# Latest papers in fluid mechanics

### Electrically switchable surface waves and bouncing droplets excited on a liquid metal bath

Physical Review Fluids - Thu, 12/27/2018 - 10:00

Author(s): Xi Zhao, Jianbo Tang, and Jing Liu

We conduct experiments on Faraday wave patterns and bouncing droplets with a high-density/surface tension liquid metal fluid. Bouncing liquid metal droplets can be sustained on the wavy surface, self-assembling into various lattice structures which can be switched with an electric field.

[Phys. Rev. Fluids 3, 124804] Published Thu Dec 27, 2018

### Nuclear-magnetic-resonance relaxation rates for fluid confined to closed, channel, or planar pores

Physical Review E - Wed, 12/26/2018 - 10:00

Author(s): D. A. Faux and P. J. McDonald

Fast-field-cycling nuclear-magnetic-resonance (FFC NMR) experimentation measures the spin-lattice relaxation rate T1−1=R1 as a function of NMR frequency f. It is a proven technique for probing the nanoscale dynamics of H1 spins over multiple timescales. In many porous systems, fluid is confined to q...

[Phys. Rev. E 98, 063110] Published Wed Dec 26, 2018

### Response of monoflagellate pullers to a shearing flow: A simulation study of microswimmer guidance

Physical Review E - Wed, 12/26/2018 - 10:00

Author(s): Benjamin J. Walker, Kenta Ishimoto, Richard J. Wheeler, and Eamonn A. Gaffney

Microscale swimming may be intuited to be dominated by background flows, sweeping away any untethered bodies with the prevalent flow direction. However, it has been observed that many microswimmers utilize ambient flows as guidance cues, in some cases resulting in net motion upstream, contrary to th...

[Phys. Rev. E 98, 063111] Published Wed Dec 26, 2018

### Dynamic behavior of two neighboring nanobubbles induced by various gas-liquid-solid interactions

Physical Review Fluids - Wed, 12/26/2018 - 10:00

Author(s): Chenliang Li, Shi-Ping Wang, A-Man Zhang, and Yunlong Liu

The dynamic behavior of two neighboring nanobubbles is investigated for various gas-liquid-solid interactions. Two neighboring unsaturated surface nanobubbles can form a gas-rich layer on a solid surface, as long as the interaction between the solid and the gas is sufficiently strong.

[Phys. Rev. Fluids 3, 123604] Published Wed Dec 26, 2018

### When giant vesicles mimic red blood cell dynamics: Swinging of two-phase vesicles in shear flow

Physical Review Fluids - Wed, 12/26/2018 - 10:00

Author(s): Simon Tusch, Etienne Loiseau, Al-Hair Al-Halifa, Kamel Khelloufi, Emmanuèle Helfer, and Annie Viallat

Side view of the full rotation of a two-phase giant vesicle doing a tanktreading motion under a shear rate of 5 s−1. The major axis of the vesicle oscillates showing the vesicle swings similarly to a red blood cell.

[Phys. Rev. Fluids 3, 123605] Published Wed Dec 26, 2018

### Transient dynamics in drop impact on a superheated surface

Physical Review Fluids - Wed, 12/26/2018 - 10:00

Author(s): Sang-Hyeon Lee, Sang Jun Lee, Ji San Lee, Kamel Fezzaa, and Jung Ho Je

Transient dynamics of a Leidenfrost vapor layer in drop impact is studied using x-ray imaging. It is shown that a vapor disk first forms, growing in thickness, following Fourier’s law. At a certain thickness, ripples generate near the edge and propagate to the center by capillary waves, improving evaporation.

