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15 Nov 2018 at 01:32
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Bibliography on: Reynolds Number


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RJR: Recommended Bibliography 15 Nov 2018 at 01:32 Created: 

Reynolds Number

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

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

Citations The Papers (from PubMed®)

RevDate: 2018-11-14

Rigatelli G, Zuin M, Dell'Avvocata F, et al (2018)

Non-invasive Evaluation of Fluid Dynamic of Aortoiliac Atherosclerotic Disease: Impact of Bifurcation Angle and Different Stent Configurations.

Journal of translational internal medicine, 6(3):138-145 pii:jtim-2018-0020.

Objectives: To non-invasively evaluate by computational fluid dynamic (CFD) analysis the physiology and rheology of aortoiliac bifurcation disease at different angles and different stent configurations.

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

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

Conclusion: Bifurcation angle deeply impacts the physiology of aortoiliac bifurcations, which are used to predict the fluid dynamic profile after stenting. CFD, having the potential to be derived both from computed tomography scan or invasive angiography, appears to be an ideal tool to predict fluid dynamic profile before and after stenting in aortoiliac bifurcation.

RevDate: 2018-11-14

Sadri M, Hejranfar K, M Ebrahimi (2018)

Prediction of fluid flow and acoustic field of a supersonic jet using vorticity confinement.

The Journal of the Acoustical Society of America, 144(3):1521.

In this study, the numerical simulation of the fluid flow and acoustic field of a supersonic jet is performed by using high-order discretization and the vorticity confinement (VC) method on coarse grids. The three-dimensional Navier-Stokes equations are considered in the generalized curvilinear coordinate system and the high-order compact finite-difference scheme is applied for the space discretization, and the time integration is performed by the fourth-order Runge-Kutta scheme. A low-pass high-order filter is applied to stabilize the numerical solution. The non-reflecting boundary conditions are adopted for all the free boundaries, and the Kirchhoff surface integration is utilized to obtain the far-field sound pressure levels in a number of observer locations. Comparisons of the jet mean flow and jet aeroacoustics results with the other numerical and experimental data at similar flow conditions are made and show a reasonable agreement. The study shows that the proposed solution methodology based on the high-order compact finite-difference scheme in conjunction with the VC method can reasonably predict the near-field flow and the far-field noise of high Reynolds number jets with a fairly coarser grid than that used in the large eddy simulations and, thus, the computational cost can be significantly decreased.

RevDate: 2018-11-14

Jung BJ, Kim J, Kim JA, et al (2018)

PDMS-Parylene Hybrid, Flexible Microfluidics for Real-Time Modulation of 3D Helical Inertial Microfluidics.

Micromachines, 9(6): pii:mi9060255.

Inertial microfluidics has drawn much attention for its applications for circulating tumor cell separations from blood. The fluid flows and the inertial particle focusing in inertial microfluidic systems are highly dependent on the channel geometry and structure. Flexible microfluidic systems can have adjustable 3D channel geometries by curving planar 2D channels into 3D structures, which will enable tunable inertial separation. We present a poly(dimethylsiloxane) (PDMS)-parylene hybrid thin-film microfluidic system that can provide high flexibility for 3D channel shaping while maintaining the channel cross-sectional shape. The PDMS-parylene hybrid microfluidic channels were fabricated by a molding and bonding technique using initiated chemical vapor deposition (iCVD) bonding. We constructed 3D helical inertial microfluidic channels by coiling a straight 2D channel and studied the inertial focusing while varying radius of curvature and Reynolds number. This thin film structure allows for high channel curvature and high Dean numbers which leads to faster inertial particle focusing and shorter channel lengths than 2D spiral channels. Most importantly, the focusing positions of particles and cells in the microchannel can be tuned in real time by simply modulating the channel curvature. The simple mechanical modulation of these 3D structure microfluidic systems is expected to provide unique advantages of convenient tuning of cell separation thresholds with a single device.

RevDate: 2018-11-14

Ansari MA, Kim KY, SM Kim (2018)

Numerical and Experimental Study on Mixing Performances of Simple and Vortex Micro T-Mixers.

Micromachines, 9(5): pii:mi9050204.

Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the mixing performance was compared with a simple micro T-mixer. In the vortex micro T-mixer, the height of the inlet channels is half of the height of the main mixing channel. The inlet channel connects to the main mixing channel (micromixer) at the one end at an offset position in a fashion that creates vortex flow. In the simple micro T-mixer, the height of the inlet channels is equal to the height of the channel after connection (main mixing channel). Mixing of fluids and flow field have been analyzed for Reynolds numbers in a range from 1⁻80. The study has been further extended to planar serpentine microchannels, which were combined with a simple and a vortex T-junction, to evaluate and verify their mixing performances. The mixing performance of the vortex T-mixer is higher than the simple T-mixer and significantly increases with the Reynolds number. The design is promising for efficiently increasing mixing simply at the T-junction and can be applied to all micromixers.

RevDate: 2018-11-14

Raza W, Ma SB, KY Kim (2018)

Multi-Objective Optimizations of a Serpentine Micromixer with Crossing Channels at Low and High Reynolds Numbers.

Micromachines, 9(3): pii:mi9030110.

In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the micromixer were performed using three-dimensional Navier-Stokes equations and convection-diffusion equation. Three dimensionless design variables that were related to the geometry of the micromixer were selected as design variables for optimization. Mixing index at the exit and pressure drop through the micromixer were employed as two objective functions. A parametric study was carried out to explore the effects of the design variables on the objective functions. Latin hypercube sampling method as a design-of-experiment technique has been used to select design points in the design space. Surrogate modeling of the objective functions was performed by using radial basis neural network. Concave Pareto-optimal curves comprising of Pareto-optimal solutions that represents the trade-off between the objective functions were obtained using a multi-objective genetic algorithm at Re = 1 and 120. Through the optimizations, maximum enhancements of 18.8% and 6.0% in mixing index were achieved at Re = 1 and 120, respectively.

RevDate: 2018-11-09

Galitski V, Kargarian M, S Syzranov (2018)

Dynamo Effect and Turbulence in Hydrodynamic Weyl Metals.

Physical review letters, 121(17):176603.

The dynamo effect is a class of macroscopic phenomena responsible for generating and maintaining magnetic fields in astrophysical bodies. It hinges on the hydrodynamic three-dimensional motion of conducting gases and plasmas that achieve high hydrodynamic and/or magnetic Reynolds numbers due to the large length scales involved. The existing laboratory experiments modeling dynamos are challenging and involve large apparatuses containing conducting fluids subject to fast helical flows. Here we propose that electronic solid-state materials-in particular, hydrodynamic metals-may serve as an alternative platform to observe some aspects of the dynamo effect. Motivated by recent experimental developments, this Letter focuses on hydrodynamic Weyl semimetals, where the dominant scattering mechanism is due to interactions. We derive Navier-Stokes equations along with equations of magnetohydrodynamics that describe the transport of a Weyl electron-hole plasma appropriate in this regime. We estimate the hydrodynamic and magnetic Reynolds numbers for this system. The latter is a key figure of merit of the dynamo mechanism. We show that it can be relatively large to enable observation of the dynamo-induced magnetic field bootstrap in an experiment. Finally, we generalize the simplest dynamo instability model-the Ponomarenko dynamo-to the case of a hydrodynamic Weyl semimetal and show that the chiral anomaly term reduces the threshold magnetic Reynolds number for the dynamo instability.

RevDate: 2018-11-08

Zhou T, Wang H, Shi L, et al (2016)

An Enhanced Electroosmotic Micromixer with an Efficient Asymmetric Lateral Structure.

Micromachines, 7(12): pii:mi7120218.

Homogeneous and rapid mixing in microfluidic devices is difficult to accomplish, owing to the low Reynolds number associated with most flows in microfluidic channels. Here, an efficient electroosmotic micromixer based on a carefully designed lateral structure is demonstrated. The electroosmotic flow in this mixer with an asymmetrical structure induces enhanced disturbance in the micro channel, helping the fluid streams' folding and stretching, thereby enabling appreciable mixing. Quantitative analysis of the mixing efficiency with respect to the potential applied and the flow rate suggests that the electroosmotic microfluidic mixer developed in the present work can achieve efficient mixing with low applied potential.

RevDate: 2018-11-08

Salieb-Beugelaar GB, Gonçalves D, Wolf MP, et al (2016)

Microfluidic 3D Helix Mixers.

Micromachines, 7(10): pii:mi7100189.

Polymeric microfluidic systems are well suited for miniaturized devices with complex functionality, and rapid prototyping methods for 3D microfluidic structures are increasingly used. Mixing at the microscale and performing chemical reactions at the microscale are important applications of such systems and we therefore explored feasibility, mixing characteristics and the ability to control a chemical reaction in helical 3D channels produced by the emerging thread template method. Mixing at the microscale is challenging because channel size reduction for improving solute diffusion comes at the price of a reduced Reynolds number that induces a strictly laminar flow regime and abolishes turbulence that would be desired for improved mixing. Microfluidic 3D helix mixers were rapidly prototyped in polydimethylsiloxane (PDMS) using low-surface energy polymeric threads, twisted to form 2-channel and 3-channel helices. Structure and flow characteristics were assessed experimentally by microscopy, hydraulic measurements and chromogenic reaction, and were modeled by computational fluid dynamics. We found that helical 3D microfluidic systems produced by thread templating allow rapid prototyping, can be used for mixing and for controlled chemical reaction with two or three reaction partners at the microscale. Compared to the conventional T-shaped microfluidic system used as a control device, enhanced mixing and faster chemical reaction was found to occur due to the combination of diffusive mixing in small channels and flow folding due to the 3D helix shape. Thus, microfluidic 3D helix mixers can be rapidly prototyped using the thread template method and are an attractive and competitive method for fluid mixing and chemical reactions at the microscale.

RevDate: 2018-11-08

Lee SJ, Kwon K, Jeon TJ, et al (2016)

Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Particle Tracking Velocimetry.

Micromachines, 7(7): pii:mi7070127.

We describe a quantitative study of vortex generation due to non-equilibrium electrokinetics near a micro/nanochannel interface. The microfluidic device is comprised of a microchannel with a set of nanochannels. These perm-selective nanochannels induce flow instability and thereby produce strong vortex generation. We performed tracking visualization of fluorescent microparticles to obtain velocity fields. Particle tracking enables the calculation of an averaged velocity field and the velocity fluctuations. We characterized the effect of applied voltages and electrolyte concentrations on vortex formation. The experimental results show that an increasing voltage or decreasing concentration results in a larger vortex region and a strong velocity fluctuation. We calculate the normalized velocity fluctuation-whose meaning is comparable to turbulent intensity-and we found that it is as high as 0.12. This value is indicative of very efficient mixing, albeit with a small Reynolds number.

RevDate: 2018-11-08

Lee SJ, Jeon TJ, Kim SM, et al (2016)

Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Spectral Analysis.

Micromachines, 7(7): pii:mi7070109.

We report on our investigation of a low Reynolds number non-equilibrium electrokinetic flow in a micro/nanochannel platform. Non-equilibrium electrokinetic phenomena include so-called concentration polarization in a moderate electric field and vortex formation in a high electric field. We conducted a spectral analysis of non-equilibrium electrokinetic vortices at a micro/nanochannel interface. We found that periodic vortices are formed while the frequency varies with the applied voltages and solution concentrations. At a frequency as high as 60 Hz, vortex generation was obtained with the strongest electric field and the lowest concentration. The power spectra show increasing frequency with increasing voltage or decreasing concentration. We expect that our spectral analysis results will be useful for micromixer developers in the micromachine research field.

RevDate: 2018-11-07

Afzal MJ, Tayyaba S, Ashraf MW, et al (2017)

Simulation, Fabrication and Analysis of Silver Based Ascending Sinusoidal Microchannel (ASMC) for Implant of Varicose Veins.

Micromachines, 8(9): pii:mi8090278.

Bioengineered veins can benefit humans needing bypass surgery, dialysis, and now, in the treatment of varicose veins. The implant of this vein in varicose veins has significant advantages over the conventional treatment methods. Deep vein thrombosis (DVT), vein patch repair, pulmonary embolus, and tissue-damaging problems can be solved with this implant. Here, the authors have proposed biomedical microdevices as an alternative for varicose veins. MATLAB and ANSYS Fluent have been used for simulations of blood flow for bioengineered veins. The silver based microchannel has been fabricated by using a micromachining process. The dimensions of the silver substrates are 51 mm, 25 mm, and 1.1 mm, in length, width, and depth respectively. The dimensions of microchannels grooved in the substrates are 0.9 mm in width and depth. The boundary conditions for pressure and velocity were considered, from 1.0 kPa to 1.50 kPa, and 0.02 m/s to 0.07 m/s, respectively. These are the actual values of pressure and velocity in varicose veins. The flow rate of 5.843 (0.1 nL/s) and velocity of 5.843 cm/s were determined at Reynolds number 164.88 in experimental testing. The graphs and results from simulations and experiments are in close agreement. These microchannels can be inserted into varicose veins as a replacement to maintain the excellent blood flow in human legs.

RevDate: 2018-11-07

Wang Q, Yuan D, W Li (2017)

Analysis of Hydrodynamic Mechanism on Particles Focusing in Micro-Channel Flows.

Micromachines, 8(7): pii:mi8070197.

In this paper, the hydrodynamic mechanism of moving particles in laminar micro-channel flows was numerically investigated. A hydrodynamic criterion was proposed to determine whether particles in channel flows can form a focusing pattern or not. A simple formula was derived to demonstrate how the focusing position varies with Reynolds number and particle size. Based on this proposed criterion, a possible hydrodynamic mechanism was discussed as to why the particles would not be focused if their sizes were too small or the channel Reynolds number was too low. The Re-λ curve (Re, λ respectively represents the channel-based Reynolds number and the particle's diameter scaled by the channel) was obtained using the data fitting with a least square method so as to obtain a parameter range of the focusing pattern. In addition, the importance of the particle rotation to the numerical modeling for the focusing of particles was discussed in view of the hydrodynamics. This research is expected to deepen the understanding of the particle transport phenomena in bounded flow, either in micro or macro fluidic scope.

RevDate: 2018-11-07

Guo X, H Qi (2017)

Analytical Solution of Electro-Osmotic Peristalsis of Fractional Jeffreys Fluid in a Micro-Channel.

Micromachines, 8(12): pii:mi8120341.

The electro-osmotic peristaltic flow of a viscoelastic fluid through a cylindrical micro-channel is studied in this paper. The fractional Jeffreys constitutive model, including the relaxation time and retardation time, is utilized to describe the viscoelasticity of the fluid. Under the assumptions of long wavelength, low Reynolds number, and Debye-Hückel linearization, the analytical solutions of pressure gradient, stream function and axial velocity are explored in terms of Mittag-Leffler function by Laplace transform method. The corresponding solutions of fractional Maxwell fluid and generalized second grade fluid are also obtained as special cases. The numerical analysis of the results are depicted graphically, and the effects of electro-osmotic parameter, external electric field, fractional parameters and viscoelastic parameters on the peristaltic flow are discussed.

RevDate: 2018-11-06

Nourazar SS, Nazari-Golshan A, F Soleymanpour (2018)

On the expedient solution of the magneto-hydrodynamic Jeffery-Hamel flow of Casson fluid.

Scientific reports, 8(1):16358 pii:10.1038/s41598-018-34778-w.

