Physical Review Fluids

Author(s): Flavio Tuteri, Sergio Chibbaro, and Alexandros Alexakis

Classical shell models of turbulence fail to reproduce the dual energy–enstrophy cascade of two-dimensional flows because they predict the wrong equilibrium spectra. Introducing a hierarchical spatial organization across scales restores the correct equilibrium scaling and leads to a statistically stationary dual cascade. The resulting model consistently captures both the equilibrium properties and the nonequilibrium cascade dynamics of two-dimensional turbulence.

[Phys. Rev. Fluids 11, 084604] Published Tue Aug 11, 2026

Author(s): Xiangyu Nie and Shengkai Wang

We report direct experimental observations of self-sustaining CH4–air flames rotating along the edge of an unheated circular Hele-Shaw cell, extending beyond previous studies in which such flames were observed only under external heating. Formed under fuel-rich conditions, these flames exhibit stable traveling-wave behavior, with edge velocities exceeding nominal laminar flame speeds and a structure comprising both premixed and diffusion branches. The rotation arises from a balance between local flame speed, flow, and wall heat loss. Parametric studies have identified regimes of single and multiple rotating waves, as well as transitions to ring flames or extinction under extreme conditions.

[Phys. Rev. Fluids 11, 083201] Published Mon Aug 10, 2026

Author(s): Suruj Kalita and Rajaraman Ganesh

We investigate subcritical turbulence in plane Couette flow using a finite-amplitude columnar vortex instead of the conventional Lundbladh-type perturbation. We show that, although the perturbation modifies the turbulent structure, the key characteristics of subcritical turbulence remain unchanged. The figure illustrates the breakdown of the columnar vortex into tripolar and quadrupolar structures in unstratified and stably stratified flows. The columnar vortex breakup provides a new mechanism for streamwise streak formation.

[Phys. Rev. Fluids 11, 083301] Published Mon Aug 10, 2026

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

We revisit the classical hoop-stress mode (HSM) instability in viscoelastic Taylor-Couette flow using the FENE-P model. We show how finite polymer extensibility modifies the onset of the hoop-stress mode for a range of gap width ratios. By systematically comparing linear stability predictions with experiments and direct numerical simulations, we identify where the model succeeds and where its limitations emerge and what are the possible reasons for the discrepancies. We also compare our linear stability results with an augmented Pakdel–McKinley criterion that incorporates finite extensibility and finite gap effects.

[Phys. Rev. Fluids 11, 083302] Published Mon Aug 10, 2026

Author(s): Meng Fan, Antoine Dazin, Gérard Bois, and Francesco Romanò

Low-flow-rate instabilities in vaneless diffusers remain a long-standing challenge in turbomachinery, with the roles of core-flow dynamics and boundary layers still debated. Using a hierarchy of linear stability analysis and two- and three-dimensional URANS simulations, we identify two distinct instability mechanisms and trace them back to their physical origins. The low-flow-rate instability is shown to arise from a two-dimensional inviscid core-flow mechanism, while a new instability, associated with inlet modulation and three-dimensional flow features, is reported at high flow rates.

[Phys. Rev. Fluids 11, 083902] Published Mon Aug 10, 2026

Author(s): Gourab Saha and Kajal Kumar Mondal

Reactive solute transport in open-channel flows is central to understanding contaminant migration in rivers, wetlands, and engineered waterways, but the combined influence of wind-induced shear, porous-bed resistance, and wall absorption has remained unresolved. This study introduces a generalized dispersion model that captures the coupled transient effects of those three influences through analytical transport coefficients and concentration distributions, validated by Brownian dynamics simulations. The findings reveal how wind direction governs pollutant dispersion, retention, and removal, and provides a predictive framework for layered environmental flows.

[Phys. Rev. Fluids 11, 084501] Published Mon Aug 10, 2026

Author(s): Francesco Carbone and Sergio Servidio

In this work, we analyze two-dimensional turbulence in a Galerkin-truncated system with pseudo-logarithmic and random mode selection in Fourier space. The results confirm the presence of the double energy cascade (k−5/3 and k−3) and show how anisotropy influences the organization of vorticity without altering universal scaling laws. Finally, particle pair dispersion follows Richardson superdiffusion (ℓ2(t)∼t3), demonstrating that preserved spectral interactions sustain turbulent transport.

