Prediction-based aircraft flyover noise synthesis

Investigation of community noise impact of aircraft flyover noise through subjective testing requires time histories of the acoustic pressure at one or more listener positions. The use of recorded aircraft flyover noise for this purpose is often problematic. Factors contributing to this include extraneous noise in the recordings (natural or man-made), a finite number of fixed recording positions, and the cost of conducting the flight test. Perhaps the most limiting factor is the inability to examine proposed aircraft, engines, flight procedures, and other conditions or configurations for which recorded data are unavailable. Synthesis of aircraft flyover noise as an alternative to recordings is thus desirable. An approach to the synthesis of broadband and narrowband aircraft component noise is presented based upon output from community noise prediction codes. These codes typically calculate aircraft flyover noise at designated listener positions in the frequency domain. The necessity to convert these to the time domain presents two challenges both relating to the fact that the predictions are, in essence, time averaged. The first of these involves the reconstruction of phase. The second is the synthesis of temporal fluctuations known to exist in real data. A semiempirical approach to calculating these effects is also presented.