Investigation Towards a Better Understanding of Noise Generation from UAV Propellers

This paper is concerned with the noise generation from small rotating blades. Experiments have been carried out to investigate the noise generation mechanism from small propellers used on unmanned aerial vehicles (UAVs) and ways to reduce the aerodynamic noise. Near-field and far-field noise data are provided for blades with different pitch angles and also blades with serrated trailing edges. The far-field noise data are collected using an array of microphones with fine polar angle resolution, enabling accurate directivity analysis. The near-field noise data have been obtained using a linear array of microphones transversed over different planes near the blades. While the far-field noise data can provide some information about the noise signature of different blades and the directivity of the radiated noise, the near-field data provide useful information on the noise generation and propagation from the blades plane. Experimental results have shown that increasing the pitch angle leads to greater broadband and tonal noise which is characteristic of the increased interaction of flow with the propeller trailing edge and tip. The investigations into the effect of trailing edge serrations on noise generation also showed that the far-field high-frequency broadband noise can be effectively reduced using such passive methods. The data provided in the current study have shown that our understanding of the noise generation from rotating blades at low Reynolds number range is very limited and further computational and experimental investigation is needed.