Physical Review Fluids

Author(s): Qian Mao, Umberto D'Ortona, and Julien Favier

Micro-scale cilia play a vital role in mucociliary clearance (MCC) in the human respiratory airways. We develop a three-dimensional model for predicting MCC with two-way coupling between the cilia and the two-phase airway surface liquid, comprising the periciliary layer (PCL) and the mucus layer (ML). Focusing on a single cilium, we systematically examine the effects of PCL thickness and the viscosity ratio between the PCL and ML, which can vary markedly under pathological conditions. The fluid transport mechanisms are clarified by identifying two competing effects, namely the balance between drag and elastic forces and the viscous diffusion of momentum, and by establishing quantitative relationships between the flow rate and the beating pattern.

[Phys. Rev. Fluids 11, 013102] Published Wed Jan 28, 2026

Author(s): Leo R. M. Maas and Eyal Heifetz

The dynamics of a stratified, rotating fluid, contained in a box and subject to differential heating in the horizontal direction, is approximated by a low-order set of five nonlinear ordinary differential equations (ODEs). Its forced and damped versions reduce to well-known ODEs for convection or long-wave dynamics. In the ideal fluid limit, one integral of motion represents initial stratification and motion. The remaining equations, capturing the essence of ‘rotating horizontal convection’, are integrable in the absence of rotation or differential heating. In general, they represent a forced, complex Duffing equation that appears to be a generalized nonintegrable 2 DOF Hamiltonian system.

[Phys. Rev. Fluids 11, 013506] Published Wed Jan 28, 2026

Author(s): Owen Thompson, Kyriakos Tapinou, Daryl Bond, and Vincent Wheatley

Shock-driven Richtmyer–Meshkov instability is central to astrophysical and inertial-confinement-fusion plasmas, where kinetic-scale effects invalidate single-fluid MHD descriptions. Using an ideal two-fluid plasma model, we show that a magnetic field parallel to the interface suppresses instability growth by transporting and phase-mixing interfacial vorticity on plasma wave packets, with increasing efficacy at smaller plasma length scales. In contrast, an out-of-plane magnetic field fails to suppress the instability and instead promotes Kelvin–Helmholtz–like roll-up through charge-separation-driven vorticity generation.

[Phys. Rev. Fluids 11, 013702] Published Wed Jan 28, 2026

Author(s): P. Beaumard, J. P. Laval, and J. C. Vassilicos

Existing large eddy simulation models suffer from a lack of physical justification. In this paper, the links between two-point equations derived from the Navier-Stokes equation and Large Eddy Simulation (LES) are examined and an approximation of an exact equation is used to design a new subgrid-scale model. This new model is tested both a priori and a posteriori and is found to capture the correct physical energy transfer between filtered scales and residual subfilter scales. This is a proof of concept that two-point equations can be used to develop new LES models and this strategy may be the right one for developing more efficient models.

[Phys. Rev. Fluids 11, 014607] Published Wed Jan 28, 2026

Author(s): David Martín, Joan Grau, and Lluís Jofre

Turbulence in supercritical fluids differs from its low-pressure counterpart due to strong thermodynamic coupling and pseudoboiling effects, yet their influence on velocity and thermodynamic fluctuations remains unclear. Using direct numerical simulations of isotropic turbulence in supercritical fluids, small-scale statistics are examined. Temperature-related quantities are particularly sensitive, exhibiting increased intermittency of temperature variance dissipation rate and reduced production of mean-square temperature gradients. Topological analysis also shows that regions of intense pseudoboiling activity suppress strain-dominated structures while enhancing vortical motions.

[Phys. Rev. Fluids 11, 014609] Published Wed Jan 28, 2026

Author(s): Ran Qiao, Kai Mu, Chengxi Zhao, and Ting Si

Although thermal fields are known to influence liquid jet instability, prior studies have focused primarily on axisymmetric disturbances. This work reveals that a temperature field can excite a dominant non-axisymmetric helical mode, driven by azimuthal Marangoni stresses. We show that enhancing the Marangoni effect or suppressing thermal diffusivity promotes this helical instability, triggering a fundamental transition from Rayleigh-Plateau to azimuthal Marangoni-driven destabilization. Phase diagrams provide criteria for predicting this mode transition, offering new insights into controlling jet stability in applications such as ink printing and fiber production.

[Phys. Rev. Fluids 11, 014006] Published Tue Jan 27, 2026

Author(s): Mano Grunwald and Claudia E. Brunner

We experimentally investigate the impact of different inflow conditions on the breakdown of wind turbine tip vortices in a high Reynolds number wind tunnel. The data in this paper is obtained through hot wire spectral analysis. While downstream evolution of the spectra exhibits a complex scale dependent behavior, here we focus on the decay of the signature of the tip vortices for which we identify three distinct regimes. These regimes are linked to an initial advection phase, vortex breakdown, and turbulence decay. Variations in the tip speed ratio have a significant impact on the breakdown rate in the second regime, while effects of mean shear and turbulence intensity are less pronounced.

