversity index around the CGCSs is higher for the staggered. It can be concluded that the elements of CGCSs in staggered manners have a better protection for riverbed and can provide a more stable fish habitat suitability. The results anticipated by the spatial-averaged occurrence probability of sweep events near bed and flow diversity in the experiment are consistent with the result of previous research on landform change and fish habitat. The research could provide a theoretical basis for the application of CGCSs for river restoration.

RevDate: 2022-04-29

Martin E, Valeije A, Sastre F, et al (2022)

Impact of Channels Aspect Ratio on the Heat Transfer in Finned Heat Sinks with Tip Clearance.

Micromachines, 13(4):.

A 3D numerical study is used to analyze the flow topology and performance, in terms of heat transfer efficiency and required pumping power, of heat sink devices with different channel aspect-ratio in the presence of tip-clearance. Seven different channel aspect ratios AR, from 0.25 to 1.75, were analyzed. The flow Reynolds numbers Re, based on the average velocity evaluated in the device channels region, were in the range of 200 to 1000. Two different behaviors of the global Nusselt were obtained depending on the flow Reynolds number: for Re<600, the heat transfer increased with the channels aspect ratio, e.g., for Re=400, the global Nusselt number increased by 14% for configuration AR=1.75 when compared to configuration AR=0.25. For Re>600, the maximum Nusselt is obtained for the squared-channel configuration, and, for some configurations, flow destabilization to a unsteady regime appeared. For Re=700, Nusselt number reduced when compared with the squared-channel device, 11% and 2% for configurations with AR=0.25 and 1.75, respectively. Dimensionless pressure drop decreased with the aspect ratio for all cases. In the context of micro-devices, where the Reynolds number is small, these results indicate that the use of channels with high aspect-ratios is more beneficial, both in terms of thermal and dynamic efficiency.

RevDate: 2022-04-29

Ayub R, Ahmad S, Ahmad S, et al (2022)

Numerical Assessment of Dipole Interaction with the Single-Phase Nanofluid Flow in an Enclosure: A Pseudo-Transient Approach.

Materials (Basel, Switzerland), 15(8):.

Nanofluids substantially enhance the physical and thermal characteristics of the base or conducting fluids specifically when interacting with the magnetic field. Several engineering processes like geothermal energy extraction, metal casting, nuclear reactor coolers, nuclear fusion, magnetohydrodynamics flow meters, petrochemicals, and pumps incorporate magnetic field interaction with the nanofluids. On the other hand, an enhancement in heat transfer due to nanofluids is essentially required in various thermal systems. The goal of this study is to figure out that how much a magnetic field affects nanofluid flow in an enclosure because of a dipole. The nanofluid is characterized using a single-phase model, and the governing partial differential equations are computed numerically. A Pseudo time based numerical algorithm is developed to numerically solve the problem. It can be deduced that the Reynolds number and the magnetic parameter have a low effect on the Nusselt number and skin friction. The Nusselt number rises near the dipole location because of an increase in the magnetic parameter Mn and the Reynolds number Re. The imposed magnetic field alters the region of high temperature nearby the dipole, while newly generated vortices rotate in alternate directions. Furthermore, nanoparticle volume fraction causes a slight change in the skin friction while it marginally reduces the Nusselt number.

RevDate: 2022-04-24

Chandrasekaran AS, Fix AJ, DM Warsinger (2022)

Combined Membrane Dehumidification with Heat Exchangers Optimized Using CFD for High Efficiency HVAC Systems.

Membranes, 12(4):.

Traditional air conditioning systems use a significant amount of energy on dehumidification by condensing water vapor out from the air. Membrane-based air conditioning systems help overcome this problem by avoiding condensation and treating the sensible and latent loads separately, using membranes that allow water vapor transport, but not air (nitrogen and oxygen). In this work, a computational fluid dynamics (CFD) model has been developed to predict the heat and mass transfer and concentration polarization performance of a novel active membrane-based energy exchanger (AMX). The novel design is the first of its kind to integrate both vapor removal via membranes and air cooling into one device. The heat transfer results from the CFD simulations are compared with common empirical correlations for similar geometries. The performance of the AMX is studied over a broad range of operating conditions using the compared CFD model. The results show that strong tradeoffs result in optimal values for the channel length (0.6-0.8 m) and the ratio of coil diameter to channel height (~0.5). Water vapor transport is best if the flow is just past the turbulence transition around 3000-5000 Reynolds number. These trends hold over a range of conditions and dimensions.

