Inertial instability of von Karman street in a rotating shallow-water layer

Abstract

The rotation alters the stability of 2D anticyclonic flow with respect to 3D perturbations. Experiments have shown that such instability induces a transient destabilization of anticyclonic vortices in von Kármán street, when w/f < -1. However, the persistence of this selective destabilization was never studied experimentally in a shallow-water layer. In order to investigate the impact of this vertical confinement on the inertial or the centrifugal instabilities we perform experiments on the LEGI Coriolis Platform, with a finite Rossby number, a small vertical to horizontal aspect ratio and a large Reynolds number (Re > 5 000). We have shown that unstable 3D-perturbations occur for large enough Rossby number (Ro > 0.8) while the Reynolds number seems to control the duration of this transient instability. According to PIV measurements we have shown that, unlike the deepwater configuration, the small-scale perturbations do not reduce the local vorticity inside the unstable antiyclone. Finally, for high Rossby numbers, when the flow becomes supercritical (Fd > 1), due to the generation of high amplitude wave wake the vortex street intensity is strongly reduced.