Latest papers in fluid mechanics

Author(s): Yee Li (Ellis) Fan, Bernardo Palacios Muñiz, Nayoung Kim, and Devaraj van der Meer

Upon the impact of a flat disk on a boiling liquid, i.e., a liquid that is in thermal equilibrium with its vapor, a thin vapor pocket is entrapped under the disk. We experimentally investigate the dynamics of the entrapped vapor pocket, focusing on its time evolution and its subsequent influence on the hydrodynamic loads under various conditions. We found that the dynamics of the entrapped vapor pocket is primarily governed by the phase change process, where condensation (vaporization) will induce (frustrate) its rapid collapse, impairing the cushioning. This differs significantly with that of a non-condensable air pocket, which is known to always provide a load reducing cushioning effect.

[Phys. Rev. Fluids 10, 100505] Published Mon Oct 27, 2025

Author(s): Ján Šimkanin and Juraj Kyselica

The impact of different buoyancy sources on convection within the Earth’s core and the resulting magnetic field is numerically investigated. To explore this, three models — thermally driven, chemically driven, and thermochemically driven dynamos — are gradually analyzed. These analyses confirm that both the magnetic field and the convective velocity field depend on the sources of buoyancy. Furthermore, the study finds that dipole polarity reversals and the super-rotation of the Earth’s inner core are influenced by different buoyancy sources. Note, as the viscosity decreases, this dependence weakens.

[Phys. Rev. Fluids 10, 103705] Published Mon Oct 27, 2025

Author(s): Zhengyang Wei and Chang Liu

Input-output analysis has been widely used to predict the transition to turbulence in wall-bounded shear flows, but it typically does not capture the full nonlinear effects. This work analyzes nonlinear input-output stability of transitional shear flows using the Small-Signal Finite-Gain (SSFG) stability theorem. This SSFG stability can predict permissible forcing amplitudes below which a finite nonlinear input-output gain can be maintained. The nonlinear input-output gain obtained from the SSFG stability theorem is higher than the linear input-output gain. The permissible forcing amplitude identified from the SSFG stability theorem is consistent with that obtained by bisection search.

[Phys. Rev. Fluids 10, 103903] Published Fri Oct 24, 2025

Author(s): Mingyun Xie, Qichao Li, Shengqi Wu, Hong Liu, and Lin Fu

In this study, we simulated liquid jets in supersonic crossflow (LJSC) under various inflow Mach numbers using the diffuse interface method. The results show that as the Mach number increases, the liquid jet exhibits reduced penetration and faster fragmentation, accompanied by different breakup modes. A theoretical model was developed to predict the near-field trajectory, which shows good agreement with experimental and numerical data. The proposed primary breakup model can be incorporated into Lagrangian methods to enhance computational accuracy.

[Phys. Rev. Fluids 10, 104006] Published Fri Oct 24, 2025

Author(s): Rémi Macadré, Frédéric Risso, Olivier Masbernat, and Roel Belt

Direct numerical simulations are used to analyze the flow in an annular plane Couette geometry in the laminar regime. A secondary flow is consistently present due to centrifugal effects associated with rotation, regardless of Reynolds number (Re). By increasing the rotation speed, the flow becomes more confined to the walls, leading to progressively thinner boundary layers. Consequently, the primary flow develops into an S-shaped profile, reminiscent of turbulent regimes. At high Re and large channel aspect ratios, an asymptotic regime is observed, the characteristics of which are discussed. This flow is well suited for studying the rheology of highly concentrated two-phase dispersed flows.

[Phys. Rev. Fluids 10, 104102] Published Fri Oct 24, 2025

Author(s): He Zhao (赵河), Zexu Yuan (苑泽旭), Wenjin Han (韩文晋), and Dengming Wang (王等明)

Granular flows of non-spherical particles exhibit complex dynamics that challenge classical rheological descriptions. Using discrete element method (DEM) simulations, we show that superballs display distinct flow behaviors, including enhanced boundary effects, modified velocity profiles, and increased bulk viscosity, compared to spheres. We develop a particle-shape-dependent constitutive model incorporating dimensionless granular temperature to capture nonlocal effects, validated through continuum simulations. This framework enables accurate prediction of flow behaviors across quasistatic and inertial regimes, advancing the modeling of granular systems with complex particle geometries.

[Phys. Rev. Fluids 10, 104306] Published Fri Oct 24, 2025

Author(s): Long Wang and Guowei He

The space-time decorrelation of a passive scalar advected by turbulent flows is dominated by three physical processes: mean-flow carrying downstream, large-eddy random sweeping, and small-eddy distortion. Each process has been investigated through Taylor’s frozen-flow hypothesis and Kraichnan’s random-sweeping and white-noise models. However, their coupling effects remain unexplored. The present paper proposes the Taylor–Kraichnan model to represent the coupled effects of the three processes and leads to the exact solution of space–time correlation. The scale invariance of the space–time correlation is found and consistent with the elliptical approximation model.

[Phys. Rev. Fluids 10, 104607] Published Fri Oct 24, 2025