# Latest papers in fluid mechanics

### A micropolar-Newtonian blood flow model through a porous layered artery in the presence of a magnetic field

In this work, we present a two-phase model of blood flow through a porous layered artery in the presence of a uniform magnetic field. The characteristic of suspensions in blood allows us to assume blood as a micropolar fluid in the core region and plasma as a Newtonian fluid in the peripheral region of a blood vessel. The wall of a blood vessel is porous and composed of a thin Brinkman transition layer followed by a Darcy porous layer of different permeabilities. A magnetic field of uniform strength is transversally applied to the direction of blood flow. The authors obtained an analytical solution of the problem of blood flow through the composite porous walled artery. Analytical expressions for the flow velocity, microrotational velocity, flow rate, and stresses at the wall have been obtained in the closed form using the modified Bessel function. The effects of various flow parameters on the two-fluid model of blood flow are analyzed graphically. An important conclusion which is drawn from the solution of the present problem is that the different permeabilities of Darcy and Brinkman regions of the porous layered artery have a significant effect on the flow. The present work is validated from the previously published literature studies.

### Marangoni instability in a heated viscoelastic liquid film: Long-wave versus short-wave perturbations

Author(s): Rajkumar Sarma and Pranab Kumar Mondal

We investigate the Marangoni instability in a thin layer of viscoelastic fluid, confined between its deformable free surface and a substrate of low thermal conductivity. Following a theoretical analysis, we study the stability of the present system for the case when the fluid layer is subjected to h...

[Phys. Rev. E 100, 013103] Published Wed Jul 10, 2019

### Coarse graining the dynamics of immersed and driven fiber assemblies

Author(s): David B. Stein and Michael J. Shelley

We develop a coarse-grained Brinkman-type model for the dynamics of ordered arrays of immersed fibers. This approach provides a simple framework for the mathematical analysis and efficient numerical solution of problems including fiber-fluid rheology, soft valves, and waves within driven fiber beds.

[Phys. Rev. Fluids 4, 073302] Published Tue Jul 09, 2019

### Forced three-wave interactions of capillary-gravity surface waves

Author(s): Annette Cazaubiel, Florence Haudin, Eric Falcon, and Michael Berhanu

Two surface waves are forced in a cylindrical tank. Their nonlinear interaction generates a third wave not obeying the dispersion relation, whose presence is shown using a laser vibrometer or a three-dimensional free-surface reconstruction. We explain this result as a forced three-wave interaction.

[Phys. Rev. Fluids 4, 074803] Published Tue Jul 09, 2019

### Efficiency limits of the three-sphere swimmer

Author(s): Babak Nasouri, Andrej Vilfan, and Ramin Golestanian

The efficiency of the three-sphere swimmer is studied and the optimal actuation sequences determined. By accounting for full hydrodynamic interactions in the low Reynolds number regime, it is shown that, surprisingly, the swimmer with unequal spheres can be more efficient than the equally sized one.

[Phys. Rev. Fluids 4, 073101] Published Mon Jul 08, 2019

### Filament formation via the instability of a stretching viscous sheet: Physical mechanism, linear theory, and fiber applications

Author(s): Bingrui Xu, Minhao Li, Feng Wang, Steven G. Johnson, Yoel Fink, and Daosheng Deng

Liquid sheets are essential for industrial applications, and during thermal drawing, a stretching viscous sheet breaks up into filaments. A theory is proposed to elucidate the underlying mechanism, shedding light on the sophisticated structures for functional devices in fibers, fabrics, or textiles.

[Phys. Rev. Fluids 4, 073902] Published Mon Jul 08, 2019

### Dipolar thermocapillary motor and swimmer

Author(s): Valeri Frumkin, Khaled Gommed, and Moran Bercovici

A circular opening in a Hele-Shaw-type confinement gives rise to thermocapillary dipole flow, which can be used to drive flow in microfluidic configurations. The same mechanism can also be leveraged for the propulsion of light-actuated surface swimmers.

[Phys. Rev. Fluids 4, 074002] Published Mon Jul 08, 2019

### Experimental and numerical investigation of phase separation due to multicomponent mixing at high-pressure conditions

Author(s): C. Traxinger, M. Pfitzner, S. Baab, G. Lamanna, and B. Weigand

Mixture-induced phase separation of an initially supercritical fluid due to the interaction with its surrounding is studied. Three different injection temperatures are investigated and qualitative characteristics of the formation process agree well between experiments and simulations.

[Phys. Rev. Fluids 4, 074303] Published Mon Jul 08, 2019

### Dynamics and wakes of freely settling and rising cubes

Author(s): Arman Seyed-Ahmadi and Anthony Wachs

Direct numerical simulations of settling and rising cubes show the prevalence of distinct helical motions, the onset of which are accompanied by a significant jump in the drag coefficient. This enhancement is associated with a combined effect of the vortex-induced drag and the cube orientation.

[Phys. Rev. Fluids 4, 074304] Published Mon Jul 08, 2019

### Polar waves and chaotic flows in thin rotating spherical shells

Author(s): F. Garcia, F. R. N. Chambers, and A. L. Watts

A study of periodic and chaotic flows in thin, rotating spherical shells at low Prandtl number finds that convection can be equatorially asymmetric and confined in one hemisphere near the onset, contrasting with previous studies. The applicability of these results to gas-giant atmospheres is explored.

