Control of supersonic jet noise using a wire device

The present study describes a new technique for the reduction of supersonic jet noise using a control wire device that is placed into the supersonic jet stream. The control wire device is composed of long cylinders with a very small diameter and its location is varied to investigate the control effectiveness of supersonic jet noise. The jet pressure ratio is varied to obtain the supersonic jets which are operated in a wide range of over-expanded to moderately under-expanded conditions. A high-quality Schlieren optical system is used to visualize the flow field of supersonic jets both with and without the control wire device. In order to quantify the control effect of the wire device on a supersonic jet, pressure measurements are also accomplished. Acoustic measurements are performed to obtain the overall sound pressure level and noise spectra. The results obtained show that the present wire device effectively breaks the shock-cell structure, reduces the shock strength, and consequently leads to a substantial suppression of supersonic jet noise. The location of the control wire device is an important factor in reducing the supersonic jet noise. The present wire device suppresses the screech tones and the broadband shock-associated noise as well as the overall sound pressure level, when it is placed at a location smaller than three times the exit diameter of nozzle in the downstream of the nozzle exit. For over-expanded jets, the noise control effectiveness of the wire device appears more significant, compared to under-expanded jets.