[Phys. Rev. Fluids 3, 124308] Published Wed Dec 26, 2018

### Two-point spectral model for variable-density homogeneous turbulence

Physical Review Fluids - Wed, 12/26/2018 - 10:00

Author(s): Nairita Pal, Susan Kurien, Timothy Clark, Denis Aslangil, and Daniel Livescu

We study buoyancy-driven variable-density homogeneous turbulence with a two-point spectral closure model and assess model accuracy relative to direct numerical simulations using standard metrics. The model captures statistics of spectral distributions and global means at low and high Atwood numbers.

[Phys. Rev. Fluids 3, 124608] Published Wed Dec 26, 2018

### Turbulence dissipation and the role of coherent structures in the near wake of a square prism

Physical Review Fluids - Wed, 12/26/2018 - 10:00

Author(s): F. Alves Portela, G. Papadakis, and J. C. Vassilicos

An analysis shows that on the centerline of a planar wake, turbulent dissipation obeys the nonequilibrium scaling, provided that the large-scale contribution of the coherent motions is disregarded. In that same region, the dissipations associated with coherent and incoherent motions vary together.

[Phys. Rev. Fluids 3, 124609] Published Wed Dec 26, 2018

### Self-sustaining process in Taylor-Couette flow

Physical Review Fluids - Fri, 12/21/2018 - 10:00

Author(s): Tommy Dessup, Laurette S. Tuckerman, José Eduardo Wesfreid, Dwight Barkley, and Ashley P. Willis

The Self-Sustaining Process (SSP) proposed in the 1990s by Waleffe is a widely-accepted building block of transition to turbulence in shear flows such as plane Couette flow. Although inspired by the rolls and waves of Taylor-Couette flow, the SSP had not been investigated for this flow until now.

[Phys. Rev. Fluids 3, 123902] Published Fri Dec 21, 2018

### Drying and percolation in correlated porous media

Physical Review Fluids - Fri, 12/21/2018 - 10:00

Author(s): Soumyajyoti Biswas, Paolo Fantinel, Oshri Borgman, Ran Holtzman, and Lucas Goehring

We show that local structure, in an otherwise random medium, can change the nature of invasion percolation phenomena, including multiphase fluid flows. By combining microfluidic drying experiments with simple models we explain how local correlations in pore sizes lead to more extreme dynamics.

[Phys. Rev. Fluids 3, 124307] Published Fri Dec 21, 2018

### Large-scale intermittency and rare events boosted at dimensional crossover in anisotropic turbulence

Physical Review Fluids - Fri, 12/21/2018 - 10:00

Author(s): Keiko Takahashi, Koji Goto, Ryo Onishi, and Masatoshi Imada

Our numerical simulation finds that flattened three dimensional turbulence generates strong intermittency at the crossover scale between two and three dimensions. This provides a mechanism for disaster causing extreme events below the synoptic scale in the atmosphere such as tropical cyclones.

[Phys. Rev. Fluids 3, 124607] Published Fri Dec 21, 2018

### Fundamental solution of unsteady Stokes equations and force on an oscillating sphere near a wall

Physical Review E - Thu, 12/20/2018 - 10:00

Author(s): Itzhak Fouxon and Alexander Leshansky

We derive the Green's function of unsteady Stokes equations near a plane boundary with no-slip boundary conditions. This provides flow due to an oscillating point force acting on fluid bounded by a wall. Our derivation is different from previous theories and resolves the apparent discrepancies of th...

[Phys. Rev. E 98, 063108] Published Thu Dec 20, 2018

### Oscillating convection and reversal flow in connected cavities

Physical Review E - Thu, 12/20/2018 - 10:00

Author(s): Yue Xiao, Jianjun Tao, Xue Ma, and Xiangming Xiong

The two-dimensional natural convection of air in upper and a lower square cavities connected with a vertical vent is studied numerically and theoretically. At high Rayleigh numbers (Ra), it is revealed by the dynamic-mode-decomposition method that the plumes yield to a new sway mode, where the plume...

