Jet Noise Reduction and Shielding by using a Spherical Reflector

Abstract

Experiments were carried out to eliminate the screech tone generated from a supersonic jet by using a spherical reflector. In order to reduce the jet screech the reflector was placed at the nozzle exit. The placement of the spherical reflector at the nozzle exit controlled the location of the image source as well as minimized the sound pressure at the nozzle exit. The weak sound pressure did not excite the unstable disturbance at the exit. Thus the loop of the feedback mechanism could not be accomplished and the jet screech was eliminated. The technique of screech reduction with a flat plate was also examined and compared with the present method. A good and effective performance in canceling the screech component by the new method was found. Experimental results indicate that the new system suppresses not only the screech tones but also the broadband noise components and reduces the overall noise of the jet. The spherical reflector was found very effective in reducing overall sound pressure level in the upstream region of the nozzle compared to a flat reflector