Physical Review Fluids

Author(s): Juan Pimienta and Jean-Luc Aider

A new method is proposed to detect rare events in a shear flow. Using Live Optical Flow Velocimetry (L-OFV), it becomes possible to monitor a flow over extended periods (hours or even days) based on quantitative measurements and predefined criteria. Once these criteria are met (typically large standard-deviation excursions in velocity probes), the time history of the 2D velocity field is recorded before and after the event. After 1.5 hours of live monitoring of a backward-facing-step flow, a single extreme event, deep in the velocity-distribution tails, was found. Analysis of the time-resolved 2D velocity fields revealed a strong upstream-directed jet burst piercing the recirculation region.

[Phys. Rev. Fluids 11, 044605] Published Thu Apr 16, 2026

Author(s): Bao Chen, Yitong Fan, Zifei Yin, and Weipeng Li

Rectangular exhaust nozzles are an attractive option in the design of high-speed propulsion systems. This study investigates the effects of V- shaped trailing edges (VTEs), a feature that improves stealth performance, on the flow and noise radiation of a hot over-expanded rectangular jet. Results show that the VTEs can effectively suppress the screech tone and overall sound pressure levels in the upstream and downstream directions. This study also demonstrates that the energy redistribution during wave interactions is modulated by the VTEs, providing an inherent explanation for the screech reduction.

[Phys. Rev. Fluids 11, 044606] Published Thu Apr 16, 2026

Author(s): A. G. Balasubramanian, A. Cremades, R. Vinuesa, and O. Tammisola

Accurate reconstruction of near-wall turbulence from limited wallmeasurements remains a central challenge in non-intrusive flow sensing, especially because conventional learning approaches often sacrifice small-scale fidelity. Building on recent data-driven advances, this study shows that a spectrally informed composite loss can markedly outperform standard mean-squared-error training for reconstructing velocity fluctuations from wall-shear and pressure signals. The method improves statistical and spectral accuracy, preserves fine-scale energy, and remains robust under noisy and coarse inputs, strengthening the case for practical turbulence sensing with neural networks.

[Phys. Rev. Fluids 11, 044907] Published Thu Apr 16, 2026

Author(s): Reda Tiani and Laurence Rongy

Chemical reactions in liquid solutions can generate self-sustained Marangoni flows driven by concentration gradients of reacting species. A nonequilibrium regime emerges involving the interplay of hydrodynamics and chemistry. Here, we show how differential diffusion shapes complex spatiotemporal dynamics by driving more extrema (2 or more) in the surface tension profiles and more convection rolls/vortices in the bulk. A striking example is the occurrence of spatial oscillations of surface tension in the strongly coupled regime. As a response to the formation of an extremum, we compute the delay time required for a roll to emerge from the continuity and tangential stress balance equations.

[Phys. Rev. Fluids 11, 044002] Published Wed Apr 15, 2026

Author(s): Zhecheng Liu and Jeff D. Eldredge

We propose a transformer-based reinforcement learning framework to learn an effective control strategy for regulating aerodynamic lift in arbitrary gust sequences via pitch control, showing that this approach can be successfully applied to disturbed flows. By using two machine learning techniques, pretraining and transfer learning, we also show that the approach can extend control policies to regimes far from the training regimes, such as arbitrarily long gust sequences. We also investigate the impact of pivot point location and show that quarter-chord pitching control can achieve superior lift regulation with substantially less control effort compared to mid-chord pitching control.

[Phys. Rev. Fluids 11, 044102] Published Wed Apr 15, 2026

Author(s): Daniel G. Boettger, Shane R. Keating, Michael L. Banner, Russel P. Morison, and Xavier Barthélémy

We examine an ensemble of numerically simulated breaking surface gravity waves and show that the inception of breaking can be characterized by the maximum local interface angle. In our simulations that include surface tension effects, we find that breaking inception occurs when the local interface angle exceeds 60°; a value twice that reported in previous studies without surface tension. We explore this result in the context of the commonly utilized kinematic inception parameter and show that these two indicators of breaking inception are related through the relative flux of energy into the wave crest.

[Phys. Rev. Fluids 11, 044803] Published Wed Apr 15, 2026

Author(s): Federico Lanza, Gaute Linga, Fabian Barras, and Eirik G. Flekkøy

An instability may arise when a hot viscous fluid enters a thin gap and cools through heat transfer to a colder surrounding environment. In this paper, we investigate this mechanism in the small Biot number regime, where cooling through the plates is weak but acts over sufficiently long times that the temperature becomes nearly uniform across the gap. From numerical simulations we show that fingering instabilities emerge in response to small inlet perturbations within a range of Péclet numbers and viscosity contrasts. From linear stability analysis we find the dispersion relation and quantify how the fastest growth rate and corresponding wavenumber depend on the global parameters.

