# Latest papers in fluid mechanics

### Acoustic radiation force acting on a heavy particle in a standing wave can be dominated by the acoustic microstreaming

Author(s): Thierry Baasch, Alen Pavlic, and Jürg Dual

We numerically investigate the contribution of the microstreaming to the acoustic radiation force acting on a small elastic spherical particle placed into an ultrasonic standing wave. When an acoustic wave scatters on a particle the acoustic radiation force and the microstreaming appear as nonlinear...

[Phys. Rev. E 100, 061102(R)] Published Mon Dec 23, 2019

### Flow-induced buckling dynamics of sperm flagella

Author(s): Manish Kumar, Derek M. Walkama, Jeffrey S. Guasto, and Arezoo M. Ardekani

The swimming sperm of many external fertilizing marine organisms face complex fluid flows during their search for egg cells. Aided by chemotaxis, relatively weak flows are known to enhance sperm-egg fertilization rates through hydrodynamic guidance. However, strong flows have the potential to mechan...

[Phys. Rev. E 100, 063107] Published Fri Dec 20, 2019

### Clustering of floating tracers in weakly divergent velocity fields

Author(s): Konstantin V. Koshel, Dmitry V. Stepanov, Eugene A. Ryzhov, Pavel Berloff, and V. I. Klyatskin

This work deals with buoyant tracers floating at the ocean surface, where the geostrophic velocity component is two dimensional and rotational (nondivergent) and the ageostrophic component can contain rotational and potential (divergent) contributions that are comparable in size. We consider a rando...

[Phys. Rev. E 100, 063108] Published Fri Dec 20, 2019

### Collapse of a liquid-saturated granular column on a horizontal plane

Author(s): Alexis Bougouin, Laurent Lacaze, and Thomas Bonometti

Using laboratory experiments, the collapse of a liquid-saturated granular column in air on a horizontal plane is analyzed in light of the “column” Bond number, the grain diameter to capillary length ratio, the initial aspect ratio, the Stokes number, and the initial volume fraction.

[Phys. Rev. Fluids 4, 124306] Published Fri Dec 20, 2019

### Bifurcation phenomena on the inertial focusing of a neutrally buoyant spherical particle suspended in square duct flows

Author(s): Hiroshi Yamashita, Tomoaki Itano, and Masako Sugihara-Seki

Several patterns of inertial particle focusing over a square cross section are experimentally observed for suspension flows through a square duct. A numerical study describes transitions between the focusing patterns in terms of the bifurcation of particle equilibrium positions.

[Phys. Rev. Fluids 4, 124307] Published Fri Dec 20, 2019

### Solution for the statistical moments of scalar turbulence

Author(s): Matteo B. Bertagni, Massimo Marro, Pietro Salizzoni, and Carlo Camporeale

The transport equation for the statistical moments of a passive scalar dispersed in a turbulent flow is solved. The analytical solution for the passive scalar variance is shown to fit wind tunnel data from a neutral turbulent boundary layer.

[Phys. Rev. Fluids 4, 124701] Published Fri Dec 20, 2019

### Active pitching of short splitters past a cylinder: Drag increase and wake

Author(s): Yaqing Jin, Shyuan Cheng, and Leonardo P. Chamorro

The flow and drag induced by active pitching of plates in the wake of a cylinder of diameter d were experimentally studied for various plate lengths L as well as pitching frequencies fp and amplitudes A0 at Reynolds number Re=1.6×104. Planar particle image velocimetry and a load cell were used to ch...

[Phys. Rev. E 100, 063106] Published Thu Dec 19, 2019

### Convection driven by internal heat sources and sinks: Heat transport beyond the mixing-length or “ultimate” scaling regime

Author(s): Benjamin Miquel, Simon Lepot, Vincent Bouillaut, and Basile Gallet

An asymptotic solution for convective flows driven by internal heating and cooling is derived. The solution is stable and realized by 2D direct numerical simulations at very high Rayleigh numbers. Even more surprisingly, it corresponds to heat transport enhancement beyond the mixing-length scaling regime.

[Phys. Rev. Fluids 4, 121501(R)] Published Thu Dec 19, 2019

### Asymptotic regimes in elastohydrodynamic and stochastic leveling on a viscous film

Author(s): Christian Pedersen, John F. Niven, Thomas Salez, Kari Dalnoki-Veress, and Andreas Carlson

The relaxation process of an elastic sheet supported by a thin viscous film is studied. Asymptotic leveling regimes are identified as a function of the supporting layer thickness when the dynamics is driven either by elastic bending or by thermal fluctuations.

[Phys. Rev. Fluids 4, 124003] Published Thu Dec 19, 2019

### Breakup of asymmetric liquid ligaments

Author(s): Carole Planchette, Francesco Marangon, Wen-Kai Hsiao, and Günter Brenn

Asymmetric liquid ligaments typically produced by inkjet printing may recoil or a drop may pinch off. Scaling laws are provided for these two competing processes, and it is shown that long and short ligaments experience different pinch-off regimes.

[Phys. Rev. Fluids 4, 124004] Published Thu Dec 19, 2019

### Short-term oscillation and falling dynamics for a water drop dripping in quiescent air

Author(s): B. Zhang, Y. Ling, P.-H. Tsai, A.-B. Wang, S. Popinet, and S. Zaleski

The short-term falling dynamics of a dripping water drop is studied by simulation and experiment. The pinching dynamics introduces a nonlinear multimode oscillation. A complex transient flow around the drop is induced by the interaction between the falling motion and the shape oscillation.

