Physical Review Fluids

Author(s): Sai Swetha Venkata Kolluru and Rahul Pandit

Following the report of numerical evidence of a finite-time singularity in the wall-bounded three-dimensional axisymmetric incompressible Euler equations, we investigate the effect of a magnetic field on this singularity. We find the HL-type singularity as well as a new “cusp”-type singularity where the nature of the singularity is sensitive to the initial strength of the magnetic field relative to the kinetic fields. This study marks the first numerical evidence for singularities in the Ideal MHD equations in a wall-bounded domain.

[Phys. Rev. Fluids 11, 063701] Published Wed Jun 10, 2026

Author(s): Antonio Pol, Riccardo Artoni, and Patrick Richard

When flowing, elongated particles may exhibit a strong inhibition of their angular motion compared with spherical grain. We use discrete element simulations to investigate the angular dynamics of elongated particles in dense, confined shear flows. We show that this inhibition does not originate from single isolated mechanisms, but is governed by the degree of collective alignment induced by shear. We propose a simple scaling law relating the average angular velocity to the local shear rate. This scaling collapses data obtained for different particle properties and flow patterns, unifies spherical and elongated particles, and remains valid across two additional flow configurations.

[Phys. Rev. Fluids 11, 064302] Published Wed Jun 10, 2026

Author(s): Parham Poureslami, Ranit Mukherjee, and Sungyon Lee

Particle-induced viscous fingering (PIVF) occurs when a non-colloidal suspension displaces air inside a Hele-Shaw cell, which leads to the formation of particle clusters, or “plumes” at the advancing interface. Despite extensive studies in the last decade, the coupling between plumes and interfacial deformations remains unexamined. In this paper, we address this coupling by deriving scaling laws that connect the interplay between capillarity, local particle concentrations, and interfacial speed. We also uncover new regimes of PIVF that are unique to rectilinear geometry, in which particle plumes interact and coalesce, resulting in enhanced mixing inside the suspension.

[Phys. Rev. Fluids 11, 064303] Published Wed Jun 10, 2026

Author(s): Alain Pumir, Muhammad Zubair Sheikh, Kristian Gustavsson, Emmanuel Lévêque, Bernhard Mehlig, and Aurore Naso

As they settle through turbulent clouds, elongated ice crystals, which form at low enough temperature, are affected by the turbulent motion of air. Such crystals, which are typically smaller than the Kolmogorov length scale of the flow, tend to align perpendicular to gravity, and to a lesser extent, parallel to vorticity. Turbulence is shown to increase the settling velocity of the crystals due to their inhomogeneous sampling of the flow.

[Phys. Rev. Fluids 11, 064608] Published Wed Jun 10, 2026

Author(s): Bo-Jie Xie, Tian-Shu Zhou, and Jin-Han Xie

We generalize the derivation of the velocity circulation area rule, initially proposed in the inertial range and stating that circulation statistics do not depend on specific loop shapes, to ranges with forcing and dissipation. With a newly proposed necessary condition, we show that the area rule cannot hold in the classic inertial range. Even so, in two-dimensional instability-driven turbulence, the variance-normalized circulation probability density function shows a weaker dependence on loop shape, suggesting that the normalized circulation statistics are potential measures of geometry-related turbulence invariances.

[Phys. Rev. Fluids 11, 064607] Published Tue Jun 09, 2026

Author(s): Ri Zhang, Lun Sun, Zhongwei Zhou, Yong Liu, and Domenico D. Meringolo

This study investigates experimentally the three-dimensional settling process of centimeter-sized spherical particles in still water using Particle Imaging Velocimetry (PIV) and Convergent Binocular Vision (CBV). When particles are released side by side, the number of particles significantly influences the settling process. Two particles settle synchronously almost in mirror-image, with random deflection largely suppressed, called the mutual support phenomenon (MSP). With more particles, the outermost two exhibit MSP, but other particles may fall like single particles. Observations of multiple particles with sophisticated instruments can reveal mechanisms of complex settling processes.

[Phys. Rev. Fluids 11, 064301] Published Mon Jun 08, 2026

Author(s): Xiang I. A. Yang, Ruifeng Hu, Rahul Deshpande, Robert Kunz, and George Huang

Two-equation RANS models often label (k) as turbulent kinetic energy, yet their (k) represents only the energy of Reynolds-stress-producing active motions in the logarithmic layer. This leaves the energy of inactive motions unresolved, despite its importance for normal stresses, curvature effects, wakes, and particle transport. We derive a transport framework for inactive-motion energy and show that its predicted scaling agrees with channel and boundary-layer DNS data.

