Systems Noise Prediction of Flight-Test Points

3 SYSTEMS NOISE PREDICTION OF FLIGHT-TEST POINTS 

After selection of the mission profile for the acoustic test was determined, NAS Patuxent River s Propulsion Department utilized their flight simulator and cycle deck for the engine to determine both aircraft and engine parameters needed to compute ground-based acoustic signatures. Table 4.2 lists all parameters needed to exercise the NASA LaRC systems noise prediction code ANOPP. In Table 4.2, 

Aj is the fully expanded jet area, 7 is the jet total temperature. Vj is the fully expanded jet velocity, RHOj is the fully expanded jet density. Ag is the nozzle exit area, Mj is the fully expanded jet Mach number, M i is the nozzle design Mach number, 7 is the ratio of specific heats at the nozzle exit. V) is the initial and final aircraft velocity, AOA is the aircraft angle of attack, and Altitude is aircraft height above ground. 

It is clear from the predicted spectra that shock noise is present and makes a significant contribution to the predicted overall sound pressure level. However, near Mil-Power (96% N2), the engine nozzle scheduling is more on-design and the relative shock-noise contribution is less compared to jet noise than can be observed with lower engine power settings. 

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