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26 Jan 2022 at 01:30
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Bibliography on: Reynolds Number


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RJR: Recommended Bibliography 26 Jan 2022 at 01:30 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: 2022-01-18

Eyink GL, Kumar S, H Quan (2022)

The Onsager theory of wall-bounded turbulence and Taylor's momentum anomaly.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 380(2218):20210079.

We discuss the Onsager theory of wall-bounded turbulence, analysing the momentum dissipation anomaly hypothesized by Taylor. Turbulent drag laws observed with both smooth and rough walls imply ultraviolet divergences of velocity gradients. These are eliminated by a coarse-graining operation, filtering out small-scale eddies and windowing out near-wall eddies, thus introducing two arbitrary regularization length-scales. The regularized equations for resolved eddies correspond to the weak formulation of the Navier-Stokes equation and contain, in addition to the usual turbulent stress, also an inertial drag force modelling momentum exchange with unresolved near-wall eddies. Using an Onsager-type argument based on the principle of renormalization group invariance, we derive an upper bound on wall friction by a function of Reynolds number determined by the modulus of continuity of the velocity at the wall. Our main result is a deterministic version of Prandtl's relation between the Blasius [Formula: see text] drag law and the 1/7 power-law profile of the mean streamwise velocity. At higher Reynolds, the von Kármán-Prandtl drag law requires instead a slow logarithmic approach of velocity to zero at the wall. We discuss briefly also the large-eddy simulation of wall-bounded flows and use of iterative renormalization group methods to establish universal statistics in the inertial sublayer. This article is part of the theme issue 'Scaling the turbulence edifice (part 1)'.

RevDate: 2022-01-18

Buaria D, Pumir A, E Bodenschatz (2022)

Generation of intense dissipation in high Reynolds number turbulence.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 380(2218):20210088.

Intense fluctuations of energy dissipation rate in turbulent flows result from the self-amplification of strain rate via a quadratic nonlinearity, with contributions from vorticity (via the vortex stretching mechanism) and pressure-Hessian-which are analysed here using direct numerical simulations of isotropic turbulence on up to [Formula: see text] grid points, and Taylor-scale Reynolds numbers in the range 140-1300. We extract the statistics involved in amplification of strain and condition them on the magnitude of strain. We find that strain is self-amplified by the quadratic nonlinearity, and depleted via vortex stretching, whereas pressure-Hessian acts to redistribute strain fluctuations towards the mean-field and hence depletes intense strain. Analysing the intense fluctuations of strain in terms of its eigenvalues reveals that the net amplification is solely produced by the third eigenvalue, resulting in strong compressive action. By contrast, the self-amplification acts to deplete the other two eigenvalues, whereas vortex stretching acts to amplify them, with both effects cancelling each other almost perfectly. The effect of the pressure-Hessian for each eigenvalue is qualitatively similar to that of vortex stretching, but significantly weaker in magnitude. Our results conform with the familiar notion that intense strain is organized in sheet-like structures, which are in the vicinity of, but never overlap with tube-like regions of intense vorticity due to fundamental differences in their amplifying mechanisms. This article is part of the theme issue 'Scaling the turbulence edifice (part 1)'.

RevDate: 2022-01-16

Chakraborty R, Maiti A, Sharma N, et al (2022)

Active matter dynamics in confined microfluidic environments.

Progress in molecular biology and translational science, 186(1):245-265.

The field of active matter is a nascent area of research in soft condensed matter physics, which is drawing on the expertise of researchers from diverse disciplines. Small scale active particles-both inorganic and biological-display non-trivial emergent dynamics and interactions that could help us understand complex biological processes and phenomena. Recently, using microfluidic technologies, several research groups have performed important experimental and theoretical studies to understand the behavior of self-propelled particles and molecular active matter within confined environments-to glean a fundamental understanding of the cellular processes occurring under ultra-low Reynolds number conditions. In this chapter, we would like to review applications of microfluidics in active matter research, highlighting a few important theoretical and experimental investigations. We will conclude the discussion with a note on the future of this field mentioning a few open questions that are at the forefront of our minds.

RevDate: 2022-01-14

Koch CM, M Wilczek (2021)

Role of Advective Inertia in Active Nematic Turbulence.

Physical review letters, 127(26):268005.

Suspensions of active agents with nematic interactions exhibit complex spatiotemporal dynamics such as mesoscale turbulence. Since the Reynolds number of microscopic flows is very small on the scale of individual agents, inertial effects are typically excluded in continuum theories of active nematic turbulence. Whether active stresses can collectively excite inertial flows is currently unclear. To address this question, we investigate a two-dimensional continuum theory for active nematic turbulence. In particular, we compare mesoscale turbulence with and without the effects of advective inertia. We find that inertial effects can influence the flow already close to the onset of the turbulent state and, moreover, give rise to large-scale fluid motion for strong active driving. A detailed analysis of the kinetic energy budget reveals an energy transfer to large scales mediated by inertial advection. While this transfer is small in comparison to energy injection and dissipation, its effects accumulate over time. The inclusion of friction, which is typically present in experiments, can compensate for this effect. The findings suggest that the inclusion of inertia and friction may be necessary for dynamically consistent theories of active nematic turbulence.

RevDate: 2022-01-12

Olsson KH, Gurka R, R Holzman (2022)

Trophic guilds of suction-feeding fishes are distinguished by their characteristic hydrodynamics of swimming and feeding.

Proceedings. Biological sciences, 289(1966):20211968.

Suction-feeding in fishes is a ubiquitous form of prey capture whose outcome depends both on the movements of the predator and the prey, and on the dynamics of the surrounding fluid, which exerts forces on the two organisms. The inherent complexity of suction-feeding has challenged previous efforts to understand how the feeding strikes are modified when species evolve to feed on different prey types. Here, we use the concept of dynamic similarity, commonly applied to understanding the mechanisms of swimming, flying, walking and aquatic feeding. We characterize the hydrodynamic regimes pertaining to (i) the forward movement of the fish (ram), and (ii) the suction flows for feeding strikes of 71 species of acanthomorph fishes. A discriminant function analysis revealed that feeding strikes of zooplanktivores, generalists and piscivores could be distinguished based on their hydrodynamic regimes. Furthermore, a phylogenetic comparative analysis revealed that there are distinctive hydrodynamic adaptive peaks associated with zooplanktivores, generalists and piscivores. The scaling of dynamic similarity across species, body sizes and feeding guilds in fishes indicates that elementary hydrodynamic principles govern the trophic evolution of suction-feeding in fishes.

RevDate: 2022-01-11

Węgrzyn D, Wrzeciono P, A Wieczorkowska (2021)

The Dependence of Flue Pipe Airflow Parameters on the Proximity of an Obstacle to the Pipe's Mouth.

Sensors (Basel, Switzerland), 22(1): pii:s22010010.

This paper describes the influence of the presence of an obstacle near the flue pipe's mouth on the air jet, which directly affects the parameters of the sound generated by the flue pipe. Labial pipes of the most common types of mouth were tested. The method of interval calculus was used instead of invasive measuring instruments. The obtained results prove that the proximity of an obstacle affects the sound's fundamental frequency, as the airflow speed coming out of the flue pipe's mouth changes. The relationship between the airflow speed, the value of the Reynolds number, and the Strouhal number was also established. The thesis of the influence of the proximity of an obstacle on the fundamental frequency of the sound of a flue pipe was generalized, and formulas for calculating the untuning of the sound of the pipe were presented for various types of mouth.

RevDate: 2022-01-07

Xu WH, Xu GD, L Shan (2022)

Real--time parametric estimation of periodic wake--foil interactions using bioinspired pressure sensing and machine learning.

Bioinspiration & biomimetics [Epub ahead of print].

Periodic wake--foil interactions occur in the collective swimming of bio-inspired robots. Wake interaction pattern estimation (and control) is crucial to thrust enhancement and propulsive efficiency optimization. In this paper, we study the wake interaction pattern estimation of two flapping foils in tandem configurations. The experiments are conducted at a Reynolds number of 1.41×10^4 in a water channel. A modified wake--foil phase parameter Φ, which unifies the influences of inter-foil distance Lx, motion phase difference ∆φ and wake convection velocity Uv, is introduced to describe the wake interaction patterns parametrically. We use a differential pressure sensor on the downstream foil to capture wake interaction characteristics. Data sets at different tandem configurations are collected. The wake--foil phase Φ is used to label the pressure signals. A one -dimensional convolutional neural networks (1D-CNN) model is used to learn an end-to-end mapping between the raw pressure measurements and the wake--foil phase Φ. The trained 1D--CNN model shows accurate estimations (average error 3.5%) on random wake interaction patterns and is fast enough (within 40 ms). Then the trained 1D -CNN model is applied to online thrust enhancement control of a downstream foil swimming in a periodic wake. Synchronous force monitoring and flow visualization demonstrate the effectiveness of the 1D--CNN model. The limitations of the model are discussed. The proposed approach can be applied to the online estimation and control of wake interactions in the collective swimming and flying of biomimetic robots.

RevDate: 2022-01-07

Khojasteh AR, Laizet S, Heitz D, et al (2022)

Lagrangian and Eulerian dataset of the wake downstream of a smooth cylinder at a Reynolds number equal to 3900.

Data in brief, 40:107725 pii:S2352-3409(21)01000-3.

The dataset contains Eulerian velocity and pressure fields, and Lagrangian particle trajectories of the wake flow downstream of a smooth cylinder at a Reynolds number equal to 3900. An open source Direct Numerical Simulation (DNS) flow solver named Incompact3d was used to calculate the Eulerian field around the cylinder. The synthetic Lagrangian tracer particles were transported using a fourth-order Runge-Kutta scheme in time and trilinear interpolations in space. Trajectories of roughly 200,000 particles for two 3D sub-domains are available to the public. This dataset can be used as a test case for tracking algorithm assessment, exploring the Lagrangian physics, statistic analyses, machine learning, and data assimilation interests.

RevDate: 2022-01-04

Dev AA, Dunne P, Hermans TM, et al (2022)

Fluid Drag Reduction by Magnetic Confinement.

Langmuir : the ACS journal of surfaces and colloids [Epub ahead of print].

The frictional forces of a viscous liquid flow are a major energy loss issue and severely limit microfluidics practical use. Reducing this drag by more than a few tens of percent remain elusive. Here, we show how cylindrical liquid-in-liquid flow leads to drag reduction of 60-99% for sub-mm and mm-sized channels, regardless of whether the viscosity of the transported liquid is larger or smaller than that of the confining one. In contrast to lubrication or sheath flow, we do not require a continuous flow of the confining lubricant, here made of a ferrofluid held in place by magnetic forces. In a laminar flow model with appropriate boundary conditions, we introduce a modified Reynolds number with a scaling that depends on geometrical factors and viscosity ratio of the two liquids. It explains our whole range of data and reveals the key design parameters for optimizing the drag reduction values. Our approach promises a new route for microfluidics designs with pressure gradient reduced by orders of magnitude.

RevDate: 2022-01-03

Daru V, Weisman C, Baltean-Carlès D, et al (2021)

A numerical study of the coupling between Rayleigh streaming and heat transfer at high acoustic level.

The Journal of the Acoustical Society of America, 150(6):4501.

Complex coupling between thermal effects and Rayleigh streaming in a standing wave guide at high acoustic levels is analyzed numerically. The approach is guided by the recent analytical study, showing that reverse streaming cells can form if the nonlinear Reynolds number exceeds a value depending on the wave frequency and thermophysical properties of the fluid and solid wall. A numerical configuration is introduced to investigate the evolution of the streaming flow structure and the average temperature field at high acoustic levels. Special attention is given to inhibit the development of shock waves. The heat conduction is accounted for in the wall. As the acoustic level is increased, the average temperature field becomes stratified transversely. The simulations show the relevance of the criterion for characterizing the appearance of additional contrarotating streaming cells near the acoustic velocity antinodes. For higher acoustic levels, these additional cells evolve into increasingly large stagnant zones, where the streaming flow is of very small amplitude and the contours of temperature are stratified longitudinally. The overall outer streaming flow decreases. These results are consistent with previous experimental observations, showing that the intrinsic coupling between the thermal effects and acoustic streaming at high levels is very well described.

RevDate: 2021-12-29

Sznitman J (2021)

Revisiting Airflow and Aerosol Transport Phenomena in the Deep Lungs with Microfluidics.

Chemical reviews [Epub ahead of print].

The dynamics of respiratory airflows and the associated transport mechanisms of inhaled aerosols characteristic of the deep regions of the lungs are of broad interest in assessing both respiratory health risks and inhalation therapy outcomes. In the present review, we present a comprehensive discussion of our current understanding of airflow and aerosol transport phenomena that take place within the unique and complex anatomical environment of the deep lungs, characterized by submillimeter 3D alveolated airspaces and nominally slow resident airflows, known as low-Reynolds-number flows. We exemplify the advances brought forward by experimental efforts, in conjunction with numerical simulations, to revisit past mechanistic theories of respiratory airflow and particle transport in the distal acinar regions. Most significantly, we highlight how microfluidic-based platforms spanning the past decade have accelerated opportunities to deliver anatomically inspired in vitro solutions that capture with sufficient realism and accuracy the leading mechanisms governing both respiratory airflow and aerosol transport at true scale. Despite ongoing challenges and limitations with microfabrication techniques, the efforts witnessed in recent years have provided previously unattainable in vitro quantifications on the local transport properties in the deep pulmonary acinar airways. These may ultimately provide new opportunities to explore improved strategies of inhaled drug delivery to the deep acinar regions by investigating further the mechanistic interactions between airborne particulate carriers and respiratory airflows at the pulmonary microscales.

RevDate: 2021-12-24

Strizhenov EM, Chugaev SS, Men'shchikov IE, et al (2021)

Heat and Mass Transfer in an Adsorbed Natural Gas Storage System Filled with Monolithic Carbon Adsorbent during Circulating Gas Charging.

Nanomaterials (Basel, Switzerland), 11(12): pii:nano11123274.

Adsorbed natural gas (ANG) technology is a promising alternative to traditional compressed (CNG) and liquefied (LNG) natural gas systems. Nevertheless, the energy efficiency and storage capacity of an ANG system strongly depends on the thermal management of its inner volume because of significant heat effects occurring during adsorption/desorption processes. In the present work, a prototype of a circulating charging system for an ANG storage tank filled with a monolithic nanoporous carbon adsorbent was studied experimentally under isobaric conditions (0.5-3.5 MPa) at a constant volumetric flow rate (8-18 m3/h) or flow mode (Reynolds number at the adsorber inlet from 100,000 to 220,000). The study of the thermal state of the monolithic adsorbent layer and internal heat exchange processes during the circulating charging of an adsorbed natural gas storage system was carried out. The correlation between the gas flow mode, the dynamic gas flow temperature, and the heat transfer coefficient between the gas and adsorbent was determined. A one-dimensional mathematical model of the circulating low-temperature charging process was developed, the results of which correspond to the experimental measurements.

RevDate: 2021-12-24

Sawka A (2021)

Deposition of Gadolinia-Doped Zirconia Layers Using Metalorganic Compounds at Low Temperatures.

Materials (Basel, Switzerland), 14(24): pii:ma14247573.

This paper shows the results of an investigation on the synthesis of non-porous and nanocrystalline ZrO2-Gd2O3 layers by metalorganic chemical vapor deposition (MOCVD) with the use of Zr(tmhd)4 (tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium(IV)) and Gd(tmhd)3 (tris(2,2,6,6-tetramethyl-3,5-heptanedionato)gadolinium(III)). Argon and air were used as carrier gases. The molar content of Gd(tmhd)3 in the gas reaction mixture was as follows: 10% and 20%. The layers were synthesized on tubular substrates made of quartz glass at the temperatures of 550-700 °C. Synthesis conditions were established using the Grx/Rex2 expression (Gr is the Grashof number; Re is the Reynolds number; x is the distance from the gas inflow point). The value of this criterion was below 0.01. ZrO2-Gd2O3 layers synthesized at 600-700 °C were crystalline. When the molar content of Gd(tmhd)3 in the gas reaction mixture was 10 mol.%, a relationship between the chemical composition of the gas reaction mixture and that of the deposited layer could be observed. The synthesized layers underwent scanning electron microscopy, as well as X-ray analysis. The transparency of coated and uncoated glass was tested using UV-Vis spectroscopy. Their chemical composition was examined with the use of an EDS analyzer.

RevDate: 2021-12-24

Kumbár V, Ondrušíková S, Trost D, et al (2021)

Rheological and Flow Behaviour of Yolk, Albumen and Liquid Whole Egg from Eggs of Six Different Poultry Species.

Foods (Basel, Switzerland), 10(12): pii:foods10123130.

