Physical Review Fluids

Author(s): Paul Kraemer, Olivier Léon, Fabien Méry, and Estelle Piot

Acoustic liners are widely used for noise reduction in aero-engines, but the physical mechanisms governing their aerodynamic drag remain insufficiently documented. Based on pressure-drop measurements in a turbulent channel over a wide range of Reynolds numbers, this study identifies distinct drag regimes and reveals two markedly different behaviors within the transitional regime. In particular, large drag increases are shown to be associated with the onset of aeroacoustic resonance at the liner resonance frequency, while the relative importance of liner geometry is captured through a frontal-solidity-based parameter.

[Phys. Rev. Fluids 11, 074608] Published Wed Jul 29, 2026

Author(s): Daniel Abdulah and Wanying Kang

[Phys. Rev. Fluids 11, 079901] Published Wed Jul 29, 2026

Author(s): Claudiu Patrascu, Victoria-Elena Plopeanu, and Ioana Rasuceanu

We embark on a 30-day journey following the flow of a high-viscosity liquid through a capillary tube to assess how existing theoretical models, which also account for the dynamic nature of the contact angle, perform in long-term imbibition processes. The journey reveals the persistent and diffusive nature of imbibition processes for liquids with extreme values of viscosity.

[Phys. Rev. Fluids 11, L072001] Published Wed Jul 29, 2026

Author(s): Nathaniel J. Wei, Adina Y. Fleisher, John W. Kurelek, and Marcus N. Hultmark

A wind-turbine wake in a pressurized-air wind tunnel was forced via slow periodic oscillations in the turbine rotation rate. Flow measurements identified traveling waves in the wake, which could be controlled by independently varying the turbine thrust and tip-speed ratio. The results demonstrate the importance of advection for the modeling and control of wind-turbine wakes, even at nominally quasi-steady time scales.

[Phys. Rev. Fluids 11, 070501] Published Tue Jul 28, 2026

Author(s): Mengqi Zhang, Dongdong Wan, and Huanshu Tan

Shear-thinning is ubiquitous in biological and industrial fluids, yet its influence on the instability of time-periodic shear flows remains poorly understood. Using Floquet stability analysis of the Stokes layer in Carreau fluids, we show that shear-thinning can either suppress or promote instability depending on the characteristic fluid response time. The study further identifies a phase-dependent energy-transfer mechanism governing instability in a time-periodic shear flow, which has not been revealed in the literature, providing a dynamic counterpart to the classical energy-production mechanism in steady shear flows.

[Phys. Rev. Fluids 11, 073902] Published Tue Jul 28, 2026

Author(s): Uday M. Rade, Shrihari D. Pande, and Ivan C. Christov

Oscillatory flows in compliant channels are common to a number of soft-hydraulic problems, from physiological transport to microfluidics. Recently, elastoinertial rectification was shown to lead to streaming in these systems. We develop this theory for a two-dimensional (2D) channel with a confined, nearly incompressible elastic layer as its wall and validate the predictions against detailed Lagrangian–Eulerian fluid–structure interaction simulations. Surprisingly, the nearly incompressible 2D layer introduces new physics: resonance-like amplification of streaming at specific Womersley numbers. Our results offer design principles for optimizing flow rectification in soft microsystems.

[Phys. Rev. Fluids 11, 074102] Published Tue Jul 28, 2026

Author(s): Rhylan A. Huss and Farrukh S. Alvi

A previously undocumented Reynolds-number-dependent transition is identified in the wake of a rounded-edge slanted afterbody, from a centerline-separated to a novel centerline-attached vortex state. The transition produces a pronounced drag reduction through the collapse of the centerline recirculation region as the upstream boundary layer becomes turbulent. These findings explore experimental evidence linking laminar separation bubble dynamics, shear-layer instability, and wake-state transitions in this canonical bluff-body geometry.

