Physical Review Fluids

Author(s): Derek Goulet, Anna Pauls, Aaron True, and John Crimaldi

Many animals leverage stereo inhalation for respiration and olfaction, drawing fluid and odors into a spatially separated pair of nares. Olfaction efficacy is known to be enhanced by the structure and dynamics of flow exterior and interior to the nares. We characterized stereo inhalation flow kinematics and capture volumes using numerical models of an idealized, dual siphon geometry, providing further context for sensory adaptations. We find capture volumes that are modulated by Reynolds number and siphon geometry, suggesting that organisms may alter morphology and inhalation dynamics at behavioral or evolutionary timescales to increase fitness.

[Phys. Rev. Fluids 11, 033102] Published Mon Mar 16, 2026

Author(s): Marco Cattaneo and Outi Supponen

Acoustic radiation force can be used to steer ultrasound contrast microbubbles toward the desired clinical target, but the link between their oscillations, displacement, and stability has remained unclear. By tracking single lipid-coated microbubbles in free space, we show that their displacement is accurately captured only when history drag is included in the force balance. A simple linear scaling connects volumetric expansion to transport distance. Above a critical radial expansion, however, shape-mode oscillations emerge and dissolution rises sharply, revealing a trade-off between transport efficiency and bubble integrity.

[Phys. Rev. Fluids 11, 033606] Published Mon Mar 16, 2026

Author(s): Thomas Appleford, Vatsal Sanjay, and Maziyar Jalaal

This paper addresses the problem of a two-dimensional (2D) droplet under shear. We introduce an analytical approach, utilizing a 2D Lamb solution to derive an expression for the apparent viscosity of a dilute 2D emulsion and to develop a deformation theory for small capillary numbers. Validated through direct numerical simulations, our findings establish benchmarks for computational fluid dynamics methods and for interpreting 2D droplet behavior.

[Phys. Rev. Fluids 11, 033607] Published Mon Mar 16, 2026

Author(s): Amlan K. Barua, Shuwang Li, John S. Lowengrub, Wenjun Ying, and Meng Zhao

While classical Hele-Shaw models focus on single interface dynamics, the mechanisms driving instabilities in multi-connected fluid domains remain largely unexplored. We reveal that the spatial configuration and viscosity of internal fluid domains fundamentally break radial symmetry, triggering viscous fingering on the outer boundary. By strategically arranging these inner interfaces under a time dependent injection flux, one can suppress unfavorable instabilities and actively promote preselected, self-similar limiting shapes.

[Phys. Rev. Fluids 11, 033902] Published Mon Mar 16, 2026

Author(s): Mario Sánchez Sanz and Antonio L. Sánchez

Classic orifice flow models, originally developed for low-Reynolds-number liquids, use the decoupling between velocity and concentration fields to simplify the analysis. This simplification fails for gaseous mixing, where composition changes directly alter the velocity field. Our study addresses the coupling in the Sc ∼ Pe ∼1 regime typical of gas-delivery systems. We introduce a unified framework that combines new analytical solutions for low Pe with simulations. This approach provides quantitative predictions for mass-transfer rates and pressure drops, and can help design the restrictive orifices critical to semiconductor manufacturing and precision gas-delivery technology.

[Phys. Rev. Fluids 11, 034103] Published Mon Mar 16, 2026

Author(s): Chengbin Zhang, Suchen Wu, Xiangdong Liu, and Yongping Chen

Simulations of interfacial mass transfer often interpolate the diffusion flux at the interface, making concentration predictions artificially sensitive to the chosen interface width. In this study, we propose a source-free phase-field-lattice-Boltzmann model that ensures bulk concentration profiles remain completely independent of interface thickness. We also introduce an additional free parameter to the evolution equation of the model, which significantly improves its numerical stability under low Henry constants. The proposed framework is highly beneficial for investigating complex multiphase systems, such as those involving surfactants or Marangoni effects.

[Phys. Rev. Fluids 11, 034501] Published Mon Mar 16, 2026

Author(s): Zhenyang Yuan, Simon Demange, Kilian Oberleithner, André V. G. Cavalieri, and Ardeshir Hanifi

Broadband trailing edge noise is generated by the scattering of three-dimensional hydrodynamic structures, but the role of spanwise wavenumber selection in acoustic radiation for a finite spanwidth airfoil remains unresolved. Wall resolved compressible large eddy simulation of a NACA0012 airfoil shows that nonzero spanwise modes become dominant above the acoustic cut-on frequency associated with obliquely convecting wavepackets identified via spectral proper orthogonal decomposition (SPOD). A reduced-order model based on extended SPOD reproduces far-field noise using only a small number of modes, providing a compact and control oriented framework for noise prediction and mitigation.

[Phys. Rev. Fluids 11, 034606] Published Mon Mar 16, 2026

Author(s): Jibu Tom Jose, Gal Friedmann, Dvir Feld, and Omri Ram

Turbulent flow through sudden pipe expansions is widely studied, yet the role of expansion angle in shaping turbulence structure remains poorly understood. Using high-resolution stereo-Particle-Imaging-Velocimetry in a refractive-index-matched facility, we directly compare abrupt (90°) and gradual (45°) axisymmetric expansions. We show that slope fundamentally reorganizes the return flow, amplifying shear-layer interaction, turbulence production, and anisotropy in gradual expansions. The results provide a mechanistic explanation for the higher losses long observed in sloped geometries.