RevDate: 2022-04-21

Torres-Saucedo OL, Morales-Cruzado B, FG Pérez-Guitérrez (2022)

Experimental determination of shear stresses on an artificial transcoelomic metastasis model using optical tweezers: A comparison with numerical simulation.

Lasers in surgery and medicine [Epub ahead of print].

BACKGROUND: One of the reported pathways of cancer spread is the transcoelomic pathway, which is understood as the spread of cancer cells in the abdominal and thoracic cavities through interstitial fluid. It has been proven that the shear stresses caused by microfluidic currents on cancer tumors in the abdominal and thoracic cavities cause the detachment of cancer cells triggering transcoelomic metastasis; however, the magnitude of shear stresses has not yet been measured experimentally.

OBJECTIVES: The objective of this study is to develop an experimental methodology using optical tweezers to approximate the shear stresses suffered by a nonporous, rigid artificial cancerous nodule model.

METHODS: Artificial cancerous nodule model was made by the agglomeration of 2 μm diameter polystyrene particles in a microfluidic platform. Optical tweezers were used as a velocimetry tool and shear stresses on the surface of the nodule model were approximated with the viscous shear stress equation. The results were verified with a numerical simulation performed in Ansys Fluent.

RESULTS: Shear stress originated by microflow over artificial cancerous nodule model were quantified both experimentally and numerically, showing good agreement between both methods. Such stress on the nodules' surface was much greater than that suffered by the wall on which the nodule model was located and dependent of the nodule model geometry. Although the experiment and simulation of this study were performed using a rigid and nonporous nodule model, the conclusion obtained about the increase of shear stresses applies to permeable, porous, and soft nodules as well, because the shear stresses are associated to the acceleration of the fluid originated by the reduction of the cross-sectional area.

CONCLUSIONS: Shear stress over artificial nodule model were successfully quantified using optical tweezer-based velocimetry technique and verified through numerical calculation. Advantages of experimental technique are: (1) it allows to control the position in a three-dimensional plane, allowing measurements in the vicinity of the analyzed surfaces, and (2) it is applicable for very low Reynolds number (Re « 1). On the other hand, as disadvantages: (1) it tends to be complicated to perform velocity measurements over obstacles and (2) it is limited in trapping distance.

RevDate: 2022-04-18

Ibrahim MG (2022)

Numerical simulation to the activation energy study on blood flow of seminal nanofluid with mixed convection effects.

Computer methods in biomechanics and biomedical engineering [Epub ahead of print].

This study sheds light on the influences of Arrhenius activation energy and variable velocity slip on MHD blood motion of Seminal nanofluid in a vertical symmetric channel. In addition, mixed convection, hall current and thermal jump are taken into consideration. The governing system of differential equations with highly nonlinear terms is simplified with facts of long wavelength and low Reynolds number. Pade' approximant and differential transform techniques are combined mathematically to obtain the semi-numerical solutions for the governing system of PDEs. The results are computed and verified graphically with aid of Mathematica 12.3. Physical parameters considered are studied in detail sketchily for the proposed model. Verification/signification of results is approved semi-numerically by comparing the prior results by the newest existing published results by Ahmad et al 2021. Results show that, Velocity of seminal fluid is diminishes with a rise in viscosity-dependent parameter that is a significant feature which can be utilized in controlling the transport of spermatozoa into the cervical canal.

RevDate: 2022-06-01

Koo D, H So (2022)

Facile microfabrication of three dimensional-patterned micromixers using additive manufacturing technology.

Scientific reports, 12(1):6346.

This study investigates the manufacturing method of oblique patterns in microchannels and the effect of these patterns on mixing performance in microchannels. To fabricate three-dimensional (3D) and oblique patterns in microchannels, 3D printing and replica methods were utilized to mold patterns and microchannels, respectively. The angle and size of the patterns were controlled by the printing angle and resolution, respectively. The mixing efficiency was experimentally characterized, and the mixing principle was analyzed using computational fluid dynamics simulation. The analysis showed that the mixing channel cast from the mold printed with a printing angle of 30° and resolution of 300 μm exhibited the best mixing efficiency with a segregation index of approximately 0.05 at a Reynolds number of 5.4. This was because, as the patterns inside the microchannel were more oblique, "split" and "recombine" behaviors between two fluids were enhanced owing to the geometrical effect. This study supports the use of the 3D printing method to create unique patterns inside microchannels and improve the mixing performance of two laminar flows for various applications such as point-of-care diagnostics, lab-on-a-chip, and chemical synthesis.

