# Latest papers in fluid mechanics

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

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

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

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

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

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 $^{4}\mathrm{He}$

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

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

### Electroconvection in a dielectric liquid between two concentric half-cylinders with rigid walls: Linear and nonlinear analysis

Author(s): Pedro A. Vázquez, Alberto T. Pérez, Philippe Traoré, and Jian Wu

We study the linear stability and nonlinear behavior of the electroconvection between two concentric half-cylinders with no-slip conditions on all boundaries. The no-slip condition makes impossible to apply the standard modal approach. Hence, we apply a finite element technique similar to the one we...

[Phys. Rev. E 97, 023106] Published Tue Feb 20, 2018

### Energy transfer in compressible magnetohydrodynamic turbulence for isothermal self-gravitating fluids

Author(s): Supratik Banerjee and Alexei G. Kritsuk

Three-dimensional, compressible, magnetohydrodynamic turbulence of an isothermal, self-gravitating fluid is analyzed using two-point statistics in the asymptotic limit of large Reynolds numbers (both kinetic and magnetic). Following an alternative formulation proposed by Banerjee and Galtier [Phys. ...

[Phys. Rev. E 97, 023107] Published Tue Feb 20, 2018

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

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

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

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

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

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

### Statistics of the relative velocity of particles in turbulent flows: Monodisperse particles

Author(s): Akshay Bhatnagar, K. Gustavsson, and Dhrubaditya Mitra

We use direct numerical simulations to calculate the joint probability density function of the relative distance R and relative radial velocity component VR for a pair of heavy inertial particles suspended in homogeneous and isotropic turbulent flows. At small scales the distribution is scale invari...

[Phys. Rev. E 97, 023105] Published Thu Feb 15, 2018

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

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

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

### Is the kinetic equation for turbulent gas-particle flows ill posed?

Author(s): M. Reeks, D. C. Swailes, and A. D. Bragg

This paper is about the kinetic equation for gas-particle flows, in particular its well-posedness and realizability and its relationship to the generalized Langevin model (GLM) probability density function (PDF) equation. Previous analyses, e.g. [J.-P. Minier and C. Profeta, Phys. Rev. E **92**, 053020 ...

[Phys. Rev. E 97, 023104] Published Tue Feb 13, 2018

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

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

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