Physical Review Fluids

Author(s): Jialiang Sun, Ning Huang, Binbin Pei, and Jie Zhang

Vegetation canopies in open-channel flows often experience time-dependent drag that reshapes turbulence near the canopy top. Using large-eddy simulation with a variable-drag model, we show that oscillatory drag reorganizes coherent vortices and shifts turbulent kinetic energy activity from the canopy-top shear layer into the canopy interior. The framework provides an efficient way to isolate how prescribed canopy drag affects turbulence structure and energy transport in large-domain simulations.

[Phys. Rev. Fluids 11, 044610] Published Mon Apr 27, 2026

Author(s): Chunxin Yuan, Shuying Zhang, Zhan Wang, and Xueen Chen

The Fully Dispersive Internal Wave (FDIW) equations, related on the two interface fluctuations in three-layer fluid, is derived from the stratified Euler equations using multiscale asymptotic expansion valid up to second-order nonlinearity. It can accommodate both mode-1 and mode-2 nonlinear internal waves and their transformations without further assumptions like the comparable phase speed of two modes needed in the well-known coupled Korteweg-de Vries (KdV) system, due to capturing all wavelengths without long-wave assumptions. The results indicate that coupled KdV equations should be used in the ocean with great caution as the difference between the KdV and FDIW equations is shown.

[Phys. Rev. Fluids 11, 044804] Published Mon Apr 27, 2026

Author(s): Hugo A. Castillo-Sánchez, Weston Ortiz, Richard Martin, Rukiye Tuna, Rekha R. Rao, and Z. Leonardo Liu

Blood flow in microcirculation exhibits complex, non-Newtonian behavior arising from red blood cell (RBC) migration and the formation of a near-wall cell-free layer (CFL), which remain challenging to capture with continuum models. Here, we introduce a modified suspension-balance model with a lift-force closure that bridges cell-level microrheology to continuum transport. The model quantitatively predicts CFL formation, hematocrit redistribution, and velocity blunting, while recovering key physiological signatures. This work provides an efficient continuum framework for capturing heterogeneous transport in concentrated deformable particle suspensions under confinement.

[Phys. Rev. Fluids 11, 043102] Published Fri Apr 24, 2026

Author(s): Kepeng Yao, Wenbin Liao, Guilai Han, and Zonglin Jiang

Oblique detonation waves are pivotal for hypersonic propulsion, but their stationary characteristics are rarely studied under controlled reaction rate distributions. Two-dimensional Euler simulations coupled with a two-step kinetic model are employed, and the effects of activation energy and reaction rate constant are isolated while induction and exothermic zone lengths are fixed. It is demonstrated that higher activation energy delays initiation and stabilizes oblique detonation, while unsteady upstream motion via thermal choking is triggered when a critical reaction rate is exceeded. A new stability criterion for oblique detonation is provided by these results.

[Phys. Rev. Fluids 11, 043202] Published Fri Apr 24, 2026

Author(s): Bikash Mohanty, Angshuman Nayak, and Aditya Bandopadhyay

We investigate the dynamics of a leaky dielectric droplet subjected to a superposed alternating and constant electric field using analytical small deformation theory and phase-field simulations. The mean and amplitude of droplet deformation depend on the mixing ratio (MR) and frequency of the superposed electric field. Results show that deformation amplitude under a superposed field is larger than in a purely alternating electric field. When the root-mean-square value of the superposed field exceeds that of the pure AC field, the mean deformation increases with increasing MR. The variation of the nondimensional oscillating interfacial kinetic energy with MR is also explored.

[Phys. Rev. Fluids 11, 043703] Published Fri Apr 24, 2026

Author(s): Weihao Ling, Zhiheng Wang, Zhenfei Wang, Wenlin Huang, and Guang Xi

We investigate the bypass transition of a flat-plate boundary layer over a three-dimensional irregular rough surface characterized by isotropic protrusions and a favorable-adverse pressure gradient. By positioning the roughness upstream of or adjacent to the separation point and introducing inlet free-stream turbulence of varying intensities and fundamental frequencies, the combined effects of pressure gradients, three-dimensional roughness, and free-stream turbulence on bypass transition and disturbance amplification are examined. Notably, when the rough surface is upstream of the separation point, intense low-frequency free-stream turbulence can excite novel elongated resonant modes.

