Physical Review Fluids

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Gyrotactic suppression and emergence of chaotic trajectories of swimming particles in three-dimensional flows

Fri, 02/23/2018 - 10:00

Author(s): S. I. Heath Richardson, A. W. Baggaley, and N. A. Hill

Pattern formation is an intriguing, and biologically important, feature of many motile microorganisms. A new study shows that gyrotatic swimmers can form complex patterns even in the presence of a chaotic background flow, through the local suppression of Lagrangian chaos.

[Phys. Rev. Fluids 3, 023102] Published Fri Feb 23, 2018

Particle-bearing currents in uniform density and two-layer fluids

Fri, 02/23/2018 - 10:00

Author(s): Bruce R. Sutherland, Murray K. Gingras, Calla Knudson, Luke Steverango, and Christopher Surma

Experiments of hypopycnal and mesopycnal currents demonstrate that the microscopic transport of fresh water in viscous boundary layers surrounding the settling particles significantly impacts the macroscopic current evolution.

[Phys. Rev. Fluids 3, 023801] Published Fri Feb 23, 2018

Evolving geometry of a vortex triangle

Fri, 02/23/2018 - 10:00

Author(s): Vikas S. Krishnamurthy, Hassan Aref, and Mark A. Stremler

A new study shows that the motion of three interacting point vortices in the plane can be formulated in terms of the size and location of the circle that circumscribes the vortex triangle, the interior angles of the triangle, and the orientation of the triangle, giving an alternate perspective on this classic problem.

[Phys. Rev. Fluids 3, 024702] Published Fri Feb 23, 2018

Predictive model for local scour downstream of hydrokinetic turbines in erodible channels

Thu, 02/22/2018 - 10:00

Author(s): Mirko Musa, Michael Heisel, and Michele Guala

Inspired by recent theoretical advances in bridge scour research, a modeling framework is derived to predict the scour induced by Hydrokinetic turbines on erodible river bed surfaces. Using a mixed scaling formulation of the Reynolds stresses, the turbine performance is linked to the scour evolution.

[Phys. Rev. Fluids 3, 024606] Published Thu Feb 22, 2018

Modeling boundary-layer transition in direct and large-eddy simulations using parabolized stability equations

Wed, 02/21/2018 - 10:00

Author(s): A. Lozano-Durán, M. J. P. Hack, and P. Moin

The potential of the nonlinear parabolized stability equations is examined to provide an accurate yet computationally efficient treatment of the laminar flow regime in direct and large-eddy simulations of transitional boundary layers.

[Phys. Rev. Fluids 3, 023901] Published Wed Feb 21, 2018

Turbulent statistics and intermittency enhancement in coflowing superfluid $^{4}\mathrm{He}$

Wed, 02/21/2018 - 10:00

Author(s): L. Biferale, D. Khomenko, V. L'vov, A. Pomyalov, I. Procaccia, and G. Sahoo

The statistics of velocity fluctuations in coflowing superfluid 4He are studied by direct numerical simulations. The statistics are highly non-Gaussian, generally more than in classical turbulence, with the maximal non-Gaussianity occurring when the super and normal fluid densities are comparable.

[Phys. Rev. Fluids 3, 024605] Published Wed Feb 21, 2018

Onset of low Prandtl number thermal convection in thin spherical shells

Wed, 02/21/2018 - 10:00

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

Low Prandtl number shell convection occurs in many geophysical and astrophysical scenarios. An exploration of the patterns that form at convective onset in this extreme regime finds new mode transitions and a triple point bifurcation.

[Phys. Rev. Fluids 3, 024801] Published Wed Feb 21, 2018

Enhanced interfacial deformation in a Marangoni flow: A measure of the dynamical surface tension

Tue, 02/20/2018 - 10:00

Author(s): Rodrigo Leite Pinto, Sébastien Le Roux, Isabelle Cantat, and Arnaud Saint-Jalmes

Once a drop of water-soluble surfactant is deposited on a bare oil-water interface, flows are induced in water and in oil (Marangoni effect). An investigation shows that the interface is also deformed, with an upward water bump into the oil, and that the vertical shape of the interface is linked to the in-plane surface tension profile.

[Phys. Rev. Fluids 3, 024003] Published Tue Feb 20, 2018

Morphing continuum analysis of energy transfer in compressible turbulence

Tue, 02/20/2018 - 10:00

Author(s): Mohamad Ibrahim Cheikh, Louis B. Wonnell, and James Chen

A computationally friendly morphing continuum theory for the energy cascade of compressible turbulence characterizes the statistical coupling of energy transfer at the length scale of eddies, with one-tenth of the computational costs required in the Navier-Stokes based DNS.

[Phys. Rev. Fluids 3, 024604] Published Tue Feb 20, 2018

Hysteretic growth and decay of a waterspout column

Tue, 02/20/2018 - 10:00

Author(s): Igor V. Naumov, Miguel A. Herrada, Bulat R. Sharifullin, and Vladimir N. Shtern

Experimental and numerical studies reveal the hysteretic formation and decay of a water column extending from the bottom to the top of a sealed vertical cylinder filled with sunflower oil and water. The fluid motion is driven by the rotating lid and appears multicellular.

