Abstract
The near-field acoustic characteristics of underexpanded jets from notched nozzles have been investigated via an optical wave microphone. This laser-based microphone not only leaves jet flow unobstructed, but it also enables us to measure the simultaneous sound propagation in both vertical and horizontal directions. As a result, through the observation of the real time fluctuation of jet noise, we came to the conclusion that the screech tone from 2-notched nozzle is propagated solely on the unnotched side with sound speed, and the strongest source of noise can be moved when the notch number is changed.
