# Latest papers in fluid mechanics

### Evolution of passive scalar statistics in a spatially developing turbulence

Author(s): I. Paul, G. Papadakis, and J. C. Vassilicos

Passive scalar fine-scale structure is studied numerically for heated grid-element scalar turbulence. Scalar variance decays earlier in space than turbulent kinetic energy (both with dissipation). A −5/3 slope in the scalar-variance spectrum is found beyond the Kolmogorov-Obukhov-Corrsin theory.

[Phys. Rev. Fluids 3, 014612] Published Wed Jan 31, 2018

### Publisher's Note: Deflection and trapping of a counter-rotating vortex pair by a flat plate [Phys. Rev. Fluids <b>2</b>, 124702 (2017)]

Author(s): Monika Nitsche

[Phys. Rev. Fluids 3, 019902] Published Wed Jan 31, 2018

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

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

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 $\mathrm{R}{\mathrm{e}}_{τ}=8000$

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

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

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

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

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

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