Simulation of Supersonic Military Aircraft Jet Noise

Background: There is a growing need to reduce significantly the noise generated by high-performance, supersonic military aircraft. The noise generated during takeoff and landing on aircraft carriers has direct impact on shipboard health and safety issues. Also, noise complaints are increasing as communities move closer to military bases or when there are changes due to base closures and realignment. There is a significant amount of literature dealing with noise reduction in civilian, subsonic aircraft; some of the techniques found effective for those aircraft might be applicable for supersonic military jets. A distinct difference between civilian aircraft engines and advanced military aircraft engines is that military engines tend to have low bypass ratios and high velocities. During certain flight conditions — such as during takeoff or landing — the exhaust from these engines tends to be non-ideally (under/over) expanded. Non-ideally expanded exhaust flows contain shock cells in the jet exhaust, causing high-amplitude screech tones and broadband shockassociated noise, components that increase the overall noise level. Therefore, our current research is focused on understanding these non-ideally expanded exhaust flow conditions and characterizing the noise sources, so that noise reduction techniques may be successfully pursued.