Physical Review Fluids

Author(s): Samuel J. Petter, Benjamin C. Musci, Gokul Pathikonda, Prasoon Suchandra, and Devesh Ranjan

This study advances the understanding of blast-driven interface instabilities by transitioning from qualitative Mie scattering to quantitative planar particle image velocimetry (PIV). The velocity field and vorticity evolution reveal key insights into mixed-mode Richtmyer-Meshkov and Rayleigh-Taylor instabilities in a cylindrical geometry. High-Atwood number cases exhibit prolonged circulation growth, consistent with stronger turbulence and earlier mixing transition. The PIV data captures how pressure impulse and decay shape the instability beyond what Mie images alone can resolve.

[Phys. Rev. Fluids 10, 093902] Published Wed Sep 17, 2025

Author(s): Haoyu Wang, Isaac J. G. Lewis, Soohyeon Kang, Yuechao Wang, Leonardo P. Chamorro, and C. Ricardo Constante-Amores

We present data-driven models for predicting the motion of a freely settling sphere in a quiescent fluid using experimentally measured trajectories. Deterministic and stochastic neural differential equations reconstruct individual particle paths and capture the statistical features of settling dynamics without resolving the surrounding flow. Our results reveal the strengths of each modeling approach. Deterministic models excel at trajectory prediction, while stochastic models reproduce long-time statistical trends, thus providing a framework for reduced-order modeling of particulate flows.

[Phys. Rev. Fluids 10, 094402] Published Wed Sep 17, 2025

Author(s): Firoozeh Foroozan, Andrea Ianiro, Stefano Discetti, and Woutijn J. Baars

Experimental measurements were performed of convective heat transfer fluctuations beneath a grazing turbulent boundary layer flow. Spatiotemporal wall-temperature fields were acquired with an infrared camera and a heated-thin-foil sensor. Inferred Nusselt number fluctuations showed elongated features with scales similar to near-wall streaks. An analysis in the frequency–wavenumber domain revealed dispersive convection: larger streaks moved near freestream velocity, while smaller energetic features traveled at 10 times the friction velocity. These measurements provide a promising method for wall-based turbulence sensing and flow control.

[Phys. Rev. Fluids 10, 094904] Published Wed Sep 17, 2025

Author(s): Yue Hao, Charles Meneveau, and Tamer A. Zaki

Data assimilation provides a rigorous framework for integrating measurements with numerical simulations to estimate the flow. We developed a machine-learning-based assimilation strategy to infer unknown upstream flow conditions in a high-speed boundary layer from sparse wall-pressure measurements. Our method uses a Bayesian optimization to efficiently search for the optimal control parameters. Applied to a transitional boundary layer, the method accurately estimates the oncoming disturbances, and subsequent direct numerical simulation (DNS) predictions using the estimated conditions show excellent agreement with the true flow.

[Phys. Rev. Fluids 10, 094905] Published Wed Sep 17, 2025

Author(s): Kunihiko Taira, Georgios Rigas, and Kai Fukami

The fluid dynamics community has increasingly adopted machine learning to analyze, model, predict, and control a wide range of flows. This perspective article offers a critical assessment of the key challenges that must be addressed for deepening our understanding of flow physics and expanding the applicability of machine learning beyond fundamental research. We also highlight the importance of community-maintained datasets and open-source code repositories, as well as effective training of fluid mechanicians. We hope this paper sparks discussions and encourages collaborative efforts to advance the integration of machine learning in fluid dynamics.

[Phys. Rev. Fluids 10, 090701] Published Tue Sep 16, 2025

Author(s): Florian Voss and Uwe Thiele

Chemomechanical phenomena lie at the core of many biological and biomimetic systems. Particularly in the presence of free interfaces, such effects arise naturally due to chemically induced gradients of interfacial tension. We study a simple, thermodynamically consistent model for liquid drops on solid substrates that captures the coupling between an autocatalytic reaction of insoluble surfactants, the Marangoni effect and wetting dynamics. In the presence of chemical fuel, drops may exhibit complex self-organized motility modes like crawling and shuttling. The underlying chemomechanical feedback and the resulting bifurcation structure are studied in detail.

[Phys. Rev. Fluids 10, 094005] Published Tue Sep 16, 2025

Author(s): Ping Wang, Jinchi Li, Qingqing Wei, and Xiaojing Zheng

Channel and zero-pressure-gradient spatially developing turbulent boundary layer are the two canonical wall-bounded flows. Despite the long-standing controversies about their similarity, there is little attention paid to the similarity/dissimilarity between these two types of particle-laden turbulence, which is one of the most important topics in turbulence research. The particle distribution, turbulent statistics, and structures in the two kinds of particle-laden flow are thoroughly compared for the identical particle Stokes number and bulk volume fraction at turbulent Reynolds number of Reτ≈400. Qualitative and quantitative differences are observed throughout the turbulence region.

