Physical Review Fluids

Author(s): Julien Sablon, Jérôme Fontane, Gabriele Nastro, and Laurent Joly

This study examines transient energy growth in a high-Reynolds and high-swirl numbers heavy q-vortex. Through nonmodal stability analysis, we identify optimal perturbations that produce energy amplifications far exceeding adjoint mode predictions over finite time horizons. The analysis reveals a robust three-stage transient mechanism combining pressure-induced energy transfers and a self-sustaining Rayleigh-Taylor feedback loop between radial velocity and density perturbations. This core-centered destabilization mechanism, absent in constant-density vortices, provides new physical insights into short-term energy amplification relevant to aircraft wake dispersion, mixing, and flow control.

[Phys. Rev. Fluids 11, 014703] Published Fri Jan 23, 2026

Author(s): Albert Dombret, Adrien Sutter, Baptiste Coquinot, Nikita Kavokine, Benoit Coasne, and Lydéric Bocquet

Building on a fluctuating Darcy framework, this work shows that porosity fluctuations can strongly and nontrivially reshape the hydrodynamic permeability of a porous matrix or membrane. The permeability is expressed in terms of the matrix fluctuation spectrum, revealing a “frequency‑matching” regime where solid and fluid modes resonate. Exploring different excitation scenarios – breathing matrices, phonon‑like modes and active forcing – unveils new strategies to optimize membrane separation processes and potentially bypass the usual permeability–selectivity trade‑off.

[Phys. Rev. Fluids 11, 014201] Published Wed Jan 21, 2026

Author(s): Guang-Yao Xia, Jian-Zhao Wu, Bo-Fu Wang, Kai Leong Chong, and Quan Zhou

The multistability and bifurcation in thermal vibrational convection have been systematically studied via direct numerical simulations. Two distinct states are clarified: a periodic one with single-roll dominance and higher mean heat/momentum transport, and a chaotic one with multimode interplay. Bifurcations occur primarily near St=1, where resonant sensitivity to initial conditions leads to hysteresis across varying vibrational Rayleigh number and aspect ratio. This work elucidates the underlying mechanisms of flow state transitions, providing a framework for understanding multistability and flow control in unsteady regimes.

[Phys. Rev. Fluids 11, 014401] Published Wed Jan 21, 2026

Author(s): Satori Tsuzuki

Knowing when turbulence reaches peak dissipation matters for theory and for adaptive simulation and measurement strategies. Using direct numerical simulations of the Taylor–Green vortex, we introduce a spectral diagnostic based on the curl-of-vorticity spectrum, equivalent to a k^4-weighted energy spectrum. Its peak wavenumber stabilizes before the dissipation maximum across resolutions. The resulting early-warning signal links spectral evolution to the emergence of filamentary vortical structures and can support adaptive meshing and output scheduling.

[Phys. Rev. Fluids 11, L012601] Published Tue Jan 20, 2026

Author(s): Cal J. Rising, Eric J. Ching, and Ryan F. Johnson

Three-dimensional simulations of a reacting hydrogen jet in supersonic crossflow are performed using a discontinuous Galerkin (DG) method, which is appealing for its high-order accuracy and geometric flexibility. Analysis of the coupled chemistry and compressible flow shows a predominantly non-premixed combustion mode with localized premixed regions. A key result is the accurate prediction of this configuration on a fully unstructured tetrahedral mesh, demonstrating the potential of DG methods to capture complex physics in high-speed reacting flows.

[Phys. Rev. Fluids 11, 013203] Published Fri Jan 16, 2026

Author(s): Feng Wang, Yihong Du, Xueyi Xie, Enrico Calzavarini, and Chao Sun

In this work, we experimentally investigate the freezing and ice aging dynamics in saline water under natural convection. We show that the rapid formation of a mushy ice layer is followed by desalination processes that might lead to a slow asymptotic decrease of the ice thickness. Desalination of mushy ice reduces its porosity, which alters the dynamic thermal equilibrium and ice thickness by weakening buoyancy-driven convection within mushy ice. In turn, changes in brine convection and ice thickness further affect the desalination process. The long-term dynamics can be predicted by a one-dimensional model based on appropriate parameterizations of global heat and mass transfer properties.

[Phys. Rev. Fluids 11, 013504] Published Thu Jan 15, 2026

Author(s): Loïc Rousseau, Laurence Girolami, Mohammed Boussafir, and Frédéric Risso

The dynamics of unconfined, low-inertia, fluidized beds is investigated. The fluidization velocity is well described by a universal function of the volume fraction involving a prefactor that depends on particle inertia, confinement, Reynolds number and inlet flow disturbances. Bed surface oscillations are used to probe concentration fluctuations within the suspension, revealing the role of vertical concentration waves upon the transition toward the heterogeneous regime at low concentrations.