[Phys. Rev. Fluids 11, 074702] Published Tue Jul 28, 2026

Author(s): Lukas Bentkamp and Michael Wilczek

The comprehensive statistics of a turbulent flow field can in principle be captured by Hopf’s functional approach; however, the resulting functional equations have remained largely intractable. We here study a simplified passive vector model, whose Hopf equation is solved exactly by an ensemble of Gaussian fields. Based on both theory and simulations, we find that the model displays a fluctuating energy flux from large to small scales. The resulting intermittency at the small scales can be understood as arising from a probabilistic mixture of Gaussian sub-ensembles.

[Phys. Rev. Fluids 11, 074606] Published Thu Jul 23, 2026

Author(s): Hongsik Kim and Sunghwan Jung

Put a soap bubble in an electric field and it stretches into a taller, smooth dome. Turn the field up and, past a critical point, the top sharpens into a pointed cone that fires off a thin jet. Imaging the bubble from the side, we follow this whole sequence in one experiment and find two things. Bubbles of different sizes deform along the same curve once the field is rescaled by bubble size and surface tension, so one balance between electric and capillary forces sets the shape. And the cone is far sharper than Taylor’s classic value, because it is selected while the film is still rushing toward the jet rather than resting in equilibrium.

[Phys. Rev. Fluids 11, 074003] Published Wed Jul 22, 2026

Author(s): Yatin Darbar, Ahmed Said Ismail, Thomas C. Sykes, David Harbottle, Harvey M. Thompson, and Mark C. T. Wilson

Droplet mixing is vital in many practical applications, yet the underlying physical mechanisms remain poorly understood. This work uses carefully validated numerical simulations to investigate the mixing dynamics of inkjet printed droplets. Our results show that impact-driven flows contribute only weakly to mixing, while molecular diffusion governs homogenization over a timescale of seconds. We perform studies to understand how droplet size, spacing, volume ratio, and substrate wettability influence mixing, producing methods to estimate mixing times for droplet-based manufacturing processes.

[Phys. Rev. Fluids 11, 073603] Published Tue Jul 21, 2026

Author(s): Suresh Behara

Rotating bluff bodies are widely used to control wake instabilities and fluid forces, but the role of wake–body interactions in multi-body configurations remains less understood. Direct simulations of isolated and tandem transversely rotating spheres show that rotation can suppress classical shedding and reorganize the wake into double-threaded vortical structures. However, tandem interactions can overturn this stabilizing effect, sustaining unsteady wakes and strongly modulating drag and lift.

[Phys. Rev. Fluids 11, 074101] Published Tue Jul 21, 2026

Author(s): Luis H. Hatashita, Pranav Nathan, and Suhas S. Jain

High-fidelity simulations have become indispensable for uncovering the physics of turbulent two-phase flows, yet quantitative guidelines for the grid and time-step requirements needed to accurately resolve interface dynamics have been lacking. We derive scaling laws that predict these computational requirements as functions of Reynolds, Weber, and Capillary numbers; identify distinct inertia- and viscous-dominated regimes; and introduce a new dimensionless parameter that unifies their classification. The resulting framework provides practical a priori resolution criteria and computational cost estimates for predictive interface-resolved simulations.

[Phys. Rev. Fluids 11, 074303] Published Mon Jul 20, 2026

Author(s): Wouter J. T. Bos

Invariants, such as energy or enstrophy, are central to turbulence theory. Some systems behave in a sub-space between two well-known limits where invariants are known. Here, we demonstrate that invariants can also be defined for these intermediate cases. Knowledge of the invariants enables the development of simple models for the multiscale dynamics of such systems.

[Phys. Rev. Fluids 11, 074605] Published Fri Jul 17, 2026

Author(s): Naoya Okamoto, Takashi Ishihara, Mitsuo Yokokawa, and Yukio Kaneda

Using direct numerical simulations of incompressible turbulence at Taylor-scale Reynolds numbers Rλ up to about 1740, we examine spectra, two-point correlations, and second-order local-average moments of the energy dissipation rate ϵ and enstrophy Ω. Correlations and local-average moments exhibit larger scaling exponents for fluctuating fields than for total fields over nearby but distinct ranges. In both statistics, squared-mean contributions are nonnegligible relative to fluctuating contributions. Thus, total- and fluctuation-field exponents need not coincide over these ranges. Results suggest Rλ ≈ 1740 remains insufficient to reach the asymptotic regime assumed in intermittency theories.

