Physical Review Fluids

Author(s): Chulan Hu and Xuebo Li

Wall-attached motions leave an intermittent footprint on the near-wall flow, but conventional coherence analyses reveal only its time-averaged behavior. Using synchronized two-point hot-wire measurements in a high-Reynolds-number turbulent boundary layer, we develop a wavelet-based framework that resolves this wall imprint in time and scale while recovering established mean coherence scaling. The results show that the characteristic persistence scale grows with wall distance even as coherence at that scale weakens, and that strongly wall-imprinted events exhibit systematic wall-normal changes in scale-local energy transfer and energy distribution.

[Phys. Rev. Fluids 11, 084609] Published Mon Aug 24, 2026

Author(s): Georg Rempfer, Mae Nesenberend, Chengkai Zhu, Bart Stam, Debabrata Panja, and Joost de Graaf

Numerical studies of viscoelastic Stokes flow often regularize the stress singularities predicted by the Oldroyd-B model, obscuring their underlying structure. We introduce an efficient FFT-based projection solver for incompressible flow and validate it in the classical four-roll mill. By analyzing the polymeric stress directly in Fourier space, we quantify its power-law scaling with resolution and determine the critical Weissenberg number for steady-state convergence without adding artificial stress diffusion.

[Phys. Rev. Fluids 11, 084901] Published Mon Aug 24, 2026

Author(s): A. Bongarzone, C. Content, D. Sipp, and C. Leclercq

Resolvent analysis is a cornerstone tool for predicting how flows respond to external forcing, but for unsteady flows the choice of linear operator is not obvious. The common mean-flow resolvent, linearized about the time-averaged flow, can misidentify the dominant receptivity mechanisms, whereas the statistically optimal mean resolvent correctly captures physically relevant phenomena such as the vortex pairing in jets presented here. This work introduces a projection method that enables mean resolvent analysis at low computational cost without resorting to adjoint equations about the unsteady attractor, thereby opening a path toward more complex flows.

[Phys. Rev. Fluids 11, 083903] Published Mon Aug 17, 2026

Author(s): Gourab Chakraborty, Vinod Narayanan, and Uddipta Ghosh

Reactive fronts in porous media are often destabilized by concentration dependent viscosity of the constituent fluids, leading to viscous fingering. These processes are known to be strongly influenced by hydrodynamic dispersion, originating from incomplete mixing at the pore scale. Yet, their impact and the resulting instabilities remain poorly understood. This study combines transient and quasi-steady-state linear stability analysis to reveal how hydrodynamic dispersion and diffusivity contrasts govern the growth and onset of instabilities, providing new physical insights, with potential applications in contaminant remediation, enhanced oil recovery, and carbon sequestration.

[Phys. Rev. Fluids 11, 083904] Published Mon Aug 17, 2026

Author(s): Binjian Ma, Xiaoyu He, Yuexuan Mao, Zixuan Wang, Yonggang Zhu, Huizhu Yang, and Xiaozhou He

Classical similarity theory describes the far field of a laminar jet, but not how a finite Poiseuille inlet loses its memory and reaches that state. We develop a self-consistent two-mode analytical model that predicts this pre-asymptotic evolution without empirical fitting. The theory uncovers a universal Reynolds-scaled centerline decay and shows that the transition length grows linearly with Reynolds number, while reproducing full velocity profiles for both round and slot jets in close agreement with Navier–Stokes simulations.

[Phys. Rev. Fluids 11, 084101] Published Mon Aug 17, 2026

Author(s): Tanmay Agrawal, Vamsi Krishna Chalamalla, and Narsing Kumar Jha

Air curtains restrict buoyancy-driven exchange through building doorways, but sealing effectiveness saturates near about 80 to 85% and the transport pathways fluid takes to leak through have remained unclear. We combine large-eddy simulation with Lagrangian particle tracking to follow individual fluid parcels, classifying their trajectories into three pathways: a gravity current active only before the curtain establishes, and two turbulent-entrainment routes that dominate afterward. Once the curtain is established, the residual leakage is shown to be governed by entrainment at the jet interface rather than by buoyancy.

[Phys. Rev. Fluids 11, 084504] Published Mon Aug 17, 2026

Author(s): Xianliang Chen, Zhiye Zhao, Jianping Gan, and Lin Fu

The velocity law of the wall is a well-known law for wall turbulence. In compressible turbulence, the temperature law of the wall is also of interest, but its overall accuracy is inferior to its velocity counterpart. We propose to construct the compressible law of the wall for heat energy using total enthalpy. A semilocal total enthalpy transformation of no fitted parameters is constructed for channel flows, which is structurally analogous and comparable in accuracy to the Trettel–Larsson velocity transformation. This new transformation can potentially serve as a wall model for energy equations to accurately predict the enthalpy or temperature in compressible turbulence.

