Effect of localized wall cooling or heating on streaks in high-speed boundary layers

High-amplitude upstream disturbances and wall surface roughness elements trigger streamwise/Görtler vortices and the associated streaks in boundary layers over flat or concave surfaces. Following the transient growth phase, the fully-developed vortices become sensitive to inviscid secondary instabilities, which ultimately result in a premature transition to turbulence. Our work aims at investigating the effect of cooling/heating on the initiation and development of such streaks in an attempt to gain a better understanding of the conditions and governing mechanisms leading to secondary instabilities in high-speed compressible boundary layers. We conduct a parametric study via a robust and efficient numerical solution to the non-linear compressible boundary region equations (NCBRE) to identify the impact of varying the wall temperature on the development of streaks in supersonic and hypersonic boundary layer flows.