WAVES PRODUCED FROM A HARMONIC POINT-SOURCE IN A SUPERSONIC BOUNDARY-LAYER FLOW

The disturbance wave pattern produced from a harmonic point source in a compressible flat-plate boundary layer is computed using linear stability theory and the direct numerical integration approach. Receptivity coefficients are computed for a wide band of least-stable spanwise modes generated at the source, which are followed in the streamwise direction in order to study the wave-interference pattern. The effect of boundary-layer growth on the development of linear waves is determined by using the method of multiple scales. Results are presented for Mach numbers of 0, 2 and 7. It is found that disturbances spread in wedge-shaped regions behind the source and the wedge angle decreases with Mach number. The lateral spreading angle for the instability waves turns out to be quite close to the angle found experimentally for lateral contamination of turbulence. It is found that, owing to wave cancellation, the computed maximum disturbance amplitude is significantly lower than that obtained by following the most-amplified single normal mode.