New Papers in Fluid Mechanics

Author(s): Fumiya Tokoro, Hideki Takayama, Shinji Deguchi, Andreas Zöttl, and Daiki Matsunaga

How do planar beating microswimmers discover efficient swimming gaits under local energetic limits? Using reinforcement learning on a discretized bead–bend–spring filamentous microswimmer with locally constrained torques, we reveal emergent waveforms (frequency, amplitude, wavelength) set by a three-way competition between active torques, elastic stiffness, and the action-update interval. Our work offers a new framework for how local constraints determine optimum swimming patterns for undulatory locomotion.

[Phys. Rev. Fluids 11, 023102] Published Mon Feb 09, 2026

Author(s): Nihal Tawdi, Christophe Almarcha, and Michael Le Bars

Intermingling between buoyancy induced by a density gradient and externally imposed turbulence on propagation of a reactive interface is investigated through an autocatalytic reaction forming a thin front in an aqueous incompressible medium. Turbulence generated by oscillating grids, either spatially decaying or nearly homogeneous, allows flow effects to be isolated. Measurements with velocimetry and fluorescence reveal both the classical Huygens-type propagation and a reactive mixing regime where turbulent advection ignites dispersed reactions. Minute density variations are shown to influence front dynamics, highlighting a tight coupling between chemical kinetics and turbulent transport.

[Phys. Rev. Fluids 11, 024604] Published Mon Feb 09, 2026

Author(s): Tanu Singla, Jean-Baptiste Gorce, and Eric Falcon

Wave turbulence describes the dynamical properties of random nonlinear wavefields in infinite systems. Here, we experimentally investigate finite-size effects on gravity-capillary wave turbulence, using local magnetic forcing to generate a random, homogeneous wavefield – unlike previous studies that relied on oscillating tanks where global forcing dominates. We observe a smooth transition from continuous to discrete wave turbulence with increasing confinement, as finite-size effects weaken three-wave resonant interactions. This study bridges the gap between idealized infinite systems and confined environments, offering new insights into the role of boundaries in wave turbulence.

[Phys. Rev. Fluids 11, 024801] Published Mon Feb 09, 2026

Author(s): Dabao Li, Lang Qin, Zhigang Zuo, and Guangzhao Zhou

A chain of ascending bubbles can occasionally form stable, regular, and aesthetically striking patterns on a liquid’s free surface: a captivating phenomenon that also poses a fundamental challenge in fluid mechanics. This work establishes a framework linking the pattern morphology to the local dynamic interplays between the bubbles, the free surface, and the surrounding liquid flow. A heuristic model is proposed and validated against simulations and existing experimental data. The present study provides insights into understanding, designing, and controlling collective behaviors in broader self-organized systems.

[Phys. Rev. Fluids 11, 023602] Published Fri Feb 06, 2026

Author(s): Ming Hong, Beichen Tian, Qin Wu, and Biao Huang

Cavitation around marine propellers operating in nonuniform wake flows spans multiple spatial and temporal scales, yet its relationship to pressure pulsations is poorly understood. This study integrates pressure measurements with high-speed imaging and digital inline holography to resolve the evolution from large-scale sheet cavities and vortex tubes to intermediate-scale cloud clusters and microbubbles. We show that distinct cavitation regimes have characteristic spectra, with cloud cavitation producing the strongest multiscale coupling. By reconstructing phase-resolved microbubble statistics, a bubble model is developed that accurately reproduces mid- and high-frequency pressure components.

[Phys. Rev. Fluids 11, 024303] Published Fri Feb 06, 2026

Author(s): Georgy Zinchenko and Jörg Schumacher

Compressible turbulence adds further mechanisms of anomalous energy dissipation in comparison to its incompressible counterpart. They are caused by pre-shocks and shocks. To quantify these contributions, we extend the framework of Duchon and Robert to the compressible flow case and analyze anomalous dissipation for one-dimensional gas dynamics examples.

[Phys. Rev. Fluids 11, 024603] Published Fri Feb 06, 2026

Author(s): Mengfan Xu, Bowen Zhu, Zhanzhou Hao, and Bo Yin

Inspired by stiffness modulation in biological fish and advances in smart materials, we study the propulsion of a self-propelled swimmer with spatially nonuniform and dynamically varying stiffness. We demonstrate how different stiffness modulation strategies affect swimming performance and internal actuation requirements. By introducing a cycle-averaged equivalent stiffness, the required actuation strength can be consistently scaled across different modulation patterns.