[Phys. Rev. Fluids 11, 043905] Published Fri Apr 24, 2026

Author(s): Yuan Li and Chenglong Tang

Unlike-doublet impinging jets are widely used in hypergolic liquid rocket engines, but the role of inertia disparity in shaping atomization and mixing has remained unclear. Using high-fidelity Volume of Fluid simulations with intra-liquid species transport, we show that increasing inertia disparity narrows the spray, shortens liquid-sheet breakup, and reduces mixing efficiency. At high disparity, the jets exhibit central-axis collapse and mutual penetration, producing a distinctive flow-rate distribution. Flow topology analysis links these behaviors to Kelvin–Helmholtz type shear instabilities that generate vortices and drive liquid sheet collapse.

[Phys. Rev. Fluids 11, 044303] Published Fri Apr 24, 2026

Author(s): Rohini Uma-Vaideswaran and P. K. Yeung

The second-order Lagrangian velocity structure function in turbulence is a fundamental quantity for which clear inertial range scaling has been much more elusive than corresponding Eulerian measures. In this work direct numerical simulation at high Reynolds number is used to better understand the question of asymptotic constancy of the supposed scaling constant through effects of the acceleration autocorrelation function. A spatial-temporal decomposition of the Lagrangian velocity increment exposes strong but incomplete cancellation between convective and local contributions, with rapid approach of particle displacements towards inertial range values having an important role.

[Phys. Rev. Fluids 11, 044607] Published Fri Apr 24, 2026

Author(s): Taihang Zhu, Chao Xia, Jiabin Pang, Olivier Cadot, and Jonathan F. Morrison

We introduce a momentum decomposition framework to analyze the pressure field. It establishes a generic relationship between the mean pressure and flow statistics for turbulent flow, manifesting as fundamental mechanisms of pressure-gradient contributions in Cartesian coordinates involving mean flow accelerations, Reynolds stresses, and viscous stresses. With a focus on bluff body flows, this framework is validated in both laminar and turbulent regimes, providing a physical basis for flow analysis and control.

[Phys. Rev. Fluids 11, 044608] Published Fri Apr 24, 2026

Author(s): Xiaodong Wu, De Li, and Zhiming Lu

Counter-gradient transport in stably stratified shear turbulence remains poorly understood, particularly from a structural perspective. Using direct numerical simulations combined with the clustering method, this study identifies and characterizes coherent structures responsible for counter-gradient transport of heat and momentum. We find that such transport is dominated by structures larger than the Corrsin scale and primarily organized as paired Q1–Q3 events. Distinct physical mechanisms are revealed, with heat transport arising from both vortex-induced rotation and fluid parcel interactions, while momentum transport is governed solely by vortex-induced rotation.

[Phys. Rev. Fluids 11, 044609] Published Fri Apr 24, 2026

Author(s): Frederik R. Gareis and Walter Zimmermann

Outward-diffusing vorticity fields form around particles and droplets in time-periodic fluid motions. As a result, the time-dependent shear gradients in the fluid and at the particle surface are typically greater than those of the classical steady-state Stokes velocity profile. This leads to an additional viscous force, the Basset–Boussinesq history force (BBH), which depends on the past motion of the particle that created the vortices. An experiment with particles in a shaken fluid is proposed to measure the parameter dependence of the BBH, and parameter ranges are also predicted in which the BBH becomes comparable to or stronger than classical Stokes friction.

[Phys. Rev. Fluids 11, 043604] Published Wed Apr 22, 2026

Author(s): N. Sampara, G. Hunter-Brown, K. A. Baldwin, M. M. Scase, and R. J. A. Hill

While the coalescence of similarly-sized air bubbles in water is known to eject satellite bubbles, a complete model has remained elusive. Suspending unconstrained air bubbles using magnetic levitation, this study combines experiments and simulations to reveal how initial size ratios dictate the outcome, including twin satellites for equal-sized precursors. A timing model shows satellite production is governed by the coincidence of converging capillary waves and the retraction of the coalescing bubbles’ poles. Analysis of the capillary waves offers insight into why similarly-sized drops do not eject satellites in the same manner as bubbles.

[Phys. Rev. Fluids 11, 043605] Published Wed Apr 22, 2026

Author(s): Zehan Cao and Alan C. H. Tsang

Microswimmers under weak confinement exhibit flow fields that are highly dependent on the spatial arrangement of their propulsion and drag forces, as well as their geometry. These flow fields can be approximated by placing Stokeslets and source dipoles at proper positions of the swimmer. We observe versatile swimming trajectories, such as centerline sliding and amplified oscillations, depending on the relative strengths of the Stokeslets and source dipoles.

