Executive Summary : | The rapid advancement of unmanned aerial vehicle (UAV) technologies has led to a growing environmental noise pollution problem, with annoyance reactions to drone noise likely to occur in an increasing percentage of the population. This project aims to understand the noise generation mechanism(s) and develop innovative control solutions to reduce noise emissions. Aeroacoustics experiments will be conducted to acquire far-field acoustic data and wake velocity spectra for a multi-blade rotor rig. The experiments will be conducted on a stationary two-blade propeller in a low-speed aeroacoustic wind-tunnel, and on rotating propeller blades in an anechoic chamber. The data will be used to obtain acoustic source distribution along the tip and trailing-edge (TE) of the propeller blades, and near-wake aerodynamic data will explain the generation of acoustic sources. Treatments at the blade TE, such as serrations, porosity, or poroelastic extensions, will be carefully designed to break large coherent structures generated in the wake into smaller incoherent parts or dampen local acoustic sources. Customized lightweight mufflers will also be designed to reduce noise emitted by small volume two-stroke engines powering UAVs. A quieter drone/UAV will have numerous societal benefits, including promoting public health and well-being, and enhancing acoustic stealth during surveillance operations. |