RevDate: 2022-04-18

Ilg P (2022)

Multiparticle collision dynamics for ferrofluids.

The Journal of chemical physics, 156(14):144905.

Detailed studies of the intriguing field-dependent dynamics and transport properties of confined flowing ferrofluids require efficient mesoscopic simulation methods that account for fluctuating ferrohydrodynamics. Here, we propose such a new mesoscopic model for the dynamics and flow of ferrofluids, where we couple the multi-particle collision dynamics method as a solver for the fluctuating hydrodynamics equations to the stochastic magnetization dynamics of suspended magnetic nanoparticles. This hybrid model is validated by reproducing the magnetoviscous effect in Poiseuille flow, obtaining the rotational viscosity in quantitative agreement with theoretical predictions. We also illustrate the new method for the benchmark problem of flow around a square cylinder. Interestingly, we observe that the length of the recirculation region is increased, whereas the drag coefficient is decreased in ferrofluids when an external magnetic field is applied compared with the field-free case at the same effective Reynolds number. The presence of thermal fluctuations and the flexibility of this particle-based mesoscopic method provide a promising tool to investigate a broad range of flow phenomena of magnetic fluids, and the method could also serve as an efficient way to simulate solvent effects when colloidal particles are immersed in ferrofluids.

RevDate: 2022-04-18

Nagy PT (2022)

Enstrophy change of the Reynolds-Orr solution in channel flow.

Physical review. E, 105(3-2):035108.

The plane Poiseuille flow is one of the elementary flow configurations. Although its laminar-turbulent transition mechanism has been investigated intensively in the last century, the significant difference in the critical Reynolds number between the experiments and the theory lacks a clear explanation. In this paper, an attempt is made to reduce this gap by analyzing the solution of the Reynolds-Orr equation. Recent published results have shown that the usage of enstrophy (the volume integral of the squared vorticity) instead of the kinetic energy as the norm of perturbations predicts higher Reynolds numbers in the two-dimensional case. In addition, other research show has shown an improvement of the original Reynolds-Orr energy equation using the weighted norm in a tilted coordinate system. In this paper the enstrophy is used in three dimensions combined with the tilted coordinate system approach. The zero-enstrophy-growth constraint is applied to the classical Reynolds-Orr equation, and then the solution is further refined in the tilted coordinate system. The results are compared to direct numerical simulations published previously.

RevDate: 2022-04-18

Steiros K (2022)

Balanced nonstationary turbulence.

Physical review. E, 105(3-2):035109.

Kolmogorov's 1941 (K41) framework remains central to the understanding of turbulent flows. However, in unsteady turbulence, K41's critical equilibrium assumption is expected to hold in an asymptotic manner, as the Reynolds number and wave numbers tend to infinity, rendering K41 not strictly valid at finite wave numbers. This work proposes a generalization of K41 for out-of-equilibrium effects and cascades far from initial conditions. The main result is a correction to the -5/3 law for out-of-equilibrium eddies, unrelated to intermittency effects. Experimental and numerical evidence is provided in support of the theoretical results.

RevDate: 2022-04-18

Rana N, P Perlekar (2022)

Phase ordering, topological defects, and turbulence in the three-dimensional incompressible Toner-Tu equation.

Physical review. E, 105(3):L032603.

We investigate the phase-ordering dynamics of the incompressible Toner-Tu equation in three dimensions. We show that the phase ordering proceeds via defect merger events and the dynamics is controlled by the Reynolds number Re. At low Re, the dynamics is similar to that of the Ginzburg-Landau equation. At high Re, turbulence controls phase ordering. In particular, we observe a forward energy cascade from the coarsening length scale to the dissipation scale, clustering of defects, and multiscaling in velocity correlations.

RevDate: 2022-05-19
CmpDate: 2022-05-19

Thurgood P, Chheang C, Needham S, et al (2022)

Generation of dynamic vortices in a microfluidic system incorporating stenosis barrier by tube oscillation.

