Physical Review Fluids

Author(s): Charles J. Klewicki, Bjoern F. Klose, Gustaaf B. Jacobs, and Geoffrey R. Spedding

Laminar separation plays a crucial role in wing aerodynamics during the transition to turbulence and, depending on the flow parameters and conditions, can lead to multiple stable states. In the presence of bounding walls, the flow is inherently three-dimensional, with strong spanwise motions observed within the boundary layer up to the wing midspan. These effects persist even in time-averaged views and have important implications for potential control strategies.

[Phys. Rev. Fluids 10, 073905] Published Wed Jul 30, 2025

Author(s): Chenlin Zhu, Boyu Zhang, Lijuan Qian, and Hang Ding

This experimental investigation examines water droplet impacts on hydrophobic or super-hydrophobic surfaces across moderate Weber numbers (3 ≤ We ≤ 120) and size ratios (1.04 ≤ Ω ≤ 2.08). Through high-speed imaging, we observe distinct regime transitions as Ω increases, identifying the maximum spreading angle (θ_max > 90°) as the critical transition criterion. An energy-based theoretical model is developed for predicting regime boundaries and maximum spreading behavior.

[Phys. Rev. Fluids 10, 073605] Published Tue Jul 29, 2025

Author(s): You Wei Ho and Jae Wook Kim

In this study, we perform wall-resolved large-eddy simulations to investigate flow-acoustic resonances in deep cavities (D/L = 2.632) at three inclination angles and two Mach numbers. We discover that inclined cavities generate acoustic responses more than 30 dB stronger at a surprisingly low frequency (St=0.276) than the orthogonal cavity. Through modal and resolvent analyses, we identify the distinctive vortex dynamics mechanism at play and reveal the primary factors that contribute to the enhanced aeroacoustic responses in the inclined cavities. Finally, we propose a predictive criterion for the onset of deep cavity resonance associated with the distinctive vortex dynamics identified.

[Phys. Rev. Fluids 10, 074603] Published Tue Jul 29, 2025

Author(s): Masanari Hattori and Shigeru Takata

A laminar duct flow is considered based on the kinetic theory of gases. An asymptotic analysis for small Knudsen numbers reveals that the thermal stress, which is missing in the Navier-Stokes equation, must be included in the momentum balance in the duct’s cross-sectional directions. This stress arises from the nonuniform temperature field developed by viscous dissipation of the main axial flow. It induces a slow secondary flow in the cross-sectional plane, which, through convection, produces finite effects on the axial velocity and temperature fields.

[Phys. Rev. Fluids 10, 073402] Published Mon Jul 28, 2025

Author(s): Nicolò Galvani, Sylvie Cohen-Addad, Brice Saint-Michel, and Olivier Pitois

The yield stress of a plastic matrix embedding bubbles can give rise to distinct coarsening regimes, depending on the balance between plastic and capillary forces. These include: (i) classical coarsening, with bubble growth similar to that in simple liquids; (ii) damped coarsening, where growth slows progressively; and (iii) complete arrest of coarsening once a critical threshold is exceeded.

[Phys. Rev. Fluids 10, 073604] Published Mon Jul 28, 2025

Author(s): Matteo Polimeno, Changho Kim, and François Blanchette

In this paper we numerically characterize the stresses experienced by low-Reynolds-number aggregates of various sizes and fractal dimensions. Our work extends previous studies focussed on the stresses felt by settling aggregates, relaxing the low-fractal-dimension assumption through proper accounting for the presence of neighboring particles in the aggregates. We also consider aggregates subjected to a shear background flow, a case experimentally relevant but numerically understudied. Our findings provide insights on the distribution of the stresses felt by aggregates, which could be used to develop refined dynamical models of aggregation that include breakup mechanisms.

[Phys. Rev. Fluids 10, 074304] Published Mon Jul 28, 2025

Author(s): Yunxing Su, Mija Jovchevska, and Nicole W. Xu

Typically, flow visualization uses specialized particles, such as silver-coated glass microbeads, illuminated with laser light; however, synthetic particles might cause potential health risks or environmental concerns. In our new study, we characterize how starch – a safe, plant-based material – can be used as tracers in underwater experiments with foils, jellyfish, and brine shrimp. Starch particles are effective for particle image velocimetry, pose fewer health risks for humans and animals, are environmentally friendly, and cost a fraction of commercial-grade options. This work is intended to promote more sustainable and ethical research practices in biology and traditional fluid dynamics.

