Stationary global instabilities in shock wave/ hypersonic laminar boundary layer interaction

Instabilities in canonical two-dimensional shock-wave boundary layer interactions can provide insight into three-dimensional flow structures and their wall imprints. We identify and report two distinct stationary instabilities in steady two-dimensional shock boundary layer interaction as the free-stream Reynolds number is increased. While both instabilities are associated with three-dimensional flow in the recirculation bubble, the long span instability marks the development of recirculation span cells and the short span instability marks the split of the recirculation core. The appearance of distinct spanwise length scales associated with the two instabilities is confirmed with experimental observations. The physics of perturbation growth is analyzed for both global instabilities and perturbation compressibility is found to play a role in the mechanism. Lastly, we compare and contrast the behavior of the global instabilities with the Gortler instability prevalent in the region of large curvature near boundary layer reattachment.