Lab on a chip, 22(10):1917-1928.

Microfluidic systems incorporating sudden expansions are widely used for generation of vortex flow patterns. However, the formation of vortices requires high flow rates to induce inertial effects. Here, we introduce a new method for generating dynamic vortices in microfluidics at low static flow rates. Human blood is driven through a microfluidic channel incorporating a semi-circular stenosis barrier. The inlet tube of the channel is axially oscillated using a computer-controlled audio-speaker. The tube oscillation induces high transient flow rates in the channel, which generates dynamic vortices across the stenosis barrier. The size of the vortices can be modulated by varying the frequency and amplitude of tube oscillation. Various vortex flow patterns can be generated by varying the flow rate. The formation and size of the vortices can be predicted using the Reynolds number of the oscillating tube. We demonstrate the potential application of the system for investigating the adhesion and phagocytosis of circulating immune cells under pathologically high shear rates induced at the stenosis. This approach facilitates the development of versatile and controllable inertial microfluidic systems for performing various cellular assays while operating at low static flow rates and low sample volumes.

RevDate: 2022-04-19

Behura AK, Mohanty CP, Singh MR, et al (2022)

Performance Analysis of Three Side Roughened Solar Air Heater: A Preliminary Investigation.

Materials (Basel, Switzerland), 15(7):.

In recent years, sunlight has been used in several fields such as photovoltaic cells, flat plate collectors, solar cookers, green buildings, and agricultural applications. Improved thermal performance has been seen which comes of three sides absorber plate with glass cover compared to the traditional one. This paper presents the Nusselt (Nu) number, collector efficiency factor (CEF), and collector heat removal factor (CHRF) for the optimal solution of three sides artificially roughened solar air heater. Five input variables such as Reynolds (Re) number, relative roughness pitch, relative roughness height, mass flow rate, and air temperature of the duct are taken into account for improved efficiency optimization of collector, collector heat removal factor, and Nu number. Technique for order of preference by similarity to ideal solution (TOPSIS) technique is used to identify the best alternative amongst a number of performance measures by converting them into an equivalent single variable. Moreover, the results revealed the high accuracy of the CEF, CHRF, and Nu number of 75-80%, 74-78%, and 63-71%, respectively. Meanwhile, it has been also observed that roughness Re number varies between 12,500 and 13,500, and height of relative roughness is 0.0245, including pitch of relative roughness 10 along with the rate of mass flow is 0.041 kg/s.

RevDate: 2022-04-23

Bhatti MM, Bég OA, SI Abdelsalam (2022)

Computational Framework of Magnetized MgO-Ni/Water-Based Stagnation Nanoflow Past an Elastic Stretching Surface: Application in Solar Energy Coatings.

Nanomaterials (Basel, Switzerland), 12(7):.

In this article, motivated by novel nanofluid solar energy coating systems, a mathematical model of hybrid magnesium oxide (MgO) and nickel (Ni) nanofluid magnetohydrodynamic (MHD) stagnation point flow impinging on a porous elastic stretching surface in a porous medium is developed. The hybrid nanofluid is electrically conducted, and a magnetic Reynolds number is sufficiently large enough to invoke an induced magnetic field. A Darcy model is adopted for the isotropic, homogenous porous medium. The boundary conditions account for the impacts of the velocity slip and thermal slip. Heat generation (source)/absorption (sink) and also viscous dissipation effects are included. The mathematical formulation has been performed with the help of similarity variables, and the resulting coupled nonlinear dimensionless ordinary differential equations have been solved numerically with the help of the shooting method. In order to test the validity of the current results and the convergence of the solutions, a numerical comparison with previously published results is included. Numerical results are plotted for the effect of emerging parameters on velocity, temperature, magnetic induction, skin friction, and Nusselt number. With an increment in nanoparticle volume fraction of both MgO and Ni nanoparticles, the temperature and thermal boundary layer thickness of the nanofluid are elevated. An increase in the porous medium parameter (Darcy number), velocity slip, and thermal Grashof number all enhance the induced magnetic field. Initial increments in the nanoparticle volume fraction for both MgO and Ni suppress the magnetic induction near the wall, although, subsequently, when further from the wall, this effect is reversed. Temperature is enhanced with heat generation, whereas it is depleted with heat absorption and thermal slip effects. Overall, excellent thermal enhancement is achieved by the hybrid nanofluid.

