Latest papers in fluid mechanics

Author(s): Sijie Wang, Yuxiao Cheng, Zifei Yin, Paul Durbin, and Weipeng Li

A new hybrid Reynolds-Averaged-Navier-Stokes/Large Eddy Simulation (RANS/LES) model is proposed. With the discontinuous Galerkin spectral element method (DGSEM), it gives a robust and efficient approach for simulating high-speed and high-Reynolds-number turbulent flows. A change of variable from omega in the k-omega model to g, gives the k-g model, which avoids the singularity near the wall and makes the model work in DGSEM. The model is tested in various cases, including wall-bounded turbulence, wall-modeled LES, flow separation, and compressible flows, with good performance.

[Phys. Rev. Fluids 10, 094902] Published Wed Sep 10, 2025

Author(s): Lorenzo Piro, Massimo Cencini, and Roberto Benzi

Extreme Lagrangian acceleration in turbulence is often attributed to particle trapping in coherent vortex structures. Here, we show that shell models, despite lacking vortex filaments, reproduce the extreme intermittent fluctuations of Lagrangian acceleration seen in real flows. Within the multifractal framework, we accurately predict acceleration moments and full probability distribution functions (PDFs) across a wide range of Reynolds numbers. This shows extreme Lagrangian fluctuations can arise from inertial-range dynamics alone, supporting the universality of multifractal statistics and highlighting shell models as effective tools to capture key features of turbulence.

[Phys. Rev. Fluids 10, L092601] Published Wed Sep 10, 2025

Author(s): Fabio Guglietta, Diego Taglienti, and Mauro Sbragaglia

We study the statistics of deformation of neutrally buoyant droplets in homogeneous isotropic turbulence (HIT), wherein the characteristic droplet size R is smaller than the characteristic Kolmogorov scale η of the turbulent flow. We systematically focus on the characterization of droplet deformatio…

[Phys. Rev. Fluids 10, 093601] Published Tue Sep 09, 2025

Author(s): Chenyue Wang, Jihui Ou, and Jie Chen

Near-space hypersonic vehicles at 40–60 km altitude encounter local rarefaction effects that influence the boundary-layer stability and the laminar–turbulent transition. By incorporating slip boundary conditions and nonlinear constitutive relations into the Navier–Stokes equations and linear stability theory, we systematically investigate hypersonic boundary-layer stability over a blunt cone under near-continuum conditions. The results show that rarefaction thins the boundary layer and stabilizes second-mode instabilities, particularly at high wall temperatures or with small bluntness. These results offer new insights into hypersonic stability and transition in the near-continuum regime.

[Phys. Rev. Fluids 10, 093901] Published Thu Sep 04, 2025

Author(s): Eric Parish and Matthew Barone

The wall-normal Reynolds stress has a negligible contribution to the wall-normal momentum equation in low-Mach, zero pressure gradient boundary layers, and conservation of momentum indicates that pressure is uniform throughout the boundary layer. In hypersonic boundary layers analysis suggests the wall-normal Reynolds stress becomes significant compared to mean pressure and that it must balance with pressure. We validate this and show that the wall-normal Reynolds stress results in non-negligible pressure deficits. We show that errors in standard RANS models for the wall-normal Reynolds stress have a noticeable impact (5% for a Mach 14 cold-wall flow) on wall quantities of interest.

[Phys. Rev. Fluids 10, 094601] Published Thu Sep 04, 2025

Author(s): Yu Qiu, Luis Cueto-Felgueroso, Amir A. Pahlavan, Bauyrzhan K. Primkulov, and Ruben Juanes

Contact lines, where fluid interfaces meet solid surfaces, pose a fundamental challenge to modeling fluid-fluid displacement in confined geometries, as they violate the classical no-slip boundary condition. Recent experiments reveal that contact-line motion in a capillary tube produces compact displacement at low flow rates and unstable fingering at high flow rates. We present a phase-field model with a novel formulation of the boundary wetting conditions. Our model captures the equilibrium configurations at arbitrary wettability, and also predicts dynamic configurations, including wetting transitions, thin-film formation and interface pinch-off, in quantitative agreement with experiments.

[Phys. Rev. Fluids 10, 094004] Published Wed Sep 03, 2025

Author(s): Clément Bret, Pantxo Diribarne, Jérôme Duplat, and Bernard Rousset

Quantum vortex lines are angstrom-scale tubes with quantized circulation ±κ, the Feynman–Onsager constant, that form the backbone of the superfluid velocity field in He-II flows. When forced to turbulence, they organize into a tangle characterized by its mean intervortex spacing. Combining second-sound resonant cavity measurements with 3D Lagrangian tracking for the first time, we observe that the mean intervortex spacing scales with the κ based Reynolds number following a Kolmogorov-like –3/4 power law. We then show both this scaling and the prefactor value can be explained with classical turbulence formalism due to the quantum restricted depth of the superfluid component energy cascade.

