An approach to noise reduction of a supersonic jet with a spherical reflector

Abstract

A new method of reducing the jet screech is explained. A spherical reflector is placed at the nozzle exit for reducing this screech component. The placement of the spherical reflector at the nozzle exit controls the location of the image source as well as minimizes the sound pressure at the nozzle exit. The weak sound pressure does not excite the unstable disturbance at the exit, thus the loop of the feedback mechanism cannot be accomplished and the jet screech is not generated. The technique of screech reduction with the flat plate is also examined and compared with the present method. A good and effective performance in canceling the screech component by the new method is found by the investigation. Experimental results indicate that the new system suppresses not only the screech tones but also the broadband noise components and reduces the overall noise. The spherical reflector is very effective in reducing overall sound pressure level in the upstream region of the nozzle compared to a flat plate. The proposed spherical reflector can, accordingly, protect the upstream noise propagation.