Latest papers in fluid mechanics

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

Author(s): M. Rubio, S. Rodríguez-Aparicio, M. G. Cabezas, J. M. Montanero, and M. A. Herrada

Tip streaming in a coflowing device is probably the simplest way to generate quasi‑monodisperse droplets that are much smaller than the device’s fluid passages. We show that flow stability cannot be determined from the linear stability analysis of the steady microjetting mode but from the linear superposition of decaying eigenmodes triggered by an initial perturbation. The red line in the image corresponds to a direct numerical simulation of an asymptotically stable microjetting. The experiment and simulation show the perturbation growth leading to jet breakup. These results call into question the validity of linear stability analysis applied to coflowing and similar configurations.

[Phys. Rev. Fluids 11, 024001] Published Mon Feb 02, 2026

Author(s): Yunpeng Wang, Huiyu Yang, Zelong Yuan, Zhijie Li, Wenhui Peng, and Jianchun Wang

A machine-learning-based surrogate model is proposed for the large-eddy simulation of three-dimensional turbulent flows over curved boundaries with strong flow separation. The model, termed as hybrid U-Net and Fourier neural operator (HUFNO), is based on an integrated framework of convolutional neural networks and Fourier neural operators, tailored for problems involving mixed periodic and non-periodic boundary conditions. The HUFNO model is validated in the fast prediction of turbulent dynamics of periodic-hill flow, with transferable accuracy to unseen initial conditions, Reynolds numbers, and hill shapes.

[Phys. Rev. Fluids 11, 024601] Published Mon Feb 02, 2026

Author(s): A. Shrestha, E. Kirkinis, and M. Olvera de la Cruz

Electrolyte-filled channels with modulated wall charge distribution subjected to an applied DC electric field form time-independent vortices whose sense of circulation is determined by the field direction [Phys. Rev. Lett. 75, 755 (1995)]. In this paper, we show that an electrolyte in a channel or c…

[Phys. Rev. E 113, 015106] Published Fri Jan 30, 2026

Author(s): Yi Zhang, Apurav Tambe, and Zhao Pan

The maximum droplet volume that a fiber can retain is a classic problem in the physics of droplet-fiber interactions, with established results for horizontal and Λ-shaped bent fibers. However, this question has remained less explored for V-shaped bent fibers, despite their relevance to fog harvesting and condensation technologies. Here, we develop a free-energy- based analytical model to predict the maximum droplet volume on V-shaped fibers and validate it experimentally using multiple liquid-fiber pairs. We reveal a non-monotonic dependence of the maximum droplet volume on the fiber opening angle, identifying a transition regime that facilitates droplet detachment.

[Phys. Rev. Fluids 11, 013604] Published Thu Jan 29, 2026

Author(s): Santiago Caro, Riccardo Artoni, Patrick Richard, Michele Larcher, and James T. Jenkins

Sheared polydisperse granular materials exhibit a subtle balance between size segregation and diffusion that governs their transverse dynamics. Combining annular shear cell experiments with discrete numerical simulations, we investigate how confinement, shear localization, granular temperature, and mixture composition control segregation in nonuniform flows. Beyond the classical gravity-driven mechanism, we identify inverse and horizontal segregation modes that emerge from flow kinematics and geometry. These mechanisms hinder complete segregation, explaining the persistence of mixing in steady-state granular systems.

[Phys. Rev. Fluids 11, 014305] Published Thu Jan 29, 2026

Author(s): Linhao Li, Md M. A. Sohag, Kan Liu, Jian Wu, and Xiufeng Yang

This work investigates the dynamics of dual-drop impact on a solid surface, encompassing both simultaneous and nonsimultaneous side-by-side impact of equal-sized drops, as well as successive impact of unequal-sized drops. Numerical simulations are performed using smoothed particle hydrodynamics meth…

[Phys. Rev. E 113, 015105] Published Thu Jan 29, 2026