Physical Review Fluids

Author(s): Simon M. Finney, Matthew G. Hennessy, Andreas Münch, and Sarah L. Waters

Analytical solutions for the deformation, translational velocity, and rotational velocity of a linear poroelastic particle in an unbounded Stokes flow are provided. The solutions are specialized to the cases of shear and Poiseuille flows. Surprisingly, the rotation of the particle is not influenced by its poroelastic nature.

[Phys. Rev. Fluids 10, 093603] Published Tue Sep 23, 2025

Author(s): Xiao Shao, Marian Albers, Matthias Meinke, and Wolfgang Schröder

We examine the effect of compressibility on drag reduction in turbulent boundary layers actuated by spanwise traveling transversal surface waves. Wall-resolved simulations are performed at Mach numbers M1=0.2 and M2=0.7 over the same actuation space. The results show that drag reduction is greater at higher Mach number, but at M2=0.7 the increased wave speed induces spanwise shock waves. These shocks disrupt turbulence, redistribute turbulent kinetic energy, and alter skin-friction contributions. The findings highlight the trade-off between enhanced drag reduction and reduced actuation efficiency in compressible flows.

[Phys. Rev. Fluids 10, 094603] Published Tue Sep 23, 2025

Author(s): Rupayan Jana and Shubhadeep Mandal

We investigate the low-Reynolds-number hydrodynamics of rigid circular and spherical particles near a plane wall in a heterogeneous viscous environment comprising both ambient and disturbance viscosity fields. Focusing on the resistance problem, we theoretically and numerically compute the forces and torques acting on the particle. Our results demonstrate that viscosity gradients induce novel hydrodynamic cross-couplings in near-wall particle motion, which are also directly reflected in the resulting trajectories. These findings have potential implications for controlled transport, sorting, and separation in microfluidic applications.

[Phys. Rev. Fluids 10, 094204] Published Mon Sep 22, 2025

Author(s): Tristan P. W. Bunnage, Douglas R. Brumley, and Edward M. Hinton

The paper examines rectilinear two-dimensional miscible viscous fingering in response to both injection and withdrawal of low viscosity fluid. Whether or not substantial fingering occurred during the injection controls the dynamics in the withdrawal period. At the end of injection, the fingers generally have a tip with a localized peak in concentration of the low viscosity fluid. This region then changes direction upon withdrawal. The low viscosity tip retraces the original finger because flow there is preferential as the viscosity is lower relative to the ambient fluid.

[Phys. Rev. Fluids 10, 094501] Published Mon Sep 22, 2025

Author(s): Tao Shu, Yuan Xue, Abhishek Saha, Jialong Huo, Hua Zhou, Zhuyin Ren, and Chung K. Law

Characterization of the turbulent flow field in a constant-pressure, dual-chamber, expanding flame apparatus is presented, based on high-resolution particle imaging velocimetry. Turbulent flame speeds were measured for C2H4/air and NH3/CH4/air mixtures across turbulent Reynolds number ranges of 29–2706 and 69–2560, respectively. An extended scaling correlation for turbulent flame speed is proposed, applicable to both corrugated flamelets and thin reaction zones regimes. The proposed model demonstrates improved accuracy, with the mean absolute percentage error between experimental and predicted values of 7.8% for C2H4/air and 8.5% for NH3/CH4/air flames, demonstrating a comparative advantage over existing scaling models.

[Phys. Rev. Fluids 10, 094602] Published Mon Sep 22, 2025

Author(s): Minki Kim, Shahaboddin Alahyari Beig, and Eric Johnsen

The inertial collapse of a cavitation bubble concentrates potential energy within the bubble. This process redistributes energy between the bubble and the surrounding liquid, while also emitting a shock wave. In the incompressible limit, bubble dynamics are governed by the driving pressure, but at high collapse speeds, compressibility effects become critical. We present a theoretical framework that corrects radiated energy estimates, derives closed-form expressions for bubble energy and volume at collapse, and relates shock pressure directly to governing parameters. Our results provide a foundation for describing more complex systems, such as bubble clouds and bubbles near boundaries.

[Phys. Rev. Fluids 10, 093602] Published Fri Sep 19, 2025

Author(s): Charles Paul Moore, Hiba Belkadi, Brouna Safi, Gabriel Amselem, and Charles N. Baroud

Cells and other soft particles are often forced to flow in confined geometries in both laboratory and natural environments, where the elastic deformation induces an additional drag and pressure drop across the particle. We start by measuring the pressure drop across a single spherical hydrogel particle as it flows in a microfluidic comparator. This pressure is found to depend on the amount of confinement, elastic modulus, fluid viscosity and velocity. A model for the force balance on the particle is then proposed, by incorporating the above ingredients and relying on simulations of bead geometry and lubrication flow considerations.