[Phys. Rev. Fluids 11, 084603] Published Mon Aug 10, 2026

Author(s): Wanqiu Zhang, Fei Zhang, and Xinping Zhou

Capillary attachment is a fundamental phenomenon in microengineering, yet the lack of comprehensive theories makes it difficult to predict a pendant drop’s particle-lifting capability. We investigate the critical roles of stability in this process, specifically addressing how to maximize lifting capacity. Our work establishes the theoretical framework required to successfully lift particles in practical applications.

[Phys. Rev. Fluids 11, 084001] Published Fri Aug 07, 2026

Author(s): Suraj Kumar Nayak, Vishwanath Shukla, and Akshay Bhatnagar

Direct numerical simulations reveal the orientation and transport of spherical, spheroidal, and rod-like gyrotactic microswimmers in three-dimensional turbulence. Strongly gyrotactic swimmers preferentially align with the vertical, while weakly gyrotactic swimmers are nearly isotropic. Rod-like swimmers are more strongly affected by fluid shear and align with the principal strain direction. Orientation correlations depend on the gyrotactic response time, and all shapes transition from ballistic to diffusive transport. A reduced two-dimensional model for spherical swimmers reproduces the key statistics.

[Phys. Rev. Fluids 11, 084602] Published Tue Aug 04, 2026

Author(s): Avraham Moriel, Howard A. Stone, and Simon Mendez

The ability of red blood cells to deform under shear flow is critical to cardiovascular function, yet capturing their complex fluid-structure interactions remains challenging. We extend a perturbative approach to capture cellular enucleation, and probe the emergence of shape instabilities under shear flow. This method isolates how a cell’s initial orientation, membrane mechanics, and viscosity contrast drive morphological instabilities, such as stomatocytes and trilobes. Ultimately, this framework provides a baseline for understanding how disorders like sickle cell disease and malaria compromise cells dynamics.

[Phys. Rev. Fluids 11, 083601] Published Mon Aug 03, 2026

Author(s): Cheng-Quan Fu, Zongqiang Ma, Yang Song, Cunbo Zhang, Sijia Lyu, Chenyue Xie, Anmin He, Nan-Sheng Liu, and Pei Wang

Rayleigh-Taylor mixing is important in natural phenomena and engineering applications, but limited spatial resolution in practical experiments and simulations constrains studies of this mixing process. Resolution-limited fields preserve only large-scale features such as mean profiles and mixing widths, but fail to resolve small-scale structures, resulting in lower fluctuation variance and higher apparent mixedness. Convolutional neural network (CNN) based superresolution reconstructs multiscale flow fields and recovers mixedness evolution, with robust generalization across unseen phases and flow parameters.

[Phys. Rev. Fluids 11, 083901] Published Mon Aug 03, 2026

Author(s): Kristoffer S. Moen, Jørgen R. Aarnes, Simen Å. Ellingsen, and J. Nathan Kutz

The turbulent flow beneath a water surface is difficult to measure directly, yet it governs important processes such as mixing and air–water gas exchange. We show that the SHallow REcurrent Decoder (SHRED), a lightweight recurrent neural network, can reconstruct subsurface turbulent flow fields using only three sparse measurements of the surface height. The method performs well on both numerical simulations and laboratory experiments, highlighting its potential for future remote sensing of rivers and other free-surface flows.

[Phys. Rev. Fluids 11, 084601] Published Mon Aug 03, 2026

Author(s): Shu Yang, Fahim Tanfeez Mahmood, and C. Ricardo Constante-Amores

We study how viscoplastic filaments retract and break. Unlike Newtonian liquids, viscoplastic fluids can resist motion through a yield stress. We identify two mechanisms that can prevent droplet detachment from its edge depending on the shear-dependence: shear thickening reopens due to generation of vorticity near the neck, whereas strong shear-thinning allows capillary pressure to reopen it due to curvature changes. Remarkably, this latter mechanism also arises in the Newtonian limit as the viscosity approaches zero, demonstrating that an almost inviscid filament need not undergo classical end pinching, contrary to the prevailing picture in the literature.