[Phys. Rev. Fluids 11, 084608] Published Mon Aug 17, 2026

Author(s): Charlie J. Lloyd and Robert M. Dorrell

The offshore wind industry is expanding in deep, seasonally stratified waters, where infrastructure-induced mixing may alter ocean dynamics and ecosystems. We present the first fully structure-resolved direct numerical simulations of stratified flow past a vertical cylinder as an idealized model for flow interactions with offshore wind foundations. We identify two distinct wake regimes: a weakly stratified regime characterized by a narrow turbulent wake, and a strongly stratified regime characterized by thermocline-spanning recirculation cells and stationary internal waves, providing a new mechanism for far-field energy transport and a possible explanation for wake persistence discrepancies.

[Phys. Rev. Fluids 11, 084802] Published Mon Aug 17, 2026

Author(s): Schahin Akbari, Mostafa Noori, Yongqi Wang, and Martin Oberlack

This study investigates nonaxisymmetric shape oscillations of an inviscid droplet. A highly accurate Galerkin framework is extended to fully three-dimensional droplet oscillations, and modal coupling is examined for different initial configurations, beginning with four nonaxisymmetric initial shapes (see Figure). The results show that the droplet keeps the symmetries of its initial shape and velocity throughout the oscillation. Only those modes that exhibit all symmetries of the initial configuration are excited. Conversely, modes which violate the symmetries are not excited.

[Phys. Rev. Fluids 11, 083602] Published Fri Aug 14, 2026

Author(s): Victor Botez, André Giesecke, Caroline Nore, Loïc Cappanera, and Frank Stefani

In preparation for the DRESDYN precession dynamo experiment, we numerically investigate how wall material properties impact the growth of magnetic modes driven by a precessing flow. We identify two oscillating magnetic modes - dipolar and quadrupolar – whose competition explains the drastic changes in dynamo thresholds for different types of boundaries. For given hydrodynamic parameters, these modes are paramount for a comprehensive understanding of all electromagnetic configurations, including the realistic modeling of the upcoming first liquid sodium campaign.

[Phys. Rev. Fluids 11, 083701] Published Fri Aug 14, 2026

Author(s): Sanghasri Mukhopadhyay, Séverine Millet, Bastien Di Pierro, and Asim Mukhopadhyay

Gravity-driven thin films laden with soluble surfactants play a central role in coating technologies and microfluidic systems, where reduced-order models are widely used to predict interfacial dynamics. Some weighted-residual formulations, however, introduce spurious interfacial mass growth, violating total surfactant conservation. We resolve this inconsistency by developing a conservative weighted-residual model that consistently couples wall slip, adsorption-desorption, and the Marangoni effect while rigorously preserving total surfactant mass. The resulting framework provides physically consistent predictions of instability onset, nonlinear wave dynamics, and surfactant transport.

[Phys. Rev. Fluids 11, 084004] Published Fri Aug 14, 2026

Author(s): Wenhao Cheng and Zeng Liu

Wind-driven wave evolution is commonly viewed as a two-stage process: initial wave growth followed by frequency downshift. Here, we reveal a previously unrecognized intermediate stage in the evolution of capillary–gravity waves under wind forcing and dissipation. This stage is characterized by coupled three- and four-wave near-resonant interactions that generate new wave components, broaden the spectrum, and may reduce total wave energy. These findings constitute a major step forward in understanding the evolution of wind waves from small ripples (2.5 cm) to larger-scale waves.

[Phys. Rev. Fluids 11, 084801] Published Fri Aug 14, 2026

Author(s): Írio M. Coutinho, Liam C. Morrow, and Scott W. McCue

Interfacial Hele-Shaw flows often involve fingering instabilities, tip-splitting phenomena and striking pattern formations. This study revisits a simplified model that characterizes the complexity of these fingering patterns and identifies some universal features. We test this model using fully nonlinear numerical simulations and find that it is very effective at predicting near-universal properties of the fingering patterns for one-phase flows with a sufficiently small surface tension parameter. For larger values of this parameter and for two-phase flows, there are discrepancies between the model and our observations, which we explain by studying the morphology of the advancing fingers.

[Phys. Rev. Fluids 11, 084003] Published Thu Aug 13, 2026

Author(s): Haowei Qiu, Adam Jiankang Yang, and Baafour Nyantekyi-Kwakye

Ocean Alkalinity Enhancement (OAE) is a promising marine carbon dioxide removal strategy involving the release of alkaline particles into the ocean. However, its effectiveness depends on how these particles disperse. This study uses high-resolution simulations to show that collective convective instabilities, rather than individual Stokes settling, fundamentally govern particle settling. These instabilities can accelerate vertical particle transport by up to two orders of magnitude, significantly limiting horizontal spread and surface residence time. These fundamental fluid-dynamic constraints provide essential guidance for optimizing future OAE deployments.

