New Papers in Fluid Mechanics

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

Author(s): Dana L. O.-L. Lavacot, Ali Mani, and Brandon E. Morgan

This work seeks to understand the importance of nonlocality in modeling scalar transport in turbulent Rayleigh-Taylor instability (RTI) at different Atwood numbers. We apply the Macroscopic Forcing Method to determine moments of the eddy diffusivity from high-fidelity numerical simulations of RTI. We additionally present a framework for incorporating nonlocality for modeling RTI at different Atwood numbers. We find that nonlocality is important for modeling RT and appears to increase in importance with Atwood number.

[Phys. Rev. Fluids 10, 124501] Published Mon Dec 01, 2025

Author(s): Victor E. Ambruş, Elisa Bellantoni, Sergiu Busuioc, Alessandro Gabbana, and Federico Toschi

This paper presents a lattice Boltzmann model based on the vielbein formalism for simulating fluid flows on spherical surfaces. By capturing the underlying geometry of spherical surfaces, the model enables Cartesian treatment of velocity space while ensuring fluid trajectories stay confined to the manifold. Validated against exact solutions for sound and shear waves, and tested with shockwave and vortex dynamics, this approach enhances the study of geophysical flows and provides a robust framework for future turbulence modeling on curved manifolds.

[Phys. Rev. Fluids 10, 124901] Published Mon Dec 01, 2025

Author(s): Anunay Prasanna, Guillaume T. Bokman, Samuele Fiorini, Armand Sieber, Bratislav Lukić, Daniel Foster, and Outi Supponen

Perfluorohexane is a biocompatible material that serves as a liquid core for acoustically responsive agents in biomedical applications. Despite its relatively widespread usage, there is a lack of experimental data determining its thermodynamic properties. This challenges numerical simulations to pre…

[Phys. Rev. E 112, 065101] Published Mon Dec 01, 2025

Author(s): Írio M. Coutinho and José A. Miranda

In standard rotating Hele-Shaw cell flows, an initially circular fluid drop, surrounded by an outer fluid of negligible density and viscosity, is centered at the rotation axis of the cell. The interplay of centrifugal and surface tension forces leads to the emergence of intricate interfacial pattern…

[Phys. Rev. E 112, 065102] Published Mon Dec 01, 2025

Author(s): Tanya Rastogi and Om P. Suthar

When a porous layer beneath a fluid layer is heated from below, the region in which convective instability develops depends on the intrinsic properties of the coupled fluid–porous system. The present study proposes periodic heating of the superposed system, bounded by a free surface above and an impermeable surface below, to confine convective motion to a desired region and to regulate its onset without altering the system’s physical properties. The amplitude of modulated heating serves as an external control parameter, governing both the onset and the region of convection in a configuration where a thin fluid layer overlies a porous layer, allowing control without modifying the system.

[Phys. Rev. Fluids 10, 113502] Published Wed Nov 26, 2025

Author(s): M. Leonard and N. Vandewalle

On smooth surfaces, condensing droplets grow, merge, and eventually slide away. Add narrow grooves, and the same water follows a hidden path: it drains through the surface itself. Using a high-throughput condensation setup, we show that groove spacing governs the transition between droplet shedding and capillary drainage. Below a critical spacing, grooves collect and channel all water before large drops can form, offering new routes for efficient dew harvesting and cooling.

[Phys. Rev. Fluids 10, 114001] Published Tue Nov 25, 2025

Author(s): Bjarne Vincent, Daniel Henry, Abhishek Kumar, Valéry Botton, Alban Pothérat, and Sophie Miralles

In this work, we use numerical simulations to investigate the physical mechanisms at play along a laminar jet driven by an axisymmetric beam of traveling sound waves (Eckart streaming). In particular, we derive scaling laws capturing both the magnitude and longitudinal distribution of the jet velocity along its axis. These scaling laws are defined on distinct regions of the jet, ranging from regions of high acoustic forcing close to the source to forcing-free regions where the beam is fully attenuated. By highlighting the different flow regimes along the jet, these scaling laws are thus able to inform the design of experimental and industrial setups involving Eckart streaming jets

[Phys. Rev. Fluids 10, 114103] Published Tue Nov 25, 2025

Author(s): Pierre-Brice Bintein, Pierre-Yves Passaggia, Nicolas Mazellier, and Adrien Bussonnière

When immersed in water, a solid coated with a superhydrophobic surface traps an air layer, called a plastron, that shields it from liquid contact. This layer enables underwater respiration in animals and provides drag reduction, anti-corrosion, and antifouling effects. However, plastrons are sensitive to external disturbances and can destabilize. This study demonstrates how plastron acoustic resonance can be used to monitor and measure the trapped air layer volume. Validated against direct observations, the method is portable, noninvasive, and effective for studying plastron stability under realistic conditions and various flow conditions.

[Phys. Rev. Fluids 10, 114905] Published Tue Nov 25, 2025

Author(s): Louis-S. Bouchard and Seulgi Moon

Debris flows often exhibit coherent wave structures—shocklike roll waves on steeper slopes and weaker, more sinusoidal dispersive pulses on gentler slopes. Coarse-rich heads raise basal resistance, whereas fines-rich tails lower it; in gentle reaches, small-amplitude pulses can locally transport mom…

[Phys. Rev. E 112, 055112] Published Mon Nov 24, 2025