Effect of a two-dimensional smooth hump on linear instability of hypersonic boundary layer is studied. Parabolized stability equations (PSE) is employed to analyze the linear evolution of mode S over a hump in Mach 4.5 and 5.92 flat plate and Mach 7.1 sharp cone boundary layers. Mean flow for stability analysis is obtained by solving the parabolized Navier-Stokes (PNS) equations. Hump with height smaller than local boundary layer thickness is used. The case of flat plate and sharp cone without the hump are also studied to provide comparable data. For flat plate boundary layers, destabilization and stabilization effect of hump located at upstream and downstream of synchronization point are confirmed. Results of parametric studies to examine the effect of hump height, location, etc. are also given. For sharp cone boundary layer, stabilization influence of hump is also identified for a specific range of frequency. Stabilization influence of hump on convective instability of mode S is found to be a possible cause of previous experimental observations of delaying transition in hypersonic boundary layers.
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