# Latest papers in fluid mechanics

### Flow speed has little impact on propulsive characteristics of oscillating foils

Physical Review Fluids - Tue, 01/30/2018 - 10:00

Author(s): T. Van Buren, D. Floryan, N. Wei, and A. J. Smits

Experiments show that swimming speed has little impact on the forces or wake produced by a fishlike propulsor. Both continuous and intermittent swimming styles are explored. The results indicate that there may be no need to mimic a free-swimming (self-propelled) condition in laboratory studies.

[Phys. Rev. Fluids 3, 013103] Published Tue Jan 30, 2018

### Competitive dynamics of two erosion patterns around a cylinder

Physical Review Fluids - Mon, 01/29/2018 - 10:00

Author(s): F. Lachaussée, Y. Bertho, C. Morize, A. Sauret, and P. Gondret

Two different patterns of erosion are observed in steady flow past a vertical cylinder emerging from a granular bed: a large hole at the base of the cylinder or two side-by-side elongated holes in the wake of the cylinder.

[Phys. Rev. Fluids 3, 012302(R)] Published Mon Jan 29, 2018

### Numerical evidence of logarithmic regions in channel flow at $\mathrm{R}{\mathrm{e}}_{τ}=8000$

Physical Review Fluids - Mon, 01/29/2018 - 10:00

Author(s): Yoshinobu Yamamoto and Yoshiyuki Tsuji

Direct numerical simulations of turbulent channel flows up to Reτ=8000 find logarithmic variations both in the mean velocity and streamwise turbulent variance, although these logarithmic regions do not agree with each other.

[Phys. Rev. Fluids 3, 012602(R)] Published Mon Jan 29, 2018

### Underwater oblique shock wave reflection

Physical Review Fluids - Mon, 01/29/2018 - 10:00

Author(s): Ritwik Ghoshal and Nilanjan Mitra

Domains of regular and irregular reflection for underwater oblique shock waves have been identified theoretically. We compare the Tait and Mie-Grüneisen equations of state in their ability to demonstrate physics of shock wave reflection and find implications for designing blast mitigation devices.

[Phys. Rev. Fluids 3, 013403] Published Mon Jan 29, 2018

### High-frequency forcing to mitigate unsteady separation from a bursting separation bubble

Physical Review Fluids - Mon, 01/29/2018 - 10:00

Author(s): Stuart I. Benton and Miguel R. Visbal

Very-low-amplitude, high-frequency forcing is used to manipulate the laminar separation bubble on a NACA 0012 airfoil pitching at a constant rate. Properly tuning the forcing frequency to track the changing Kelvin-Helmholtz instability results in significant delay of the onset of dynamic stall.

[Phys. Rev. Fluids 3, 013907] Published Mon Jan 29, 2018

### Self-propelled colloidal particle near a planar wall: A Brownian dynamics study

Physical Review Fluids - Mon, 01/29/2018 - 10:00

Author(s): Ali Mozaffari, Nima Sharifi-Mood, Joel Koplik, and Charles Maldarelli

The stability of the boundary-guided motion of a diffusiophoretically self-propelled locomotor along a planar wall to mechanical disturbances and Brownian forces is examined theoretically. The main goal is to understand the conditions under which this passively guided motion is stable.

[Phys. Rev. Fluids 3, 014104] Published Mon Jan 29, 2018

### Cohesion and agglomeration of wet powders

Physical Review Fluids - Mon, 01/29/2018 - 10:00

Author(s): Pascal S. Raux and Anne-Laure Biance

The cohesion of a wet grain assembly is encountered in many situations, such as in the fabrication of sandcastles, the preparation of couscous, crumbles, or other granulated systems. Two simple experiments on model liquid/bead mixtures are performed to understand the behavior of such systems.

[Phys. Rev. Fluids 3, 014301] Published Mon Jan 29, 2018

### Tracking coherent structures in massively-separated and turbulent flows

Physical Review Fluids - Mon, 01/29/2018 - 10:00

Author(s): Matthew Rockwood, Yangzi Huang, and Melissa Green

Coherent vortex structures are tracked in simulations of massively-separated and turbulent flows using Lagrangian saddles found as intersections of positive and negative finite-time Lyapunov exponent ridges. This allows vortices to be tracked objectively in time and space in a variety of flows.

[Phys. Rev. Fluids 3, 014702] Published Mon Jan 29, 2018

### Simulation and stability analysis of oblique shock-wave/boundary-layer interactions at Mach 5.92

Physical Review Fluids - Fri, 01/26/2018 - 10:00

Author(s): Nathaniel Hildebrand, Anubhav Dwivedi, Joseph W. Nichols, Mihailo R. Jovanović, and Graham V. Candler

Above a critical angle, an oblique shock impinging on a Mach 5.92 boundary layer causes the resulting separated flow to become unstable. Direct numerical simulation and global stability analysis reveal the physical mechanism that drives this three-dimensional instability.

[Phys. Rev. Fluids 3, 013906] Published Fri Jan 26, 2018

### Steady displacement of long gas bubbles in channels and tubes filled by a Bingham fluid

Physical Review Fluids - Thu, 01/25/2018 - 10:00

Author(s): Parsa Zamankhan, Shuichi Takayama, and James B. Grotberg

Creeping motion of a long bubble in 2D planar channels and axisymmetric tubes filled by a Bingham fluid is studied numerically. Bingham and capillary number effects on bubble shape, flow field, yield surfaces, and the wall shear stress profile are discussed and applied to human respiratory airways.

