Receptivity of the flow on the stagnation streamline of a blunt body in supersonic flow

The receptivity of the inviscid flow on the stagnation streamline of a blunt body in supersonic flow is investigated theoretically for incoming free-stream disturbances. The wave transmission and coupling are quantified by solving the linearised shock-fitting problem with a spectral method, whereas the steady base flow is obtained using a nonlinear shock-fitting spectral solver. Revisiting previous theoretical work, we identify and correct an error in a key coefficient in the analysis by Morkovin (1960 J. Appl. Mech. , 27 , pp. 223–229), overturning the prior conclusion of body-induced damping and revealing amplification instead. The post-shock entropy disturbances display singular behaviour near the stagnation point, which is treated analytically. Acoustic disturbances dominate pressure and velocity responses, while density is affected by both acoustic and entropy modes. The base flow pressure gradient introduces weak coupling between the acoustic and entropic components of the response. The actual stagnation-line base flow amplifies all disturbances more than the simplified model of uniform post-shock flow; as well as a shock without a body, and the differences are quantified for a range of Mach numbers. The responses to entropy, fast acoustic and slow acoustic waves are compared as functions of the free-stream Mach number.