The equation of magneto-hydrodynamic Jeffery-Hamel flow of non-Newtonian Casson fluid in a stretching/shrinking convergent/divergent channel is derived and solved using a new modified Adomian decomposition method (ADM). So far in all problems where semi-analytical methods are used the boundary conditions are not satisfied completely. In the present research, a hybrid of the Fourier transform and the Adomian decomposition method (FTADM), is presented in order to incorporate all boundary conditions into our solution of magneto-hydrodynamic Jeffery-Hamel flow of non-Newtonian Casson fluid in a stretching/shrinking convergent/divergent channel flow. The effects of various emerging parameters such as channel angle, stretching/shrinking parameter, Casson fluid parameter, Reynolds number and Hartmann number on velocity profile are considered. The results using the FTADM are compared with the results of ADM and numerical Range-Kutta fourth-order method. The comparison reveals that, for the same number of components of the recursive sequences over a wide range of spatial domain, the relative errors associated with the new method, FTADM, are much less than the ADM. The results of the new method show that the method is an accurate and expedient approximate analytic method in solving the third-order nonlinear equation of Jeffery-Hamel flow of non-Newtonian Casson fluid.

RevDate: 2018-11-05

Shahzad K, Aeken WV, Mottaghi M, et al (2018)

Aggregation and clogging phenomena of rigid microparticles in microfluidics: Comparison of a discrete element method (DEM) and CFD-DEM coupling method.

Microfluidics and nanofluidics, 22(9):104.

We developed a numerical tool to investigate the phenomena of aggregation and clogging of rigid microparticles suspended in a Newtonian fluid transported through a straight microchannel. In a first step, we implement a time-dependent one-way coupling Discrete Element Method (DEM) technique to simulate the movement and effect of adhesion on rigid microparticles in two- and three-dimensional computational domains. The Johnson-Kendall-Roberts (JKR) theory of adhesion is applied to investigate the contact mechanics of particle-particle and particle-wall interactions. Using the one-way coupled solver, the agglomeration, aggregation and deposition behavior of the microparticles is studied by varying the Reynolds number and the particle adhesion. In a second step, we apply a two-way coupling CFD-DEM approach, which solves the equation of motion for each particle, and transfers the force field corresponding to particle-fluid interactions to the CFD toolbox OpenFOAM. Results for the one-way (DEM) and two-way (CFD-DEM) coupling techniques are compared in terms of aggregate size, aggregate percentages, spatial and temporal evaluation of aggregates in 2D and 3D. We conclude that two-way coupling is the more realistic approach, which can accurately capture the particle-fluid dynamics in microfluidic applications.

RevDate: 2018-11-05

Ma N, Duan Z, Ma H, et al (2018)

Lattice Boltzmann Simulation of the Hydrodynamic Entrance Region of Rectangular Microchannels in the Slip Regime.

Micromachines, 9(2): pii:mi9020087.

Developing a three-dimensional laminar flow in the entrance region of rectangular microchannels has been investigated in this paper. When the hydrodynamic development length is the same magnitude as the microchannel length, entrance effects have to be taken into account, especially in relatively short ducts. Simultaneously, there are a variety of non-continuum or rarefaction effects, such as velocity slip and temperature jump. The available data in the literature appearing on this issue is quite limited, the available study is the semi-theoretical approximate model to predict pressure drop of developing slip flow in rectangular microchannels with different aspect ratios. In this paper, we apply the lattice Boltzmann equation method (LBE) to investigate the developing slip flow through a rectangular microchannel. The effects of the Reynolds number (1 < Re < 1000), channel aspect ratio (0 < ε < 1), and Knudsen number (0.001 < Kn < 0.1) on the dimensionless hydrodynamic entrance length, and the apparent friction factor, and Reynolds number product, are examined in detail. The numerical solution of LBM can recover excellent agreement with the available data in the literature, which proves its accuracy in capturing fundamental fluid characteristics in the slip-flow regime.

RevDate: 2018-11-05

Afzal MJ, Ashraf MW, Tayyaba S, et al (2018)

Sinusoidal Microchannel with Descending Curves for Varicose Veins Implantation.

Micromachines, 9(2): pii:mi9020059.

Approximately 26% of adult people, mostly females, are affected by varicose veins in old age. It is a common reason for distress, loss of efficiency, and worsening living conditions. Several traditional treatment techniques (sclerotherapy and foam sclerotherapy of large veins, laser surgeries and radiofrequency ablation, vein ligation and stripping, ambulatory phlebectomy, and endoscopic vein surgery) have failed to handle this disease effectively. Herein, authors have presented an alternative varicose vein implant method-the descending sinusoidal microchannel (DSMC). DSMC was simulated by Fuzzy logic MATLAB (The MathWorks, Natick, MA, USA) and ANSYS (ANSYS 18.2, perpetual license purchased by Ibadat Education Trust, The University of Lahore, Pakistan) with real and actual conditions. After simulations of DSMC, fabrication and testing were performed. The silver DSMC was manufactured by utilizing a micromachining procedure. The length, width, and depth of the silver substrate were 51 mm, 25 mm, and 1.1 mm, respectively. The measurements of the DSMC channel in the silver wafer substrate were 0.9 mm in width and 0.9 mm in depth. The three descending curves of the DSMC were 7 mm, 6 mm, and 5 mm in height. For pressure, actual conditions were carefully taken as 1.0 kPa to 1.5 kPa for varicose veins. For velocity, actual conditions were carefully taken as 0.02 m/s to 0.07 m/s for these veins. These are real and standard values used in simulations and experiments. At Reynolds number 323, the flow rate and velocity were determined as 1001.0 (0.1 nL/s), 11.4 cm/s and 1015.3 (0.1 nL/s), 12.19 cm/s by MATLAB (The MathWorks, Natick, MA, USA) and ANSYS simulations, respectively. The flow rate and velocity were determined to be 995.3 (0.1 nL/s) and 12.2 cm/s, respectively, at the same Reynolds number (323) in the experiment. Moreover, the Dean number was also calculated to observe Dean vortices. All simulated and experimental results were in close agreement. Consequently, DSMC can be implanted in varicose veins as a new treatment to preserve excellent blood flow in human legs from the original place to avoid tissue damage and other problems.

RevDate: 2018-11-03

Amiri Delouei A, Sajjadi H, Mohebbi R, et al (2018)

Experimental study on inlet turbulent flow under ultrasonic vibration: Pressure drop and heat transfer enhancement.

Ultrasonics sonochemistry pii:S1350-4177(18)30352-3 [Epub ahead of print].

This experimental study examines the impact of ultrasonic vibration on pressure drop and heat transfer enhancement of inlet turbulent flows. A stainless steel tube connected to an ultrasonic transducer and immersed in a constant temperature two-phase fluid was considered as the test section. Regarding the designed configuration, the ultrasonic transducer utilized had an acoustic frequency of 28 kHz and two different power levels of 75 W and 100 W. The experiments were conducted for different ultrasonic power levels, inlet temperatures, and flow rates. The accuracy of measurements was successfully validated via the existing empirical correlations. The results indicate that the effect of ultrasonic vibration on pressure drop and heat transfer enhancement diminishes with the growth of both Reynolds number and inlet temperature. Based on previously reported results on inlet flows with a laminar flow regime, the effect of ultrasonic vibration is very trivial in current turbulent inlet flows (up to 7.28% for heat convection enhancement). The results of the present study will be beneficial for future investigations on designing vibrating heat exchangers.

RevDate: 2018-11-02

Falkovich G, N Vladimirova (2018)

Turbulence Appearance and Nonappearance in Thin Fluid Layers.

Physical review letters, 121(16):164501.

Flows in fluid layers are ubiquitous in industry, geophysics, and astrophysics. Large-scale flows in thin layers can be considered two dimensional with bottom friction added. Here we find that the properties of such flows depend dramatically on the way they are driven. We argue that a wall-driven (Couette) flow cannot sustain turbulence, no matter how small the viscosity and friction. Direct numerical simulations (DNSs) up to the Reynolds number Re=10^{6} confirm that all perturbations die in a plane Couette flow. On the contrary, for sufficiently small viscosity and friction, perturbations destroy the pressure-driven laminar (Poiseuille) flow. What appears instead is a traveling wave in the form of a jet slithering between wall vortices. For 5×10^{3}

RevDate: 2018-11-02

Dong C, Wang L, Huang YM, et al (2018)

Role of the Plasmoid Instability in Magnetohydrodynamic Turbulence.

Physical review letters, 121(16):165101.

The plasmoid instability in evolving current sheets has been widely studied due to its effects on the disruption of current sheets, the formation of plasmoids, and the resultant fast magnetic reconnection. In this Letter, we study the role of the plasmoid instability in two-dimensional magnetohydrodynamic (MHD) turbulence by means of high-resolution direct numerical simulations. At a sufficiently large magnetic Reynolds number (R_{m}=10^{6}), the combined effects of dynamic alignment and turbulent intermittency lead to a copious formation of plasmoids in a multitude of intense current sheets. The disruption of current sheet structures facilitates the energy cascade towards small scales, leading to the breaking and steepening of the energy spectrum. In the plasmoid-mediated regime, the energy spectrum displays a scaling that is close to the spectral index -2.2 as proposed by recent analytic theories. We also demonstrate that the scale-dependent dynamic alignment exists in 2D MHD turbulence and the corresponding slope of the alignment angle is close to 0.25.

RevDate: 2018-10-30

Jhun CS, Siedlecki C, Xu L, et al (2018)

Stress and Exposure Time on von Willebrand Factor Degradation.

Artificial organs [Epub ahead of print].

RevDate: 2018-10-26

Kim H, Kim J, H Choi (2018)

Flow structure modifications by leading-edge tubercles on a 3D wing.

Bioinspiration & biomimetics, 13(6):066011.

Leading-edge tubercles on a humpback whale flipper are known to enhance its hydrodynamic performance at post-stall angles of attack (Miklosovic et al 2004 Phys. Fluids 16 39-42). We investigate vortical structures above a three-dimensional wing with tubercles using surface-oil-flow visualization and particle image velocimetry measurement. Two wing models with and without tubercles, previously studied by Miklosovic et al (2004 Phys. Fluids 16 39-42), are considered at the Reynolds number of 180 000 based on the free-stream velocity and mean chord length. At this Reynolds number, tubercles delay the stall angle by 7° and increase the maximum lift coefficient by about 22%. At a low angle of attack, flow separation first occurs near the tip region for both wing models. While flow separation rapidly progresses inboard (toward the wing root) for the model without tubercles with increasing angle of attack, tubercles produce two types of vortical motions and block the inboard progression of flow separation, resulting in delayed stall from α = 8° to 15°. One of these two vortical structures is pairs of counter-rotating streamwise vortices evolving from hemi-spherical separation bubbles near the leading-edge troughs at pre-, near-, and post-stall angles of attack, and the other is asymmetric pairs of streamwise vortices evolving from separated flow regions after the mid-chord region at near-stall angle of attack. At a post-stall angle of attack (α = 16°), strong clockwise and counter-clockwise streamwise vortices are generated from foci at the root and tip near the trailing edge, respectively, and delay flow separation in the mid-span, resulting in a higher lift coefficient than that without tubercles.

RevDate: 2018-10-23

Bass K, PW Longest (2018)

Recommendations for Simulating Microparticle Deposition at Conditions Similar to the Upper Airways with Two-Equation Turbulence Models.

Journal of aerosol science, 119:31-50.

The development of a CFD model, from initial geometry to experimentally validated result with engineering insight, can be a time-consuming process that often requires several iterations of meshing and solver set-up. Applying a set of guidelines in the early stages can help to streamline the process and improve consistency between different models. The objective of this study was to determine both mesh and CFD solution parameters that enable the accurate simulation of microparticle deposition under flow conditions consistent with the upper respiratory airways including turbulent flow. A 90° bend geometry was used as a characteristic model that occurs throughout the airways and for which high-quality experimental aerosol deposition data is available in the transitional and turbulent flow regimes. Four meshes with varying degrees of near-wall resolution were compared, and key solver settings were applied to determine the parameters that minimize sensitivity to the near-wall (NW) mesh. The Low Reynolds number (LRN) k-ω model was used to resolve the turbulence field, which is a numerically efficient two-equation turbulence model, but has recently been considered overly simplistic. Some recent studies have used more complex turbulence models, such as Large Eddy Simulation (LES), to overcome the perceived weaknesses of two-equation models. Therefore, the secondary objective was to determine whether the more computationally efficient LRN k-ω model was capable of providing deposition results that were comparable to LES. Results show how NW mesh sensitivity is reduced through application of the Green-Gauss Node-based gradient discretization scheme and physically realistic near-wall corrections. Using the newly recommended meshing parameters and solution guidelines gives an excellent match to experimental data. Furthermore, deposition data from the LRN k-ω model compares favorably with LES results for the same characteristic geometry. In summary, this study provides a set of meshing and solution guidelines for simulating aerosol deposition in transitional and turbulent flows found in the upper respiratory airways using the numerically efficient LRN k-ω approach.

RevDate: 2018-10-23

Karakas F, D'Oliveira D, Maas AE, et al (2018)

Using a shell as a wing: pairing of dissimilar appendages in Atlantiid heteropod swimming.

The Journal of experimental biology pii:jeb.192062 [Epub ahead of print].

Atlantiid heteropods are zooplanktonic marine snails which have a calcium carbonate shell and single swimming fin. They actively swim to hunt prey and vertically migrate. Previous accounts of atlantiid heteropod swimming described these animals sculling with the swimming fin while the shell passively hung beneath the body. Here we show, via high speed stereophotogrammetric measurements of body, fin, and shell kinematics, that the atlantiid heteropod Atlanta selvagensis actively flaps both the swimming fin and shell in a highly coordinated wing-like manner in order to swim in the intermediate Reynolds number regime (Re=10-100). The fin and shell kinematics indicate that atlantiid heteropods use unsteady hydrodynamic mechanisms such as the clap and fling and delayed stall. Unique features of atlantid heteropod swimming include the coordinated pairing of dissimilar appendages, use of the clap and fling mechanism twice during each stroke cycle, and the fin's extremely large stroke amplitude which exceeds 180°.

RevDate: 2018-10-22

Astumian RD (2018)

Trajectory and Cycle-Based Thermodynamics and Kinetics of Molecular Machines: The Importance of Microscopic Reversibility.

Accounts of chemical research [Epub ahead of print].

A molecular machine is a nanoscale device that provides a mechanism for coupling energy from two (or more) processes that in the absence of the machine would be independent of one another. Examples include walking of a protein in one direction along a polymeric track (process 1, driving "force" X1 = - F⃗· l⃗) and hydrolyzing ATP (process 2, driving "force" X2 = ΔμATP); or synthesis of ATP (process 1, X1 = -ΔμATP) and transport of protons from the periplasm to the cytoplasm across a membrane (process 2, X2 = ΔμH+); or rotation of a flagellum (process 1, X1 = -torque) and transport of protons across a membrane (process 2, X2 = ΔμH+). In some ways, the function of a molecular machine is similar to that of a macroscopic machine such as a car that couples combustion of gasoline to translational motion. However, the low Reynolds number regime in which molecular machines operate is very different from that relevant for macroscopic machines. Inertia is negligible in comparison to viscous drag, and omnipresent thermal noise causes the machine to undergo continual transition among many states even at thermodynamic equilibrium. Cyclic trajectories among the states of the machine that result in a change in the environment can be broken into two classes: those in which process 1 in either the forward or backward direction ([Formula: see text]) occurs and which thereby exchange work [Formula: see text] with the environment; and those in which process 2 in either the forward or backward direction ([Formula: see text]) occurs and which thereby exchange work [Formula: see text] with the evironment. These two types of trajectories, [Formula: see text] and [Formula: see text], overlap, i.e., there are some trajectories in which both process 1 and process 2 occur, and for which the work exchanged is [Formula: see text]. The four subclasses of overlap trajectories [(+1,+2), (+1,-2), (-1,+2), (-1,-2)] are the coupled processes. The net probabilities for process 1 and process 2 are designated π+2 - π-2 and π+1 - π-1, respectively. The probabilities [Formula: see text] for any single trajectory [Formula: see text] and [Formula: see text] for its microscopic reverse [Formula: see text] are related by microscopic reversibility (MR), [Formula: see text], an equality that holds arbitrarily far from thermodynamic equilibrium, i.e., irrespective of the magnitudes of X1 and X2, and where [Formula: see text]. Using this formalism, we arrive at a remarkably simple and general expression for the rates of the processes, [Formula: see text], i = 1, 2, where the angle brackets indicate an average over the ensemble of all microscopic reverse trajectories. Stochastic description of coupling is doubtless less familiar than typical mechanical depictions of chemical coupling in terms of ATP induced violent kicks, judo throws, force generation and power-strokes. While the mechanical description of molecular machines is comforting in its familiarity, conclusions based on such a phenomenological perspective are often wrong. Specifically, a "power-stroke" model (i.e., a model based on energy driven "promotion" of a molecular machine to a high energy state followed by directional relaxation to a lower energy state) that has been the focus of mechanistic discussions of biomolecular machines for over a half century is, for catalysis driven molecular machines, incorrect. Instead, the key principle by which catalysis driven motors work is kinetic gating by a mechanism known as an information ratchet. Amazingly, this same principle is that by which catalytic molecular systems undergo adaptation to new steady states while facilitating an exergonic chemical reaction.

