Aeroacoustic Testing of UAS-Scale Rotors for a Quadcopter in Hover and Forward Flight

A series of experiments was conducted in an anechoic chamber and wind tunnel to investigate the noise and performance of an optimum hovering rotor design. The optimum hovering rotor experimental data set presented in this paper provides the community with a rotor that is theoretically easier to model. Isolated rotors were tested in an anechoic hover chamber as well as on a representative quadcopter vehicle. In the anechoic chamber, performance and acoustic measurements were taken at various rotor speeds to compare to those of a commercial-off-the-shelf (COTS) rotor. In the wind tunnel, free-stream velocity, vehicle pitch, and rotor rotation rates were varied to achieve various hover and forward flight operating conditions. Previous investigation of a small quadcopter in the Low Speed Aeroacoustic Wind Tunnel (LSAWT) had identified possible broadband and interactional noise sources due to rotor airframe interaction and rotor-rotor interaction. These publications identified separation, turbulent boundary layer trailing edge, and bluntness vortex shedding as the main sources of self-generated airfoil noise. By replacing the COTS rotor with an optimum hovering rotor design, self-generated broadband noise was reduced for both hover and forward flight conditions for isolated rotor runs. However, the optimum rotors only reduced noise levels for full-vehicle hover conditions, and had little to no reduction in full-vehicle forward flight conditions.