Validation of a Helicopter Noise Prediction System

This paper presents validations of a prediction system of helicopter external noise. This system has been jointly developed by Advanced Technology Institute of Commuter-helicopter, Ltd. (ATIC) and National Aerospace Laboratory (NAL) in a research program of helicopter noise reduction. In the system, a trim code, aerodynamic codes, and acoustic codes are combined to predict helicopter ground noise. The calculated results are compared with the experimental data of a 1/3-scaled model rotor obtained by ATIC at the German Dutch Windtunnel (DNW). Reasonable agreements are obtained in hover and forward flight cases but some discrepancies are observed in the measured and calculated tip-vortex trajectories in a descending flight condition. The difficulty of the accurate prediction of tip-vortex trajectories causes some discrepancies in pressure time histories at blade leading-edge and carpet noise contours on the plane below the rotor. A validation of the present system is also done by comparing the calculated results with flight test data obtained by ATIC using a light helicopter. The predicted PNLT time histories at the middle microphone position agree well with the flight test results. However, the predictions at side microphone positions are not satisfactory.