JET NOISE REDUCTION BY A CROSS WIRE DEVICE IN SUPERSONIC JET ISSUING FROM A CONVERGENT-DIVERGENT NOZZLE

摘要

The present study describes experimental work on a method of reducing supersonic jet noise. A cross wire device is placed inside a supersonic jet stream, operating from over-expanded to moderately under-expanded conditions. Acoustic measurement is performed to obtain overall sound pressure level and noise spectra with regard to the screech tones and the broadband shock-associated noise. A schlieren optical system is used to visualize the jet flow with and without the noise control device. The obtained results show that by suitably placing the cross wire device in the downstream of the nozzle exit, the present noise control device breaks the shock-cell structures, leading to a reduction in the shock strength, and the suppression of the screech tones and the broadband shock-associated noise. For over-expanded jets, the noise control effect using the cross wire device appears more remarkable, compared with moderately under-expanded jets.