[Phys. Rev. Fluids 10, L092201] Published Fri Sep 19, 2025

Author(s): Martino Andrea Scarpolini, Giovanni Vagnoli, Fabio Guglietta, Roberto Verzicco, and Francesco Viola

Choosing the mounting position of an aortic prosthesis—intra- or supra-annular—remains debated, as clinical comparisons rarely isolate hemodynamic effects of valve replacement procedures. We perform fluid-structure interaction simulations of a patient-specific left heart, testing the same bioprosthetic valve in both configurations on the same patient, rationalizing mounting and valve size effects. Supra-annular implantation consistently lowers transvalvular pressure gradients, increases orifice area, and reduces shear and hemolysis risk (see figure). These results provide controlled evidence to guide implantation strategy and device selection in cases of patient-prosthesis mismatch risk.

[Phys. Rev. Fluids 10, 090501] Published Thu Sep 18, 2025

Author(s): R. Shapiro and A. Manela

The impact of gas rarefaction on the two-dimensional aerodynamic ground effect over a flat plate is analyzed. The free-molecular problem was studied analytically based on the collisionless Boltzmann equation and Maxwell boundary conditions, and compared with direct simulation Monte Carlo at finite Knudsen numbers (Kn). The results indicate that the ground invariably increases aerodynamic loading on the plate and shifts the maximum lift to lower angles of attack compared with the non-confined configuration (NC). While the ground may contribute negatively to the lift in the ideal-flow limit, its relative difference compared with NC is found to be significantly larger and positive at high Kn.

[Phys. Rev. Fluids 10, 093401] Published Thu Sep 18, 2025

Author(s): Jason K. Kabarowski, Aditya S. Khair, and Rahil N. Valani

A mathematical model is developed for the spontaneous Qunicke rotation of a dielectric sphere in an electric field, which accounts for fluid and particle inertia. The particle dynamics obey an integro-differential dynamical system that is a generalization of the celebrated Lorenz equations. Analysis and numerical solution of these modified Lorenz equations show that fluid inertia inhibits chaotic particle rotation, in qualitative agreement with prior experimental observations.

[Phys. Rev. Fluids 10, 093701] Published Thu Sep 18, 2025

Author(s): Haosen Liu and Benshuai Lyu

The stability characteristics of a compressible shear flow confined by two rigid plates are important in applications such as open-jet facilities and launching rockets. By performing linear spatiotemporal stability analysis, we identify the critical parametric regions within which absolute instability occurs. In particular, we show that at sufficiently high Mach numbers, a new type of absolutely unstable mode occurs, which arises from a feedback process due to the reflection of compressible waves by the rigid plates.

[Phys. Rev. Fluids 10, 093903] Published Thu Sep 18, 2025

Author(s): Yingtao Sun, Di Bian, Yuchen Wang, Kai Zhang, Jianfeng Zhou, and Zhigang Li

Superhydrophobic grooves offer substantial slip and drag reduction; however, real fluids are seldom completely clean. Using many-body dissipative particle dynamics simulations, we demonstrate that the presence of contaminant particles at the interface significantly decreases both local and effective slip. The primary factors influencing this effect are particle wettability and interfacial coverage, while particle size and mass have a minor role. The reduction in effective slip follows Philip’s model, providing a rule-of-thumb predictor and informing designs that can tolerate or manage contamination.

[Phys. Rev. Fluids 10, 094202] Published Thu Sep 18, 2025

Author(s): Daniel J. Booth and Thomas D. Montenegro-Johnson

Precise, localized flow control in microfluidic devices remains a difficult challenge. We demonstrate, theoretically, how active droplets might be harnessed to overcome this challenge. Active droplets are produced along the microchannel wall via stimulation of a responsive hydrogel, and the ensuing phoretic slip flows drive transport and mixing in the microfluidic device.

[Phys. Rev. Fluids 10, 094203] Published Thu Sep 18, 2025

Author(s): Jinyu Yao, Xinshu Zhang, Huawei Zhou, Xingyu Song, and Alessandro Toffoli

We develop a nonlinear wave reconstruction and prediction model with a dynamic averaging algorithm, in which shipborne radar images are used for data assimilation to improve the accuracy of wave reconstruction and prediction. Waves around the ship can be accurately predicted for the next few minutes under various sea states. Compared with the linear and second- order models, the new model includes the third-order nonlinear effects; thus, it significantly improves the prediction accuracy of extreme waves under rough sea states, providing effective safety guarantees for ship navigation and operations.