[Phys. Rev. Fluids 11, 014608] Published Tue Jan 27, 2026

Author(s): Gonzalo G. de Diego and Georg Stadler

Polar sea ice is a crucial component of Earth’s climate system which is generally modeled as a non-Newtonian fluid in climate simulations. To overcome the accuracy limitations of existing non-Newtonian models for sea ice, we present a framework for learning an effective shear viscosity function for sea ice from velocity data. We apply our approach to data generated from a complex sea ice discrete element method (DEM). The learned rheology is capable of reproducing the DEM velocity data accurately.

[Phys. Rev. Fluids 11, 013301] Published Mon Jan 26, 2026

Author(s): Maria Vlachomitrou, Georges Chabouh, Alkmini Lytra, and Nikos Pelekasis

This paper offers new insight into the nature of active matter and the design of coated microbubbles to act as microswimmers for ultrasound assisted drug delivery, by clarifying the role of shape imperfections in their dynamics. It shows that even small initial defects can significantly reduce the buckling threshold, while the symmetry of the imperfection governs the emerging post-buckling shapes. The resulting asymmetric shapes induce translational motion in the direction of concavity, with velocities that strongly depend on the acoustic frequency and shell properties.

[Phys. Rev. Fluids 11, 013603] Published Mon Jan 26, 2026

Author(s): Yu Zhang, Hong-Fei Xie, Kang Luo, Jian Wu, and Hong-Liang Yi

Electro-thermoconvection (ETC) turbulence can enhance heat transfer under microgravity conditions. Using direct numerical simulation for ETC turbulence in a cavity, we find that the flow field exhibits several main modes. In contrast, the temperature and charge fields are only dominated by a specific mode in ETC turbulence. The heat transfer efficiency of ETC turbulence can be up to two orders of magnitude compared to a conduction state. It is also found that there is a potential scaling law between the Nusselt number and electric-driven parameters.

[Phys. Rev. Fluids 11, 013701] Published Mon Jan 26, 2026

Author(s): Ryuta X. Suzuki, Yusuke Nabae, and Hiroya Mamori

Partially miscible viscous fingering differs from the classical Saffman–Taylor instability by producing droplets through flow-induced phase separation. Experiments in a PEG–Na2SO4–water system reveal how Hele–Shaw gap confinement and flow rate control droplet formation and interfacial complexity. The total interfacial length collapses onto a universal scaling with the flow-rate-to-gap ratio, with an exponent consistent with a balance between inertial and capillary stresses. These findings identify an inertia-modified capillary regime and offer predictive insight into pattern selection in partially miscible displacement flows.

[Phys. Rev. Fluids 11, 014005] Published Mon Jan 26, 2026

Author(s): Evgeny V. Polyachenko, Ilia G. Shukhman, and Michael Karp

The exponential decay due to Landau damping, unlike unstable modes, corresponds to no eigenmode - it lacks an eigenfunction, being a continuous superposition of singular van Kampen modes with real eigenfrequencies. Introducing arbitrarily small dissipation qualitatively transforms this: an exponentially decaying eigenfunction emerges, while the eigenvalue remains nearly identical to the Landau damping rate. Using hyperbolic tangent flow, we trace the vorticity transition in plane-parallel shear flows from nearly inviscid to purely inviscid conditions and study corresponding eigenfunction structure. Local vorticity disturbances in initial-value problems quickly assume this eigenfunction form.

[Phys. Rev. Fluids 11, 014101] Published Mon Jan 26, 2026

Author(s): Dongjie Jia, Mohammad Majidi, Kurt D. Ristroph, and Arezoo Ardekani

We used a high-fidelity simulation framework to study the fluid and mixing dynamics inside two turbulent mixers: the multi-inlet vortex mixer (MIVM) and the confined impinging jets mixer, operating under various conditions. We identify differences in turbulence onset, total energy, and mixing performance of two MIVM configurations. This study demonstrates the importance of a high-accuracy numerical scheme for simulating turbulent mixers and understanding performance differences among them.

[Phys. Rev. Fluids 11, 014502] Published Mon Jan 26, 2026

Author(s): Ashish Mishra, Paolo Personnettaz, George Mamatsashvili, Vladimir Galindo, and Frank Stefani

Effect of endcaps are of fundamental interest in Taylor-Couette (TC) experiments, including magnetorotational instability (MRI)-experiments. Understanding their influence on the TC flow dynamics is essential for the interpretation of experimental results. In this work, we studied the endcap effects in a Rayleigh-stable TC flow at high, experimentally relevant Reynolds numbers. The main result is that split-endcaps reduce Ekman pumping in the bulk flow and induce turbulence, which however remains localized in their vicinity. Endcaps modify the mean azimuthal velocity profile that in turn results in the lower threshold of the MRI onset, potentially facilitating its experimental detection.