[Phys. Rev. Fluids 10, 094303] Published Tue Sep 16, 2025

Author(s): Guillermo L. Nozaleda, Javier Alaminos-Quesada, Cándido Gutiérrez-Montes, and Antonio L. Sánchez

Oscillatory flows in porous environments arise in both biological and technological systems, yet their time-averaged steady streaming has been largely overlooked. Here we analyze steady streaming in slender channels with porous interiors using a homogenized model with Darcy resistance. We find that porous media not only attenuate streaming compared to unobstructed channels but also alter its structure. These results provide new insight into fluid transport in oscillatory flows through porous environments.

[Phys. Rev. Fluids 10, 093103] Published Mon Sep 15, 2025

Author(s): Xiaoxiao Yang, Darius Marin, Charlotte Py, Olivier Cardoso, Anke Lindner, and Sandra Lerouge

Elastic instabilities and turbulence driven by elastic hoop stresses are likely to develop on top of shear-banding flows in giant micelles. We show the existence of a generic flow diagram in an operating space built on the curvature ratio Λ of the Taylor-Couette flow and the Weissenberg number Wi, which compares elastic and viscous stresses. Two different pathways to purely elastic turbulence are identified depending on Λ, with clear signatures in the stress response. The geometric scaling of the onset of elastic turbulence is found to be reminiscent of the Pakdel-McKinley criterion that recasts the different mechanisms and most unstable instability modes of flows with curved streamlines.

[Phys. Rev. Fluids 10, 093302] Published Mon Sep 15, 2025

Author(s): Romane Le Dizès Castell, Marc Prat, Noushine Shahidzadeh, and Sara Jabbari-Farouji

Drying of complex fluids in porous media is crucial for applications such as preserving cultural heritage materials, yet the role of sol–gel transitions in evaporation kinetics remains unclear. We develop a pore-network model to investigate the emergence of gel-like skin at the evaporation interface. By incorporating pore size gradients and a viscosity-dependent vapor pressure rule, the model captures skin formation. Its predictions quantitatively match experiments and explain the evaporation slowdown during sol–gel transition.

[Phys. Rev. Fluids 10, 094302] Published Mon Sep 15, 2025

Author(s): Bobae Johnson, Scott Weady, Zihan Zhang, Alison Kim, and Leif Ristroph

Ice melting is an important part of the climate system that involves complex fluid dynamics and interactive processes. Here we address the capsize problem in which melting-induced changes in size and shape of free floating ice can trigger it to rotate and turn over. Experiments show that “lab icebergs” lock to the waterline while gradually melting, then abruptly lose stability and roll over to assume a new posture, and this process repeats many times as the ice melts down. A particular angle of rotation is selected and, consequently, the ice tends towards a polygonal shape. These results are reproduced by a model that predicts the coupled shape-posture dynamics and uncovers the key mechanisms.

[Phys. Rev. Fluids 10, 093801] Published Fri Sep 12, 2025

Author(s): Jiajun Hu, Zhen Lu, and Yue Yang

Machine learning can accelerate the prediction of fluid flow around obstacles, but existing models often struggle to generalize to geometries not seen during training. We introduce a generative diffusion model that uses an obstacle’s geometry as a conditional prompt to predict the corresponding instantaneous flow field. Trained only on elementary shapes, the model demonstrates superior generalization by capturing key features like vortex shedding and pressure distributions for unseen and complex geometries. By generating more physically consistent results, it outperforms standard neural network and variational autoencoder models, showing promise for accelerating CFD workflows.

[Phys. Rev. Fluids 10, 094903] Published Fri Sep 12, 2025

Author(s): Emad Chaparian

In this study, a comprehensive Darcy-type law for viscoplastic fluids is proposed. The two extreme limits of a yield-stress fluid flow in a porous medium are addressed individually and then are combined to propose a Darcy-type law which is valid across the entire range of the Bingham numbers (i.e. the ratio of the fluid’s yield stress to the characteristic viscous stress). These two extreme limits are namely the viscous limit (infinitely large pressure gradient compared to the yield stress of the fluid – ultra low Bingham number) and the plastic/yield limit (infinitely large Bingham number).

