Noise source imaging measurements for small-scale multi-propeller systems

Noise source features of multi-propeller systems are experimentally studied in this paper. Noise sources on a pair of side-by-side placed small-scale propellers and a flying quad-copter are investigated separately using microphone arrays and the conventional beamforming algorithm. A high-intensity noise source spot is identified within the gap area between two propeller disks, which is a result of the interaction between the blade tip and upwash flow within the gap area. As the two propellers move away from each other, the noise source spot becomes weaker. Similarly, for a quad-copter under realistic flight conditions, the strongest noise sources are observed within the gap between each of two adjacent propellers, showing the feasibility and repeatability of the result obtained in the lab. The results discussed in this paper show that for the low-noise design of a multi-propeller drone, not only is the single propeller noise, but also the propeller interactional noise shall be taken into account.