[Phys. Rev. Fluids 11, 064606] Published Mon Jun 08, 2026

Author(s): Eric Lauga and Beverley McKeon

[Phys. Rev. Fluids 11, 060001] Published Fri Jun 05, 2026

Author(s): Francesca Mangani, Alessio Roccon, and Alfredo Soldati

Oil–water emulsions exhibit viscosity contrasts that can significantly influence scalar transport and mixing. Using phase-field-based direct numerical simulations, we investigate the role of viscosity on the transient evolution of a passive scalar (temperature), initially confined in the dispersed phase and subsequently transferred to the carrier phase, in two opposite configurations: water-in-oli and oil-in-water emulsions. Despite fundamentally different local mixing dynamics in oil and water, reversing the continuous and dispersed phases redistributes these mixing mechanisms, preserving similar global heat-transfer rates and thermal transient in the two systems.

[Phys. Rev. Fluids 11, 064502] Published Fri Jun 05, 2026

Author(s): Yijie Wang, Jun Chen, and Leonardo P. Chamorro

Turbulence subjected to background rotation underlies many geophysical and engineering flows, yet its anisotropic development away from the rotation axis remains poorly constrained experimentally. This laboratory study examines nearly isotropic turbulence under controlled off-axis rotation using high-resolution PIV, revealing how rotation induces scale-dependent anisotropy in directional velocity spectra. The onset of spectral anisotropy follows a simple scaling with the inverse turbulent Rossby number, directly linking large-scale rotation to small-scale energy redistribution. These results offer experimentally grounded constraints for modeling rotating turbulence in non-inertial frames.

[Phys. Rev. Fluids 11, 064605] Published Fri Jun 05, 2026

Author(s): Yonghao Wen, Yingjie Wei, Cong Wang, and Jiawen Yin

The present study extends existing investigations of waves generated by granular collapse into water from two-dimensional configurations to three-dimensional axisymmetric cases, revealing both similarities and fundamental differences between them. Wave-generation mechanisms are proposed, demonstrating that the competition between horizontal and vertical granular flow governs the transition between different regimes. A predictive framework for wave classification and maximum wave amplitude estimation has been provided.

[Phys. Rev. Fluids 11, 064802] Published Fri Jun 05, 2026

Author(s): Dušan Božić, Anubhav Dwivedi, and Mihailo R. Jovanović

Subcritical transition in shear flows arise from the interplay between linear non-modal amplification and nonlinear interactions, yet their quantitative connection remains unresolved. We bridge this gap by deriving a framework from the Navier–Stokes equations, in which a forcing-amplitude expansion links oblique disturbances to finite-amplitude streaks consistent with direct numerical simulations. This hierarchy shows that the same resolvent structure governing linear amplification organizes the dynamics at all orders in the perturbation series. Breakdown of this series marks the onset of secondary instability, providing a quantitative bridge between non-modal growth and classical transition theory.

[Phys. Rev. Fluids 11, 063901] Published Thu Jun 04, 2026

Author(s): Fabio Guglietta, Martino Andrea Scarpolini, Francesco Viola, and Luca Biferale

Blood flow in the human heart is far from a smooth stream: it is a rapidly changing, intermittent motion shaped by moving walls, valves, and pulsatile forcing. By following Lagrangian tracers through a patient-specific simulation of the left heart, this study reveals where and when turbulent fluctuations become most intense. The results show that Lagrangian statistics can expose chamber-specific flow signatures and detect the enhanced intermittency produced by a stiffened aortic valve, opening a route toward sharper assessment of pathological cardiac flows.

[Phys. Rev. Fluids 11, 064604] Published Thu Jun 04, 2026

Author(s): Antoine Parrenin, Cees van Rijn, and Daniel Bonn

The characteristic fanning out of spray clouds, whether spraying perfume or spray painting, is familiar. We studied spray cloud formation for parallel jet nozzles as a function of the pressure of the surrounding air. Our microfabricated nozzles with parallel 4μm holes produce multiple microjets; we find that these form conical spray clouds via air friction through a Kelvin-Helmholtz instability. As a consequence, if the air pressure is lowered in the transparent vacuum chamber in which we perform our experiments, the spray cloud disappears altogether. As shown in the figure, below a critical air pressure characteristic of the instability, the jets then simply propagate in straight lines.