RevDate: 2018-10-17

Zhang H, Liu C, Ou Y, et al (2018)

Development of a helical coagulation reactor for harvesting microalgae.

Journal of bioscience and bioengineering pii:S1389-1723(18)30625-X [Epub ahead of print].

In this study, an innovative helical coagulation reactor (HCR) was developed for harvesting microalgae by sedimentation with polyaluminium chloride (PAC). The effects of construction and hydrodynamic characteristics on harvesting performance were investigated. Results showed that a higher harvesting efficiency, 96.37%, was achieved for the large and compact flocs generated by the HCR, and the settling rate of flocs was substantially influenced by the velocity gradient (G) and the Reynolds number (Re). When the Reynolds number closed to the transition between laminar and turbulent flow (4000), the flocs settled faster (20.51 m h-1), although settling slowed as the Reynolds number increased further because of ruptured flocs. The settling rate of flocs could be further improved to 23.27 m h-1 by a pulse flow field, mainly due to larger and more compact flocs forming in the plug pipe flow. Furthermore, a comparative investigation of a mechanically agitated vessel and the HCR with the same Camp number (Gt) showed that the HCR achieved higher settling rates and a shorter residence time than those with a mechanical agitator. The HCR provided a uniform dissipation of energy and high velocity gradient while avoiding electrical and mechanical energy consumption, suggesting this reactor is an efficient and economic option for microalgae harvesting.

RevDate: 2018-10-17

Hong W, Shi H, Huang Z, et al (2019)

Design and Simulation of a Passive Micromixer with Gourd-Shaped Channel.

Journal of nanoscience and nanotechnology, 19(1):206-212.

A gourd-shaped contraction-expansion design is proposed for a passive planar micromixer in this study. The mixing performance of the micromixer is analyzed numerically and compared with a T-shaped planar micromixer. The gourd-shaped contraction-expansion structure can enhance the vortex-formation and mixing abilities of the micromixer. The numerical simulation reveals that the gourd-shaped structure can improved vortex generation and mixing efficiency within a high Reynolds number range. The micromixer with an optimized waist width of 50 μm reaches a mixing efficiency of approximately 83.25% and maintains a moderate pressure drop of 4860 Pa at Re = 100. This study can shed light on the design of new 2D micromixers from the point view of bionics.

RevDate: 2018-10-17
CmpDate: 2018-10-17

Sun B, Wang P, Luo J, et al (2018)

A Flexible Hot-Film Sensor Array for Underwater Shear Stress and Transition Measurement.

Sensors (Basel, Switzerland), 18(10): pii:s18103469.

A flexible hot-film sensor array for wall shear stress, flow separation, and transition measurement has been fabricated and implemented in experiments. Parylene C waterproof layer is vapor phase deposited to encapsulate the sensor. Experimental studies of shear stress and flow transition on a flat plate have been undertaken in a water tunnel with the sensor array. Compared with the shear stress derived from velocity profile and empirical formulas, the measuring errors of the hot-film sensors are less than 5%. In addition, boundary layer transition of the flat plate has also been detected successfully. Ensemble-averaged mean, normalized root mean square, and power spectra of the sensor output voltage indicate that the Reynolds number when transition begins at where the sensor array located is 1.82 × 10⁵, 50% intermittency transition is 2.52 × 10⁵, and transition finishes is 3.96 × 10⁵. These results have a good agreement with the transition Reynolds numbers, as measured by the Laser Doppler Velocimetry (LDV) system.

RevDate: 2018-10-10

Tiwari A, SS Chauhan (2018)

Effect of Varying Viscosity on Two-Fluid Model of Blood Flow through Constricted Blood Vessels: A Comparative Study.

Cardiovascular engineering and technology pii:10.1007/s13239-018-00379-x [Epub ahead of print].

PURPOSE: Most of the previously studied non-Newtonian blood flow models considered blood viscosity to be constant but for correct measurement of flow rate and flow resistance, the hematocrit dependent viscosity will be better as various literature suggested the variable nature of blood viscosity. Present work concerns the steady and pulsatile nature of blood flow through constricted blood vessels. Two-fluid model for blood is considered with the suspension of all the RBCs (erythrocytes) in the core region as a non-Newtonian (Herschel-Bulkley) fluid and the plasma in the cell free region near wall as a Newtonian fluid. No slip condition on the wall and radially varying viscosity has been taken.

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

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

CONCLUSIONS: The two-phase fluid model is more significant than the single-fluid model. Effect of viscosity parameter on various hemodynamical quantities has been obtained. It is also concluded that a rising viscosity parameter (varying nature of viscosity) significantly distinguishes the single and two-fluid models in terms of changes in blood flow resistance. The outcome of present study may leave a significant impact on analyzing blood flow through small blood vessels with constriction, where correct measurement of flow rate and flow resistance for medical treatment is very important.

RevDate: 2018-10-14

Karathanassis IK, Trickett K, Koukouvinis P, et al (2018)

Illustrating the effect of viscoelastic additives on cavitation and turbulence with X-ray imaging.

Scientific reports, 8(1):14968 pii:10.1038/s41598-018-32996-w.

The effect of viscoelastic additives on the topology and dynamics of the two-phase flow arising within an axisymmetric orifice with a flow path constriction along its main axis has been investigated employing high-flux synchrotron radiation. X-ray Phase Contrast Imaging (XPCI) has been conducted to visualise the cavitating flow of different types of diesel fuel within the orifice. An additised blend containing Quaternary Ammonium Salt (QAS) additives with a concentration of 500 ppm has been comparatively examined against a pure (base) diesel compound. A high-flux, 12 keV X-ray beam has been utilised to obtain time resolved radiographs depicting the vapour extent within the orifice from two views (side and top) with reference to its main axis. Different test cases have been examined for both fuel types and for a range of flow conditions characterised by Reynolds number of 35500 and cavitation numbers (CN) lying in the range 3.0-7.7. It has been established that the behaviour of viscoelastic micelles in the regions of shear flow is not consistent depending on the cavitation regimes encountered. Namely, viscoelastic effects enhance vortical (string) cavitation, whereas hinder cloud cavitation. Furthermore, the use of additised fuel has been demonstrated to suppress the level of turbulence within the orifice.

RevDate: 2018-10-03

de Matos DB, Barbosa MPR, Leite OM, et al (2018)

Characterization of a tubular electrochemical reactor for the degradation of the commercial diuron herbicide.

Environmental technology [Epub ahead of print].

After designing and constructing an electrochemical reactor with concentric electrodes and tangential feed (RECT), it is necessary to characterize it and to study its performance. The experimental study of the residence time distribution (RTD) was conducted for flow rates of 2.78 × 10-6 m3 s-1, 8.33 × 10-6 m3 s-1 and 13.9 × 10-6 m3 s-1. According to the values obtained from the Pe number (0.67 to 1.52), the RECT fits as tubular with great dispersion. The determined empirical correlation (Sh = 18.16 Re0.50 Sc0.33) showed a laminar flow behavior in the range of Reynolds number (Re) between 23 and 117. In order to use RECT in effluent treatment, an electrochemical oxidation study of the Diuron model molecule (Nortox®) was performed to analyze reactor performance in a closed system with total reflux. A decay kinetics of pseudo-first order was associated with the decay of the concentration of diuron and 30% mineralization in 180 min of process were obtained, having a total volume of 4 × 10-3 m3 and an initial concentration of commercial Diuron in 215.83 mg dm-3. Eleven by-products were identified by HPLC-MS analysis and, from this, it was possible to propose a route of degradation of the diuron. From these observations, it can be inferred that the studied electrochemical reactor had applicability in the degradation of recalcitrant compounds, as is the case of commercial diuron. Make some changes in the electrochemical reactor studied and other advanced oxidative processes, such as electro-Fenton, can be associated with the studied system to achieve a better conversion efficiency.

RevDate: 2018-09-22

Waldrop LD, He Y, S Khatri (2018)

What Can Computational Modeling Tell Us about the Diversity of Odor-Capture Structures in the Pancrustacea?.

Journal of chemical ecology pii:10.1007/s10886-018-1017-2 [Epub ahead of print].

A major transition in the history of the Pancrustacea was the invasion of several lineages of these animals onto land. We investigated the functional performance of odor-capture organs, antennae with olfactory sensilla arrays, through the use of a computational model of advection and diffusion of odorants to olfactory sensilla while varying three parameters thought to be important to odor capture (Reynolds number, gap-width-to-sensillum-diameter ratio, and angle of the sensilla array with respect to oncoming flow). We also performed a sensitivity analysis on these parameters using uncertainty quantification to analyze their relative contributions to odor-capture performance. The results of this analysis indicate that odor capture in water and in air are fundamentally different. Odor capture in water and leakiness of the array are highly sensitive to Reynolds number and moderately sensitive to angle, whereas odor capture in air is highly sensitive to gap widths between sensilla and moderately sensitive to angle. Leakiness is not a good predictor of odor capture in air, likely due to the relative importance of diffusion to odor transport in air compared to water. We also used the sensitivity analysis to make predictions about morphological and kinematic diversity in extant groups of aquatic and terrestrial crustaceans. Aquatic crustaceans will likely exhibit denser arrays and induce flow within the arrays, whereas terrestrial crustaceans will rely on more sparse arrays with wider gaps and little-to-no animal-induced currents.

RevDate: 2018-10-09

Fu Q, Chen H, Liao Q, et al (2018)

Drag reduction and shear-induced cells migration behavior of microalgae slurry in tube flow.

Bioresource technology, 270:38-45 pii:S0960-8524(18)31237-9 [Epub ahead of print].

To optimize the designing of microalgae slurry pumping system and enhance the efficiency of microalgae products production, the flow characteristics of microalgae slurries (Chlorella pyrenoidosa) in tube flow were for the first time investigated combining experiments and numerical simulation. The drag reduction behavior of microalgae slurry in the fully developed laminar flow regime was studied. In addition, the transition Reynolds number of microalgae slurries from laminar flow to turbulent flow was about 1000-1300, which was similar to the expression of two-phase flow. To provide a further understanding of flow feature of microalgae slurries in tube, a two-phase mixture model was proposed by considering the heterogeneity of concentration due to the shear-induced microalgae cells migration behavior. Simulation results revealed that the heterogeneous distribution of concentration was affected by average velocity and volume fraction of microalgae slurries, significantly affecting the flow resistance and flow stability of microalgae slurry in the tube flow.

RevDate: 2018-09-13

Bergersen AW, Mortensen M, K Valen-Sendstad (2018)

The FDA Nozzle Benchmark: In Theory There Is No Difference Between Theory and Practice, But in Practice There Is.

International journal for numerical methods in biomedical engineering [Epub ahead of print].

The utility of flow simulations relies on the robustness of computational fluid dynamics (CFD) solvers and reproducibility of results. The aim of this study was to validate the Oasis CFD solver against in-vitro experimental measurements of jet breakdown location from the FDA nozzle benchmark at Reynolds number 3500, which is in the particularly-challenging transitional regime. Simulations were performed on meshes consisting of 5, 10, 17 and 28 million (M) tetrahedra, with Δt = 10-5 seconds. The 5 and 10M simulation jets broke down in reasonable agreement with the experiments. However, the 17 and 28M simulation jets broke down further downstream. But which of our simulations are 'correct'? From a theoretical point of view, they are all wrong because the jet should not break down in the absence of disturbances. The geometry is axisymmetric with no geometrical features that can generate angular velocities. A stable flow was supported by linear stability analysis. From a physical point of view, a finite amount of 'noise' will always be present in experiments, which lowers transition point. To replicate noise numerically, we prescribed minor random angular velocities (∼0.31%), much smaller than the reported flow asymmetry (∼3%) and model accuracy (∼1%), at the inlet of the 17M simulation, which shifted the jet breakdown location closer to the measurements. Hence, the high-resolution simulations and 'noise' experiment can potentially explain discrepancies in transition between sometimes 'sterile' CFD and inherently noisy 'ground truth' experiments. Thus, we have shown that numerical simulations can agree with experiments, but for the wrong reasons.

RevDate: 2018-10-11

Wan G, Jin C, Trase I, et al (2018)

Helical Structures Mimicking Chiral Seedpod Opening and Tendril Coiling.

Sensors (Basel, Switzerland), 18(9): pii:s18092973.

Helical structures are ubiquitous in natural and engineered systems across multiple length scales. Examples include DNA molecules, plants' tendrils, sea snails' shells, and spiral nanoribbons. Although this symmetry-breaking shape has shown excellent performance in elastic springs or propulsion generation in a low-Reynolds-number environment, a general principle to produce a helical structure with programmable geometry regardless of length scales is still in demand. In recent years, inspired by the chiral opening of Bauhinia variegata's seedpod and the coiling of plant's tendril, researchers have made significant breakthroughs in synthesizing state-of-the-art 3D helical structures through creating intrinsic curvatures in 2D rod-like or ribbon-like precursors. The intrinsic curvature results from the differential response to a variety of external stimuli of functional materials, such as hydrogels, liquid crystal elastomers, and shape memory polymers. In this review, we give a brief overview of the shape transformation mechanisms of these two plant's structures and then review recent progress in the fabrication of biomimetic helical structures that are categorized by the stimuli-responsive materials involved. By providing this survey on important recent advances along with our perspectives, we hope to solicit new inspirations and insights on the development and fabrication of helical structures, as well as the future development of interdisciplinary research at the interface of physics, engineering, and biology.

RevDate: 2018-09-19
CmpDate: 2018-09-19

Daddi-Moussa-Ider A, Löwen H, S Gekle (2018)

Creeping motion of a solid particle inside a spherical elastic cavity⋆.

The European physical journal. E, Soft matter, 41(9):104 pii:10.1140/epje/i2018-11715-7.

On the basis of the linear hydrodynamic equations, we present an analytical theory for the low-Reynolds-number motion of a solid particle moving inside a larger spherical elastic cavity which can be seen as a model system for a fluid vesicle. In the particular situation where the particle is concentric with the cavity, we use the stream function technique to find exact analytical solutions of the fluid motion equations on both sides of the elastic cavity. In this particular situation, we find that the solution of the hydrodynamic equations is solely determined by membrane shear properties and that bending does not play a role. For an arbitrary position of the solid particle within the spherical cavity, we employ the image solution technique to compute the axisymmetric flow field induced by a point force (Stokeslet). We then obtain analytical expressions of the leading-order mobility function describing the fluid-mediated hydrodynamic interactions between the particle and the confining elastic cavity. In the quasi-steady limit of vanishing frequency, we find that the particle self-mobility function is higher than that predicted inside a rigid no-slip cavity. Considering the cavity motion, we find that the pair-mobility function is determined only by membrane shear properties. Our analytical predictions are supplemented and validated by fully resolved boundary integral simulations where a very good agreement is obtained over the whole range of applied forcing frequencies.

