New Papers in Fluid Mechanics

Author(s): F. Novotný, M. Talíř, E. Varga, and L. Skrbek

Temporal decay of rotating turbulent thermal counterflow of He II is probed by second sound and found to display interesting new features. Two effects are observed, acting against each other and affecting the late temporal decay of vortex line density, L(t). The first one is gradual decrease of the decay exponent of the power law L(t), confirming that turbulent thermal counterflow under rotation acquires 2D features. The second one is the influence of the effective Ekman layer built within the effective quantum Ekman time. For increasing rotation rates, L(t) gradually ceases to display a clear power law. Instead, rounded and ever steeper decays occur, gradually shifted toward shorter times.

[Phys. Rev. Fluids 11, 034603] Published Tue Mar 03, 2026

Author(s): Ruifeng Yuan and Lei Wu

Smaller gas-solid contact area or smaller bifurcation angle? What happens when inlet and outlet conditions are exchanged? This study employs topology optimization to investigate optimal manifold configurations across gas rarefaction regimes and uncovers two counterintuitive phenomena: a wetted-area minimum in the slip regime and inlet–outlet reciprocity in free-molecular flows. These findings provide crucial guidance for microfluidic and vacuum system applications.

[Phys. Rev. Fluids 11, 033401] Published Mon Mar 02, 2026

Author(s): Ashish S. Nair, Narendra Singh, Marco Panesi, Justin Sirignano, and Jonathan F. MacArt

Hypersonic boundary layers in the transition–continuum regime (Knudsen number Kn ≈ 0.1–10) challenge Navier–Stokes solvers due to the breakdown of transport laws and slip/jump wall conditions. We embed physics-constrained neural closures for viscous stress and heat flux directly in the partial differential equations and train them using adjoint-computed gradients to match direct simulation Monte Carlo target data. A distribution-function wall model built from mixtures of skewed Gaussians replaces empirical slip-velocity models, substantially improving bulk flow and boundary-layer predictions and generalizing across unseen Mach numbers, Knudsen numbers, and geometries.

[Phys. Rev. Fluids 11, 033402] Published Mon Mar 02, 2026

Author(s): Thomas Boeck

Wall-attached Rayleigh-Bénard convection arises in the presence of a damping body force, e.g. the Coriolis or Lorentz force, when this force is less effective near a lateral boundary than in the bulk. The shape of the container is important in this context. A numerical linear stability analysis of Rayleigh-Bénard magnetoconvection in a wide rectangular container with a vertical magnetic field and electrically insulating walls shows that the least stable mode of convection becomes localized in the corners rather than spread out over the whole circumference of the container. This corner mode has a similar dependence on the magnetic field strength as the ordinary wall-attached mode.

[Phys. Rev. Fluids 11, 033501] Published Mon Mar 02, 2026

Author(s): Abdallah Daddi-Moussa-Ider, Jakob Mihatsch, Michael J. Mitchell, Elsen Tjhung, and Andreas M. Menzel

Wedge-shaped confinements are increasingly relevant in low-Reynolds-number microfluidics, yet existing Green’s functions describe only flows driven by point forces. We derive the flow induced by localized torques using a Fourier–Kontorovich–Lebedev framework combined with the Papkovich–Neuber representation. The resulting solutions reveal how geometric asymmetry couples rotation and translation and yield the full torque– mobility tensor. These analytical results provide predictive tools for controlling particle motion in confined microfluidic systems.

[Phys. Rev. Fluids 11, 034101] Published Mon Mar 02, 2026

Author(s): Yutaro Motoori, Pierre Bragança, and Susumu Goto

We introduce a simple method to objectively identify the axes of coherent vortices in turbulence using only the velocity-gradient tensor. The method is readily applicable to experimental data. As an example, applying it to stereo-PIV measurements of a wind-tunnel turbulent boundary layer, we quantitatively show that boundary-layer-scale vortices form hairpin shapes.

[Phys. Rev. Fluids 11, 034601] Published Mon Mar 02, 2026

Author(s): Francesca De Serio

In rotating geophysical flows, turbulence can either drive small-scale mixing or build large-scale coherent eddies. Here, a very large rotating-tank jet experiment with planar particle imaging velocimetry (PIV) is used to map the local energy flux across scales. The results show that stress–strain alignment and a local jet Rossby number organize where and how long inverse energy-cascade patches appear. This identifies a local control parameter for steering energy pathways in jet-like environmental flows.

[Phys. Rev. Fluids 11, 034602] Published Mon Mar 02, 2026