New Papers in Fluid Mechanics

Author(s): J.-P. Mollicone, A. Cimarelli, E. De Angelis, and M. van Reeuwijk

This study explores conditional one- and two-point velocity fluctuation correlations relative to the turbulent/non-turbulent interface (TNTI) in a temporal jet. By comparing classical and TNTI-conditioned averages, it reveals new spatial correlations, scaling behaviors and peculiar turbulent production regions which may affect turbulence models. The analysis uncovers distinct correlation peaks tied to the TNTI’s variability that point to large-scale turbulent motions influenced by the interface and that may be missed by conventional one-point or unconditioned analyses.

[Phys. Rev. Fluids 10, 084602] Published Thu Aug 07, 2025

Author(s): Enrico Corato, David van Assche, Ola Jakobsson, Wei Qiu, and Per Augustsson

Thermoacoustic effects arise when a temperature gradient is present in a sound field. This work investigates the interplay of orthogonal sound and thermal fields in a water-filled microchannel. We measured the three-dimensional streaming in the water-filled cavity for only sound applied, for only th…

[Phys. Rev. E 112, 025102] Published Mon Aug 04, 2025

Author(s): Justin P. Cooke, George I. Park, Douglas J. Jerolmack, and Paulo E. Arratia

Internal Boundary Layers (IBL) form when turbulent flows encounter sudden changes in surface roughness. The IBL introduces new length- and time-scales to the flow, characterizing the turbulent motions within. We introduce an alternative scaling for velocity profiles within the IBL using IBL-based parameters: the IBL height and edge velocity. Using our numerical simulations and two experimental datasets, we demonstrate the capability of these new scaling parameters for a variety of flow and surface conditions, offering a simpler, more unified way to understand the behavior within this spatially developing turbulent region.

[Phys. Rev. Fluids 10, 084601] Published Mon Aug 04, 2025

Author(s): Jianxun Zhu, Cai Tian, Lars Erik Holmedal, and Helge I. Andersson

Dimples – localized indentations in otherwise smooth surfaces – have attracted attention in both numerical simulations and experiments due to their practical applications. Direct numerical simulations have been performed to examine the flow in a zero-pressure-gradient boundary layer over a single deep circular dimple. The flow is characterized by the presence of a tornado-like vortex pair within the dimple, followed downstream by a quasiperiodic shedding of hairpin vortices forming a vortex street. Downstream of the dimple, both sinuous and varicose streak instabilities develop, contributing to the generation of hairpin vortices and the periodic meandering of these vortices, respectively.

[Phys. Rev. Fluids 10, 084701] Published Mon Aug 04, 2025

Author(s): Avinash Kumar Pandey and Rajneesh Bhardwaj

While splitter plates are typically employed to suppress flow-induced vibration in bluff bodies, this study reveals an opposite outcome. In a new configuration, attaching a splitter plate to the windward side of a circular cylinder leads to amplified rotational vibrations. Numerical simulations at low Reynolds numbers uncover several regimes, including large-amplitude oscillations, chaos, and symmetry breaking — driven by vortex-structure interactions. The findings highlight the role of leading-edge vortices and demonstrate synchronized structural oscillations with enhanced energy transfer between fluid and structure, offering potential applications in energy harvesting.

[Phys. Rev. Fluids 10, 084702] Published Mon Aug 04, 2025

Author(s): Jingyi Li, Laurel Ohm, and Saverio E. Spagnolie

A mean-field theory is derived for a dilute suspension of active particles in a nematic liquid crystal. Beyond a critical active Ericksen number or particle concentration, the suspension first comes into alignment, then buckles via a classical bend instability. Rather than entering the fully developed roiling state observed in isotropic fluids, the development is arrested into a steady, flowing state by fluid elasticity. The image shows the fluid’s elastic energy in such an arrested state. If the particles are motile, they can surf along the bent environment of their own creation.

[Phys. Rev. Fluids 10, 083301] Published Fri Aug 01, 2025

Author(s): Azeddine Zaidni and Philip J. Morrison

A unified thermodynamic algorithm is presented for constructing thermodynamically consistent dynamical systems, i.e., systems that have Hamiltonian and dissipative parts that conserve energy while producing entropy. The algorithm is based on the metriplectic 4-bracket given in Morrison and Updike [P…

[Phys. Rev. E 112, 025101] Published Fri Aug 01, 2025

Author(s): Daeun Song (송다은), Young-Jin Yoon (윤영진), and Haecheon Choi (최해천)

The flow over a circular cylinder at Re = 220 exhibits mode-A instability, characterized by a spanwise wavelength of around 4d, where d is the cylinder diameter. In the present study, the spanwise domain is extended up to 252d to investigate if the flow field indeed exhibits a periodic pattern with such a spanwise wavelength of 4d. The results reveal that, in addition to the parallel shedding of approximately 4d, very long oblique shedding up to 45d and vortex dislocation are observed in the cylinder wake. In contrast, at Re = 300, where the flow exhibits mode-B instability, such oblique shedding or vortex dislocation does not occur even with a long spanwise domain.

[Phys. Rev. Fluids 10, 074103] Published Thu Jul 31, 2025

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): Andrej Vilfan, Bogdan Cichocki, and Jeffrey C. Everts

We study the hydrodynamic drag force exerted on a sphere in a static anisotropic porous medium. This problem is analyzed using the Brinkman-Debye-Bueche equations with an axisymmetric shielding (or permeability) tensor. Using the exact Green's functions for this model fluid within a single-layer bou…

[Phys. Rev. E 112, 015107] 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