Latest papers in fluid mechanics

Author(s): Haoqi Hu, Wenli Chen, Hui Li, and Donglai Gao

Dense suspensions of finite-size particles exhibit strongly heterogeneous modulation of wall-bounded turbulence. Using interface-resolved Direct Numerical Simulations over a wide range of particle inertia, we show that low-inertia particles homogenize near-wall flow topology and restore a symmetric tear-drop structure in the Q–R plane, whereas high-inertia particles generate asymmetric wake-driven topology, suppress Reynolds stresses, and reorganize the momentum and energy budgets. These results establish a clear physical link between particle-migration-induced flow topology and the regional modulation of turbulence in dense suspensions.

[Phys. Rev. Fluids 10, 124304] Published Tue Dec 09, 2025

Author(s): Maziyar Hassanpour, Robert J. Martinuzzi, and Ugo Piomelli

In turbomachinery and aerodynamics, wake-induced transition can trigger turbulence in boundary layers, yet how wake-separated boundary layer interactions drive transitions is not well understood. We use direct numerical simulations to reveal a hybrid transition pathway — a fusion of classical separated boundary layer instability and wake-driven bypass transition — in boundary layers at moderate gap ratios. Unlike abrupt classical transitions, this process unfolds in distinct stages — linear amplification, nonlinear saturation, and turbulent breakdown — driven by coherent Λ-vortices synchronized with the wake. Our findings offer new insights for transition control in engineering systems.

[Phys. Rev. Fluids 10, 124604] Published Tue Dec 09, 2025

Author(s): Çayan Demirkır, Rui Yang, Aleksandr Bashkatov, Vatsal Sanjay, Detlef Lohse, and Dominik Krug

Early bubble release is vital in electrochemical and boiling systems. Coalescence can trigger bubble departure, but it can also leave bubbles pinned to the electrode surface. By observing the contact-line dynamics and quantifying adhesion and dissipation energies, this work identifies the threshold conditions governing this transition. The developed general energy-balance framework predicts bubble detachment in agreement with available experimental and numerical data.

[Phys. Rev. Fluids 10, 123602] Published Mon Dec 08, 2025

Author(s): Vitor H. C. Cunha, Øivind Wilhelmsen, Carlos Alberto Dorao, and Maria Fernandino

Understanding how intermolecular forces govern nanoscale wetting and phase change requires tools that can link molecular and continuum scales. This work develops a continuum framework that integrates non-local solid-fluid interactions into the Navier-Stokes-Korteweg model, enabling the study of adsorption and thin film dynamics with thermodynamic consistency from the continuum level. By incorporating these interactions directly into the free energy, the model captures near-wall density reorganization and thin film stabilization during phase change, thus providing a consistent framework for examining nanoscale interfacial dynamics while maintaining a clear connection to molecular-level physics.

[Phys. Rev. Fluids 10, 124001] Published Mon Dec 08, 2025

Author(s): Marine Aulnette, Noa Burshtein, Arash Alizad Banaei, Luca Brandt, Simon J. Haward, Amy Q. Shen, Blaise Delmotte, and Anke Lindner

This study explores the transport of microparticles in a three-dimensional stationary vortex generated in a microfluidic cross-slot geometry. Experiments and numerical simulations show that, when increasing particle diameter, particles are progressively excluded from the vortex core. Initially, small particles follow a Burgers vortex-like self-similar motion, but for larger particle diameters, deviations from this trend emerge due to fluid inertia and finite-size effects.

[Phys. Rev. Fluids 10, 124201] Published Mon Dec 08, 2025

Author(s): Daphné Lemasquerier

Turbulent zonal (east–west) jets are ubiquitous in atmospheres, oceans, and planetary interiors. Predicting their long-term nonlinear equilibration is challenging due to complex feedback effects with the underlying turbulence and waves. We address this by deriving a nonlocal closure model that parameterizes Rossby waves and their interaction with large-scale jets. Our new quasilinear model, based on a WKB expansion of the wave field, is the first purely zonal closure to naturally produce zonal jets separated by a Rhines scale. It also reproduces a transition between locally driven and globally driven jets observed in laboratory experiments.