[Phys. Rev. Fluids 11, 023101] Published Thu Feb 05, 2026

Author(s): Qingyang Meng and Chihyung Wen

This study investigates the characteristics of detonation structure and droplet behavior in n-heptane spray detonations where droplets experience a thermodynamic critical event, using the Eulerian-Lagrangian method. The droplet behavior at the critical state in the post-detonation area is captured and the resulting influence on the detonation structure and propagation is emphasized. The contribution of the droplet at the critical state to detonation is quantitatively estimated by the critical droplet fraction.

[Phys. Rev. Fluids 11, 023201] Published Thu Feb 05, 2026

Author(s): Bowen Du, Qi Li, Mingwei Ge, Xintao Li, and Yongqian Liu

In mesoscale modeling, wind turbines are commonly parameterized as single-column momentum sinks and sources of turbulence kinetic energy, which can lead to substantial errors when turbines are located near grid boundaries. This study proposes a Gaussian-based multi-column spatial distribution method that analytically allocates sink and source terms across multiple grid columns. When implemented within the Fitch wind farm parametrization, the proposed method significantly improves the modeling accuracy of wind farms, particularly when turbine rotors span multiple grid columns. The method provides a robust and physically consistent improvement for future mesoscale wind-farm simulations.

[Phys. Rev. Fluids 11, 023801] Published Thu Feb 05, 2026

Author(s): Zaicheng Zhang, Zeyu Wang, and Abdelhamid Maali

Air–water interfaces are often assumed to be either mobile or rigid, yet in practice their mechanical response is governed by a subtle interplay between hydrodynamic stresses, trace surfactants, and capillary deformation. Using dynamic colloidal-probe AFM, we probe the frequency-dependent viscoelastic response of an air–water interface at micrometer to nanometer separations. We show how surfactant transport induces a transition from mobile to immobilized behavior, while hydrodynamic pressure generates an additional capillary stiffness at small gaps. Together, these effects reveal a unified visco-capillary framework for interfacial rheology beyond purely viscous descriptions.

[Phys. Rev. Fluids 11, 024002] Published Thu Feb 05, 2026

Author(s): Xander M. de Wit, Hessel J. Adelerhof, André Freitas, Rudie P. J. Kunnen, Herman J. H. Clercx, and Federico Toschi

We study homogeneous isotropic turbulence laden with a very large number of small bubbles. Using an efficient four-way coupled point-particle method, this work quantifies when and how bubble–bubble interactions and feedback on the fluid become relevant. While the back-reaction of microbubbles leaves the turbulent energy budget largely unchanged under typical circumstances, excluded-volume interactions can significantly modify Lagrangian bubble statistics, suppressing preferential concentration once vortex filaments are filled up. These results identify limits of validity for one-way coupling and reveal new ways bubbles can probe coherent structures in turbulence.

[Phys. Rev. Fluids 11, 024602] Published Thu Feb 05, 2026

Author(s): F. M. Rocha, H. Lhuissier, Y. Forterre, and B. Metzger

Despite the burst in studies on shear-thickening (ST) suspensions over the past decade, a simple and yet fundamental question has remained unanswered: what is the the drag on a solid object moving in such medium? By addressing this problem, we reveal a novel stress-focusing phenomenology in discontinuous ST suspensions, which we term jamming rays. Key features of these anisotropic and intermittent structures, such as their propagation direction, trigger force, and characteristic width, cannot be reconciled within the current understanding of ST suspensions. This work therefore opens a new avenue in the field by questioning the dynamics of these suspensions in nonuniform and unconfined flows.

[Phys. Rev. Fluids 11, 023302] Published Wed Feb 04, 2026

Author(s): Shunta Kikuchi and Hiroshi Watanabe

Molecular dynamics simulations show how the Rayleigh-Plateau instability of a nanoscale liquid filament evolves with and without imposed interfacial perturbations between two immiscible liquids of equal viscosity. For a single-mode perturbation, the growth rate deviates from classical theory at small radii but converges to macroscopic predictions for thicker filaments. Without imposed perturbations, thermally induced breakup has a power-law dependence of breakup time on minimum filament radius. These results demonstrate that continuum theory remains valid down to scales of about 15 molecular diameters, while thermal fluctuations are increasingly important in thinner liquid filaments.

