Aerodynamics and Aeroacoustics Characterisation of Isolated Rotor in Hover and Transition to Forward Flight

The characteristics of aerodynamic noise and thrust of an isolated tilt-rotor system were experimentally investigated at hover and multiple tilting positions of the rotor disc. In this study, the effects of rotational speed, freestream flow velocity, and tilt angle were examined in an anechoic wind tunnel. Load measurements and far-field acoustic pressure measurements were performed in static condition and under freestream velocities ranging from 8 m/s to 24 m/s. Tests were conducted at a rotor diameter-based advance ratio between 0 and 0.3, and at rotor shaft tilt angle spanning from 0° to 30°. The aerodynamic coefficients, the sound power spectral density and the sound pressure level were studied and discussed. The results demonstrate dependency between the loading and noise signatures to the rotor tilting position. At a settings of rotation speed and freestream inflow velocity, the results show a significant noise attenuation at a higher tilting angle while maintaining a similar directivity of far-field noise radiation. However, at the same setting of rotational speed and inflow velocity, the aerodynamic thrust generating capability of the rotor is adversely affected by the rotor disc tilting angle.