Tilt Rotor Broadband Hover Aeroacoustics

Abstract

To improve the acoustic characteristics of tilt rotor aircraft, the dominant noise mechanisms must be understood. Toward this goal, a method was developed to identify and predict the dominant broadband noise mechanism of a hovering tilt rotor. Predictions are presented for a range of azimuthal observer locations and polar observer angles and are compared to NASA full scale tilt rotor hover noise data. Comparisons between experiment and prediction indicate that the polar and azimuthal directionality trends are captured. The predicted sound spectrum levels are generally within 5 dB of the experiment. The results of this study indicate that the highly turbulent recirculating fountain flow is the dominant broadband noise mechanism for a tilt rotor aircraft in hover.