Multirotor Noise Source Separation and Characterization from Ground-Based Acoustic Measurements

Aeroacoustic characterization of multirotor aircraft is a challenging task, especially due to the variability in the rotational speed of rotors. This problem is exacerbated by the use of variable RPM control, because changes in RPM change the noise sources of the aircraft in a time-dynamic way. As a consequence of the constant variations in noise sources, an accurate assessment of the acoustic characteristics of the aircraft can be difficult to obtain. A possible solution to this problem is to separate the noise sources of the aircraft on a rotor-to-rotor basis and understand the variations based on each rotor's operating states. To achieve this, a source separation process based on the Vold-Kalman filtering approach is applied to separate the contributions of the individual rotors from ground-based acoustic measurements of a hexacopter. The source separation process was applied to separate the tonal noise of each rotor based on the rotor speed measurement and the results were analyzed for a level flight flyover case. The rotor speed has a strong correlation to the A-weighted SPL throughout the flyover and the variations in RPM directly affect the tonal noise levels, as expected from theory.