Rotor Noise Predictions in Hover and Forward Flight Using Different Aeroacoustic Methods.

Abstract

This paper presents an aeroacoustic program system for the noise prediction of rotors in hover and forward flight. The nonlinear field solution is computed by an Euler solver. The pressure signal at a microphone in the near field can be extracted directly from the Euler solution. The sound propagation to the far field is computed with different linear acoustic methods, namely the Farassat method to solve the linear part of the Ffowcs Williams/Hawkings equation and the Kirchhoff method using rotating or nonrotating integration surface. All acoustic methods are combined in a single computer tool, whose features are demonstrated for three different rotors with various tip speed and advance ratio. The comparison with experimental data shows, that the Kirchhoff method is an accurate and efficient tool for the prediction of rotor noise phenomena, such as high-speed impulsive noise and blade-vortex interaction noise, for various microphone locations. The direct Euler method is accurate.