Strato-rotational instability in Rayleigh-stable regimes

Naturally-occurring and engineering flow systems are commonly influenced by stratification and rotation. While the Coriolis force induced by the rotation can suppress or promote centrifugal instability (CI) depending on its direction and strength, following the Rayleigh’s criterion for CI, stable stratification tends to suppress the vertical fluid motion leading to the delay of the onset of CI and its turbulence. Regardless, with stratification and rotation, inertia-gravity waves can be triggered and their resonance can lead to a new type of instability called the strato-rotational instability (SRI). The regime of SRI is different from that of CI as the instability does not depend on the profile of rotation but it depends rather on stratification strengths, boundary conditions, etc. In this talk, we will present some recent progress on SRI occurring in stratified Taylor-Couette (TC) flow, a shear flow between two concentric cylinders rotating independently. Following a previous work [1], we will unveil different SRI regimes, which lie outside the regime of CI predicted by the Rayleigh’s criterion, by a parametric investigation with linear stability analysis. We will also discuss about effects of stratification and diffusion, as similarly done in [2] for CI, on the dynamics of SRI with a focus on nonlinear phenomena such as saturation, secondary instability or laminar-turbulent transition in stratified TC flow, the phenomena explored by direct numerical simulations.