Effects of local suction on boundary-layer instability and acoustic radiation

Abstract eng:
When a boundary—layer instability mode propagates through a region of rapid distortion, its amplitude changes substantially while at the same time a sound wave is radiated, both due to the ensuing scattering. This paper focuses particularly on the impact of a local suction on an incident T—S wave by employing a Local Scattering Theory. The central idea is to introduce a transmission coefficient, defined as the ratio of the T—S wave amplitude downstream of the scatter to that upstream. The mathematical description is based on the triple—deck formulism, but in order to accommodate the acoustic field, the unsteady terms in the upper deck are retained. It is found that a suction slot would suppress the oncoming T—S wave. The intensity of the radiated sound increases with the mass flux if the latter is not too large, but is suppressed when the flux exceeds a critical value.

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