[Phys. Rev. Fluids 11, 014303] Published Thu Jan 15, 2026

Author(s): Prasanna Kumar Billa, Cameron Tropea, and Pallab Sinha Mahapatra

A superhydrophobic sphere entering a quiescent water pool entrains an air cavity whose evolution governs its subsequent dynamics. The cavity remains axisymmetric up to the primary pinch-off, after which multiple pinch-off events occur. For lighter spheres, the entrained air volume can trigger a transition from downward penetration to upward motion due to enhanced buoyancy. Both primary and secondary pinch-offs induce abrupt buoyancy changes and force rebalancing, captured using orthogonal high-speed imaging. The coupling between cavity evolution, pinch-off dynamics, and trajectory reversal depends on impact conditions and sphere density.

[Phys. Rev. Fluids 11, 014304] Published Thu Jan 15, 2026

Author(s): Xiaohua Wu, Carlos A. Gonzalez, and Rahul Agrawal

A comprehensive dataset resulting from DNS of bypass transition in the narrow sense with inlet freestream turbulent intensity (FSTI) levels 0.75%, 1.5%, 2.25%, 3.0%, and 6.0% is reported. It is found that boundary-layer freestream scales evolve similarly to their spatially developing isotropic turbulence flow counterparts. Further, at an intermediate FSTI of 2.25%, two turbulent spot inception mechanisms coexist: the long low-speed streak primary and secondary instabilities (low FSTI) and the self-amplifying process of oblique vortex filaments interacting with a Delta-shaped low-speed patch underneath (high FSTI).

[Phys. Rev. Fluids 11, 014605] Published Thu Jan 15, 2026

Author(s): Kunihiko Taira

Small air vehicles that operate in urban canyons, around mountainous terrains, and in the wakes of marine vessels could encounter highly unsteady atmospheric conditions with relatively strong gusts. The gust ratio can exceed 1 in these extreme flight environments, making stable flight difficult, if not currently impossible. We refer to the study of aerodynamics for gust ratios over 1 as extreme aerodynamics and identify major challenges that require breakthroughs, particularly with data-driven approaches.

[Phys. Rev. Fluids 11, 014702] Published Thu Jan 15, 2026

Author(s): John M. Lawson

The widespread adoption of Lagrangian particle tracking (LPT) and Particle Tracking Velocimetry (PTV) methods motivate the reconstruction of continuous velocity fields from sparse, noisy particle tracking data. This work introduces a physics-informed Gaussian process regression (GPR) framework that incorporates mass conservation, boundary conditions, and statistical symmetries directly into the assimilation process. The method provides optimal interpolation, quantifies prediction uncertainty and estimates two-point velocity covariances. Validated across canonical turbulent flows, GPR significantly outperforms the industry standard, offering improved resolution and predictive accuracy.

[Phys. Rev. Fluids 11, 014902] Published Thu Jan 15, 2026

Author(s): Hugo Felippe da Silva Lui and William Roberto Wolf

Shock–boundary layer interactions over the convex wall of a supersonic turbine vane are explored through a detailed analysis of extreme separation bubble events. By conditionally sampling expanding and contracting bubble states and using finite-time Lyapunov exponents together with a deforming control-volume framework, this study reveals how near-wall streaks and streamwise vortices influence the separation bubble unsteadiness and the mass flux along its surface.

[Phys. Rev. Fluids 11, 013401] Published Tue Jan 13, 2026

Author(s): Rishish Mishra, Harish Pothukuchi, Harinadha Gidituri, and Juho Lintuvuori

The interface crossing behavior of a microswimmer is strongly dependent upon the capillary number (Ca), which is defined as the ratio of swimming to interfacial forces. When the interfacial forces dominate, the swimmer gets trapped. We propose a model, where the swimmers are trapped due to a wetting-induced thermodynamic potential. The translational motion of a prolate swimmer is accompanied by reorientation driven by the combined action of hydrodynamic and thermodynamic torques.

[Phys. Rev. Fluids 11, 014002] Published Tue Jan 13, 2026

Author(s): T. Preskett, M. Virgilio, P. Jaiswal, and B. Ganapathisubramani

Smooth and rough wall turbulent boundary layers often occur with external pressure gradients, which affect their development. This work presents an experimental investigation of high Reynolds number boundary layers, focusing on the effect of pressure gradient history on turbulence characteristics. Taking the turbulent spectra, we isolate both the effect of pressure gradient history and how the surface affects the response to a given pressure gradient history. The final part of this work looks at whether it’s possible to capture some of the effects on the turbulence spectra, particularly the peaks present within the spectra.

