Physical Review Fluids

Author(s): Johannes N. Hillestad, Srikar Yadala, Leon Li, R. Jason Hearst, and Nicholas A. Worth

In this paper, the volumetric velocimetry measurement technique Shake-the-Box is applied to the near wake of a model wind turbine to investigate the vortex dynamics present in the wake. The interaction and breakdown of the tip vortices is visualized using three-dimensional iso-surfaces of Lamb vector magnitude, a technique and physical quantity only accessible using volumetric techniques. The paper describes the influence of the tip vortex interaction process on properties of the tip vortex, such as circulation and the circularity and inclination of the tip vortex contour itself.

[Phys. Rev. Fluids 11, 014701] Published Thu Jan 08, 2026

Author(s): Ming Li, Sung Goon Park, Fotis Sotiropoulos, and Lian Shen

A flexible body can interact with an incident water wave passively and extract wave energy to generate a thrust force. In this paper, direct numerical simulation is performed to investigate the wave energy extraction mechanism in the passive propulsion of a flexible foil. Kinematics studies show that the passive flapping motion is up–down asymmetric, with a direct impact on propulsive performance under unsteady motion. At high Strouhal numbers, a passing-over leading-edge vortex is observed, which is responsible for the enhanced thrust force.

[Phys. Rev. Fluids 11, 014801] Published Thu Jan 08, 2026

Author(s): Valeria Garbin

This article briefly reviews recent developments in understanding and utilizing bubble dynamics in complex fluids. Bubble dynamics impart deformations and probe properties on time scales as short as the relaxation times of complex fluids containing suspended particles or macromolecules. Examples from our research group with increasing complexity are presented: from linear rheology of soft solids using ultrasound-driven bubbles, to bubble removal from yield-stress fluids, to self-assembly in colloidal gels driven by bubble dynamics. The growing synergy between the communities of cavitation and rheology will help address new challenges in characterization and manipulation of complex fluids.

[Phys. Rev. Fluids 11, 010502] Published Wed Jan 07, 2026

Author(s): Tarek Echekki

Data from experiments or simulations enables tools to accelerate simulations and develop accurate predictions of important turbulence-chemistry interactions in turbulent combustion flows. Several methods designed to exploit this data are presented and discussed. They are motivated by and rooted in traditional paradigms in turbulent combustion that rely heavily on the existence of a low-dimensional manifold for the composition space and its coupling with turbulent transport. These methods include surrogate DNS with principal component transport, the extraction of closure models from multiscalar measurements, and deep operator networks for chemistry integration and acceleration.

[Phys. Rev. Fluids 11, 010501] Published Tue Jan 06, 2026

Author(s): Bradley W. Hindman and J. R. Fuentes

Turbulent mixing at the interface between a convection zone and a neighboring stably stratified region in a star or planet often causes the convective region to grow. This mixing process therefore plays a key role in shaping the internal structure and long-term evolution of stars and planets, especially when compositional gradients contribute substantially to the density stratification. Our numerical simulations show, however, that when the compositional stratification is sufficiently strong, chemical diffusion can halt the expansion of the convection zone. Taken together, these results suggest that chemical diffusion sets a limit to convective penetration in strongly stratified interiors.

[Phys. Rev. Fluids 11, 013501] Published Mon Jan 05, 2026

Author(s): Christian Reartes, Pablo D. Mininni, and Raffaele Marino

In stably stratified turbulence, vertical transport is typically suppressed by buoyancy; however, intense vertical drafts can intermittently develop. Using direct numerical simulations and a Lagrangian approach based on particle pair dispersion, we show that these extreme events play a crucial role in vertical mixing, leading to strong departures from classical dispersion behavior. Our results demonstrate that a small fraction of particles experiencing extreme vertical drafts contributes disproportionately to vertical transport and mixing, highlighting the central role of large-scale intermittency in stratified turbulent flows.

[Phys. Rev. Fluids 11, 014501] Published Mon Jan 05, 2026

Author(s): Jun Eshima, Tristan Aurégan, Palas Kumar Farsoiya, Stéphane Popinet, Howard A. Stone, and Luc Deike

When bubbles burst on the ocean surface, small drops are emitted. In this work, we find that when there are surfactants, a particularly common type of contamination found on fluid surfaces, small bubbles can emit drops that are significantly larger than expected without contamination. For the bubbles considered in our experiment and simulations, we see up to a 5 times increase in the size of the emitted drop. Previous studies involving large bubbles saw the opposite effect, where the drop size decreased in the presence of surfactants. This finding therefore has fundamental implications for our understanding of aerosol production from bubble bursting.