[Phys. Rev. Fluids 4, 123604] Published Wed Dec 18, 2019

### Electrohydrodynamic generation of atmospheric turbulence

Author(s): Yuan Yao and Jesse Capecelatro

The role of electrohydrodynamics on the generation of atmospheric turbulence is studied theoretically and numerically. A nonlinear feedback loop is identified whereby charged aerosols self-induce an electric field, resulting in a body force on the ionized air, augmenting the atmospheric turbulence.

[Phys. Rev. Fluids 4, 123701] Published Wed Dec 18, 2019

### Gas-assisted discharge flow of granular media from silos

Author(s): Y. Zhou, P.-Y. Lagrée, S. Popinet, P. Ruyer, and P. Aussillous

Experiments and a two-phase continuum model are used to study how gas flow enhances silo discharge. A modified Hagen-Beverloo law is proposed, taking into account the gas flow rate, the particle size, and the silo and orifice geometry.

[Phys. Rev. Fluids 4, 124305] Published Wed Dec 18, 2019

### Phase-space dynamics of near-wall streaks in wall-bounded turbulence with spanwise oscillation

This work presents systematical investigations on the skin-friction drag reduction (DR) of turbulent channel flow subjected to spanwise wall oscillation using direct numerical simulation. Altogether 12 different oscillatory cases have been studied with a reference at Reτ = 200, varying the controlling parameters characterized by maximum wall velocity Wm+ and oscillation period T+. Some of the previously established facts have been reproduced by our analysis with a new focus on the phase-space dynamics of the near-wall streaks, on the basis of statistical data over entire oscillation periods and over phasewise variations. It is revealed that streamwise vortices are generated in the vicinity of oscillation walls, disrupting the formation of near-wall low-speed streaks. Although the overall turbulence is weakened, the Stokes layer is thicker within wall acceleration phases for larger Wm+, which causes the turbulence intensity to increase in the upper viscous sublayer. In addition, regarding the effect of T+, a long oscillation period promotes the formation of energetic near-wall structures, while for short T+, the streak-generation time scale preferentially restricts the growth of spanwise streaks. From a new vorticity-transport perspective of the Reynolds shear stress, our results further indicate that high drag-reducing phenomena are connected to the near-wall sweep events, and the shear stress variation is principally driven by the distortion of the spanwise transport of wall-normal vorticity, i.e., vortex tilting/stretching. The DR process is seen to be linked to the increase in enstrophy and turbulence-energy dissipation in the near-wall region.

### Application of the stochastic closure theory to the Townsend-Perry constants

Author(s): John Kaminsky, Joe Klewicki, and Björn Birnir

We compare the stochastic closure theory (SCT) to the Townsend-Perry constants as estimated from measurements in the Flow Physic Facility (FPF) at the University of New Hampshire. First, we explain the derivation of the Townsend-Perry constants, which were originally formulated by Meneveau and Marus...

[Phys. Rev. E 100, 061101(R)] Published Mon Dec 16, 2019

### Elastoplastic behavior of yield stress fluids

Author(s): E. N’Gouamba, J. Goyon, and P. Coussot

Experiments show that the solid-liquid transition of yield stress fluids (emulsions, gels, foams, suspensions, etc.) is associated with the breakage (collapse) of a basic elastic network for a critical deformation, while progressively larger additional elastoplastic deformations take place in the system up to yielding.

[Phys. Rev. Fluids 4, 123301] Published Mon Dec 16, 2019

### On response spectra and Kramers-Kronig relations in superposition rheometry

In a recent paper, we derived expressions for determining the rate-dependent response spectra directly from parallel superposition rheometry data for the case of a certain Lodge-type integral constitutive model. It was shown that, within the confines of linear Yamamoto perturbation theory, the corresponding parallel superposition moduli satisfy the classical Kramers-Kronig relations. Special bases were presented to convert parallel superposition moduli to orthogonal superposition moduli. In the current paper, we obtain similar results for the integral models of Wagner I and, more generally, K-BKZ. These results facilitate the physical interpretation of parallel superposition moduli and direct model-based comparison of parallel and orthogonal superposition moduli in the study of weak nonlinear response.

### Jet direction in bubble collapse within rectangular and triangular channels

Author(s): Lebo Molefe and Ivo R. Peters

A vapor bubble collapsing near a solid boundary in a liquid produces a liquid jet that points toward the boundary. The direction of this jet has been studied for boundaries such as flat planes and parallel walls enclosing a channel. Extending these investigations to enclosed polygonal boundaries, we...

[Phys. Rev. E 100, 063105] Published Fri Dec 13, 2019

### Integral model for multiple forced plumes arranged around a circle in a linearly stratified environment

Author(s): Zhiguo He and Yingzhong Lou

An integral model is developed to predict the mixing of multiple forced plumes evenly spaced around a circle in a stratified environment, e.g., buoyant plumes in nature. The model reasonably captures the significant plume boundary distortion caused by plume interactions at the touching height.

[Phys. Rev. Fluids 4, 123501] Published Fri Dec 13, 2019

### Self-organized dip-coating patterns of simple, partially wetting, nonvolatile liquids

Author(s): Walter Tewes, Markus Wilczek, Svetlana V. Gurevich, and Uwe Thiele

Using analytical and numerical methods we examine a solid substrate withdrawn from a liquid bath. After withdrawal the substrate may be macroscopically dry or coated homogeneously by a liquid film. We show that a regular liquid ridge pattern oriented parallel to the meniscus can also be deposited.

[Phys. Rev. Fluids 4, 123903] Published Fri Dec 13, 2019