[Phys. Rev. Fluids 11, 073303] Published Thu Jul 30, 2026

Author(s): Torsten Trittel, Christoph Klopp, Caterina Tosarelli, Emmanuelle Lacaze, and Ralf Stannarius

In this work smectic bubbles with millimeter diameters, but only nanometer film thicknesses, are exposed in microgravity experiments to high electric fields to study field effects on film inclusions. The observed motion of islands and droplets in the film plane can be considered as a quasi-two-dimensional analogue of electrospraying. Different mobilities of anions and cations of the ionic dopants make the effect polarity dependent. The image shows the motion of islands (color coded blue to brown) when a high electric field at the anode (brown bar) is switched off at time t=0.

[Phys. Rev. Fluids 11, 073606] Published Thu Jul 30, 2026

Author(s): Maria Rosaria Acquaviva and Ivan Langella

Water injection is a promising technology for mitigating pollutant emissions from hydrogen combustion. However, the high reactivity and diffusivity of hydrogen flames make droplet–flame interactions particularly intricate. Using two-dimensional detailed-chemistry simulations, we show that a single droplet locally modifies the flame displacement speed and heat release rate, while altering flame stretch through droplet-induced curvature. We also propose a phenomenological model to predict the local flame displacement and velocity during the droplet-flame interaction.

[Phys. Rev. Fluids 11, 073201] Published Wed Jul 29, 2026

Author(s): Satoi Suzuki and Toshiyuki Sanada

Why do clean spherical bubbles spread laterally even after they leave each other’s wakes? Experiments and reduced-order modeling reveal that bubble chains disperse through two successive mechanisms: wake-induced lift initiates lateral dispersion, while a bubble-induced upward flow drives the second stage. The findings reveal how pairwise wake interactions give rise to collective bubble dynamics.

[Phys. Rev. Fluids 11, 073604] Published Wed Jul 29, 2026

Author(s): Vincent Gourmandie, Jeanne Chauris, Remi Fechter, Valentin Leroy, Caroline Derec, and Juliette Pierre

The sound produced by a detaching bubble is known to arise from its volumetric oscillations, but the factors driving the oscillation amplitude has remained an open question. We perform experiments using two bubble-generation methods, and observe that both the shape and amplitude of the pressure signal depend strongly on the bubble formation mechanisms. Using a large set of experimental data, we identify that the oscillation amplitude is mainly controlled by the initial growth velocity of the bubble. Furthermore, we propose a simple model that captures the onset of the acoustic signal as a consequence of the bubble pinch-off dynamics.

[Phys. Rev. Fluids 11, 073605] Published Wed Jul 29, 2026

Author(s): C. Rajarshi and Rama Govindarajan

We study collisions of small inertial particles suspended in a background flow. These particles may be inert plankton in the ocean or water droplets in clouds. Previous studies have shown that such collisions or caustics require particles to pass through regions of high strain in the flow. Our work finds that the type of strain is crucial, not just its magnitude. Regions of large compressive strain trigger caustics, whereas particles survive caustics despite encountering large strain if they come from extensional strain. Extending the study of caustics to finitely dense particles, we show that the level of strain required for caustics increases with decreasing particle density.

[Phys. Rev. Fluids 11, 074304] Published Wed Jul 29, 2026

Author(s): Chenyu Wu, Shaoguang Zhang, and Yufei Zhang

We introduce a sequential approach to augment the shear stress transport-conditioned (SST-CND) model, which was originally trained on 2D flows, in 3D scenarios. 3D field inversion is first performed to obtain the distribution of the augmentation term. Then, features that are nonzero only in 3D scenarios are selected to build the expression using symbolic regression. The resultant SST-CND3D model preserves the original model’s capabilities in 2D flows, while showing significant improvement in 3D complex cases, including a real-world high-lift device.

[Phys. Rev. Fluids 11, 074607] Published Wed Jul 29, 2026

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