Latest papers in fluid mechanics

Author(s): Hugo Poncelet and Gautier Verhille

We investigated experimentally for the first time the rotational dynamics of flexible fibers in homogeneous and isotropic turbulence. The rotation and the deformation of the fibers have been measured thanks to an efficient three-dimensional reconstruction algorithm from three simultaneous images. We show that an increase of fiber flexibility enhances the rotation rate. We show that this phenomenon is directly related to the amplitude of deformation.

[Phys. Rev. Fluids 11, 034301] Published Wed Mar 11, 2026

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

The motion of rigid bodies in viscous fluids at vanishing Reynolds number is governed entirely by its geometry. While highly symmetric particles like spheres and flat circular disks sediment without reorientation and chiral bodies follow helical trajectories, the dynamics of weakly asymmetric shapes remain difficult to predict. Here, we combine numerical simulations and experiments to investigate “pinched” U-shaped disks with a single plane of symmetry. By varying the degree of pinching, we demonstrate that this class of achiral particles can realize the complete spectrum of inertialess sedimentation behavior, from straight settling to robust quasiperiodic spiraling.

[Phys. Rev. Fluids 11, 034102] Published Tue Mar 10, 2026

Author(s): Stéphane Dorbolo, Floriane Weyer, Alexandre Delory, Apurav Tambe, and Zhao Pan

A water droplet hanging from the tip of a vertical sugar fiber seems destined to fall as gravity overcomes capillarity. However, the droplet is also gradually dissolving its own support. Will the droplet fall? Sometimes. However, it may instead suddenly jump upward and climb the very fiber it consumes. We show how this counterintuitive motion emerges from the interplay of surface tension, gravity, and dissolution, and identify the conditions that determine whether the droplet falls or rises. This process may again occur until the droplet is full.

[Phys. Rev. Fluids 11, 033605] Published Mon Mar 09, 2026

Author(s): Tetsuro Tsuji, Shoma Hashimoto, and Satoshi Taguchi

When tracers are scarce in flow measurement using particle imaging velocimetry (PIV), experimenters must wait for tracers to come in the test section, making measurements inefficient. To address this ill-suited case for PIV, the paper introduces optical trapping of a tracer; briefly let it go so the flow moves it, then pull it back at the same initial position. The method, termed as optically-trapped particle tracking velocimetry, is validated by measuring a slow microflow in a square microchannel. The authors also demonstrate an application to optothermal flows where tracers are depleted near the heat source, showing how ot-PTV can still probe tracer motion in an ill-suited case for PIV.

[Phys. Rev. Fluids 11, 034901] Published Mon Mar 09, 2026

Author(s): Darren Crowdy

In a recent study of the formation of electric charge caps on a leaky dielectric droplet, it has been shown that, in the limit of high electric Reynolds number, the electric field problem satisfies a non-standard boundary value problem of mixed type. By using novel techniques involving consideration of a so-called prime function, this paper shows that it is possible to solve this mixed boundary value problem analytically.

[Phys. Rev. Fluids 11, 034902] Published Mon Mar 09, 2026

Author(s): Ole Milark, Jean-Baptiste Salmon, and Benjamin Sobac

Drying of complex fluids is crucial in many natural and technological processes, yet predicting it and probing associated transport phenomena remain challenging. We introduce an original interferometry‑based method for confined two-dimensional droplets in a humidity‑controlled chamber, enabling simultaneous high‑precision, high‑resolution measurement of drying kinetics and internal concentration fields, providing a powerful tool to accurately characterize drying dynamics and transport in complex fluids.

[Phys. Rev. Fluids 11, 033603] Published Fri Mar 06, 2026

Author(s): Xingsheng Li and Jing Li

Existing research on Worthington jets has paid most attention to those forced by cavity collapse. Focusing on the cavity-free regime across various sphere-liquid impact configurations, we derive a universal scaling law for the maximum jet height from first principles and identify three distinct pinch-off modes governed by Rayleigh–Plateau instability. Self-similar analysis accurately captures the evolution of jet shape and height, revealing gravity-dominated jet dynamics. These findings confirm that this jet undergoes a fundamentally different physical process from that in air-entrainment scenarios, thereby significantly enriching the classical Worthington jet phenomenon.