[Phys. Rev. Fluids 11, 074603] Published Thu Jul 16, 2026

Author(s): Paul Bataillie, Maxime Casanova, and Pedro Stefanin Volpiani

Data assimilation and symbolic regression are used to formulate an analytical correction to the Spalart-Allmaras model, addressing local deficiencies in its production term. The correction improves separated-flow predictions while preserving the performance of the baseline model for wall-attached flows. Tests on multiple two-dimensional flow cases confirm the applicability of the correction across diverse configurations.

[Phys. Rev. Fluids 11, 074604] Published Thu Jul 16, 2026

Author(s): Nishanth Murugan, Donald Koch, and Sarah Hormozi

Dense non-Brownian suspensions undergo a rheological transition with increasing shear rate, from a Newtonian scaling where stress grows linearly, to a Bagnoldian scaling where it grows quadratically. For suspensions devoid of frictional contacts due to electrostatic repulsive forces keeping the particles apart, our discrete element simulations reveal the shear rate marking the onset of the inertial regime to exhibit a critical behavior as the suspension approaches jamming. Our results show this criticality to be tied to a diverging microstructural length scale, larger than any individual particle, that governs the emergence of inertial effects within the suspension.

[Phys. Rev. Fluids 11, 074302] Published Wed Jul 15, 2026

Author(s): Soumya R. Nanda, Talluri Vamsi Krishna, Jacob Cohen, and S. K. Karthick

Using qualitative flow diagnostics and quantitative pressure measurements, this study investigates hypersonic flow over a cone-mounted axisymmetric cavity to assess the influence of Reynolds number, aspect ratio, and excess rear-face height. A distinct mode-shifting behavior from flapping-dominated to Kelvin-Helmholtz-dominated oscillations is identified at the highest aspect ratio, owing to a possible turbulent transition of the shear layer with a change in Reynolds number, which is found to be absent in the two-dimensional cavity configuration. The excess rear-face-height cases also demonstrate the ability to alter the dominant instability mechanism and resonance characteristics.

[Phys. Rev. Fluids 11, 073401] Published Tue Jul 14, 2026

Author(s): Rajnandan Borthakur and Uddipta Ghosh

Electrophoresis is often used in combination with external flows for enhanced particle separation. However, the resulting motion when particles have nonuniform surface charge remains poorly understood. This dynamic problem is solved here using an efficient and exact reduced order model. It reveals the diverse set of trajectories emerging from the coupling between the particle’s rotation and its uneven surface charge with potential applications in medical diagnosis and analytical chemistry.

[Phys. Rev. Fluids 11, 073702] Published Tue Jul 14, 2026

Author(s): Connor Toppings, Theodoros Michelis, Marios Kotsonis, and Serhiy Yarusevych

Low Reynolds number airfoils may stall abruptly due to laminar separation bubble bursting. Periodic boundary layer forcing can promote transition through the excitation of natural instabilities, and thereby delay or prevent stall. In this study, forcing is provided by a plasma actuator and the influence of varying forcing amplitude on the bursting transient is examined using particle-image velocimetry and surface pressure measurements. Increasing the forcing amplitude delays and increases the variance in the bursting start time. However, the dynamics of the bursting process are largely insensitive to forcing amplitude. For higher forcing amplitudes, bursting is entirely prevented.

[Phys. Rev. Fluids 11, 073901] Published Tue Jul 14, 2026

Author(s): J. Vahé and F. Thiesset

In multiphase turbulent flows, kinetic and interfacial energies usually coexist in a subtle balance, but their mutual conversion often goes unnoticed in statistically steady regimes. Our work introduces a controlled, time-periodic forcing to break this steadiness, thereby revealing the dynamic cycle of energy injection, conversion, and dissipation. By extending the k−ϵ model to include surface energy and nonequilibrium effects, and by linearizing the system, we uncover the intricate time scales that govern the coupling between these processes.

[Phys. Rev. Fluids 11, 074002] Published Tue Jul 14, 2026