# Latest papers in fluid mechanics

### Collisions of drops with an immiscible liquid jet

Author(s): Carole Planchette, Sylvain Petit, Hannes Hinterbichler, and Günter Brenn

The collisions of a drop stream with an immiscible jet are experimentally studied revealing the formation of several complex structures classified in four main regimes. When neither the drops nor the jet fragment,“drops in jet” are observed that could be hardened to produce advanced fibers.

[Phys. Rev. Fluids 3, 093603] Published Wed Sep 12, 2018

### Thermophoresis of Janus particles at large Knudsen numbers

Author(s): Tobias Baier, Sudarshan Tiwari, Samir Shrestha, Axel Klar, and Steffen Hardt

At large Knudsen numbers a Janus particle in a thermal gradient shows a preferred orientation. The interplay between rotational diffusion and thermophoretic motion is investigated.

[Phys. Rev. Fluids 3, 094202] Published Wed Sep 12, 2018

### Shear-induced migration and orientation of rigid fibers in an oscillatory pipe flow

Author(s): Scott Strednak, Saif Shaikh, Jason E. Butler, and Élisabeth Guazzelli

Fibers in suspension migrate towards the center of the pipe where they are more aligned with the flow. The migration depends on the fraction of the volume of the suspension swept out by the rotating fibers.

[Phys. Rev. Fluids 3, 091301(R)] Published Mon Sep 10, 2018

### Forced wakes far from threshold: Stuart-Landau equation applied to experimental data

Author(s): S. Boury, B. Thiria, R. Godoy-Diana, G. Artana, J. E. Wesfreid, and J. D'Adamo

The Stuart-Landau reduced order model is tested with experimental data from the wake of a cylinder wake forced by plasma actuators, finding an important role played by the changing mean flow.

[Phys. Rev. Fluids 3, 091901(R)] Published Mon Sep 10, 2018

### Entrainment model for fully-developed wind farms: Effects of atmospheric stability and an ideal limit for wind farm performance

Author(s): Paolo Luzzatto-Fegiz and Colm-cille P. Caulfield

A new model of wind farm aerodynamics establishes an upper bound for power density, which is an order of magnitude larger than achieved by contemporary turbine arrays. The model also provides a one-equation prediction for the output of existing wind farms, and can include atmospheric stability.

[Phys. Rev. Fluids 3, 093802] Published Mon Sep 10, 2018

### Asymmetric concentration dependence of segregation fluxes in granular flows

Author(s): Ryan P. Jones, Austin B. Isner, Hongyi Xiao, Julio M. Ottino, Paul B. Umbanhowar, and Richard M. Lueptow

Particles differing in size or density segregate in dense granular flows. In bidisperse mixtures, the sinking (small or heavy) species concentration that maximizes the segregation flux is <50% and decreases with increasing size or density ratio, matching a classic kinetic-sieving model.

[Phys. Rev. Fluids 3, 094304] Published Mon Sep 10, 2018

### Extremes, intermittency, and time directionality of atmospheric turbulence at the crossover from production to inertial scales

Author(s): E. Zorzetto, A. D. Bragg, and G. Katul

A study of how the interplay between mechanical and buoyant production of turbulent kinetic energy affects fully developed atmospheric turbulent flows finds impacts both on the frequency of extreme scalar fluctuations and on the time-directional properties of scalar Eulerian measurements.

[Phys. Rev. Fluids 3, 094604] Published Mon Sep 10, 2018

### Linear stability of a contaminated fluid flow down a slippery inclined plane

Author(s): Farooq Ahmad Bhat and Arghya Samanta

The linear stability analysis of a fluid flow down a slippery inclined plane is carried out when the free surface of the fluid is contaminated by a monolayer of insoluble surfactant. The aim is to extend the earlier study [Samanta *et al.*, J. Fluid Mech. **684**, 353 (2011)] for low to high values of the...

[Phys. Rev. E 98, 033108] Published Fri Sep 07, 2018

### Fluidity, anisotropy, and velocity correlations in frictionless, collisional grain flows

Author(s): Diego Berzi and James T. Jenkins

We propose corrections to the kinetic theory for fluidity in granular flows near random close packing, in order to take account of anisotropy and increases in granular temperature.

[Phys. Rev. Fluids 3, 094303] Published Fri Sep 07, 2018

### Statistics of incremental averages of passive scalar fluctuations

Author(s): Colin R. Meyer, Laurent Mydlarski, and Luminita Danaila

An investigation of the statistics of incremental averages of passive scalar fluctuations shows that, unlike statistics of their differences, they inherit information from the scalar field’s large scales, for averages over all increment sizes, and can differ from analogous statistics for the velocity field.

