Installation and Manufacturing Effects of Propeller Trailing Edge Serrations

Trailing edge noise is one of the dominant broadband noise sources of UAV rotors while hovering. Trailing edge serrations may help alleviate the noise without impacting the aerodynamics significantly. Theoretical models for serrated edges, such as Ayton's model, provide predictions for the trailing edge noise generated by a fully turbulent flow over an infinitesimally thin plane. This study assesses the validity of these assumptions by considering serration installation and manufacturing effects. Several propellers of the same design were 3D printed with cut-in and add-on serrations. To overcome the influence of laminar to turbulent transition over the blade surface, some propellers also include additional surface roughness to trigger the turbulence. All propellers are tested in an anechoic room, where far-field noise and aerodynamic performances are collected. The results show that serrations are a viable method to control trailing edge noise at low RPM, where broadband noise dominates over tonal noise, and that the add-on serrations with a trip are in better agreement with the theoretical results, thus highlighting the importance of the manufacturing method during the design phase.