Liquid egg products are one of the basic raw materials for the food industry. Knowledge of their rheological and flow behaviour in real technical elements is absolutely necessary for the selection of suitable technological equipment for their processing. In this article, the rheological properties of liquid egg products were determined. Eggs from six different species of poultry are used: domestic hen (Gallus gallus domesticus) hybrid Hisex Brown; Japanese quail (Coturnix japonica); German carrier goose (Anser anser f. domestica); domestic ducks (Anas platyrhynchos f. domestica); domestic guinea fowl (Numida meleagris f. domestica); and domestic turkeys (Meleagris gallopavo f. domestica). Liquid egg products showed pseudoplastic behaviour in range of shear strain rates from 0.2 up to 200 s-1 and at the temperature of 18 °C. Thus, the flow curves were constructed using the Ostwald-de Waele rheological model, with respect to the pseudoplastic behaviour of liquid egg products. According to the values of the coefficients of determination (R2), the sum of squared estimate of errors (SSE) and the root mean square error (RMSE), this model was appropriately chosen. Using the consistency coefficient K, the flow index n and the adjusted equations for the flow rate of technical and biological fluids in standard pipelines, the 3D velocity profiles of liquid egg products were successfully modelled. The values of the Reynolds number of the individual liquid egg products were calculated, and the type of flow was also determined. A turbulent flow has been detected for some liquid egg products.

RevDate: 2021-12-24

Fukuda T, MR Harada (2021)

Analysis of Aspect Ratio in a Miniature Rectangle Channel for Low Frictional Resistance.

Micromachines, 12(12): pii:mi12121580.

We conducted a theoretical investigation of the cross-sectional aspect ratio of a rectangular channel to have sufficiently low frictional resistance under less than 150 of the Reynolds number. From the theoretical consideration, it was clarified that 3.40 or more is recommended as a criterion for determining the aspect ratio. This addresses the problem of determining the interval of rectangle channels, installed in a plate reactor. There is a concern that the real system does not follow the analytical solution, assuming laminar flow, since the higher aspect ratio leads to disturbances of the flow such as the emergence of vortices. However, in the channel's volume range of (W × H × L) = (7.0 mm × 0.38 mm × 0.26 m), such a turbulence was not observed in the detailed numerical calculation by CFD, where both calculation results were in agreement to within 3% accuracy. Moreover, even in an experimental system with a surface roughness of ca. 7%, friction resistance took agreement within an accuracy of ±30%.

RevDate: 2021-12-24

Juraeva M, DJ Kang (2021)

Mixing Performance of a Passive Micro-Mixer with Mixing Units Stacked in Cross Flow Direction.

Micromachines, 12(12): pii:mi12121530.

A new passive micro-mixer with mixing units stacked in the cross flow direction was proposed, and its performance was evaluated numerically. The present micro-mixer consisted of eight mixing units. Each mixing unit had four baffles, and they were arranged alternatively in the cross flow and transverse direction. The mixing units were stacked in four different ways: one step, two step, four step, and eight step stacking. A numerical study was carried out for the Reynolds numbers from 0.5 to 50. The corresponding volume flow rate ranged from 6.33 μL/min to 633 μL/min. The mixing performance was analyzed in terms of the degree of mixing (DOM) and relative mixing energy cost (MEC). The numerical results showed a noticeable enhancement of the mixing performance compared with other micromixers. The mixing enhancement was achieved by two flow characteristics: baffle wall impingement by a stream of high concentration and swirl motion within the mixing unit. The baffle wall impingement by a stream of high concentration was observed throughout all Reynolds numbers. The swirl motion inside the mixing unit was observed in the cross flow direction, and became significant as the Reynolds number increased to larger than about five. The eight step stacking showed the best performance for Reynolds numbers larger than about two, while the two step stacking was better for Reynolds numbers less than about two.

RevDate: 2021-12-24

Mahammedi A, Tayeb NT, Kim KY, et al (2021)

Mixing Enhancement of Non-Newtonian Shear-Thinning Fluid for a Kenics Micromixer.

Micromachines, 12(12): pii:mi12121494.

In this work, a numerical investigation was analyzed to exhibit the mixing behaviors of non-Newtonian shear-thinning fluids in Kenics micromixers. The numerical analysis was performed using the computational fluid dynamic (CFD) tool to solve 3D Navier-Stokes equations with the species transport equations. The efficiency of mixing is estimated by the calculation of the mixing index for different cases of Reynolds number. The geometry of micro Kenics collected with a series of six helical elements twisted 180° and arranged alternately to achieve the higher level of chaotic mixing, inside a pipe with a Y-inlet. Under a wide range of Reynolds numbers between 0.1 to 500 and the carboxymethyl cellulose (CMC) solutions with power-law indices among 1 to 0.49, the micro-Kenics proves high mixing Performances at low and high Reynolds number. Moreover the pressure losses of the shear-thinning fluids for different Reynolds numbers was validated and represented.

RevDate: 2021-12-24

Gizynski K, Makuch K, Paczesny J, et al (2021)

Internal energy in compressible Poiseuille flow.

Physical review. E, 104(5-2):055107.

We analyze a compressible Poiseuille flow of ideal gas in a plane channel. We provide the form of internal energy U for a nonequilibrium stationary state that includes viscous dissipation and pressure work. We demonstrate that U depends strongly on the ratio Δp/p_{0}, where Δp is the pressure difference between inlet and outlet and p_{0} is the outlet's pressure. In addition, U depends on two other variables: the channel aspect ratio and the parameter equivalent to Reynolds number. The stored internal energy, ΔU=U-U_{0}, is small compared to the internal energy U_{0} of the equilibrium state for a moderate range of values of Δp/p_{0}. However, ΔU can become large for big Δp or close to vacuum conditions at the outlet (p_{0}≈0Pa).

RevDate: 2021-12-20

Nejatipour P, B Khorsandi (2021)

Effect of nozzle geometry on the dynamics and mixing of self-similar turbulent jets.

Water science and technology : a journal of the International Association on Water Pollution Research, 84(12):3907-3915.

The effect of nozzle geometry on the dynamics and mixing of turbulent jets is experimentally investigated. The jets with a Reynolds number of 13,000 were issued from four different pipes with circular, elliptical, square and triangular cross sections. The velocity field was measured in the self-similar region of the jets using an acoustic Doppler velocimeter. Statistical parameters, such as the mean velocities, velocity variances, spreading rates, mass flow rates, and entrainment rates are presented. The results show that despite having approximately similar decay rates for the mean centerline velocities, the radial profiles of the axial mean velocity varied in jets with different nozzle cross sections and were widest for elliptical jets and narrowest for the triangular ones. On the other hand, velocity variances were greatest for the triangular jet when compared to the jets released from cross sections of other geometries. Furthermore, the spreading rate, mass flow rate, and entrainment rate were highest for the elliptical jet, and lowest for the triangular jet. From this it can be inferred that the elliptical jet has the highest mixing and dilution. The results of this study could help to improve the initial mixing of pollutants by optimizing the initial conditions.

RevDate: 2021-12-14

Shahzad H, Wang X, Sarris I, et al (2021)

Study of Non-Newtonian biomagnetic blood flow in a stenosed bifurcated artery having elastic walls.

Scientific reports, 11(1):23835.

Fluid structure interaction (FSI) gained attention of researchers and scientist due to its applications in science fields like biomedical engineering, mechanical engineering etc. One of the major application in FSI is to study elastic wall behavior of stenotic arteries. In this paper we discussed an incompressible Non-Newtonian blood flow analysis in an elastic bifurcated artery. A magnetic field is applied along [Formula: see text] direction. For coupling of the problem an Arbitrary Lagrangian-Eulerian formulation is used by two-way fluid structure interaction. To discretize the problem, we employed [Formula: see text] finite element technique to approximate the velocity, displacement and pressure and then linearized system of equations is solved using Newton iteration method. Analysis is carried out for power law index, Reynolds number and Hartmann number. Hemodynamic effects on elastic walls, stenotic artery and bifurcated region are evaluated by using velocity profile, pressure and loads on the walls. Study shows there is significant increase in wall shear stresses with an increase in Power law index and Hartmann number. While as expected increase in Reynolds number decreases the wall shear stresses. Also load on the upper wall is calculated against Hartmann number for different values of power law index. Results show load increases as the Hartmann number and power law index increases. From hemodynamic point of view, the load on the walls is minimum for shear thinning case but when power law index increased i.e. for shear thickening case load on the walls increased.

RevDate: 2021-12-08

Pichler M, Haddadi B, Jordan C, et al (2021)

Dataset for the simulated biomass pyrolysis in rotary kilns with varying particle residence time distributions.

Data in brief, 39:107603 pii:S2352-3409(21)00878-7.

Slow pyrolysis of biomass is commonly performed in rotary kilns. The effect of the particle residence time distribution on biomass conversion is often neglected when numerically modeling such systems. But this effect might be significant under certain conditions. The data presented here are results of numerical simulation of the biomass pyrolysis in rotary kilns under numerous operating conditions and levels of axial dispersion of biomass particles. The varied operating conditions are the kiln diameter (D = 0.1 -1 m), the ratio of particle to kiln diameter (d / D = 5 × 10 - 3 - 40 × 10 - 3), the ratio of kiln length to kiln diameter (L / D = 1 -10), the kiln's inclination angle (β = 0.1 -8 ∘), the Froude number (Fr = 10 - 3 - 10 - 2), the rotational Reynolds number (Re = 10 2 - 16 × 10 3), and the Péclet number (Pe = 5 -100). Data of 13,851 single case simulations are provided with this article. This includes the mean particle residence time, gas, bed and kiln wall temperatures, solid and gaseous species mass flows, heat fluxes, and the solid bed height over the kiln length. These comprehensive data have the potential to help in modeling, design, analysis, and optimization of rotary kilns used for the pyrolysis of biomass. The main characterization and interpretation is presented in the related main research paper by Pichler et al. (2021)[1].

RevDate: 2021-12-02

Casas-Arozamena C, Otero-Cacho A, Carnero B, et al (2021)

Haemodynamic-dependent arrest of circulating tumour cells at large blood vessel bifurcations as new model for metastasis.

Scientific reports, 11(1):23231.

Homing of circulating tumour cells (CTC) at distant sites represents a critical event in metastasis dissemination. In addition to physical entrapment, probably responsible of the majority of the homing events, the vascular system provides with geometrical factors that govern the flow biomechanics and impact on the fate of the CTC. Here we mathematically explored the distribution of velocities and the corresponding streamlines at the bifurcations of large blood vessel and characterized an area of low-velocity at the carina of bifurcation that favours the residence of CTC. In addition to this fluid physics effect, the adhesive capabilities of the CTC provide with a biological competitive advantage resulting in a marginal but systematic arrest as evidenced by dynamic in vitro recirculation in Y-microchannels and by perfusion in in vivo mice models. Our results also demonstrate that viscosity, as a main determinant of the Reynolds number that define flow biomechanics, may be modulated to limit or impair CTC accumulation at the bifurcation of blood vessels, in agreement with the apparent positive effect observed in the clinical setting by anticoagulants in advanced oncology disease.

RevDate: 2021-12-01

Behera S, Dogra DP, Bandyopadhyay MK, et al (2021)

Crowd Characterization in Surveillance Videos Using Deep-Graph Convolutional Neural Network.

IEEE transactions on cybernetics, PP: [Epub ahead of print].

Crowd behavior is a natural phenomenon that can provide valuable insight into the crowd characterization process. Modeling the visual appearance of a large crowd gathering can reveal meaningful information about its dynamics. Parametric modeling can be used to develop efficient and robust crowd monitoring systems. A crowd can be structured or unstructured based on the organization. In this article, crowd characterization has been mapped to a graph classification problem to classify movements based on order parameter (φ), active force components, and steadiness (Reynolds number). The graphs are constructed from the motion groups obtained using an active Langevin framework. These graphs are processed using a deep graph convolutional neural network for crowd characterization. For experimentation, we have prepared a dataset comprising of videos from popular publicly available datasets and our own recorded videos. The proposed framework has been compared with the latest deep learning-based frameworks in terms of accuracy and area under the curve (AUC). We have obtained a 4%-5% improvement in accuracy and AUC values over the existing frameworks. The insights obtained from the proposed framework can be used for better crowd monitoring and management.

RevDate: 2021-12-01

Corda JV, Shenoy BS, Ahmad KA, et al (2021)

Nasal airflow comparison in neonates, infant and adult nasal cavities using computational fluid dynamics.

Computer methods and programs in biomedicine pii:S0169-2607(21)00612-X [Epub ahead of print].

BACKGROUND AND OBJECTIVE: Neonates are preferential nasal breathers up to 3 months of age. The nasal anatomy in neonates and infants is at developing stages whereas the adult nasal cavities are fully grown which implies that the study of airflow dynamics in the neonates and infants are significant. In the present study, the nasal airways of the neonate, infant and adult are anatomically compared and their airflow patterns are investigated.

METHODS: Computational Fluid Dynamics (CFD) approach is used to simulate the airflow in a neonate, an infant and an adult in sedentary breathing conditions. The healthy CT scans are segmented using MIMICS 21.0 (Materialise, Ann arbor, MI). The patient-specific 3D airway models are analyzed for low Reynolds number flow using ANSYS FLUENT 2020 R2. The applicability of the Grid Convergence Index (GCI) for polyhedral mesh adopted in this work is also verified.

RESULTS: This study shows that the inferior meatus of neonates accounted for only 15% of the total airflow. This was in contrast to the infants and adults who experienced 49 and 31% of airflow at the inferior meatus region. Superior meatus experienced 25% of total flow which is more than normal for the neonate. The highest velocity of 1.8, 2.6 and 3.7 m/s was observed at the nasal valve region for neonates, infants and adults, respectively. The anterior portion of the nasal cavity experienced maximum wall shear stress with average values of 0.48, 0.25 and 0.58 Pa for the neonates, infants and adults.

CONCLUSIONS: The neonates have an underdeveloped nasal cavity which significantly affects their airway distribution. The absence of inferior meatus in the neonates has limited the flow through the inferior regions and resulted in uneven flow distribution.

RevDate: 2021-11-30

Kim AR, Mitra SK, B Zhao (2021)

Reduced Pressure Drop in Viscoelastic Polydimethylsiloxane Wall Channels.

Langmuir : the ACS journal of surfaces and colloids [Epub ahead of print].

Polydimethylsiloxane (PDMS) is an important viscoelastic material that finds applications in a large number of engineering systems, particularly lab-on-chip microfluidic devices built with a flexible substrate. Channels made of PDMS, used for transporting analytes, are integral to these applications. The PDMS viscoelastic nature can induce additional hydrodynamic contributions at the soft wall/fluid interface compared to rigid walls. In this research, we investigated the pressure drop within PDMS channels bounded by rigid tubes (cellulose tubes). The bulging effect of the PDMS was limited by the rigid tubes under flowing fluids. The PDMS viscoelasticity was modulated by changing the ratio of the base to the cross-linker from 10:1 to 35:1. We observed that the pressure drop of the flowing fluids within the channel decreased with the increased loss tangent of the PDMS in the examined laminar regime [Reynolds number (Re) ∼ 23-58.6 for water and Re ∼ 0.69-8.69 for glycerol solution]. The elastic PDMS 10:1 wall channels followed the classical Hagen Poiseuille's equation, but the PDMS walls with lower cross-linker concentrations and thicker walls decreased pressure drops. The friction factor (f) for the PDMS channels with the two working fluids could be approximated as f = 47/Re. We provide a correlation between the pressure drop and PDMS viscoelasticity based on experimental findings. In the correlation, the loss tangent predominates; the larger the loss tangent, the smaller is the pressure drop. The research findings appear to be unexpected if only considering the energy dissipation of viscoelastic PDMS walls. We attributed the reduction in the pressure drop to a lubricating effect of the viscoelastic PDMS walls in the presence of the working fluids. Our results reveal the importance of the subtle diffusion of the residual oligomers and water from the bulk to the soft wall/fluid interface for the observed pressure drop in soft wall channels.

RevDate: 2021-11-30

Chen X, Zhan Y, Fu YI, et al (2021)

The effect of stenosis rate and Reynolds number on local flow characteristics and plaque formation around the atherosclerotic stenosis.

Acta of bioengineering and biomechanics, 23(1):135-147.

PURPOSE: Atherosclerosis causes plaque to build-up in arteries. Effect of the specific local hemodynamic environment around an atherosclerotic plaque on the thrombosis formation does not remain quite clear but is believed to be crucial. The aim of this study is to uncover the flow effects on plaques formation.

METHODS: To study the mechanically regulated plaque formation, the flow fields in artery blood vessels with different stenosis rates at various Reynolds numbers were simulated numerically with the two-dimensional axisymmetric models, and the hemodynamic characteristics around the plaque were scaled with stenosis rate and Reynolds number.

