Physical Review Fluids

Author(s): Yuke Li and Victor Steinberg

Discovered stochastic resonance (SR) in viscoelastic inertialess channel flow at a fixed location far from inlet has Wi as control parameter (CP), the ratio of elastic stress to its relaxation. By tracking SR downstream along channel locations at Wi>Wic, we find that a SR existence range first broadens in Wi values and then remains constant until the outlet, with perturbation intensity as the second CP defining the range of SR appearance. SR existence should satisfy three conditions: chaotic streamwise and flat, weak intensity spanwise power spectra with extremely small elastic wave intensity. Thus, SR plays the key role in stochastic routes to promote sustained chaotic flow at Wi>Wic.

[Phys. Rev. Fluids 10, L081901] Published Mon Aug 25, 2025

Author(s): Tanumoy Dhar, Michael J. Shelley, and David Saintillan

We investigate the stability of two configurations: a passive viscous Newtonian droplet immersed in an active nematic liquid crystal, and an active nematic droplet surrounded by a passive layer, both under circular confinement. Our results reveal how capillary, active, elastic, and viscous stresses interact to govern droplet dynamics. These findings may inform our understanding of diverse biological systems featuring interfaces between active and passive fluids, from droplets in bacterial suspensions to subcellular compartments within the cytoplasm and cell nucleus.

[Phys. Rev. Fluids 10, 083103] Published Thu Aug 21, 2025

Author(s): Yuejia Zhang, Nicholas J. Moore, and Jinzi Mac Huang

Heavy fluid sinks while light fluid rises – these are the very basics of convection. Here we derive a set of reaction-diffusion equations from the governing dynamics of convection, whose solutions reveal complex flows that display both order and chaos. By tuning the strength of buoyancy (Rayleigh number), a series of transitions between conducting, circulating, and reversing flows appears, leading to an enhanced heat transfer (Nusselt number). This model also reveals a ¼ power-law scaling between the Nusselt and Rayleigh numbers that is verified by both numerical simulations and asymptotic analysis, bringing us one step closer towards understanding the complex physics of convective heat transfer.

[Phys. Rev. Fluids 10, 083501] Published Thu Aug 21, 2025

Author(s): Zhe Feng

This study provides a plausible explanation for the longstanding discrepancy between experiments and simulations of electroconvective flows by systematically incorporating Navier-slip boundary conditions. It demonstrates that partial slip can significantly lower both linear and nonlinear instability thresholds and enhances electric transport efficiency. A previously unreported transition from convective to zonal flows is also uncovered, offering a physical mechanism for the saturation of electric transport observed in experiments. These findings establish a predictive framework linking boundary slip to the stability and turbulent transport characteristics of electroconvective flows.

[Phys. Rev. Fluids 10, 083701] Published Thu Aug 21, 2025

Author(s): Anubhav Dubey, Constantin Habes, Holger Marschall, and Sakir Amiroudine

Binary fluids with miscibility gap exhibit property variation in response to a stimuli, making them useful for applications like targeted drug delivery, protein extraction, and others. We present a novel phase-field approach to track the continuous evolution of such fluid pairs from initially immiscible/partially miscible state to miscible state with a tunable miscibility framework. The model is used to investigate classical single mode Rayleigh-Taylor instability. Three qualitatively distinct growth patterns of the imposed perturbation are found based on the Atwood and Weber numbers. A secondary instability of Kelvin-Helmholtz rolls is found to be dependent on system temperature.

[Phys. Rev. Fluids 10, 084004] Published Thu Aug 21, 2025

Author(s): Gabriel Marchetti and Pablo D. Mininni

Three dimensional rotating turbulent flows can sometimes transfer energy from the injection scale to the largest scale available in the domain, generating large coherent structures in the process. For intermediate values of the Rossby number, however, a flux–loop mechanism can be achieved, in which the energy transferred upscale is arrested at a scale smaller than the domain size. This mechanism also produces coherent structures similar to the vortex crystals usually found in many physical systems. In this work we study these structures via direct numerical simulations, focusing on their evolution and morphology, and we identify their key controlling parameters.

