THEORETICAL MODELING OF HIGH-SPEED HELICOPTER IMPULSIVE NOISE.

A simple theoretical model of high-speed helicopter impulsive noise, based on the Ffowcs Williams and Hawkings theoretical formulation, is developed. The model depends primarily on the large-scale features of the rotor's aerodynamic flow field. For acoustic radiation near the rotor's tip-path-plane, monopole, dipole, and quadrupole sources all contribute - with the monopole term dominating for high subsonic advancing tip Mach numbers (M//a//t). Predicted pulse shapes show good agreement with experimental data below M//a//t equals 0. 9 and poor agreement above. Predicted peak amplitudes show generally poor agreement, becoming worse as M//a//t approaches 1. 0. Several methods of improving theory-data correlation are suggested.