RevDate: 2018-08-24

Molony D, Park J, Zhou L, et al (2018)

Bulk Flow and Near Wall Hemodynamics of the Rabbit Aortic Arch: A 4D PC-MRI Derived CFD Study.

Journal of biomechanical engineering pii:2698120 [Epub ahead of print].

Animal models offer a flexible experimental environment for studying atherosclerosis. The mouse is the most commonly used animal, however, the underlying hemodynamics in larger animals such as the rabbit are far closer to that of humans. The aortic arch is a vessel with complex helical flow and highly heterogeneous shear stress patterns which may influence where atherosclerotic lesions form. A better understanding of intra-species flow variation and the impact of geometry on flow may improve our understanding of where disease forms. In this work we use Magnetic Resonance Angiography (MRA) and 4D Phase contrast magnetic resonance imaging (PC-MRI) to image and measure blood velocity in the rabbit aortic arch. Measured flow rates from the PC-MRI were used as boundary conditions in computational fluid dynamics models of the arches. Helical flow, cross flow index (CFI) and time-averaged wall shear stress (TAWSS) were determined from the simulated flow field. Both traditional geometric metrics and shape modes derived from statistical shape analysis were analyzed with respect to flow helicity. High CFI and low TAWSS were found to co-localize in the ascending aorta and to a lesser extent on the inner curvature of the aortic arch. The Reynolds number was linearly associated with an increase in helical flow intensity (R=0.85, p<.05). Both traditional and statistical shape analysis correlated with increased helical flow symmetry. However, a stronger correlation was obtained from the statistical shape analysis demonstrating its potential for discerning the role of shape in hemodynamic studies.

RevDate: 2018-08-27

Krastev VK, Amati G, Succi S, et al (2018)

On the effects of surface corrugation on the hydrodynamic performance of cylindrical rigid structures.

The European physical journal. E, Soft matter, 41(8):95 pii:10.1140/epje/i2018-11703-y.

In this work, we perform fully three-dimensional numerical simulations of the flow field surrounding cylindrical structures characterized by different types of corrugated surface. The simulations are carried out using the Lattice Boltzmann Method (LBM), considering a flow regime with a Reynolds number [Formula: see text]. The fluid-dynamic wake structure and stability are investigated by means of PSD analyses of the velocity components and by visual inspection of the vortical coherent structure evolution. Moreover, the energy dissipation of the flow is assessed by considering an equivalent discharge coefficient [Formula: see text], which measures the total pressure losses of the flow moving around the various layout under investigation. Outcomes from our study demonstrate that the helical ridges augment energy dissipation, but might also have a role in the passive control of the characteristic frequencies of the unsteady wake flow.

RevDate: 2018-09-14

Lee YJ, KB Lua (2018)

Wing-wake interaction: comparison of 2D and 3D flapping wings in hover flight.

Bioinspiration & biomimetics, 13(6):066003.

The wing-wake interaction of flapping wings while hovering has been investigated, with the focus on the difference in wing-wake interaction between 2D and 3D flapping wings. Numerical simulations are conducted at a Reynolds number of 100, and the flapping configurations are divided into the 2D, quasi-3D and 3D categories. Variations of the aspect ratio and Rossby number allow the flapping configuration to morph gradually between categories. The wing-wake interaction mechanisms are identified and the effect of three-dimensionality on these mechanisms is discussed. Three-dimensionality affects wing-wake interaction through four primary aerodynamic mechanisms, namely, induced jet, downwash/upwash, leading-edge vortex (LEV) shedding due to vortex pairing, and the formation of a closely attached LEV. The first two mechanisms are well-established in the literature. With regard to the LEV shedding mechanism, it is revealed that the interaction between the LEV and the residue vortex from the previous stroke plays an important role in the early vortex shedding of 2D flapping wings. This effect diminishes with increasing three-dimensionality. With regard to the mechanism of the closely attached LEV, the wake encourages the formation of an LEV that is closely attached to the wing's top surface, which is beneficial to lift generation. This closely attached LEV mechanism accounts for most of the lift enhancement that arises from wake effects. Three-dimensionality alters the efficacy of the different aerodynamic mechanisms. Consequently, the dual peak lift coefficient pattern typically seen on 2D flapping wings transforms into the single peak lift coefficient pattern of the 3D flapping wing. It is also demonstrated that the mean lift enhancement due to wing-wake interaction diminishes rapidly when three-dimensionality is introduced. Results suggest that, for wings with parameters close to those of natural flyers, wing-wake interaction yields marginal lift enhancement and a small increase in energy consumption.

RevDate: 2018-09-24

Espeso DR, Martínez-García E, Carpio A, et al (2018)

Dynamics of Pseudomonas putida biofilms in an upscale experimental framework.

Journal of industrial microbiology & biotechnology, 45(10):899-911.

Exploitation of biofilms for industrial processes requires them to adopt suitable physical structures for rendering them efficient and predictable. While hydrodynamics could be used to control material features of biofilms of the platform strain Pseudomonas putida KT2440 there is a dearth of experimental data on surface-associated growth behavior in such settings. Millimeter scale biofilm patterns formed by its parental strain P. putida mt-2 under different Reynolds numbers (Re) within laminar regime were analyzed using an upscale experimental continuous cultivation assembly. A tile-scan image acquisition process combined with a customized image analysis revealed patterns of dense heterogeneous structures at Re = 1000, but mostly flattened coverings sparsely patched for Re < 400. These results not only fix the somewhat narrow hydrodynamic regime under which P. putida cells form stable coatings on surfaces destined for large-scale processes, but also provide useful sets of parameters for engineering catalytic biofilms based on this important bacterium as a cell factory.

RevDate: 2018-09-27

Lee J, Estlack Z, Somaweera H, et al (2018)

A microfluidic cardiac flow profile generator for studying the effect of shear stress on valvular endothelial cells.

Lab on a chip, 18(19):2946-2954.

To precisely investigate the mechanobiological responses of valvular endothelial cells, we developed a microfluidic flow profile generator using a pneumatically-actuated micropump consisting of microvalves of various sizes. By controlling the closing pressures and the actuation times of these microvalves, we modulated the magnitude and frequency of the shear stress to mimic mitral and aortic inflow profiles with frequencies in the range of 0.8-2 Hz and shear stresses up to 20 dyn cm-2. To demonstrate this flow profile generator, aortic inflow with an average of 5.9 dyn cm-2 shear stress at a frequency of 1.2 Hz with a Reynolds number of 2.75, a Womersley number of 0.27, and an oscillatory shear index (OSI) value of 0.2 was applied to porcine aortic valvular endothelial cells (PAVECs) for mechanobiological studies. The cell alignment, cell elongation, and alpha-smooth muscle actin (αSMA) expression of PAVECs under perfusion, steady flow, and aortic inflow conditions were analyzed to determine their shear-induced cell migration and trans-differentiation. In this morphological and immunocytochemical study, we found that the PAVECs elongated and aligned themselves perpendicular to the directions of the steady flow and the aortic inflow. In contrast, under perfusion with a fluidic shear stress of 0.47 dyn cm-2, the PAVECs elongated and aligned themselves parallel to the direction of flow. The PAVECs exposed to the aortic inflow upregulated their αSMA-protein expression to a greater degree than those exposed to perfusion and steady flow. By comparing these results to those of previous studies of pulsatile flow, we also found that the ratio of positive to negative shear stress plays an important role in determining PAVECs' trans-differentiation and adaptation to flow. This microfluidic cardiac flow profile generator will enable future valvular mechanobiological studies to determine the roles of magnitude and frequency of shear stresses.

RevDate: 2018-08-20
CmpDate: 2018-08-20

Gao J, J Katz (2018)

Self-calibrated microscopic dual-view tomographic holography for 3D flow measurements.

Optics express, 26(13):16708-16725.

This paper introduces the application of microscopic dual-view tomographic holography (M-DTH) to measure the 3D position and motion of micro-particles located in dense suspensions. Pairing of elongated traces of the same particle in the two inclined reconstructed fields requires precise matching of the entire sample volume that accounts for the inherent distortions in each view. It is achieved by an iterative volumetric self-calibration method, consisting of mapping one view onto the next, dividing the sample volume into slabs, and cross-correlating the two views. Testing of the procedures using synthetic particle fields with imposed distortion and realistic errors in particle locations shows that the self-calibration method achieves a 3D uncertainty of about 1µm, a third of the particle diameter. Multiplying the corrected intensity fields is used for truncating the elongated traces, whose centers are located within 1µm of the exact value. Without correction, only a small fraction of the traces even overlap. The distortion correction also increases the number of intersecting traces in experimental data along with their intensity. Application of this method for 3D velocity measurements is based on the centroids of the truncated/shortened particle traces. Matching of these traces in successive fields is guided by several criteria, including results of volumetric cross-correlation of the multiplied intensity fields. The resulting 3D velocity distribution is substantially more divergence-free, i.e., satisfies conservation of mass, compared to analysis performed using single-view data. Sample application of the new method shows the 3D flow structure around a pair of cubic roughness elements embedded in the inner part of a high Reynolds number turbulent boundary layer.

RevDate: 2018-08-21
CmpDate: 2018-08-21

Mathai V, Huisman SG, Sun C, et al (2018)

Dispersion of Air Bubbles in Isotropic Turbulence.

Physical review letters, 121(5):054501.

Bubbles play an important role in the transport of chemicals and nutrients in many natural and industrial flows. Their dispersion is crucial to understanding the mixing processes in these flows. Here we report on the dispersion of millimetric air bubbles in a homogeneous and isotropic turbulent flow with a Taylor Reynolds number from 110 to 310. We find that the mean squared displacement (MSD) of the bubbles far exceeds that of fluid tracers in turbulence. The MSD shows two regimes. At short times, it grows ballistically (∝τ^{2}), while at larger times, it approaches the diffusive regime where the MSD∝τ. Strikingly, for the bubbles, the ballistic-to-diffusive transition occurs one decade earlier than for the fluid. We reveal that both the enhanced dispersion and the early transition to the diffusive regime can be traced back to the unsteady wake-induced motion of the bubbles. Further, the diffusion transition for bubbles is not set by the integral timescale of the turbulence (as it is for fluid tracers and microbubbles), but instead, by a timescale of eddy crossing of the rising bubbles. The present findings provide a Lagrangian perspective towards understanding mixing in turbulent bubbly flows.

RevDate: 2018-08-21
CmpDate: 2018-08-21

Oettinger D, Ault JT, Stone HA, et al (2018)

Invisible Anchors Trap Particles in Branching Junctions.

Physical review letters, 121(5):054502.

We combine numerical simulations and an analytic approach to show that the capture of finite, inertial particles during flow in branching junctions is due to invisible, anchor-shaped three-dimensional flow structures. These Reynolds-number-dependent anchors define trapping regions that confine particles to the junction. For a wide range of Stokes numbers, these structures occupy a large part of the flow domain. For flow in a V-shaped junction, at a critical Stokes number, we observe a topological transition due to the merger of two anchors into one. From a stability analysis, we identify the parameter region of particle sizes and densities where capture due to anchors occurs.

RevDate: 2018-08-21
CmpDate: 2018-08-21

Karaminejad S, Askari MH, M Ashjaee (2018)

Temperature field investigation of hydrogen/air and syngas/air axisymmetric laminar flames using Mach-Zehnder interferometry.

Applied optics, 57(18):5057-5067.

In this study, the optical method of Mach-Zehnder interferometry (MZI) is utilized in order to explore the flame structure and temperature field of syngas/air and hydrogen/air flames. Two axisymmetric burners with inner diameters of 4 mm and 6 mm are used for temperature field measurement of hydrogen and syngas, respectively. The effects of fuel composition, equivalence ratio, and Reynolds number (Re) are investigated at ambient condition (P=0.87 bar, T=300 K). Three different H2/CO fuel compositions with hydrogen fractions of 30%, 50%, and 100% are studied. Temperature profiles are reported at four different sections above the burner tip. Measured temperatures using the interferometry method are compared with thermocouple data and good agreement between them is observed. The results obtained in this investigation indicated that the MZI can be applied for accurate determination of flame front and temperature field, especially for high-temperature flames where other methods cannot be properly utilized. Analyses of the data reduction method revealed that the exact determination of the refractive index distribution and reference temperature is critical for accurate determination of the temperature field. The results indicated that by increasing the Re, the maximum flame temperature is enhanced. Increasing the equivalence ratio leads to expansion of the flame radial distribution (at the same distance from the burner tip). At higher distances from the burner tip, temperature increases uniformly from the flame boundary toward the flame axis, while at lower heights it shows reduction at the burner axis. By increasing the CO content of fuel, the maximum flame temperature increases at all equivalence ratios except at the stoichiometric condition, where SH100 illustrates the highest maximum flame temperature.

RevDate: 2018-08-17

Bhat SS, Zhao J, Sheridan J, et al (2018)

The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size.

Royal Society open science, 5(7):172197 pii:rsos172197.

Stable attachment of a leading-edge vortex (LEV) plays a key role in generating the high lift on rotating wings with a central body. The central body size can affect the LEV structure broadly in two ways. First, an overall change in the size changes the Reynolds number, which is known to have an influence on the LEV structure. Second, it may affect the Coriolis acceleration acting across the wing, depending on the wing-offset from the axis of rotation. To investigate this, the effects of Reynolds number and the wing-offset are independently studied for a rotating wing. The three-dimensional LEV structure is mapped using a scanning particle image velocimetry technique. The rapid acquisition of images and their correlation are carefully validated. The results presented in this paper show that the LEV structure changes mainly with the Reynolds number. The LEV-split is found to be only minimally affected by changing the central body radius in the range of small offsets, which interestingly includes the range for most insects. However, beyond this small offset range, the LEV-split is found to change dramatically.

RevDate: 2018-08-08

Gilmer GG, Deshpande V, Chou CL, et al (2018)

Flow Resistance along the Rat Renal Tubule.

American journal of physiology. Renal physiology [Epub ahead of print].

The Reynolds number in the renal tubule is extremely low, consistent with laminar flow. Consequently, luminal flow can be described by the Hagen-Poiseuille laminar flow equation. This equation calculates the volumetric flow rate from values of the axial pressure gradient and flow resistance, which is dependent on the length and diameter of each renal tubule segment. Our goal was to calculate the pressure drop along each segment of the renal tubule and determine the points of highest resistance. When the Hagen-Poiseuille equation was used for rat superficial nephrons based on known flow rates, tubule lengths, and diameters for each renal tubule segment, it was found that maximum pressure drop occurred in two segments: the thin descending limbs of Henle and the inner medullary collecting ducts. The high resistance in the thin descending limbs is due to their small diameters. The steep pressure drop observed in the inner medullary collecting ducts is due to the convergent structure of the tubules, which channels flow into fewer and fewer tubules toward the papillary tip. For short-looped nephrons, the calculated glomerular capsular pressure matched measured values, even with the high collecting duct flow rates seen in water diuresis, providing that tubule compliance was taken into account. In long-looped nephrons, the greater length of thin limb segments is compensated for by a larger luminal diameter. Simulation of the effect of proximal diuretics, viz. acetazolamide or SGLT2-inhibitors, predicts a substantial back pressure in Bowman's capsule, which may contribute to observed decreases in glomerular filtration rate.

RevDate: 2018-09-05

Mateos-Maroto A, Guerrero-Martínez A, Rubio RG, et al (2018)

Magnetic Biohybrid Vesicles Transported by an Internal Propulsion Mechanism.