[Phys. Rev. E 98, 063109] Published Thu Dec 20, 2018

### Effects of disturbance on detonation initiation in ${\mathrm{H}}_{2}/{\mathrm{O}}_{2}/{\mathrm{N}}_{2}$ mixture

Physical Review Fluids - Thu, 12/20/2018 - 10:00

Author(s): Yuan Wang, Wang Han, Ralf Deiterding, and Zheng Chen

Two-dimensional simulations are conducted to assess the effects of disturbance on detonation initiation. A disturbance can induce a complex shock wave interaction which induces a local explosion. Disturbances can thus be used to promote detonation initiation.

[Phys. Rev. Fluids 3, 123201] Published Thu Dec 20, 2018

### Multifractality of fine bubbles in turbulence due to lift

Physical Review Fluids - Thu, 12/20/2018 - 10:00

Author(s): Itzhak Fouxon, Gihun Shim, Seulgi Lee, and Changhoon Lee

An equation of motion is derived for isolated bubbles in turbulence, an equation similar to that governing phytoplankton. Simulations show the clustering of bubbles in vertical columns.

[Phys. Rev. Fluids 3, 124305] Published Thu Dec 20, 2018

### Morphodynamics of a sediment bed in a fluid-filled cylinder during spin-down: An experimental study

Physical Review Fluids - Thu, 12/20/2018 - 10:00

Author(s): A. S. González-Vera, M. Duran-Matute, and G. J. F. van Heijst

Laboratory experiments on the evolution of a sediment bed under a spin-down flow show the emergence of diverse types of patterns. The net radially inward sediment transport is quantified and explained through an analytical derivation of the total radial force exerted on the bed.

[Phys. Rev. Fluids 3, 124306] Published Thu Dec 20, 2018

### Magnetic structure, dipole reversals, and $1/f$ noise in resistive MHD spherical dynamos

Physical Review Fluids - Wed, 12/19/2018 - 10:00

Author(s): M. Fontana, P. D. Mininni, and P. Dmitruk

A parametric study of dynamos in a rotating sphere shows a rich space of dynamic solutions, with stationary, aperiodic, and small-scale dynamo regimes controlled by Ekman and Reynolds numbers. Magnetic reversals are observed, displaying 1/f noise and statistics reminiscent of geodynamo observations.

[Phys. Rev. Fluids 3, 123702] Published Wed Dec 19, 2018

### Film coating on a small sphere crossing an oil-water interface

Physical Review Fluids - Wed, 12/19/2018 - 10:00

Author(s): Haosheng Chen (陈皓生), Qinda Xu (徐勤达), Shuaishuai Liang (梁帅帅), and Jiang Li (李疆)

Experiments show that small spheres can pass through an oil-water interface and be coated with a predictable oil film when the Bond number is between 1.5 and 7.5. The film thickness is approximately proportional to the Bond number, which makes it a convenient method to coat particles with a designed film thickness.

[Phys. Rev. Fluids 3, 124003] Published Wed Dec 19, 2018

### Influence of particle dynamics on the instability for pattern formation in shallow pulsed beds

Physical Review Fluids - Wed, 12/19/2018 - 10:00

Author(s): Lilian de Martín

Standing wave patterns can occur both in vibrated granular layers and pulsed fluidized beds. Although the different type of excitation results in a different definition of the driving parameters and instability curve, a theoretical study shows that the instability criterion in both systems is similar.

[Phys. Rev. Fluids 3, 124304] Published Wed Dec 19, 2018

### Drag on pairs of square section obstacles in free-surface flows

Physical Review Fluids - Tue, 12/18/2018 - 10:00

Author(s): Francis H. Robertson and Gregory F. Lane-Serff

The effect of one obstacle on the drag on a second obstacle is measured for square obstacles in subcritical open channel flow. The lowest drag occurs when one obstacle is shielded directly behind another, and the largest drag occurs on a slightly upstream obstacle in near side-by-side arrangements.

[Phys. Rev. Fluids 3, 123802] Published Tue Dec 18, 2018