[Phys. Rev. Fluids 11, 044101] Published Tue Apr 14, 2026

Author(s): Rauoof Wani and Sanat Tiwari

Turbulence in viscoelastic media is typically associated with polymeric fluids, where elasticity drives chaotic flows even at low Reynolds numbers. Here, we demonstrate that strongly coupled plasmas, despite lacking molecular chains, exhibit intermittent viscoelastic turbulence arising from long-range inter-particle interactions. Using large-scale three-dimensional molecular dynamics simulations, we uncover a cascade of kinetic and elastic energy with steeper power-law scaling than Kolmogorov k−5/3 and intermittency. These results establish dusty plasmas as a microscopic platform for exploring viscoelastic turbulence beyond conventional fluid systems.

[Phys. Rev. Fluids 11, 043301] Published Mon Apr 13, 2026

Author(s): Tristan Aurégan, Noé Daniel, Megan Mazzatenta, and Luc Deike

When bubbles burst at the surface, they eject droplets through the formation of a fast upwards jet. We study how this jet is modified when bubbles are grouped together in rafts at the surface, and find that the presence of these neighbors strongly reduces the size of the ejected droplets and increases their upwards velocity. This effect significantly broadens the drop size distribution of the whole raft and shifts the peak towards smaller sizes.

[Phys. Rev. Fluids 11, 043601] Published Mon Apr 13, 2026

Author(s): Weiyu Shen, Yuchen Ge, Zishuo Han, Yaomin Zhao, and Yue Yang

Wall-bounded turbulence exhibits coherent vortical structures whose geometry and multiscale organization remain difficult to capture in physics-based models. We construct turbulence fields as ensembles of hierarchically organized hairpin vortex packets with height-dependent core size. The model quantitatively reproduces statistical and structural features of high-Reynolds-number turbulence, including both attached and detached motions. It further elucidates how vortex geometry and packet organization govern these features, while enabling rapid initialization of fully developed turbulence at substantially reduced cost.

[Phys. Rev. Fluids 11, 044604] Published Mon Apr 13, 2026

Author(s): Dongheyu Zhang, Junkang Mao, Peng Zhang, John P. Verboncoeur, and Yangyang Fu

Laser-sustained plasma (LSP) is a novel light source for bright-field wafer defect inspection in chip manufacturing, but the inherent spatiotemporal instabilities severely limit performance. Through experiments and multiphysics modeling, this work reveals that these periodic fluctuations originate from buoyancy-driven vortex ring dynamics. A generalized scaling law incorporating the gas density ratio is established for accurate frequency prediction, demonstrating that the Prandtl and Péclet numbers govern the oscillation threshold and patterns. These findings provide a mechanistic framework for the development of stable LSP light sources.

[Phys. Rev. Fluids 11, 044701] Published Mon Apr 13, 2026

Author(s): Jie Sun, Yicun Wang, Shumeng Xie, Salim M. Shaik, and Huangwei Zhang

Building on prior studies of obstacle–detonation interactions, this work uses two-dimensional detailed-chemistry simulations to examine how obstacle configurations affect detonation attenuation and flame acceleration. Increased dispersion enhances attenuation by fragmenting the front and leads to distinct reinitiation modes compared to concentrated obstacles. With extended obstacle sections, propagation transitions from quasi-detonation to choking, governed by a critical blockage ratio that decreases with increasing cell width. A scaling is proposed to predict regime transitions and capture the balance between shock attenuation and flame acceleration.

[Phys. Rev. Fluids 11, 043201] Published Thu Apr 09, 2026

Author(s): Feng Ren, Yuanpu Zhao, Jian Song, Boo Cheong Khoo, Yongdong Cui, Zhaokun Wang, and Dong Song

Deep reinforcement learning (DRL) for active flow control in turbulent regimes has been challenging due to prohibitive computational costs. This study overcomes this barrier by integrating a GPU-accelerated lattice Boltzmann solver with a two-stage exploration strategy, making DRL feasible for turbulent flow applications. For the canonical case of flow past a circular cylinder, the DRL-guided controller reduces drag by 55% and lift fluctuation by 26%, through significantly modifying the wake dynamics and turbulent features. Follow-up tests demonstrate that online-smoothed actuation performs as effectively as high-frequency inputs, offering practical advantages for real-world implementation.

