Testing Installed Propulsion for Shielded Exhaust Configurations

Jet-surface interaction (JSI) can be a significant factor in the exhaust noise of installed propulsion systems. Tests to further the understanding and prediction of the acoustic impacts of JSI have been described. While there were many objectives for the test, the overall objective was to prepare for a future test validating the design of a low-noise, lowboom supersonic commercial airliner. In this paper we explore design requirements for a partial aircraft model to be used in subscale acoustic testing, especially focusing on the amount of aircraft body that must be included to produce the acoustic environment between propulsion exhaust system and observer. We document the dual-stream jets, both nozzle and flow conditions, which were tested to extend JSI acoustic modeling from simple singlestream jets to realistic dual-stream exhaust nozzles. Sample observations are provided of changes to far-field sound as surface geometry and flow conditions were varied. Initial measurements are presented for integrating the propulsion on the airframe for a supersonic airliner with simulated airframe geometries and nozzles. Acoustic impacts of installation were modest, resulting in variations of less than 3 EPNdB in most configurations.