[Phys. Rev. Fluids 3, 024701] Published Tue Feb 20, 2018

Reduced viscosity for flagella moving in a solution of long polymer chains

Fri, 02/16/2018 - 10:00

Author(s): Yuchen Zhang, Gaojin Li, and Arezoo M. Ardekani

Brownian dynamics simulations of polymer molecules near bacterial flagella show that they experience a reduced viscosity in a long chain polymer solution. This can lead to an enhanced swimming speed when flagellum thickness is smaller than the radius of gyration of polymer molecules.

[Phys. Rev. Fluids 3, 023101] Published Fri Feb 16, 2018

Shock-wave structure for a polyatomic gas with large bulk viscosity

Fri, 02/16/2018 - 10:00

Author(s): Shingo Kosuge and Kazuo Aoki

Numerical simulation and theoretical analysis based on a model Boltzmann equation show that a plane shock wave in a polyatomic gas with large bulk viscosity exhibits three different types of structure, depending on the upstream Mach number.

[Phys. Rev. Fluids 3, 023401] Published Fri Feb 16, 2018

Taylor dispersion in premixed combustion: Questions from turbulent combustion answered for laminar flames

Wed, 02/14/2018 - 10:00

Author(s): Joel Daou, Philip Pearce, and Faisal Al-Malki

We study Taylor dispersion in premixed combustion. Analytical formulas are derived which answer fundamental questions related to Damköhler’s second hypothesis of turbulent combustion and occurrence of the “bending-effect” of turbulent flame speed, when the questions are for laminar one-scale flows.

[Phys. Rev. Fluids 3, 023201] Published Wed Feb 14, 2018

Inelastic accretion of inertial particles by a towed sphere

Wed, 02/14/2018 - 10:00

Author(s): Robin Vallée, Christophe Henry, Elie Hachem, and Jérémie Bec

A large sphere moving through a fluid at rest collects small suspended particles. Estimating the efficiency of this process is of importance for wet aerosol deposition or planet formation. Multiple bounces do not lead to inelastic collapse but are still shown to significantly enhance accretion.

[Phys. Rev. Fluids 3, 024303] Published Wed Feb 14, 2018

High-order moments of streamwise fluctuations in a turbulent channel flow with spanwise rotation

Tue, 02/13/2018 - 10:00

Author(s): Zhenhua Xia, Geert Brethouwer, and Shiyi Chen

Analysis of recent direct numerical simulations of wall-bounded turbulence with spanwise rotation find that even-order moments up to the 12th in the streamwise velocity fluctuations vary linearly with distance from the wall.

[Phys. Rev. Fluids 3, 022601(R)] Published Tue Feb 13, 2018

Degeneracy of velocity strain-rate tensor statistics in random isotropic incompressible flows

Tue, 02/13/2018 - 10:00

Author(s): A. V. Kopyev

We find a strong degeneracy in the strain-rate tensor probability distribution in numerical simulations of isotropic turbulence in incompressible flows, reducing the distribution to a function of one variable. We also find a universal distribution for the ratio of strain tensor eigenvalues.

[Phys. Rev. Fluids 3, 024603] Published Tue Feb 13, 2018

Irreversibility inversions in two-dimensional turbulence

Mon, 02/12/2018 - 10:00

Author(s): Andrew D. Bragg, Filippo De Lillo, and Guido Boffetta

An analysis shows that in 2D turbulence the nature of the irreversibility of two-particle dispersion inverts when the particle inertia exceeds a certain threshold. The results also imply that in turbulent flows with an inverse energy flux, inertial particle-pairs may yet exhibit a downscale flux of energy.

[Phys. Rev. Fluids 3, 024302] Published Mon Feb 12, 2018

Experimental test of the crossover between the inertial and the dissipative range in a turbulent swirling flow

Fri, 02/09/2018 - 10:00

Author(s): Paul Debue, Denis Kuzzay, Ewe-Wei Saw, François Daviaud, Bérengère Dubrulle, Léonie Canet, Vincent Rossetto, and Nicolás Wschebor

A crossover from a Kolmogorov decay of two decades in the inertial range to a stretched exponential in the dissipative range is unveiled in the experimental spatial energy spectrum of a turbulent swirling flow, as recently predicted based on nonperturbative renormalization group theory.

[Phys. Rev. Fluids 3, 024602] Published Fri Feb 09, 2018

Marangoni-flow-induced partial coalescence of a droplet on a liquid/air interface

Thu, 02/08/2018 - 10:00

Author(s): Kai Sun, Peng Zhang, Zhizhao Che, and Tianyou Wang

Numerical simulations show that the coalescence of a droplet on a liquid-air interface of lower surface tension manifests the nonmonotonic phenomena of emergence, disappearance, and re-emergence of “partial coalescence” with increasing surface-tension difference.

[Phys. Rev. Fluids 3, 023602] Published Thu Feb 08, 2018

Direct numerical simulation of a compressible boundary-layer flow past an isolated three-dimensional hump in a high-speed subsonic regime

Thu, 02/08/2018 - 10:00

Author(s): D. De Grazia, D. Moxey, S. J. Sherwin, M. A. Kravtsova, and A. I. Ruban

The boundary-layer separation produced by a small hump in a high-speed subsonic regime typical of civil aviation is studied. Different heights of the hump are considered, with the larger resulting in a fully nonlinear regime and the formation of a pair of streamwise counterrotating vortices.

[Phys. Rev. Fluids 3, 024101] Published Thu Feb 08, 2018