Aeroacoustics and noise mitigation of micro quadcopter

Abstract

In the last few years, there has been an increase in interest and adoption of unmanned aerial vehicles (UAV) for both commercial and private use. However, UAV represent a relatively new source of noise pollution with unique noise signatures for the communities exposed to UAV operation. Thus, a series of experiments were conducted in the University of Bristol’s aeroacoustic wind tunnel to investigate the noise characteristics of a micro quadcopter in hover, hover in free stream and forward flight. Also, noise mitigation effects of rotor blade modifications on the trailing edge and rotor tips were tested in hover and forward flight. A total of eight different rotor configurations were designed and produced using additive manufacturing including a baseline. Radiated far-field noise data was collected, processed, and analysed. Hover and forward flight exhibited similar noise dipole directivity while directivity during hover in free stream was biased towards upstream. Various rotor modifications were successful in reducing the magnitude of noise with some changing the directivity. The finlet rotor configuration showed promise by reducing noise by up to 1.5 dB in all directions. Noise mitigation effects were lower compared to isolated rotors. Characteristics of noise mitigation was similar in hover and forward flight but appears to be sensitive to flow alignment and rotor geometry. Through this project, a deeper understanding of micro quadcopter noise characteristics and noise mitigation was gained.