This study investigates the focusing of inertial waves (IW) generated by an axisymmetric torus oscillating in a rotating fluid. A full range of vertical kinetic energy propagation angles at the focal point was explored using direct numerical simulations (DNS). A systematic comparison was made between linear DNS and nonlinear DNS. It was found that there is an optimal angle that maximizes energy transfer from the torus to the focal zone. In addition, triadic IW resonances were identified as a source of turbulence and a large central vertical vortex was also identified in agreement with the theory of Davidson et al. (2006).

We present an open-source Direct Numerical Simulation framework to analyze surfactant-laden flows. With adaptive mesh refinement and parallelization, this tool enables researchers to explore the effects of surfactants on interfacial flows, particularly their impact on rising bubbles. The simulations show that surfactants slow down bubbles and alter their trajectory. Such numerical frameworks on the solutal Marangoni effect are crucial for understanding and predicting the behavior of multiphase flows in natural and industrial processes.

A universal energy cascade is studied for incompressible ferrofluid turbulence by means of exact relations. Under weak external magnetic field, kinetic and total energy cascades occur at similar rates. Upon increasing the strength of the external magnetic field, the total energy cascade becomes nonstationary and occurs at a rate different from that of the kinetic energy cascade. However, the scale independent nature of the cascade remains universal.

Through numerical simulations we reveal the three phase flow as a newtonian droplet comes in contact with an immiscible viscoelastic liquid film. The droplet dynamics becomes insensitive to the film height when the viscoelastic effects dominate. A viscoelastic ridge forms at the moving contact line, which evolves with a power-law dependence on time.

This study uses deep reinforcement learning to design airfoil pitch control for minimizing lift variations in disturbed flows. Tested in both classical unsteady and nonlinear viscous flow environments, the reinforcement learning controller, enhanced with wake information from pressure sensors and memory of past observations, matches or exceeds the performance of traditional linear controllers. The findings highlight the potential of reinforcement learning for improved aerodynamic control during random disturbances.

Only under certain conditions does a drop falling onto a bath entrap an air bubble. We propose a phenomenological law that describes these bubbling conditions in terms of Froude, Weber, and capillary numbers.

Modulational instability is the major energy transfer mechanism between ocean surface waves in deep water. In this work we explore the effects of nonuniform damping, such as that encountered by waves propagating through sea ice, on this important instability. We relax common assumptions about narrow spectral width but are nevertheless able to capture the dynamics of the unstable triad of waves using dynamical systems techniques. We elucidate the differences between uniform and nonuniform damping and explore the consequences for subsequent spectral broadening.

Cavitation near the critical point is unusual because the compressibility becomes very high and the density difference between liquid and vapor becomes small and vanishes completely in the single phase supercritical region. We have investigated laser-induced cavitation in this unusual regime with high speed video at up to 5 million frames per second using liquid helium as the working fluid. Our theoretical analysis shows that the pressure in the liquid outside a bubble can be much lower than the ambient pressure. Near the critical point, the low pressure liquid becomes unstable and generates a cloud of microbubbles, which is consistent with predictions of nucleation theory near the spinodal.

The Rayleigh-Plateau instability occurs when a liquid film flows down a cylindrical surface. Using long-wave theory and stability analysis, we show that this instability can be modulated by coating the cylindrical surface with a thin layer of soft solids. In particular, we find that the elasticity of the soft layer can cause the film flow from being absolutely to convectively unstable. Our findings are also verified by transient numerical solutions of the full asymptotic model.

To find a blow-up solution to the Euler equations in an infinite domain is related to the zero viscosity limit of the Clay Institute’s sixth Millennium Problem. Evidence of a point-like, self-similar, blow-up solution occurring in an axisymmetric flow with infinite domain is provided by solving a nonlinear eigenvalue problem for a self-similar velocity with an unknown exponent. An angular expansion is used to map the problem into an infinite hierarchy of ODEs, which shows a convergent scenario of solutions for different truncations. This approach suggests an exponent of approximately 2. This solution contrasts with the previously found annular blow-up at a cylindrical domain boundary, which exhibited an exponent of 2.91.

Dense granular mixtures consisting of particles of different sizes tend to segregate based on size during shear flow, yet predicting the evolution of the composition of a granular mixture in general geometries remains a challenge. This paper systematically studies a key aspect of the three-dimensional nature of segregation and diffusion in dense, bidisperse granular mixtures: segregation and diffusion acting along the direction perpendicular to the plane of shearing, referred to as the anti-plane mode. We utilize discrete-element method simulations to inform, calibrate, and test constitutive equations for the segregation and diffusion fluxes in their anti-plane modes.

In this work, the results of a linear stability analysis of air-water stratified flows in horizontal circular pipes are presented. The computed stability boundaries are found to compare well with available experimental data. The stability analysis considered three-dimensional infinitesimal perturbations of all possible wavelengths and took into account deformations of the air-water interface. Comparing stability boundaries obtained in pipe, square duct, and two-plate geometries, it is shown that there are cases where the simplified geometry of two parallel plates can be useful to model the stability boundary in a realistic geometry reasonably well.