[Phys. Rev. Fluids 11, 033604] Published Fri Mar 06, 2026

Author(s): S. P. Mousavi, H. Hassanzadeh, Y. Fan, F. Larachi, C. D. Ohl, and S. M. Taghavi

Cavitation bubbles near free surfaces are known to move rapidly away from the liquid surface and generate high-speed microjets. We demonstrate that viscoplastic fluids can fundamentally change this outcome by arresting the bubble and trapping it beneath the surface once a critical yield number is exceeded. A regime map classifies the flow into four regimes (swelling, trapped, bullet jet, and vapor jet), and a force-balance model provides a predictive framework for the bubble penetration depth.

[Phys. Rev. Fluids 11, 033301] Published Thu Mar 05, 2026

Author(s): Schahin Akbari, Kilian Vinzenz Wilhelm, Dominik Plümacher, Florian Kummer, Yongqi Wang, and Martin Oberlack

We investigate the nonlinear axisymmetric oscillations of non-viscous droplets with a focus on superimposed initial deformations, in which an even mode with large amplitude is superimposed on an odd mode at small amplitude. Our analysis of modal coupling shows that the even mode with large amplitude strongly influences the odd mode with small amplitude due to asymmetries in local curvature and restoring forces between flattened and elongated shapes (as in the image), while the odd mode with small amplitude has only a minor influence in return.

[Phys. Rev. Fluids 11, 033602] Published Thu Mar 05, 2026

Author(s): Georgios Giamagas, Cyrille Bonamy, Koen Blanckaert, and Julien Chauchat

Large-eddy simulations of the Navier–Stokes equations under the Boussinesq approximation investigate the hydrodynamics of a three-dimensional hyperpycnal plume over a sloping bed. In the unconfined configuration, plunging is governed by lateral slumping rather than by a critical densimetric Froude number, producing a characteristic triangular surface pattern and a distinct downstream wake. The wake extent increases significantly with increasing inflow densimetric Froude number and agrees with field observations of the Rhone River inflow into Lake Geneva. Total entrainment increases with decreasing densimetric Froude number due to enhanced lateral spreading and increased underflow velocity.

[Phys. Rev. Fluids 11, 033801] Published Thu Mar 05, 2026

Author(s): Gaspare Li Causi, Enrico Amico, and Jacopo Serpieri

The recent literature on wall blowing flow control was here adapted to suction-based laminar flow control (LFC) to study efficient control scenarios. These are evaluated by means of a numerical framework deploying fast and relatively accurate CFD and flow transition solvers embedded in an efficient optimization routine. More than 700 combinations of LFC parameters were explored showcasing the flow sensitivity to the deployed control and yielding to power savings overcoming the value of 30%.

[Phys. Rev. Fluids 11, 033901] Published Thu Mar 05, 2026

Author(s): Joseph J. Williams, Zachary G. Nicolaou, J. Nathan Kutz, and Steven L. Brunton

The vortex shedding phenomenon has long fascinated researchers, yet only recently has the behavior of unstable growth and saturation been placed on firm mathematical footing through the Stuart–Landau and Ginzburg–Landau equations. While these models capture key aspects of the dynamics, a complete understanding of vortex shedding remains elusive. Here, we use data-driven methods trained on coarse-grained numerical flow data to learn distinct local models at multiple stations in the downstream wake. This approach yields new insight into the nature of the instability, the wavemaker region, and vortex shedding itself.

[Phys. Rev. Fluids 11, 034401] Published Thu Mar 05, 2026

Author(s): F. M. Ventrella, V. J. Valadão, G. Boffetta, S. Musacchio, and F. De Lillo

In the presence of linear friction, the properties of two-dimensional turbulence deviate from the classical Kraichnan phenomenology. The enstrophy flux in the direct cascade is suppressed resulting in a steeper energy spectrum. The spectral exponent can be predicted in terms of the statistics of the Lagrangian finite time Lyapunov exponent. We numerically verify this prediction and propose a simple phenomenological model for the dependence of the Lyapunov exponent on friction intensity.

[Phys. Rev. Fluids 11, 034604] Published Thu Mar 05, 2026

Author(s): Alexei A. Mailybaev

Spontaneous stochasticity—persistent randomness in the limit of vanishing noise and viscosity—has been observed in turbulence models, yet its universality lacked a theoretical explanation. We develop a renormalization-group (RG) framework for the fluctuating Sabra shell model, showing that the ideal turbulent dynamics is governed by a fixed-point RG attractor. This approach explains universality across dissipation and noise mechanisms and predicts a complex RG eigenvalue responsible for the slow, oscillatory convergence observed numerically.

