Unconventional application of serrated trailing edges for quieter propeller drones

This article presents an experimental investigation into the use of serrations to reduce propeller trailing edge noise. The study aims to demonstrate the potential of serrated drone blades in reducing tonal noise components while concurrently influencing the broadband noise components in the acoustic spectrum. A series of propellers was designed, manufactured, and tested to establish a relationship between serration geometry and noise mitigation. Subsequently, an aerodynamic and aeroacoustic characterization was performed using load cells, microphone arrays, and Particle Image Velocimetry measurements in an anechoic wind tunnel facility. The results suggest that a proper design of serration geometry can lead to a significant reduction in both tonal and broadband noise components, with the main drawback being a loss in thrust coefficient. Additionally, serrated trailing edge propellers promote enhanced diffusion of peak vorticity in the tip-vortex region, potentially reducing the noise produced by the interaction of the propeller tip-vortex and the surrounding drone structures. Finally, the breakdown of the fluid dynamic correlation length is observed, leading to the reduction of broadband noise.