To study the evolution of large-scale helical structures in natural and engineering flows, we investigate the dual-channel characteristics of large- scale helicity transfer in compressible turbulent flows theoretically and numerically. Theoretical analysis and well-resolved direct numerical simulations indicate an alternative route to sustain the large-scale helical structures, through the cross-scale interaction at inertial scales and inverse dissipation at small scales under the expansion conditions.

In fluids with broken parity and time-reversal symmetry, odd viscosity introduces the possibility of unique behaviors such as lift force on an obstacle in a symmetric geometry. As incompressible odd viscous fluids are known to not show lift on cylinders under no-slip boundary conditions, this study examines the effect of a finite slip length. While it follows from the Lorentz reciprocal theorem that lift does not arise at first order in slip length, we find that lift does arise at second order upon solving for the fluid profile explicitly. Extending to Oseen flow, we derive a fluid profile that offers new insights into lift force on a cylinder at low Reynolds numbers.

Dynamic mixed scale-similarity/Smagorinsky type models (DMM) are promising as they typically have a high $a$ $priori$ correlation with subgrid stresses, and provide sufficient subgrid dissipation to be robust for practical applications. However, past DMMs require two or more levels of test filtering, making them unattractive for production codes. We propose an efficient DMM with a single level of test filtering, and through $a$ $posteriori$ LES tests of turbulent channel flow and wall-modeled LES of turbulent smooth-body separation (see figure, for a Gaussian bump), demonstrate their robustness and improved accuracy with under 5% additional cost compared to the standard Dynamic Smagorinsky Model.

The rebound of liquid droplets falling on a hot substrate, known as the Leidenfrost phenomenon, is a well-documented and widely studied topic. However, research on the rebound of droplets on cold surfaces, particularly regarding the inverse Leidenfrost phenomenon, remains relatively limited. In this paper, we experimentally investigate the rebound dynamics of droplets on dry ice surfaces, explore the influencing factors of the inverse Leidenfrost phenomenon, and develop a theoretical model to predict its occurrence.

Turbulence is by definition an out-of-equilibrium phenomenon, with energy flowing continuously from the large, input scales, to the small, dissipative ones. Temporal fluctuations in this energy flux produce corrections to the Kolmogorov energy spectrum which can be predicted using a multiscale perturbative approach. Here we investigate this problem in the Surface Quasi-Geostrophic model of turbulence, comparing the theoretical predictions with the outcome of high-resolution direct numerical simulations.

From Townsend’s attached-eddy model (AEM), the scalings of velocity moments of attached eddies have been widely investigated in literature. We derive analytically the scalings of the moments of velocity gradients of attached eddies by using the AEM, indicating -2 and -3 scalings for second- and third-order moments respectively, which are in agreement with direct numerical simulation (DNS) data. In addition, non-negligible influences of the small-scale eddies on the velocity gradients in the logarithmic region are discussed.

The policy requires authors to explain where research data can be found starting Sept. 4.

When determining the authorship list for your next paper, be generous yet disciplined.

APS has selected 156 Outstanding Referees for 2024 who have demonstrated exceptional work in the assessment of manuscripts published in the Physical Review journals. A full list of the Outstanding Referees is available online.

The recipients of the 40th François Naftali Frenkiel Award for Fluid Mechanics are Aliénor Rivière, Daniel J. Ruth, Wouter Mostert, Luc Deike, and Stéphane Perrard for their paper “Capillary driven fragmentation of large gas bubbles in turbulence” which was published in Physical Review Fluids 7, 083602 (2022).

Physical Review Fluids publishes a collection of papers associated with the 2022 Gallery of Fluid Motion. These award winning works were presented at the annual meeting of the APS Division of Fluid Dynamics.

See the 2022 Gallery for the original entries.

The 75th Annual Meeting of the American Physical Society (APS) − Division of Fluid Mechanics was held in Indianapolis, IN from November 20–22, 2022.

The Collection is based on presentations at the 2022 meeting of the APS Division of Fluid Dynamics in Indianapolis, Indiana. Each year the editors of Physical Review Fluids invite the authors of selected presentations made at the Annual meeting of the APS Division of Fluid Dynamics to submit a paper based on their talk to the journal. The selections are made based on the importance and interest of the talk and the submitted papers are peer reviewed. The current set of invited papers is based on presentations made at the 75th Annual meeting of the APS Division of Fluid Dynamics in November 2022. The papers may contain both original research as well as a perspective on the field they cover.

The Editors of Physical Review Fluids highlight the journal’s achievements, its editorial standards, and its special relationship with the APS Division of Fluid Dynamics (DFD).

Beverley McKeon and Eric Lauga describe their vision as new Co-Lead Editors for Physical Review Fluids, which celebrates its fifth anniversary this year.