[Phys. Rev. Fluids 10, 124802] Published Mon Dec 08, 2025

Author(s): Julie Deleuze, Ilias Sibgatullin, Philippe Odier, and Sylvain Joubaud

For a stratified fluid in a closed geometry, high amplitude internal waves can be generated by forcing global modes of the domain. These waves can then destabilize through triadic resonant instability (TRI), generating secondary waves. This experimental study, together with an interpretation based on a weakly nonlinear analysis, shows that the combination of box resonance conditions and nonlinear resonance conditions governs the nature of the secondary waves, causing in some cases a significant deviation from the internal waves dispersion relation and in general complex nonlinear interaction dynamics, with multiple pairs of secondary waves appearing dynamically.

[Phys. Rev. Fluids 10, 124803] Published Mon Dec 08, 2025

Author(s): B. Mohammadikalakoo, M. Kotsonis, and N. A. K. Doan

This work presents a real-time, model-free control framework that utilizes single-step deep reinforcement learning to suppress Tollmien-Schlichting waves in a two-dimensional boundary layer. By learning an opposition-control strategy directly from sensor feedback, the controller outperforms a classical adaptive Filtered-x Least Mean Square (FXLMS) approach in both effectiveness and robustness. The results demonstrate a compact and experimentally feasible AI-based solution for real-time control of convective instabilities.

[Phys. Rev. Fluids 10, 124902] Published Mon Dec 08, 2025

Author(s): Rahil N. Valani and David M. Paganin

Active particles are nonequilibrium entities that uptake energy and convert it into self-propulsion. A dynamically rich class of inertial active particles having features of wave-particle coupling and wave memory are walking/superwalking droplets. Such classical, active wave-particle entities (WPEs)…

[Phys. Rev. E 112, 065103] Published Mon Dec 08, 2025

Author(s): Guanghang Wang, Jingzhu Wang, Xiangyan Chen, Jianlin Huang, Guangyi Song, Qingyun Zeng, and Yiwei Wang

As a bubble oscillates close to a water surface, a new phenomenon of partial ventilation which the bubble’s exposure to the surrounding air is observed induced by the Rayleigh-Taylor instability penetrating the bubble wall. Depending on the exposure, three distinct types of bubble behaviors with decreasing dimensionless stand-off distance are summarized: (i) nonventilation; (ii) partial ventilation; and (iii) complete ventilation. The boundaries for ventilation time and stand-off distance are obtained by solving the analytical model comprising a small-amplitude model and a bubble-oscillation model, which agrees well with the experimental observations and numerical results.

[Phys. Rev. Fluids 10, 123601] Published Fri Dec 05, 2025

Author(s): Cem Bingol, Matias Duran-Matute, Eckart Meiburg, and Herman J. H. Clercx

The paper presents a study of the evolution of two-dimensional gravity currents, propagating against constant and pulsating counter flow. The effect of mean and oscillatory velocity amplitude on the gravity current evolution, the onset of interfacial shear instabilities such as Kelvin-Helmholtz billows, unstable near-bed density stratification, and the resulting density redistribution is addressed. Two non-hydrostatic processes, shear-driven Kelvin-Helmholtz billows and Rayleigh-Taylor-like overturning induced by differential advection, enhance vertical mixing and horizontal transport of dense fluid within the gravity current and are expected to affect salt intrusion in estuaries.

[Phys. Rev. Fluids 10, 123801] Published Thu Dec 04, 2025

Author(s): Ralph J. Volino and Michael P. Schultz

A method for determining the friction velocity in wall bounded flows has been extended for use with rough surfaces. The original method (Dixit et al.) is applicable to smooth wall flows, and requires only the mean streamwise velocity profile at a single location. It does not rely on any assumptions about the shape of the profile, and is applicable in both zero and non-zero pressure gradients. The new method is the same as the original, with the exception that the kinematic viscosity is replaced with an effective viscosity that is proportional to the product of the roughness height and flow velocity.

[Phys. Rev. Fluids 10, 124602] Published Thu Dec 04, 2025

Author(s): Ruibo Zhang (章瑞博), Xiaoning Wang (王小宁), Jianchun Wang (王建春), and Shiyi Chen (陈十一)

The isosurfaces of zero fluctuating streamwise velocity within the turbulent region of spatially developing compressible mixing layers are defined as the interfaces of high- and low-speed large-scale structures (LSSs). This study advances the knowledge of local flow characteristics at the interfaces of LSSs for different streamwise regions and compressibility (Mc=0.3 and Mc=0.8). For the first time, enstrophy transfer is systematically analyzed at LSS interfaces, and local topology conditioned on interface orientation is used to explain flow patterns near these interfaces.

