SCREECH TONES OF SUPERSONIC JETS FROM BEVELED RECTANGULAR NOZZLES

It is known experimentally that an imperfectly expanded rectangular je t from a thin-lip convergent nozzle emits only a single dominant scree ch tone. The frequency of the screech tone decreases continuously with an increase in jet Mach number. However, for a supersonic jet issued from a bevelled nozzle or a convergent-divergent nozzle with straight side walls, the shock cell structure and the screech frequency pattern are fairly complicated and have not been predicted before. It is show n that the shock cell structures of these jets can be decomposed into waveguide modes of the jet flow. The screech frequencies are related t o the higher-order waveguide modes following the weakest link screech tone theory. The measured screech frequencies are found to compare web with the predicted screech frequency curves.