[Phys. Rev. Fluids 11, 034605] Published Thu Mar 05, 2026

Author(s): Sthavishtha R. Bhopalam, Ruben Juanes, and Hector Gomez

Droplet transport in deformable constrictions is important in microfluidics, enhanced oil recovery, biomedical systems, and surface-acoustic-wave-driven platforms. We study how actuation controls droplet motion in a constricted deformable tube using high resolution multicomponent fluid-structure interaction simulations. We show that oscillatory traction on the tube walls exhibits resonance, i.e., the droplet’s mobilization time is minimized when the traction frequency nears the tube’s natural frequency. However, actuation via oscillatory fluid forcing exhibits no such resonance. Our findings provide design guidelines for tunable, actuation-controlled droplet motion in soft confined geometries.

[Phys. Rev. Fluids 11, 033601] Published Tue Mar 03, 2026

Author(s): F. Novotný, M. Talíř, E. Varga, and L. Skrbek

Temporal decay of rotating turbulent thermal counterflow of He II is probed by second sound and found to display interesting new features. Two effects are observed, acting against each other and affecting the late temporal decay of vortex line density, L(t). The first one is gradual decrease of the decay exponent of the power law L(t), confirming that turbulent thermal counterflow under rotation acquires 2D features. The second one is the influence of the effective Ekman layer built within the effective quantum Ekman time. For increasing rotation rates, L(t) gradually ceases to display a clear power law. Instead, rounded and ever steeper decays occur, gradually shifted toward shorter times.

[Phys. Rev. Fluids 11, 034603] Published Tue Mar 03, 2026

Author(s): A. V. Kopyev, V. A. Sirota, A. S. Il'yn, and K. P. Zybin

We develop the Kazantsev theory of small-scale dynamo generation at small Prandtl numbers near the generation threshold and restore the concordance between the theory and numerical simulations: the theory predicted a power-law decay below the threshold, while simulations demonstrate exponential deca…

[Phys. Rev. E 113, 035101] Published Mon Mar 02, 2026

Author(s): Ruifeng Yuan and Lei Wu

Smaller gas-solid contact area or smaller bifurcation angle? What happens when inlet and outlet conditions are exchanged? This study employs topology optimization to investigate optimal manifold configurations across gas rarefaction regimes and uncovers two counterintuitive phenomena: a wetted-area minimum in the slip regime and inlet–outlet reciprocity in free-molecular flows. These findings provide crucial guidance for microfluidic and vacuum system applications.

[Phys. Rev. Fluids 11, 033401] Published Mon Mar 02, 2026

Author(s): Ashish S. Nair, Narendra Singh, Marco Panesi, Justin Sirignano, and Jonathan F. MacArt

Hypersonic boundary layers in the transition–continuum regime (Knudsen number Kn ≈ 0.1–10) challenge Navier–Stokes solvers due to the breakdown of transport laws and slip/jump wall conditions. We embed physics-constrained neural closures for viscous stress and heat flux directly in the partial differential equations and train them using adjoint-computed gradients to match direct simulation Monte Carlo target data. A distribution-function wall model built from mixtures of skewed Gaussians replaces empirical slip-velocity models, substantially improving bulk flow and boundary-layer predictions and generalizing across unseen Mach numbers, Knudsen numbers, and geometries.

[Phys. Rev. Fluids 11, 033402] Published Mon Mar 02, 2026

Author(s): Thomas Boeck

Wall-attached Rayleigh-Bénard convection arises in the presence of a damping body force, e.g. the Coriolis or Lorentz force, when this force is less effective near a lateral boundary than in the bulk. The shape of the container is important in this context. A numerical linear stability analysis of Rayleigh-Bénard magnetoconvection in a wide rectangular container with a vertical magnetic field and electrically insulating walls shows that the least stable mode of convection becomes localized in the corners rather than spread out over the whole circumference of the container. This corner mode has a similar dependence on the magnetic field strength as the ordinary wall-attached mode.

[Phys. Rev. Fluids 11, 033501] Published Mon Mar 02, 2026