[Phys. Rev. Fluids 4, 074802] Published Mon Jul 08, 2019

### Numerical computation of the Rayleigh-Taylor instability for a viscous fluid with regularized interface properties

Author(s): L. M. González-Gutiérrez and A. de Andrea González

In this article, the computation of the linear growth rates and eigenfunctions of the viscous version of the Rayleigh-Taylor instability by numerically solving the corresponding eigenvalue problem in the case of one-dimensional (1D) and two-dimensional (2D) geometries is studied. The 1D version is f...

[Phys. Rev. E 100, 013101] Published Wed Jul 03, 2019

### Single-spectrum prediction of kurtosis of water waves in a nonconservative model

Author(s): D. Eeltink, A. Armaroli, Y. M. Ducimetière, J. Kasparian, and M. Brunetti

We study statistical properties after a sudden episode of wind for water waves propagating in one direction. A wave with random initial conditions is propagated using a forced-damped higher-order nonlinear Schrödinger equation. During the wind episode, the wave action increases, the spectrum broaden...

[Phys. Rev. E 100, 013102] Published Wed Jul 03, 2019

### Role of surrounding gas in the outcome of droplet splashing

Author(s): David A. Burzynski and Stephan E. Bansmer

An experimental study demonstrates how surrounding gas affects secondary droplets ejected during splashing at high Weber and Reynolds numbers. It provides evidence that splashing is influenced primarily by the density, followed by the viscosity, and finally by the mean-free path of the gas.

[Phys. Rev. Fluids 4, 073601] Published Wed Jul 03, 2019

### Diffusion characteristics of air pockets on hydrophobic surfaces in channel flow: Three-dimensional measurement of air-water interface

Author(s): Hyunseok Kim and Hyungmin Park

Temporal variations of the three-dimensional air-water interface shape of trapped air pockets on hydrophobic surfaces in turbulent flows are directly measured. Depending on the shape regimes, the corresponding diffusion rate of air pockets is modeled as a function of flow and geometric parameters.

[Phys. Rev. Fluids 4, 074001] Published Wed Jul 03, 2019

### Sedimentation of gas-fluidized particles with random shape and size

Author(s): Laurence Girolami and Frédéric Risso

Observations of the settling velocity of suspensions of irregular particles are found to depend on (i) the difference of density between the particles and the suspension and (ii) a viscosity which depends on the ratio of the concentration to the loose packing concentration.

[Phys. Rev. Fluids 4, 074301] Published Wed Jul 03, 2019

### Quantifying silo flow using MRI velocimetry for testing granular flow models

Author(s): Luke Fullard, Daniel J. Holland, Petrik Galvosas, Clive Davies, Pierre-Yves Lagrée, and Stéphane Popinet

Compared to fluid dynamics, granular material flow is poorly understood. Magnetic resonance imaging of poppy seeds flowing through three silos reveals three distinct flow regimes. A continuum mathematical model using an effective viscosity captures the dynamics in two of the three regimes.

[Phys. Rev. Fluids 4, 074302] Published Wed Jul 03, 2019

### Sharp transitions in rotating turbulent convection: Lagrangian acceleration statistics reveal a second critical Rossby number

Author(s): Kim M. J. Alards, Rudie P. J. Kunnen, Richard J. A. M. Stevens, Detlef Lohse, Federico Toschi, and Herman J. H. Clercx

The sharp transition in flow behavior in turbulent weakly rotating thermal convection is explored with Lagrangian velocity and acceleration statistics of fluid particles. The transition consists of two distinct phenomena: 1) transition in heat transfer and 2) emergence of cyclonic vortical plumes.

[Phys. Rev. Fluids 4, 074601] Published Wed Jul 03, 2019

### Rate of decay of turbulent kinetic energy in abruptly stabilized Ekman boundary layers

Author(s): Stimit Shah and Elie Bou-Zeid

In the late afternoon, the surface temperature drops below air temperature and the lower atmosphere’s density stratification becomes stable. A simple model that predicts the rate at which turbulence kinetic energy and mixing decrease after the onset of stable stratification is presented.

[Phys. Rev. Fluids 4, 074602] Published Wed Jul 03, 2019

### Dynamics of a trapped vortex in rotating convection

Author(s): J. W. Atkinson, P. A. Davidson, and J. E. G. Perry

Numerical simulations of rotating convection as a simple model for atmospheric vortices show that the eye that forms at the center may become unstable and bifurcate into an oscillatory state. It is proposed that these oscillations result from a trapped inertial wave at the core.

[Phys. Rev. Fluids 4, 074701] Published Wed Jul 03, 2019

### Identifying four-wave-resonant interactions in a surface gravity wave turbulence experiment

Author(s): Antoine Campagne, Roumaissa Hassaini, Ivan Redor, Thomas Valran, Samuel Viboud, Joël Sommeria, and Nicolas Mordant

The level of nonlinearity of experimental surface gravity wave turbulence is investigated. The measured average steepness of 10% is considered high. It is shown that the high nonlinearity of our flow is mainly supplied by bound waves, the free waves being in a weakly nonlinear state.

[Phys. Rev. Fluids 4, 074801] Published Wed Jul 03, 2019