Latest papers in fluid mechanics

Author(s): Zhi Zhou, Petia M. Vlahovska, and Michael J. Miksis

The hydrodynamic force and torque exerted on a moving spherical particle with surface slip and a three-phase contact angle on a gas-liquid interface is investigated. Perturbation theory is employed to estimate the drag and torque on the particle in the limit of small capillary number and small deviations of the contact angle from 90 degrees. The interactions between two translating and rotating particles at a large separation distance are also examined.

[Phys. Rev. Fluids 10, 104007] Published Fri Oct 31, 2025

Author(s): Shilong Li, Zhideng Zhou, Xiaolei Yang, Guowei He, and Haitao Chen

The role of surface roughness on flow separation is yet to be fully understood. Our high-fidelity simulations of flows over periodic hills reveal that roughness systematically enlarges the separation bubble and shifts its position. A key finding is a universal geometric similarity across all rough surfaces, where bubble outlines collapse under a single coordinate transformation. Furthermore, we identify a dual role of roughness: it simultaneously depletes near-wall momentum and counteracts the adverse pressure induced by the hill slope, with momentum loss becoming the dominant driver of flow separation at high roughness.

[Phys. Rev. Fluids 10, 104608] Published Fri Oct 31, 2025

Author(s): Mingming Gu, Zilong Deng, and Yongping Chen

This work proposes a model to simulate transient flow of a gas mixture at arbitrary rarefaction parameters and molar fractions through a long capillary. The transient model is based on the linear relationship between the thermodynamic fluxes (mass flow rate, diffusion flux, etc.) and the thermodynam…

[Phys. Rev. E 112, 045110] Published Fri Oct 31, 2025

Author(s): Adnan Morshed, Ricardo Cortez, and Lisa Fauci

We present a novel framework using regularized Stokeslet surfaces and regularized Stokeslet segments to model long, filiform swimmers inside tubular confinements of arbitrary geometry. Swimmer motion results from the dynamic interaction between time-varying preferred curvatures and elastoviscous forces, which depend on properties of the fluid and flagellum, and the confinement geometry. The image demonstrates that the no-slip condition at the tube wall is maintained while the swimmer moves downward.

[Phys. Rev. Fluids 10, 104903] Published Thu Oct 30, 2025

Author(s): Yu Jun Loo and Silas Alben

We present a numerical method for thin plates falling in inviscid fluid that incorporates leading-edge vortex shedding. Including leading-edge vortex shedding restores physical dynamics to inviscid vortex sheet simulations, enabling large-amplitude fluttering and tumbling.

[Phys. Rev. Fluids 10, 104701] Published Wed Oct 29, 2025

Author(s): Daniel M. Harris and Jack-William Barotta

When a floating body is internally or externally vibrated, its self-generated wavefield can lead to steady propulsion along the interface. In this article, we review several related and recently discovered systems that leverage this propulsion mechanism and interact hydrodynamically with one another via these surface waves. These accessible, tunable, and visually appealing systems motivate future investigations into a number of outstanding questions in fundamental fluid mechanics, while potentially also informing advances in the fields of active matter, hydrodynamic quantum analogs, and robotics.

[Phys. Rev. Fluids 10, 100503] Published Mon Oct 27, 2025

Author(s): Javier Jiménez

We review the efforts during the past 50 years to characterize turbulent flows in terms of coherent structures, but remark that, in the same way as the cycle of water on Earth cannot be fully described by ‘coherent’ rivers or storms, 80% of the volume of turbulent flows cannot yet be represented in terms of structures. The objects in the accompanying figure (originally from A. Lozano-Durán, 2011) are Reynolds-stress structures and vortices in a turbulent channel, but most of the volume is empty. We point to specific problem areas, and discuss what the future role of new analysis techniques could be.

[Phys. Rev. Fluids 10, 100504] Published Mon Oct 27, 2025

Author(s): Yee Li (Ellis) Fan, Bernardo Palacios Muñiz, Nayoung Kim, and Devaraj van der Meer

Upon the impact of a flat disk on a boiling liquid, i.e., a liquid that is in thermal equilibrium with its vapor, a thin vapor pocket is entrapped under the disk. We experimentally investigate the dynamics of the entrapped vapor pocket, focusing on its time evolution and its subsequent influence on the hydrodynamic loads under various conditions. We found that the dynamics of the entrapped vapor pocket is primarily governed by the phase change process, where condensation (vaporization) will induce (frustrate) its rapid collapse, impairing the cushioning. This differs significantly with that of a non-condensable air pocket, which is known to always provide a load reducing cushioning effect.