ACS applied materials & interfaces, 10(35):29367-29377.

Some biological microorganisms can crawl or swim due to coordinated motions of their cytoskeleton or the flagella located inside their bodies, which push the cells forward through intracellular forces. To date, there is no demonstration of synthetic systems propelling at low Reynolds number via the precise actuation of the material confined within an enclosing lipid membrane. Here, we report lipid vesicles and other more complex self-assembled biohybrid structures able to propel due to the advection flows generated by the actuated rotation of the superparamagnetic particles they contain. The proposed swimming and release strategies, based on cooperative hydrodynamic mechanisms and near-infrared laser pulse-triggered destabilization of the phospholipid membranes, open new possibilities for the on-command transport of minute quantities of drugs, fluid or nano-objects. The lipid membranes protect the confined substances from the outside environment during transportation, thus enabling them to work in physiological conditions.

RevDate: 2018-08-09

Vidal EAG, Zeidberg LD, EJ Buskey (2018)

Development of Swimming Abilities in Squid Paralarvae: Behavioral and Ecological Implications for Dispersal.

Frontiers in physiology, 9:954.

This study investigates the development of swimming abilities and its relationship with morphology, growth, and nourishment of reared Doryteuthis opalescens paralarvae from hatching to 60 days of age. Paralarvae (2.5-11 mm mantle length - ML) were videotaped, and their behavior quantified throughout development using computerized motion analysis. Hatchlings swim dispersed maintaining large nearest neighbor distances (NND, 8.7 ML), with swimming speeds (SS) of 3-8 mm s-1 and paths with long horizontal displacements, resulting in high net to gross displacement ratios (NGDR). For 15-day-old paralarvae, swimming paths are more consistent between jets, growth of fins, length, and mass increases. The swimming pattern of 18-day-old paralarvae starved for 72 h exhibited a significant reduction in mean SS and inability to perform escape jets. A key morphological, behavioral, and ecological transition occurs at about 6 mm ML (>35-day old), when there is a clear change in body shape, swimming performance, and behavior, paths are more regularly repeated and directional swimming is evident, suggesting that morphological changes incur in swimming performance. These squid are able to perform sustained swimming and hover against a current at significantly closer NND (2.0 ML), as path displacement is reduced and maneuverability increases. As paralarvae reach 6-7 mm ML, they are able to attain speeds up to 562 mm s-1 and to form schools. Social feeding interactions (kleptoparasitism) are often observed prior to the formation of schools. Schools are always formed within areas of high flow gradient in the tanks and are dependent on squid size and current speed. Fin development is a requisite for synchronized and maneuverable swimming of schooling early juveniles. Although average speeds of paralarvae are within intermediate Reynolds numbers (Re < 100), they make the transition to the inertia-dominated realm during escape jets of high propulsion (Re > 3200), transitioning from plankton to nekton after their first month of life. The progressive development of swimming capabilities and social interactions enable juvenile squid to school, while also accelerates learning, orientation and cognition. These observations indicate that modeling of the lifecycle should include competency to exert influence over small currents and dispersal patterns after the first month of life.

RevDate: 2018-10-12
CmpDate: 2018-10-12

Gritti F (2018)

High-resolution turbulent flow chromatography.

Journal of chromatography. A, 1570:135-147.

The resolution power of turbulent flow chromatography using carbon dioxide as the mobile phase and coated (crosslinked methyl phenyl polysiloxane) open tube columns (OTCs) as the stationary phase was investigated under retentive conditions (0

RevDate: 2018-08-05

Rosti ME, Omidyeganeh M, A Pinelli (2018)

Numerical Simulation of a Passive Control of the Flow Around an Aerofoil Using a Flexible, Self Adaptive Flaplet.

Flow, turbulence and combustion, 100(4):1111-1143.

RevDate: 2018-08-02

Vernet JA, Örlü R, Söderblom D, et al (2018)

Plasma Streamwise Vortex Generators for Flow Separation Control on Trucks: A Proof-of-concept Experiment.

Flow, turbulence and combustion, 100(4):1101-1109.

An experimental study of the effect of Dielectric Barrier Discharge plasma actuators on the flow separation on the A-pillar of a modern truck under cross-wind conditions has been carried out. The experiments were done in a wind tunnel with a 1:6 scale model of a tractor-trailer combination. The actuators were used as vortex generators positioned on the A-pillar on the leeward side of the tractor and the drag force was measured with a wind-tunnel balance. The results show that the effect at the largest yaw angle (9 degrees) can give a drag reduction of about 20% and that it results in a net power reduction. At lower yaw angles the reduction was smaller. The present results were obtained at a lower Reynolds number and a lower speed than for real driving conditions so it is still not yet confirmed if a similar positive result can be obtained in full scale.

RevDate: 2018-08-05

Ahmadi S, Roccon A, Zonta F, et al (2018)

Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface.

Flow, turbulence and combustion, 100(4):979-993.

RevDate: 2018-08-02

Sundstrom LRJ, MJ Cervantes (2018)

On the Similarity of Pulsating and Accelerating Turbulent Pipe Flows.

Flow, turbulence and combustion, 100(2):417-436.

RevDate: 2018-07-25

Dey KK (2018)

Dynamic Coupling at Low Reynolds Number.

Angewandte Chemie (International ed. in English) [Epub ahead of print].

Collective and emergent behaviors of active colloidal assemblies provide useful insights into the statistical physics of out-of-equilibrium systems. Colloidal suspensions containing microscopic active swimmers have recently been studied with much vigor to understand principles of energy transfer at low Reynolds number conditions. Using molecules of active enzymes and ångström sized organometallic catalysts it has further been demonstrated that energy can be transferred even by molecules to their surroundings, influencing substantially the overall dynamics of the systems. Monitoring the diffusion of non-reacting tracers dispersed in active solutions, it has been shown that the nature of energy transfer in systems containing different swimmers is surprisingly similar - irrespective of their differences in sizes, modes of energy transduction and propulsion strategies. These observations provide motivation not only to characterize reaction generated force fields under complex fluidic environment but also to look for possible similarity in their behavior across multiple length scales. This review discusses research results obtained so far in this direction, highlighting the common features observed regarding dynamic coupling of swimmers with their surroundings. Activity-induced force generation and its collective effects are expected to find wide importance in transport and organization of materials at smaller length scales. Underscoring the nature of reaction generated perturbations, especially under crowded cytosolic conditions, is further likely to advance our knowledge of intracellular mechanics of small molecules during various metabolic processes and chemical transformations.

RevDate: 2018-08-08

Oh S, H Choi (2018)

A predictive model of the drag coefficient for a revolving wing at low Reynolds number.

Bioinspiration & biomimetics, 13(5):054001.

A predictive model of the drag coefficient for a revolving wing at low Reynolds number is suggested. Unlike the previous model (Wang et al 2016 J. Fluid Mech. 800 688-719), the present model includes a viscous drag on the wing from laminar boundary layer theory and thus predicts the drag force more accurately at low angles of attack and low Reynolds numbers. Also, in determining the model constants, we consider the attack angle of π/4 at which the resultant force on the wing is assumed to be perpendicular to the wing chord. The present aerodynamic model more accurately predicts drag forces of four different revolving wings than the existing ones.

RevDate: 2018-07-31

Dai L, He G, Zhang X, et al (2018)

Intermittent locomotion of a fish-like swimmer driven by passive elastic mechanism.

Bioinspiration & biomimetics, 13(5):056011.

The intermittent locomotion performance of a fish-like elastic swimmer is studied numerically in this paper. The actuation is imposed only at the head and the locomotion is indirectly driven by passive elastic mechanism. For intermittent swimming, certain time durations of passive coasting are interspersed between two half-periods of active bursting. To facilitate the comparison of energy efficiencies in continuous and intermittent swimming at the same cruising speed, we consider both intermittent swimming at various duty cycles and also continuous swimming at reduced actuation frequencies. The result indicates that the intermittent style is more economical than the continuous style only when the cruising Reynolds number is sufficiently large and the duty cycle is moderate. We also explore the passive tail-beating pattern and wake structure for intermittent swimming. It is found that the kinematics of the tail contains a preparatory burst phase which lies in between the active bursting and the passive coasting phases. Three vortex streets are found in the wake structures behind the intermittent swimmers. The two oblique streets consist of strong vortex dipoles and the horizontal street is made up of weak vortices. The results of this study can provide some insight into the burst-and-coast swimming of fish and also inform the design of efficient bio-mimetic under-water vehicles.

RevDate: 2018-09-05

Tang Y, Zhu DZ, B van Duin (2018)

Note on sediment removal efficiency in oil-grit separators.

Water science and technology : a journal of the International Association on Water Pollution Research, 2017(3):729-735.

Oil-grit separators (OGSs) are one type of best management practice, designed to remove oil and grit from stormwater runoff (e.g., from parking lots and paved roads). This note examines scaling parameters for OGS removal efficiency. Three dimensionless parameters are chosen as scaling parameters: Hazen number (Ha), Reynolds number (Re) and Froude number (Fr). The Hazen number is a ratio of hydraulic residence time to particle settling time. The Reynolds number measures the surrounding turbulence effects on sediment removal efficiency. The Froude number represents the ratio of inertial and gravitational forces, which indicates the influence of gravity on fluid motion. The collected data from the literature on sediment removal in OGSs can be represented by a single curve when the Hazen, Reynolds, and Froude numbers are combined into a new scaling parameter (HRF = Ha(Re/Fr)). A general form is proposed to correlate the sediment removal efficiency with this new parameter. This generalized prediction method can be used as a preliminary performance indicator for OGS units. The obtained curve can also be used to adjust raw laboratory and field measurement data to improve the evaluation of the performance of various OGSs.

RevDate: 2018-07-20
CmpDate: 2018-07-20

Fraternale F, Domenicale L, Staffilani G, et al (2018)

Internal waves in sheared flows: Lower bound of the vorticity growth and propagation discontinuities in the parameter space.

Physical review. E, 97(6-1):063102.

This study provides sufficient conditions for the temporal monotonic decay of enstrophy for two-dimensional perturbations traveling in the incompressible, viscous, plane Poiseuille, and Couette flows. Extension of Synge's procedure [J. L. Synge, Proc. Fifth Int. Congress Appl. Mech. 2, 326 (1938); Semicentenn. Publ. Am. Math. Soc. 2, 227 (1938)] to the initial-value problem allow us to find the region of the wave-number-Reynolds-number map where the enstrophy of any initial disturbance cannot grow. This region is wider than that of the kinetic energy. We also show that the parameter space is split into two regions with clearly distinct propagation and dispersion properties.

RevDate: 2018-09-17
CmpDate: 2018-09-17

Mutlu BR, Edd JF, M Toner (2018)

Oscillatory inertial focusing in infinite microchannels.

Proceedings of the National Academy of Sciences of the United States of America, 115(30):7682-7687.

RevDate: 2018-07-12
CmpDate: 2018-07-10

Musacchio S, Cencini M, Plan ELCVM, et al (2018)

Enhancement of mixing by rodlike polymers.

The European physical journal. E, Soft matter, 41(7):84 pii:10.1140/epje/i2018-11692-9.

We study the mixing of a passive scalar field dispersed in a solution of rodlike polymers in two dimensions, by means of numerical simulations of a rheological model for the polymer solution. The flow is driven by a parallel sinusoidal force (Kolmogorov flow). Although the Reynolds number is lower than the critical value for inertial instabilities, the rotational dynamics of the polymers generates a chaotic flow similar to the so-called elastic-turbulence regime observed in extensible polymer solutions. The temporal decay of the variance of the scalar field and its gradients shows that this chaotic flow strongly enhances mixing.

RevDate: 2018-08-04
CmpDate: 2018-07-24

Bell GRR, SR Collins (2018)

"Rho"ing a Cellular Boat with Rearward Membrane Flow.

Developmental cell, 46(1):1-3.

The physicist Edward Purcell wrote in 1977 about mechanisms that cells could use to propel themselves in a low Reynolds number environment. Reporting in Developmental Cell, O'Neill et al. (2018) provide direct evidence for one of these mechanisms by optogenetically driving the migration of cells suspended in liquid through RhoA activation.

RevDate: 2018-07-20
CmpDate: 2018-07-20

Bukowicki M, ML Ekiel-Jeżewska (2018)

Different bending models predict different dynamics of sedimenting elastic trumbbells.

Soft matter, 14(28):5786-5799.

The main goal of this paper is to examine theoretically and numerically the impact of a chosen bending model on the dynamics of elastic filaments settling in a viscous fluid under gravity at low-Reynolds-number. We use the bead-spring approximation of a filament and the Rotne-Prager mobility matrix to describe hydrodynamic interactions between the beads. We analyze the dynamics of trumbbells, for which bending angles are typically larger than for thin and long filaments. Each trumbbell is made of three beads connected by springs and it exhibits a bending resistance, described by the harmonic or - alternatively - by the 'cosine' (also called the Kratky-Porod) bending models, both often used in the literature. Using the harmonic bending potential, and coupling it to the spring potential by the Young's modulus, we find simple benchmark solutions: stable stationary configurations of a single elastic trumbbell and attraction of two elastic trumbbells towards a periodic long-lasting orbit. As the most significant result of this paper, we show that for very elastic trumbbells at the same initial conditions, the Kratky-Porod bending potential can lead to qualitatively and quantitatively different spurious dynamics, with artificially large bending angles and unrealistic shapes. We point out that for the bead models of an elastic filament, the range of applicability of the Kratky-Porod model might not go beyond bending angles smaller than π/2 for touching beads and beyond an even much lower value for beads well-separated from each other. The existence of stable stationary configurations of elastic trumbbells and a family of periodic oscillations of two elastic trumbbells are very important findings on their own.

RevDate: 2018-07-02
CmpDate: 2018-07-02

Kawata T, PH Alfredsson (2018)

Inverse Interscale Transport of the Reynolds Shear Stress in Plane Couette Turbulence.

Physical review letters, 120(24):244501.

Interscale interaction between small-scale structures near the wall and large-scale structures away from the wall plays an increasingly important role with increasing Reynolds number in wall-bounded turbulence. While the top-down influence from the large- to small-scale structures is well known, it has been unclear whether the small scales near the wall also affect the large scales away from the wall. In this Letter we show that the small-scale near-wall structures indeed play a role to maintain the large-scale structures away from the wall, by showing that the Reynolds shear stress is transferred from small to large scales throughout the channel. This is in contrast to the turbulent kinetic energy transport which is from large to small scales. Such an "inverse" interscale transport of the Reynolds shear stress eventually supports the turbulent energy production at large scales.

RevDate: 2018-07-17

Jardin T, T Colonius (2018)

On the lift-optimal aspect ratio of a revolving wing at low Reynolds number.

Journal of the Royal Society, Interface, 15(143):.

Lentink & Dickinson (2009 J. Exp. Biol.212, 2705-2719. (doi:10.1242/jeb.022269)) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.

RevDate: 2018-06-19

Maldaner CH, Quinn PM, Cherry JA, et al (2018)

Improving estimates of groundwater velocity in a fractured rock borehole using hydraulic and tracer dilution methods.

Journal of contaminant hydrology, 214:75-86.

