New Papers in Fluid Mechanics

Author(s): Luiz Eduardo Czelusniak, Tim Niklas Bingert, Stephan Simonis, Alexander J. Wagner, and Mathias J. Krause

An analytical solution based on a diffuse-interface model is presented for an isothermal evaporation problem at subsaturated vapor pressure. The macroscopic equations are derived from the free-energy formulation widely used in the lattice Boltzmann literature, distinguishing our approach from conven…

[Phys. Rev. E 113, 045103] Published Fri Apr 10, 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): Rongji Hu, Zhikang Huang, Geng Zhao, Xue-Lu Xiong, Feng Liu, Jian Fang, and Yi Zhou

The generation of skin friction in a spatially evolving turbulent boundary layer at a Mach number Ma∞=2.9 is analyzed using direct numerical simulation (DNS). Particular attention is paid to clarifying the impact of the turbulent/nonturbulent interface (TNTI) height on the skin friction. In contrast…

[Phys. Rev. E 113, 045102] Published Tue Apr 07, 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

Author(s): Eric Ibarra, Fabien Candelier, and Gautier Verhille

From previous studies on rigid isotropic particles, one might expect that heavy particles would be centrifuged out of vortices. However, during experimental runs, we observed thin, heavy, flexible discs trapped in stable orbits near a vortex core. By reconstructing their three-dimensional shape and motion, we show how deformability and anisotropy alter the classical force balance. The results raise new questions about how form and flexibility impact transport in vortical flows.

[Phys. Rev. Fluids 11, 044302] Published Mon Apr 06, 2026

Author(s): Kirill Goncharuk, Saichand Chowkampally, Yuri Feldman, and Oz Oshri

The relaxation of a buckled elastic sheet in a fluid involves a balance between bending, inertia, and hydrodynamic forces. We show that a minimal inviscid model predicts both the oscillation frequency about the stable mode and the growth rate of unstable modes, in agreement with more general viscous simulations. The framework also captures the temporal transition from unstable to stable configurations.

[Phys. Rev. Fluids 11, 044401] Published Mon Apr 06, 2026

Author(s): Zishuo Han, Weiyu Shen, and Yue Yang

We model turbulence using coherent vortices distributed within a multiscale statistical framework, termed woven turbulence, which naturally captures key turbulence features. Based on explicitly controllable vortices, we find that the scale-independent hierarchical vortex density corresponds to the −5/3 law of the energy spectrum, while the Reynolds-number-independent total vortex density corresponds to the intermittent scaling of the structure function. Woven turbulence also serves as a fast turbulence synthesis method, requiring only the Taylor-Reynolds number as input and exhibiting extremely low computational cost comparable to the random Fourier modes method.

[Phys. Rev. Fluids 11, 044602] Published Mon Apr 06, 2026

Author(s): Prem Chand Chandolu and Balachandra Suri

Horizontally driven shallow electrolyte flows are widely employed laboratory analogs of oceanic and two-dimensional flows. Although previous studies investigated the presence of three-dimensional circulations within the bulk of turbulent shallow flows, relatively little attention was paid to whether the fluid layer thickness itself remains spatiotemporally uniform. In this study, we report experimental measurements of free-surface deformations in shallow flows. For certain Reynolds number and fluid layer height combinations that characterize the flow, we show that the free surface undergoes significant deformation, thereby rendering an otherwise shallow flow geometrically three-dimensional.

[Phys. Rev. Fluids 11, 044801] Published Mon Apr 06, 2026

Author(s): Qiwei Chen and C. Ricardo Constante-Amores

Rayleigh–Bénard convection is a canonical system for studying turbulent heat transport, yet controlling it at high Rayleigh numbers remains computationally prohibitive. Here, we combine data-driven manifold dynamics with reinforcement learning to construct a reduced-order environment that enables efficient training of control policies. When deployed in direct numerical simulations, the learned strategies achieve up to 23% reduction in heat transfer by stabilizing near-wall dynamics and suppressing plume emission. This work establishes a scalable and physically interpretable route to controlling high-dimensional turbulent flows.

[Phys. Rev. Fluids 11, 044903] Published Mon Apr 06, 2026

Author(s): Githin Tom Zachariah and Harry E. A. Van den Akker

The Lattice Boltzmann Method (LBM) exploits its nearly incompressible nature to relate local density to pressure, avoiding iterative Poisson solvers. However, this pressure–density coupling makes robust extension of LBM to the Two-Fluid equations particularly challenging. In this work, we propose two complementary approaches to address this problem: a mixture model for dilute suspensions prioritizing computational efficiency, and a well-balanced formulation employing a pressure-free LBM with an explicit Poisson solver for maximum accuracy. Both methods are validated on standard benchmarks and isotropic turbulent flows, demonstrating accuracy and robustness across challenging flow regimes.

[Phys. Rev. Fluids 11, 044904] Published Mon Apr 06, 2026

Author(s): Marco Raiola and Jochen Kriegseis

Advective flows are often characterized by wavepackets. Hilbert proper orthogonal decomposition (HPOD) extracts these coherent structures from flow field data by exploiting their representation as modulated traveling waves. HPOD is a complex valued extension of proper orthogonal decomposition, where the analytic signal is obtained via a Hilbert transform applied either in time (conventional HPOD) or along the advection direction (space-only HPOD). Both HPOD formulations yield equivalent decompositions for advecting wavepackets. The resulting modes exhibit amplitude and frequency modulation in space and time, enabling instantaneous, local flow analysis.

[Phys. Rev. Fluids 11, 044905] Published Mon Apr 06, 2026

Author(s): Ankit Gautam and Tim Berk

The decay of turbulent kinetic energy is strongly influenced by large-scale coherent structures. Using a synthetic-jet-driven turbulence facility and the Proper Orthogonal Decomposition (POD) method, we show that slowly decaying modes persistent across repeated experiments bias the observed decay rates. Removing these modes reveals a stochastic turbulence field with decay consistent with classical theory. This framework helps resolve discrepancies in reported decay rates and distinguishes whether variations arise from specific coherent modes or changes in the underlying stochastic turbulence.

[Phys. Rev. Fluids 11, 044906] Published Mon Apr 06, 2026

Author(s): Niccolò Tonioni, Lionel Agostini, Franck Kerhervé, Laurent Cordier, and Ricardo Vinuesa

Sparse-sensing reconstruction of turbulent flows remains challenging due to high sensor requirements and poor fidelity near solid interfaces. VIVALDy, a machine learning framework, addresses these limitations through a hybrid β-Variational Autoencoder-Generative Adversarial Network (β-VAE-GAN) and a bidirectional transformer to compress flow fields into a compact latent space and predict temporal evolution from minimal inputs. Masked convolutions are used to enhance fidelity at solid boundaries. Validated against experimental data for a moving cylinder, the framework reconstructs diverse fluid-structure interaction regimes using only cylinder displacement.

[Phys. Rev. Fluids 11, 044902] Published Fri Apr 03, 2026