RevDate: 2022-04-13

Fang L, Li H, B Li (2022)

Dynamic Analysis of Deep Water Highway Tunnel under Ocean Current.

Computational intelligence and neuroscience, 2022:9551792.

Comprehensively comparing the merits and demerits of the existing means of transportation across the water, a new underwater transportation structure for crossing the wide water area, named as "deep water highway tunnel" (hereinafter called "DWHT"), is proposed. The characteristics of flow field around the typical section of DWHT at different flow velocities are investigated, which can provide reference for the values of hydrodynamic coefficient at high Reynolds number. The vibration modes and natural by the sound-solid coupling method. In addition, considering the factors of fluid-structure coupling, the dynamic response of displacement and internal force is analyzed based on CFD for the weak parts of the structure. The results show that the deepening of water and the increase of flow will significantly increase the flow field pressure and structure stress, and when the span (or width-span ratio) of the tunnel body extends beyond a certain range, the dynamic characteristics and dynamic response rules of the structure will change.

RevDate: 2022-04-13

Ghorbani N, Targhi MZ, Heyhat MM, et al (2022)

Investigation of wavy microchannel ability on electronic devices cooling with the case study of choosing the most efficient microchannel pattern.

Scientific reports, 12(1):5882.

A numerical study was conducted to investigate the ability of wavy microchannels to damp the temperature fluctuations generates in electronic devices. Five wavy patterns are considered with the amplitude and wavelength in the ranges of 62.5 to 250 μm and 1250 to 5000 μm, respectively to study the effect of governing phenomena of flow within wavy patterns on thermal-hydraulic performance. The flow regime is laminar and the Reynolds number is in the range of 300 to 900, and a relatively high heat flux of 80 W/cm2 is applied to the microchannels substrate. Also, variable flux condition is studied for heat fluxes of 80, 120, 160, 200, and 240 W/cm2 and for the most efficient wavy and straight microchannels. Results showed that the geometries with larger amplitude to wavelength ratio have a lower radius of curvature and larger Dean number, and as a result of transverse flow (secondary flow) amplification, they have enhanced heat transfer. Also, by comparing the ratio of the transverse velocity components to the axial component, it was found that by decreasing the radius of curvature and increasing the Dean number, transverse velocity increases, which intensifies the heat transfer between the wall and the fluid. The appraisement of the performance evaluation criterion (PEC) illustrates that the wavy case with an amplitude of 250 μm and wavelength of 2500 μm is the best geometry from the thermal-hydraulic point of view in the studied range. Finally, with variable flux condition, the wavy microchannel has responded well to the temperature increase and has created a much more uniform surface temperature compared to straight pattern. The proposed wavy pattern ensures that there are no hotspots which could damage the electronic chip. Presented wavy patterns can be used in heat sinks heat transfer enhancement to allow the chip to run in higher heat fluxes.

RevDate: 2022-06-21

Almerol JLO, MP Liponhay (2022)

Clustering of fast gyrotactic particles in low-Reynolds-number flow.

PloS one, 17(4):e0266611.

Systems of particles in turbulent flows exhibit clustering where particles form patches in certain regions of space. Previous studies have shown that motile particles accumulate inside the vortices and in downwelling regions, while light and heavy non-motile particles accumulate inside and outside the vortices, respectively. While strong clustering is generated in regions of high vorticity, clustering of motile particles is still observed in fluid flows where vortices are short-lived. In this study, we investigate the clustering of fast swimming particles in a low-Reynolds-number turbulent flow and characterize the probability distributions of particle speed and acceleration and their influence on particle clustering. We simulate gyrotactic swimming particles in a cubic system with homogeneous and isotropic turbulent flow. Here, the swimming velocity explored is relatively faster than what has been explored in other reports. The fluid flow is produced by conducting a direct numerical simulation of the Navier-Stokes equation. In contrast with the previous results, our results show that swimming particles can accumulate outside the vortices, and clustering is dictated by the swimming number and is invariant with the stability number. We have also found that highly clustered particles are sufficiently characterized by their acceleration, where the increase in the acceleration frequency distribution of the most clustered particles suggests a direct influence of acceleration on clustering. Furthermore, the acceleration of the most clustered particles resides in acceleration values where a cross-over in the acceleration PDFs are observed, an indicator that particle acceleration generates clustering. Our findings on motile particles clustering can be applied to understanding the behavior of faster natural or artificial swimmers.

