# Latest papers in fluid mechanics

### Evolution of anisotropy in direct numerical simulations of MHD turbulence in a strong magnetic field on elongated periodic domains

Author(s): X. M. Zhai and P. K. Yeung

Time development (from top to bottom) of vortical structures (in red) in background of low vorticity (blue) in planar cross-sections of turbulence subjected to magnetic field on an elongated domain of aspect ratio 8, at 16384×20482 grid resolution.

[Phys. Rev. Fluids 3, 084602] Published Tue Aug 07, 2018

### Intense structures of different momentum fluxes in turbulent channels

Author(s): Kosuke Osawa and Javier Jiménez

The effects of the ambiguity in the definition of the Reynolds stresses to the coherent structures in wall turbulence are studied. It is confirmed that sweeps, ejections, and rollers are robust features of the flow.

[Phys. Rev. Fluids 3, 084603] Published Tue Aug 07, 2018

### Oscillatory instability in a reaction front separating fluids of different densities

Author(s): Dan Coroian and Desiderio A. Vasquez

Reaction fronts described by the Kuramoto-Sivashinsky (KS) equation can exhibit complex behavior as they separate reacted from unreacted fluids. If the fluid of higher density is above a fluid of lower density, then the Rayleigh-Taylor instability can lead to fluid motion. In the reverse situation, ...

[Phys. Rev. E 98, 023102] Published Mon Aug 06, 2018

### Ion partitioning effect on the electrophoresis of a soft particle with hydrophobic core

Author(s): Saurabh K. Maurya, Partha P. Gopmandal, S. Bhattacharyya, and H. Ohshima

A theoretical study on the electrophoresis of a soft particle made up of a charged hydrophobic inner core surrounded by polyelectrolyte layer (PEL) is made. The dielectric permittivity of the PEL and aqueous solution are considered to be different, which creates the ion partitioning effect. The ion ...

[Phys. Rev. E 98, 023103] Published Mon Aug 06, 2018

### Rivulet flow of generalized Newtonian fluids

Author(s): F. H. H. Al Mukahal, B. R. Duffy, and S. K. Wilson

The general parametric solution for the steady unidirectional flow of a thin rivulet of a generalized Newtonian fluid is obtained and illustrated for Carreau and Ellis fluids. In particular, the solution is used to describe the behavior of a rivulet of a strongly shear-thinning Ellis fluid.

[Phys. Rev. Fluids 3, 083302] Published Mon Aug 06, 2018

### Turbulent magnetohydrodynamic flow in a square duct: Comparison of zero and finite magnetic Reynolds number cases

Author(s): Vinodh Bandaru, Thomas Boeck, and Jörg Schumacher

The effect of finite magnetic Reynolds numbers (Rm∼102) on MHD flow in a square duct was studied using direct numerical simulations. The structure of the secondary mean flow is modified significantly and the streamwise anisotropy is strongly enhanced away from the boundary layers.

[Phys. Rev. Fluids 3, 083701] Published Mon Aug 06, 2018

### Numerical study of the effects of chemical dispersant on oil transport from an idealized underwater blowout

Author(s): Bicheng Chen, Di Yang, Charles Meneveau, and Marcelo Chamecki

To investigate how chemical dispersant impacts the transport of oil slicks such as the one from the Deepwater Horizon, a multiscale large-eddy simulation approach is used to show that the breakup of the oil slick into small droplets changes the mean transport direction and horizontal spread of the oil plume.

[Phys. Rev. Fluids 3, 083801] Published Mon Aug 06, 2018

### Smart inertial particles

Author(s): Simona Colabrese, Kristian Gustavsson, Antonio Celani, and Luca Biferale

A reinforcement learning algorithm is applied to find quasi-optimal policies for buoyancy control of inertial probes/particles in order to avoid trapping and to reach specific regions when navigating in complex two- and three-dimensional flows.

[Phys. Rev. Fluids 3, 084301] Published Mon Aug 06, 2018

### Scale locality of the energy cascade using real space quantities

Author(s): N. A. K. Doan, N. Swaminathan, P. A. Davidson, and M. Tanahashi

Scale locality of the energy cascade is demonstrated using direct numerical simulations data of homogeneous isotropic turbulence with Taylor microscale Reynolds numbers ranging from 37 to 1131. The range of influential scales for this scale locality is found to be independent of Reynolds number.

[Phys. Rev. Fluids 3, 084601] Published Mon Aug 06, 2018

### Inertial spheroids in homogeneous, isotropic turbulence

Author(s): Amal Roy, Anupam Gupta, and Samriddhi Sankar Ray

We study the rotational dynamics of *inertial* disks and rods in three-dimensional, homogeneous, isotropic turbulence. In particular, we show how the alignment and the decorrelation timescales of such spheroids depend, critically, on both the level of inertia and the aspect ratio of these particles. T...