RESULTS: The results showed that increases of both Reynolds number and stenosis rate facilitated the occurrence of flow separation phenomenon, extended recirculation zone, and upregulated the maximum normalized wall shear stress near the plaque throat section while downregulated the minimal normalized wall shear stress at the front shoulder of plaque, as it should be; in the atherosclerotic plaque leeside of the recirculation zone, an obvious catch bond region of wall shear stress might exist especially under low Reynolds number with stenosis rate smaller than 30%. This catch bond region in the plaque leeside might be responsible for the LBF (low blood flow)-enhanced formation of the atherosclerotic plaque.

CONCLUSIONS: This work may provide a novel insight into understanding the biomechanical effects behind the formation and damage of atherosclerotic plaques and propose a new strategy for preventing atherosclerotic diseases.

RevDate: 2021-11-30
CmpDate: 2021-11-30

Patel K, H Stark (2021)

Instability of a liquid sheet with viscosity contrast in inertial microfluidics.

The European physical journal. E, Soft matter, 44(11):144 pii:10.1140/epje/s10189-021-00147-1.

Flows at moderate Reynolds numbers in inertial microfluidics enable high throughput and inertial focusing of particles and cells with relevance in biomedical applications. In the present work, we consider a viscosity-stratified three-layer flow in the inertial regime. We investigate the interfacial instability of a liquid sheet surrounded by a density-matched but more viscous fluid in a channel flow. We use linear stability analysis based on the Orr-Sommerfeld equation and direct numerical simulations with the lattice Boltzmann method (LBM) to perform an extensive parameter study. Our aim is to contribute to a controlled droplet production in inertial microfluidics. In the first part, on the linear stability analysis we show that the growth rate of the fastest growing mode [Formula: see text] increases with the Reynolds number [Formula: see text] and that its wavelength [Formula: see text] is always smaller than the channel width w for sufficiently small interfacial tension [Formula: see text]. For thin sheets we find the scaling relation [Formula: see text], where m is viscosity ratio and [Formula: see text] the sheet thickness. In contrast, for thicker sheets [Formula: see text] decreases with increasing [Formula: see text] or m due to the nearby channel walls. Examining the eigenvalue spectra, we identify Yih modes at the interface. In the second part on the LBM simulations, the thin liquid sheet develops two distinct dynamic states: waves traveling along the interface and breakup into droplets with bullet shape. For smaller flow rates and larger sheet thicknesses, we also observe ligament formation and the sheet eventually evolves irregularly. Our work gives some indication how droplet formation can be controlled with a suitable parameter set [Formula: see text].

RevDate: 2021-11-30

Pang M, Zhang T, Meng Y, et al (2021)

Experimental study on the permeability of crushed coal medium based on the Ergun equation.

Scientific reports, 11(1):23030.

Accurate determination of the permeability of crushed coal medium is the basis for the study of their permeability characteristics. To investigate the permeability characteristics of this special porous medium composed of crushed coal particles, the permeability parameters of crushed coal specimens of different initial porosities were measured by designing a lateral-limit compression seepage test system. Parameters were determined separately for specimens of different initial porosities. (1) the Reynolds number distribution region characterising the seepage state was determined and obtained. Specimens with initial porosity distribution between 0.02 and 0.08, and seepage Reynolds number distribution in the low-permeability zone, under Darcy flow; (2) the intrinsic permeability of the crushed coal medium was obtained by using the Ergun equation. The complex inverse proportional relationship between the drag coefficient and Reynolds number was derived; (3) Through the determination of the permeability of the crushed coal medium, the mean value of βK value was obtained to be about 45.7, and the analysis of the permeability of porous medium can determine its critical permeability. The relationship between the Forchheimer number Fo and critical Reynolds number was measured. The results indicate that it conforms to a linear distribution. In-depth analysis of these two parameters can be used to explore the flow transition process between laminar, transition, and turbulent flow. This study provides insight into the permeability characteristics of the media in fractured coal bodies.

RevDate: 2021-11-29

Krane M (2021)

Vortex Formation Times in the Glottal Jet, Measured in a Scaled-Up Model.

Fluids (Basel, Switzerland), 6(11):.

In this paper, the timing of vortex formation on the glottal jet is studied using previously published velocity measurements of flow through a scaled-up model of the human vocal folds. The relative timing of the pulsatile glottal jet and the instability vortices are acoustically important since they determine the harmonic and broadband content of the voice signal. Glottis exit jet velocity time series were extracted from time-resolved planar DPIV measurements. These measurements were acquired at four glottal flow speeds (u SS = 16.1-38 cm/s) and four glottis open times (T o = 5.67-23.7 s), providing a Reynolds number range Re = 4100-9700 and reduced vibration frequency f* = 0.01-0.06. Exit velocity waveforms showed temporal behavior on two time scales, one that correlates to the period of vibration and another characterized by short, sharp velocity peaks (which correlate to the passage of instability vortices through the glottis exit plane). The vortex formation time, estimated by computing the time difference between subsequent peaks, was shown to be not well-correlated from one vibration cycle to the next. The principal finding is that vortex formation time depends not only on cycle phase, but varies strongly with reduced frequency of vibration. In all cases, a strong high-frequency burst of vortex motion occurs near the end of the cycle, consistent with perceptual studies using synthesized speech.

RevDate: 2021-11-27

Jbeili M, J Zhang (2021)

Effects of Microscopic Properties on Macroscopic Thermal Conductivity for Convective Heat Transfer in Porous Materials.

Micromachines, 12(11): pii:mi12111369.

Porous materials are widely used in many heat transfer applications. Modeling porous materials at the microscopic level can accurately incorporate the detailed structure and substance parameters and thus provides valuable information for the complex heat transfer processes in such media. In this study, we use the generalized periodic boundary condition for pore-scale simulations of thermal flows in porous materials. A two-dimensional porous model consisting of circular solid domains is considered, and comprehensive simulations are performed to study the influences on macroscopic thermal conductivity from several microscopic system parameters, including the porosity, Reynolds number, and periodic unit aspect ratio and the thermal conductance at the solid-fluid interface. Our results show that, even at the same porosity and Reynolds number, the aspect ratio of the periodic unit and the interfacial thermal conductance can significantly affect the macroscopic thermal behaviors of porous materials. Qualitative analysis is also provided to relate the apparent thermal conductivity to the complex flow and temperature distributions in the microscopic porous structure. The method, findings and discussions presented in this paper could be useful for fundamental studies, material development, and engineering applications of porous thermal flow systems.

RevDate: 2021-11-27

Li W, Xie Z, Xi K, et al (2021)

Constructal Optimization of Rectangular Microchannel Heat Sink with Porous Medium for Entropy Generation Minimization.

Entropy (Basel, Switzerland), 23(11): pii:e23111528.

A model of rectangular microchannel heat sink (MCHS) with porous medium (PM) is developed. Aspect ratio of heat sink (HS) cell and length-width ratio of HS are optimized by numerical simulation method for entropy generation minimization (EGM) according to constructal theory. The effects of inlet Reynolds number (Re) of coolant, heat flux on bottom, porosity and volume proportion of PM on dimensionless entropy generation rate (DEGR) are analyzed. From the results, there are optimal aspect ratios to minimize DEGR. Given the initial condition, DEGR is 33.10% lower than its initial value after the aspect ratio is optimized. With the increase of Re, the optimal aspect ratio declines, and the minimum DEGR drops as well. DEGR gets larger and the optimal aspect ratio remains constant with the increasing of heat flux on bottom. For the different volume proportion of PM, the optimal aspect ratios are diverse, but the minimum DEGR almost stays unchanged. The twice minimized DEGR, which results from aspect ratio and length-width ratio optimized simultaneously, is 10.70% lower than the once minimized DEGR. For a rectangular bottom, a lower DEGR can be reached by choosing the proper direction of fluid flow.

RevDate: 2021-11-27

Khan MF, Sulaiman M, Tavera Romero CA, et al (2021)

A Hybrid Metaheuristic Based on Neurocomputing for Analysis of Unipolar Electrohydrodynamic Pump Flow.

Entropy (Basel, Switzerland), 23(11): pii:e23111513.

A unipolar electrohydrodynamic (UP-EHD) pump flow is studied with known electric potential at the emitter and zero electric potential at the collector. The model is designed for electric potential, charge density, and electric field. The dimensionless parameters, namely the electrical source number (Es), the electrical Reynolds number (ReE), and electrical slip number (Esl), are considered with wide ranges of variation to analyze the UP-EHD pump flow. To interpret the pump flow of the UP-EHD model, a hybrid metaheuristic solver is designed, consisting of the recently developed technique sine-cosine algorithm (SCA) and sequential quadratic programming (SQP) under the influence of an artificial neural network. The method is abbreviated as ANN-SCA-SQP. The superiority of the technique is shown by comparing the solution with reference solutions. For a large data set, the technique is executed for one hundred independent experiments. The performance is evaluated through performance operators and convergence plots.

RevDate: 2021-11-27

Jia Y, Huang J, Wang J, et al (2021)

Heat Transfer and Fluid Flow Characteristics of Microchannel with Oval-Shaped Micro Pin Fins.

Entropy (Basel, Switzerland), 23(11): pii:e23111482.

A novel microchannel heat sink with oval-shaped micro pin fins (MOPF) is proposed and the characteristics of fluid flow and heat transfer are studied numerically for Reynolds number (Re) ranging from 157 to 668. In order to study the influence of geometry on flow and heat transfer characteristics, three non-dimensional variables are defined, such as the fin axial length ratio (α), width ratio (β), and height ratio (γ). The thermal enhancement factor (η) is adopted as an evaluation criterion to evaluate the best comprehensive thermal-hydraulic performance of MOPF. Results indicate that the oval-shaped pin fins in the microchannel can effectively prevent the rise of heat surface temperature along the flow direction, which improves the temperature distribution uniformity. In addition, results show that for the studied Reynolds number range and microchannel geometries in this paper, the thermal enhancement factor η increases firstly and then decreases with the increase of α and β. In addition, except for Re = 157, η decreases first and then increases with the increase of the fin height ratio γ. The thermal enhancement factor for MOPF with α = 4, β = 0.3, and γ = 0.5 achieves 1.56 at Re = 668. The results can provide a theoretical basis for the design of a microchannel heat exchanger.

RevDate: 2021-11-24

Hernández Meza JM, Cordero JRV, Ramirez Saito MLÁ, et al (2021)

Particle/wall electroviscous effects at the micron scale: comparison between experiments, analytical and numerical models.

Journal of physics. Condensed matter : an Institute of Physics journal [Epub ahead of print].

We report a experimental study of the motion of 1μm single particles interacting with functionalized walls at low and moderate ionic strengths conditions. The 3D particle's trajectories were obtained by analyzing the diffracted particle images (point spread function). The studied particle/wall systems include negatively charged particles interacting with bare glass, glass covered with polyelectrolytes and glass covered with a lipid monolayer. In the low salt regime (pure water) we observed a retardation effect of the short-time diffusion coefficients when the particle interacts with a negatively charged wall; this effect is more severe in the perpendicular than in the lateral component. The decrease of the diffusion as a function of the particle-wall distance h was similar regardless the origin of the negative charge at the wall. When surface charge was screened or salt was added to the medium (10mM), the diffusivity curves recover the classical hydrodynamic behavior. Electroviscous theory based on the thin electrical double layer (EDL) approximation reproduces the experimental data except for small h. On the other hand, 2D numerical solutions of the electrokinetic equations showed good qualitative agreement with experiments. The numerical model also showed that the hydrodynamic and Maxwellian part of the electroviscous total drag tend to zero as h → 0 and how this is linked with the merging of both EDL's at close proximity.

RevDate: 2021-11-24
CmpDate: 2021-11-24

Díaz MV (2021)

On the long-time persistence of hydrodynamic memory.

The European physical journal. E, Soft matter, 44(11):141.

The Basset-Boussinesq-Oseen (BBO) equation correctly describes the nonuniform motion of a spherical particle at a low Reynolds number. It contains an integral term with a singular kernel which accounts for the diffusion of vorticity around the particle throughout its entire history. However, if there are any departures in either rigidity or shape from a solid sphere, besides the integral force with a singular kernel, the Basset history force, we should add a second history force with a non-singular kernel, related to the shape or composition of the particle. In this work, we introduce a fractional generalized Basset-Boussinesq-Oseen equation which includes both history terms as fractional derivatives. Using the Laplace transform, an integral representation of the solution is obtained. For a driven single particle, the solution shows that memory effects persist indefinitely under rather general driving conditions.

RevDate: 2021-11-22

Yin B, Yue W, Sohan ASMMF, et al (2021)

Micromixer with Fine-Tuned Mathematical Spiral Structures.

ACS omega, 6(45):30779-30789.

Micromixers with the microchannel structure can enable rapid and efficient mixing of multiple types of fluids on a microfluidic chip. Herein, we report the mixing performance of three passive micromixers based on the different mathematical spiral structures. We study the fluid flow characteristics of Archimedes spiral, Fermat spiral, and hyperbolic spiral structures with various channel widths and Reynolds number (Re) ranging from 0 to 10 via numerical simulation and visualization experiments. In addition, we analyze the mechanism of streamlines and Dean vortices at different cross sections during fluid flows. As the fluid flows in the Fermat spiral channel, the centrifugal force induces the Dean vortex to form a chaotic advection, enhancing the fluid mixing performance. By integrating the Fermat spiral channel into a microfluidic chip, we successfully detect acute myocardial infarction (AMI) marker with the double-antibody sandwich method and reduce the detection time to 10 min. This method has a low reagent consumption and a high reaction efficiency and demonstrates great potential in point-of-care testing (POCT).

RevDate: 2021-11-19

Jaccod A, S Chibbaro (2021)

Constrained Reversible System for Navier-Stokes Turbulence.

Physical review letters, 127(19):194501.

Following a Gallavotti's conjecture, stationary states of Navier-Stokes fluids are proposed to be described equivalently by alternative equations besides the Navier-Stokes equation itself. We discuss a model system symmetric under time reversal based on the Navier-Stokes equations constrained to keep the enstrophy constant. It is demonstrated through highly resolved numerical experiments that the reversible model evolves to a stationary state which reproduces quite accurately all statistical observables relevant for the physics of turbulence extracted by direct numerical simulations (DNS) at different Reynolds numbers. The possibility of using reversible models to mimic turbulence dynamics is of practical importance for the coarse-grained version of Navier-Stokes equations, as used in large-eddy simulations. Furthermore, the reversible model appears mathematically simpler, since enstrophy is bounded to be constant for every Reynolds number. Finally, the theoretical interest in the context of statistical mechanics is briefly discussed.

RevDate: 2021-11-16

An X, Dong B, Wang Y, et al (2021)

Coupled lattice Boltzmann-large eddy simulation model for three-dimensional multiphase flows at large density ratio and high Reynolds number.

Physical review. E, 104(4-2):045305.

A coupled lattice Boltzmann-large eddy simulation model is developed for modeling three-dimensional multiphase flows at large density ratios and high Reynolds numbers. In the framework of the lattice Boltzmann method, the model is proposed based on the standard Smagorinsky subgrid-scale approach, and a reconstructed multiple-relaxation-time collision operator is adopted. The conservative Allen-Cahn equation and Navier-Stokes equations are solved through the lattice Boltzmann discretization scheme for the interface tracking and velocity field evolution, respectively. Relevant benchmark cases are carried out to validate the performance of this model in simulating multiphase flows at a large density ratio and a high Reynolds number, including a stationary droplet, the process of spinodal decomposition, the Rayleigh-Taylor instability, the phenomenon of a droplet splashing on a thin liquid film, and the liquid jet breakup process. The maximum values of density ratio and Re number are 1000 and 10 240, respectively. The capability and reliability of the proposed model have been demonstrated by the good agreement between simulation results and the analytical solutions or the previously available results.

RevDate: 2021-11-15

Braun S, Scheichl S, D Kuzdas (2021)

The triple-deck stage of marginal separation.

Journal of engineering mathematics, 128(1):16.

The method of matched asymptotic expansions is applied to the investigation of transitional separation bubbles. The problem-specific Reynolds number is assumed to be large and acts as the primary perturbation parameter. Four subsequent stages can be identified as playing key roles in the characterization of the incipient laminar-turbulent transition process: due to the action of an adverse pressure gradient, a classical laminar boundary layer is forced to separate marginally (I). Taking into account viscous-inviscid interaction then enables the description of localized, predominantly steady, reverse flow regions (II). However, certain conditions (e.g. imposed perturbations) may lead to a finite-time breakdown of the underlying reduced set of equations. The ensuing consideration of even shorter spatio-temporal scales results in the flow being governed by another triple-deck interaction. This model is capable of both resolving the finite-time singularity and reproducing the spike formation (III) that, as known from experimental observations and direct numerical simulations, sets in prior to vortex shedding at the rear of the bubble. Usually, the triple-deck stage again terminates in the form of a finite-time blow-up. The study of this event gives rise to a noninteracting Euler-Prandtl stage (IV) associated with unsteady separation, where the vortex wind-up and shedding process takes place. The focus of the present paper lies on the triple-deck stage III and is twofold: firstly, a comprehensive numerical investigation based on a Chebyshev collocation method is presented. Secondly, a composite asymptotic model for the regularization of the ill-posed Cauchy problem is developed.

