An experimental investigation into the acoustic characteristics of hot high-subsonic three-stream axisymmetric and offset jets was conducted. The exhaust system consisted of externally-mixed convergent nozzles and an external plug. Jet offset was created by anally offsetting the tertiary stream. Bypass-to-core area ratios equal to 1.0, 1.5, and 2.5 with tertiary-to-core area ratios equal to 0.8 and 1.0 were investigated. The effects of core-nozzle cowl length, fan-nozzle cowl length, and nozzle area ratios on the resulting far-field radiation were studied. For the axisymmetric configurations, decreasing the core-nozzle cowl length increased low-frequency radiation at all polar angles while the fan-nozzle cowl length had no impact on acoustic radiation. For the offset configurations, the acoustic radiation appeared to be impacted by the nozzle internal contours rather than nozzle cowl lengths. The largest noise reductions were achieved with the small (0.8) tertiary-to-core area ratio nozzles and were found to provide a 0.5 EPNdB reduction over that of the axisymmetric jets at full scale for NASA's N+2 Supersonic Aircraft.
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