Physical Review Fluids

Author(s): Wei Cai, ShuaiShuai Jiang, He Wang, Pei Wang, DongJun Ma, and Ting Si

While shock-tube experiments on the Richtmyer-Meshkov instability (RMI) have been extensively conducted under weak-shock conditions, such experiments under strong-shock conditions remain rare. This study presents the first shock-tube experiments on RMI at V-shaped interfaces driven by shocks with Mach numbers exceeding 3.0, demonstrating that interface evolution depends on initial amplitude and involves compressibility, Mach-reflection, shock-proximity, and secondary-compression effects absent under weak-shock conditions. These effects render existing linear and nonlinear models inadequate. Guided by present experimental findings and physical understanding, empirical models are developed.

[Phys. Rev. Fluids 10, 104005] Published Thu Oct 16, 2025

Author(s): Yangyang Sha, Yuhang Xu, Yingjie Wei, Xiaojian Ma, and Cong Wang

In fluid experiments, obtaining velocity fields at high temporal resolution is often prohibitively expensive. This study introduces a semi-supervised deep learning framework that leverages low-cost, high-speed cavitation phase imaging to eliminate the need for high-frequency velocity labels. Applied to cavitating hydrofoil flows, the method reconstructs temporally super-resolved velocity fields from sparse, low-frequency samples and demonstrates robust generalization under unsteady conditions. These results highlight an efficient and economical approach for modeling complex multiphase flows.

[Phys. Rev. Fluids 10, 104301] Published Thu Oct 16, 2025

Author(s): Li Wei, Xiaoxian Guo, and Xuefeng Wang

Deep learning models for particle imaging velocimetry (PIV) often suffer from complex, black-box architectures that limit efficiency and real-world generalization. We propose a physics-informed variational framework that explicitly embeds classical fluid principles, like incompressibility, into its multi-scale inference structure. This principled design eliminates the need for complex black-box components and achieves new state-of-the-art accuracy on challenging flows. Crucially, the model shows outstanding generalization, applying directly to riverine data without retraining, defining a new path for robust and physically consistent flow measurement.

[Phys. Rev. Fluids 10, 104902] Published Thu Oct 16, 2025

Author(s): Oscar Flores and Manuel Garcia-Villalba

While biological systems like dragonflies and schooling fish achieve remarkable performance through coordinated hydrodynamic interactions, the current understanding of the underlying mechanisms remains incomplete. This review examines how vortex dynamics, structural flexibility, and 3D effects influence performance in tandem flapping wing systems. It is shown that for tandems of spanwise-flexible wings, the forewing achieves maximum thrust through fluid-structure resonance while moderately stiff hindwings effectively capture upstream wake structures leading to increased overall performance. The mechanisms by which self-propelled systems achieve energy savings are also discussed.

[Phys. Rev. Fluids 10, 100502] Published Wed Oct 15, 2025

Author(s): Thibault Maurel-Oujia and Kazuki Maeda

Nonequilibrium reactive molecular dynamics simulations reveal detailed structures of a Mach 5 shock wave in a gaseous H2/O2 mixture, driven by the large mass disparity between H2 and O2 molecules.

[Phys. Rev. Fluids 10, 103201] Published Wed Oct 15, 2025

Author(s): Ming Yu, Siwei Dong, Zhigong Tang, and Xianxu Yuan

Rarefaction effects in compressible turbulent boundary layers is investigated by imposing slip boundary conditions at the wall. The Kolmogorov and viscous length scales are an order of magnitude higher than the molecular mean free path. The influences of the slip boundary conditions on turbulent flow statistics are restricted within the viscous sublayer. The mean wall heat flux, vorticity and velocity divergence fluctuation intensities are obviously affected.

[Phys. Rev. Fluids 10, 103401] Published Wed Oct 15, 2025

Author(s): R. J. Teed and E. Dormy

Recent numerical experiments of dynamo action relevant to the generation of the geomagnetic field have produced different regime branches identified within bifurcation diagrams. In this work, we identify a variety of dynamo states on the weak-field branch beyond the known dipolar solutions. Some solutions exhibit clear scale separation between small-scale flow and large-scale magnetic field, despite the large ratio of viscosity to magnetic diffusion. Numerical solutions in this regime have not been observed before and they offer a first connection with earlier theoretical work based on mean-field theory.