Supplementary Information: The online version contains supplementary material available at 10.1007/s10665-021-10125-3.

RevDate: 2021-11-12

Yu P, V Durgesh (2021)

Application of Dynamic Mode Decomposition to Study Temporal Flow Behavior in a Saccular Aneurysm.

Journal of biomechanical engineering pii:1127960 [Epub ahead of print].

Aneurysms are abnormal expansion of weakened blood vessels which can cause mortality or long-term disability upon rupture. Several studies have shown that inflow conditions spatially and temporally influence aneurysm flow behavior. The objective of this investigation is to identify impact of inflow conditions on spatio-temporal flow behavior in an aneurysm using Dynamic Mode Decomposition (DMD). For this purpose, low-frame rate velocity field measurements are performed in an idealized aneurysm model using Particle Image Velocimetry (PIV). The inflow conditions are precisely controlled using a ViVitro SuperPump system where non-dimensional fluid parameters such as peak Reynolds number (Rep) and Womersely number (α) are varied from 50-270 and 2-5, respectively. The results show the ability of DMD to identify the spatial flow structures and their frequency content. Furthermore, DMD captured the impact of inflow conditions, and change in mode shapes, amplitudes, frequency, and growth rate information is observed. The DMD low-order flow reconstruction also showed the complex interplay of flow features for each inflow scenario. Furthermore, the low-order reconstruction results provided a mathematical description of the flow behavior in the aneurysm which captured the vortex formation, evolution, and convection in detail. These results indicated that the vortical structure behavior varied with the change in α while its strength and presence of secondary structures is influenced by the change in Rep.

RevDate: 2021-11-10

Hu F, Zhang S, Wang X, et al (2021)

Quantitative hydrodynamic characterization of high solid anaerobic digestion: correlation of "mixing-fluidity-energy" and scale-up effect.

Bioresource technology pii:S0960-8524(21)01579-0 [Epub ahead of print].

High solid anaerobic digestion (HSAD)'s complex rheological behavior exhibits short-circuiting and dead zone. Mixing optimization is potential to enhance HSAD hydrodynamics. Besides, scale-up effect is quite essential for HSAD's applications, but remains rarely studied yet. Effect of impeller with different width on the correlation of "mixing-fluidity-energy" at different rotating speeds was first investigated at pilot-scale in present work. Then, scale-up effect based on rotating speed and a generalized Reynolds number was revealed from the aspects of fluidity and energy consumption. Results show that impeller width of 100 mm (10 rpm), 200 mm and 300 mm (5 and 10 rpm) are preferred for hydrodynamics and energy economics. Furthermore, Re similarity has better referential significance for the scale-up. In this study, new insight is gained into the correlation of "mixing-fluidity-energy" within a pilot-scale digester. Scale-up effect based Re similarity could potentially offer guidance for HSAD's application in the practical engineering.

RevDate: 2021-11-08

Lian SJ, Hu ZX, Lan Z, et al (2021)

Optimal Operation of an Oscillatory Flow Crystallizer: Coupling Disturbance and Stability.

ACS omega, 6(43):28912-28922.

In the process of industrial crystallization, it is always difficult to balance the secondary nucleation rate and metastable zone width (MSZW). Herein, we report an experimental and numerical study for the cooling crystallization of paracetamol in an oscillatory flow crystallizer (OFC), finding the optimal operating conditions for balancing the secondary nucleation rate and MSZW. The results show that the MSZW decreases with the increase of oscillation Reynolds number (Re o). Compared to the traditional stirring system, the OFC has an MSZW three times larger than that of the stirring system under a similar power density of consumption. With the numerical simulation, the OFC can produce a stable space environment and instantaneous strong disturbance, which is conducive to the crystallization process. Above all, a high Re o is favorable to produce a sufficient nucleation rate, which may inevitably constrict the MSZW to a certain degree. Then, the optimization strategy of the operating parameter (Re o) in the OFC is proposed.

RevDate: 2021-11-05

Bott AFA, Chen L, Boutoux G, et al (2021)

Inefficient Magnetic-Field Amplification in Supersonic Laser-Plasma Turbulence.

Physical review letters, 127(17):175002.

We report a laser-plasma experiment that was carried out at the LMJ-PETAL facility and realized the first magnetized, turbulent, supersonic (Ma_{turb}≈2.5) plasma with a large magnetic Reynolds number (Rm≈45) in the laboratory. Initial seed magnetic fields were amplified, but only moderately so, and did not become dynamically significant. A notable absence of magnetic energy at scales smaller than the outer scale of the turbulent cascade was also observed. Our results support the notion that moderately supersonic, low-magnetic-Prandtl-number plasma turbulence is inefficient at amplifying magnetic fields compared to its subsonic, incompressible counterpart.

RevDate: 2021-11-05

Behera S, Bhardwaj R, A Agrawal (2021)

Effect of co-flow on fluid dynamics of a cough jet with implications in spread of COVID-19.

Physics of fluids (Woodbury, N.Y. : 1994), 33(10):101701.

We discuss the temporal evolution of a cough jet of an infected subject in the context of the spread of COVID-19. Computations were carried out using large eddy simulation, and, in particular, the effect of the co-flow (5% and 10% of maximum cough velocity) on the evolution of the jet was quantified. The Reynolds number (Re) of the cough jet, based on the mouth opening diameter (D) and the average cough velocity, is 13 002. The time-varying inlet velocity profile of the cough jet is represented as a combination of gamma-probability-distribution functions. Simulations reveal the detailed structure of cough jet with and without a co-flow for the first time, to the best of our knowledge. The cough jet temporal evolution is similar to that of a continuous free-jet and follows the same routes of instability, as documented for a free-jet. The convection velocity of the cough jet decays with time and distance, following a power-law variation. The cough jet is observed to travel a distance of approximately 1.1 m in half a second. However, in the presence of 10% co-flow, the cough jet travels faster and covers the similar distance in just 0.33 s. Therefore, in the presence of a co-flow, the probability of transmission of COVID-19 by airborne droplets and droplet nuclei increases, since they can travel a larger distance. The cough jet without the co-flow corresponds to a larger volume content compared to that with the co-flow and spreads more within the same range of distance. These simulations are significant as they help to reveal the intricate structure of the cough jet and show that the presence of a co-flow can significantly augment the risk of infection of COVID-19.

RevDate: 2021-11-04

Choueiri GH, Lopez JM, Varshney A, et al (2021)

Experimental observation of the origin and structure of elastoinertial turbulence.

Proceedings of the National Academy of Sciences of the United States of America, 118(45):.

Turbulence generally arises in shear flows if velocities and hence, inertial forces are sufficiently large. In striking contrast, viscoelastic fluids can exhibit disordered motion even at vanishing inertia. Intermediate between these cases, a state of chaotic motion, "elastoinertial turbulence" (EIT), has been observed in a narrow Reynolds number interval. We here determine the origin of EIT in experiments and show that characteristic EIT structures can be detected across an unexpectedly wide range of parameters. Close to onset, a pattern of chevron-shaped streaks emerges in qualitative agreement with linear and weakly nonlinear theory. However, in experiments, the dynamics remain weakly chaotic, and the instability can be traced to far lower Reynolds numbers than permitted by theory. For increasing inertia, the flow undergoes a transformation to a wall mode composed of inclined near-wall streaks and shear layers. This mode persists to what is known as the "maximum drag reduction limit," and overall EIT is found to dominate viscoelastic flows across more than three orders of magnitude in Reynolds number.

RevDate: 2021-11-04

Zhou Y, Wang DM, Liu L, et al (2021)

The morphometric of lycopsid sporophylls and the evaluation of their dispersal potential: an example from the Upper Devonian of Zhejiang Province, China.

BMC ecology and evolution, 21(1):198.

BACKGROUND: Previous studies have discussed the special structural adaptations of Late Palaeozoic lycopsids, for example, the dispersal potential of reproductive organs. Based on materials from the Upper Devonian Wutong Formation in Changxing County, Zhejiang Province, China, we now analyze the morphometric and perform some calculation to evaluate the dispersal of sporophyll units of lycopsids.

RESULTS: The fossil sporophyll units are divided into two types in view of obvious difference in shape and we name two new (form) species for them. We also analyze the falling process and give the calculation method of dispersal distance.

CONCLUSIONS: The fossil sporophyll units show relatively poor potential of wind dispersal compared with modern samaras, and show potential adaptation to the turbulent environment.

RevDate: 2021-11-03

Miles JG, NA Battista (2021)

Exploring the sensitivity in jellyfish locomotion under variations in scale, frequency, and duty cycle.

Journal of mathematical biology, 83(5):56.

Jellyfish have been called one of the most energy-efficient animals in the world due to the ease in which they move through their fluid environment, by product of their bell kinematics coupled with their morphological, muscular, material properties. We investigated jellyfish locomotion by conducting in silico comparative studies and explored swimming performance across different fluid scales (i.e., Reynolds Number), bell contraction frequencies, and contraction phase kinematics (duty cycle) for a jellyfish with a fineness ratio of 1 (ratio of bell height to bell diameter). To study these relationships, an open source implementation of the immersed boundary method was used (IB2d) to solve the fully coupled fluid-structure interaction problem of a flexible jellyfish bell in a viscous fluid. Thorough 2D parameter subspace explorations illustrated optimal parameter combinations in which give rise to enhanced swimming performance. All performance metrics indicated a higher sensitivity to bell actuation frequency than fluid scale or duty cycle, via Sobol sensitivity analysis, on a higher performance parameter subspace. Moreover, Pareto-like fronts were identified in the overall performance space involving the cost of transport and forward swimming speed. Patterns emerged within these performance spaces when highlighting different parameter regions, which complemented the global sensitivity results. Lastly, an open source computational model for jellyfish locomotion is offered to the science community that can be used as a starting place for future numerical experimentation.

RevDate: 2021-10-25

Grande Gutiérrez N, Shankar KN, Sinno T, et al (2021)

Thrombosis and Hemodynamics: external and intrathrombus gradients.

Current opinion in biomedical engineering, 19:.

Distinct from dilute, isotropic, and homogeneous reaction systems typically used in laboratory kinetic assays, blood is concentrated, two-phase, flowing, and highly anisotropic when clotting on a surface. This review focuses on spatial gradients that are generated and can dictate thrombus structure and function. Novel experimental and computational tools have recently emerged to explore reaction-transport coupling during clotting. Multiscale simulations help bridge tissue length scales (the coronary arteries) to millimeter scales of a growing clot to the microscopic scale of single-cell signaling and adhesion. Microfluidic devices help create and control pathological velocity profiles, albeit at a low Reynolds number. Since rate processes and force loading are often coupled, this review highlights prevailing convective-diffusive transport physics that modulate cellular and molecular processes during thrombus formation.

RevDate: 2021-10-22

Christov IC (2021)

Soft hydraulics: from Newtonian to complex fluid flows through compliant conduits.

Journal of physics. Condensed matter : an Institute of Physics journal [Epub ahead of print].

Microfluidic devices manufactured from soft polymeric materials have emerged as a paradigm for cheap, disposable and easy-to-prototype fluidic platforms for integrating chemical and biological assays and analyses. The interplay between the flow forces and the inherently compliant conduits of such microfluidic devices requires careful consideration. While mechanical compliance was initially a side-effect of the manufacturing process and materials used, compliance has now become a paradigm, enabling new approaches to microrheological measurements, new modalities of micromixing, and improved sieving of micro- and nano-particles, to name a few applications. This topical review provides an introduction to the physics of these systems. Specifically, the goal of this review is to summarize the recent progress towards a mechanistic understanding of the interaction between non-Newtonian (complex) fluid flows and their deformable confining boundaries. In this context, key experimental results and relevant applications are also explored, hand-in-hand with the fundamental principles for their physics-based modeling. The key topics covered include shear-dependent viscosity of non-Newtonian fluids, hydrodynamic pressure gradients during flow, the elastic response (deformation and bulging) of soft conduits due to flow within, the effect of cross-sectional conduit geometry on the resulting fluid--structure interaction, and key dimensionless groups describing the coupled physics. Open problems and future directions in this nascent field of soft hydraulics, at the intersection of non-Newtonian fluid mechanics, soft matter physics, and microfluidics, are noted.

RevDate: 2021-10-22

Park NS, Yoon S, Jeong W, et al (2021)

A Study on the Evaluation of Flow Distribution Evenness in Parallel-Arrayed-Type Low-Pressure Membrane Module Piping.

Membranes, 11(10): pii:membranes11100751.

The objectives of this study were to measure the flow rate distribution from a header pipe to each module installed in parallel for a water treatment membrane filtration process in operation and to investigate the reason for an uneven distribution of the flow rate via the CFD technique. In addition, this study attempted to propose the ratio of the branch pipe to the header pipe required to equalize the flow distribution for the same membrane filtration process. Finally, the relationship between the Reynolds number in the header pipe and the degree of the manifold flow distribution evenness was investigated. Mobile ultrasonic flow meter was used to measure the flow rate flowing from the membrane module pipe to each module, and the CFD technique was used to verify this. From the results of the actual measurement using ultrasonic flow meter and CFD simulation, it was confirmed that the outflow flow rate from the branch pipe located at the end of the header pipe was three times higher than that of the branch pipe near the inlet. The reason was that the differential pressure generated between each membrane module was higher toward the end of the header pipe. When the ratio of the sum of the cross-sectional area of the branch pipe and the cross-sectional area of the header pipe was reduced by about 30 times, it was confirmed that the flow rate flowing from each branch pipe to the membrane module was almost equal. Also, if the flow in the header pipe is transitional or laminar (Reynolds No. is approximately 4000 or less), the flow rate flowing from each branch pipe to the membrane module can be more even.

RevDate: 2021-10-22

Kim KT, Park JE, Jung SY, et al (2021)

Fouling Mitigation via Chaotic Advection in a Flat Membrane Module with a Patterned Surface.

Membranes, 11(10): pii:membranes11100724.

Fouling mitigation using chaotic advection caused by herringbone-shaped grooves in a flat membrane module is numerically investigated. The feed flow is laminar with the Reynolds number (Re) ranging from 50 to 500. In addition, we assume a constant permeate flux on the membrane surface. Typical flow characteristics include two counter-rotating flows and downwelling flows, which are highly influenced by the groove depth at each Re. Poincaré sections are plotted to represent the dynamical systems of the flows and to analyze mixing. The flow systems become globally chaotic as the groove depth increases above a threshold value. Fouling mitigation via chaotic advection is demonstrated using the dimensionless average concentration (c¯w*) on the membrane and its growth rate. When the flow system is chaotic, the growth rate of c¯w* drops significantly compared to that predicted from the film theory, demonstrating that chaotic advection is an attractive hydrodynamic technique that mitigates membrane fouling. At each Re, there exists an optimal groove depth minimizing c¯w* and the growth rate of c¯w*. Under the optimum groove geometry, foulants near the membrane are transported back to the bulk flow via the downwelling flows, distributed uniformly in the entire channel via chaotic advection.

RevDate: 2021-10-23

Sun X, Mohammed HI, Tiji ME, et al (2021)

Investigation of Heat Transfer Enhancement in a Triple Tube Latent Heat Storage System Using Circular Fins with Inline and Staggered Arrangements.

Nanomaterials (Basel, Switzerland), 11(10): pii:nano11102647.

Inherent fluctuations in the availability of energy from renewables, particularly solar, remain a substantial impediment to their widespread deployment worldwide. Employing phase-change materials (PCMs) as media, saving energy for later consumption, offers a promising solution for overcoming the problem. However, the heat conductivities of most PCMs are limited, which severely limits the energy storage potential of these materials. This study suggests employing circular fins with staggered distribution to achieve improved thermal response rates of PCM in a vertical triple-tube heat exchanger involving two opposite flow streams of the heat-transfer fluid (HTF). Since heat diffusion is not the same at various portions of the PCM unit, different fin configurations, fin dimensions and HTF flow boundary conditions were explored using computational studies of melting in the PCM triple-tube system. Staggered configuration of fin distribution resulted in significant increases in the rates of PCM melting. The results indicate that the melting rate and heat charging rate could be increased by 37.2 and 59.1%, respectively, in the case of staggered distribution. Furthermore, the use of lengthy fins with smaller thickness in the vertical direction of the storage unit resulted in a better positive role of natural convection; thus, faster melting rates were achieved. With fin dimensions of 0.666 mm × 15 mm, the melting rate was found to be increased by 23.6%, when compared to the base case of 2 mm × 5 mm. Finally, it was confirmed that the values of the Reynolds number and inlet temperatures of the HTF had a significant impact on melting time savings when circular fins of staggered distribution were included.

