New Papers in Fluid Mechanics

Author(s): Aidan Hunt, Brian Polagye, Ari Athair, and Owen Williams

The efficiency of an array of turbines operating in a channel is influenced by how much of the channel the array occupies, represented as the blockage ratio. In this work, the performance and near-wake flow field of a cross-flow turbine array are evaluated across a range of blockage ratios through laboratory experiments. An analytical linear momentum actuator disk model is found to be predictive of the measured velocity of the fluid that bypasses the array. When the array performance is scaled by the bypass velocity in a manner inspired by Maskell’s bluff-body theory, self-similar performance is observed across blockage ratios, highlighting the salient dynamics of highly-confined turbines.

[Phys. Rev. Fluids 10, 084802] Published Tue Aug 19, 2025

Author(s): Arupjyoti Das, Manohar Sharma, Avishek Ranjan, and Mahendra K. Verma

A coherent vortex column in rotating turbulence forms, bursts apart due to instabilities, and reforms again — a cycle driven by a tug-of-war between the destabilizing effect of elliptical instability and the stabilizing influence of rotation. Using Fourier-space analysis, including ring spectra and mode-to-mode energy transfer, we identify a forward energy cascade and the activation of vertical modes (kz = 2, 3) as precursors to bursting, indicating how spectral energy transfer drives the collapse and reformation of the structure.

[Phys. Rev. Fluids 10, 084803] Published Tue Aug 19, 2025

Author(s): Patrick M. McGah

The work considers the normal mode stability of plane Poiseuille flow under stable density stratification. The problem is analyzed at low Peclet numbers representing liquid metal flows of interest in advanced nuclear reactor designs. The eigenvalue problem is solved numerically, and a perturbation series is also developed for small stratification. Numerical and perturbation series results indicate that stratification has a purely stabilizing effect on the normal modes. All normal modes are found to be stable when a modified Richardson number, R = Ri × Pe, is greater than about 0.33.

[Phys. Rev. Fluids 10, 083901] Published Mon Aug 18, 2025