Phased array aeroacoustic measurements of an unmanned aerial vehicle

This paper reports the results of the aeroacoustics study of an Unmanned Aerial Vehicle (UAV) experimentally investigated on a scaled prototype model. The measurement campaign were performed at the RUAG Large Subsonic Wind Tunnel in Emmen. The model was mounted on a ceiling strut in the 7-by-5 meters test section. The aeroacoustic noise generated by the UAV was evaluated analysing the pressure fluctuations acquired through a phased array of 144 microphones installed on a flat-plate on the ground of the test section floor. Pressure fluctuations were acquired in different configurations. The main parameters varied during the tests were: the velocity of the air-flow, the incidence angle of the UAV and the presence of the landing gears. Flaps were always deployed. The directivity source contribution to the overall noise at various emission angles is determined as well, for each configuration, moving the array along the flow direction. Data were processed and then analysed in the frequency domain and using a conventional beamforming algorithm to retrieve the sound source map over the areas of interest. Source maps were deconvolved with a CLEAN-SC routine and single source contributions determined through integration of auto-powers. The resulting spectra were finally scaled to flight conditions.