Physical Review Fluids

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

Author(s): Lorenzo Piro, Massimo Cencini, and Roberto Benzi

Extreme Lagrangian acceleration in turbulence is often attributed to particle trapping in coherent vortex structures. Here, we show that shell models, despite lacking vortex filaments, reproduce the extreme intermittent fluctuations of Lagrangian acceleration seen in real flows. Within the multifractal framework, we accurately predict acceleration moments and full probability distribution functions (PDFs) across a wide range of Reynolds numbers. This shows extreme Lagrangian fluctuations can arise from inertial-range dynamics alone, supporting the universality of multifractal statistics and highlighting shell models as effective tools to capture key features of turbulence.

[Phys. Rev. Fluids 10, L092601] Published Wed Sep 10, 2025

Author(s): Fabio Guglietta, Diego Taglienti, and Mauro Sbragaglia

We study the statistics of deformation of neutrally buoyant droplets in homogeneous isotropic turbulence (HIT), wherein the characteristic droplet size R is smaller than the characteristic Kolmogorov scale η of the turbulent flow. We systematically focus on the characterization of droplet deformatio…

[Phys. Rev. Fluids 10, 093601] Published Tue Sep 09, 2025

Author(s): Chenyue Wang, Jihui Ou, and Jie Chen

Near-space hypersonic vehicles at 40–60 km altitude encounter local rarefaction effects that influence the boundary-layer stability and the laminar–turbulent transition. By incorporating slip boundary conditions and nonlinear constitutive relations into the Navier–Stokes equations and linear stability theory, we systematically investigate hypersonic boundary-layer stability over a blunt cone under near-continuum conditions. The results show that rarefaction thins the boundary layer and stabilizes second-mode instabilities, particularly at high wall temperatures or with small bluntness. These results offer new insights into hypersonic stability and transition in the near-continuum regime.

[Phys. Rev. Fluids 10, 093901] Published Thu Sep 04, 2025

Author(s): Eric Parish and Matthew Barone

The wall-normal Reynolds stress has a negligible contribution to the wall-normal momentum equation in low-Mach, zero pressure gradient boundary layers, and conservation of momentum indicates that pressure is uniform throughout the boundary layer. In hypersonic boundary layers analysis suggests the wall-normal Reynolds stress becomes significant compared to mean pressure and that it must balance with pressure. We validate this and show that the wall-normal Reynolds stress results in non-negligible pressure deficits. We show that errors in standard RANS models for the wall-normal Reynolds stress have a noticeable impact (5% for a Mach 14 cold-wall flow) on wall quantities of interest.

[Phys. Rev. Fluids 10, 094601] Published Thu Sep 04, 2025

Author(s): Yu Qiu, Luis Cueto-Felgueroso, Amir A. Pahlavan, Bauyrzhan K. Primkulov, and Ruben Juanes

Contact lines, where fluid interfaces meet solid surfaces, pose a fundamental challenge to modeling fluid-fluid displacement in confined geometries, as they violate the classical no-slip boundary condition. Recent experiments reveal that contact-line motion in a capillary tube produces compact displacement at low flow rates and unstable fingering at high flow rates. We present a phase-field model with a novel formulation of the boundary wetting conditions. Our model captures the equilibrium configurations at arbitrary wettability, and also predicts dynamic configurations, including wetting transitions, thin-film formation and interface pinch-off, in quantitative agreement with experiments.

[Phys. Rev. Fluids 10, 094004] Published Wed Sep 03, 2025

Author(s): Clément Bret, Pantxo Diribarne, Jérôme Duplat, and Bernard Rousset

Quantum vortex lines are angstrom-scale tubes with quantized circulation ±κ, the Feynman–Onsager constant, that form the backbone of the superfluid velocity field in He-II flows. When forced to turbulence, they organize into a tangle characterized by its mean intervortex spacing. Combining second-sound resonant cavity measurements with 3D Lagrangian tracking for the first time, we observe that the mean intervortex spacing scales with the κ based Reynolds number following a Kolmogorov-like –3/4 power law. We then show both this scaling and the prefactor value can be explained with classical turbulence formalism due to the quantum restricted depth of the superfluid component energy cascade.

[Phys. Rev. Fluids 10, 094701] Published Wed Sep 03, 2025