New Papers in Fluid Mechanics

Author(s): Ory Schnitzer and Ehud Yariv

We show that grooved surfaces fully wetted by a relatively inviscid lubricant may exhibit a large apparent slip length. Exploring this singular limit, we map the key asymptotic regimes defined by the encapsulation height and the submerged ridge area fraction. Our theory bridges classical superhydrophobic models with a newly predicted giant-slip regime. This transition is described by an exterior flow problem where the thin lubricant films wetting the ridges are effectively replaced by a Navier-slip condition.

[Phys. Rev. Fluids 11, 054202] Published Tue May 26, 2026

Author(s): Ya-Ting Jiang, Zi-Mo Liao, Chen-Yue Xie, Peng-Jun-Yi Zhang, Nan-Sheng Liu, and Xi-Yun Lu

Particle-laden turbulence is commonly modeled through two-way coupling, but inter-particle collisions can become significant when inertial particles accumulate near the walls. By comparing the two-way and four-way coupled point-particle direct numerical simulations in channel flow, this work shows that inter-particle collisions can substantially weaken near-wall particle accumulation, enhance turbulence attenuation, and promote drag reduction. These effects arise from the enhanced particle dispersion and the amplified slip-velocity fluctuations, highlighting the importance of four-way coupling for accurately modeling particle-laden turbulent flows.

[Phys. Rev. Fluids 11, 054308] Published Tue May 26, 2026

Author(s): Xianzhang Xu, Daria Skalitzky, and Krishnan Mahesh

Estimating minimum pressure from particle measurements is important for vortex flows, especially when particles are sparse, noisy, or absent near vortex cores. While physics-informed neural networks have been used for flow-field assimilation, their accuracy for minimum-pressure recovery under controlled particle density, particle distribution, incomplete observations, and noise in spatial coordinates and velocity measurements has not been systematically quantified. This work fills that gap using analytical two-/three-dimensional vortices and a turbulent flow of interacting counter-rotating vortices of unequal strength obtained from Large-Eddy Simulations.

[Phys. Rev. Fluids 11, 054604] Published Tue May 26, 2026

Author(s): Shiyi Lu, Anjia Ying, Mengqian Lu, and Lin Fu

An accurate inflow description for atmospheric boundary-layer (ABL) large-eddy simulation (LES) is critical, yet conventional mapping of homogeneous turbulence to inhomogeneous ABLs can distort spatial correlations and disrupt turbulence continuity. In this article, an adaptive energy-preserving mapping (AEPM) strategy is proposed, which preserves target energy profiles while maintaining spatial-correlation properties. An a priori numerical test and three LES cases (neutral/unstable building flows and a flat-plate boundary-layer flow) demonstrate the robustness of the AEPM method and its capability to reproduce realistic inlet and downstream turbulence statistics.

[Phys. Rev. Fluids 11, 054605] Published Tue May 26, 2026

Author(s): Sijie Huang and Jeonglae Kim

Low-frequency unsteadiness (LFU) in separated flows is often linked to drag modulation and recirculation-bubble dynamics, but its governing mechanisms remain unclear. This work introduces a reduced-order, physics-based framework that describes LFU through kinetic-energy transport within the mean recirculation region using vorticity-based quantities derived from the rotational Navier–Stokes equations. For the wake of a normal plate, the analysis reveals that Bernoulli-energy transport and Lamb-vector dynamics govern the charging and discharging processes underlying LFU.

[Phys. Rev. Fluids 11, 054704] Published Tue May 26, 2026

Author(s): Isaak Rubinstein, Gil Himmelhoch, Victor Steinberg, and Boris Zaltzman

We show that the classical Rayleigh–Bénard instability and nonequilibrium electroconvection become strongly intertwined at the limiting current in charge-selective systems. The resulting interaction lowers the instability threshold and removes the short-wave singularity characteristic of electroconvective instability.

[Phys. Rev. Fluids 11, 053703] Published Fri May 22, 2026

Author(s): Basheer A. Khan, Shai Arogeti, Oriel Shoshani, and Alexander Yakhot

Turbulent puffs in pipe flow persist for a prolonged duration before suddenly transitioning to laminar flow via viscous exponential decay. Prior to the onset of relaminarization, the configuration of sectional streamlines indicates the existence of multiple saddles and nodal points near the wall. During relaminarization, they move from the near-wall region and may undergo saddle-node bifurcations that destroy saddle-node pairs. In such cases, the saddle/nodal distance follows the Riccati equation.