[Phys. Rev. Fluids 10, 103702] Published Wed Oct 15, 2025

Author(s): Dongqi Li, Zhibing Yang, Renjun Zhang, Amir A. Pahlavan, Ran Hu, and Yi-Feng Chen

Understanding particle-mediated interfacial processes in confined spaces undergoing deformation is important for many natural and industrial processes. Here, we combine laboratory experiments and theoretical analysis to investigate how particle dynamics shapes suspension-air interfacial pattern formation when the suspension is stretched. It is found that even slightly nonuniform particle concentration promotes wavy and finger-like morphologies, while particle perturbations lead to dendritic pattern with strong finger branching.

[Phys. Rev. Fluids 10, 104004] Published Wed Oct 15, 2025

Author(s): Darren Crowdy

The mechanism of surfactant diffusion between two edges of the active face of a Janus swimmer is shown to lead to a translational-rotational coupling leading to swimming in circles. The mechanism is exemplified using a two-dimensional model system amenable to closed-form representation of the swimmer trajectory and the Stokes flow it generates.

[Phys. Rev. Fluids 10, 104101] Published Wed Oct 15, 2025

Author(s): Dario De Marinis, Domenico Careccia, Francesco Ferrara, and Marco Donato de Tullio

This study employs a Lattice Boltzmann-based fluid-structure interaction framework to investigate how channel geometry, particle properties, and flow regimes affect inertial migration and secondary flows in curved microchannels. After validation against benchmark cases, the work reports, for the first time, fully resolved numerical simulations of multiple-particle focusing in realistic serpentine microchannel geometries.

[Phys. Rev. Fluids 10, 104202] Published Wed Oct 15, 2025

Author(s): Jun Hu, Ruiwei Xing, and Baofang Song

This study explores instabilities of an upward mixed convection flow in a vertical heated pipe under a transverse magnetic field through linear global stability analysis and direct numerical simulations. The critical curves in the parameter plane of the Rayleigh number and the Hartmann number are presented for both thermal-buoyant and thermal-shear instabilities, and reveal that under the action of the magnetic field the two plane symmetric spiral modes are broken into two asymmetric branches. Direct numerical simulations are further used to investigate the transition routes from regular laminar flows to more complex nonlinear spatiotemporal structures.

[Phys. Rev. Fluids 10, 103901] Published Tue Oct 14, 2025

Author(s): Megan Delens and Nicolas Vandewalle

Capillary-driven self-assembly at liquid interfaces, often illustrated by the “Cheerios effect,” has been limited to simple configurations. By introducing anisotropic, saddle-shaped particles, we demonstrate how quadrupolar capillary interactions can be encoded to achieve both end-to-end and side-by-side attraction; what we call the “Pringles effect.” Our theoretical model and experiments with 3D-printed objects reveal a versatile route to reprogrammable mesoscale assemblies, bridging capillarity and design for complex self-organization.

[Phys. Rev. Fluids 10, 104003] Published Tue Oct 14, 2025

Author(s): Nataly Maroundik, Dotan Ilssar, and Evgeniy Boyko

Diffusioosmotic flow, driven by solute concentration gradients, is a widely used method for fluid manipulation in microfluidic devices, often fabricated from soft materials such as PDMS. We show that such soft diffusioosmotic flow systems may exhibit fluid-structure instability. To provide insight into the underlying instability mechanism, we develop a theoretical model describing the interaction between diffusioosmotic flow and an elastic substrate. We find that above a certain concentration gradient threshold, negative pressures induced by diffusioosmotic flow cause the collapse of the elastic top substrate onto the bottom surface.

[Phys. Rev. Fluids 10, 104203] Published Tue Oct 14, 2025

Author(s): Imran Hayat and George Ilhwan Park

Three-dimensional turbulent boundary layers subject to pressure gradients and undergoing separation remain a key challenge for wall modeling. Using DNS datasets of swept and unswept separation bubbles, this study employs the Renard–Deck skin-friction decomposition to isolate and analyze nonequilibrium contributions critical to near-wall modeling. Wall-modeled LES demonstrates that only wall models capturing the spatial growth term accurately reproduce the true energy balance in nonequilibrium zones. The analysis highlights when and why nonequilibrium effects must be incorporated, providing physics-based guidance for improving wall model predictions in practical flows.