[Phys. Rev. Fluids 11, 014606] Published Mon Jan 26, 2026

Author(s): Uttam Cadambi Padmanaban, Bharathram Ganapathisubramani, and Sean Symon

Assimilating planar experimental data using standard two-dimensional constraints often distorts the momentum balance, as the model artificially compensates for the lack of divergence in the measurements. We demonstrate that enforcing three-dimensional constraints (3DVar) resolves this ambiguity in deep stall flows. By enabling spanwise flow development, 3DVar balances experimental divergence errors with physical gradients rather than artificial forcing. This isolates measurement inconsistencies from turbulence model deficits, yielding physically consistent reconstructions of unmeasured quantities like pressure and eddy viscosity.

[Phys. Rev. Fluids 11, 014904] Published Mon Jan 26, 2026

Author(s): Yangyang Cao, Alexander Kurganov, Masoud Rostami, Chenxi Wang, and Vladimir Zeitlin

We introduce the Magnetohydrodynamic Thermal Rotating Shallow Water (MTRSW) model, a novel framework for studying thin, magnetized, and stratified fluid layers in geophysical and astrophysical contexts, such as the solar tachocline. This model integrates thermal gradients and magnetic fields with rotation, revealing their coupled impact on stability. Furthermore, we incorporate Hall effects, enabling the model to capture essential small-scale physics like fast magnetic reconnection.

[Phys. Rev. Fluids 11, L011701] Published Mon Jan 26, 2026

Author(s): Praphul Kumar and Jason R. Picardo

Phytoplankton, like dinoflagellates, produce mesmerizing displays of light when subjected to the turbulent flow in breaking waves and ship wakes. Here, we ask how bioluminescence is affected by turbulence, given that dinoflagellates flash with an intensity that increases with both the extent and rate of deformation. Introducing a light-emitting dumbbell as a minimal model, we show that intermittent fluctuations of the velocity-gradient subjects dinoflagellates to bursts of extreme straining, which in turn produces bright flashes. Comparisons with steady and Gaussian-fluctuating flows demonstrate that light emission is strongly promoted by the dissipation-scale intermittency of turbulence.

[Phys. Rev. Fluids 11, L012602] Published Mon Jan 26, 2026

Author(s): Alexandre Vierron and Chérifa Abid

This study investigates the effect of the thermal conductivity of titanium dioxide (TiO2) nanoparticles suspended in water on heat transfer dynamics and the formation of convection cells. Experimental observations reveal that colloidal stability and nanoparticle sedimentation strongly influence the evolution of convection patterns and overall heat transfer. Due to the low particle concentration and small size, a thin heat-conducting sediment layer forms within the thermal boundary layer. This locally enhances the conductive heat flux in the lower boundary layer, leading to an asymmetry in the temperature profile between the top and bottom of the cavity.

[Phys. Rev. Fluids 11, 013505] Published Fri Jan 23, 2026

Author(s): Davis J. Evans, Bauyrzhan K. Primkulov, and John W. M. Bush

Droplets walking on a vibrating liquid bath have provided a platform for exploring the boundary between classical and quantum physics. The system is typically considered with monochromatic bath forcing, in a parameter regime in which the droplets bounce either in-phase or out-of-phase with respect to each other. We demonstrate here that the application of an additional subharmonic forcing allows for control of the droplets’ relative phase. The figure shows (a) an irregular array of bouncing drops in which the leftmost drop (blue) is out-of-phase with its neighbours (red) transforming into (b) an array in which all droplets bounce in synchrony in response to the subharmonic forcing.

[Phys. Rev. Fluids 11, 014003] Published Fri Jan 23, 2026

Author(s): Sihang Liu, Ran Gao, Shuai Yin, Zhi Tao, Haiwang Li, and Yi Huang

Droplet impact on liquid pools has long been analyzed using energy-balance models dominated by inertial and gravitational effects. In the low-Froude-number regime relevant to immiscible droplet encapsulation and interfacial processing, however, the partitioning of impact energy remains poorly understood. Here we show experimentally that, alongside gravitational potential energy, surface energy and viscous dissipation make significant contributions to cavity dynamics. By incorporating cavity shape deviations and viscous losses into a revised energy framework, we establish an improved scaling description for cavity penetration in immiscible liquid impacts.

[Phys. Rev. Fluids 11, 014004] Published Fri Jan 23, 2026