[Phys. Rev. Fluids 10, 084603] Published Thu Aug 21, 2025

Author(s): Ranit Mukherjee, Zih-Yin Chen, Xiang Cheng, and Sungyon Lee

Particle rafts — fluid-fluid interfaces covered with particles — form wrinkles and folds when compressed, like a crumpled piece of paper. Nevertheless, composed of discrete particles, rafts under compression can also fail by expelling single particles, which cannot be explained by existing continuum models. We develop a composite model that incorporates the contact line dynamics of individual particles to fully describe both the elastic and granular responses of the compressed particle rafts. By using this new model framework, we also demonstrate the control of raft behaviors by tuning the physicochemical properties of individual particles.

[Phys. Rev. Fluids 10, 084003] Published Wed Aug 20, 2025

Author(s): Harshal S. Raut, Jung-Hee Seo, and Rajat Mittal

Wave-powered propulsion using flapping foils is a relatively new idea with great potential, but the performance of these systems depends strongly on foil geometry and pitch control. Using high-fidelity fluid–structure simulations, this study examines pitch-limiting strategies and foil shapes that can maximize thrust across a range of sea states. A simple pitch angle-limiter offers performance benefits especially in low amplitude waves, while a thin elliptical foil outperforms other foil shapes. These results provide practical design guidelines for efficient wave-powered flapping foil propulsion systems.

[Phys. Rev. Fluids 10, 084705] Published Tue Aug 19, 2025

Author(s): Samaresh Midya and Sean Symon

This study describes the wake behind a multi-wake model using three mean velocity components, obtained using stereo-particle image velocimetry, at a Reynolds number of 5.64×105. The near-wake is dominated by a separation bubble that forms immediately downstream of the model. Shear layers detached from the model periphery morph into a single connected bound vortex that stays inside the separation bubble. The far-wake dynamics are dominated by four corner vortices that originate from each slant edge, and they remain coherent several body lengths behind the vehicle. The surface slant angles significantly influence the evolution of the wake and have important implications for drag reduction.

[Phys. Rev. Fluids 10, 084706] Published Tue Aug 19, 2025

Author(s): Aidan Hunt, Brian Polagye, Ari Athair, and Owen Williams

The efficiency of an array of turbines operating in a channel is influenced by how much of the channel the array occupies, represented as the blockage ratio. In this work, the performance and near-wake flow field of a cross-flow turbine array are evaluated across a range of blockage ratios through laboratory experiments. An analytical linear momentum actuator disk model is found to be predictive of the measured velocity of the fluid that bypasses the array. When the array performance is scaled by the bypass velocity in a manner inspired by Maskell’s bluff-body theory, self-similar performance is observed across blockage ratios, highlighting the salient dynamics of highly-confined turbines.

[Phys. Rev. Fluids 10, 084802] Published Tue Aug 19, 2025

Author(s): Arupjyoti Das, Manohar Sharma, Avishek Ranjan, and Mahendra K. Verma

A coherent vortex column in rotating turbulence forms, bursts apart due to instabilities, and reforms again — a cycle driven by a tug-of-war between the destabilizing effect of elliptical instability and the stabilizing influence of rotation. Using Fourier-space analysis, including ring spectra and mode-to-mode energy transfer, we identify a forward energy cascade and the activation of vertical modes (kz = 2, 3) as precursors to bursting, indicating how spectral energy transfer drives the collapse and reformation of the structure.

[Phys. Rev. Fluids 10, 084803] Published Tue Aug 19, 2025

Author(s): Patrick M. McGah

The work considers the normal mode stability of plane Poiseuille flow under stable density stratification. The problem is analyzed at low Peclet numbers representing liquid metal flows of interest in advanced nuclear reactor designs. The eigenvalue problem is solved numerically, and a perturbation series is also developed for small stratification. Numerical and perturbation series results indicate that stratification has a purely stabilizing effect on the normal modes. All normal modes are found to be stable when a modified Richardson number, R = Ri × Pe, is greater than about 0.33.

[Phys. Rev. Fluids 10, 083901] Published Mon Aug 18, 2025