Abstract: The Leading-Edge (LE) serrations on owls’ wings are known to be responsible for silent flight. However, this design has rarely been applied to reduce the noise of rotational rotor propellers and the morphologies of the existing serration designs are diverse. Here, we present a comparative study of LE serrations with different morphologies in terms of the effectiveness in suppressing noise and promoting thrust forces. The performances of biomimetic propellers are investigated by Computational Fluid Dynamics (CFD) simulations and rotation experiments. The simulation results reveal that LE serrations could reduce velocity fluctuations and change the 
lamina-turbulent transition and turbulence distribution on the suction surface of propeller, but the morphology of the serrations influences its effectiveness. Rotation testing results indicate that the sawtooth propeller has the best performance on noise reduction (on average 
2.43 dB and in maximum 4.18 dB) and simultaneously enhancing the thrust forces (3.53%). The largest practical noise reductions (4.73 dB and 3.79 dB) using the sawtooth propeller are observed when the quad-rotor Unmanned-Aerial Vehicle (UAV) is hovering at heights of 5 m and 8 m, respectively. Our results indicate the robustness and usefulness of owl-inspired biomimetic serration devices for aero-acoustic control and aerodynamic performance promotion on propeller designs. This finding is expected to contribute to suppressing the sound of propeller and the rotor-based aircraft.

Key words: unmanned-aerial vehicle, biomimetic, noise reduction, LE serration, rotor propeller