Hypersonic Boundary-Layer Receptivity over a Small Bluntness Wedge to Freestream Disturbances

Direct numerical simulations are performed to investigate the receptivity of a Mach 5 hypersonic boundary layer over a blunt wedge with a nose radius of 0.1 mm to planar freestream fast/slow acoustic, vorticity, and entropy waves. Isothermal and adiabatic wall conditions are used to study second-mode and first-mode receptivity, respectively. For the second mode, two distinct mechanisms are identified: fast acoustic waves generate a fast mode that evolves into the second mode via intermodal exchange, whereas other disturbances excite the second mode primarily via postshock nonmodal disturbances. Consequently, the receptivity coefficient for slow acoustic waves is approximately an order of magnitude smaller than that for fast acoustic waves. For the first mode, slow acoustic waves demonstrate the strongest excitation capability. The analysis reveals that the receptivity mechanism is intrinsically governed by the specific postshock disturbance distribution. It is these distinct receptivity pathways determined by the postshock field that lead to the substantial variations observed in receptivity coefficients.