[Phys. Rev. Fluids 11, 023901] Published Wed Feb 04, 2026

Author(s): Xiaohui Meng and Ewe-Wei Saw

Predicting particle collisions in turbulence is critical for applications from cloud formation to industry, yet a model for mean radial relative velocity (MRV) remains elusive. Using direct numerical simulations, we investigate the motion of colliding particles and establish the relationship between MRV at collisional distances, and the particle Stokes and flow Reynolds numbers. A resonant length scale, the spatial scale where inertial particles capture momentum from turbulent flow, is introduced. By finding the relationship between this scale and particle and flow parameters, we provide inputs for a robust framework to predict particle MRV at collisional scale across a range of conditions.

[Phys. Rev. Fluids 11, 024301] Published Wed Feb 04, 2026

Author(s): Adam Jiankang Yang, Mary-Louise Timmermans, and Mona Rahmani

Kelvin–Helmholtz (KH) instability can dramatically reshape how particles settle and spread in stratified shear flows. Using direct numerical simulations with Lagrangian tracking, we show that KH billows can either slow, trap, or strongly accelerate particle settling depending on particle size, with small particles settling up to seven times faster than their Stokes velocity. The results reveal how preferential sampling of coherent flow structures and limited encounter times with turbulence fundamentally alter particle dispersion and sediment transport in mixed layers.

[Phys. Rev. Fluids 11, 024302] Published Wed Feb 04, 2026

Author(s): Serge Mora, Martine Le Berre, and Yves Pomeau

The free fall of a sphere is a seminal problem in fluid mechanics that becomes remarkably complex as its velocity approaches the “drag crisis” regime. This study demonstrates that intermittency in the drag coefficient at this critical stage renders the temporal evolution of the velocity intrinsically unpredictable. By combining numerical simulations with a stochastic two-state model, we reveal huge velocity dispersions. These findings highlight the necessity of statistical descriptions for bodies falling at high Reynolds numbers, with direct implications for ballistics and sports aerodynamics.

[Phys. Rev. Fluids 11, 024401] Published Wed Feb 04, 2026

Author(s): Outi Supponen

Experimental high-speed visualization techniques are evolving rapidly and provide valuable tools for learning about ultrafast bubble dynamics that cause unwanted but also desirable damage, such as cavitation and acoustically driven bubbles and droplets relevant for biomedical applications. This article offers my personal perspective on the quest to illuminate the hidden physics of externally stimulated bubbles that have a remarkable ability to focus energy. The focus is given to advanced experimental techniques including ultrafast videomicroscopy and synchrotron x-ray imaging to characterize bubble jetting, vapor bubble nucleation and shape deformations of periodically driven bubbles.

[Phys. Rev. Fluids 11, 023601] Published Tue Feb 03, 2026

Author(s): Mahesh Kumar, Harshad Sanjay Gaikwad, and Pranab Kumar Mondal

We present a theoretical investigation of the mixing dynamics of two constituent fluids within a soft rotating microfluidic channel. We solve a coupled system of transport equations, governing the mixing dynamics in this endeavor, with the associated symmetric and antisymmetric boundary conditions u…

[Phys. Rev. E 113, 025101] Published Mon Feb 02, 2026

Author(s): J. Tauber, J. Asnacios, and L. Mahadevan

With experiment and theory we consider the branching morphodynamics of injecting a shear-thinning liquid from a point source to a point sink in a Hele-Shaw cell filled with a yield-stress fluid which has a sudden transition in its response as the local stress crosses a threshold. As the injection rate is increased an abrupt transition occurs, from a direct path connecting source to sink at low flow rates, to a rapid branching morphology at high flow rates, eventually converging to the sink. We show that global constraints imposed by boundary conditions, including source-sink separation, injection rate, and plate properties, shape branching morphodynamics and determine the transition point.

[Phys. Rev. Fluids 11, 023301] Published Mon Feb 02, 2026

Author(s): Zhanwen Wang, Michael J. Miksis, and Petia M. Vlahovska

The dynamics of a spherical particle undergoing Quincke electro-rotation in the vicinity of a planar electrode are investigated. Increasing the electric field induces a transition from steady rolling to periodic and then chaotic oscillations, with the onset threshold depending on the particle–surface gap and particle inertia. When allowing for normal motion of the particle the electrostatic attraction reduces the gap, which in turn suppresses chaotic behavior and reestablishes a steady rolling state.

[Phys. Rev. Fluids 11, 023701] Published Mon Feb 02, 2026