RevDate: 2022-05-19

Letendre F, CB Cameron (2022)

The capture of crude oil droplets by filter feeders at high and low Reynolds numbers.

The Journal of experimental biology, 225(8):.

Crustacean filter feeders capture oil droplets with the use of their ramified appendages. These appendages behave as paddles or sieves, based on the system's Reynolds number. Here, we used high-speed videography, scanning electron microscopy and fluid mechanics to study the capturing mechanisms of crude oil droplets and the filtering appendage's wettability by two species of barnacles (Balanus glandula and Balanus crenatus) and of the freshwater cladoceran Daphnia magna. Our results show that barnacle appendages behave as paddles and capture droplets in their boundary layers at low Reynolds number. At high Reynolds number, droplets are most likely to be captured via direct interception. There is an intermediate range of Reynolds number where droplets can be captured by both mechanisms at the same time. Daphnia magna captures droplets in the boundary layers of the third and fourth pair of thoracic legs with a metachronal motion of the appendages. All studied surfaces were revealed to be highly lipophobic, demonstrating captured oil droplets with high contact angles. We also discuss implications of such capture mechanisms and wettability on potential ingestion of crude oil by filter feeders. These results further our understanding of the capture of crude oil by filter feeders, shedding light on the main entry point of oil in marine food webs.

RevDate: 2022-04-06

Wang J, Dong Y, Ma P, et al (2022)

Intelligent Micro/nanorobot for Cancer Theragnostic.

Advanced materials (Deerfield Beach, Fla.) [Epub ahead of print].

Cancer is one of the most intractable diseases owing to its high mortality rate and lack of effective diagnostic and treatment tools. Advancements in micro/nanorobot (MNR)-assisted sensing, imaging, and therapeutics offer unprecedented opportunities to develop MNR-based cancer theragnostic platforms. Unlike ordinary nanoparticles which exhibit Brownian motion in biofluids, MNRs overcome viscous resistance in an ultralow Reynolds number (Re<<1) environment by effective self-propulsion. This unique locomotion property has motivated the advanced design and functionalization of MNRs as a basis for next-generation cancer therapy platforms, which offer the potential for precise distribution and improved permeation of therapeutic agents. Enhanced barrier penetration, imaging-guided operation, and biosensing have additionally been studied to enable the promising cancer-related applications of MNRs. This review comprehensively addresses recent advances in MNR-based cancer therapy, including in actuation engines, diagnostics, medical imaging, and targeted drug delivery; we highlight promising research opportunities that could have a profound impact on cancer therapy over the next decade. This article is protected by copyright. All rights reserved.

RevDate: 2022-04-05

Saeed Khan MW, Ali N, OA Bég (2022)

Thermal entrance problem for blood flow inside an axisymmetric tube: The classical Graetz problem extended for Quemada's bio-rheological fluid with axial conduction.

Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine [Epub ahead of print].

The heat-conducting nature of blood is critical in the human circulatory system and features also in important thermal regulation and blood processing systems in biomedicine. Motivated by these applications, in the present investigation, the classical Graetz problem in heat transfer is extended to the case of a bio-rheological fluid model. The Quemada bio-rheological fluid model is selected since it has been shown to be accurate in mimicking physiological flows (blood) at different shear rates and hematocrits. The steady two-dimensional energy equation without viscous dissipation in stationary regime is tackled via a separation of variables approach for the isothermal wall temperature case. Following the introduction of transformation variables, the ensuing dimensionless boundary value problem is solved numerically via MATLAB based algorithm known as bvp5c (a finite difference code that implements the four-stage Lobatto IIIa collocation formula). Numerical validation is also presented against two analytical approaches namely, series solutions and Kummer function techniques. Axial conduction in terms of Péclet number is also considered. Typical values of Reynolds number and Prandtl number are used to categorize the vascular regions. The graphical representation of mean temperature, temperature gradient, and Nusselt numbers along with detail discussions are presented for the effects of Quemada non-Newtonian parameters and Péclet number. The current analysis may also have potential applications for the development of microfluidic and biofluidic devices particularly which are used in the diagnosis of diseases in addition to blood oxygenation technologies.