A straddle-packer system for use in boreholes in fractured rock was modified to investigate the average linear groundwater velocity (v¯f) in fractures under ambient flow conditions. This packer system allows two different tests to be conducted in the same interval between packers without redeploying the system: (1) forced gradient hydraulic tests to determine the interval transmissivity (T), and (2) borehole dilution experiments to determine the groundwater flow rate (Qt) across the test interval. The constant head step test method provides assurance that flow is Darcian when determining T for each interval and identifies the flow rate at the onset of non-Darcian flow. The critical Reynolds number method uses this flow rate to provide the number of hydraulically active fractures (N) in each interval, the average hydraulic aperture for the test interval and the effective bulk fracture porosity. The borehole dilution method provides Qt values for the interval at the time of the test, and v¯f can be estimated from Qt using the flow area derived from the hydraulic tests. The method was assessed by application to seven test intervals in a borehole 73 m deep in a densely fractured dolostone aquifer used for municipal water supply. The critical Reynolds number method identified one or two fractures in each test interval (1.1 m long), which provided v¯f values in the range of 10 to 8000 m/day. This velocity range is consistent with values reported in the literature for ambient flow in this aquifer. However, when hydraulically active fractures in each interval is identified and measured from acoustic and optical televiewer logs, the calculated v¯f values are unreasonably low as are the calculated values of the hydraulic gradient needed to provide the Qt value for each tested interval. The combination of hydraulic and dilution tests in the same interval is an improved method to obtain values of groundwater velocity in fractured rock aquifers.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Ngoma J, Philippe P, Bonelli S, et al (2018)

Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods.

Physical review. E, 97(5-1):052902.

We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed.

RevDate: 2018-06-22
CmpDate: 2018-06-22

Baker NT, Pothérat A, Davoust L, et al (2018)

Inverse and Direct Energy Cascades in Three-Dimensional Magnetohydrodynamic Turbulence at Low Magnetic Reynolds Number.

Physical review letters, 120(22):224502.

This experimental study analyzes the relationship between the dimensionality of turbulence and the upscale or downscale nature of its energy transfers. We do so by forcing low-Rm magnetohydrodynamic turbulence in a confined channel, while precisely controlling its dimensionality by means of an externally applied magnetic field. We first identify a specific length scale l[over ^]_{⊥}^{c} that separates smaller 3D structures from larger quasi-2D ones. We then show that an inverse energy cascade of horizontal kinetic energy along horizontal scales is always observable at large scales, and that it extends well into the region of 3D structures. At the same time, a direct energy cascade confined to the smallest and strongly 3D scales is observed. These dynamics therefore appear not to be simply determined by the dimensionality of individual scales, nor by the forcing scale, unlike in other studies. In fact, our findings suggest that the relationship between kinematics and dynamics is not universal and may strongly depend on the forcing and dissipating mechanisms at play.

RevDate: 2018-06-26

Parise JAR, FEM Saboya (2018)

Experimental data on transport coefficients for developing laminar flow in isosceles triangular ducts using the naphthalene sublimation technique.

Data in brief, 18:1350-1359 pii:S2352-3409(18)30303-2.

The data presented in this article are related to the research article entitled "Transport coefficients for developing laminar flow in isosceles triangular ducts" (Parise and Saboya, 1999) [1]. The article describes an experiment involving the determination of transport coefficients in the laminar entrance region of 30°, 45°, 60° and 90° isosceles triangular ducts. Data were obtained by application of the naphthalene sublimation technique in conjunction with the heat to mass transfer analogy. Experimental conditions (duct sides made of naphthalene and base made of metal) simulated developing velocity and temperature fields in an isosceles triangular duct with isothermal lateral walls and adiabatic base. The Reynolds number ranged from 100 to 1800 and the duct length to hydraulic diameter ratio, from 2 to 40. The experiment consisted of mounting a test section (triangular duct) with the lateral walls made of naphthalene. Air was forced past the test section and naphthalene walls were weighed prior and after each data run, providing the rate of mass transfer for given flow conditions. Raw data, for a total of 77 experimental runs, include: test section geometry, air flow and mass transfer conditions. Processed data comprise the relevant non-dimensional groups, namely: Reynolds, non-dimensional axial duct length and Sherwood numbers.

RevDate: 2018-06-13

McCombe D, JD Ackerman (2018)

Collector Motion Affects Particle Capture in Physical Models and in Wind Pollination.

The American naturalist, 192(1):81-93.

Particle capture is important for ecological processes in aquatic and terrestrial ecosystems. The current model is based on a stationary collector for which predictions about capture efficiency (η; flux of captured particles ∶ flux of particles) are based on the collector flow environment (i.e., collector Reynolds number, Rec; inertial force ∶ viscous force). This model does not account for the movement of collectors in nature. We examined the effect of collector motion (transverse and longitudinal to the flow) on η using a cylindrical model in the lab and the grass species Phleum pratense in the field. Collector motion increased η (up to 400% and 20% in the lab and field, respectively) and also affected the spatial distribution of particles on collectors, especially at low Rec. The effect was greatest for collectors moving transversely at large magnitude, which encountered more particles with higher relative momentum. These results, which differ from the stationary model, can be predicted by considering both Rec and the particle dynamics given by the Stokes number (Stk; particle stopping distance ∶ collector radius) and helped to resolve an existing controversy about pollination mechanisms. Collector motion should be considered in wind pollination and other ecological processes involving particle capture.

RevDate: 2018-08-06
CmpDate: 2018-08-06

Gritti F, M Fogwill (2018)

Molecular dispersion in pre-turbulent and sustained turbulent flow of carbon dioxide.

Journal of chromatography. A, 1564:176-187.

The average dispersion coefficients, Da¯, of two small molecules (acetonitrile and coronene) were measured under laminar, transient, and sustained turbulent flow regimes along fused silica open tubular capillary (OTC) columns (180 μm inner diameter by 20 m length). Carbon dioxide was used as the mobile phase at room temperature (296 K) and at average pressures in the range from 1500 to 2700 psi. The Reynolds number (Re) was increased from 600 to 5000. The measurement of Da¯ is based on the observed plate height of the non-retained analytes as a function of the applied Reynolds number. Da¯ values are directly estimated from the best fit of the general Golay HETP equation to the experimental plate height curves. The experimental data revealed that under a pre-turbulent flow regime (Re < 2000), Da¯ is 2-6 times larger (3.5 × 10-4 cm2/s) than the bulk diffusion coefficients Dm of the analyte (1.6 × 10-4 and 5.8 × 10-5 cm2/s for acetonitrile and coronene, respectively). This result was explained by the random formation of decaying or vanishing turbulent puffs under pre-turbulent flow regime. Yet, the peak width remains controlled exclusively by the slow mass transfer in the mobile phase across the inner diameter (i.d.) of the OTC. Under sustained turbulent flow regime (Re > 2500), Da¯ is about four to five orders of magnitude larger than Dm. The experimental data slightly overestimated the turbulent dispersion coefficients predicted by Flint-Eisenklam model (Da¯=4 cm2/s). The discrepancy is explained by the approximate nature of the general Golay equation, which assumes that Da¯ is strictly uniform across the entire i.d. of the OTC. In fact, both the viscous and buffer wall layers, in which viscous effects dominate inertial effects, cannot be considered as fully developed turbulent regions. Remarkably, the mass transfer mechanism in OTC under sustained turbulent flow regime is not only controlled by longitudinal dispersion but also by a slow mass transfer in the mobile phase across the thick buffer layer and the thin viscous layer. Altogether, these layers occupy as much as 35% of the OTC volume at Re = 4000. From a theoretical viewpoint, the general Golay HETP equation is only an approximate model which should be refined based on the actual profile of the analyte dispersion coefficient across the OTC i.d. In practice, the measured plate height of non-retained analytes under sustained turbulent flow of carbon dioxide are two orders of magnitude smaller than those expected under hypothetical laminar flow regime.

RevDate: 2018-09-07
CmpDate: 2018-07-30

Kaiser SC, Werner S, Jossen V, et al (2018)

Power Input Measurements in Stirred Bioreactors at Laboratory Scale.

Journal of visualized experiments : JoVE.

The power input in stirred bioreactors is an important scaling-up parameter and can be measured through the torque that acts on the impeller shaft during rotation. However, the experimental determination of the power input in small-scale vessels is still challenging due to relatively high friction losses inside typically used bushings, bearings and/or shaft seals and the accuracy of commercially available torque meters. Thus, only limited data for small-scale bioreactors, in particular single-use systems, is available in the literature, making comparisons among different single-use systems and their conventional counterparts difficult. This manuscript provides a protocol on how to measure power inputs in benchtop scale bioreactors over a wide range of turbulence conditions, which can be described by the dimensionless Reynolds number (Re). The aforementioned friction losses are effectively reduced by the use of an air bearing. The procedure on how to set up, conduct and evaluate a torque-based power input measurement, with special focus on cell culture typical agitation conditions with low to moderate turbulence (100 < Re < 2·104), is described in detail. The power input of several multi-use and single-use bioreactors is provided by the dimensionless power number (also called Newton number, P0), which is determined to be in the range of P0 ≈ 0.3 and P0 ≈ 4.5 for the maximum Reynolds numbers in the different bioreactors.

RevDate: 2018-06-07

Herbig BA, Yu X, SL Diamond (2018)

Using microfluidic devices to study thrombosis in pathological blood flows.

Biomicrofluidics, 12(4):042201 pii:001891BMF.

Extreme flows can exist within pathological vessel geometries or mechanical assist devices which create complex forces and lead to thrombogenic problems associated with disease. Turbulence and boundary layer separation are difficult to obtain in microfluidics due to the low Reynolds number flow in small channels. However, elongational flows, extreme shear rates and stresses, and stagnation point flows are possible using microfluidics and small perfusion volumes. In this review, a series of microfluidic devices used to study pathological blood flows are described. In an extreme stenosis channel pre-coated with fibrillar collagen that rapidly narrows from 500 μm to 15 μm, the plasma von Willebrand Factor (VWF) will elongate and assemble into thick fiber bundles on the collagen. Using a micropost-impingement device, plasma flow impinging on the micropost generates strong elongational and wall shear stresses that trigger the growth of a VWF bundle around the post (no collagen required). Using a stagnation-point device to mimic the zone near flow reattachment, blood can be directly impinged upon a procoagulant surface of collagen and the tissue factor. Clots formed at the stagnation point of flow impingement have a classic core-shell architecture where the core is highly activated (P-selectin positive platelets and fibrin rich). Finally, within occlusive clots that fill a microchannel, the Darcy flow driven by ΔP/L > 70 mm-Hg/mm-clot is sufficient to drive NETosis of entrapped neutrophils, an event not requiring either thrombin or fibrin. Novel microfluidic devices are powerful tools to access physical environments that exist in human disease.

RevDate: 2018-05-23

Montoya Segnini J, Bocanegra Evans H, L Castillo (2018)

Flow Recirculation in Cartilaginous Ring Cavities of Human Trachea Model.

Journal of aerosol medicine and pulmonary drug delivery [Epub ahead of print].

BACKGROUND: Despite the prevailing assumption of "smooth trachea walls" in respiratory fluid dynamics research, recent investigations have demonstrated that cartilaginous rings in the trachea and main bronchi have a significant effect on the flow behavior and in particle deposition. However, there is not enough detailed information about the underlying physics of the interaction between the cartilage rings and the flow.

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

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

CONCLUSIONS: The detection of recirculation zones in the cartilage ring cavities sheds light on the particle deposition mechanism and helps explain results from previous studies that have observed an enhancement of particle deposition in models with cartilage rings. These results bring to light the importance of including cartilage rings in experimental, numerical, and theoretical models to better understand particle deposition in the trachea and bronchi. In addition, the results provide scientists and medical staff with new insights for improving drug delivery.

RevDate: 2018-10-15
CmpDate: 2018-10-15

Bordones AD, Leroux M, Kheyfets VO, et al (2018)

Computational Fluid Dynamics Modeling of the Human Pulmonary Arteries with Experimental Validation.

Annals of biomedical engineering, 46(9):1309-1324.

Pulmonary hypertension (PH) is a chronic progressive disease characterized by elevated pulmonary arterial pressure, caused by an increase in pulmonary arterial impedance. Computational fluid dynamics (CFD) can be used to identify metrics representative of the stage of PH disease. However, experimental validation of CFD models is often not pursued due to the geometric complexity of the model or uncertainties in the reproduction of the required flow conditions. The goal of this work is to validate experimentally a CFD model of a pulmonary artery phantom using a particle image velocimetry (PIV) technique. Rapid prototyping was used for the construction of the patient-specific pulmonary geometry, derived from chest computed tomography angiography images. CFD simulations were performed with the pulmonary model with a Reynolds number matching those of the experiments. Flow rates, the velocity field, and shear stress distributions obtained with the CFD simulations were compared to their counterparts from the PIV flow visualization experiments. Computationally predicted flow rates were within 1% of the experimental measurements for three of the four branches of the CFD model. The mean velocities in four transversal planes of study were within 5.9 to 13.1% of the experimental mean velocities. Shear stresses were qualitatively similar between the two methods with some discrepancies in the regions of high velocity gradients. The fluid flow differences between the CFD model and the PIV phantom are attributed to experimental inaccuracies and the relative compliance of the phantom. This comparative analysis yielded valuable information on the accuracy of CFD predicted hemodynamics in pulmonary circulation models.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Zhu B, Ji Z, Lou Z, et al (2018)

Torque scaling in small-gap Taylor-Couette flow with smooth or grooved wall.

Physical review. E, 97(3-1):033110.

The torque in the Taylor-Couette flow for radius ratios η≥0.97, with smooth or grooved wall static outer cylinders, is studied experimentally, with the Reynolds number of the inner cylinder reaching up to Re_{i}=2×10^{5}, corresponding to the Taylor number up to Ta=5×10^{10}. The grooves are perpendicular to the mean flow, and similar to the structure of a submersible motor stator. It is found that the dimensionless torque G, at a given Re_{i} and η, is significantly greater for grooved cases than smooth cases. We compare our experimental torques for the smooth cases to the fit proposed by Wendt [F. Wendt, Ing.-Arch. 4, 577 (1993)10.1007/BF02084936] and the fit proposed by Bilgen and Boulos [E. Bilgen and R. Boulos, J Fluids Eng. 95, 122 (1973)10.1115/1.3446944], which shows both fits are outside their range for small gaps. Furthermore, an additional dimensionless torque (angular velocity flux) Nu_{ω} in the smooth cases exhibits an effective scaling of Nu_{ω}∼Ta^{0.39} in the ultimate regime, which occurs at a lower Taylor number, Ta≈3.5×10^{7}, than the well-explored η=0.714 case (at Ta≈3×10^{8}). The same effective scaling exponent, 0.39, is also evident in the grooved cases, but for η=0.97 and 0.985, there is a peak before this exponent appears.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Liang H, Xu J, Chen J, et al (2018)

Phase-field-based lattice Boltzmann modeling of large-density-ratio two-phase flows.

Physical review. E, 97(3-1):033309.

In this paper, we present a simple and accurate lattice Boltzmann (LB) model for immiscible two-phase flows, which is able to deal with large density contrasts. This model utilizes two LB equations, one of which is used to solve the conservative Allen-Cahn equation, and the other is adopted to solve the incompressible Navier-Stokes equations. A forcing distribution function is elaborately designed in the LB equation for the Navier-Stokes equations, which make it much simpler than the existing LB models. In addition, the proposed model can achieve superior numerical accuracy compared with previous Allen-Cahn type of LB models. Several benchmark two-phase problems, including static droplet, layered Poiseuille flow, and spinodal decomposition are simulated to validate the present LB model. It is found that the present model can achieve relatively small spurious velocity in the LB community, and the obtained numerical results also show good agreement with the analytical solutions or some available results. Lastly, we use the present model to investigate the droplet impact on a thin liquid film with a large density ratio of 1000 and the Reynolds number ranging from 20 to 500. The fascinating phenomena of droplet splashing is successfully reproduced by the present model and the numerically predicted spreading radius exhibits to obey the power law reported in the literature.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Oyama N, Teshigawara K, Molina JJ, et al (2018)

Reynolds-number-dependent dynamical transitions on hydrodynamic synchronization modes of externally driven colloids.

Physical review. E, 97(3-1):032611.