[Phys. Rev. Fluids 11, 034607] Published Mon Mar 16, 2026

Author(s): Shuangqian Han, Zhe Ma, Yonglin Qin, and Baoshan Zhu

Rotating stall in reversible pump-turbines operating in the S-shaped region degrades stability and drives strong torque and pressure oscillations, yet quantitative inception prediction remains limited. Based on small-disturbance theory, we couple runner perturbation dynamics with the external system characteristic to analyze resonance and stability of disturbance waves and predict stall onset, wave speed, and cell number. Unsteady CFD ramp-downs from runaway to low flow under four guide-vane openings, with wavelet analysis of vaneless area pressure, validate the model’s accuracy in predicting stall onset.

[Phys. Rev. Fluids 11, 034702] Published Mon Mar 16, 2026

Author(s): Kaiyuan Shi, Renchuan Zhu, and Yulong Li

Traditional simulations of large-scale fully nonlinear free-surface wave–body interactions remain computationally demanding. We present a spectral–fundamental solution (SFS) method that combines global spectral bases with local fundamental solutions, achieving high efficiency across large domains while maintaining accuracy near the body surface. Using this method, we investigate nonlinear ship-wave dynamics in extensive domains. The simulations reveal the physical origins of distinct energy bands in ship wakes, the effects of acceleration on wake evolution, and the mechanism behind wake-angle narrowing at high speeds.

[Phys. Rev. Fluids 11, 034801] Published Mon Mar 16, 2026

Author(s): Michael Berhanu, Amit Dawadi, Martin Chaigne, Jérôme Jovet, and Arshad Kudrolli

We demonstrate that asymmetric ice blocks floating in water can self‑propel while melting. Experiments with triangular ice prisms show that melting generates a directed, buoyancy‑driven gravity current along the inclined face, producing steady translation. A momentum‑balance model quantitatively predicts the propulsion velocity as a function of ice geometry and bath temperature. This mechanism persists in saltwater at sufficiently warm temperatures, highlighting melting as a generic propulsion mechanism in buoyancy‑driven flows and a possible secondary contributor to iceberg drift.

[Phys. Rev. Fluids 11, 033802] Published Fri Mar 13, 2026

Author(s): Giuseppe Procopio

Singular solutions in the stationary Stokes regime are reported for fluids confined by cylindrical walls. The stokeslet, stresslet, couplet, point source, and point source dipole are obtained internally, externally, and within the annular region between cylindrical walls using bitensorial calculus. Beyond providing hydrodynamic solutions relevant to particle transport in confined environments, this work highlights the strength of bitensorial calculus in handling curved geometries and systematically yielding hydrodynamic singularities within a unified framework. Forces on sedimenting particles and active microswimmers near cylindrical walls are investigated as an application.

[Phys. Rev. Fluids 11, 034201] Published Fri Mar 13, 2026

Author(s): Melisa Y. Vinograd, Joaquín Cullen, and Patricio Clark Di Leoni

How many degrees of freedom characterize turbulent flow? We investigate the dimensionality of two-dimensional Kolmogorov flow across Reynolds numbers and forcing scales using convolutional autoencoders and Lyapunov analysis. Two dynamical transitions are identified, first associated with periodic-orbit destabilization and later with large-scale saturation. The resulting saturation dimension scales linearly with the forcing wavenumber rather than with the total number of available Fourier modes.

[Phys. Rev. Fluids 11, 034402] Published Fri Mar 13, 2026

Author(s): Bowen Jin, Jiadong Wang, and Jian Deng

Intermittent swimming boosts efficiency—but at what cost? Using two-dimensional simulations of an unconstrained pitching foil, we show that burst-and-coast motion induces pronounced lateral drift and a sharp, amplitude-driven reversal in trajectory direction. The deflection is governed by Strouhal-controlled scaling and wake realignment across burst and glide phases. These results uncover how intermittent kinematics trade stability for energetic advantage.

[Phys. Rev. Fluids 11, 034701] Published Fri Mar 13, 2026

Author(s): Aaron Winn and Eleni Katifori

Peristaltic pumping drives flow in diverse biological and engineered systems. Previous models focus solely on radius-imposed contraction waves or neglect the elastic coupling between radial and longitudinal strains. By describing the fluid using the material coordinates of the deforming wall, we analyze flow in a tube undergoing simultaneous transverse and longitudinal contractions. We show that the elastic coupling between circumferential and longitudinal strains strongly alters net transport, reflux, and trapping, as compared to the case with radial contractions alone.

[Phys. Rev. Fluids 11, 033101] Published Thu Mar 12, 2026

Author(s): Dongfang Zhao, Yumin Shi, and Shengkai Wang

We developed a new method for high-resolution measurement of CO2 transport across the air–water interface, addressing a critical need in physical oceanography studies and in modern carbon sequestration applications. This method forgoes conventional probe-based sampling and statistical correlation, and exploits precision laser spectroscopy with rapid spatial beam scanning to directly quantify gas-phase CO2 distribution near the interface at millimeter and millisecond resolutions. To our knowledge, this is the first time such a level of resolution has been achieved. This method should prove useful in both field measurements and laboratory studies of cross-interface gas transport.

[Phys. Rev. Fluids 11, 034903] Published Thu Mar 12, 2026

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