[Phys. Rev. Fluids 10, 124603] Published Thu Dec 04, 2025

Author(s): Léo Claus, Marie Couliou, and Vincent Brion

A wind-tunnel experiment mimicking an airplane in cruise flight reveals how a wingtip vortex interacts with the nearby parallel jet depending on their mutual spacing. By tracking the wake up to 20 wingspans, the work clarifies how jet placement governs entrainment, spiraling mixing, or even trapping by the vortex core, while the vortex itself remains largely resilient. The findings show increased vortex motion downstream and the influence of the deteriorated central part of the wake on this dynamic. Besides the jet is shown to sustain increased dispersion with vortex proximity. The dataset also offers valuable benchmarks for validating numerical simulations of vortex wakes.

[Phys. Rev. Fluids 10, 124701] Published Thu Dec 04, 2025

Author(s): Soniya Kumawat, Vishnu Kumar Sahu, and Anurag Tripathi

Can we predict how mixed grains unmix themselves? A continuum model couples particle-level segregation forces with mixture rheology to capture the inherently linked evolution of flow and segregation in bi-disperse granular systems. It reveals the crucial role of composition-dependent packing arising from size disparity in accurately predicting segregation dynamics. The model successfully reproduces segregation evolution across diverse configurations, compositions, and size ratios, closely matching Discrete Element Method simulations.

[Phys. Rev. Fluids 10, L122301] Published Thu Dec 04, 2025

Author(s): Michael Ullman, Ral Bielawski, and Venkat Raman

Shock-induced breakup of liquid droplets is critical to the development of novel detonation-based propulsion devices, but the fundamental breakup processes are difficult to quantify experimentally. To address this need, this work presents three-dimensional multiphase simulations of shock-induced catastrophic droplet breakup, analyzing the droplet deformation, displacement, and distributions of secondary droplet sizes. The results agree well with existing experimental data and provide insights into how instabilities along the droplets’ surfaces help to facilitate their atomization.

[Phys. Rev. Fluids 10, 124301] Published Wed Dec 03, 2025

Author(s): Mohammad Hashemi, Saman Shalbaf, Mehdi Jadidi, and Ali Dolatabadi

Liquid jets injected into crossflows characterized by very low gaseous Reynolds numbers, low momentum flux ratios, and extreme density ratios experience intensified bending, rapid surface stripping, and early column fracture compared with classical air-flow conditions. In this regime, ligament formation becomes strongly aligned with the crossflow, and instability waves wrap around the entire jet circumference rather than remaining on the windward side. Our results show that Kelvin–Helmholtz, rather than Rayleigh–Taylor, controls the breakup dynamics, with surface wavelengths remaining independent of the Weber number.

[Phys. Rev. Fluids 10, 124302] Published Wed Dec 03, 2025

Author(s): Xiaolong Yang, WenXiao Long, Feng Xiao, Fei Li, DaPeng Xiong, HongBo Wang, PeiBo Li, and MingBo Sun

The pronounced particle streaks will be observed when particle-laden turbulent boundary layers sweep over a concave surface. Its underlying dynamical mechanism provides new insights into the interaction between turbulence and particles.

[Phys. Rev. Fluids 10, 124303] Published Wed Dec 03, 2025

Author(s): Fujihiro Hamba

A nonlocal expression for the Reynolds stress and passive vector flux was investigated using a direct numerical simulation (DNS) of homogeneous isotropic turbulence with an inhomogeneous passive vector. The Green’s function for the passive vector was evaluated to obtain the nonlocal eddy viscosity. The nonlocal expression for the passive vector flux agreed with the DNS data, and the nonlocal effects accounted for the overestimation by the local expression, as well as the phenomenon of counter-gradient diffusion. A model for the nonlocal eddy viscosity was also proposed and validated using the DNS data.

[Phys. Rev. Fluids 10, 124601] Published Wed Dec 03, 2025

Author(s): Matthew Durey and Paul A. Milewski

Subsurface variations of water density enable internal waves, which play a key role in oceanic mixing and energy transport. Internal waves are affected by resonant three-wave interactions, which, in the ocean, form only when different interfaces (i.e. vertical modes) interact. For confined basins, however, a new paradigm emerges: resonant triads may form between different “sloshing” modes at a single interface, so include only the lowest vertical mode. We characterize this abundant new class of triads for the case of two-layer flows in basins of arbitrary cross section with vertical walls and discuss the implications on inverse energy cascades and internal seiching in lakes and harbors.

[Phys. Rev. Fluids 10, 124801] Published Wed Dec 03, 2025