[Phys. Rev. Fluids 11, 053902] Published Fri May 22, 2026

Author(s): M. Leonard, D. Maity, N. Vandewalle, and T. Truscott

Stretch an elastic sheet between your hands and let go; it snaps back. Thin water films do the same, rupturing almost as soon as they form. The authors had a simple idea: instead of changing the liquid or coating the surface, just hold the film edges. Two laser-engraved grooves on a plain acrylic plate pin a film of pure water over more than thirty centimeters. When the grooves end, the film ruptures and drips in a steady rhythm. The stability comes not from chemistry, but from geometry.

[Phys. Rev. Fluids 11, 054004] Published Fri May 22, 2026

Author(s): Shiyu Li and Zhixiong Gong

Single-beam acoustic tweezers based on focused ultrasound provide a compact and biocompatible platform for single cell trapping, yet stable three-dimensional trapping is often hindered by acoustic bulk streaming at high frequencies. Here, we develop a unified theoretical– numerical framework to quantify the competition between acoustic radiation force and streaming-induced drag force across viscous-to-inertial flow regimes. We derive pressure-scaling laws for streaming velocity and show trapping performance varies non-monotonically with focal pressure, contrary to conventional expectations. These findings offer practical guidelines for optimizing high-frequency acoustic tweezers for robust cell trapping.

[Phys. Rev. Fluids 11, 054201] Published Fri May 22, 2026

Author(s): Hojun Lee, Itzhak Fouxon, and Changhoon Lee

We report the first direct numerical simulations using a recently introduced exact director-based formulation of the equations of motion for inertial spheroids in turbulence. The results reveal that particle shape and finite inertia induce complex, nonmonotonic trends in preferential clustering. Gravity markedly alters these dynamics, enhancing small-scale clustering for rod- and disk-like particles while suppressing clustering for nearly spherical particles. We confirm that at weak inertia, rod-like spheroids tend to align with the flow’s major stretching direction, whereas disk-like spheroids align with its major shrinking direction.

[Phys. Rev. Fluids 11, 054306] Published Fri May 22, 2026

Author(s): Sourav Kumar Singh, Vishant Tyagi, and Aritra Santra

Dense suspensions of non-Brownian particles encountered in industrial processes like concrete mixing, chocolate refining, and ceramic processing are well known to show abrupt jamming transition under shear flow, yet, the effects of particle size distribution on this transition remain poorly understood. Using Discrete Element Method-based simulations in two dimensions, the authors show that polydisperse suspensions undergo critical rigidity transition preceding shear jamming, with scaling exponents consistent with percolation theory. Remarkably, the order parameter, susceptibility, and the microstructural properties of polydisperse suspensions are found to be identical to those of the statistically equivalent bidisperse systems

[Phys. Rev. Fluids 11, 054307] Published Fri May 22, 2026

Author(s): Itzhak Fouxon, Hojun Lee, and Changhoon Lee

Fluids in nature are usually turbulent and contain small particles, a phenomenon observed in paper production, rain formation, astrophysics, and the oceans, among other places. These particles are more often than not nonspherical, such as fibers in paper. Particle orientation in the flow determines how the flow drags them and, eventually, how the particles distribute in space and orient. We use a symmetry-based simplification, analogous to a classical description of neutrally buoyant spheroids, to introduce a new framework for flows with nonspherical particles, which yields a compact set of evolution equations with fewer degrees of freedom.

[Phys. Rev. Fluids 11, 054903] Published Fri May 22, 2026

Author(s): Pratyush Kumar Mohanty, P. S. D. Surya Phani Tej, Ganesh Subramanian, and V. Shankar

The eigenspectrum of bounded viscoelastic shearing flows comprises a continuous spectrum (CS) whose eigenvalues form continuous curves or line segments in the complex plane, in addition to a discrete spectrum of isolated eigenvalues. While the Oldroyd-B model possesses only two line-segment CS, we show that the more realistic FENE-P model admits up to six distinct CS. Our analytical predictions provide a framework for interpreting numerically computed spectra of viscoelastic shearing flows.