[Phys. Rev. Fluids 10, 093301] Published Thu Sep 11, 2025

Author(s): Adrian Herrera-Amaya, Nils B. Tack, Zhipeng Lou, Chengyu Li, and Monica M. Wilhelmus

Shrimp thrive in a wide range of climates, from the tropics to polar waters and inland freshwater. Our research shows how their swimming style has evolved to be highly resilient to environmentally driven changes in water properties. Our findings highlight the ability of the large biomass of shrimp-like crustaceans to adapt to vastly different water temperatures and viscosities. It also shows the potential for crustacean-inspired underwater vehicles; such drones could navigate environments with variable viscosity, such as phytoplankton blooms or oil spills, without requiring modifications to their control algorithms.

[Phys. Rev. Fluids 10, 093101] Published Wed Sep 10, 2025

Author(s): Hao Ye, Zhenyu Ouyang, and Jianzhong Lin

Active fluids can influence the behavior of passive particles, with sedimentation being an important such process. We investigate how the velocity of a sphere varies when settling in a square tube filled with active nematic fluids. While the direct active forces exerted on the sphere are weak in our study, activity can still significantly modify settling velocity by altering the flow structure and nematic field. The results manifest mechanisms of activity-induced shear thinning and thickening for various anchoring conditions and activity. As activity increases, transitions between flow patterns further influence settling, with different effects observed in extensile and contractile fluids.

[Phys. Rev. Fluids 10, 093102] Published Wed Sep 10, 2025

Author(s): Charbel Habchi, Aurelien Joly, and Pierre Moussou

The evaluation of added and coupling mass is central to fluid-structure interaction studies. Revisiting Batchelor’s 1967 framework, this work introduces a refined approach based on superposition of acceleration fields and numerical evaluation of kinetic energy in potential flows. By distinguishing between added and coupling mass, the method clarifies inertial forces for diverse body geometries and highlights implications for seismic design, underwater dynamics, and multiphase flow modeling.

[Phys. Rev. Fluids 10, 094301] Published Wed Sep 10, 2025

Author(s): T. Zemach

Previous research on gravity currents, the flow of a denser fluid through a less dense one, has largely focused on channels with rectangular cross-sections. How do these currents flow through more complex, nonrectangular shapes found in nature, like river estuaries or valleys? A generalized model that accounts for crucial effects of entrainment and drag in channels of various shapes is presented. This model reveals how these factors significantly reduce the current’s propagation speed while increasing its height and volume, especially in nonrectangular geometries. This work provides enhanced understanding of these flows, with findings that can be applied to diverse natural and engineered systems.

[Phys. Rev. Fluids 10, 094401] Published Wed Sep 10, 2025

Author(s): Guangtao Li, Liangquan Zhang, Xin Wang, Wen-Li Chen, Hui Li, and Donglai Gao

The interaction of vortex rings with solid surfaces is a classic problem in fluid dynamics, yet their collision with concave hemicylindrical shells remains poorly understood. This experimental study investigates vortex ring impingement on concave surfaces with varying curvature ratios (Dm /De = 15,10,5,2,1) at Re=1500. Using planar laser-induced fluorescence and particle image velocimetry, we reveal how curvature controls secondary vortex formation, rotation, and three-dimensional evolution. Dynamic models are proposed to explain the transition from tertiary to secondary vortex dominance as curvature increases, offering new insights into confined vortex-wall interactions.

[Phys. Rev. Fluids 10, 094702] Published Wed Sep 10, 2025

Author(s): F. C. Martins and J. C. F. Pereira

We study the counter-rotating vortex pair in laminar jets in crossflow via a vorticity transport analysis at various jet-to-crossflow velocity ratios (R). At high R, most vorticity is generated in the pipe, but boundary layer vorticity is entrained into the pair at low R.

The vortex pair undergoes bubble vortex breakdown at low-to-intermediate R, due to the adverse pressure gradient through the vortex cores. Breakdown persists at the onset of hairpin vortex shedding with decreasing R, but disappears upon further growth in instability amplitude. A new low frequency and spanwise symmetry-breaking instability characterized by alternating breakdown of the vortex pair was also identified.

[Phys. Rev. Fluids 10, 094703] Published Wed Sep 10, 2025

Author(s): Sijie Wang, Yuxiao Cheng, Zifei Yin, Paul Durbin, and Weipeng Li

A new hybrid Reynolds-Averaged-Navier-Stokes/Large Eddy Simulation (RANS/LES) model is proposed. With the discontinuous Galerkin spectral element method (DGSEM), it gives a robust and efficient approach for simulating high-speed and high-Reynolds-number turbulent flows. A change of variable from omega in the k-omega model to g, gives the k-g model, which avoids the singularity near the wall and makes the model work in DGSEM. The model is tested in various cases, including wall-bounded turbulence, wall-modeled LES, flow separation, and compressible flows, with good performance.

[Phys. Rev. Fluids 10, 094902] Published Wed Sep 10, 2025