RevDate: 2021-10-23

Yamashita H, Akinaga T, M Sugihara-Seki (2021)

Pattern Transition on Inertial Focusing of Neutrally Buoyant Particles Suspended in Rectangular Duct Flows.

Micromachines, 12(10): pii:mi12101242.

The continuous separation and filtration of particles immersed in fluid flows are important interests in various applications. Although the inertial focusing of particles suspended in a duct flow is promising in microfluidics, predicting the focusing positions depending on the parameters, such as the shape of the duct cross-section and the Reynolds number (Re) has not been achieved owing to the diversity of the inertial-focusing phenomena. In this study, we aimed to elucidate the variation of the inertial focusing depending on Re in rectangular duct flows. We performed a numerical simulation of the lift force exerted on a spherical particle flowing in a rectangular duct and determined the lift-force map within the duct cross-section over a wide range of Re. We estimated the particle trajectories based on the lift map and Stokes drag, and identified the particle-focusing points appeared in the cross-section. For an aspect ratio of the duct cross-section of 2, we found that the blockage ratio changes transition structure of particle focusing. For blockage ratios smaller than 0.3, particles focus near the centres of the long sides of the cross-section at low Re and near the centres of both the long and short sides at relatively higher Re. This transition is expressed as a subcritical pitchfork bifurcation. For blockage ratio larger than 0.3, another focusing pattern appears between these two focusing regimes, where particles are focused on the centres of the long sides and at intermediate positions near the corners. Thus, there are three regimes; the transition between adjacent regimes at lower Re is found to be expressed as a saddle-node bifurcation and the other transition as a supercritical pitchfork bifurcation.

RevDate: 2021-10-19

Khan WU, Imran A, Raja MAZ, et al (2021)

A novel mathematical modeling with solution for movement of fluid through ciliary caused metachronal waves in a channel.

Scientific reports, 11(1):20601.

In the present research, a novel mathematical model for the motion of cilia using non-linear rheological fluid in a symmetric channel is developed. The strength of analytical perturbation technique is employed for the solution of proposed physical process using mectachoronal rhythm based on Cilia induced flow for pseudo plastic nano fluid model by considering the low Reynolds number and long wave length approximation phenomena. The role of ciliary motion for the fluid transport in various animals is explained. Analytical expressions are gathered for stream function, concentration, temperature profiles, axial velocity, and pressure gradient. Whereas, transverse velocity, pressure rise per wave length, and frictional force on the wall of the tubule are investigated with aid of numerical computations and their outcomes are demonstrated graphically. A comprehensive analysis for comparison of Perturb and numerical solution is done. This analysis validates the analytical solution.

RevDate: 2021-10-18

Cui PY, Chen WQ, Wang JQ, et al (2021)

Numerical studies on issues of Re-independence for indoor airflow and pollutant dispersion within an isolated building.

Building simulation pii:846 [Epub ahead of print].

This study conducted the numerical models validated by wind-tunnel experiments to investigate the issues of Re-independence of indoor airflow and pollutant dispersion within an isolated building. The window Reynolds number (Re w) was specified to characterize the indoor flow and dispersion. The indicators of RRC (ratio of relative change) or DR (K_DR) (difference ratio of dimensionless concentration) ≤ 5% were applied to quantitatively determine the critical Re w for indoor flow and turbulent diffusion. The results show that the critical Re (Re crit) value is position-dependent, and Re crit at the most unfavorable position should be suggested as the optimal value within the whole areas of interest. Thus Re H,crit = 27,000 is recommended for the outdoor flows; while Re w,crit = 15,000 is determined for the indoor flows due to the lower part below the window showing the most unfavorable. The suggested Re w,crit (=15,000) for indoor airflow and cross ventilation is independence of the window size. Moreover, taking K_DR ≤ 5% as the indicator, the suggested Re w,crit for ensuring indoor pollutant diffusion enter the Re-independence regime should also be 15,000, indicating that indoor passive diffusion is completely determined by the flow structures. The contours of dimensionless velocity (U/U 0) and concentration (K) against the increasing Re w further confirmed this critical value. This study further reveals the Re-independence issues for indoor flow and dispersion to ensure the reliability of the data obtained by reduced-scale numerical or wind-tunnel models.

RevDate: 2021-10-17

Moitoi AJ, S Shaw (2021)

Magnetic drug targeting during Caputo-Fabrizio fractionalized blood flow through a permeable vessel.

Microvascular research pii:S0026-2862(21)00132-1 [Epub ahead of print].

Nanoparticle-based drug targeting is an important platform for the treatment of cardiovascular disorders. Magnetic drug targeting is more significant as it is a noninvasive procedure and biocompatible. The present problem aims to understand magnetic drug delivery to a specific location in a permeable blood vessel under the vibration and magnetic environment. Caputo-Fabrizio fractional-order time derivatives are used in the governing equations. The momentum equations are solved analytically and presented in the form of Lorenzo-Hartley and Robotonov-Hartley functions and convolution of the Laplace transform. Convolution integrations are solved by using the numerical integration technique. The Fourth order Runge-Kutta method (RK4) is used to solve the force balance equation. The influence of pertinent parameters such as Reynolds number, pulsatile frequency, magnetic field strength, Darcy number and fractional-order parameters are presented through graphs. It is observed that increasing Reynolds number results in decreasing the tendency of the drug to capture near the tumor site, whereas the pulsatile frequency presents an opposite phenomenon. Increasing the magnetic field strength and Darcy number boosts the capture efficiency of drug particles near the tumor site. The short memory effect efficiently captures the magnetic drug carriers to a specific location under the action of suitable magnetic field strength.

RevDate: 2021-10-18

Calderer MC, Golovaty D, Yao L, et al (2021)

Shear flow of active matter in thin channels.

Physical review. E, 104(3-1):034607.

We study the shear flow of active filaments confined in a thin channel for extensile and contractile fibers. We apply the Ericksen-Leslie equations of liquid crystal flow with an activity source term. The dimensionless form of this system includes the Ericksen, activity, and Reynolds numbers, together with the aspect ratio of the channel, as the main driving parameters. We perform a normal mode stability analysis of the base shear flow. For both types of fibers, we arrive at a comprehensive description of the stability properties and their dependence on the parameters of the system. The transition to unstable frequencies in extensile fibers occurs at a positive threshold value of the activity parameter, whereas for contractile ones a complex behavior is found at low absolute value of the activity number. The latter might be an indication of the biologically relevant plasticity and phase transition issues. In contrast with extensile fibers, flows of contractile ones are also found to be highly sensitive to the Reynolds number. The work on extensile fibers is guided by experiments on active filaments in confined channels and aims at quantifying their findings in the prechaotic regime.

RevDate: 2021-10-15

Gallen AF, Castro M, A Hernandez-Machado (2021)

Red blood cells in low Reynolds number flow: A vorticity-based characterization of shapes in two dimensions.

Soft matter [Epub ahead of print].

Studies on the mechanical properties of red blood cells improve the diagnosis of some blood-related diseases. Some existing numerical methods have successfully simulated the coupling between a fluid and red blood cells. This paper introduces an alternative phase-field model formulation of two-dimensional cells that solves the vorticity and stream function that simplifies the numerical implementation. We integrate red blood cell dynamics immersed in a Poiseuille flow and reproduce previously reported morphologies (slippers or parachutes). In the case of flow in a very wide channel, we discover a new metastable shape referred to as 'anti-parachute' that evolves into a horizontal slipper centered on the channel. This sort of metastable morphology may contribute to the dynamical response of the blood.

RevDate: 2021-10-13

Truong H, Engels T, Wehmann H, et al (2021)

An experimental data-driven mass-spring model of flexibleCalliphorawings.

Bioinspiration & biomimetics [Epub ahead of print].

Insect wings can undergo significant deformation during flapping motion owing to inertial, elastic and aerodynamic forces. Changes in shape then alter aerodynamic forces, resulting in a fully coupled Fluid-Structure Interaction (FSI) problem. Here, we present detailed three-dimensional FSI simulations of deformable blowfly (Calliphora vomitoria) wings in flapping flight. A wing model is proposed using a multi-parameter mass-spring approach chosen for its implementation simplicity and computational efficiency. We train the model to reproduce static elasticity measurements by optimizing its parameters using a genetic algorithm with covariance matrix adaptation (CMA-ES). Wing models trained with experimental data are then coupled to a high-performance flow solver run on massively parallel supercomputers. Different features of the modeling approach and the intra-species variability of elastic properties are discussed. We found that individuals with different wing stiffness exhibit similar aerodynamic properties characterized by dimensionless forces and power at the same Reynolds number. We further study the influence of wing flexibility by comparing between the flexible wings and their rigid counterparts. Under equal prescribed kinematic conditions for rigid and flexible wings, wing flexibility improves lift-to-drag ratio as well as lift-to-power ratio and reduces peak force observed during wing rotation.

RevDate: 2021-10-13

Ali A, Kanwal T, Awais M, et al (2021)

Impact of thermal radiation and non-uniform heat flux on MHD hybrid nanofluid along a stretching cylinder.

Scientific reports, 11(1):20262.

The current research investigates the thermal radiations and non-uniform heat flux impacts on magnetohydrodynamic hybrid nanofluid (CuO-Fe2O3/H2O) flow along a stretching cylinder, which is the main aim of this study. The velocity slip conditions have been invoked to investigate the slippage phenomenon on the flow. The impact of induced magnetic field with the assumption of low Reynolds number is imperceptible. Through the use of appropriate non-dimensional parameters and similarity transformations, the ruling PDE's (partial differential equations) are reduced to set of ODE's (ordinary differential equations), which are then numerically solved using Adams-Bashforth Predictor-Corrector method. Velocity and temperature fields with distinct physical parameters are investigated and explored graphically. The main observations about the hybrid nanofluid and non-uniform heat flux are analyzed graphically. A decrease in the velocity of the fluid is noted with addition of Hybrid nanofluid particles while temperature of the fluid increases by adding the CuO-Fe2O3 particles to the base fluid. Also, velocity of the fluid decreases when we incorporate the effects of magnetic field and slip. Raise in curvature parameter γ caused enhancement of velocity and temperature fields at a distance from the cylinder but displays opposite behavior nearby the surface of cylinder. The existence of heat generation and absorption for both mass dependent and time dependent parameters increases the temperature of the fluid.

RevDate: 2021-10-12

Ho TM, Yang J, PA Tsai (2021)

Microfluidic mass transfer of CO2 at elevated pressures: implications for carbon storage in deep saline aquifers.

Lab on a chip, 21(20):3942-3951.

Carbon capture and sequestration (CCS) in a deep saline aquifer is one of the most promising technologies to mitigate anthropologically emitted carbon dioxide. Accurately quantifying the mass transport of CO2 at pore-scales is crucial but challenging for successful CCS deployment. Here, we conduct high-pressure microfluidic experiments, mimicking reservoir conditions up to 9.5 MPa and 35 °C, to elucidate the microfluidic mass transfer process of CO2 at three different states (i.e., gas, liquid, and supercritical phase) into water. We measure the size change of CO2 micro-bubbles/droplets generated using a microfluidic T-junction to estimate the volumetric mass transfer coefficient (kLa), quantifying the rate change of CO2 concentration under the driving force of concentration gradient. The results show that bubbles/droplets under high-pressure conditions reach a steady state faster than low pressure. The measured volumetric mass transfer coefficient increases with the Reynolds number (based on the liquid slug) and is nearly independent of the injection pressure for both the gas and liquid phases. In addition, kLa significantly enlarges with increasing high pressure at the supercritical state. Compared with various chemical engineering applications using millimeter-sized capillaries (with typical kLa measured ranging from ≈0.005 to 0.8 s-1), the microfluidic results show a significant increase in the volumetric mass transfer of CO2 into water by two to three orders of magnitude, O (102-103), with decreasing hydrodynamic diameter (of ≈50 μm).

RevDate: 2021-10-12

Liao Y, Mechulam Y, B Lassalle-Kaiser (2021)

A millisecond passive micromixer with low flow rate, low sample consumption and easy fabrication.

Scientific reports, 11(1):20119.

Fast mixing of small volumes of solutions in microfluidic devices is essential for an accurate control and observation of the dynamics of a reaction in biological or chemical studies. It is often, however, a challenging task, as the Reynolds number (Re) in microscopic devices is typically < 100. In this report, we detail a novel mixer based on the "staggered herring bone" (SHB) pattern and "split-recombination" strategies with an optimized geometry, the periodic rotation of the flow structure can be controlled and recombined in a way that the vortices and phase shifts of the flow induce intertwined lamellar structures, thus increasing the contact surface and enhancing mixing. The optimization improves the mixing while using a low flow rate, hence a small volume for mixing and moderate pressure drops. The performances of the patterns were first simulated using COMSOL Multiphysics under different operating conditions. The simulation indicates that at very low flow rate (1-12 µL·min-1) and Re (3.3-40), as well as a very small working volume (~ 3 nL), a very good mixing (~ 98%) can be achieved in the ms time range (4.5-78 ms). The most promising design was then visualized experimentally, showing results that are consistent with the outcomes of the simulations. Importantly, the devices were fabricated using a classical soft-lithography method, as opposed to additive manufacturing often used to generate complex mixing structures. This new device minimizes the sample consumption and could therefore be applied for studies using precious samples.

RevDate: 2021-10-09

Hussain A, Hassan A, Mdallal QA, et al (2021)

Comsolic solution of an elliptic cylindrical compressible fluid flow.

Scientific reports, 11(1):20030.

In this article, the primary focus is to investigate the heat transfer effects with viscous compressible laminar flow in the permeable elliptic cylinder. The Reynolds number is kept 100 for flow to be laminar. The physics of heat transfer is selected to be coupled with the laminar flow. The results for particular step-size time for Velocity distribution, pressure profile, temperature profile, isothermal temperature contours, and drag coefficient have been analyzed. Mesh has been generated through COMSOL, mesh entities have been elaborated statistically. The maximum and minimum velocity profile is observed at the elliptical cylinder's walls and upper, lower boundary respectively. The maximum velocity observed is 2.22 m/s. Pressure profile around elliptic corners is found maximum, distinct patterns are observed even under the influence of applied heat. Temperature is observed maximum at walls but it gradually increases as moving from the upper boundary towards the lower boundary. The isothermal contour patterns are observed maximum near the walls, drag coefficient of gradual decrease is observed. COMSOL multi-physics is utilized for mathematical modeling of problems and the Backward-Differentiation-Formula has been exploited to handle problems numerically. The results will help greatly to understand the characterizations of viscous fluids and in industries like air furnaces and automobile cooling systems.

RevDate: 2021-10-08

Khalid M, Shankar V, G Subramanian (2021)

Continuous Pathway between the Elasto-Inertial and Elastic Turbulent States in Viscoelastic Channel Flow.

Physical review letters, 127(13):134502.

Viscoelastic plane Poiseuille flow is shown to become linearly unstable in the absence of inertia, in the limit of high elasticities, for ultradilute polymer solutions. While inertialess elastic instabilities have been predicted for curvilinear shear flows, this is the first ever report of a purely elastic linear instability in a rectilinear shear flow. The novel instability continues up to a Reynolds number (Re) of O(1000), corresponding to the recently identified elasto-inertial turbulent state believed to underlie the maximum-drag-reduced regime. Thus, for highly elastic ultradilute polymer solutions, a single linearly unstable modal branch may underlie transition to elastic turbulence at zero Re and to elasto-inertial turbulence at moderate Re, implying the existence of continuous pathways connecting the turbulent states to each other and to the laminar base state.

RevDate: 2021-10-05

Marusic I, Chandran D, Rouhi A, et al (2021)

An energy-efficient pathway to turbulent drag reduction.

Nature communications, 12(1):5805.

Simulations and experiments at low Reynolds numbers have suggested that skin-friction drag generated by turbulent fluid flow over a surface can be decreased by oscillatory motion in the surface, with the amount of drag reduction predicted to decline with increasing Reynolds number. Here, we report direct measurements of substantial drag reduction achieved by using spanwise surface oscillations at high friction Reynolds numbers ([Formula: see text]) up to 12,800. The drag reduction occurs via two distinct physical pathways. The first pathway, as studied previously, involves actuating the surface at frequencies comparable to those of the small-scale eddies that dominate turbulence near the surface. We show that this strategy leads to drag reduction levels up to 25% at [Formula: see text] = 6,000, but with a power cost that exceeds any drag-reduction savings. The second pathway is new, and it involves actuation at frequencies comparable to those of the large-scale eddies farther from the surface. This alternate pathway produces drag reduction of 13% at [Formula: see text] = 12,800. It requires significantly less power and the drag reduction grows with Reynolds number, thereby opening up potential new avenues for reducing fuel consumption by transport vehicles and increasing power generation by wind turbines.

