Physical Review Fluids

Author(s): Ping-Fan Yang, Haitao Xu, and Alain Pumir

The intense fluctuations of the rate of energy dissipation, an essential aspect of intermittency, are of constant interest in turbulence research. Measuring the energy dissipation, however, is extremely challenging: Most of our knowledge comes from hot-wire measurements of the derivative of the streamwise velocity component, which is generally regarded as a surrogate of the energy dissipation. Here we show that the moments of the energy dissipation cannot reduce to those of its surrogate, as a consequence of a fundamental property of the rate of strain tensor in turbulence. However, the predictions based on assuming a simplified strain rate tensor are accurate to within a few percent.

[Phys. Rev. Fluids 11, 074601] Published Fri Jul 10, 2026

Author(s): Rabia Sonmez, Robert A. Handler, David B. Goldstein, Anton Burtsev, Ryan Kelly, and Saikishan Suryanarayanan

We show that the interaction of a vortex pair with a localized polymeric fluid layer can generate secondary and tertiary vortices through polymer stress gradients. Numerical simulations reveal that elastic stresses significantly modify vorticity production and energy transfer, leading to flow behaviors not observed in Newtonian fluids. The image shows the vorticity field during the interaction.

[Phys. Rev. Fluids 11, 073301] Published Mon Jul 06, 2026

Author(s): Paolo Botticini, Davide Picchi, Santanu Sinha, and Alex Hansen

We characterize the nonlinear pressure drop–flow rate relation of elongated bubble trains in capillary tubes by incorporating thin-film hydrodynamics at low capillary numbers. We show that pore-scale statistical heterogeneity in capillary bundles induces systematic deviations from the single-phase limit, controlled by both the pore-size distribution and flow parameters. We identify a crossover between sublinear regimes with exponents ranging from 2/3 to 1, connecting the Bretherton and Darcy limits and in qualitative agreement with values reported for immiscible two-phase flow in porous media.

[Phys. Rev. Fluids 11, 073601] Published Mon Jul 06, 2026

Author(s): Linsheng Zhang (张林生), Weixing Zhou (周伟星), and Robert J. Poole

We revisit the classical homogeneous shear assumption in cone-and-plate rheometry over a slip boundary condition, and resolve inconsistencies between two slip boundary formulations. Our results show that a fixed slip-length model induces radial shear-rate non-uniformity, whereas a constant wall-stress formulation restores homogeneous shear via a radius-dependent slip length. Extending our work to shear-thinning Carreau fluids, we demonstrate a strong shear-rate dependence of drag reduction and effective slip length. Despite distinct local flow structures, both models yield consistent area-averaged slip from torque measurements, providing a unified framework for slip quantification.

[Phys. Rev. Fluids 11, 074001] Published Mon Jul 06, 2026

Author(s): George Lucas S. Torres, Ashok Gopalarathnam, and Flávio D. Marques

Unsteady thin-airfoil theory is a straightforward reduced-order framework for arbitrary airfoil motions and geometries. However, an inconsistency appears when recovering classical unsteady problems: Glauert’s bound-vorticity expansion is not uniformly convergent at the trailing edge in unsteady motion. Revisiting Wagner’s problem through the unsteady Kutta condition, this work derives a recurrence for the bound-vorticity coefficients and builds a uniformly convergent bound vortex-sheet formulation with a discrete-vortex equivalent. With few terms, the method ensures bound-wake continuity, zero trailing-edge loading, and smooth transient predictions for Wagner’s indicial problem

[Phys. Rev. Fluids 11, 074701] Published Mon Jul 06, 2026

Author(s): Nayoung Kim, Felix Schindler, Sylvie Su, Sven Eckert, and Tobias Vogt

Turbulent thermal convection often organizes into large-scale flow structures that control heat and momentum transport, yet their dynamics in very wide systems remain largely unexplored. Using a liquid-metal Rayleigh–Bénard convection experiment with an extreme aspect ratio of 25, we demonstrate that jump rope vortex dynamics persist even within turbulent convective superstructures. The observed oscillatory behavior follows the same scaling laws previously identified in much smaller systems, indicating that jump rope vortex dynamics are not confined to specific geometries but remain relevant even in spatially extended convection at extreme aspect ratios.

[Phys. Rev. Fluids 11, 063503] Published Tue Jun 30, 2026

Author(s): Mohd. Hanzla, Christopher Ruhl, and Arindam Banerjee

Active grids are widely used to generate turbulence, yet their near-grid region remains poorly understood. We show that global blockage is a key parameter governing near-grid turbulence statistics, driving qualitatively different behavior when grid configuration changes, in contrast to trends observed further downstream. We further reveal that forcing signatures persist strongly at large scales but decay toward dissipative scales, marking a transition from forcing-dominated to more universal turbulence.