The collective dynamics of externally driven N_{p}-colloidal systems (1≤N_{p}≤4) in a confined viscous fluid have been investigated using three-dimensional direct numerical simulations with fully resolved hydrodynamics. The dynamical modes of collective particle motion are studied by changing the particle Reynolds number as determined by the strength of the external driving force and the confining wall distance. For a system with N_{p}=3, we found that at a critical Reynolds number a dynamical mode transition occurs from the doublet-singlet mode to the triplet mode, which has not been reported experimentally. The dynamical mode transition was analyzed in detail from the following two viewpoints: (1) spectrum analysis of the time evolution of a tagged particle velocity and (2) the relative acceleration of the doublet cluster with respect to the singlet particle. For a system with N_{p}=4, we found similar dynamical mode transitions from the doublet-singlet-singlet mode to the triplet-singlet mode and further to the quartet mode.

RevDate: 2018-09-02

Markwalter CE, RK Prud'homme (2018)

Design of a Small-Scale Multi-Inlet Vortex Mixer for Scalable Nanoparticle Production and Application to the Encapsulation of Biologics by Inverse Flash NanoPrecipitation.

Journal of pharmaceutical sciences, 107(9):2465-2471.

Flash NanoPrecipitation is a scalable approach to generate polymeric nanoparticles using rapid micromixing in specially designed geometries such as a confined impinging jets mixer or a Multi-Inlet Vortex Mixer (MIVM). A major limitation of formulation screening using the MIVM is that a single run requires tens of milligrams of the therapeutic. To overcome this, we have developed a scaled-down version of the MIVM, requiring as little as 0.2 mg of therapeutic, for formulation screening. The redesigned mixer can then be attached to pumps for scale-up of the identified formulation. It was shown that Reynolds number allowed accurate scaling between the 2 MIVM designs. The utility of the small-scale MIVM for formulation development was demonstrated through the encapsulation of a number of hydrophilic macromolecules using inverse Flash NanoPrecipitation with target loadings as high as 50% by mass.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Sanjeevi SKP, Zarghami A, JT Padding (2018)

Choice of no-slip curved boundary condition for lattice Boltzmann simulations of high-Reynolds-number flows.

Physical review. E, 97(4-1):043305.

Various curved no-slip boundary conditions available in literature improve the accuracy of lattice Boltzmann simulations compared to the traditional staircase approximation of curved geometries. Usually, the required unknown distribution functions emerging from the solid nodes are computed based on the known distribution functions using interpolation or extrapolation schemes. On using such curved boundary schemes, there will be mass loss or gain at each time step during the simulations, especially apparent at high Reynolds numbers, which is called mass leakage. Such an issue becomes severe in periodic flows, where the mass leakage accumulation would affect the computed flow fields over time. In this paper, we examine mass leakage of the most well-known curved boundary treatments for high-Reynolds-number flows. Apart from the existing schemes, we also test different forced mass conservation schemes and a constant density scheme. The capability of each scheme is investigated and, finally, recommendations for choosing a proper boundary condition scheme are given for stable and accurate simulations.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Mahalinkam R, Gong F, AS Khair (2018)

Reduced-order model for inertial locomotion of a slender swimmer.

Physical review. E, 97(4-1):043102.

The inertial locomotion of an elongated model swimmer in a Newtonian fluid is quantified, wherein self-propulsion is achieved via steady tangential surface treadmilling. The swimmer has a length 2l and a circular cross section of longitudinal profile aR(z), where a is the characteristic width of the cross section, R(z) is a dimensionless shape function, and z is a dimensionless coordinate, normalized by l, along the centerline of the body. It is assumed that the swimmer is slender, ε=a/l≪1. Hence, we utilize slender-body theory to analyze the Navier-Stokes equations that describe the flow around the swimmer. Therefrom, we compute an asymptotic approximation to the swimming speed, U, as U/u_{s}=1-β[V(Re)-1/2∫_{-1}^{1}zlnR(z)dz]/ln(1/ε)+O[1/ln^{2}(1/ε)], where u_{s} is the characteristic speed of the surface treadmilling, Re is the Reynolds number based on the body length, and β is a dimensionless parameter that differentiates between "pusher" (propelled from the rear, β<0) and "puller" (propelled from the front, β>0) -type swimmers. The function V(Re) increases monotonically with increasing Re; hence, fluid inertia causes an increase (decrease) in the swimming speed of a pusher (puller). Next, we demonstrate that the power expenditure of the swimmer increases monotonically with increasing Re. Further, the power expenditures of a puller and pusher with the same value of |β| are equal. Therefore, pushers are superior in inertial locomotion as compared to pullers, in that they achieve a faster swimming speed for the same power expended. Finally, it is demonstrated that the flow structure predicted from our reduced-order model is consistent with that from direct numerical simulation of swimmers at intermediate Re.

RevDate: 2018-06-01

Daddi-Moussa-Ider A, Lisicki M, Mathijssen AJTM, et al (2018)

State diagram of a three-sphere microswimmer in a channel.

Journal of physics. Condensed matter : an Institute of Physics journal, 30(25):254004.

Geometric confinements are frequently encountered in soft matter systems and in particular significantly alter the dynamics of swimming microorganisms in viscous media. Surface-related effects on the motility of microswimmers can lead to important consequences in a large number of biological systems, such as biofilm formation, bacterial adhesion and microbial activity. On the basis of low-Reynolds-number hydrodynamics, we explore the state diagram of a three-sphere microswimmer under channel confinement in a slit geometry and fully characterize the swimming behavior and trajectories for neutral swimmers, puller- and pusher-type swimmers. While pushers always end up trapped at the channel walls, neutral swimmers and pullers may further perform a gliding motion and maintain a stable navigation along the channel. We find that the resulting dynamical system exhibits a supercritical pitchfork bifurcation in which swimming in the mid-plane becomes unstable beyond a transition channel height while two new stable limit cycles or fixed points that are symmetrically disposed with respect to the channel mid-height emerge. Additionally, we show that an accurate description of the averaged swimming velocity and rotation rate in a channel can be captured analytically using the method of hydrodynamic images, provided that the swimmer size is much smaller than the channel height.

RevDate: 2018-06-14

Tottori S, BJ Nelson (2018)

Controlled Propulsion of Two-Dimensional Microswimmers in a Precessing Magnetic Field.

Small (Weinheim an der Bergstrasse, Germany), 14(24):e1800722.

Magnetically actuated micro-/nanoswimmers can potentially be used in noninvasive biomedical applications, such as targeted drug delivery and micromanipulation. Herein, two-dimensional (2D) rigid ferromagnetic microstructures are shown to be capable of propelling themselves in three dimensions at low Reynolds numbers in a precessing field. Importantly, the above propulsion relies neither on soft structure deformation nor on the geometrical chirality of swimmers, but is rather driven by the dynamic chirality generated by field precession, which allows an almost unconstrained choice of materials and fabrication methods. Therefore, the swimming performance is systematically investigated as a function of precession angle and geometric design. One disadvantage of the described propulsion method is that the fabricated 2D swimmers are achiral, which means that the forward/backward swimming direction cannot be controlled. However, it has been found that asymmetric 2D swimmers always propel themselves toward their longer arm, which implies that dynamic chirality can be constrained to be either right-handed or left-handed by permanent magnetization. Thus, the simplicity of fabrication and possibility of dynamic chirality control make the developed method ideal for applications and fundamental studies that require a large number of swimmers.

RevDate: 2018-06-05

Perrin A, Herbelin P, Jorand FPA, et al (2018)

Design of a rotating disk reactor to assess the colonization of biofilms by free-living amoebae under high shear rates.

Biofouling, 34(4):368-377.

The present study was aimed at designing and optimizing a rotating disk reactor simulating high hydrodynamic shear rates (γ), which are representative of cooling circuits. The characteristics of the hydrodynamic conditions in the reactor and the complex approach used to engineer it are described. A 60 l tank was filled with freshwater containing free-living amoebae (FLA) and bacteria. Adhesion of the bacteria and formation of a biofilm on the stainless steel coupons were observed. FLA were able to establish in these biofilms under γ as high as 85,000 s-1. Several physical mechanisms (convection, diffusion, sedimentation) could explain the accumulation of amoeboid cells on surfaces, but further research is required to fully understand and model the fine mechanisms governing such transport under γ similar to those encountered in the industrial environment. This technological advance may enable research into these topics.

RevDate: 2018-05-10

Zhang S, Luo X, Z Cai (2018)

Three-dimensional flows in a hyperelastic vessel under external pressure.

Biomechanics and modeling in mechanobiology pii:10.1007/s10237-018-1022-y [Epub ahead of print].

We study the collapsible behaviour of a vessel conveying viscous flows subject to external pressure, a scenario that could occur in many physiological applications. The vessel is modelled as a three-dimensional cylindrical tube of nonlinear hyperelastic material. To solve the fully coupled fluid-structure interaction, we have developed a novel approach based on the Arbitrary Lagrangian-Eulerian (ALE) method and the frontal solver. The method of rotating spines is used to enable an automatic mesh adaptation. The numerical code is verified extensively with published results and those obtained using the commercial packages in simpler cases, e.g. ANSYS for the structure with the prescribed flow, and FLUENT for the fluid flow with prescribed structure deformation. We examine three different hyperelastic material models for the tube for the first time in this context and show that at the small strain, all three material models give similar results. However, for the large strain, results differ depending on the material model used. We further study the behaviour of the tube under a mode-3 buckling and reveal its complex flow patterns under various external pressures. To understand these flow patterns, we show how energy dissipation is associated with the boundary layers created at the narrowest collapsed section of the tube, and how the transverse flow forms a virtual sink to feed a strong axial jet. We found that the energy dissipation associated with the recirculation does not coincide with the flow separation zone itself, but overlaps with the streamlines that divide the three recirculation zones. Finally, we examine the bifurcation diagrams for both mode-3 and mode-2 collapses and reveal that multiple solutions exist for a range of the Reynolds number. Our work is a step towards modelling more realistic physiological flows in collapsible arteries and veins.

RevDate: 2018-05-11

Zhou Y, Lee C, J Wang (2018)

The Computational Fluid Dynamics Analyses on Hemodynamic Characteristics in Stenosed Arterial Models.

Journal of healthcare engineering, 2018:4312415.

Arterial stenosis plays an important role in the progressions of thrombosis and stroke. In the present study, a standard axisymmetric tube model of the stenotic artery is introduced and the degree of stenosis η is evaluated by the area ratio of the blockage to the normal vessel. A normal case (η = 0) and four stenotic cases of η = 0.25, 0.5, 0.625, and 0.75 with a constant Reynolds number of 300 are simulated by computational fluid dynamics (CFD), respectively, with the Newtonian and Carreau models for comparison. Results show that for both models, the poststenotic separation vortex length increases exponentially with the growth of stenosis degree. However, the vortex length of the Carreau model is shorter than that of the Newtonian model. The artery narrowing accelerates blood flow, which causes high blood pressure and wall shear stress (WSS). The pressure drop of the η = 0.75 case is nearly 8 times that of the normal value, while the WSS peak at the stenosis region of η = 0.75 case even reaches up to 15 times that of the normal value. The present conclusions are of generality and contribute to the understanding of the dynamic mechanisms of artery stenosis diseases.

RevDate: 2018-10-15
CmpDate: 2018-10-15

García-Salazar G, de la Luz Zambrano-Zaragoza M, D Quintanar-Guerrero (2018)

Preparation of nanodispersions by solvent displacement using the Venturi tube.

International journal of pharmaceutics, 545(1-2):254-260.

The Venturi tube (VT) is an apparatus that produces turbulence which is taken advantage of to produce nanoparticles (NP) by solvent displacement. The objective of this study was to evaluate the potential of this device for preparing NP of poly-ε-caprolactone. Response Surface Methodology was used to determine the effect of the operating conditions and optimization. The NP produced by VT were characterized by Dynamic Light-Scattering to determine their particle size distribution (PS) and polydispersity index (PDI). Results showed that the Reynolds number (Re) has a strong effect on both PS and process yield (PY).The turbulence regime is key to the efficient formation of NP. The optimal conditions for obtaining NP were a polymer concentration of 1.6 w/v, a recirculation rate of 4.8 L/min, and a stabilizer concentration of 1.1 w/v. The predicted response of the PY was 99.7%, with a PS of 333 nm, and a PDI of 0.2. Maintaining the same preparation conditions will make it possible to obtain NP using other polymers with similar properties. Our results show that VT is a reproducible and versatile method for manufacturing NP, and so may be a feasible method for industrial-scale nanoprecipitation production.

RevDate: 2018-09-18

Sandeep N, Kumaran G, S Saleem (2018)

The influence of cross diffusion on magnetohydrodynamic flow of Carreau liquid in the presence of buoyancy force.

Journal of integrative neuroscience, 17(3-4):525-546.

The flow of magnetohydrodynamic Carreau liquid with the Brownian moment, thermophoresis and cross diffusion effects is investigated numerically. The buoyancy persuades on the flow is contemplated in such a way that the surface is neither perpendicular/horizontal nor wedge/cone. This is very helpful in the design of jet-engine. The equations govern the flow are transmuted using acceptable similarity variables and numerically solved by recruiting Runge-Kutta based Newtons method. The graphical results are obtained to discuss the stimulus of flow, thermal and concentration fields for different parameters of interest. The wall friction, local Nusselt and Sherwood numbers are examined with the assistance of tables. It is noticed that the parabolic flow is controlled by the buoyant forces developed by the temperature difference. Since the flow is laminar, the Reynolds number considered as <1000. This study has applicable in man-made products and various industries like pumps and oil purification, petroleum production, power engineering and chemical engineering processes.

RevDate: 2018-09-10
CmpDate: 2018-09-10

Gao S, Liao Q, Liu W, et al (2018)

Nanodroplets Impact on Rough Surfaces: A Simulation and Theoretical Study.

Langmuir : the ACS journal of surfaces and colloids, 34(20):5910-5917.

Impact of droplets is widespread in life, and modulating the dynamics of impinging droplets is a significant problem in production. However, on textured surfaces, the micromorphologic change and mechanism of impinging nanodroplets are not well-understood; furthermore, the accuracy of the theoretical model for nanodroplets needs to be improved. Here, considering the great challenge of conducting experiments on nanodroplets, a molecular dynamics simulation is performed to visualize the impact process of nanodroplets on nanopillar surfaces. Compared with macroscale droplets, apart from the similar relation of restitution coefficient with the Weber number, we found some distinctive results: the maximum spreading time is described as a power law of impact velocity, and the relation of maximum spreading factor with impact velocity or the Reynolds number is exponential. Moreover, the roughness of substrates plays a prominent role in the dynamics of impact nanodroplets, and on surfaces with lower solid fraction, the lower attraction force induces an easier rebound of impact nanodroplets. At last, on the basis of the energy balance, through modifying the estimation of viscous dissipation and surface energy terms, we proposed an improved model for the maximum spreading factor, which shows greater accuracy for nanodroplets, especially in the low-to-moderate velocity range. The outcome of this study demonstrates that a distinctive dynamical behavior of impinging nanodroplets, the fundamental insight, and more accurate prediction are very useful in the improvement of the hydrodynamic behavior of the nanodroplets.

RevDate: 2018-07-30
CmpDate: 2018-07-30

Vilfan M, Osterman N, A Vilfan (2018)

Magnetically driven omnidirectional artificial microswimmers.

Soft matter, 14(17):3415-3422.

