Scaling of Entropy Layer Instabilities in High-Speed Flows

This study discusses entropy layer instabilities and proposes a way to scale them with the free-stream Mach number. The entropy layer that develops over a blunt body in hypersonic flow is calculated in the inviscid limit, using a high-precision spectral shock-fitting method that solves the nonlinear Euler equations within the shock layer. Linear stability theory is employed to examine instabilities linked to the generalized inflection point within the entropy layer on a blunted 30-degree wedge, serving as a model geometry. These instabilities are found to be largely independent of the Mach number when appropriately normalized. Our findings suggest that, under the assumption of a calorically perfect gas, instabilities at different Mach numbers can be related to each other.