New Papers in Fluid Mechanics

Author(s): M. Rubio, S. Rodríguez-Aparicio, M. G. Cabezas, J. M. Montanero, and M. A. Herrada

Tip streaming in a coflowing device is probably the simplest way to generate quasi‑monodisperse droplets that are much smaller than the device’s fluid passages. We show that flow stability cannot be determined from the linear stability analysis of the steady microjetting mode but from the linear superposition of decaying eigenmodes triggered by an initial perturbation. The red line in the image corresponds to a direct numerical simulation of an asymptotically stable microjetting. The experiment and simulation show the perturbation growth leading to jet breakup. These results call into question the validity of linear stability analysis applied to coflowing and similar configurations.

[Phys. Rev. Fluids 11, 024001] Published Mon Feb 02, 2026

Author(s): Yunpeng Wang, Huiyu Yang, Zelong Yuan, Zhijie Li, Wenhui Peng, and Jianchun Wang

A machine-learning-based surrogate model is proposed for the large-eddy simulation of three-dimensional turbulent flows over curved boundaries with strong flow separation. The model, termed as hybrid U-Net and Fourier neural operator (HUFNO), is based on an integrated framework of convolutional neural networks and Fourier neural operators, tailored for problems involving mixed periodic and non-periodic boundary conditions. The HUFNO model is validated in the fast prediction of turbulent dynamics of periodic-hill flow, with transferable accuracy to unseen initial conditions, Reynolds numbers, and hill shapes.

[Phys. Rev. Fluids 11, 024601] Published Mon Feb 02, 2026

Author(s): A. Shrestha, E. Kirkinis, and M. Olvera de la Cruz

Electrolyte-filled channels with modulated wall charge distribution subjected to an applied DC electric field form time-independent vortices whose sense of circulation is determined by the field direction [Phys. Rev. Lett. 75, 755 (1995)]. In this paper, we show that an electrolyte in a channel or c…

[Phys. Rev. E 113, 015106] Published Fri Jan 30, 2026

Author(s): Yi Zhang, Apurav Tambe, and Zhao Pan

The maximum droplet volume that a fiber can retain is a classic problem in the physics of droplet-fiber interactions, with established results for horizontal and Λ-shaped bent fibers. However, this question has remained less explored for V-shaped bent fibers, despite their relevance to fog harvesting and condensation technologies. Here, we develop a free-energy- based analytical model to predict the maximum droplet volume on V-shaped fibers and validate it experimentally using multiple liquid-fiber pairs. We reveal a non-monotonic dependence of the maximum droplet volume on the fiber opening angle, identifying a transition regime that facilitates droplet detachment.

[Phys. Rev. Fluids 11, 013604] Published Thu Jan 29, 2026

Author(s): Santiago Caro, Riccardo Artoni, Patrick Richard, Michele Larcher, and James T. Jenkins

Sheared polydisperse granular materials exhibit a subtle balance between size segregation and diffusion that governs their transverse dynamics. Combining annular shear cell experiments with discrete numerical simulations, we investigate how confinement, shear localization, granular temperature, and mixture composition control segregation in nonuniform flows. Beyond the classical gravity-driven mechanism, we identify inverse and horizontal segregation modes that emerge from flow kinematics and geometry. These mechanisms hinder complete segregation, explaining the persistence of mixing in steady-state granular systems.

[Phys. Rev. Fluids 11, 014305] Published Thu Jan 29, 2026

Author(s): Linhao Li, Md M. A. Sohag, Kan Liu, Jian Wu, and Xiufeng Yang

This work investigates the dynamics of dual-drop impact on a solid surface, encompassing both simultaneous and nonsimultaneous side-by-side impact of equal-sized drops, as well as successive impact of unequal-sized drops. Numerical simulations are performed using smoothed particle hydrodynamics meth…

[Phys. Rev. E 113, 015105] Published Thu Jan 29, 2026

Author(s): Beverley McKeon and Eric Lauga

[Phys. Rev. Fluids 11, 010001] Published Wed Jan 28, 2026

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): Y. M. Zhang, H. González, F. J. García de Bollullos, P. A. Vazquez, and H. L. Yi

A single droplet can be effectively isolated from a capillary liquid jet by applying a short-duration velocity oscillatory pulse at its exit from the nozzle outlet. The previous temporal analysis of F. J. García et al. [Phys. Rev. E 100, 053111 (2019)], which modeled the jet as an infinite liquid c…

[Phys. Rev. E 113, 015104] Published Tue Jan 27, 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