Noise reduction and aerodynamics of isolated multi-copter rotors with serrated trailing edges during forward flight

Inspired by owl wings, trailing edge (TE) serrations are adopted for noise reduction of multi-copter rotors. By choosing different parameters of serrations, i.e. the height to wave-length ratio, retrofitted manners of add-on and cut-in, as well as the radial range, aerodynamic and acoustic performance of isolated multi-copter rotors are compared at the forward flight condition. Rotors with add-on serrations generate higher thrust than the Baseline (BL) rotor at the same rotational speed, and the opposite trend is found for the rotors with cut-in serrations. The add-on models considered in this study have lower power consumption than the cut-in and BL models while generating the same thrust. In order to compare the noise reduction of different designs from the application perspective, analysis of Overall Sound Pressure Level (OASPL) at the same thrust is conducted. Serrated models considered in this study have lower OASPL than the BL model for most cases, which is contributed by both the broadband and tonal noise reductions. In addition, the model with half-span serrations achieves approximately the same OASPL reduction as that with full-span serrations.