There has been a renewed interest in studying hypersonic boundary layer stability in flows with highly-cooled walls due to its applicability to experiments and some real flight conditions. One physical phenomenon that occurs in these flows is the creation of a supersonic mode, also referred to as the spontaneous radiation of sound. The spontaneous radiation of sound is associated with an unstable Mack's second mode synchronizing with the slow acoustic spectrum, causing the disturbance to travel upstream supersonically relative to the meanflow outside the boundary layer. Previous studies have focused specifically on a two-dimensional flat plate geometry and have assumed chemical equilibrium, or have focused on a sharp cone geometry. However, the spontaneous radiation of sound is yet to be investigated in detail on an axisymmetric blunt cone. This study aims to investigate the existence of the spontaneous radiation of sound in Mach 5 flow over a 1 mm nose radius cold-wall cone using thermochemical nonequilibrium LST and DNS studies and investigate in further detail the impact of supersonic modes on disturbance growth. Results indicate that the supersonic mode creates an abnormal growth pattern that is not observed in traditional flows with second-mode transition. This behavior could have an impact on energy transfer and boundary layer stability.
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