Physical Review Fluids

Author(s): Rahul Deshpande, Abdelrahman Hassanein, and Woutijn J. Baars

The space-time variations of wall-pressure fluctuations (p_w) provide key insights into the dynamics of turbulent boundary layers, yet accurate measurements of their large-scale frequency-wavenumber spectrum remain challenging at high friction Reynolds numbers (Re). Using a bespoke 63-microphone array designed to resolve the large-scale p_w field with minimal aliasing errors, we report novel measurements spanning across 1400 < Re < 5200. The results reveal that p_w scaled on the boundary-layer thickness is most strongly correlated with turbulence in the logarithmic region, identifying it as the dominant source of large-scale scale p_w relevant to turbulence sensing, modeling, and control.

[Phys. Rev. Fluids 11, 064612] Published Thu Jun 18, 2026

Author(s): Hiromichi Kobayashi and Toshiyuki Gotoh

Cloud supersaturation is modeled as a passive scalar with a phase-relaxation time under a uniform vertical gradient. Large eddy simulations with grid points of 10243 confirm the theoretical prediction that one −5/3 spectrum by the phase relaxation and another by the turbulence cascade coexist at low and high wavenumbers in the inertial range, respectively. As the phase relaxation time becomes shorter the transition wavenumber between the two ranges shifts to higher wavenumbers, consistent with theory. Probability density function tails of the supersaturation at small-scales become longer than that of the velocity, stronger intermittency, as the phase relaxation time becomes longer.

[Phys. Rev. Fluids 11, 064613] Published Thu Jun 18, 2026

Author(s): Tymoteusz Miara, Draga Pihler-Puzović, Matthias Heil, and Anne Juel

We characterize the three-dimensional shape of an elastic, transparent sheet as it translates, rotates, and deforms - a key experimental challenge in the study of particle-laden flows – with a high-resolution, single-camera method. We scan the object nonintrusively to capture its illuminated surface and couple the space-time representation of its surface with a neural autoencoder to reconstruct the 3D shape of the object. This method enables the study of motion and deformation of objects with a wide range of surface geometries.

[Phys. Rev. Fluids 11, 064901] Published Thu Jun 18, 2026

Author(s): Hiroshi Otomo and Alexander J. Wagner

Lattice Boltzmann models for nonideal fluids rely on mesoscopic force formulations whose connection to microscopic physics remains unclear. By constructing lattice Boltzmann distribution functions directly from molecular dynamics simulations, this work provides a framework for assessing force models against microscopic particle behavior. The analysis shows that a balanced combination of pseudopotential and free-energy formulations best reproduces the moments of the molecularly derived distribution functions, establishing a direct link between microscopic dynamics and mesoscopic fluid modeling.

[Phys. Rev. Fluids 11, L062901] Published Thu Jun 18, 2026

Author(s): Zengshuang Chen, Xueguang Meng, Pengyuan Yang, and Gang Chen

Most insects generate forward thrust by tilting the stroke plane or adjusting the wing angle of attack. This study reveals that mosquitoes adopt a fundamentally different strategy: while maintaining a nearly horizontal stroke plane, they achieve forward flight through highly asymmetric wing pitching between downstroke and upstroke. Two novel thrust mechanisms are identified under this motion pattern—asymmetric pitch-down acceleration and asymmetric pitch-up amplitude. These findings deepen our understanding of insect flight diversity and offer new design principles for micro flapping-wing vehicles.

[Phys. Rev. Fluids 11, 063101] Published Wed Jun 17, 2026

Author(s): Israel Gabay, Omer Luria, Edward Balaban, Amir D. Gat, and Moran Bercovici

Large-aperture telescopes are currently limited by launch vehicle constraints. The Fluidic Telescope (FLUTE) concept seeks to overcome this by using liquid mirrors which, in microgravity, naturally relax into a precise spherical shape. However, necessary telescope maneuvers subject the liquid to body forces that perturb this interface. This study provides an experimentally validated analytical model for such liquid dynamics by solving for the non-self-adjoint problem of a thin liquid film pinned in a circular domain. Using the model to simulate decades of operation, we show that while edge disturbances build up, the inner 80% of the aperture remains optically precise for over 20 years.

[Phys. Rev. Fluids 11, 064003] Published Tue Jun 16, 2026

Author(s): Jugal Shah, Max Huisman, Devendra Deshmukh, Dag Hanstorp, and Javier Tello Marmolejo

The authors find that micrometric droplets heated up by strong irradiation exhibit a reversal of the classical diffusive evaporation: the speed at which they shrink slows down instead of speeding up. Using laser trapping, they measure tiny levitating droplets and see an initial deceleration in the shrinking decelerate followed by a return to the classical evaporation behavior below ~4 μm. This behavior can be explained with an scaling argument based on volumetric heating. The results show a new facet of irradiative evaporation of aerosols and fuel droplets in combustion systems where droplets can be strongly irradiated by flames or sunshine.

[Phys. Rev. Fluids 11, 063603] Published Mon Jun 15, 2026

Author(s): Shyuan Cheng, Ali M. Hamed, Matias Colombo, and Leonardo P. Chamorro

Flows over natural and engineered surfaces often involve roughness superimposed on larger topography, yet how this multiscale geometry modifies turbulence remains incompletely characterized. Using refractive-index-matched particle imaging velocimetry (PIV), this study shows that modest sinusoidal roughness on a wavy wall induces larger near-wall coherent motions and suppresses ejection events. This weakens local turbulence production and attenuates the separated shear layer in the adverse-pressure-gradient region, clarifying how multiscale surface geometry modulates momentum exchange over complex walls.

[Phys. Rev. Fluids 11, 064611] Published Mon Jun 15, 2026

Author(s): Charles W. Wolgemuth

[Phys. Rev. Fluids 11, 069901] Published Mon Jun 15, 2026

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): 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