Physical Review Fluids

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Updated: 23 hours 16 min ago

Efficiency limits of the three-sphere swimmer

Mon, 07/08/2019 - 11:00

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

Mon, 07/08/2019 - 11:00

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

Mon, 07/08/2019 - 11:00

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

Mon, 07/08/2019 - 11:00

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

Mon, 07/08/2019 - 11:00

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

Mon, 07/08/2019 - 11:00

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

Role of surrounding gas in the outcome of droplet splashing

Wed, 07/03/2019 - 11:00

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

Wed, 07/03/2019 - 11:00

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

Wed, 07/03/2019 - 11:00

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

Wed, 07/03/2019 - 11:00

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

Wed, 07/03/2019 - 11:00

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

Wed, 07/03/2019 - 11:00

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

Wed, 07/03/2019 - 11:00

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

Wed, 07/03/2019 - 11:00

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

Flow dynamics of a dandelion pappus: A linear stability approach

Tue, 07/02/2019 - 11:00

Author(s): P. G. Ledda, L. Siconolfi, F. Viola, S. Camarri, and F. Gallaire

A dandelion pappus is modelled as a porous disk. A stability analysis finds that if the disk is sufficiently porous the steady wake is stable and consists in a separated recirculating vortex ring, which allows a long-distance dispersal of the dandelion seeds.

[Phys. Rev. Fluids 4, 071901(R)] Published Tue Jul 02, 2019

Effect of the irreversible $\text{A}+\text{B}→\text{C}$ reaction on the onset and the growth of the buoyancy-driven instability in a porous medium: Asymptotic, linear, and nonlinear stability analyses

Tue, 07/02/2019 - 11:00

Author(s): Min Chan Kim

A theoretical analysis of the effect of an irreversible A+B→C reaction on the growth of a buoyancy-driven instability in a Hele-Shaw cell, taking different diffusivities into account, is presented.

[Phys. Rev. Fluids 4, 073901] Published Tue Jul 02, 2019

Oscillations of small bubbles and medium yielding in elastoviscoplastic fluids

Mon, 07/01/2019 - 11:00

Author(s): Marco De Corato, Brice Saint-Michel, George Makrigiorgos, Yannis Dimakopoulos, John Tsamopoulos, and Valeria Garbin

Bubble removal from yield-stress fluids by ultrasound is studied theoretically by combining the governing equation of bubble dynamics with an elastoviscoplastic constitutive model. The radius of the yielded region oscillates at twice the frequency of the ultrasound-driven bubble oscillations.

[Phys. Rev. Fluids 4, 073301] Published Mon Jul 01, 2019

Pore-scale study of dissolution-driven density instability with reaction $A+B→C$ in porous media

Fri, 06/28/2019 - 11:00

Author(s): Timan Lei and Kai H. Luo

A dissolution-driven density instability with reaction A+B→C is simulated in both homogeneous and heterogeneous media at pore scale. Six types of fingering scenarios are found in each medium, and it is shown that media with large pore size in the top layer can enhance the storage of solute A in the host fluid.

[Phys. Rev. Fluids 4, 063907] Published Fri Jun 28, 2019

Incompressible models of magnetohydrodynamic Richtmyer-Meshkov instability in cylindrical geometry

Thu, 06/27/2019 - 11:00

Author(s): A. Bakhsh and R. Samtaney

With a cylindrical and incompressible model of an impulsively accelerated conducting fluid interface, effects of normal or azimuthal magnetic fields on interface growth rates are studied. In the normal case growth decays at late times and in the azimuthal one a growth perturbation oscillates.

[Phys. Rev. Fluids 4, 063906] Published Thu Jun 27, 2019

Drop impact on hairy surfaces

Wed, 06/26/2019 - 11:00

Author(s): Alice Nasto, P.-T. Brun, and A. E. Hosoi

A study of the impact of liquid drops on millimeter-scale hairy surfaces finds that the behavior of the impacting drops depends on the amount of kinetic energy dissipated through the hairs via a balance of inertia, viscosity, and surface tension.

[Phys. Rev. Fluids 4, 064004] Published Wed Jun 26, 2019