Experimental Analysis of Small-Scale Rotors with Serrated Trailing Edge for Quiet Drone Propulsion

Drones are a growing business in Europe, delivering services in all environments, including urban areas: delivery of goods and e–commerce, precision agriculture, mapping, infrastructure inspections. In order to allow the integration of this platform in urban areas and to obtain public acceptance, it is necessary to significantly reduce the noise produced by the propellers. Currently, the level of noise generated by propellers is too relevant in terms of annoying effects induced on living beings. In particular, low altitude flights have been found to disturb citizens and frighten animals. With the aim to tackle such an issue, this paper describes an experimental parametric analysis of a passive noise control technique to reduce the signature generated by small–scale propeller employed for mini unmanned aerial propulsion. The noise control strategy here proposed is based on a serration pattern realized at the trailing edge (TE) of the blade. Despite the same approach has already been successfully employed to mitigate noise generated by wind turbines and fixed wing aircraft, few studies have been devoted to investigate the effects of a serration pattern on small propellers. A large number of different serration were realized by varying height, width and teeth distribution. The idea is to find the optimal serration geometry in terms of acoustic requirements and to highlight the role of teeth number. Results shows a sensible reduction in the noise propeller signature. Serration effects seems to depend strongly from the polar angle identifying different region of operation. Spectral Analysis points out that the serration affect the low frequency region and even the tonal component of aerodynamic noise. Statistical analysis shows a departure from a gaussian distribution and an effect of damping on distribution tails.