Hypersonic vehicles in real flight environment involve high-enthalpy conditions. As a result, the study of the boundary-layer laminar-turbulent transition for such vehicles needs to consider thermochemical non-equilibrium phenomena. Non-equilibrium effects on hypersonic boundary-layer stability and transition are a subject of ongoing research. In this paper, two cases of hypersonic flow are investigated: a high-enthalpy Mach 11.18 flow over a blunt cone and a low-enthalpy AEDC boundary-layer transition experiment over a sharp cone. We have documented the effects of non-equilibrium on steady flow solutions for both the high-enthalpy case and the low-enthalpy cases. For the high-enthalpy case, unsteady simulations based on perfect gas model and a lumped Landau-Teller vibrational relaxation model are conducted by imposing multi-frequency slow acoustic waves in the freestream. The results show the excitation of the first mode near the leading edge. In addition, non-equilibrium effects generally destabilize the first mode.
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