We present an experimental realisation of two new artificial microswimmers that swim at low Reynolds number. The swimmers are externally driven with a periodically modulated magnetic field that induces an alternating attractive/repulsive interaction between the swimmer parts. The field sequence also modulates the drag on the swimmer components, making the working cycle non-reciprocal. The resulting net translational displacement leads to velocities of up to 2 micrometers per second. The swimmers can be made omnidirectional, meaning that the same magnetic field sequence can drive swimmers in any direction in the sample plane. Although the direction of their swimming is determined by the momentary orientation of the swimmer, their motion can be guided by solid boundaries. We demonstrate their omnidirectionality by letting them travel through a circular microfluidic channel. We use simple scaling arguments as well as more detailed numerical simulations to explain the measured velocity as a function of the actuation frequency.

RevDate: 2018-05-01

Govindarajan V, Mousel J, Udaykumar HS, et al (2018)

Synergy between Diastolic Mitral Valve Function and Left Ventricular Flow Aids in Valve Closure and Blood Transport during Systole.

Scientific reports, 8(1):6187 pii:10.1038/s41598-018-24469-x.

Highly resolved three-dimensional (3D) fluid structure interaction (FSI) simulation using patient-specific echocardiographic data can be a powerful tool for accurately and thoroughly elucidating the biomechanics of mitral valve (MV) function and left ventricular (LV) fluid dynamics. We developed and validated a strongly coupled FSI algorithm to fully characterize the LV flow field during diastolic MV opening under physiologic conditions. Our model revealed that distinct MV deformation and LV flow patterns developed during different diastolic stages. A vortex ring that strongly depended on MV deformation formed during early diastole. At peak E wave, the MV fully opened, with a local Reynolds number of ~5500, indicating that the flow was in the laminar-turbulent transitional regime. Our results showed that during diastasis, the vortex structures caused the MV leaflets to converge, thus increasing mitral jet's velocity. The vortex ring became asymmetrical, with the vortex structures on the anterior side being larger than on the posterior side. During the late diastolic stages, the flow structures advected toward the LV outflow tract, enhancing fluid transport to the aorta. This 3D-FSI study demonstrated the importance of leaflet dynamics, their effect on the vortex ring, and their influence on MV function and fluid transport within the LV during diastole.

RevDate: 2018-04-18

Li H, S Guo (2018)

Aerodynamic efficiency of a bioinspired flapping wing rotor at low Reynolds number.

Royal Society open science, 5(3):171307 pii:rsos171307.

This study investigates the aerodynamic efficiency of a bioinspired flapping wing rotor kinematics which combines an active vertical flapping motion and a passive horizontal rotation induced by aerodynamic thrust. The aerodynamic efficiencies for producing both vertical lift and horizontal thrust of the wing are obtained using a quasi-steady aerodynamic model and two-dimensional (2D) CFD analysis at Reynolds number of 2500. The calculated efficiency data show that both efficiencies (propulsive efficiency-ηp, and efficiency for producing lift-Pf) of the wing are optimized at Strouhal number (St) between 0.1 and 0.5 for a range of wing pitch angles (upstroke angle of attack αu less than 45°); the St for high Pf (St = 0.1 ∼ 0.3) is generally lower than for high ηp (St = 0.2 ∼ 0.5), while the St for equilibrium rotation states lies between the two. Further systematic calculations show that the natural equilibrium of the passive rotating wing automatically converges to high-efficiency states: above 85% of maximum Pf can be obtained for a wide range of prescribed wing kinematics. This study provides insight into the aerodynamic efficiency of biological flyers in cruising flight, as well as practical applications for micro air vehicle design.

RevDate: 2018-05-25

Wang C, H Tang (2018)

Enhancement of aerodynamic performance of a heaving airfoil using synthetic-jet based active flow control.

Bioinspiration & biomimetics, 13(4):046005.

In this study, we explore the use of synthetic jet (SJ) in manipulating the vortices around a rigid heaving airfoil, so as to enhance its aerodynamic performance. The airfoil heaves at two fixed pitching angles, with the Strouhal number, reduced frequency and Reynolds number chosen as St = 0.3, k = 0.25 and Re = 100, respectively, all falling in the ranges for natural flyers. As such, the vortex force plays a dominant role in determining the airfoil's aerodynamic performance. A pair of in-phase SJs is implemented on the airfoil's upper and lower surfaces, operating with the same strength but in opposite directions. Such a fluid-structure interaction problem is numerically solved using a lattice Boltzmann method based numerical framework. It is found that, as the airfoil heaves with zero pitching angle, its lift and drag can be improved concurrently when the SJ phase angle [Formula: see text] relative to the heave motion varies between [Formula: see text] and [Formula: see text]. But this concurrent improvement does not occur as the airfoil heaves with [Formula: see text] pitching angle. Detailed inspection of the vortex evolution and fluid stress over the airfoil surface reveals that, if at good timing, the suction and blowing strokes of the SJ pair can effectively delay or promote the shedding of leading edge vortices, and mitigate or even eliminate the generation of trailing edge vortices, so as to enhance the airfoil's aerodynamic performance. Based on these understandings, an intermittent operation of the SJ pair is then proposed to realize concurrent lift and drag improvement for the heaving airfoil with [Formula: see text] pitching angle.

RevDate: 2018-09-10
CmpDate: 2018-09-10

Bordbar A, Taassob A, Khojasteh D, et al (2018)

Maximum Spreading and Rebound of a Droplet Impacting onto a Spherical Surface at Low Weber Numbers.

Langmuir : the ACS journal of surfaces and colloids, 34(17):5149-5158.

The spreading and rebound patterns of low-viscous droplets upon impacting spherical solid surfaces are investigated numerically. The studied cases consider a droplet impinging onto hydrophobic and superhydrophobic surfaces with various parameters varied throughout the study, and their effects on the postimpingement behavior are discussed. These parameters include impact Weber number (through varying the surface tension and impingement velocity), the size ratio of the droplet to the solid surface, and the surface contact angle. According to the findings, the maximum spreading diameter increases with the impact velocity, with an increase of the sphere diameter, with a lower surface wettability, and with a lower surface tension. Typical outcomes of the impact include (1) complete rebound, (2) splash, and (3) a final deposition stage after a series of spreading and recoiling phases. Finally, a novel, practical model is proposed, which can reasonably predict the maximum deformation of low Reynolds number impact of droplets onto hydrophobic or superhydrophobic spherical solid surfaces.

RevDate: 2018-06-15

Hopgood M, Reynolds G, R Barker (2018)

Using Computational Fluid Dynamics to Compare Shear Rate and Turbulence in the TIM-Automated Gastric Compartment With USP Apparatus II.

Journal of pharmaceutical sciences, 107(7):1911-1919.

We use computational fluid dynamics to compare the shear rate and turbulence in an advanced in vitro gastric model (TIMagc) during its simulation of fasted state Migrating Motor Complex phases I and II, with the United States Pharmacopeia paddle dissolution apparatus II (USPII). A specific focus is placed on how shear rate in these apparatus affects erosion-based solid oral dosage forms. The study finds that tablet surface shear rates in TIMagc are strongly time dependant and fluctuate between 0.001 and 360 s-1. In USPII, tablet surface shear rates are approximately constant for a given paddle speed and increase linearly from 9 s-1 to 36 s-1 as the paddle speed is increased from 25 to 100 rpm. A strong linear relationship is observed between tablet surface shear rate and tablet erosion rate in USPII, whereas TIMagc shows highly variable behavior. The flow regimes present in each apparatus are compared to in vivo predictions using Reynolds number analysis. Reynolds numbers for flow in TIMagc lie predominantly within the predicted in vivo bounds (0.01-30), whereas Reynolds numbers for flow in USPII lie above the predicted upper bound when operating with paddle speeds as low as 25 rpm (33).

RevDate: 2018-05-09

Prakash J, Ramesh K, Tripathi D, et al (2018)

Numerical simulation of heat transfer in blood flow altered by electroosmosis through tapered micro-vessels.

Microvascular research, 118:162-172.

A numerical simulation is presented to study the heat and flow characteristics of blood flow altered by electroosmosis through the tapered micro-vessels. Blood is assumed as non-Newtonian (micropolar) nanofluids. The flow regime is considered as asymmetric diverging (tapered) microchannel for more realistic micro-vessels which is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The Rosseland approximation is employed to model the radiation heat transfer and temperatures of the walls are presumed constants. The mathematical formulation of the present problem is simplified under the long-wavelength, low-Reynolds number and Debye-Hückel linearization approximations. The influence of various dominant physical parameters are discussed for axial velocity, microrotation distribution, thermal temperature distribution and nanoparticle volume fraction field. However, our foremost emphasis is to determine the effects of thermal radiation and coupling number on the axial velocity and microrotation distribution beneath electroosmotic environment. This analysis places a significant observation on the thermal radiation and coupling number which plays an influential role in hearten fluid velocity. This study is encouraged by exploring the nanofluid-dynamics in peristaltic transport as symbolized by heat transport in biological flows and also in novel pharmacodynamics pumps and gastro-intestinal motility enhancement.

RevDate: 2018-04-19
CmpDate: 2018-04-19

Jing H, S Das (2018)

Theory of diffusioosmosis in a charged nanochannel.

Physical chemistry chemical physics : PCCP, 20(15):10204-10212.

We probe the diffusioosmotic transport in a charged nanofluidic channel in the presence of an applied tangential salt concentration gradient. Ionic salt gradient driven diffusioosmosis or ionic diffusioosmosis (IDO) is characterized by the generation of an induced tangential electric field and a diffusioosmotic velocity (DOSV) that is a combination of an electroosmotic velocity (EOSV) triggered by this electric field and a chemiosmotic velocity (COSV) triggered by an induced tangential pressure gradient. We explain that unlike the existing theories on IDO, it is more appropriate to apply the zero net current conditions (formulation F2) and not more restrictive zero net local flux conditions (formulation F1) particularly for the case where one considers a nanochannel connected to two reservoirs. We pinpoint limitations in the existing literature in correctly predicting the diffusioosmotic behavior even for the case where formulation F1 is used. We address these limitations and establish that (a) the induced electric field is an interplay of the differences in ionic diffusivity, the EDL-induced imbalance in ion concentrations, and the advection effects, (b) formulation F1 may overpredict or underpredict the electric field and the EOSV leading to an overprediction/underprediction of the DOSV and (c) formulation F2 demonstrates remarkable fluid physics of localized backflows owing to a dominant local influence of the COSV, which is missed by formulation F1. We anticipate that our theory will provide the first rigorous understanding of nanofluidic IDO with applications in multiple areas of low Reynolds number transport such as biofluidics, microfluidic separation, and colloidal transport.

RevDate: 2018-09-04
CmpDate: 2018-09-04

Rigatelli G, Zuin M, Dell'Avvocata F, et al (2018)

Rheolytic effects of left main mid-shaft/distal stenting: a computational flow dynamic analysis.

Therapeutic advances in cardiovascular disease, 12(6):161-168.

Background The aim of this study was to evaluate the rheolytic effects of stenting a mid-shaft/distal left main coronary artery (LMCA) lesion with and without ostial coverage. Stenting of the LMCA has emerged as a valid alternative in place of traditional coronary bypass graft surgery. However, in case of mid-shaft/distal lesion, there is no consensus regarding the extension of the strut coverage up to the ostium or to stent only the culprit lesion. Methods We reconstructed a left main-left descending coronary artery (LM-LCA)-left circumflex (LCX) bifurcation after analysing 100 consecutive patients (mean age 71.4 ± 9.3, 49 males) with LM mid-shaft/distal disease. The mean diameter of proximal LM, left anterior descending (LAD) and LCX, evaluated with quantitative coronary angiography (QCA) was 4.62 ± 0.86 mm, 3.31 ± 0.92 mm, and 2.74 ± 0.93 mm, respectively. For the stent simulation, a third-generation, everolimus-eluting stent was virtually reconstructed. Results After virtual stenting, the net area averaged wall shear stress (WSS) of the model and the WSS at the LCA-LCX bifurcation resulted higher when the stent covered the culprit mid-shaft lesion only compared with the extension of the stent covering the ostium (3.68 versus 2.06 Pa, p = 0.01 and 3.97 versus 1.98 Pa, p < 0.001, respectively. Similarly, the static pressure and the Reynolds number were significantly higher after stent implantation covering up the ostium. At the ostium, the flow resulted more laminar when stenting only the mid-shaft lesion than including the ostium. Conclusions Although these findings cannot be translated directly into real practice our brief study suggests that stenting lesion 1:1 or extending the stent to cover the LM ostium impacts differently the rheolytic properties of LMCA bifurcation with potential insights for restenosis or thrombosis.

RevDate: 2018-09-04
CmpDate: 2018-09-04

Xi J, Hu Q, Zhao L, et al (2018)

Molecular Binding Contributes to Concentration Dependent Acrolein Deposition in Rat Upper Airways: CFD and Molecular Dynamics Analyses.

International journal of molecular sciences, 19(4): pii:ijms19040997.

Existing in vivo experiments show significantly decreased acrolein uptake in rats with increasing inhaled acrolein concentrations. Considering that high-polarity chemicals are prone to bond with each other, it is hypothesized that molecular binding between acrolein and water will contribute to the experimentally observed deposition decrease by decreasing the effective diffusivity. The objective of this study is to quantify the probability of molecular binding for acrolein, as well as its effects on acrolein deposition, using multiscale simulations. An image-based rat airway geometry was used to predict the transport and deposition of acrolein using the chemical species model. The low Reynolds number turbulence model was used to simulate the airflows. Molecular dynamic (MD) simulations were used to study the molecular binding of acrolein in different media and at different acrolein concentrations. MD results show that significant molecular binding can happen between acrolein and water molecules in human and rat airways. With 72 acrolein embedded in 800 water molecules, about 48% of acrolein compounds contain one hydrogen bond and 10% contain two hydrogen bonds, which agreed favorably with previous MD results. The percentage of hydrogen-bonded acrolein compounds is higher at higher acrolein concentrations or in a medium with higher polarity. Computational dosimetry results show that the size increase caused by the molecular binding reduces the effective diffusivity of acrolein and lowers the chemical deposition onto the airway surfaces. This result is consistent with the experimentally observed deposition decrease at higher concentrations. However, this size increase can only explain part of the concentration-dependent variation of the acrolein uptake and acts as a concurrent mechanism with the uptake-limiting tissue ration rate. Intermolecular interactions and associated variation in diffusivity should be considered in future dosimetry modeling of high-polarity chemicals such as acrolein.

RevDate: 2018-03-27
CmpDate: 2018-03-21

Gupta A, Clercx HJH, F Toschi (2018)

Computational study of radial particle migration and stresslet distributions in particle-laden turbulent pipe flow.

The European physical journal. E, Soft matter, 41(3):34 pii:10.1140/epje/i2018-11638-3.

Particle-laden turbulent flows occur in a variety of industrial applications as well as in naturally occurring flows. While the numerical simulation of such flows has seen significant advances in recent years, it still remains a challenging problem. Many studies investigated the rheology of dense suspensions in laminar flows as well as the dynamics of point-particles in turbulence. Here we employ a fully-resolved numerical simulation based on a lattice Boltzmann scheme, to investigate turbulent flow with large neutrally buoyant particles in a pipe flow at low Reynolds number and in dilute regimes. The energy input is kept fixed resulting in a Reynolds number based on the friction velocity around 250. Two different particle radii were used giving a particle-pipe diameter ratio of 0.05 and 0.075. The number of particles is kept constant resulting in a volume fraction of 0.54% and 1.83%, respectively. We investigated Eulerian and Lagrangian statistics along with the stresslet exerted by the fluid on the spherical particles. It was observed that the high particle-to-fluid slip velocity close to the wall corresponds locally to events of high energy dissipation, which are not present in the single-phase flow. The migration of particles from the inner to the outer region of the pipe, the dependence of the stresslet on the particle radial positions and a proxy for the fragmentation rate of the particles computed using the stresslet have been investigated.


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

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Curriculum Vitae for R J Robbins

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