RevDate: 2021-10-04

Yogarathinam LT, Velswamy K, Gangasalam A, et al (2021)

Performance evaluation of whey flux in dead-end and cross-flow modes via convolutional neural networks.

Journal of environmental management, 301:113872 pii:S0301-4797(21)01934-4 [Epub ahead of print].

Effluent originating from cheese production puts pressure onto environment due to its high organic load. Therefore, the main objective of this work was to compare the influence of different process variables (transmembrane pressure (TMP), Reynolds number and feed pH) on whey protein recovery from synthetic and industrial cheese whey using polyethersulfone (PES 30 kDa) membrane in dead-end and cross-flow modes. Analysis on the fouling mechanistic model indicates that cake layer formation is dominant as compared to other pore blocking phenomena evaluated. Among the input variables, pH of whey protein solution has the biggest influence towards membrane flux and protein rejection performances. At pH 4, electrostatic attraction experienced by whey protein molecules prompted a decline in flux. Cross-flow filtration system exhibited a whey rejection value of 0.97 with an average flux of 69.40 L/m2h and at an experimental condition of 250 kPa and 8 for TMP and pH, respectively. The dynamic behavior of whey effluent flux was modeled using machine learning (ML) tool convolutional neural networks (CNN) and recursive one-step prediction scheme was utilized. Linear and non-linear correlation indicated that CNN model (R2 - 0.99) correlated well with the dynamic flux experimental data. PES 30 kDa membrane displayed a total protein rejection coefficient of 0.96 with 55% of water recovery for the industrial cheese whey effluent. Overall, these filtration studies revealed that this dynamic whey flux data studies using the CNN modeling also has a wider scope as it can be applied in sensor tuning to monitor flux online by means of enhancing whey recovery efficiency.

RevDate: 2021-10-02

Almalki MM, Alaidarous ES, Maturi DA, et al (2021)

Intelligent computing technique based supervised learning for squeezing flow model.

Scientific reports, 11(1):19597.

In this study, the unsteady squeezing flow between circular parallel plates (USF-CPP) is investigated through the intelligent computing paradigm of Levenberg-Marquard backpropagation neural networks (LMBNN). Similarity transformation introduces the fluidic system of the governing partial differential equations into nonlinear ordinary differential equations. A dataset is generated based on squeezing fluid flow system USF-CPP for the LMBNN through the Runge-Kutta method by the suitable variations of Reynolds number and volume flow rate. To attain approximation solutions for USF-CPP to different scenarios and cases of LMBNN, the operations of training, testing, and validation are prepared and then the outcomes are compared with the reference data set to ensure the suggested model's accuracy. The output of LMBNN is discussed by the mean square error, dynamics of state transition, analysis of error histograms, and regression illustrations.

RevDate: 2021-09-30

Ramzan M, Khan NS, P Kumam (2021)

Mechanical analysis of non-Newtonian nanofluid past a thin needle with dipole effect and entropic characteristics.

Scientific reports, 11(1):19378.

The study concerns with the mechanical characteristics of heat and mass transfer flow of a second grade nanofluid as well as gyrotatic microorganism motion past a thin needle with dipole effect, entropy generation, thermal radiation, Arrhenius activation energy and binar chemical reaction. The governing equations and boundary conditions are simplified by the use of suitable similarity transformations. Homotopy analysis method is implemented to obtain the series solution of non-linear ordinary differential equations. Physical behaviors of heat and mass transfer flow with gyrotatic microorganisms and entropy generation are investigated through the embedded parameters. The nanofluid velocity is enhanced for higher values of the ferromagnetic parameter, local Grashof number, bioconvection Rayleigh number and radiation parameter. The Reynolds number, radiation parameter and Eckert number decrease the nanofluid temperature. The entropy generation is increased with the enhancement of radiation parameter, Eckert number, Lewis number, temperature difference parameter, dimensionless constant parameter, Curie temperature, Prandtl number and concentration difference parameter.

RevDate: 2021-09-29

Treiser MD, Miles MR, Albino FP, et al (2021)

Long-Term Patency and Fluid Dynamics of Recipient Artery after End-to-Side Anastomosis for Free Tissue Transfer.

Plastic and reconstructive surgery pii:00006534-990000000-00400 [Epub ahead of print].

BACKGROUND: End-to-end microvascular anastomoses sacrifice downstream inline perfusion of the recipient vessels. End-to-side anastomoses, in theory, maintain distal inline flow of the recipient vessel. The proposed benefit of the end-to-side technique depends on patency of the distal vessels and subsequent flow parameters, but maintenance of distal perfusion has not been conclusively demonstrated.

METHODS: Fifteen patients who underwent a successful extremity free flap procedure via end-to-side anastomoses to a noncritical vessel between 2003 and 2017 were enrolled. Recipient artery patency distal to the anastomosis was assessed using pulse volume recordings and duplex ultrasound imaging. Resistance indices, flow velocities, vessel diameters, volumetric flow, and turbulent flow dimensionless number (Reynolds number) were measured. Comparisons were made to the ipsilateral collateral vessel as well as to the vessels on the nonoperative contralateral limb using paired t tests.

RESULTS: Downstream flow was identified in 14 of 15 patients (93 percent patency). There was no statistical difference in resistive indices comparing the anastomotic vessel (0.859 ± 0.300) and the collateral vessel (0.853 ± 0.179) of the ipsilateral extremity. Ultrasound flows were similar; the anastomotic vessel demonstrated downstream volumetric flows of 139 ± 92.0 cm3/min versus 137 ± 41.6 cm3/min within the same vessel of the nonoperative contralateral limb. The anastomotic vessel had Reynolds numbers well below the turbulent threshold (448 ± 202 and 493 ± 127 for the anastomotic and nonoperative contralateral limb, respectively).

CONCLUSION: End-to-side anastomosis to noncritical vessels resulted in a 93 percent long-term recipient vessel patency rate, with no statistically significant changes in volumetric flows, resistive indices, or fluid dynamics in the vessels that remained patent.

RevDate: 2021-09-28

Huang L, Du J, Z Zhu (2021)

Neutrally Buoyant Particle Migration in Poiseuille Flow Driven by Pulsatile Velocity.

Micromachines, 12(9): pii:mi12091075.

A neutrally buoyant circular particle migration in two-dimensional (2D) Poiseuille channel flow driven by pulsatile velocity is numerical studied by using immersed boundary-lattice Boltzmann method (IB-LBM). The effects of Reynolds number (25≤Re≤200) and blockage ratio (0.15≤k≤0.40) on particle migration driven by pulsatile and non-pulsatile velocity are all numerically investigated for comparison. The results show that, different from non-pulsatile cases, the particle will migrate back to channel centerline with underdamped oscillation during the time period with zero-velocity in pulsatile cases. The maximum lateral travel distance of the particle in one cycle of periodic motion will increase with increasing Re, while k has little impact. The quasi frequency of such oscillation has almost no business with Re and k. Moreover, Re plays an essential role in the damping ratio. Pulsatile flow field is ubiquitous in aorta and other arteries. This article is conducive to understanding nanoparticle migration in those arteries.

RevDate: 2021-09-28

Farahinia A, Jamaati J, Niazmand H, et al (2021)

Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index.

Micromachines, 12(9): pii:mi12091055.

One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz-Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

RevDate: 2021-09-28

Gimsa J, U Gimsa (2021)

Contributions to a Discussion of Spinosaurus aegyptiacus as a Capable Swimmer and Deep-Water Predator.

Life (Basel, Switzerland), 11(9): pii:life11090889.

The new findings on Spinosaurus' swim tail strongly suggest that Spinosaurus was a specialized deep-water predator. However, the tail must be seen in the context of the propelled body. The comparison of the flow characteristics of Spinosaurus with geometrically similar animals and their swimming abilities under water must take their Reynolds numbers into account and provide a common context for the properties of Spinosaurus' tail and dorsal sail. Head shape adaptations such as the head crest reduced hydrodynamic disturbance and facilitated stealthy advance, especially when hunting without visual contact, when Spinosaurus could have used its rostral integumentary mechanoreceptors for prey detection. The muscular neck permitted 'pivot' feeding, where the prey's escape abilities were overcome by rapid dorsoventral head movement, facilitated by crest-mediated lower friction.

RevDate: 2021-09-23

Wu R, Xie F, Wei J, et al (2021)

Study on Soot Emission Characteristics of Methane/Oxygen Inverse Diffusion Flame.

ACS omega, 6(36):23191-23202.

Inverse diffusion flame (IDF) is an effective and widely used reaction form in the process of noncatalytic partial oxidation (NC-POX) of gaseous hydrocarbons (such as natural gas and coke oven gas). However, soot is generated in the combustion chamber in the case of unreasonable feeding conditions, and thus causes serious damage to the wall and nozzle. In this study, the effects of the equivalence ratio ([O/C]e), the oxygen flow rate, and the Reynolds number on the soot and CH* emission characteristics of CH4/O2 inverse diffusion flame were comprehensively analyzed based on a hyperspectral imaging system. In addition, the relationship between CH* and soot is explored using Ansys Fluent simulation. The experimental results show that the soot radiation core generation area is located in the outer ring of the flame, and the radial distribution of the radiation intensity is bimodal. With the increase in [O/C]e, the initial position for soot radiation and the overall radiation intensity of soot decrease. In addition, the CH* radiation intensity decreases as [O/C]e increases, and CH* exists in the whole flame. The simulation results clearly show that the existence of CH* is conducive to soot production. The emission intensity and the core area of soot formation increase with the increase in the oxygen velocity. Additionally, the soot emission region increases and the flame tip changes from a round blunt to symmetrical tip with the increase in the Reynolds number.

RevDate: 2021-09-21

Haider N, Shahzad A, Qadri MNM, et al (2021)

Aerodynamic analysis of hummingbird-like hovering flight.

Bioinspiration & biomimetics [Epub ahead of print].

Flapping wing micro aerial vehicles are studied as the substitute for fixed and rotary wing micro aerial vehicles because of the advantages such as agility, maneuverability, and employability in confined environments. Hummingbird's sustainable hovering capability inspires many researchers to develop micro aerial vehicles with similar dynamics. In this research, a wing of a ruby-throated hummingbird is modeled as an insect wing using membrane and stiffeners. The effect of flexibility on the aerodynamic performance of a wing in hovering flight has been studied numerically by using a Fluid-Structure Interaction scheme at a Reynolds Number of 3000. Different wings have been developed by using different positions and thicknesses of the stiffeners. The chordwise and spanwise flexural stiffnesses of all the wings modeled in this work are comparable to insects of similar span and chord length. When the position of the stiffener is varied, the best-performing wing has an average lift coefficient of 0.51. Subsequently, the average lift coefficient is increased to 0.56 when the appropriate thickness of the stiffeners is chosen. The best flexible wing outperforms its rigid counterpart and produces lift and power economy comparable to a real hummingbird's wing. That is, the average lift coefficient and power economy of 0.56 and 0.88 for the best flexible wing as compared to 0.61 and 1.07 for the hummingbird's wing. It can be concluded that a simple manufacturable flexible wing design based on appropriate positioning and thickness of stiffeners can serve as a potential candidate for bio-inspired flapping-wing Micro Aerial Vehicles.

RevDate: 2021-09-16

Javid K, Hassan M, Tripathi D, et al (2021)

Double-diffusion convective biomimetic flow of nanofluid in a complex divergent porous wavy medium under magnetic effects.

Journal of biological physics [Epub ahead of print].

We explore the physical influence of magnetic field on double-diffusive convection in complex biomimetic (peristaltic) propulsion of nanofluid through a two-dimensional divergent channel. Additionally, porosity effects along with rheological properties of the fluid are also retained in the analysis. The mathematical model is developed by equations of continuity, momentum, energy, and mass concentration. First, scaling analysis is introduced to simplify the rheological equations in the wave frame of reference and then get the final form of equations after applying the low Reynolds number and lubrication approach. The obtained equations are solved analytically by using integration method. Physical interpretation of velocity, pressure gradient, pumping phenomena, trapping phenomena, heat, and mass transfer mechanisms are discussed in detail under magnetic and porous environment. The magnitude of velocity profile is reduced by increasing Grashof parameter. The bolus circulations disappeared from trapping phenomena for larger strength of magnetic and porosity medium. The magnitude of temperature profile and mass concentration are increasing by enhancing the Brownian motion parameter. This study can be productive in manufacturing non-uniform and divergent shapes of micro-lab-chip devices for thermal engineering, industrial, and medical technologies.

RevDate: 2021-09-10

Pinto Costa R, Simplice Talla Nwotchouang B, Yao J, et al (2021)

Transition to Turbulence Downstream of a Stenosis for Whole Blood and a Newtonian Analog Under Steady Flow Conditions.

Journal of biomechanical engineering pii:1119455 [Epub ahead of print].

Blood, a multiphase fluid comprised of plasma, blood cells, and platelets, is known to exhibit a shear-thinning behavior at low shear rates and near-Newtonian behavior at higher shear rates. However, less is known about the impact of its multiphase nature on the transition to turbulence. In this study, we experimentally determined the critical Reynolds number at which the flow began to transition to turbulence downstream of an eccentric stenosis for whole porcine blood and a Newtonian blood analog (water-glycerin mixture). Velocity profiles for both fluids were measured under steady-state flow conditions using an ultrasound Doppler probe placed 12 diameters downstream of an eccentric stenosis. Velocity was recorded at 21 locations along the diameter at 11 different flow rates. Normalized turbulent kinetic energy was used to determine the critical Reynolds number for each fluid. Blood rheology was measured before and after each experiment. Tests were conducted on five samples of each fluid inside a temperature-controlled in-vitro flow system. The viscosity at shear rate 1000 s 1 was used to define the Reynolds number for each fluid. The mean critical Reynolds numbers for blood and water-glycerin were 470 ± 27.5 and 395 ± 10, respectively, indicating a ~19% delay in transition to turbulence for whole blood compared to the Newtonian fluid. This finding is consistent with a previous report for steady flow in a straight pipe, suggesting some aspect of blood rheology may serve to suppress, or at least delay, the onset of turbulence in vivo.

RevDate: 2021-09-10

Bu X, Zhou S, Sun M, et al (2021)

Exploring the Relationships between Gas Dispersion Parameters and Differential Pressure Fluctuations in a Column Flotation.

ACS omega, 6(34):21900-21908.

Flotation separation, which is the most important mineral beneficiation technique, is dependent on gas dispersion (hydrodynamic conditions). Thus, many investigations have focused on the precise determination of hydrodynamic conditions such as Reynolds number of the bubbles, bubble velocity, and bubble diameter. However, few studies have examined their relationships with pressure fluctuations in a column flotation. This study introduced the differential pressure fluctuations as an actual variable that could be considered to determine the collection zone's hydrodynamic conditions in a cyclonic microbubble flotation column. In general, the outcomes indicated that superficial gas velocity had the most substantial relationship with the differential pressure fluctuations among other flotation factors (such as pump speed, superficial gas velocity, superficial water velocity, and frother dosage). Furthermore, a high coefficient of determination (R 2 > 0.77) for the equation generated to assess the relationships demonstrated that differential pressure fluctuations could be used as a promising tool to determine the hydrodynamic parameters' characteristics in the flotation columns.

RevDate: 2021-09-12

Aghamiri H, Niknejadi M, D Toghraie (2021)

Analysis of the forced convection of two-phase Ferro-nanofluid flow in a completely porous microchannel containing rotating cylinders.

Scientific reports, 11(1):17811.

In the present work, the forced convection of nanofluid flow in a microchannel containing rotating cylinders is investigated in different geometries. The heat flux applied to the microchannel wall is 10,000 W m-2. The effects of Reynolds number, the volume fraction of nanoparticles, and the porosity percentage of the porous medium are investigated on the flow fields, temperature, and heat transfer rate. Reynolds number values vary from Re = 250-1000, non-dimensional rotational velocities 1 and 2, respectively, and volume fraction of nanoparticles 0-2%. The results show that increasing the velocity of rotating cylinders increases the heat transfer; also, increasing the Reynolds number and volume fraction of nanoparticles increases the heat transfer, pressure drop, and Cf,ave. By comparing the porosity percentages with each other, it is concluded that due to the greater contact of the nanofluid with the porous medium and the creation of higher velocity gradients, the porosity percentage is 45% and the values of are 90% higher than the porosity percentage. Comparing porosity percentages with each other, at porosity percentage 90% is greater than at porosity percentage 45%. On the other hand, increasing the Reynolds number reduces the entropy generation due to heat transfer and increases the entropy generation due to friction. Increasing the volume fraction of nanoparticles increases the entropy generations due to heat transfer and friction.