[Phys. Rev. Fluids 3, 094603] Published Fri Sep 07, 2018

### Axially symmetric and latitudinally propagating nonlinear patterns in rotating spherical convection

Author(s): Dali Kong, Keke Zhang, Kameng Lam, and Ashley P. Willis

We report a nonlinear phenomenon discovered in the classical problem of thermal convection in rapidly rotating, self-gravitating, internally heated Boussinesq fluid spheres. When linear convective instability (the most unstable mode of convection) is in the form of an axially symmetric, equatorially...

[Phys. Rev. E 98, 031101(R)] Published Thu Sep 06, 2018

### Turbulence-driven reverse lift on two-dimensional and three-dimensional structures

Author(s): Yaqing Jin, Lin Yan, Haotian Qiu, and Leonardo P. Chamorro

Using laboratory experiments and simplified theoretical arguments, we show that the level of turbulence may reverse the direction of the mean lift on two- and three-dimensional structures with relatively short, deflected splitters. Planar particle image velocimetry and a high-resolution load cell we...

[Phys. Rev. E 98, 033106] Published Thu Sep 06, 2018

### Long-time behavior of three-dimensional gravity-capillary solitary waves on deep water generated by a moving air-blowing forcing: Numerical study

Author(s): Yeunwoo Cho

Long-time simulations are conducted on a forced three-dimensional (3D) nonlinear viscous gravity-capillary wave equation that describes the surface wave pattern when the forcing moves on the surface of deep water with speeds less than the linear phase speed cmin=23cm/s. Three different states are id...

[Phys. Rev. E 98, 033107] Published Thu Sep 06, 2018

### Expansion and retraction dynamics in drop-on-drop impacts on nonwetting surfaces

Author(s): Maher Damak and Kripa Varanasi

When a drop impacts a stationary drop on a non-wetting surface, the two drops coalesce, spread on the surface and retract, sometimes bouncing off. We measure the maximum diameter and retraction time for a wide range of parameter values and generalize known single drop models to drop-on-drop impacts.

[Phys. Rev. Fluids 3, 093602] Published Thu Sep 06, 2018

### Reaction analogy based forcing for incompressible scalar turbulence

Author(s): Don Daniel, Daniel Livescu, and Jaiyoung Ryu

A new forcing method for generating statistically stationary scalar fields in incompressible turbulence is proposed based on an analogy with chemical reactions.

[Phys. Rev. Fluids 3, 094602] Published Thu Sep 06, 2018

### Curvature dependence of heat transfer at a fluid-solid interface

Author(s): Ali Dinler, Robert W. Barber, Stefan K. Stefanov, and David R. Emerson

This study reports an opposing effect of curvature on the interfacial heat transfer, which implies a monotonic increase in the temperature jump over a convex surface and, conversely, a monotonic decrease in the temperature jump over a concave surface, as the curvature of the surface increases. The s...

[Phys. Rev. E 98, 033104] Published Wed Sep 05, 2018

### Inviscid vortex shedding model for the clap and fling motion of insect flights

Author(s): Sung-Ik Sohn

In this paper, we study the clap and fling motion of insect flights by applying an inviscid vortex shedding model. We describe separated vortices from the edges of two wings by vortex sheets and extend the model to the two bodies with symmetry. The model demonstrates sucking of leading edge vortices...

[Phys. Rev. E 98, 033105] Published Wed Sep 05, 2018

### Dielectrically driven convection in spherical gap geometry

Author(s): Florian Zaussinger, Peter Haun, Matthias Neben, Torsten Seelig, Vadim Travnikov, Christoph Egbers, Harunori Yoshikawa, and Innocent Mutabazi

Thermal convection in the spherical gap geometry induced by dielectric heating is studied by means of an extended thermoelectric hydrodynamics model. Numerical simulations based on this model are validated on the ISS experiment GeoFlow.

[Phys. Rev. Fluids 3, 093501] Published Wed Sep 05, 2018

### Pairwise interactions in inertially driven one-dimensional microfluidic crystals

Author(s): Kaitlyn Hood and Marcus Roper

In microfluidic devices, inertia drives particles to focus on a streamline and form one-dimensional microfluidic crystals. Asymptotic theory for the pairwise particle interactions shows that particles assemble into stable equilibria, and the dynamics are analogous to the motion of a damped spring.

[Phys. Rev. Fluids 3, 094201] Published Wed Sep 05, 2018

### Geometrical focusing of surface waves

Author(s): Gerardo Ruiz Chavarria, Patrice Le Gal, and Michael Le Bars

In an experimental investigation, water surface waves are focused at the Huygens’ cusp of a parabolic wave maker. Small amplitude waves behave linearly and similarly to light waves, following the diffraction laws. Large amplitude nonlinear waves are distorted by a large scale flow and focus before the expected cusp.

[Phys. Rev. Fluids 3, 094803] Published Wed Sep 05, 2018