[Phys. Rev. Fluids 10, 123604] Published Tue Dec 30, 2025

Author(s): Yang Huang, Qing Xiao, and Qiang Zhu

Using large-eddy simulation with overset grids, this work reveals how launch angle shapes the water-exit dynamics of a neutrally buoyant sphere. The sphere exhibits nonlinear velocity attenuation, angle-dependent rotation switching, and systematic lateral deflection driven by shed vortices and image-induced pressure asymmetry. Two exit phases with distinct hydrodynamic signatures are identified. The findings deepen mechanistic understanding of water exit and aid the control of trans-medium bodies.

[Phys. Rev. Fluids 10, 124805] Published Tue Dec 30, 2025

Author(s): Enzo Francisco, Julien Lambret, and Sébastien Aumaître

We present a novel experimental technique based on Diffusing-Wave Spectroscopy that, for the first time, provides high-resolution spatiotemporal maps of energy dissipation at the boundary of a turbulent flow. The flow, generated by an impeller, exhibits Reynolds numbers in the range 1.5×104 to 6×105. Measurements were performed at the boundary of a square container, within a 5×5cm² region at the impeller height. This method enables a direct experimental characterization of the statistical properties of turbulent structures near flow boundaries, offering new insights into boundary-layer dynamics in highly turbulent regimes.

[Phys. Rev. Fluids 10, 124606] Published Mon Dec 29, 2025

Author(s): Hannah M. Clercx and Rudie P. J. Kunnen

We measure the efficiency of convective heat transfer (Nusselt number) by turbulent convection in a rapidly rotating Rayleigh-Bénard convection experiment. Series of measurements are done at two constant values of the Rayleigh number. Using water at different mean temperatures, we change the Prandtl number. Raising the Prandtl number leads to a reduction of the Nusselt number with a significantly stronger dependence than without rotation. We hypothesize that this dependence is caused by the changing ratio of the thermal and kinetic boundary layer thicknesses.

[Phys. Rev. Fluids 10, 123503] Published Fri Dec 26, 2025

Author(s): Vedant Kumar and Johan Larsson

Two new modeling components for the energy equation in ordinary-differential-equation-based wall-models are proposed in order to improve the accuracy of heat flux predictions in high-speed turbulent boundary layers: a model for the diffusion of turbulence kinetic energy, and an altered near-wall damping of the thermal eddy diffusivity. These modeling additions reduce the a priori error in the heat flux to within 5% across the tested conditions. A decomposition of the a posteriori error shows the presence of two other error sources in wall-modeled large eddy simulations, which are found to contribute up to 5-10% additional error.

[Phys. Rev. Fluids 10, 124605] Published Wed Dec 24, 2025

Author(s): Yasuhide Fukumoto, Satoshi Oshiro, and Taxpulat Ruzi

Streamlines of an exact solution of the Hall-MHD equation for a spherical vortex containing toroidal magnetic flux, wrapped by a vortex sheet. The magnetic tension acts to accelerate the traveling speed of a spherical vortex. The Hall effect, originating from relative fluctuations of electrons and ions, provides further acceleration. Besides, a singular solution specific to Hall-MHD is found for the spherical vortex, which vanishes when the Hall effect is switched off.

[Phys. Rev. Fluids 10, 124703] Published Wed Dec 24, 2025

Author(s): Caroline Cardinale, Steven L. Brunton, and Tim Colonius

Spectral proper orthogonal decomposition (SPOD) finds orthogonal space-time modes that best capture the 2nd order statistics of a data set. However, SPOD is limited to uniform time-resolved data. Many experimental systems are limited by camera speed. Leveraging the relaxed requirement of pairwise data for dynamic mode decomposition (DMD), we propose a pairwise SPOD algorithm that estimates SPOD modes of nonuniformly sampled data. Using 2 PIV setups in tandem, the time delay within a data pair satisfies the Nyquist criterion, but the time between pairs does not, allowing time to process the last snapshot. Computational data is used for validation and the algorithm is of general use.

[Phys. Rev. Fluids 10, 124904] Published Wed Dec 24, 2025