Supersonic Jet Exhaust Noise

An empirical model to predict the effects of flight on the noise from a supersonic transport is developed. This model is based on an analysis of the exhaust jet noise from high subsonic flights of the F-15 ACTIVE Aircraft. Acoustic comparisons previously attainable only in a wind tunnel were accomplished through the control of both flight operations and exhaust nozzle exit diameter. Independent parametric variations of both flight and exhaust jet Mach numbers at given supersonic nozzle pressure ratios enabled excellent correlations to be made for both jet broadband shock noise and jet mixing noise at flight speeds up to Mach 0.8. Shock noise correlated with flight speed and emission angle through a Doppler factor exponent of about 2.6. Mixing noise at all downstream angles was found to correlate well with a jet relative velocity exponent of about 7.3, with deviations from this behavior only at supersonic eddy convection speeds and at very high flight Mach numbers. The acoustic database from the flight test is also provided.Norum, Thomas D. and Garber, Donald P. and Golub, Robert A. and Santa Maria, Odilyn L. and Orme, John S.Armstrong Flight Research Center; Langley Research CenterJET AIRCRAFT NOISE; JET EXHAUST; SUBSONIC SPEED; SUPERSONIC SPEED; MATHEMATICAL MODELS; AEROACOUSTICS; FLIGHT TESTS; SHOCK WAVES; SUPERSONIC TRANSPORTS; MACH NUMBER; JET MIXING FLOW; F-15 AIRCRAFT; PRESSURE RATIO; EXHAUST NOZZLES; VORTICES; DATA REDUCTION; DATA ACQUISITION

The report summarizes the results obtained at General Electric during the first phase of the Air Force Supersonic Exhaust Noise - Velocity Model Program. The overall objective of the program is to develop the technology to significantly reduce supersonic aircraft propulsion system noise with minimum associated performance and weight penalties. To fulfill that objective, research is being carried out to develop the experimental techniques and the necessary theory to reveal the basic mechanisms of jet generated noise through the range of velocities and temperatures typical of present and future military and commercial supersonic aircraft propulsion systems. A comprehensive aerodynamic analytical model describing the flow mechanisms in supersonic jets is presented and compared with experimental data. A large number of theoretical models describing supersonic far field jet noise are evaluated. (Author).

This progress report summarizes the major theoretical and experimental efforts performed during the first year of a two-year program sponsored by the Air Force and the Department of Transportation on Supersonic Jet Exhaust Noise. The overall objective of the program is to develop the technology to significantly reduce supersonic aircraft propulsion system noise with minimum associated performance and weight penalties. To reach the objectives of this program a varied and comprehensive research program is being carried out to develop the basic theory and experimental methods for understanding and quantizing the acoustic characteristics of simple supersonic jets for a range of velocities and temperatures typical of present and future military and commercial supersonic aircraft propulsion systems. (Modified author abstract).

This report discusses detailed accounts of major theoretical and experimental investigations directed toward obtaining better understanding and mathematical specification of supersonic turbulent jets. Complete theoretical discussions are given describing the influence of a jet's mean flow shrouding on acoustic radiation of heated and unheated jets, approximate closed form acoustic expressions for turbulent mixing noise characterized by self-noise and shear-noise are given, and theoretical aero-acoustic formulations for the orderly structure of supersonic jets are reviewed. Extensive theory/data comparisons of developed acoustic models are given. Experimental investigations aimed at studying high velocity jet refraction, and the influence of jet swirl and upstream combustion roughness on jet noise is presented. Additionally, an extensive series of laser velocimeter measurements for high velocity and high temperature simple circular jets is discussed. Results include hot-film/laser velocimeter comparisons for ambient jets, mean velocity and turbulent velocity plume surveys of heated supersonic shock-free and shocked flow nozzles, and a demonstration experiment illustrating the capability of performing in-jet turbulence to far-field acoustic cross-correlation. (Author).

This report summarizes major theoretical aerodynamic and acoustic developments and experimental findings aimed at providing a better understanding and a detailed mathematical specification of the noise-producing sources of simple exhaust jets. A review is given of calculation procedures for shock wave structure and flow field properties of simple circular jets. Results of new theoretical acoustic developments illustrating the influence of a jet's mean flow shrouding on jet acoustic radiation for unheated and heated jets are outlined. Additional discussions of interesting insights regarding the classical turbulent mixing theory of jet noise and the aeroacoustic formulations for a jet's orderly structure are given. Summaries of a series of high velocity, high temperature velocity field measurements using a General Electric developed laser velocimeter are discussed, and the application of the velocimeter for performing turbulence spectra and in-jet to far-field cross-correlation type measurements is reviewed. Key experiments illustrating the influence of swirl and combustion roughness on jet noise generation/reduction are presented. Results of high velocity and high temperature refraction experiments are also discussed, as well as discussions concerning jet flow amplifying effects of injected low frequency noise. Additionally, suggestions concerning shock-related noise as related to full-size engines are given. And finally, recommendations for future investigations are given. (Author).