Hypersonic flow over spherically blunted double cones

A hypersonic shock wave/laminar boundary-layer interaction over a canonical double-cone configuration is numerically investigated. A moderate-enthalpy flow of with a Mach number of 9.87 and a unit Reynolds number of is considered. Special emphasis is given to the influence of leading-edge bluntness. The results indicate that the double-cone flow is insensitive to small bluntness in terms of shock structures, separation region sizes and surface pressure and heat flux distributions. A critical nose radius is observed, beyond which the separation bubble grows dramatically. The numerical data are analysed and interpreted based on a triple-deck formulation. It is shown that the sudden change in flow features is mainly caused by pressure overexpansion on the first cone due to leading-edge bluntness, such that the skin friction upstream of the separation is significantly reduced and the upstream pressure can no longer resist the large adverse pressure gradient induced by shock impingement. An estimation of the critical radius is established based on the pressure correlations of Blick & Francis (AIAA J., vol. 4 (3), 1966, pp. 547-549) for spherically blunted cones. Simulations at a higher enthalpy with the presence of both vibrational relaxation and air chemistry show a similar trend with increasing nose radius. The proposed criterion agrees well with the experimental observations.