[Phys. Rev. Fluids 11, 014603] Published Tue Jan 13, 2026

Author(s): Pranav Nath and Jean-Pierre Hickey

The complexity of wall-bounded turbulent flows has given rise to a variety of models that capture the essence of this physical problem. Townsend’s Attached Eddy Model (AEM) utilizes eddies that exhibit geometric scaling with their distance from the wall. In contrast, the One-Dimensional Turbulence (ODT) model is built on a completely different set of modeling assumptions. We re-write the ODT formulation as a Markov process and simplify some modeling assumptions, which allows us to recast the equations into a form analogous to AEM. By distilling and simplifying ODT, we highlight the implicit similarities with the modeling assumptions found in AEM.

[Phys. Rev. Fluids 11, 014604] Published Tue Jan 13, 2026

Author(s): Yinghui Li, Filippo Coletti, Monika Colombo, Yingchao Meng, and Andrew deMello

In dense suspensions, both rigid particles and deformable red blood cells (RBCs) exhibit a tendency to migrate away from the walls and towards the center of the vessel in which they flow. Here we experimentally investigate the transport of microparticles along with RBCs in bifurcating vessels, which is particularly relevant for targeted drug delivery. Via high-speed imaging and Lagrangian tracking, we observe that particles marginate and form layers adjacent to the sidewalls of bifurcation, while the deformable RBCs populate the center of the vessel. Our results show that the margination behavior of spherical particles is quantitatively controlled by the RBC-to-particle volume ratio.

[Phys. Rev. Fluids 11, 013101] Published Mon Jan 12, 2026

Author(s): Mykola Stretovych, Eddy Timmermans, and Dmitry Mozyrsky

Understanding the dynamics of gas discharges is critical for numerous technological applications. While the physics of electric breakdown in gas, such as air, has been studied for many decades, the early stages of the discharge dynamics remain to be an active subject of research. In this paper we provide a simple approach that helps us understand such early stages of dynamics and explains the structure of the discharge channel at the qualitative level. Comparison with experimental data shows a good agreement of the approach with the measured characteristics, such as discharge current, at small times after the discharge initiation.

[Phys. Rev. Fluids 11, 013202] Published Mon Jan 12, 2026

Author(s): J. O. Oyero and A. De Wit

If a denser solution of a solute A lies above a less dense solution of a solute B in the gravity field, a Rayleigh-Taylor instability can trigger convective motions which favor mixing of the two fluids. We show by numerical simulations that double-diffusive effects occuring when A and B diffuse at different rates can modify the scalings of the onset time and acceleration of the instability. Moreover, the difference in diffusion of the solutes can be used to optimize mixing between the two solutions.

[Phys. Rev. Fluids 11, 013503] Published Mon Jan 12, 2026

Author(s): Zeyang Mou, Zheng Zheng, Zhen Jian, Carlo Antonini, Christophe Josserand, and Marie-Jean Thoraval

The singular collapse of a cavity can produce extremely fast and fine jets from the dynamics of larger systems. These jets have a wide range of applications, from printing technologies to cavitation bubbles or the formation of aerosols. We investigate the formation of extremely fast singular jets generated when a coaxial water‑in‑oil compound drop impacts a solid surface. Experiments and simulations reveal how cavity collapse, controlled by impact velocity and volumetric ratio, produces high‑speed jets and microdroplets. Two distinct collapse regimes emerge, governed by 1/2 and 2/3 self‑similar power laws.

[Phys. Rev. Fluids 11, 013602] Published Mon Jan 12, 2026

Author(s): Haotian Chen, Hanbing Zou, Sheng Xu, and Bing Wang

Using the stiffened-gas equation of state (SG-EOS), we extend the classical shock dynamics theory to underwater scenarios. The Chester-Chisnell-Whitham (CCW) relation and its two-dimensional characteristic relations are systematically modified. We further propose a method of designing a shock tube that transforms planar underwater shock waves into cylindrical ones with pre-set intensity and curvature. Numerical tests demonstrate that the shock intensity and curvature can be accurately controlled to match predicted values. This work provides a theoretical framework for geometric control of shock waves in compressible liquids.

[Phys. Rev. Fluids 11, 014302] Published Mon Jan 12, 2026