RevDate: 2021-09-11

Mandell JG, Loke YH, Mass PN, et al (2021)

Altered hemodynamics by 4D flow cardiovascular magnetic resonance predict exercise intolerance in repaired coarctation of the aorta: an in vitro study.

Journal of cardiovascular magnetic resonance : official journal of the Society for Cardiovascular Magnetic Resonance, 23(1):99.

BACKGROUND: Coarctation of the aorta (CoA) is associated with decreased exercise capacity despite successful repair. Altered flow patterns have been identified due to abnormal aortic arch geometry. Our previous work demonstrated aorta size mismatch to be associated with exercise intolerance in this population. In this study, we studied aortic flow patterns during simulations of exercise in repaired CoA using 4D flow cardiovascular magnetic resonance (CMR) using aortic replicas connected to an in vitro flow pump and correlated findings with exercise stress test results to identify biomarkers of exercise intolerance.

METHODS: Patients with CoA repair were retrospectively analyzed after CMR and exercise stress test. Each aorta was manually segmented and 3D printed. Pressure gradient measurements from ascending aorta (AAo) to descending aorta (DAo) and 4D flow CMR were performed during simulations of rest and exercise using a mock circulatory flow loop. Changes in wall shear stress (WSS) and secondary flow formation (vorticity and helicity) from rest to exercise were quantified, as well as estimated DAo Reynolds number. Parameters were correlated with percent predicted peak oxygen consumption (VO2max) and aorta size mismatch (DAAo/DDAo).

RESULTS: Fifteen patients were identified (VO2max 47 to 126% predicted). Pressure gradient did not correlate with VO2max at rest or exercise. VO2max correlated positively with the change in peak vorticity (R = 0.55, p = 0.03), peak helicity (R = 0.54, p = 0.04), peak WSS in the AAo (R = 0.68, p = 0.005) and negatively with peak WSS in the DAo (R = - 0.57, p = 0.03) from rest to exercise. DAAo/DDAo correlated strongly with change in vorticity (R = - 0.38, p = 0.01), helicity (R = - 0.66, p = 0.007), and WSS in the AAo (R = - 0.73, p = 0.002) and DAo (R = 0.58, p = 0.02). Estimated DAo Reynolds number negatively correlated with VO2max for exercise (R = - 0.59, p = 0.02), but not rest (R = - 0.28, p = 0.31). Visualization of streamline patterns demonstrated more secondary flow formation in aortic arches with better exercise capacity, larger DAo, and lower Reynolds number.

CONCLUSIONS: There are important associations between secondary flow characteristics and exercise capacity in repaired CoA that are not captured by traditional pressure gradient, likely due to increased turbulence and inefficient flow. These 4D flow CMR parameters are a target of investigation to identify optimal aortic arch geometry and improve long term clinical outcomes after CoA repair.

RevDate: 2021-08-30

Simonis S, Haussmann M, Kronberg L, et al (2021)

Linear and brute force stability of orthogonal moment multiple-relaxation-time lattice Boltzmann methods applied to homogeneous isotropic turbulence.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 379(2208):20200405.

Multiple-relaxation-time (MRT) lattice Boltzmann methods (LBM) based on orthogonal moments exhibit lattice Mach number dependent instabilities in diffusive scaling. The present work renders an explicit formulation of stability sets for orthogonal moment MRT LBM. The stability sets are defined via the spectral radius of linearized amplification matrices of the MRT collision operator with variable relaxation frequencies. Numerical investigations are carried out for the three-dimensional Taylor-Green vortex benchmark at Reynolds number 1600. Extensive brute force computations of specific relaxation frequency ranges for the full test case are opposed to the von Neumann stability set prediction. Based on that, we prove numerically that a scan over the full wave space, including scaled mean flow variations, is required to draw conclusions on the overall stability of LBM in turbulent flow simulations. Furthermore, the von Neumann results show that a grid dependence is hardly possible to include in the notion of linear stability for LBM. Lastly, via brute force stability investigations based on empirical data from a total number of 22 696 simulations, the existence of a deterministic influence of the grid resolution is deduced. This article is part of the theme issue 'Progress in mesoscale methods for fluid dynamics simulation'.

RevDate: 2021-08-29

Ali A, Jana RN, S Das (2021)

Significance of entropy generation and heat source: the case of peristaltic blood flow through a ciliated tube conveying Cu-Ag nanoparticles using Phan-Thien-Tanner model.

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

The present speculative investigation is concentrated to analyze the entropy generation and heat transfer phenomena in ciliary induced peristalsis of blood with the suspension of hybrid nanoparticles in a tube with heat source impact. The blood is assumed to contain copper (Cu) and silver (Ag) nanoparticles (NPs). The ciliary inner wall of the tube has been considered with small hair-like structures. The Phan-Thien-Tanner (PTT) fluid model is employed to describe the non-Newtonian rheological characteristics of blood. The conservative equations are normalized and simplified by utilizing scaling analysis with the assumption of low Reynolds number and large wavelength approximations. The analytical inspection exposes that the total entropy generation gets a decrement for mounting values of cilia length, while reversed impact is detected for an increment in heat source parameter. Hybrid nano-blood exhibits a greater total entropy number than mono nano-blood. This research study may be beneficial to medical experts and researchers in the field of embryology. Cysts in the ciliated fallopian tube, where embryos develop, are removed by using nanoparticles (nano-drug delivery).

RevDate: 2021-08-31

Parveen N, Awais M, Awan SE, et al (2021)

Entropy Generation Analysis and Radiated Heat Transfer in MHD (Al2O3-Cu/Water) Hybrid Nanofluid Flow.

Micromachines, 12(8):.

This research concerns the heat transfer and entropy generation analysis in the MHD axisymmetric flow of Al2O3-Cu/H2O hybrid nanofluid. The magnetic induction effect is considered for large magnetic Reynolds number. The influences of thermal radiations, viscous dissipation and convective temperature conditions over flow are studied. The problem is modeled using boundary layer theory, Maxwell's equations and Fourier's conduction law along with defined physical factors. Similarity transformations are utilized for model simplification which is analytically solved with the homotopy analysis method. The h-curves up to 20th order for solutions establishes the stability and convergence of the adopted computational method. Rheological impacts of involved parameters on flow variables and entropy generation number are demonstrated via graphs and tables. The study reveals that entropy in system of hybrid nanofluid affected by magnetic induction declines for β while it enhances for Bi, R and λ. Moreover, heat transfer rate elevates for large Bi with convective conditions at surface.

RevDate: 2021-08-29

Ahammad NA, Badruddin IA, Kamangar S, et al (2021)

Heat Transfer and Entropy in a Vertical Porous Plate Subjected to Suction Velocity and MHD.

Entropy (Basel, Switzerland), 23(8):.

This article presents an investigation of heat transfer in a porous medium adjacent to a vertical plate. The porous medium is subjected to a magnetohydrodynamic effect and suction velocity. The governing equations are nondepersonalized and converted into ordinary differential equations. The resulting equations are solved with the help of the finite difference method. The impact of various parameters, such as the Prandtl number, Grashof number, permeability parameter, radiation parameter, Eckert number, viscous dissipation parameter, and magnetic parameter, on fluid flow characteristics inside the porous medium is discussed. Entropy generation in the medium is analyzed with respect to various parameters, including the Brinkman number and Reynolds number. It is noted that the velocity profile decreases in magnitude with respect to the Prandtl number, but increases with the radiation parameter. The Eckert number has a marginal effect on the velocity profile. An increased radiation effect leads to a reduced thermal gradient at the hot surface.

RevDate: 2021-09-08

Gu R, JM Lehn (2021)

Constitutional Dynamic Selection at Low Reynolds Number in a Triple Dynamic System: Covalent Dynamic Adaptation Driven by Double Supramolecular Self-Assembly.

Journal of the American Chemical Society, 143(35):14136-14146.

A triple dynamic complex system has been designed, implementing a dynamic covalent process coupled to two supramolecular self-assembly steps. To this end, two dynamic covalent libraries (DCLs), DCL-1 and DCL-2, have been established on the basis of dynamic covalent C═C/C═N organo-metathesis between two Knoevenagel derivatives and two imines. Each DCL contains a barbituric acid-based Knoevenagel constituent that may undergo a sequential double self-organization process involving first the formation of hydrogen-bonded hexameric supramolecular macrocycles that subsequently undergo stacking to generate a supramolecular polymer SP yielding a viscous gel state. Both DCLs display selective self-organization-driven amplification of the constituent that leads to the SP. Dissociation of the SP on heating causes reversible randomization of the constituent distributions of the DCLs as a function of temperature. Furthermore, diverse distribution patterns of DCL-2 were induced by modulation of temperature and solvent composition. The present dynamic systems display remarkable self-organization-driven constitutional adaption and tunable composition by coupling between dynamic covalent component selection and two-stage supramolecular organization. In more general terms, they reveal dynamic adaptation by component selection in low Reynolds number conditions of living systems where frictional effects dominate inertial behavior.

RevDate: 2021-08-19

Herrera-Amaya A, Seber EK, Murphy DW, et al (2021)

Spatiotemporal Asymmetry in Metachronal Rowing at Intermediate Reynolds Numbers.

Integrative and comparative biology pii:6354788 [Epub ahead of print].

In drag-based swimming, individual propulsors operating at low Reynolds numbers (where viscous forces dominate over inertial forces) must execute a spatially asymmetric stroke to produce net fluid displacement. Temporal asymmetry (that is, differing duration between the power vs. recovery stroke) does not affect the overall generated thrust in this time-reversible regime. Metachronal rowing, in which multiple appendages beat sequentially, is used by a wide variety of organisms from low to intermediate Reynolds numbers. At the upper end of this range, inertia becomes important, and increasing temporal asymmetry can be an effective way to increase thrust. However, the combined effects of spatial and temporal asymmetry are not fully understood in the context of metachronal rowing. To explore the role of spatiotemporal asymmetry in metachronal rowing, we combine laboratory experiments and reduced-order analytical modeling. We measure beat kinematics and generated flows in two species of lobate ctenophores across a range of body sizes, from 7 mm to 40 mm in length. We observe characteristically different flows in ctenophores of differing body size and Reynolds number, and a general decrease in spatial asymmetry and increase in temporal asymmetry with increasing Reynolds number. We also construct a one-dimensional mathematical model consisting of a row of oscillating flat plates whose flow-normal areas change with time, and use it to explore the propulsive forces generated across a range of Reynolds numbers and kinematic parameters. The model results show that while both types of asymmetry increase force production, they have different effects in different regions of the parameter space. These results may have strong biological implications, as temporal asymmetry can be actively controlled while spatial asymmetry is likely to be partially or entirely driven by passive fluid-structure interaction.

RevDate: 2021-08-15

Pattnaik PK, Abbas MA, Mishra S, et al (2021)

Free convective flow of Hamilton-Crosser model gold-water nanofluid through a channel with permeable moving walls.

Combinatorial chemistry & high throughput screening pii:CCHTS-EPUB-117335 [Epub ahead of print].

BACKGROUND: The present manuscript analyses the influence of buoyant forces of a conducting time-dependent nanofluid flow through porous moving walls. The medium is also filled with porous materials. In addition to that, uniform heat source and absorption parameters are considered that affect the nanofluid model.

INTRODUCTION: The model is based on the thermophysical properties of Hamilton-Crosser's nanofluid model, in which a gold nanoparticle is submerged into the base fluid water. Before simulation is obtained by a numerical method, suitable transformation is used to convert nonlinear coupled PDEs to ODEs.

METHOD: Runge-Kutta fourth-order scheme is applied successfully for the first-order ODEs in conjunction with the shooting technique.

RESULT: Computations for the coefficients of rate constants are presented through graphs, along with the behavior of several physical parameters augmented the flow phenomena.

CONCLUSION: The present investigation may be compatible with the applications of biotechnology. It is seen that, inclusion of volume concentration the fluid velocity enhances near the middle layer of the channel and retards near the permeable walls. Also, augmented values of the Reynolds number and both cooling and heating of the wall increases the rate of shear stress.

RevDate: 2021-09-06

Luo Y, Wright M, Xiao Q, et al (2021)

Fluid-structure interaction analysis on motion control of a self-propelled flexible plate near a rigid body utilizing PD control.

Bioinspiration & biomimetics, 16(6):.

Inspired by a previous experimental study of fish swimming near a cylinder, we numerically investigate the swimming and station-holding behavior of a flexible plate ahead of a circular cylinder whose motion is controlled by a proportional-derivative (PD) controller. Specifically, the deformation of this two-dimensional plate is actuated by a periodically varying external force applied on the body surface, which mimics the fish muscle force to produce propulsive thrust. The actuation force amplitude is dynamically adjusted by a feedback controller to instruct the plate to swim the desired distance from an initial position to a target location and then hold the station there. Instead of directly using the instantaneous position signal, an average speed measured over one force actuation period is proposed with the inclusion of instantaneous position information to form the tracking error for the PD control. Our results show that the motion control of swimming and station holding has been achieved by this simple but effective feedback control without large overshoot when approaching the target at different flow conditions and actuation force formulas. Although the swimming distance remains the same, a plate whose initial position is closer to the cylinder requires less energy expenditure to swim to the target location and hold the station there. This is because the low-pressure zone near the trailing edge of the plate is reduced in size, which provides drag reduction, contributing to reduced swimming energy. A higher Reynolds number also leads to energy savings. Under the same control strategy, the swimming performance is more affected by the force-frequency while the phase shift of the actuation force has a less significant impact.

RevDate: 2021-08-15

Lin P, Liu X, Xiong N, et al (2021)

Numerical study on the influence of wall temperature gradient on aerodynamic characteristics of low aspect ratio flying wing configuration.

Scientific reports, 11(1):16295.

With the aim for a low-aspect-ratio flying wing configuration, this study explores the influence of wall temperature gradient on the laminar and turbulent boundary layers of aircraft surface and determines the effect on the transition Reynolds number and wall friction drag. A four-equation turbulence model with transition mode is used to numerically simulate the flow around the model. The variation of wall friction coefficient, transition Reynolds number, and turbulent boundary layer flow with wall temperature are emphatically investigated. Results show that when the wall temperature increases from 288 to 500 K, the boundary layer transition Reynolds number for the wing section increased by approximately 28% and the surface friction drags decreases by approximately 10.7%. The hot wall enhances the viscous effects of the laminar temperature boundary layer, reduces the Reynolds shear stress and turbulent kinetic energy, and increases the flow stability. However, the velocity gradient and shear stress in the bottom of the turbulent boundary layer decreases, which leads to reduced friction shear stress on the wall surface. Therefore, for the low-aspect-ratio flying wing model, the hot wall can delay the boundary layer transition and reduce the friction drag coefficient in the turbulent region.

RevDate: 2021-08-13

Xia WF, Hafeez MU, Khan MI, et al (2021)

Entropy optimized dissipative flow of hybrid nanofluid in the presence of non-linear thermal radiation and Joule heating.

Scientific reports, 11(1):16067.

Present article reads three dimensional flow analysis of incompressible viscous hybrid nanofluid in a rotating frame. Ethylene glycol is used as a base liquid while nanoparticles are of copper and silver. Fluid is bounded between two parallel surfaces in which the lower surface stretches linearly. Fluid is conducting hence uniform magnetic field is applied. Effects of non-linear thermal radiation, Joule heating and viscous dissipation are entertained. Interesting quantities namely surface drag force and Nusselt number are discussed. Rate of entropy generation is examined. Bvp4c numerical scheme is used for the solution of transformed O.D.Es. Results regarding various flow parameters are obtained via bvp4c technique in MATLAB Software version 2019, and displayed through different plots. Our obtained results presents that velocity field decreases with respect to higher values of magnetic parameter, Reynolds number and rotation parameter. It is also observed that the temperature field boots subject to radiation parameter. Results are compared with Ishak et al. (Nonlinear Anal R World Appl 10:2909-2913, 2009) and found very good agreement with them. This agreement shows that the results are 99.99% match with each other.

RevDate: 2021-08-13
CmpDate: 2021-08-12

Alihosseini Y, Azaddel MR, Moslemi S, et al (2021)

Effect of liquid cooling on PCR performance with the parametric study of cross-section shapes of microchannels.

Scientific reports, 11(1):16072.

