Low-frequency unsteadiness in hypersonic swept shock wave-boundary layer interactions

We carry out a numerical study of swept shock wave/turbulent boundary layer interaction in the hypersonic regime. Starting from a numerical/experimental benchmark case of a nearly adiabatic two-dimensional hypersonic interaction, a crossflow velocity component is added to the incoming flow to mimic three-dimensional interactions with cylindrical symmetry. We observe, for a fixed streamwise Mach number, monotonic increase of the extent of the interaction region for the swept cases. An attempt at extending the free-interaction theory to hypersonic swept interactions is made, which is found to apply only to the initial part of the interaction region. The spatiotemporal dynamics of wall pressure on mean separation line features large-scale pressure corrugations, which are advected at a phase speed which is a fraction of the mean crossflow velocity, if present. The characteristic wavelength of the corrugation is found to be a multiple of the separation bubble size. The numerically estimated peak frequencies well conform with the previously introduced formula for swept supersonic interactions [Ceci et al., J. Fluid Mech. 956, R1 (2023)]. Proper orthogonal decomposition is applied to investigate the spatial structure of the corrugation at the separation point and educe phase relations between the flow structure and pressure oscillations at the reattachment point. The present analysis leads us to conclude that the same phenomenology found in swept supersonic interactions also holds in the hypersonic case.