New Papers in Fluid Mechanics

Author(s): F. Dabbagh and S. Schneiderbauer

Dynamic Taylor-based gradient models are derived forsubgrid turbulent heat flux and drift temperature components which arise in filtered heat transfer two-fluid model for turbulent gas-particle flows. Among them, the dynamic model coefficient based on optimal estimator procedure POpt, improves the predictive accuracy of actual turbulent heat flux PA, in comparison to the conventional dynamic Smagorinsky-type approach PS, and the most common turbulent diffusivity linear gradient model PG

[Phys. Rev. Fluids 11, 064304] Published Fri Jun 12, 2026

Author(s): Lan Hu, Jiao Chen, Huan Zhang, and Xuebo Li

We quantify how momentum-flux transport is organized across scales in the unstable atmospheric surface layer. Using multi-height SLTEST measurements, we show that cumulative cospectral ogives provide a compact description of scale allocation in the weak-cancellation regime. Increasing instability and relative height shift the dominant transport toward larger wavelengths, enhance outer-scale contributions, and strengthen scale-by-scale cancellation, while event-based diagnostics indicate a concurrent concentration of transport into fewer intermittent bursts.

[Phys. Rev. Fluids 11, 064609] Published Fri Jun 12, 2026

Author(s): Xing-Liang Lyu, Zi-Ju Liao, and Wei-Dong Su

Turbulent von Kármán flows in a cylinder with a height-to-diameter ratio of two show permanent strong inhomogeneity and anisotropy. Using helical-wave decomposition, the authors find an unusual -5/4 scaling law for the global energy spectrum of fluctuating velocity within an intermediate wave-number range while the structure function remains a classical 2/3 scaling within the corresponding scale range in physical space. Unlike homogeneous isotropic turbulence, energy transfer between scales remains nonzero in the scaling range, revealing how moving boundaries reshape the cascade of turbulent fluctuations

[Phys. Rev. Fluids 11, 064610] Published Fri Jun 12, 2026

Author(s): Tao Zhang, Jianrui Cheng, Haochen Xiong, Ralf Deiterding, Chongguang Shi, Chengxiang Zhu, and Yancheng You

This paper presents an analytical model for Mach reflection in axisymmetric internal supersonic flows that explicitly accounts for a center body. Using the curved shock theory and the method of curved shock characteristics, the model accurately predicts key flow features including the slip line shape and Mach disk size. A key advance is the identification of a negative pressure gradient behind the reflected shock that can form a sonic throat independently of the trailing-edge expansion fan, an effect achievable only for sufficiently small wedge angles where slip line deflection is mild.

[Phys. Rev. Fluids 11, 064803] Published Fri Jun 12, 2026

Author(s): Pierre-Yves Goffin, Yves Dubief, and Vincent E. Terrapon

The interactions between flow structures and thin sheets of large polymer stress are investigated for a steady arrowhead coherent structure in a two-dimensional viscoelastic channel flow. We show that expressing the polymer body force in a coordinate system associated with stresslines, lines tangential to the stress principal axes, allows for an intuitive interpretation of these interactions. Approximating a polymer stress sheet by a stressline, across which the solution is discontinuous, we provide an expression for the jump conditions and show that the pressure difference across a polymer stress sheet is directly related to the local curvature of the stressline, and thus of the sheet.

[Phys. Rev. Fluids 11, L061301] Published Fri Jun 12, 2026

Author(s): Theodoros T. Koutserimpas

In even spatial dimensions, solutions of the wave equation violate Huygens' principle, producing a persistent wake tail inside the light cone rather than a sharply localized propagating front. This intrinsic tail complicates refocusing. Here, we examine how the wake-tail structure of the two-dimensi…

[Phys. Rev. E 113, 065102] Published Thu Jun 11, 2026

Author(s): Thomas Micol, Alexander A. Doinikov, Cyril Mauger, and Claude Inserra

We present an analytical model for the frequency response of a gas microbubble oscillating near a spherical inclusion of arbitrary size and mechanical nature (rigid, fluid, or viscoelastic) immersed in a viscous compressible fluid. The model considers both radial and nonspherical oscillations in the…

[Phys. Rev. E 113, 065103] Published Thu Jun 11, 2026

Author(s): Sai Swetha Venkata Kolluru and Rahul Pandit

Following the report of numerical evidence of a finite-time singularity in the wall-bounded three-dimensional axisymmetric incompressible Euler equations, we investigate the effect of a magnetic field on this singularity. We find the HL-type singularity as well as a new “cusp”-type singularity where the nature of the singularity is sensitive to the initial strength of the magnetic field relative to the kinetic fields. This study marks the first numerical evidence for singularities in the Ideal MHD equations in a wall-bounded domain.