In recent years, PCR-based methods as a rapid and high accurate technique in the industry and medical fields have been expanded rapidly. Where we are faced with the COVID-19 pandemic, the necessity of a rapid diagnosis has felt more than ever. In the current interdisciplinary study, we have proposed, developed, and characterized a state-of-the-art liquid cooling design to accelerate the PCR procedure. A numerical simulation approach is utilized to evaluate 15 different cross-sections of the microchannel heat sink and select the best shape to achieve this goal. Also, crucial heat sink parameters are characterized, e.g., heat transfer coefficient, pressure drop, performance evaluation criteria, and fluid flow. The achieved result showed that the circular cross-section is the most efficient shape for the microchannel heat sink, which has a maximum heat transfer enhancement of 25% compared to the square shape at the Reynolds number of 1150. In the next phase of the study, the circular cross-section microchannel is located below the PCR device to evaluate the cooling rate of the PCR. Also, the results demonstrate that it takes 16.5 s to cool saliva samples in the PCR well, which saves up to 157.5 s for the whole amplification procedure compared to the conventional air fans. Another advantage of using the microchannel heat sink is that it takes up a little space compared to other common cooling methods.

RevDate: 2021-08-13

Costantini M, Henne U, Klein C, et al (2021)

Skin-Friction-Based Identification of the Critical Lines in a Transonic, High Reynolds Number Flow via Temperature-Sensitive Paint.

Sensors (Basel, Switzerland), 21(15):.

In this contribution, three methodologies based on temperature-sensitive paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shock-wave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Göttingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data.

RevDate: 2021-09-01

Diaz K, Robinson TL, Aydin YO, et al (2021)

A minimal robophysical model of quadriflagellate self-propulsion.

Bioinspiration & biomimetics, 16(6):.

Locomotion at the microscale is remarkably sophisticated. Microorganisms have evolved diverse strategies to move within highly viscous environments, using deformable, propulsion-generating appendages such as cilia and flagella to drive helical or undulatory motion. In single-celled algae, these appendages can be arranged in different ways around an approximately 10 μm long cell body, and coordinated in distinct temporal patterns. Inspired by the observation that some quadriflagellates (bearing four flagella) have an outwardly similar morphology and flagellar beat pattern, yet swim at different speeds, this study seeks to determine whether variations in swimming performance could arise solely from differences in swimming gait. Robotics approaches are particularly suited to such investigations, where the phase relationships between appendages can be readily manipulated. Here, we developed autonomous, algae-inspired robophysical models that can self-propel in a viscous fluid. These macroscopic robots (length and width = 8.5 cm, height = 2 cm) have four independently actuated 'flagella' (length = 13 cm) that oscillate under low-Reynolds number conditions (Re∼O(10-1)). We tested the swimming performance of these robot models with appendages arranged two distinct configurations, and coordinated in three distinct gaits. The gaits, namely the pronk, the trot, and the gallop, correspond to gaits adopted by distinct microalgal species. When the appendages are inserted perpendicularly around a central 'body', the robot achieved a net performance of 0.15-0.63 body lengths per cycle, with the trot gait being the fastest. Robotic swimming performance was found to be comparable to that of the algal microswimmers across all gaits. By creating a minimal robot that can successfully reproduce cilia-inspired drag-based swimming, our work paves the way for the design of next-generation devices that have the capacity to autonomously navigate aqueous environments.

RevDate: 2021-08-09

Li L, Chen Q, Sui G, et al (2021)

A Three-Dimensional Micromixer Using Oblique Embedded Ridges.

Micromachines, 12(7):.

A micromixer is one of the most significant components in a microfluidic system. A three-dimensional micromixer was developed with advantages of high efficiency, simple fabrication, easy integration, and ease of mass production. The designed principle is based on the concepts of splitting-recombination and chaotic advection. A numerical model of this micromixer was established to characterize the mixing performance for different parameters. A critical Reynolds number (Re) was obtained from the simulation results. When the Re number is smaller than the critical value, the fluid mixing is mainly dependent on the mechanism of splitting-recombination, therefore, the length of the channel capable of complete mixing (complete mixing length) increases as the Re number increases. When the Re number is larger than the critical value, the fluid mixing is dominated by chaotic advection, and the complete mixing length decreases as the Re number increases. For normal fluids, a complete mixing length of 500 µm can be achieved at a very small Re number of 0.007 and increases to 2400 µm as the Re number increases to the critical value of 4.7. As the Re number keep increasing and passes the critical Re number, the complete mixing length continues to descend to 650 µm at the Re number of 66.7. For hard-to-mix fluids (generally referring to fluids with high viscosity and low diffusion coefficient, which are difficult to mix), even though no evidence of strong chaotic advection is presented in the simulation, the micromixer can still achieve a complete mixing length of 2550 µm. The mixing performance of the micromixer was also verified by experiments. The experimental results showed a consistent trend with the numerical simulation results, which both climb upward when the Re number is around 0.007 (flow rate of 0.03 μm/min) to around 10 (flow rate of 50 μm/min), then descend when the Re number is around 13.3 (flow rate of 60 µm/min).

RevDate: 2021-08-09

Nichka VS, Nikonenko VV, L Bazinet (2021)

Fouling Mitigation by Optimizing Flow Rate and Pulsed Electric Field during Bipolar Membrane Electroacidification of Caseinate Solution.

Membranes, 11(7):.

The efficiency of separation processes using ion exchange membranes (IEMs), especially in the food industry, is significantly limited by the fouling phenomenon, which is the process of the attachment and growth of certain species on the surface and inside the membrane. Pulsed electric field (PEF) mode, which consists in the application of constant current density pulses during a fixed time (Ton) alternated with pause lapses (Toff), has a positive antifouling impact. The aim of this study was to investigate the combined effect of three different relatively high flow rates of feed solution (corresponding to Reynolds numbers of 187, 374 and 560) and various pulse-pause ratios of PEF current regime on protein fouling kinetics during electrodialysis with bipolar membranes (EDBM) of a model caseinate solution. Four different pulse/pause regimes (with Ton/Toff ratios equal to 10 s/10 s, 10 s/20 s, 10 s/33 s and 10 s/50 s) during electrodialysis (ED) treatment were evaluated at a current density of 5 mA/cm2. It was found that increasing the pause duration and caseinate solution flow rate had a positive impact on the minimization of protein fouling occurring on the cationic surface of the bipolar membrane (BPM) during the EDBM. Both a long pause and high flow rate contribute to a more effective decrease in the concentration of protons and caseinate anions at the BPM surface: a very good membrane performance was achieved with 50 s of pause duration of PEF and a flow rate corresponding to Re = 374. A further increase in PEF pause duration (above 50 s) or flow rate (above Re = 374) did not lead to a significant decrease in the amount of fouling.

RevDate: 2021-08-06

Ferroni C, Bracconi M, Ambrosetti M, et al (2021)

A Fundamental Investigation of Gas/Solid Heat and Mass Transfer in Structured Catalysts Based on Periodic Open Cellular Structures (POCS).

Industrial & engineering chemistry research, 60(29):10522-10538.

In this work, we investigate the gas-solid heat and mass transfer in catalytically activated periodic open cellular structures, which are considered a promising solution for intensification of catalytic processes limited by external transport, aiming at the derivation of suitable correlations. Computational fluid dynamics is employed to investigate the Tetrakaidekahedral and Diamond lattice structures. The influence of the morphological features and flow conditions on the external transport properties is assessed. The strut diameter is an adequate characteristic length for the formulation of heat and mass transfer correlations; accordingly, a power-law dependence of the Sherwood number to the Reynolds number between 0.33 and 0.67 was found according to the flow regimes in the range 1-128 of the Reynolds number. An additional -1.5-order dependence on the porosity is found. The formulated correlations are in good agreement with the simulation results and allow for the accurate evaluation of the external transfer coefficients for POCS.

RevDate: 2021-08-03

Liu K, Allahyari M, Salinas J, et al (2021)

Investigation of theoretical scaling laws using large eddy simulations for airborne spreading of viral contagion from sneezing and coughing.

Physics of fluids (Woodbury, N.Y. : 1994), 33(6):063318.

Using a set of large eddy point-particle simulations, we explore the fluid dynamics of an ejected puff resulting from a cough/sneeze. The ejection contains over 61 000 potentially virus-laden droplets at an injection Reynolds number of about 46 000, comparable to an actual cough/sneeze. We observe that global puff properties, such as centroid, puff volume, momentum, and buoyancy vary little across realizations. Other properties, such as maximum extent, shape, and edge velocity of the puff, may exhibit substantial variation. In many realizations, a portion of the puff splits off and advances along a random direction, while keeping airborne droplet nuclei afloat. This peeled-off portion provides a mechanism for virus-laden droplets to travel over large distances in a short amount of time. We also observe that the vast majority of droplets remain suspended within the puff after all liquid has evaporated. The main objectives of the study are to (i) evaluate assumptions of Balachandar's et al. theory [Int. J. Multiphase Flow 132, 103439 (2020)], which include buoyancy effects, shape of the puff, and droplet evaporation rate, (ii) obtain values of closure parameters, which include location and time of the virtual origin, and puff entrainment and drag coefficients, and (iii) evaluate the accuracy of the theory in predicting the shape, size, and location of the puff, as well as droplet number density long after ejection. The theory adequately predicts global puff properties including size, velocity, and distance traveled, the largest size of droplets that exit the puff due to settling, and the droplet size distribution within the puff long after ejection.

RevDate: 2021-08-10

Singh RK, Mahato LK, DK Mandal (2021)

Airflow-Assisted Impact of Drops of Various Viscosities: The Role of Viscous Dissipation, Normal Imposed Pressure, and Shear Flow of Air.

Langmuir : the ACS journal of surfaces and colloids, 37(31):9504-9517.

The role of liquid viscosity on the spreading for an airflow-assisted impact of drops on a surface is investigated. The spreading diameter is found to increase with the Reynolds number of the airflow (Reair) for a given viscosity and impact Weber number (We) compared to the still air. The increment is higher at a low We for viscous drops, whereas the effect of Reair dominates at the intermediate We as the viscosity decreases. Two extra forces, the normal imposed pressure and shear force of air, act on the drop and influence the spreading along with the viscous dissipation. The drop's curvature decreases depending on the viscosity and impact velocity while spreading. Large-scale eddies near the drop-surface region are observed due to the separation of the incident airflow. The formation of eddies signifies low-pressure zones, which extract the trapped air, causing the spreading diameter of the viscous drop to increase at a low We. With the increase in the We, the lamella thickness of low-viscosity drops decreases and is pushed out by the air shear causing the spreading factor to increase. The boundary layer thickness is estimated using the energy balance method to predict the maximum spreading factor. The prediction compares well with the experimental one for higher viscosities. The accuracy improves when the effect of low pressure is incorporated. To confirm, the experimental spreading is compared with that obtained from three existing models, and one, which considers the influence, is observed to provide a better prediction.

RevDate: 2021-09-20

Sharifi A, Gendernalik A, Garrity D, et al (2021)

Valveless pumping behavior of the simulated embryonic heart tube as a function of contractile patterns and myocardial stiffness.

Biomechanics and modeling in mechanobiology, 20(5):2001-2012.

During development, the heart begins pumping as a valveless multilayered tube capable of driving blood flow throughout the embryonic vasculature. The mechanical properties and how they interface with pumping function are not well-defined at this stage. Here, we evaluate pumping patterns using a fluid-structure interaction computational model, combined with experimental data and an energetic analysis to investigate myocardial mechanical properties. Through this work, we propose that a myocardium modeled as a Neo-Hookean material with a material constant on the order of 10 kPa is necessary for the heart tube to function with an optimal pressure and cardiac output.

RevDate: 2021-07-23

Akram S, Athar M, Saeed K, et al (2021)

Crossbreed impact of double-diffusivity convection on peristaltic pumping of magneto Sisko nanofluids in non-uniform inclined channel: A bio-nanoengineering model.

Science progress, 104(3):368504211033677.

The consequences of double-diffusivity convection on the peristaltic transport of Sisko nanofluids in the non-uniform inclined channel and induced magnetic field are discussed in this article. The mathematical modeling of Sisko nanofluids with induced magnetic field and double-diffusivity convection is given. To simplify PDEs that are highly nonlinear in nature, the low but finite Reynolds number, and long wavelength estimation are used. The Numerical solution is calculated for the non-linear PDEs. The exact solution of concentration, temperature and nanoparticle are obtained. The effect of various physical parameters of flow quantities is shown in numerical and graphical data. The outcomes show that as the thermophoresis and Dufour parameters are raised, the profiles of temperature, concentration, and nanoparticle fraction all significantly increase.

RevDate: 2021-09-14

Kasoju VT, Moen DS, Ford MP, et al (2021)

Interspecific variation in bristle number on forewings of tiny insects does not influence clap-and-fling aerodynamics.

The Journal of experimental biology, 224(18):.

Miniature insects must overcome significant viscous resistance in order to fly. They typically possess wings with long bristles on the fringes and use a clap-and-fling mechanism to augment lift. These unique solutions to the extreme conditions of flight at tiny sizes (<2 mm body length) suggest that natural selection has optimized wing design for better aerodynamic performance. However, species vary in wingspan, number of bristles (n) and bristle gap (G) to diameter (D) ratio (G/D). How this variation relates to body length (BL) and its effects on aerodynamics remain unknown. We measured forewing images of 38 species of thrips and 21 species of fairyflies. Our phylogenetic comparative analyses showed that n and wingspan scaled positively and similarly with BL across both groups, whereas G/D decreased with BL, with a sharper decline in thrips. We next measured aerodynamic forces and visualized flow on physical models of bristled wings performing clap-and-fling kinematics at a chord-based Reynolds number of 10 using a dynamically scaled robotic platform. We examined the effects of dimensional (G, D, wingspan) and non-dimensional (n, G/D) geometric variables on dimensionless lift and drag. We found that: (1) increasing G reduced drag more than decreasing D; (2) changing n had minimal impact on lift generation; and (3) varying G/D minimally affected aerodynamic forces. These aerodynamic results suggest little pressure to functionally optimize n and G/D. Combined with the scaling relationships between wing variables and BL, much wing variation in tiny flying insects might be best explained by underlying shared growth factors.


RJR Experience and Expertise


Robbins holds BS, MS, and PhD degrees in the life sciences. He served as a tenured faculty member in the Zoology and Biological Science departments at Michigan State University. He is currently exploring the intersection between genomics, microbial ecology, and biodiversity — an area that promises to transform our understanding of the biosphere.


Robbins has extensive experience in college-level education: At MSU he taught introductory biology, genetics, and population genetics. At JHU, he was an instructor for a special course on biological database design. At FHCRC, he team-taught a graduate-level course on the history of genetics. At Bellevue College he taught medical informatics.


Robbins has been involved in science administration at both the federal and the institutional levels. At NSF he was a program officer for database activities in the life sciences, at DOE he was a program officer for information infrastructure in the human genome project. At the Fred Hutchinson Cancer Research Center, he served as a vice president for fifteen years.


Robbins has been involved with information technology since writing his first Fortran program as a college student. At NSF he was the first program officer for database activities in the life sciences. At JHU he held an appointment in the CS department and served as director of the informatics core for the Genome Data Base. At the FHCRC he was VP for Information Technology.


While still at Michigan State, Robbins started his first publishing venture, founding a small company that addressed the short-run publishing needs of instructors in very large undergraduate classes. For more than 20 years, Robbins has been operating The Electronic Scholarly Publishing Project, a web site dedicated to the digital publishing of critical works in science, especially classical genetics.


Robbins is well-known for his speaking abilities and is often called upon to provide keynote or plenary addresses at international meetings. For example, in July, 2012, he gave a well-received keynote address at the Global Biodiversity Informatics Congress, sponsored by GBIF and held in Copenhagen. The slides from that talk can be seen HERE.


Robbins is a skilled meeting facilitator. He prefers a participatory approach, with part of the meeting involving dynamic breakout groups, created by the participants in real time: (1) individuals propose breakout groups; (2) everyone signs up for one (or more) groups; (3) the groups with the most interested parties then meet, with reports from each group presented and discussed in a subsequent plenary session.


Robbins has been engaged with photography and design since the 1960s, when he worked for a professional photography laboratory. He now prefers digital photography and tools for their precision and reproducibility. He designed his first web site more than 20 years ago and he personally designed and implemented this web site. He engages in graphic design as a hobby.

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E-mail: RJR8222@gmail.com

Collection of publications by R J Robbins

Reprints and preprints of publications, slide presentations, instructional materials, and data compilations written or prepared by Robert Robbins. Most papers deal with computational biology, genome informatics, using information technology to support biomedical research, and related matters.

Research Gate page for R J Robbins

ResearchGate is a social networking site for scientists and researchers to share papers, ask and answer questions, and find collaborators. According to a study by Nature and an article in Times Higher Education , it is the largest academic social network in terms of active users.

Curriculum Vitae for R J Robbins

short personal version

Curriculum Vitae for R J Robbins

long standard version

RJR Picks from Around the Web (updated 11 MAY 2018 )