Numerical and experimental studies on the owl-inspired propellers with various serrated trailing edges

The present study investigates owl-inspired propellers with various serrated trailing edge configurations. An analysis utilizes a numerical model that integrates computational fluid dynamics (CFD) with Large Eddy Simulation (LES) and Lighthill acoustic analogy. The simulation aims to clarify the mechanism behind noise reduction in the bionic propeller by comparing tip vortices and wake region vortices with or without serrated trailing edge structures. Additionally, a thorough assessment of noise and aerodynamic performance is carried out on bionic propellers with varied serrated ratios, shapes, and coverage degrees, through experimental measurements conducted under varying rotation speeds and thrust levels. Experimental results demonstrated the significant noise reduction capabilities of sawtooth bionic structures across various rotation speeds. Notably, the bionic propeller with a round-serrated trailing edge, a serrated ratio of 0.9, an arc radius of 0.3 mm, and 50 % serration coverage achieves a noteworthy noise reduction of up to 4.4 dBA. The findings highlight a significant correlation between the propeller's flow structure and its aerodynamic noise characteristics. The findings highlight a correlation between the propeller's flow structure and its aerodynamic noise characteristics. Serrated trailing edges disrupt propeller tip vortices, expediting the vortex shedding and dissipation processes, thereby mitigating trailing edge noise. Additionally, a distinctive inward shift of the wake at the trailing edge promotes the intermixing of flow structures, enhancing collisions and mixing of vortices, ultimately resulting in a significant broadband noise reduction.