[Phys. Rev. Fluids 10, 100505] Published Mon Oct 27, 2025

Author(s): Ján Šimkanin and Juraj Kyselica

The impact of different buoyancy sources on convection within the Earth’s core and the resulting magnetic field is numerically investigated. To explore this, three models — thermally driven, chemically driven, and thermochemically driven dynamos — are gradually analyzed. These analyses confirm that both the magnetic field and the convective velocity field depend on the sources of buoyancy. Furthermore, the study finds that dipole polarity reversals and the super-rotation of the Earth’s inner core are influenced by different buoyancy sources. Note, as the viscosity decreases, this dependence weakens.

[Phys. Rev. Fluids 10, 103705] Published Mon Oct 27, 2025

Author(s): Zhengyang Wei and Chang Liu

Input-output analysis has been widely used to predict the transition to turbulence in wall-bounded shear flows, but it typically does not capture the full nonlinear effects. This work analyzes nonlinear input-output stability of transitional shear flows using the Small-Signal Finite-Gain (SSFG) stability theorem. This SSFG stability can predict permissible forcing amplitudes below which a finite nonlinear input-output gain can be maintained. The nonlinear input-output gain obtained from the SSFG stability theorem is higher than the linear input-output gain. The permissible forcing amplitude identified from the SSFG stability theorem is consistent with that obtained by bisection search.

[Phys. Rev. Fluids 10, 103903] Published Fri Oct 24, 2025

Author(s): Mingyun Xie, Qichao Li, Shengqi Wu, Hong Liu, and Lin Fu

In this study, we simulated liquid jets in supersonic crossflow (LJSC) under various inflow Mach numbers using the diffuse interface method. The results show that as the Mach number increases, the liquid jet exhibits reduced penetration and faster fragmentation, accompanied by different breakup modes. A theoretical model was developed to predict the near-field trajectory, which shows good agreement with experimental and numerical data. The proposed primary breakup model can be incorporated into Lagrangian methods to enhance computational accuracy.

[Phys. Rev. Fluids 10, 104006] Published Fri Oct 24, 2025

Author(s): Rémi Macadré, Frédéric Risso, Olivier Masbernat, and Roel Belt

Direct numerical simulations are used to analyze the flow in an annular plane Couette geometry in the laminar regime. A secondary flow is consistently present due to centrifugal effects associated with rotation, regardless of Reynolds number (Re). By increasing the rotation speed, the flow becomes more confined to the walls, leading to progressively thinner boundary layers. Consequently, the primary flow develops into an S-shaped profile, reminiscent of turbulent regimes. At high Re and large channel aspect ratios, an asymptotic regime is observed, the characteristics of which are discussed. This flow is well suited for studying the rheology of highly concentrated two-phase dispersed flows.

[Phys. Rev. Fluids 10, 104102] Published Fri Oct 24, 2025

Author(s): He Zhao (赵河), Zexu Yuan (苑泽旭), Wenjin Han (韩文晋), and Dengming Wang (王等明)

Granular flows of non-spherical particles exhibit complex dynamics that challenge classical rheological descriptions. Using discrete element method (DEM) simulations, we show that superballs display distinct flow behaviors, including enhanced boundary effects, modified velocity profiles, and increased bulk viscosity, compared to spheres. We develop a particle-shape-dependent constitutive model incorporating dimensionless granular temperature to capture nonlocal effects, validated through continuum simulations. This framework enables accurate prediction of flow behaviors across quasistatic and inertial regimes, advancing the modeling of granular systems with complex particle geometries.

