Trailing edge noise of innovative mini-RPA propeller blades geometry

This paper aims at computing the trailing edge noise spectrum of an innovative mini- RPA propeller geometry and assessing the performance, in terms of noise reduction, when applying sawtooth serrations on its trailing edge. For that reason, a recent frequency- domain analytical model is implemented using a strip approach, where the blade is divided in a number of spanwise segments for which the corresponding mean flow and boundary layer quantities are evaluated from a CFD solution. The model is assessed by comparison with time-domain LBM simulations. The first order approximation is found to predict with a good accuracy the results but with higher computational cost. The number of segments affects the analytical solution and converge for a large number of segments. The results show that the serrations reduce the noise emitted by the propeller at low to mid frequencies but induces a noise increase at high frequencies. The sharpest serrations are the most effective in reducing the emitted noise. The study of the directivity patterns show that the trailing edge serrations do not modify the directivity of the radiated trailing edge noise and their effect on the radiated noise is independent of the observer position.