Exploratory investigation of jet engine silencing with plug nozzle configurations

Abstract : The objective in the present exploratory investigation was to determine experimentally whether significant silencing could be obtained with noise suppressors that could be conveniently incorporated within the plug nozzle configuration. The 1/3-octave band sound power radiated by the plug nozzle incorporating various suppressor concepts was compared with that of the conventional converging-diverging nozzle and with that of the conventional multi-tube nozzle noise suppressor. Comparisons were also made of the measured thrust of the various nozzles and of the directivity of the radiated sound. Shadow-graph pictures of the flow from some of the nozzles were obtained. The tests were made mainly at a ratio of nozzle total pressure to ambient pressure of 3 which is representative of the pressure ratios during take-off in high performance turbojet engines (jet Mach number approximately 1.4). (Author)