Analytical investigation of turbulence interaction noise of mini-rpa serrated blades

This paper presents an implementation to compute analytically the turbulence interaction noise of a mini-RPA propeller and to assess the noise reduction, when applying innovative features such as sawtooth serrations on its leading edge. A recent frequency-domain analytical model, for predicting the leading edge noise from airfoils with serrated edges, is implemented and extended to rotating blades using a strip approach. The implementation has already been validated with available airfoil data. A parametric study is conducted to investigate the effects of leading edge serrations, with varying ratios h/L_t and h/λ related to the serration amplitude 2h, the serration wavelength λ and the length scale of the incoming turbulence L_t. Obtained results show that the serrations reduce the turbulence interaction noise at high frequencies. The noise reduction increases with the increased serration amplitude but it is not affected by the serration wavelength. Effects of flow conditions such as the advance ratio and the turbulence intensity are also investigated along with the directivity patterns.