[Phys. Rev. Fluids 11, 064617] Published Tue Jun 30, 2026

Author(s): Jinbo Cheng, Wang Han, Yihao Tang, and Lijun Yang

Soot formation in aero-engine combustors is influenced by coherent structures of confined turbulent swirling flows. This work combines large-eddy simulation with state-of-the-art soot models and spectral Proper Orthogonal Decomposition (POD) to identify flow dynamics directly from raw transient data. The results reveal a scale-dependent response: Polycyclic aromatic hydrocarbons (PAH) are mainly affected by high-frequency processing vortex core motion, whereas soot is governed by low-frequency dynamics. Dilution jets weaken high-frequency flow motions and modify the coupling among coherent structures, gas-phase precursors, and soot evolution.

[Phys. Rev. Fluids 11, 063201] Published Mon Jun 29, 2026

Author(s): S. K. Bohling, S. S. Tanikella, J. P. Raimondi, N. D. Jones, and E. Dressaire

Hair-covered appendages serve a variety of purposes in Nature, from chemical sensing to drag generation. To understand how these natural systems control flow, we study how confinement, porosity, and Reynolds number affect flow through and around a finite array of cylinders, using a combination of experiments and numerical simulations. Our results show that the confinement focuses the flow in the array and shifts the domains of existence of the flow regimes. We perform a theoretical analysis based on Sampson flows through rectangular slits to predict the flow rate through the array. The model is quantitatively consistent with the numerical results.

[Phys. Rev. Fluids 11, 064104] Published Mon Jun 29, 2026

Author(s): Marcel M. Louis, Lekwetje Maureen Ramaube, Sonya T. Smith, and Howard A. Stone

The influence of a temperature-dependent viscosity and wall slip are considered for high-Reynolds-number flow over a heated flat plate. In the limit of a small dimensionless slip length, which serves as a perturbation parameter, similarity solutions are developed. The results are used to study the combined effect of temperature-dependent viscosity and wall slip on the coefficients of friction and the Nusselt number. For example, the asymptotic solutions show that the slip contributions to the flow are enhanced by temperature-dependent viscosity.

[Phys. Rev. Fluids 11, 064105] Published Mon Jun 29, 2026

Author(s): Alessandro Chiarini, Rahul K. Singh, and Marco E. Rosti

Polymeric flows exhibit phenomena that sit at odds with our conventional understanding of turbulence. In this work, we show how a characteristic far-from-Kolmogorov self-similarity of polymeric turbulence owes its emergence to a phenomenon possible only in multiphase flows: polymers deplete the fluid energy cascade at a constant rate across scales. This constant loss of flux from fluid to polymers emerges as a second invariant of the turbulent, strongly coupled, fluid-polymer system (in addition to the total constant flux of energy from large to small scales). This invariant loss of flux dictates turbulence statistics in polymeric flows and gives it a distinct universal power-law behavior.

[Phys. Rev. Fluids 11, 064616] Published Mon Jun 29, 2026

Author(s): R. Mathis, S. Cazin, J. Methel, F. Charru, J. Magnaudet, F. Moisy, and M. Rabaud

The growth of wind-generated waves may depend on free-stream turbulence, a parameter that is generally neglected in existing models. Here, we investigate this effect experimentally using grid-generated turbulence blowing over a viscous fluid. Our results show that free-stream turbulence enhances the amplitude of three-dimensional wrinkles and lowers the critical wind velocity for the onset of regular two-dimensional waves, while the wrinkle–wave transition remains associated with an approximately constant friction velocity. A qualitative model explains why the observed decrease of the friction velocity with the fetch results in a non-monotonic variation of the wave amplitude.

[Phys. Rev. Fluids 11, 064804] Published Fri Jun 26, 2026

Author(s): Yifan Ma, Chenren Chen, and Zhigang Zhai

This work develops a linear model under a “total transmission” condition that isolates adjacent and cross-interface couplings in a three-interface system by suppressing reverberating waves. We then demonstrate bidirectional modulation of interface evolution by layer spacing and initial amplitude, showing that coupling can either stabilize or destabilize interfaces. Finally, we analytically derive “freeze-out” criteria for single-interface stagnation via parameter tuning and validate it numerically. These results advance multilayer Richtmyer-Meshkov instability physics, provide control strategies for shock-accelerated mixing in inertial confinement fusion, and impact reflected-wave studies.

