High-Speed Jet Noise Reduction Using Microjets on a Jet Engine

Abstract

by a jet engine. Experiments were conducted at the NASA Ames Research Center using a General Electric YJ97-GE-3 turbofan jet engine that was equipped with a 317.5 mm converging nozzle. The engine was operated at conditions that resulted in jets with fully expanded Mach numbers of 0.9 and 1.3. The microjets were generated using up to 48 evenly spaced micro-nozzles that had exit diameters of 1.2 and 2.4 mm. The operating pressure of the microjets was varied from 7.9 to 42.4 bar. Various microjet configurations were used resulting in a total mass flux of the microjets that ranged from 0.5 to 2.3 % of the primary mass flux for the subsonic jet and from 0.3 to 1.0 % of the primary mass flux for the supersonic jet. Through the various configurations it was found that reductions of up to 2 dB in the OASPL could be obtained for both the subsonic and supersonic jets. The reductions for the subsonic jet were seen at all frequencies while they were seen primarily at the higher frequencies for the supersonic jet. A reduction of about 2 dB in the shock noise of the supersonic jet was also observed.