[Phys. Rev. Fluids 10, 104602] Published Tue Oct 14, 2025

Author(s): G. D'Avino, M. M. Villone, M. De Corato, S. Villa, M. Nobili, and D. Larobina

The mobility of elongated colloidal particles near fluid interfaces is crucial in fields ranging from biofilm formation to thin-film technologies. This study numerically investigates the resistance matrix of a prolate spheroid close to a two-dimensional incompressible liquid–gas interface, revealing that surface incompressibility mimics slip conditions for parallel motion and no-slip for orthogonal motion. The results align with recent experimental data and highlight the role of interface hydrodynamics in colloidal transport.

[Phys. Rev. Fluids 10, 104002] Published Fri Oct 10, 2025

Author(s): Ethan Coleman and Ankur Gupta

Electrolytic diffusiophoresis refers to the movement of charged particles in electrolytes. This motion typically proceeds either up or down an electrolyte concentration gradient. However, when multiple electrolyte gradients are present, such as an acid-base reaction, the direction may be reversed, inducing the formation of a focal band. While the results were reported experimentally, an understanding of the phenomena has remained elusive. Here, we computationally show that a pH-dependent zeta-potential is required for focusing to occur. Our model provides an intuitive understanding of the governing physics and a compelling match to prior experimental reports.

[Phys. Rev. Fluids 10, 103701] Published Thu Oct 09, 2025

Author(s): Daniel Papa, Christophe Josserand, and Caroline Cohen

Do ice stalagmites grow purely vertically? Our work shows that depending on the substrate temperature and the water flow rate, ice stalagmites can take a wide variety of shapes and forms. We determined a criterion that distinguish a purely vertical growth to a combined vertical and lateral growth dynamics. We also show that the main driving factor is the heat diffusion at the stalagmite’s tip and that the combined knowledge of both the vertical and lateral growth allows us to determine the asymptotic aspect ratio of the ice stalagmites. Our predictions are compared and validated by experiments and can serve as a model experiment to study related physical phenomena.

[Phys. Rev. Fluids 10, L101602] Published Thu Oct 09, 2025

Author(s): Laura K. Currie and Chris A. Jones

Jupiter’s zonal winds extend down about 3000 km into its interior but the mechanism that determines this depth is currently unknown. Here we explore a mechanism by which the surface zonal flows of giant planets can be gradually attenuated. We show that the combination of a stably stratified surface layer, a zonal flow driven near the surface, and convection in thermal wind balance can lead to zonal jets that extend deep into the interior, consistent with gravity data from observations.

[Phys. Rev. Fluids 10, 103501] Published Tue Oct 07, 2025

Author(s): Romain Noël, Feifei Qin, Linlin Fei, and Jan Carmeliet

We propose an alternative surface tension adjustment approach in the pseudopotential lattice Boltzmann (LB) model, which can be easily and straightforwardly incorporated into different widely used collision operators, such as single relaxation time (SRT or LBGK), multiple relaxation time (MRT) and entropic-MRT (KBC) operators. Benefiting from the proposed surface tension adjustment method, a remarkable tunable surface tension range of 140 times can be achieved. We have also successfully modeled the droplet impact and splashing dynamics on thin liquid films with a Weber number up to 10,500, achieving one order of magnitude higher than LB simulations reported in the literature.

[Phys. Rev. Fluids 10, 104901] Published Tue Oct 07, 2025

Author(s): Guilhem Balvet, Yelva Roustan, and Martin Ferrand

This study presents a consistent framework for high-Reynolds-number, thermally stratified surface boundary layers, linking turbulence models to universal profiles of velocity and temperature. By deriving algebraic solutions for second-order moments and iteratively resolving dissipation, the approach recovers correct stable and unstable asymptotics. Implications for Lagrangian stochastic models are explored, highlighting the need for consistent turbulence closures and wall-boundary treatments in predicting buoyant plume rise and dispersion.

[Phys. Rev. Fluids 10, 103801] Published Mon Oct 06, 2025