An experimental study on rotor aeroacoustics under unsteady rotational speed

Acoustic annoyance is a keen factor in the social acceptance of novel urban air mobility concepts. Although regulations and certification requirements exist for such operations, they rely on measurements of the vehicle under controlled, and mostly steady, conditions. These conditions differ significantly from real envisioned operations, where turbulence from the urban environment, rapid maneuvers, system automatic control, and gusts can affect the vehicle's noise emissions. To assess such differences, this work focuses on the study of rotors, commonly applied to urban air mobility and transport vehicles, under varying rotational speeds. An experimental campaign is carried out in the anechoic wind tunnel of the Delft University of Technology, where an unsteady rotational speed of the rotor is prescribed. Acoustic measurements are carried out along with the integral loads of the rotor. The work explores both the aerodynamic effects of such an operation and its impact on noise emissions, overall levels, and annoyance perception. The final goal is to create a global picture of the relevance and physics of rotor noise under non-steady rotational speeds.