Spectral Peaks Due to ‘Guided Jet Waves’ in Plug Nozzle Flows

An experimental study was conducted to investigate the characteristics of ‘guided jet wave’ resonance tones occurring in nozzles with a center plug. The pressure fluctuation spectral peaks in the vicinity of the jet due to the resonance (referred as ‘GW peaks’) occur at frequencies that are an order of magnitude larger than those noted with simple round nozzles. It appears that the exit gap width of the plug nozzle is the characteristic length-scale that dictates the corresponding GW peaks. The relationship between the exit gap width and the GW peak frequencies is established based on near-field microphone measurements in experiments with varying plugs having different lengths, conical angles, and gap widths.