Effects of nozzle configuration and bypass ratio on the aeroacoustics of dual stream supersonic jets

Multi-stream, variable cycle point, low bypass ratio, turbofan engines are in consideration for future tactical aircraft. Such engine architectures aim to cycle between high-thrust and high-efficiency operation as required by the demands of the flight profile. There exists a need to improve the understanding of the aeroacoustic characteristics of low bypass ratio, multi-stream exhaust jets. This work reports on far field acoustic measurements of heat-simulated, supersonic jets exhausting from small-scale dual stream, rectangular nozzles. Comparisons are made to elucidate the effects of bypass ratio on the radiated noise. Comparisons are made on a combined constant mass flow rate and constant estimated thrust basis. Data are compared with far field noise measurements of an asymmetric, dual stream circular jet operating at the same total pressures and (simulated) total temperatures. The results of acoustic measurements indicate how components of the noise are influenced by the flow geometry and changes in dual stream nozzle operating conditions.