[Phys. Rev. Fluids 11, 044402] Published Wed Apr 22, 2026

Author(s): Cyril André, Cyriaque Amerein, Jonas Miguet, Benoit Scheid, and Stéphane Dorbolo

Antibubbles are the structural inverse of soap bubbles: they consist of a liquid core enclosed by a thin quasi-spherical gas shell, immersed in a liquid medium. Producing multilayer antibubbles, i.e. antibubbles enclosed by multiple soap/air films, has been a challenge in the past years, as it requires a delicate balance between surface tension and inertia. In this paper, we investigate a method that uses one or more soap films and a soapy liquid droplet to generate multilayer antibubbles. We also identify the optimal parameters for forming single-layer and multilayer antibubbles across three different viscosities.

[Phys. Rev. Fluids 11, 043603] Published Tue Apr 21, 2026

Author(s): Manthan Verma, Abhishek K. Jha, and Mahendra K. Verma

The total energy spectrum exhibits a Kolmogorov-like scaling, consistent with the conservation of total energy in the system. However, the kinetic and magnetic energy spectra often diverge from the −5/3 scaling. In this paper, we show that this divergence arises from energy transfer between the velocity and magnetic fields, either from velocity to magnetic field or vice versa. Our extensive numerical simulations therefore demonstrate Kolmogorov-like phenomenology for isotropic MHD turbulence.

[Phys. Rev. Fluids 11, 043701] Published Tue Apr 21, 2026

Author(s): Manthan Verma, Abhishek K. Jha, Shashwat Nirgudkar, and Mahendra K. Verma

For isotropic magnetohydrodynamic (MHD) turbulence, we employ high-resolution numerical simulations and compute the energy spectra and fluxes, as well as the structure functions, of Elsässer variables. While the competing spectral indices 5/3 and 3/2 are too close, the 5/3 index still provides a better fit to the energy spectra. More importantly, the structure functions strongly support the Kolmogorov-like phenomenology. Additionally, the energy fluxes in imbalanced MHD are consistent with the predictions of the Kolmogorov-like model. The figure shows normalized cross helicity of 0.65.

[Phys. Rev. Fluids 11, 043702] Published Tue Apr 21, 2026

Author(s): Armin Kalita, Bryan Oller, Thomas Paula, Alexander Bußmann, Sebastian Marte, Gabriel Blaj, Raymond G. Sierra, Sandra Mous, Kirk A. Larsen, Xinxin Cheng, Matt J. Hayes, Kelsey Banta, Stella Lisova, Peter Nguyen, Serge A. H. Guillet, Divya Thanasekaran, Silke Nelson, Mengning Liang, Stefan Adami, Nikolaus A. Adams, and Claudiu A. Stan

Optical images of transparent objects depend in a complicated way on their three-dimensional properties, which made it difficult to simulate such images accurately. Using ray tracing with calibrated illumination, we simulated with high fidelity images of drops with complex shapes, and images of pressure waves inside drops. The simulated images can be used to visualize, validate, and refine fluid dynamics models. They can also be used to determine multiple three-dimensional properties from experimental images.

[Phys. Rev. Fluids 11, 044908] Published Mon Apr 20, 2026

Author(s): Yali Kedem, Bimalendu Mahapatra, and Evgeniy Boyko

Viscoelastic flows through narrow, nonuniform geometries are common in engineering and biological systems, yet the pressure drop behavior of such fluids remains poorly understood. We develop a theoretical model for the flow of an Oldroyd-B fluid in slowly varying constrictions, deriving closed-form expressions for the elastic stresses and pressure drop valid for all Deborah numbers in the ultra-dilute limit. Our theory is in excellent agreement with numerical simulations and reveals key differences between constrictions and contractions, including a plateau in the pressure drop at high Deborah numbers and a significantly shorter relaxation length in the exit channel of the constriction.

[Phys. Rev. Fluids 11, 043303] Published Mon Apr 20, 2026

Author(s): Jingyu Cui, Xiang Zhu, Yiting Zhang, Zuchao Zhu, and Yuzhen Jin

We perform a comprehensive numerical study of standard, inverted, and wall-mounted flag models to reveal how flag-induced dynamics and vortex organization control thermal transport. The results identify distinct vortex-generation mechanisms for each configuration and map their high-efficiency regimes in the parameter space of bending stiffness and Reynolds number. These findings clarify the thermo-hydraulic performance limits of flexible flags and provide guidance for designing efficient passive heat transfer enhancers.

[Phys. Rev. Fluids 11, 044103] Published Fri Apr 17, 2026

Author(s): Bérengère Dubrulle, Antoine Barlet, Amaury Barral, Adam Cheminet, Guillaume Costa, Pietro Dragoni, Abhishek Harikrishnan, Adrien Lopez, Kirone Mallick, and Quentin Pikeroen

[Phys. Rev. Fluids 11, 049901] Published Fri Apr 17, 2026