Control of supersonic jet noise with a spherical reflector

Abstract

Jet screech is considered to be generated from a feedback cycle in an underexpanded supersonic jet. Experiments were carried out to control the screech tone by placing a spherical reflector at the nozzle exit. The reflector controlled the location of the sound image-source and minimized the sound pressure at the nozzle exit. The weak sound could not excite the unstable disturbances at the exit and the feedback mechanism was cancelled and finally screech tone was eliminated. The new technique suppressed not only the screech tones but also the broadband noise and reduced the overall sound pressure of the jet. The performance of the proposed technique was checked with different sizes of reflectors by placing the reflectors at different upstream positions of the nozzle exit for different pressure ratios and the result was very good. [The research was supported by a grant from JSPS of the government of Japan.]