Sensitivity of a supersonic boundary layer to acoustic disturbances (Q1317651)

The results are obtained in the case of arbitrary angles of incidence of the external wave. It is possible to distinguish two excitation channels: the first is connected with the diffraction of the acoustic wave by the spatial inhomogeneity resulting from the displacing action of the boundary layer, and the second with the presence of concentrated acoustic field sources associated with the scattering of the wave at the leading edge. At low angles of incidence, there is a singularity which can be revealed by introducing narrow intervals in the neighbourhood of the limiting values of the wave numbers, where the two excitation channels are approximately equivalent. It is possible to obtain composite expressions for the initial amplitudes of the unstable modes uniformly valid for all angles of incidence of the acoustic wave.