[Phys. Rev. E 98, 021101(R)] Published Fri Aug 03, 2018

### Fluctuation analysis of the atmospheric energy cycle

Author(s): Richard Blender, Denny Gohlke, and Frank Lunkeit

The atmosphere gains available potential energy by solar radiation and dissipates kinetic energy mainly in the atmospheric boundary layer. We analyze the fluctuations of the global mean energy cycle defined by Lorenz in a simulation with a simplified hydrostatic model. The energy current densities a...

[Phys. Rev. E 98, 023101] Published Fri Aug 03, 2018

### Diffusion of self-propelled particles in complex media

Author(s): Juan L. Aragones, Shahrzad Yazdi, and Alfredo Alexander-Katz

An investigation of the behavior of self-propelled particles in complex media finds a transition from thermal diffusion to collision-driven diffusion as the particle area fraction is increased. Collisions with passive particles increases the rotational diffusion of the self-propelled particles, leading to their “self-trapping.”

[Phys. Rev. Fluids 3, 083301] Published Thu Aug 02, 2018

### Angular multiscale statistics of turbulence in a porous bed

Author(s): Xiaoliang He, Sourabh Apte, Kai Schneider, and Benjamin Kadoch

The physics of turbulent flow in porous media is explored in the Lagrangian frame. The evolution of curvature angles along the fluid trajectories reveals the multiscale nature of turbulence. The asymptotic value of the curvature angle quantifies the effect of geometric confinement on turbulence.

[Phys. Rev. Fluids 3, 084501] Published Thu Aug 02, 2018

### Steady thermocapillary migration of a droplet in a uniform temperature gradient combined with a radiation energy source at large Marangoni numbers

Author(s): Zuo-Bing Wu

Steady thermocapillary droplet migration in a uniform temperature gradient combined with a radiation energy source at large Reynolds and Marangoni numbers is studied. To reach a terminal quasisteady process, the magnitude of the radiation energy source is required to preserve the conservative integr...

[Phys. Rev. E 98, 013110] Published Tue Jul 31, 2018

### Mixing mechanism in a two-dimensional bubble column

Author(s): Elise Alméras, Frédéric Risso, Véronique Roig, Cécile Plais, and Frédéric Augier

A large-scale model for transport by secondary open wakes is proposed to describe the spatiotemporal evolution of the concentration field in a homogeneous bidimensional bubble swarm rising at high Reynolds number.

[Phys. Rev. Fluids 3, 074307] Published Tue Jul 31, 2018

### Magnetohydrodynamics- and magnetosolutal-transport-mediated evaporation dynamics in paramagnetic pendant droplets under field stimulus

Author(s): Vivek Jaiswal, Raghvendra Kumar Dwivedi, A. R. Harikrishnan, and Purbarun Dhar

Evaporation kinetics of pendant droplets is an area of immense importance in several applications, in addition to possessing rich fluid dynamics and thermal transport physics. This article experimentally and analytically sheds insight into the augmented evaporation dynamics of paramagnetic pendant d...

[Phys. Rev. E 98, 013109] Published Mon Jul 30, 2018

### Elucidating the mechanism of step emulsification

Author(s): Andrea Montessori, Marco Lauricella, Sauro Succi, Elad Stolovicki, and David Weitz

Three-dimensional Lattice Boltzmann simulations contrast backflow from an external reservoir into a confined microchannel in a dripping mode where the drop breaks off towards the end of the microchannel with a jetting mode at higher flows with drop break off further downstream inside the reservoir.

[Phys. Rev. Fluids 3, 072202(R)] Published Mon Jul 30, 2018

### Delayed coalescence of surfactant containing sessile droplets

Author(s): M. A. Bruning, M. Costalonga, S. Karpitschka, and J. H. Snoeijer

The coalescence of surfactant solutions on a substrate is studied. By varying both the contact angle of the droplets and their difference in surface tension, various regimes with distinct timescales of noncoalescence are identified.

[Phys. Rev. Fluids 3, 073605] Published Mon Jul 30, 2018

### Stratified flows in axially rotating pipes

Author(s): S. Lyu and S. M. Taghavi

There is considerable research to improve the displacement efficiency in buoyant two-fluid flow systems, e.g., when a heavy fluid is injected to displace a light one from a pipe. Experiments show that a pipe rotation helps to completely remove the displaced fluid.

[Phys. Rev. Fluids 3, 074003] Published Mon Jul 30, 2018

### Granular bed consolidation, creep, and armoring under subcritical fluid flow

Author(s): Benjamin Allen and Arshad Kudrolli

Internal imaging shows that a granular bed consolidates and creeps under the action of fluid flow well below the bedload transport critical rate. The bed is shown to be armored with a systematic increase in erosion threshold depending on the duration and strength of applied subcritical shear.

[Phys. Rev. Fluids 3, 074305] Published Mon Jul 30, 2018