Instability and Transition Induced by Distributed Roughness in High-Speed Boundary Layer

This study investigated distributed-roughness-induced instability and boundary-layer transition in high-speed boundary layers using direct numerical simulation, BiGlobal linear stability analysis, and plane-marching parabolized stability equations. Sinusoidal roughness patterns with different wavelengths and freestream Mach numbers were examined. Despite changes in the geometric parameters of the roughness, two types of counter-rotating streamwise vortex pairs were consistently observed to disto