[Phys. Rev. Fluids 11, 084503] Published Thu Aug 13, 2026

Author(s): Shreyashri Sarkar and Rishita Das

Small-scale intermittency is conventionally modeled by power laws of higher-order moments, which include both kinematic and turbulence-driven effects. By using Kullback-Leibler divergence relative to a Gaussian random field, we isolate purely turbulence-induced intermittency, which scales logarithmically with the Taylor Reynolds number. This reveals an emergent symmetry between the turbulence intermittency of dissipation rate and enstrophy, showing that enstrophy appears more intermittent for purely kinematic reasons. The work establishes an information-theoretic framework for characterizing the intermittency and uncertainty of small-scale turbulence.

[Phys. Rev. Fluids 11, 084605] Published Thu Aug 13, 2026

Author(s): Xingguang Zhou, Dalin Zhang, Xinyu Li, Wentao Ma, Hongxing Yu, Wenxi Tian, Suizheng Qiu, and Guanghui Su

Mixed convection for heavy liquid metals is still terra incognita in many aspects, because of the complex flow mechanism, strong thermal diffusivity, and optical opacity. Understanding the flow organization is key to turbulence research and practical engineering. We use high-fidelity scale-resolving numerical simulations to explore the unique large-scale longitudinal roller structures in mixed convection, while also considering the low Prandtl number effect of heavy liquid metals. A new physical interpretation for the slope modulation phenomenon of the mean velocity profile is established, which is expected to give new insights into wall function modeling in mixed convection.

[Phys. Rev. Fluids 11, 084606] Published Thu Aug 13, 2026

Author(s): Xiantao Fan, Meet Hemant Parikh, Yi Liu, Xin-Yang Liu, Junyi Guo, Meng Wang, and Jian-Xun Wang

Most studies of turbulent wall pressure reduce its dynamics to wavenumber-frequency spectral descriptions, leaving the instantaneous, spatially evolving pressure field largely inaccessible to experiments and prohibitively expensive simulations. We introduce a probabilistic generative approach that reconstructs full spatiotemporal wall-pressure fields from sparse surface measurements and a low-cost mean-pressure descriptor. Combining patchwise neural representations with latent diffusion, the model adapts to unseen sensor layouts and pressure-gradient regimes without retraining. It recovers coherent structures, temporal evolution, and key turbulence statistics.

[Phys. Rev. Fluids 11, 084607] Published Thu Aug 13, 2026

Author(s): Albert Dai and Yu-Lin Huang

When gravity currents converge inward, such as sea breezes closing in around an island or lake, their collision unfolds very differently from the situation when two gravity currents meet head-on. Using high-resolution three-dimensional simulations, this study reveals, for the first time, how such collisions generate turbulence: vorticity arises primarily through tilting of azimuthal vorticity rather than through the stretching mechanism as seen in planar collisions. The resulting eddy diffusivity data support existing mesoscale-model parameterizations used to represent gravity current collision events in atmospheric and oceanic models.

[Phys. Rev. Fluids 11, 083801] Published Wed Aug 12, 2026

Author(s): Tino Damiani, Matthew Durey, Bauyrzhan K. Primkulov, and John W. M. Bush

A millimetric droplet may walk across the surface of a vibrating liquid bath, self-propelled by its own wave field. This pilot-wave hydrodynamic system has provided the basis for the field of hydrodynamic quantum analogs, the goal of which is to redefine the boundaries between classical and quantum systems. We here deepen our understanding of pilot-wave hydrodynamics through consideration of its energetics, evaluation of the partitioning between droplet and wave energies. Photo credit: Pedro Nachbin.

[Phys. Rev. Fluids 11, 084002] Published Wed Aug 12, 2026

Author(s): D. M. Escala, I. Castaldi, and A. De Wit

Previous theoretical works showed that, in double-diffusion regimes, the onset time and mixing velocity of convective fingers are controlled by a dynamic density jump across stratified layers. Here, we experimentally validate these scalings by analyzing differential diffusion-induced convection in horizontal stratifications within a Hele-Shaw cell. Using a wide range of solute combinations and concentrations, we vary the two key parameters of the problem: the diffusion coefficient and buoyancy ratios. We show that, in both double-diffusive and diffusive-layer-convection regimes, convective dynamics are governed by dynamically generated local adverse density jumps.

[Phys. Rev. Fluids 11, 084502] Published Tue Aug 11, 2026