Effects of nozzle trailing edges on acoustic field of supersonic rectangular jet

Acoustic measurements of a Mach 2, rectangular nozzle with modified trailin g edges mere carried out using three microphones, placed 90 deg apart azimu thally in a plane normal to the jet axis. The measurements were obtained at three streamwise locations, with microphone angles of 90, 60, and 30 deg w ith respect to the jet centerline. The trailing-edge modified nozzles subst antially reduced the turbulent mixing and broadband shock associated noise radiation by up to 12 dB for the underexpanded flow regime and up to 7 dB f or the overexpanded condition. However, in some symmetric modifications, th e very-high-frequency noise was increased for the overexpanded condition. S creech tones in the overexpanded how condition were either reduced or elimi nated for asymmetric modifications, but amplified for symmetric modificatio ns. The trailing-edge modifications were found to not significantly alter t he noise field for the ideally expanded flow condition.