Experimental Measurement of a UAV Rotor’s Acoustic Emission

Kurzfassung

Besides aerodynamic performance, most unmanned aerial vehicles (UAVs) are limited by noise emission in their range of application. Especially in urban areas, the acceptance of UAV noise emission by the affected population is required. Therefore, one objective of DLR’s project URBAN RESCUE is to investigate the noise emission and noise generation mechanisms of small rotors. In order to study noise emission, a test setup was established in DLR’s 1m wind tunnel. For different flight modes, acoustic measurements were conducted using a microphone array. For all test cases the noise emission of the rotor’s blade passing frequency (BPF) is higher in front of the rotor (upstream) than behind it. Due to higher relative velocities on the advancing side than on the retreating side, emission is asymmetric with respect to the flow direction. Additionally, a time-resolved background-oriented schlieren (BOS) setup was used to visualize tip vortices and study noise generation mechanisms.