Receptivity pathways of the boundary layer on a blunt hypersonic cone by adjoint Green's function

Accurate boundary-layer transition prediction on hypersonic vehicles requires flight tests to calibrate models partly due to the limitations of current ground facilities and uncertainty in the free-stream disturbance environment. The method presented here uses Green’s functions of the adjoint equations to interrogate the possible linear receptivity mechanisms by which disturbances of a certain type in the free-stream can excite the boundary layer near the location of transition. The method is validated using tunnel data and is used to provide a quantitative assessment of possible receptivity pathways on a blunt cone at Mach 8. The results provide a framework to understand how the transition location changes under different disturbance environments and at different conditions.