RevDate: 2022-04-04

Tan S, R Ni (2022)

Universality and Intermittency of Pair Dispersion in Turbulence.

Physical review letters, 128(11):114502.

Turbulence can disperse a concentrated parcel of pollutants at a rate over nine orders of magnitude higher than its purely diffusive counterpart. One intriguing signature of turbulent dispersion is its superdiffusive scaling. However, the universality of this scaling law is still in question. By leveraging a new laboratory facility, particle pairs with small initial separations can be tracked over four decades of separation in time and five decades of separation in squared displacement, thereby observing the full range of dispersion scaling laws. The results show that the classical Richardson cubic scaling will be reached not for an initial separation asymptotically close to zero but at a critical value, and this value does not appear to depend on the Reynolds number, providing an effective way to study universal dispersion dynamics. Additionally, the results agree well with the prediction based on the multifractal model and may help reconcile different reported scaling laws from laboratory experiments and field studies.


ESP Quick Facts

ESP Origins

In the early 1990's, Robert Robbins was a faculty member at Johns Hopkins, where he directed the informatics core of GDB — the human gene-mapping database of the international human genome project. To share papers with colleagues around the world, he set up a small paper-sharing section on his personal web page. This small project evolved into The Electronic Scholarly Publishing Project.

ESP Support

In 1995, Robbins became the VP/IT of the Fred Hutchinson Cancer Research Center in Seattle, WA. Soon after arriving in Seattle, Robbins secured funding, through the ELSI component of the US Human Genome Project, to create the original ESP.ORG web site, with the formal goal of providing free, world-wide access to the literature of classical genetics.

ESP Rationale

Although the methods of molecular biology can seem almost magical to the uninitiated, the original techniques of classical genetics are readily appreciated by one and all: cross individuals that differ in some inherited trait, collect all of the progeny, score their attributes, and propose mechanisms to explain the patterns of inheritance observed.

ESP Goal

In reading the early works of classical genetics, one is drawn, almost inexorably, into ever more complex models, until molecular explanations begin to seem both necessary and natural. At that point, the tools for understanding genome research are at hand. Assisting readers reach this point was the original goal of The Electronic Scholarly Publishing Project.

ESP Usage

Usage of the site grew rapidly and has remained high. Faculty began to use the site for their assigned readings. Other on-line publishers, ranging from The New York Times to Nature referenced ESP materials in their own publications. Nobel laureates (e.g., Joshua Lederberg) regularly used the site and even wrote to suggest changes and improvements.

ESP Content

When the site began, no journals were making their early content available in digital format. As a result, ESP was obliged to digitize classic literature before it could be made available. For many important papers — such as Mendel's original paper or the first genetic map — ESP had to produce entirely new typeset versions of the works, if they were to be available in a high-quality format.

ESP Help

Early support from the DOE component of the Human Genome Project was critically important for getting the ESP project on a firm foundation. Since that funding ended (nearly 20 years ago), the project has been operated as a purely volunteer effort. Anyone wishing to assist in these efforts should send an email to Robbins.

ESP Plans

With the development of methods for adding typeset side notes to PDF files, the ESP project now plans to add annotated versions of some classical papers to its holdings. We also plan to add new reference and pedagogical material. We have already started providing regularly updated, comprehensive bibliographies to the ESP.ORG site.

Electronic Scholarly Publishing
961 Red Tail Lane
Bellingham, WA 98226

E-mail: RJR8222 @

Papers in Classical Genetics

The ESP began as an effort to share a handful of key papers from the early days of classical genetics. Now the collection has grown to include hundreds of papers, in full-text format.

Digital Books

Along with papers on classical genetics, ESP offers a collection of full-text digital books, including many works by Darwin (and even a collection of poetry — Chicago Poems by Carl Sandburg).


ESP now offers a much improved and expanded collection of timelines, designed to give the user choice over subject matter and dates.


Biographical information about many key scientists.

Selected Bibliographies

Bibliographies on several topics of potential interest to the ESP community are now being automatically maintained and generated on the ESP site.

ESP Picks from Around the Web (updated 07 JUL 2018 )