[Phys. Rev. Fluids 10, 094801] Published Thu Sep 18, 2025

Author(s): Samuel J. Petter, Benjamin C. Musci, Gokul Pathikonda, Prasoon Suchandra, and Devesh Ranjan

This study advances the understanding of blast-driven interface instabilities by transitioning from qualitative Mie scattering to quantitative planar particle image velocimetry (PIV). The velocity field and vorticity evolution reveal key insights into mixed-mode Richtmyer-Meshkov and Rayleigh-Taylor instabilities in a cylindrical geometry. High-Atwood number cases exhibit prolonged circulation growth, consistent with stronger turbulence and earlier mixing transition. The PIV data captures how pressure impulse and decay shape the instability beyond what Mie images alone can resolve.

[Phys. Rev. Fluids 10, 093902] Published Wed Sep 17, 2025

Author(s): Haoyu Wang, Isaac J. G. Lewis, Soohyeon Kang, Yuechao Wang, Leonardo P. Chamorro, and C. Ricardo Constante-Amores

We present data-driven models for predicting the motion of a freely settling sphere in a quiescent fluid using experimentally measured trajectories. Deterministic and stochastic neural differential equations reconstruct individual particle paths and capture the statistical features of settling dynamics without resolving the surrounding flow. Our results reveal the strengths of each modeling approach. Deterministic models excel at trajectory prediction, while stochastic models reproduce long-time statistical trends, thus providing a framework for reduced-order modeling of particulate flows.

[Phys. Rev. Fluids 10, 094402] Published Wed Sep 17, 2025

Author(s): Firoozeh Foroozan, Andrea Ianiro, Stefano Discetti, and Woutijn J. Baars

Experimental measurements were performed of convective heat transfer fluctuations beneath a grazing turbulent boundary layer flow. Spatiotemporal wall-temperature fields were acquired with an infrared camera and a heated-thin-foil sensor. Inferred Nusselt number fluctuations showed elongated features with scales similar to near-wall streaks. An analysis in the frequency–wavenumber domain revealed dispersive convection: larger streaks moved near freestream velocity, while smaller energetic features traveled at 10 times the friction velocity. These measurements provide a promising method for wall-based turbulence sensing and flow control.

[Phys. Rev. Fluids 10, 094904] Published Wed Sep 17, 2025

Author(s): Yue Hao, Charles Meneveau, and Tamer A. Zaki

Data assimilation provides a rigorous framework for integrating measurements with numerical simulations to estimate the flow. We developed a machine-learning-based assimilation strategy to infer unknown upstream flow conditions in a high-speed boundary layer from sparse wall-pressure measurements. Our method uses a Bayesian optimization to efficiently search for the optimal control parameters. Applied to a transitional boundary layer, the method accurately estimates the oncoming disturbances, and subsequent direct numerical simulation (DNS) predictions using the estimated conditions show excellent agreement with the true flow.

[Phys. Rev. Fluids 10, 094905] Published Wed Sep 17, 2025

Author(s): Kunihiko Taira, Georgios Rigas, and Kai Fukami

The fluid dynamics community has increasingly adopted machine learning to analyze, model, predict, and control a wide range of flows. This perspective article offers a critical assessment of the key challenges that must be addressed for deepening our understanding of flow physics and expanding the applicability of machine learning beyond fundamental research. We also highlight the importance of community-maintained datasets and open-source code repositories, as well as effective training of fluid mechanicians. We hope this paper sparks discussions and encourages collaborative efforts to advance the integration of machine learning in fluid dynamics.

[Phys. Rev. Fluids 10, 090701] Published Tue Sep 16, 2025

Author(s): Florian Voss and Uwe Thiele

Chemomechanical phenomena lie at the core of many biological and biomimetic systems. Particularly in the presence of free interfaces, such effects arise naturally due to chemically induced gradients of interfacial tension. We study a simple, thermodynamically consistent model for liquid drops on solid substrates that captures the coupling between an autocatalytic reaction of insoluble surfactants, the Marangoni effect and wetting dynamics. In the presence of chemical fuel, drops may exhibit complex self-organized motility modes like crawling and shuttling. The underlying chemomechanical feedback and the resulting bifurcation structure are studied in detail.

[Phys. Rev. Fluids 10, 094005] Published Tue Sep 16, 2025