Aeroacoustic measurements of a contra-rotating UAV vehicle

The aerodynamic sound linked to the increasing presence of Unmanned Aerial Vehicles (UAVs) is becoming a societal concern. Assessing the aeroacoustics of these vehicles is of utmost importance, as it enables the evaluation and mitigation of the associated noise emissions. An experimental wind-tunnel investigation is carried out with an octo-quad multi-rotor model UAV with 4 sets of contra-rotating propellers, representative of a heavy-lifting drone, to assess the acoustic emissions of the vehicle under different flow and thrust conditions. The experiments are performed in the Open Jet Facility of the Delft University of Technology. The acoustic measurements from several microphones are combined to create the noise signature of the UAV, while the data from a balance are processed to compute the thrust. The results of this research demonstrate that it is possible to reduce the noise emissions of the drone by varying the operating input between the fore and aft motors. In particular, an attenuation in the overall sound pressure level of 5 to 8 dBA can be achieved if the RPM of the fore motors is decreased while that of the aft motors is increased.