[Phys. Rev. Fluids 11, 043903] Published Wed Apr 08, 2026

Author(s): Siyi Li, Zihao Zhu, Lei Xie, Yaguang Xie, Ruonan Wang, Qiang Du, and Junqiang Zhu

Under transient conditions, the evolution of flow in the rotor-stator cavity of an aero-engine differs markedly from the steady state. Using theory together with three-dimensional direct numerical simulations, we capture the nonlinearity and unsteady behavior in the transient evolution of rotating cavity flows. For a laminar enclosed rotor-stator cavity, the transient process primarily generates and dissipates circular waves whereas a turbulent one features small-scale fragmented vortical structures. This study elucidates three-dimensional transient evolution and flow structures in rotating cavities, providing a foundation for further investigations of transient rotating cavity flows.

[Phys. Rev. Fluids 11, 043904] Published Wed Apr 08, 2026

Author(s): M. Etchevest, P. Dmitruk, S. Karmakar, B. Semin, R. Godoy-Diana, and J. E. Wesfreid

Transition to turbulence in wall-bounded shear flows is often explained through the self-sustaining process proposed by Waleffe, where streaks, streamwise vortices, and streak waviness interact nonlinearly. Using direct numerical simulations of plane Couette–Poiseuille flow near transition, we examine how streak waviness relates to the underlying roll structures. The results show that, once the rolls reach sufficient amplitude, the waviness of the streaks scales quadratically with the rolls, clarifying a key nonlinear step of the self-sustaining process in this asymmetric shear flow.

[Phys. Rev. Fluids 11, 044603] Published Tue Apr 07, 2026

Author(s): Rundong Zhou, Adrien Lefauve, Roberto Verzicco, and Detlef Lohse

What bridges convection and stratified turbulence? Using direct numerical simulations, we reveal that in highly turbulent stratified inclined duct (SID) flow, these two phenomena can coexist within a single canonical system. At sufficiently large Reynolds number, SID undergoes a transition to the ultimate regime of turbulent convection, marked by the enhanced transport scaling Nu~Ra1/2. The transition coincides with the onset of turbulent boundary layers and is subcritical and hysteretic, as expected for the non-normal-nonlinear route to turbulence in shear flows.

[Phys. Rev. Fluids 11, 044802] Published Tue Apr 07, 2026

Author(s): Talha Mushtaq and Maziar S. Hemati

Spatially localized flow perturbations that maximize perturbation-energy amplification can reveal underlying drivers of flow instability. In this paper, we show that such spatially localized perturbations can be found by solving a particular sparse optimization problem and propose an efficient iterative method for doing so. Our approach is demonstrated on a subcritical plane Poiseuille flow, wherein we find that a subset of the perturbations identified by our method yield a comparable degree of energy amplification as their global counterparts.

[Phys. Rev. Fluids 11, 043901] Published Mon Apr 06, 2026

Author(s): Martin Oberlack, Kilian Vinzenz Wilhelm, Simon Görtz, Johannes Conrad, Alparslan Yalcin, Lara De Broeck, and Yongqi Wang

We revisit Squire’s theorem, a fundamental concept in hydrodynamic stability theory, but only valid for temporal modes, and extend it to spatiotemporal modes. This extension reveals a new class of subcritical oblique modes in which three-dimensional disturbances can become unstable at lower Reynolds numbers than their two-dimensional equivalents. While individual modes are unphysical, their superposition within a framework such as Briggs’ theory yields finite-energy perturbations. The theory provides a framework to describe spatially growing oblique structures, such as those observed in transitional shear flows.

[Phys. Rev. Fluids 11, 043902] Published Mon Apr 06, 2026

Author(s): Charul Gupta, Venkata Sai Anvesh Sangadi, Lakshmana Dora Chandrala, and Harish N Dixit

Experiments and numerical simulations of flow near a moving contact line are presented for dynamic contact angles exceeding 90°. High-resolution PIV and interface tracking deliver simultaneous measurements of velocity fields, interface shapes, and interfacial speeds across low to moderate Reynolds numbers. A central finding is the pronounced slowing down of fluid particles along the interface as they approach the contact line, providing direct experimental evidence toward resolving the classical singularity. Complementary VOF simulations with a variable-slip model reproduce the observations and demonstrate that such simulations can resolve detailed flow fields with experimental fidelity.

[Phys. Rev. Fluids 11, 044001] Published Mon Apr 06, 2026

Author(s): Gunnar G. Peng, Ehud Yariv, and Ory Schnitzer

This study investigates shear-driven flow over a microstructured surface of zero-thickness ridges separating rectangular grooves infused with a relatively low-viscosity lubricant. Asymptotic analysis in that limit reveals that viscous resistance is dominated by a boundary layer about the ridge tips that is exponentially small in the viscosity ratio μ≪1, resulting in a surprising μ−1/2 scaling for the effective slip length.

[Phys. Rev. Fluids 11, 044201] Published Mon Apr 06, 2026