Aerodynamic and aeroacoustic analyses of a UAV propeller with trailing edge serrations

Unmanned aerial vehicles (UAVs) can be observed in many applications, e.g. video taking, mapping, construction, delivery, and rescue operation. In some circumstances, the aeroacoustic noise is a big concern and quiet propellers would be more environmentally friendly. Therefore, this research imitates the serrated trailing edge of the owl wings, which are well known for their low noise emissions; the noise reduction and aerodynamic performance of the propeller with trailing edge serrations are analysed. The spectral characteristics, noise reduction and noise directivity of the propeller with serrated trailing edge are measured by microphones in an anechoic wind tunnel. The time-average loading of the propeller with serrated trailing edge and normal propeller are analyzed by a six-component balance. The results show that the noise of the propeller is alleviated, and the noise reduction depends on the Strouhal number and flight conditions. During the forward flight, the maximum noise reduction reaches 12 dB when the Strouhal number is around 4. The noise reduction effect is directional, and it is found that the noise reduction on the side of the forward moving blade is significantly larger than the other side. During the hovering condition, the maximum of the noise reduction reaches 7.5 dB when the Strouhal number is around 2, and the noise reduction is axisymmetric. The lift and drag of the serrated propeller both decrease by 5% during the forward flight condition, but the lift-to-drag ratio remains the same. The aerodynamic performance of the serrated propeller is not altered during the hovering condition.