[Phys. Rev. Fluids 11, 063701] Published Wed Jun 10, 2026

Author(s): Antonio Pol, Riccardo Artoni, and Patrick Richard

When flowing, elongated particles may exhibit a strong inhibition of their angular motion compared with spherical grain. We use discrete element simulations to investigate the angular dynamics of elongated particles in dense, confined shear flows. We show that this inhibition does not originate from single isolated mechanisms, but is governed by the degree of collective alignment induced by shear. We propose a simple scaling law relating the average angular velocity to the local shear rate. This scaling collapses data obtained for different particle properties and flow patterns, unifies spherical and elongated particles, and remains valid across two additional flow configurations.

[Phys. Rev. Fluids 11, 064302] Published Wed Jun 10, 2026

Author(s): Parham Poureslami, Ranit Mukherjee, and Sungyon Lee

Particle-induced viscous fingering (PIVF) occurs when a non-colloidal suspension displaces air inside a Hele-Shaw cell, which leads to the formation of particle clusters, or “plumes” at the advancing interface. Despite extensive studies in the last decade, the coupling between plumes and interfacial deformations remains unexamined. In this paper, we address this coupling by deriving scaling laws that connect the interplay between capillarity, local particle concentrations, and interfacial speed. We also uncover new regimes of PIVF that are unique to rectilinear geometry, in which particle plumes interact and coalesce, resulting in enhanced mixing inside the suspension.

[Phys. Rev. Fluids 11, 064303] Published Wed Jun 10, 2026

Author(s): Alain Pumir, Muhammad Zubair Sheikh, Kristian Gustavsson, Emmanuel Lévêque, Bernhard Mehlig, and Aurore Naso

As they settle through turbulent clouds, elongated ice crystals, which form at low enough temperature, are affected by the turbulent motion of air. Such crystals, which are typically smaller than the Kolmogorov length scale of the flow, tend to align perpendicular to gravity, and to a lesser extent, parallel to vorticity. Turbulence is shown to increase the settling velocity of the crystals due to their inhomogeneous sampling of the flow.

[Phys. Rev. Fluids 11, 064608] Published Wed Jun 10, 2026

Author(s): Bo-Jie Xie, Tian-Shu Zhou, and Jin-Han Xie

We generalize the derivation of the velocity circulation area rule, initially proposed in the inertial range and stating that circulation statistics do not depend on specific loop shapes, to ranges with forcing and dissipation. With a newly proposed necessary condition, we show that the area rule cannot hold in the classic inertial range. Even so, in two-dimensional instability-driven turbulence, the variance-normalized circulation probability density function shows a weaker dependence on loop shape, suggesting that the normalized circulation statistics are potential measures of geometry-related turbulence invariances.

[Phys. Rev. Fluids 11, 064607] Published Tue Jun 09, 2026

Author(s): Ri Zhang, Lun Sun, Zhongwei Zhou, Yong Liu, and Domenico D. Meringolo

This study investigates experimentally the three-dimensional settling process of centimeter-sized spherical particles in still water using Particle Imaging Velocimetry (PIV) and Convergent Binocular Vision (CBV). When particles are released side by side, the number of particles significantly influences the settling process. Two particles settle synchronously almost in mirror-image, with random deflection largely suppressed, called the mutual support phenomenon (MSP). With more particles, the outermost two exhibit MSP, but other particles may fall like single particles. Observations of multiple particles with sophisticated instruments can reveal mechanisms of complex settling processes.

