Physical Review Fluids

Author(s): Manthan Verma, Abhishek K. Jha, Shashwat Nirgudkar, and Mahendra K. Verma

For isotropic magnetohydrodynamic (MHD) turbulence, we employ high-resolution numerical simulations and compute the energy spectra and fluxes, as well as the structure functions, of Elsässer variables. While the competing spectral indices 5/3 and 3/2 are too close, the 5/3 index still provides a better fit to the energy spectra. More importantly, the structure functions strongly support the Kolmogorov-like phenomenology. Additionally, the energy fluxes in imbalanced MHD are consistent with the predictions of the Kolmogorov-like model. The figure shows normalized cross helicity of 0.65.

[Phys. Rev. Fluids 11, 043702] Published Tue Apr 21, 2026

Author(s): Armin Kalita, Bryan Oller, Thomas Paula, Alexander Bußmann, Sebastian Marte, Gabriel Blaj, Raymond G. Sierra, Sandra Mous, Kirk A. Larsen, Xinxin Cheng, Matt J. Hayes, Kelsey Banta, Stella Lisova, Peter Nguyen, Serge A. H. Guillet, Divya Thanasekaran, Silke Nelson, Mengning Liang, Stefan Adami, Nikolaus A. Adams, and Claudiu A. Stan

Optical images of transparent objects depend in a complicated way on their three-dimensional properties, which made it difficult to simulate such images accurately. Using ray tracing with calibrated illumination, we simulated with high fidelity images of drops with complex shapes, and images of pressure waves inside drops. The simulated images can be used to visualize, validate, and refine fluid dynamics models. They can also be used to determine multiple three-dimensional properties from experimental images.

[Phys. Rev. Fluids 11, 044908] Published Mon Apr 20, 2026

Author(s): Yali Kedem, Bimalendu Mahapatra, and Evgeniy Boyko

Viscoelastic flows through narrow, nonuniform geometries are common in engineering and biological systems, yet the pressure drop behavior of such fluids remains poorly understood. We develop a theoretical model for the flow of an Oldroyd-B fluid in slowly varying constrictions, deriving closed-form expressions for the elastic stresses and pressure drop valid for all Deborah numbers in the ultra-dilute limit. Our theory is in excellent agreement with numerical simulations and reveals key differences between constrictions and contractions, including a plateau in the pressure drop at high Deborah numbers and a significantly shorter relaxation length in the exit channel of the constriction.

[Phys. Rev. Fluids 11, 043303] Published Mon Apr 20, 2026

Author(s): Jingyu Cui, Xiang Zhu, Yiting Zhang, Zuchao Zhu, and Yuzhen Jin

We perform a comprehensive numerical study of standard, inverted, and wall-mounted flag models to reveal how flag-induced dynamics and vortex organization control thermal transport. The results identify distinct vortex-generation mechanisms for each configuration and map their high-efficiency regimes in the parameter space of bending stiffness and Reynolds number. These findings clarify the thermo-hydraulic performance limits of flexible flags and provide guidance for designing efficient passive heat transfer enhancers.

[Phys. Rev. Fluids 11, 044103] Published Fri Apr 17, 2026

Author(s): Bérengère Dubrulle, Antoine Barlet, Amaury Barral, Adam Cheminet, Guillaume Costa, Pietro Dragoni, Abhishek Harikrishnan, Adrien Lopez, Kirone Mallick, and Quentin Pikeroen

[Phys. Rev. Fluids 11, 049901] Published Fri Apr 17, 2026

Author(s): Manoj Mahawar, Bharat Soni, and Ameeya kumar Nayak

The purpose of the work is to understand the coupled influence of fluid and arterial wall viscoelasticity on wave dynamics, flow impedance, and energy dissipation in a compliant artery. Most theoretical models simplify this coupling by assuming Newtonian flow or purely elastic vessel walls. This study presents a comprehensive model for detailed profiling of vascular mechanics that utilizes physiological arterial parameters to assess the frequency-dependent impedance and energy dissipation behavior within the fluid-structure model.

[Phys. Rev. Fluids 11, 043101] Published Thu Apr 16, 2026

Author(s): Mateus M. Teixeira, Daniel O. A. Cruz, and Fabio Ramos

Traditional heat transfer models for shear-thinning fluids often lack the physical depth to fully capture their complex turbulent transport mechanisms. This study introduces a robust phenomenological model for power-law fluids in pipe flow, integrating Kolmogorov’s theory into an extended Prandtl-Taylor analogy. Furthermore, the introduction of a flow-independent Power-Law Prandtl number decouples the fluid’s intrinsic thermal properties from flow kinematics. The resulting correlation offers superior predictive accuracy and deeper physical insight.

[Phys. Rev. Fluids 11, 043302] Published Thu Apr 16, 2026

Author(s): Lihui Liu, Bohan Jiang, Yufeng Cheng, Runze Zhang, Yongwei Liu, Bijiao He, and Peichun Amy Tsai

Electric fields strongly elongate ionic liquid droplets in flight, but have little effect on their impact dynamics. Experiments show that despite pronounced deformation induced by Maxwell stresses, the splashing threshold and maximum spreading factor remain nearly unchanged, revealing that high viscosity suppresses electrohydrodynamic coupling during impact.

[Phys. Rev. Fluids 11, 043602] Published Thu Apr 16, 2026

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