[Phys. Rev. Fluids 3, 013302] Published Thu Jan 25, 2018

### Dynamics of jets produced by bursting bubbles

Physical Review Fluids - Thu, 01/25/2018 - 10:00

Author(s): Luc Deike, Elisabeth Ghabache, Gérard Liger-Belair, Arup K. Das, Stéphane Zaleski, Stéphane Popinet, and Thomas Séon

Bubble bursting is a ubiquitous phenomenon, impacting the climate by producing sea spray aerosols above the ocean, while also controlling the fineness of the effervescence of sparkling wine. Numerical and laboratory experiments are used to rationalize the velocity of jets formed by bubble bursting.

[Phys. Rev. Fluids 3, 013603] Published Thu Jan 25, 2018

### Bursting and critical layer frequencies in minimal turbulent dynamics and connections to exact coherent states

Physical Review Fluids - Thu, 01/25/2018 - 10:00

Author(s): Jae Sung Park, Ashwin Shekar, and Michael D. Graham

A new investigation identifies frequencies in minimal channel flow relevant to critical layer dynamics displayed by exact coherent states and shows their predominance over bursting frequencies away from the wall. It is also shown that strong bursts are related to the instability of coherent states.

[Phys. Rev. Fluids 3, 014611] Published Thu Jan 25, 2018

### Locomotion of a bioinspired flyer powered by one pair of pitching foils

Physical Review Fluids - Wed, 01/24/2018 - 10:00

Author(s): Xiang Zhang, Guowei He, Shizhao Wang, and Xing Zhang

In a numerical investigation of the flight dynamics and aerodynamics of a two-dimensional jellyfish-like ornithopter, three locomotion states are identified with the variation of control parameters. The responses of the ornithopter to physical and numerical perturbations are also examined.

[Phys. Rev. Fluids 3, 013102] Published Wed Jan 24, 2018

### Generation of anisotropy in turbulent flows subjected to rapid distortion

Physical Review E - Tue, 01/23/2018 - 10:00

Author(s): Timothy T. Clark, Susan Kurien, and Robert Rubinstein

A computational tool for the anisotropic time-evolution of the spectral velocity correlation tensor is presented. We operate in the linear, rapid distortion limit of the mean-field-coupled equations. Each term of the equations is written in the form of an expansion to arbitrary order in the basis of...

[Phys. Rev. E 97, 013112] Published Tue Jan 23, 2018

### Ultrasonic measurements of the bulk flow field in foams

Physical Review E - Tue, 01/23/2018 - 10:00

Author(s): Richard Nauber, Lars Büttner, Kerstin Eckert, Jochen Fröhlich, Jürgen Czarske, and Sascha Heitkam

The flow field of moving foams is relevant for basic research and for the optimization of industrial processes such as froth flotation. However, no adequate measurement technique exists for the local velocity distribution inside the foam bulk. We have investigated the ultrasound Doppler velocimetry ...

[Phys. Rev. E 97, 013113] Published Tue Jan 23, 2018

### Key vortical structure causing laminar-turbulent transition in a boundary layer disturbed by a short-duration jet

Physical Review Fluids - Tue, 01/23/2018 - 10:00

Author(s): Joe Yoshikawa, Yu Nishio, Seiichiro Izawa, and Yu Fukunishi

Numerical simulations show that while a short-duration jet ejected into a Blasius boundary layer directly generates hairpin vortices with narrow legs, they themselves do not lead to turbulent transition. Generation, by vortex reconnection, of a hairpin vortex with widespread legs is key in the transition to turbulence.

[Phys. Rev. Fluids 3, 013904] Published Tue Jan 23, 2018

### Experimental investigation of the wake behind a rotating sphere

Physical Review Fluids - Tue, 01/23/2018 - 10:00

Author(s): M. Skarysz, J. Rokicki, S. Goujon-Durand, and J. E. Wesfreid

Evolution of the flow regimes in the wake behind a streamwise rotating sphere was experimentally studied focusing on the Reynolds number versus rotation rate parameter plane. Four different regimes were observed in the wake and were investigated using modal decomposition and frequency analysis.

[Phys. Rev. Fluids 3, 013905] Published Tue Jan 23, 2018

### Effective viscosity of a random mixture of fluids

Physical Review Fluids - Tue, 01/23/2018 - 10:00

Author(s): Benoît Noetinger, Laurène Hume, Robin Chatelin, and Philippe Poncet

The effective viscosity of mixtures is of interest for many applications. A model is proposed that relates this effective viscosity to minimal information regarding the microstructure of the mixture. This model is validated by means of direct numerical simulations of flows of these mixtures.

[Phys. Rev. Fluids 3, 014103] Published Tue Jan 23, 2018

### Absolute and convective instabilities of a film flow down a vertical fiber subjected to a radial electric field

Physical Review E - Mon, 01/22/2018 - 10:00

Author(s): Rong Liu, Xue Chen, and Zijing Ding

We consider the motion of a gravity-driven flow down a vertical fiber subjected to a radial electric field. This flow exhibits rich dynamics including the formation of droplets, or beads, driven by a Rayleigh-Plateau mechanism modified by the presence of gravity as well as the Maxwell stress at the ...

[Phys. Rev. E 97, 013109] Published Mon Jan 22, 2018

### Three-dimensional instabilities for the flow around a heaving foil

Physical Review E - Mon, 01/22/2018 - 10:00

Author(s): Liping Sun, Jian Deng, and Xueming Shao

This paper investigates the three-dimensional instabilities of the flow past a periodically heaving airfoil. By comparison with a pitching foil [Deng et al., Phys. Rev. E 92, 063013 (2015)], here we present distinctive characteristics for the heaving foil, particulary regarding its Floquet modes. B...

[Phys. Rev. E 97, 013110] Published Mon Jan 22, 2018