[Phys. Rev. Fluids 11, L062301] Published Thu Jun 04, 2026

Author(s): Daisuke Noto and Hugo N. Ulloa

The Oberbeck–Boussinesq (OB) approximation underpins much of our understanding of thermally driven flows, yet its validity in coldwater systems remains largely unexplored. Using numerical simulations of ice-bounded horizontal and vertical convection, we show that temperature-dependent material properties significantly modify flow structures and global transport, even where density variations are weak. In some cases, they induce anomalous reversals between warm and cold circulations, leading to O(10%) errors in predicted heat fluxes and ice melt rates, highlighting the non-negligible role of thermophysical variability in cryospheric waters.

[Phys. Rev. Fluids 11, 063501] Published Wed Jun 03, 2026

Author(s): Paolo Botticini, Davide Picchi, and Pietro Poesio

Elongated bubbles in microchannels offer a promising yet still poorly quantified route to enhance convective heat transfer. We develop a one-dimensional model capturing the interplay between advection, diffusion, viscous dissipation, and wall heat flux in the thin film around the bubble. The results reveal scaling laws for the Nusselt number, linking thin-film flow dynamics directly to heat transfer efficiency.

[Phys. Rev. Fluids 11, 063602] Published Wed Jun 03, 2026

Author(s): Haozhe Geng, Wen-Li Chen, Hui Li, and Donglai Gao

Granular flows interacting with obstacles are central to geophysical hazard mitigation, yet the post-impact evolution on horizontal run-out zones remains underexplored. This experimental study reveals a converging granular front formed downstream of a single cylinder along with volume‑dependent regime transitions from shock‑induced bifurcation to rapid stabilization. Scaling laws for front velocity, run up height, and centroid displacement demonstrate that initial column geometry and basal friction dominate over obstacle size and particle diameter. These findings decouple local flow perturbations from bulk deposition, providing predictive insights for designing barriers in confined terrains.

[Phys. Rev. Fluids 11, 063801] Published Wed Jun 03, 2026

Author(s): Subhajyoti Sahoo and Ameeya Kumar Nayak

Electroosmotic transport in soft microchannels is often modeled when more often the channel geometry was fixed, but the wall deformation and surface forces strongly influence the flow in confined gaps. A nonlinear lubrication framework is developed for a constricted compliant microchannel, coupling with the Helmholtz–Smoluchowski slip, electric-field focusing, Kirchhoff–Love wall bending, and DLVO disjoining pressure. It is identified that the stiff-wall, compliance-limited, and small-gap saturation regimes provided the scaling laws which relates the throughput analysis and deformation to curvature, wall stiffness, surface conduction, and intermolecular forces.

[Phys. Rev. Fluids 11, 064201] Published Tue Jun 02, 2026

Author(s): Sunand Bhattacharjee, Sangtae Kim, and Vivek Narsimhan

Ferrofluid droplets deform under the competing action of flow, surface tension, and magnetic stresses, making ferrofluid emulsions promising magnetically tunable complex fluids. We develop an analytical small-deformation theory for droplets in general linear flows and uniform magnetic fields. The theory captures the coupling between flow and field, predicting shape evolution, droplet breakup, and the rheology of dilute emulsions.

[Phys. Rev. Fluids 11, 063601] Published Mon Jun 01, 2026

Author(s): Aliénor Rivière, David Fabre, Jacques Magnaudet, and François Gallaire

We study the linear dynamics of an incompressible gas bubble in a biaxial straining flow, characterized by two stretching and one compressing directions, in the presence of finite inertial effects. The system undergoes a saddle-node bifurcation and exhibits strongly different equilibrium shapes when varying the Ohnesorge number comparing viscous and capillary effects. Linear stability analysis reveals the rich dynamics of the system. Bubbles are found to be significantly more stable in biaxial than in uniaxial flows, which may explain why turbulent breakup mainly occurs in uniaxial regions despite biaxial regions being more common.

[Phys. Rev. Fluids 11, 064001] Published Mon Jun 01, 2026