[Phys. Rev. Fluids 10, 074905] Published Mon Jul 28, 2025

Author(s): Jean Hélder Marques Ribeiro, Hugo Felippe da Silva Lui, and William Roberto Wolf

We introduce a method to stabilize large-eddy simulations of compressible, vortex-dominated flows using a minimal yet sufficient amount of artificial diffusivity. By restraining additional shear viscosity to unstable low-pressure vortex cores, numerical stability is preserved without smearing key turbulent flow features. This strategy enables accurate, stable, and cost-effective large eddy simulations of complex flows such as bluff-body wakes and separation regions.

[Phys. Rev. Fluids 10, L071401] Published Mon Jul 28, 2025

Author(s): Saksham Sharma and D. Ian Wilson

When a thin film of sticky liquid recedes from a surface—such as during evaporation or suction—it can split into regularly-spaced thin filaments. Experiments and theory suggest that the onset of this filament formation depends on surface tension and the Hamaker constant. Varying liquid viscosities and angles of inclination confirmed that the film thickness falling below a critical threshold triggers the onset of filament, which is confirmed by bifurcation analysis and numerical analysis in Mathematica. This explains why sticky fluids, such as the pitcher plant fluids and PEO-water solutions, sometimes form such symmetric and geometrically pleasing patterns.

[Phys. Rev. Fluids 10, 074003] Published Fri Jul 25, 2025

Author(s): Himanshi Saini, Reza Yousofvand, and Jeffrey Tithof

A convolutional neural network (CNN) is constructed to predict the shape and location of arbitrarily positioned bluff obstacles in a two-dimensional channel flow, trained using either velocity or concentration fields obtained from Lattice Boltzmann simulations. We analyzed multiple cases to explore various input types and degrees of data sparsity, testing adaptability and robustness of the CNN with limited data input. This approach can be extended to three-dimensional flows, experiments, or even in vivo biological systems that are optically accessible, leading to an accurate predictive framework for determining complex geometry in a variety of biomedical, geophysical, and other systems.

[Phys. Rev. Fluids 10, 074904] Published Fri Jul 25, 2025

Author(s): Vaseem A. Shaik, Jiahao Gong, and Gwynn J. Elfring

Active particles often navigate through inhomogeneous environments. Here, we analyze the dynamics of active particles in inhomogeneous viscoelastic fluids and demonstrate that spatial variations in fluid relaxation time give rise to a novel mechanism of taxis, which we refer to as a form of durotaxis in fluids.

[Phys. Rev. Fluids 10, L071301] Published Fri Jul 25, 2025

Author(s): Jin Ge, Joran Rolland, and John Christos Vassilicos

Since David Ruelle’s 1979 estimate, the maximal Lyapunov exponent of turbulence was thought to scale with the inverse of the smallest Lagrangian time-scale (the Kolmogorov time-scale). It actually also depends on the smallest Eulerian time-scale via random sweeping of small-scale uncertainty fluctuations. This leads to a sweeping relation which involves the integral length scale of the uncertainty field which, in turn, tends towards sub-Kolmogorov scales with increasing Reynolds number. The resulting maximal Lyapunov exponent scales with the Taylor length time scale divided by the square of the Kolmogorov time scale.

[Phys. Rev. Fluids 10, L072601] Published Fri Jul 25, 2025

Author(s): Artur Gesla, Patrick Le Quéré, Yohann Duguet, and Laurent Martin Witkowski

The well-known phenomenon of circular rolls in the rotor-stator flow is analyzed using a homotopy approach. Decreasing the curvature effects changes the transition scenario from subcritical to supercritical, leading to a nonlinear branch of saturated axisymmetric rolls. Direct numerical simulations performed on this branch, together with analysis of the base flow eigenspectrum, lead to a qualitative scenario for the roll merging observed experimentally.

[Phys. Rev. Fluids 10, 073904] Published Thu Jul 24, 2025

Author(s): Dongxiao Zhao and Gaojin Li

Our high-resolution simulations demonstrate that sediment plume heights from deep-sea mining operations follow consistent, self-similar scaling patterns with vehicle speed, discharge rate, and downstream distance. This finding establishes a robust physical foundation for scaling up to large-scale sediment dispersion models across ocean basins.

[Phys. Rev. Fluids 10, 074303] Published Thu Jul 24, 2025