[Phys. Rev. Fluids 11, 064301] Published Mon Jun 08, 2026

Author(s): Xiang I. A. Yang, Ruifeng Hu, Rahul Deshpande, Robert Kunz, and George Huang

Two-equation RANS models often label (k) as turbulent kinetic energy, yet their (k) represents only the energy of Reynolds-stress-producing active motions in the logarithmic layer. This leaves the energy of inactive motions unresolved, despite its importance for normal stresses, curvature effects, wakes, and particle transport. We derive a transport framework for inactive-motion energy and show that its predicted scaling agrees with channel and boundary-layer DNS data.

[Phys. Rev. Fluids 11, 064606] Published Mon Jun 08, 2026

Author(s): Eric Lauga and Beverley McKeon

[Phys. Rev. Fluids 11, 060001] Published Fri Jun 05, 2026

Author(s): Francesca Mangani, Alessio Roccon, and Alfredo Soldati

Oil–water emulsions exhibit viscosity contrasts that can significantly influence scalar transport and mixing. Using phase-field-based direct numerical simulations, we investigate the role of viscosity on the transient evolution of a passive scalar (temperature), initially confined in the dispersed phase and subsequently transferred to the carrier phase, in two opposite configurations: water-in-oli and oil-in-water emulsions. Despite fundamentally different local mixing dynamics in oil and water, reversing the continuous and dispersed phases redistributes these mixing mechanisms, preserving similar global heat-transfer rates and thermal transient in the two systems.

[Phys. Rev. Fluids 11, 064502] Published Fri Jun 05, 2026

Author(s): Yijie Wang, Jun Chen, and Leonardo P. Chamorro

Turbulence subjected to background rotation underlies many geophysical and engineering flows, yet its anisotropic development away from the rotation axis remains poorly constrained experimentally. This laboratory study examines nearly isotropic turbulence under controlled off-axis rotation using high-resolution PIV, revealing how rotation induces scale-dependent anisotropy in directional velocity spectra. The onset of spectral anisotropy follows a simple scaling with the inverse turbulent Rossby number, directly linking large-scale rotation to small-scale energy redistribution. These results offer experimentally grounded constraints for modeling rotating turbulence in non-inertial frames.

[Phys. Rev. Fluids 11, 064605] Published Fri Jun 05, 2026

Author(s): Yonghao Wen, Yingjie Wei, Cong Wang, and Jiawen Yin

The present study extends existing investigations of waves generated by granular collapse into water from two-dimensional configurations to three-dimensional axisymmetric cases, revealing both similarities and fundamental differences between them. Wave-generation mechanisms are proposed, demonstrating that the competition between horizontal and vertical granular flow governs the transition between different regimes. A predictive framework for wave classification and maximum wave amplitude estimation has been provided.

[Phys. Rev. Fluids 11, 064802] Published Fri Jun 05, 2026

Author(s): Dušan Božić, Anubhav Dwivedi, and Mihailo R. Jovanović

Subcritical transition in shear flows arise from the interplay between linear non-modal amplification and nonlinear interactions, yet their quantitative connection remains unresolved. We bridge this gap by deriving a framework from the Navier–Stokes equations, in which a forcing-amplitude expansion links oblique disturbances to finite-amplitude streaks consistent with direct numerical simulations. This hierarchy shows that the same resolvent structure governing linear amplification organizes the dynamics at all orders in the perturbation series. Breakdown of this series marks the onset of secondary instability, providing a quantitative bridge between non-modal growth and classical transition theory.

[Phys. Rev. Fluids 11, 063901] Published Thu Jun 04, 2026

Author(s): Fabio Guglietta, Martino Andrea Scarpolini, Francesco Viola, and Luca Biferale

Blood flow in the human heart is far from a smooth stream: it is a rapidly changing, intermittent motion shaped by moving walls, valves, and pulsatile forcing. By following Lagrangian tracers through a patient-specific simulation of the left heart, this study reveals where and when turbulent fluctuations become most intense. The results show that Lagrangian statistics can expose chamber-specific flow signatures and detect the enhanced intermittency produced by a stiffened aortic valve, opening a route toward sharper assessment of pathological cardiac flows.

[Phys. Rev. Fluids 11, 064604] Published Thu Jun 04, 2026