[Phys. Rev. Fluids 11, 053304] Published Thu May 21, 2026

Author(s): Thomas Frisch, Christophe Josserand, and Sergio Rica

Direct numerical simulations and full analytical theory reveal how the geometry of obstacles determines the onset of vortex nucleation in quantum fluids such as Bose–Einstein condensates and related superfluid systems. In particular, the flows around obstacles with sharp corners such as walls and wells display a time-irreversible transition when the velocity exceeds a critical value which is well below the sound speed. This work paves the way for the study of skin friction in superfluid systems.

[Phys. Rev. Fluids 11, 054703] Published Wed May 20, 2026

Author(s): Wietze Herreman, Basile Dhote, and Frédéric Moisy

Bendable thin structures such as floating modular pontoons can be displaced, rotated and deformed by incoming gravity waves. We propose a diffractionless theory to calculate the second order mean yaw moment on slender elastic structures in waves. In the case of non-moored, freely drifting floaters, the mean yaw moment can rotate the structure to a preferential orientation with respect to the angle of incidence. Using our theory, we can predict this preferential orientation and how it varies with floater shape and its bending modulus.

[Phys. Rev. Fluids 11, 054803] Published Wed May 20, 2026

Author(s): Yuzhe Qin, Huaxiong Huang, Zilong Song, and Shixin Xu

Most electrohydrodynamic droplet models assume passive ion transport and field-induced polarization. Here we incorporate chemically powered active interfacial ion transport into a Navier–Stokes – Poisson–Nernst–Planck – Cahn–Hilliard (NS-PNP-CH) phase-field framework using an energy–dissipation–input formulation. The resulting persistent charge asymmetry reorganizes electric fields and stresses, enabling controlled deformation, breakup and recoalescence, as well as droplet separation under shear.

[Phys. Rev. Fluids 11, 053702] Published Tue May 19, 2026

Author(s): Bilal Fareed, Muhammad Nadeem, Atta Ullah, John J. Molina, Ryoichi Yamamoto, Leonardo P. Chamorro, and Adnan Hamid

Sedimentation of nonspherical particles is typically governed by orientation-dependent interactions. We show that cube-shaped particle suspensions recover classical Stokesian scaling laws associated with spheres. This behavior emerges from geometric symmetry, which suppresses anisotropy and promotes isotropic microstructure. The results identify symmetry, not sphericity, as the key determinant of collective sedimentation dynamics.

[Phys. Rev. Fluids 11, 054305] Published Tue May 19, 2026

Author(s): Juan Pimienta and Jean-Luc Aider

We demonstrate for the first time that it is possible to access in real-time (live measurements) two-dimensional instantaneous velocity fields with both high spatial resolution and high sampling frequency. Using a standard Optical Flow algorithm properly optimized, standard 4Mp snapshots can be processed live up to 460 Hz. Moreover, using the proper experimental settings, it also becomes possible to access 1 vector per pixel, leading to very high spatial resolution. Apart from considerable gain in computing time and power consumption, this approach also unlocks new experiments like very low frequency measurements, closed-loop flow control, or rare events detection.

[Phys. Rev. Fluids 11, 054902] Published Tue May 19, 2026

Author(s): Reza Haghani, Carl Fredrik Berg, and Eirik Grude Flekkøy

Diffuse interface methods for multiphase flow simulations often exhibit nonphysical droplet or bubble shrinkage, particularly when based on the Cahn-Hilliard equation. This well-known artifact introduces a critical radius below which droplets vanish, thereby limiting the fidelity of simulations invo…

[Phys. Rev. E 113, 055107] Published Mon May 18, 2026

Author(s): Ron Bessler, Tirosh Mekler, Daniel Malka, Nadia Onallah, Oshri Farhana, Rami Fishler, Saurabh Bhardwaj, Kenichiro Koshiyama, Netanel Korin, and Josué Sznitman

Existing studies of charged aerosol deposition have largely focused on isolated upper-airway or local truncated in vitro models, leaving whole-lung scale effects unresolved. Using a physiologically inspired multiscale airway-on-chip spanning conducting to acinar regions, we investigated the electrostatic contributions along with gravity, impaction, and diffusion. Our results show that charge significantly reshapes deposition patterns, enhancing early bronchiolar capture while reducing delivery to the distal acinus.

[Phys. Rev. Fluids 11, 050501] Published Mon May 18, 2026