Rotorcraft noise model

Abstract

The rotorcraft noise model (RNM) is a multiplatform computer program being developed for NASA-Langley Research Center which calculates sound levels at receiver positions on the ground from helicopter and tiltrotor operations. RNM calculates levels at positions on a uniform grid or a specific defined locations. The basic computational model written in FORTRAN calculates maximum A-weighted sound level, sound exposure level (overall, C- and A-weighted), and effective perceived noise level (EPNL). Contained within the program are sound propagation and EPNL algorithms that are the same as, or equivalent to, corresponding algorithms in NASA’s Aircraft Noise Prediction Program (ANOPP). Acoustic properties of the noise source are defined by a set of sound-pressure noise spheres. One set of noise spheres provides broadband data in the form of one-third octave band sound-pressure levels. The other set of noise spheres provides narrow-band data in the form of pure-tone sound-pressure levels and phase. RNM outputs a file that is input to NMPLOT, a noise contouring/smoothing program used by the Department of Defense (DOD) and other government agencies. This paper will describe the basic element of the noise model and compare the noise models prediction with XV-15 noise data collected by NASA-Langley.