[Phys. Rev. Fluids 10, 104306] Published Fri Oct 24, 2025

Author(s): Long Wang and Guowei He

The space-time decorrelation of a passive scalar advected by turbulent flows is dominated by three physical processes: mean-flow carrying downstream, large-eddy random sweeping, and small-eddy distortion. Each process has been investigated through Taylor’s frozen-flow hypothesis and Kraichnan’s random-sweeping and white-noise models. However, their coupling effects remain unexplored. The present paper proposes the Taylor–Kraichnan model to represent the coupled effects of the three processes and leads to the exact solution of space–time correlation. The scale invariance of the space–time correlation is found and consistent with the elliptical approximation model.

[Phys. Rev. Fluids 10, 104607] Published Fri Oct 24, 2025

Author(s): S. H. Ferguson Briggs, A. J. Mestel, and M. G. Blyth

The flow of two concentric ferrofluid layers of differing viscosity and magnetic susceptibility through an annular pipe is examined. The basic flow is driven by an axial pressure gradient and/or by the axial translation of the inner wall. In the absence of a magnetic field, the interface between the fluids is prone to capillary and shear instabilities. Axial and azimuthal magnetic fields can suppress these instabilities, though strong fields may themselves induce unstable magnetic modes. Stability boundaries are mapped across the parameter space, showing how the interplay of capillary forces, shear, and magnetic stresses determines the stability of the system.

[Phys. Rev. Fluids 10, 103704] Published Thu Oct 23, 2025

Author(s): Johan Carlier and Christophe Collewet

Feedback gains derived from balanced truncation of the respective two-dimensional linearized models for the channel and mixing-layer flows reveal spatial patterns similar to Orr structures – the transient vortical features responsible for energy amplification in shear flows. These gains oppose such structures, providing a physically interpretable mechanism by which optimal control suppresses disturbances and delays transition in these shear flows.

[Phys. Rev. Fluids 10, 103902] Published Thu Oct 23, 2025

Author(s): Prabhash Kumar, Anu V. S. Nath, Mahesh Panchagnula, and Anubhab Roy

How do tiny inertial particles behave in a vortex? We revisit this classical problem by incorporating the often-neglected added mass and history forces. Our analysis uncovers additional fixed points beyond the conventional ones, reshaping the trapping landscape, particularly in near density-matched scenarios where added mass becomes significant. Most strikingly, while the absence of the history force permits trapped, diffusive, or ballistic states depending on parameters, its inclusion releases all particles, eliminating trapping and driving them into inevitable long-time ballistic motion.

[Phys. Rev. Fluids 10, 104304] Published Thu Oct 23, 2025

Author(s): Zilong He and Sungyon Lee

We experimentally apply an oscillatory flow to a densely packed suspension plug inside a cylindrical tube in the limit of low Reynolds and high Peclet numbers. The plug becomes reversible in shape once it gradually expands and dilutes to reach a critical particle concentration, matching the previous experimental observations. Surprisingly, our particle-scale measurements reveal that above a critical strain amplitude, individual particles remain irreversible even after the plug shape has stabilized. We further explore this decoupling between particle-scale and system-scale reversibility with simplified two-dimensional simulations.

[Phys. Rev. Fluids 10, 104305] Published Thu Oct 23, 2025

Author(s): Haoqi Fei, Rui Wang, Byron Guerrero, Feng Wang, and Hui Xu

Extreme wall shear stress (WSS) events are traditionally categorized into two types: extreme positive events and backflow events. By introducing an additional azimuthal constraint, both categories can be further divided into subtypes that display distinct statistical and structural characteristics. This study underscores the crucial role of azimuthal shear stress in the formation and evolution of extreme WSS events, providing a more nuanced understanding and a fresh perspective on near-wall turbulence.

[Phys. Rev. Fluids 10, 104605] Published Thu Oct 23, 2025

Author(s): Jun-Ning Wang, Jin-Han Xie, and Xiaojing Zheng

This study investigates the potential-temperature-related third-order structure function in the atmospheric surface layer (ASL), which reflects the properties of potential-energy transfer in the flow, using theory and data from the Qingtu Lake Observation Array (QLOA). We formulated a Kármán–Howarth–Monin equation for potential energy and, using Townsend’s attached eddy hypothesis, derived that the structure function exhibits a horizontal logarithmic region and proposed a universal expression. The image reveals a distinct logarithmic region and demonstrates the validity of our expression for QLOA data.

[Phys. Rev. Fluids 10, 104606] Published Thu Oct 23, 2025