An experimental study of supersonic jet shock-associated noise

A new method of screech tone reduction in underexpanded supersonic jets is utilized to determine if the amplitude of screech is related to the level of shock-associated broadband noise. Acoustic measurements show that as the screech tone is reduced, the broadband shock-associated noise may be increased by up to 4dB at some locations. Several experiments were conducted with disturbances put into the flow upstream of the final contraction. Results from these tests support the concept of linkage between the broadband shock noise and screech tones. Some interesting preliminary results were obtained with a disturbance of the flow at several locations downstream of the nozzle. These results are also discussed.