[Phys. Rev. Fluids 11, 063902] Published Thu Jun 25, 2026

Author(s): Tachin Ruangkriengsin, Günther Turk, and Howard A. Stone

Resolving the near-wall motion of self-diffusiophoretic Janus particles is numerically challenging because of the steep solute concentration gradients within the narrow gap. We develop an asymptotic theory in the distinguished limit where the inert face is comparable in size to the lubrication region. For axisymmetric and slightly tilted configurations, we obtain explicit particle velocities and gap concentration fields that reveal how cap size influences the particle’s rotational stability near the wall.

[Phys. Rev. Fluids 11, 064103] Published Wed Jun 24, 2026

Author(s): Mrinal Jyoti Powdel and Samriddhi Sankar Ray

We show that the spread of infinitesimal perturbations in a turbulent density-stratified fluid becomes slower with increasing degree of stratification. With a higher degree of stratification, the spatial growth of the uncertainty gets more and more compressed along the direction of stratification. Despite this, the temporal growth of perturbations follows the same universal behavior: an initial decay followed by an exponential growth, ultimately leading to saturation. The rate of growth of the perturbation, however, gets affected by stratification through the strain-mediated dynamics of the underlying velocity field, rather than through direct coupling with the density fluctuations.

[Phys. Rev. Fluids 11, 064615] Published Tue Jun 23, 2026

Author(s): Boqian Yan and Xiaoyu Tang

While droplet impact on liquid pools is well studied for Newtonian fluids, particle suspensions introduce complex non-Newtonian dynamics. This work experimentally identifies five distinct impact regimes for cornstarch suspension droplets, revealing unique phenomena like “wrapped bubbles” and impact-induced jamming that are absent in simple fluids. Through an energy balance analysis, the authors demonstrate that these behaviors are dictated by a direct competition between pool cavity dynamics and suspension rheology. The resulting transition boundaries offer practical guidance for engineering applications like 3D printing.

[Phys. Rev. Fluids 11, 060501] Published Mon Jun 22, 2026

Author(s): Zhenyu Yuan (袁震宇) and Chang Shu (舒昌)

We propose a moment gas kinetic flux solver (MGKFS). Like conventional GKFS, the governing equations for mass, momentum, and energy are still solved by the finite volume method (FVM). In addition, a set of evolution equations for stresses and heat fluxes are also solved by FVM, in which numerical fluxes are evaluated by high-order moments of the distribution function at cell interfaces. That is, high-order moment equations are directly computed via moment integration of a reconstructed gas distribution function at cell interfaces. This strategy not only provides a new closure method for the 13-moment system, but also avoids tedious boundary conditions for stress and heat flux equations.

[Phys. Rev. Fluids 11, 063401] Published Mon Jun 22, 2026

Author(s): Tianpei Cheng, Haijian Yang, Mei Zhang, and Ke Xu

Rayleigh–Darcy convection (RDC) in porous media controls mass and heat transfer in many geological systems. We show that permeability heterogeneity fundamentally reshapes RDC. The permeability correlation length interacts with intrinsic flow-structure scales that determine the convection pattern. High-resolution simulations reveal three distinct heterogeneity regimes depending on Rayleigh number (Ra): (i) At low Ra stable convection cells are constrained; (ii) At intermediate Ra microplume-driven transport is enhanced; and (iii) At high Ra heterogeneity becomes negligible or boundary-layer-controlled. This provides theoretical support for predicting convective mixing and scalar transport.

[Phys. Rev. Fluids 11, 063502] Published Mon Jun 22, 2026

Author(s): Sohyeun Kang, Jaejun Kim, Minseop Lee, and Daegyoum Kim

We experimentally investigate the detachment of a bubble injected from an orifice on a horizontally moving plate. By performing theoretical analysis based on force balance without empirical constants, we introduce a dimensionless parameter Rc that characterizes a transition between vertical buoyancy-dominated “rise” and horizontal shear-dominated “lift-off” regimes. Rc successfully captures the trends of both the bubble radius and inclination angle at detachment across all experimental conditions, and Rc = 0.8 indicates the transition boundary between the two regimes.

[Phys. Rev. Fluids 11, 063604] Published Mon Jun 22, 2026

Author(s): Fubao Yang, Yuhong Zhou, Peng Jin, Jinrong Liu, Zhixin Li, Lili Zhang, Gaole Dai, Liujun Xu, and Jiping Huang

Hydrodynamic metamaterials can steer liquids without disturbing surrounding flow, but passive designs have largely been limited to fixed environments and regular geometries. We show that extreme effective viscosity anisotropy, realized through simple microchannel height modulation and solid barriers in Hele-Shaw flows, decouples a metashell’s performance from the background viscosity. The resulting free-form metadevice remains invisible under environmental changes while accelerating flow in its core, as verified by simulations and experiments, opening a route to robust microfluidic control.

[Phys. Rev. Fluids 11, 064101] Published Mon Jun 22, 2026