# Physical Review Fluids

### Role of Marangoni stress during breakup of surfactant-covered liquid threads: Reduced rates of thinning and microthread cascades

Author(s): Pritish M. Kamat, Brayden W. Wagoner, Sumeet S. Thete, and Osman A. Basaran

Simulations and experiments resolve a long-standing controversy that the gradient of surface tension—Marangoni stress—rather than surface tension lowering is responsible for decelerated thinning rates and microthread cascades during breakup of surfactant-covered threads.

[Phys. Rev. Fluids 3, 043602] Published Fri Apr 06, 2018

### Flapping instability of a liquid jet

Author(s): Antoine Delon, Alain Cartellier, and Jean-Philippe Matas

We evidence two regimes for the flapping instability of a liquid jet atomized by a gas stream: a first one where it is synchronized with an upstream shear instability, and a second one where frequency is independent of gas flow, simply controlled by the ratio of liquid velocity to liquid jet radius.

[Phys. Rev. Fluids 3, 043901] Published Fri Apr 06, 2018

### Particle dynamics and pattern formation in a rotating suspension of positively buoyant particles

Author(s): Sudarshan Konidena, Jonghoon Lee, K. Anki Reddy, and Anugrah Singh

Buoyant particle suspension in a horizontal rotating cylinder is known to exhibit axially oscillating particle bands in the centrifugal force dominant phase. Numerical simulations using Stokeslets as the particles were performed to investigate the behavior.

[Phys. Rev. Fluids 3, 044301] Published Fri Apr 06, 2018

### Impact of dissipation on the energy spectrum of experimental turbulence of gravity surface waves

Author(s): Antoine Campagne, Roumaissa Hassaini, Ivan Redor, Joël Sommeria, Thomas Valran, Samuel Viboud, and Nicolas Mordant

Experiments are performed in the Coriolis facility to investigate gravity surface wave turbulence. Results indicate that dissipation is responsible for the quantitative discrepancy between experimental and field measurement of the wave energy spectrum, which is systematically steeper in the lab.

[Phys. Rev. Fluids 3, 044801] Published Fri Apr 06, 2018

### Collective dissolution of microbubbles

Author(s): Sébastien Michelin, Etienne Guérin, and Eric Lauga

Microscopic bubble dissolution is driven by the diffusion of gas within the surrounding liquid. Asymptotic analysis is used to characterize collective shielding effects in bubble lattices, the resulting bubble lifetime and dissolution dynamics.

[Phys. Rev. Fluids 3, 043601] Published Thu Apr 05, 2018

### Eddy diffusivity of quasi-neutrally-buoyant inertial particles

Author(s): Marco Martins Afonso, Paolo Muratore-Ginanneschi, Sílvio M. A. Gama, and Andrea Mazzino

Inertial particles moving in a fluid flow are ubiquitous in nature. Despite their small size, they can actively influence Earth climate dynamics. A new perturbative strategy is proposed to obtain the sedimentation velocity and the effective diffusivity in the limit of neutrally buoyant particles.

[Phys. Rev. Fluids 3, 044501] Published Wed Apr 04, 2018

### Penetrative convection at high Rayleigh numbers

Author(s): Srikanth Toppaladoddi and John S. Wettlaufer

Penetrative convection is essential in controlling the dynamics of many geophysical and astrophysical systems. Here, we explore how a nonlinear vertical density profile influences the penetrative convection into a stable stratification.

[Phys. Rev. Fluids 3, 043501] Published Tue Apr 03, 2018

### Effect of texture randomization on the slip and interfacial robustness in turbulent flows over superhydrophobic surfaces

Author(s): Jongmin Seo and Ali Mani

Drag reduction and interfacial robustness of turbulent flows over superhydrophobic surfaces with randomly distributed textures are investigated using direct numerical simulations. Slip length, pressure fluctuations, and interface deformations are analyzed and compared against aligned textures.

[Phys. Rev. Fluids 3, 044601] Published Mon Apr 02, 2018

### Actuated rheology of magnetic micro-swimmers suspensions: Emergence of motor and brake states

Author(s): Benoit Vincenti, Carine Douarche, and Eric Clement

We develop a model of elliptical micro-swimmers with a magnetic dipole under shear flow in a dilute suspension subject to a constant magnetic field. We find at finite shear rates transitions to either a motor state in which energy can be extracted or a brake state with high resistance to shear.

[Phys. Rev. Fluids 3, 033302] Published Fri Mar 30, 2018

### Effect of a surface tension gradient on the slip flow along a superhydrophobic air-water interface

Author(s): Dong Song, Baowei Song, Haibao Hu, Xiaosong Du, Peng Du, Chang-Hwan Choi, and Jonathan P. Rothstein

The presence of a surface tension gradient is demonstrated at the air-water interface supported above a millimeter-sized discontinuous groove. It reduces the slip velocity and in some cases results in an interfacial velocity that is opposite to the main flow direction.

[Phys. Rev. Fluids 3, 033303] Published Fri Mar 30, 2018

### Structure of wall-bounded flows at transcritical conditions

Author(s): Peter C. Ma, Xiang I. A. Yang, and Matthias Ihme

Direct numerical simulations of channel flow at transcritical conditions with density change in the flow field are conducted. We find a regime with useful semi-local scaling as well as streamwise velocity and energy spectrum scaling which support the attached eddy model at transcritical conditions.

[Phys. Rev. Fluids 3, 034609] Published Fri Mar 30, 2018

### Buoyant miscible displacement flows in a nonuniform Hele-Shaw cell

Author(s): E. Walling, R. Mollaabbasi, and S. M. Taghavi

By modifying the geometry of a vertical Hele-Shaw cell—making it either converging or diverging—experimental and theoretical investigation shows that it is possible to control the stability of miscible buoyancy driven flows. This includes the promotion/inhibition of viscous fingering.

[Phys. Rev. Fluids 3, 034003] Published Thu Mar 29, 2018

### Unsteady characteristics of a slat-cove flow field

Author(s): Kyle A. Pascioni and Louis N. Cattafesta

The slat flow field of a multi-element airfoil is experimentally studied. Mean turbulence statistics and phase-locked data link shear layer structures to narrowband peaks in the surface pressure spectra. Most notably, a bulk cove oscillation related to shear layer flapping is found.

[Phys. Rev. Fluids 3, 034607] Published Thu Mar 29, 2018

### Dynamic domains of the Derviche Tourneur sodium experiment: Simulations of a spherical magnetized Couette flow

Author(s): E. J. Kaplan, H.-C. Nataf, and N. Schaeffer

A magnetized liquid sodium experiment and high-end numerical simulations are performed, both yielding similar magnetic signatures. Coherent flow structures are found to emerge from developed turbulence, some of which are related to linear instabilities of the mean flow.

[Phys. Rev. Fluids 3, 034608] Published Thu Mar 29, 2018