Numerical investigations of the linear stability regime for a separation bubble on an Axisymmetric Compression Ramp at Mach 5

Numerical investigations were carried in order to investigate the transitional shock boundary-layer interaction (SBLI) on a hollow cylinder flare geometry at Mach 5. The geometry and flow conditions were matched, as closely as possible, to those in the experiments at the Mach 5 Ludwieg Tube (LT5) at the University of Arizona (UA). In the literature, different mechanisms have been proposed to play a role in the transition process of the separated region of the SBLI, such as the shear layer as the the Görtler instability. Our previous results for low amplitude three-dimensional wave packets and various flare angles, showed evidence that both these mechanisms are present in the simulations. Estimations of the Görtler number along a streamline, showed that for all the flare angles investigated the flow is highly unstable with respect to the Görtler instability. Additionally, estimates available in the literature regarding the azimuthal wavenumber corresponding to the Görtler vortices match reasonably well with results from the wave packets. For the shear layer instability, a good match is obtained between local LST and low amplitude controlled forcing simulations.