[Phys. Rev. Fluids 10, 094701] Published Wed Sep 03, 2025

Author(s): Min Gao, Zhihao Li, and Xinpeng Xu

We propose the Diffuse-Resistance-Domain (DRD) approach — a thermodynamically consistent DNS method for microscale fluid-structure interactions (mFSI) in multicomponent multiphase flows. By unifying interfacial dynamics through Onsager’s variational principle and smooth interpolation of resistance coefficients, DRD naturally enforces complex boundary conditions — like dynamic contact angles — without ad hoc assumptions. It avoids evolving solid-phase fields, cutting computational cost while enabling high-fidelity simulations of moving or deforming boundaries. DRD accurately captures interfacial phenomena in microfluidics, active matter, and porous media, showing strong agreement with experiments.

[Phys. Rev. Fluids 10, 094001] Published Tue Sep 02, 2025

Author(s): Swarnaditya Hazra and Jason R. Picardo

When do mucus films plug lung airways? We show that the answer is not determined by just the film’s volume. While very thin films always stay open and very thick films always plug, we find a range of intermediate films for which plugging is uncertain. The fastest-growing linear mode of the Rayleigh-Plateau instability ensures that the film’s volume is divided among multiple humps. However, the nonlinear growth of these humps can occur unevenly, due to spontaneous axial sliding—a hump that slides rapidly can sweep up a disproportionate share of the film’s volume and so form a plug. This sliding-induced plugging is robust and prevails with or without gravitational and ciliary transport.

[Phys. Rev. Fluids 10, 094002] Published Tue Sep 02, 2025

Author(s): Menghua Zhao, Julien Dervaux, Tetsuharu Narita, François Lequeux, Laurent Limat, and Matthieu Roché

Liquid droplets sliding under gravity slow down markedly on viscoelastic substrates.However the influence of substrate thickness has remained elusive. Focusing on droplets with Bond numbers below one, we uncover a strong dependence of sliding velocity on thickness when the latter varies from microns to millimeters. Building upon these results, we establish a scaling relation linking velocity, droplet size, and layer thickness that capture the experimental data.

[Phys. Rev. Fluids 10, 094003] Published Tue Sep 02, 2025

Author(s): Charlotte Pheasey, Loïc Chagot, Panagiota Angeli, Lyes Kahouadji, and Omar K. Matar

Understanding the flow topology of Taylor (plug) flow in small channels and microchannels is imperative for mass and heat transfer applications, yet comprehensive analysis remains limited, particularly when viscous continuous phases are employed. This study investigates liquid-liquid flow in microchannels, examining internal vortices within Taylor plugs through experimental and computational methods. The results reveal new insights into vorticity and geometry diminishment, advancing understanding of liquid-liquid Taylor flow in microchannels and system mass transfer optimization.

[Phys. Rev. Fluids 10, 094201] Published Tue Sep 02, 2025

Author(s): Svenja Ehlers, Norbert Hoffmann, Tianning Tang, Adrian H. Callaghan, Rui Cao, Enrique M. Padilla, Yuxin Fang, and Merten Stender

This work presents a novel Physics-Informed Neural Network (PINN) approach for nonlinear ocean wave data assimilation and prediction. The method leverages potential flow theory to parameterize wave dynamics and integrates physical constraints into the loss function, enabling accurate reconstruction and prediction of phase-resolved, nonlinear, and dispersive wave fields from sparse measurements. Validated against analytical solutions and laboratory experiments, this PINN framework infers full spatiotemporal wave and velocity potential fields efficiently and thus advances the use of physics-informed machine learning for ocean wave modeling and understanding.

[Phys. Rev. Fluids 10, 094901] Published Tue Sep 02, 2025

Author(s): Yu-Chen Zang (臧雨宸), Hai-Feng Jiang (蒋海峰), Di-Chao Chen (陈帝超), Xing-Feng Zhu (朱兴凤), and Da-Jian Wu (吴大建)

A rigorous formalism is presented for the time-averaged acoustic radiation force on a spherical particle near an infinite planar boundary subjected to a plane wave. The background medium is assumed to be a weakly thermoviscous fluid, with the viscous and thermal boundary layers much smaller than eit…

[Phys. Rev. E 112, 035101] Published Tue Sep 02, 2025

Author(s): Xiaoyu Wu and Xian Wang

In this work, an improved Allen-Cahn-based phase-field lattice Boltzmann model is presented which is applicable to heat transfer in two-phase flow involving evaporation. The vapor concentration at the liquid-vapor interface serves as the driving force for vaporization. In our improved model, four di…

[Phys. Rev. E 112, 035102] Published Tue Sep 02, 2025

Author(s): Zhaowu Lin, Yuan Wang, Yufeng Quan, Zhaosheng Yu, Tong Gao, and Sheng Chen

The dynamics of microswimmers’ undulatory swimming near a wall in lyotropic liquid crystal polymers is investigated. Using asymptotic analysis and numerical study, we observe that the infinitely long sheet exhibits orientation-dependent behaviors and speeds up as it approaches the wall, accompanied by a notable increase in swimming efficiency. For the stiff finite-length swimmers, they would reorient themselves and be trapped when close enough to the wall, due to a net hydrodynamic torque induced by the asymmetric distribution of the flow field.

[Phys. Rev. Fluids 10, 083302] Published Thu Aug 28, 2025

Author(s): Garima Singh, Chhavi Shukla, and Naveen Tiwari

Stability of a liquid film containing colloidal particles flowing along the exterior of a vertical cylinder due to gravity is studied. The effect of colloidal concentration on diffusion coefficients, bulk viscosity, and surface tension is considered. The Marangoni stress at the interface stabilizes the curvature-driven instability at moderate Marangoni numbers, but introduces another unstable mode driven by surfactant at larger values. The pattern for the curvature mode indicates in-phase waves for film thickness and surface concentration, while a phase-lag is observed between the two waves for the surfactant mode.

[Phys. Rev. Fluids 10, 084005] Published Thu Aug 28, 2025

Author(s): Sreethin Sreedharan Kallyadan and Priyanka Shukla

Four interacting point vortices can form rigidly moving patterns called relative equilibria, yet a complete understanding of the possible geometrical arrangements has been elusive. Using a parametric formulation and configuration matrices, we mapped the locations of the fourth vortex that form relative equilibria for a fixed triangular arrangement of the first three vortices. The results reveal bounded and unbounded continua of vortex positions, uncovering families of relative equilibria and rich bifurcation structures in the configuration space.

[Phys. Rev. Fluids 10, 084708] Published Thu Aug 28, 2025

Author(s): Nicolas Lanchon, Samuel Boury, and Pierre-Philippe Cortet

Understanding internal wave turbulence in stratified fluids could yield improved parameterizations of the fine scales in global oceanic models. As analytical works lead to diverse predictions, the observation of a developed internal wave turbulence in laboratory experiments constitutes a major milestone to achieve. In this article, we present observations of internal wave turbulence, performed in a large-scale, three-dimensional facility, allowing access to unprecedentedly clear power laws for the energy spectra. While most of our results are in line with the phenomenology of wave turbulence, it remains to be explored whether the energy spectra we report can be explained in this framework.

[Phys. Rev. Fluids 10, 084804] Published Thu Aug 28, 2025

Author(s): Van Luc Nguyen, Dinh Thang Nguyen, Thi Dieu Thuy Phan, and Long Hoang Duong

When a vortex ring collides obliquely with a vortex tube at a Reynolds number of 12,000, a series of vortex structures can form, with the onset of turbulence set by their initial circulation ratio. Weaker vortices often wrap around stronger ones, causing deformation, twisting, and breakdown of large-scale structures into smaller scales. Vortex reconnection may produce more stable configurations; however, changes in vortex topology can trigger secondary reconnections, generating even more twisted structures. As these vortices become unstable, they create numerous small-scale structures, ultimately leading to fully developed turbulence with an energy spectrum following Kolmogorov’s −5/3 law.

[Phys. Rev. Fluids 10, 084707] Published Wed Aug 27, 2025

Author(s): Rafael L. Sterza, Leandro F. Souza, Marcio T. Mendonca, Analice C. Brandi, and André V. G. Cavalieri

The stability of viscoelastic jets is essential for industrial processes like printing and coating, but the choice of fluid model can yield vastly different predictions. This study investigates how the popular Oldroyd-B and Giesekus models affect the onset of convective instability, where disturbances grow downstream, versus absolute instability, where they grow locally. We demonstrate a key trade-off: Giesekus jets are more convectively unstable, while Oldroyd-B jets are more prone to absolute instability. These findings clarify how different fluid properties govern distinct instability pathways, guiding better process control.

[Phys. Rev. Fluids 10, 083902] Published Tue Aug 26, 2025