Propeller Optimization for Tonal Noise Reduction Using Spherical Harmonics Expansion and Blade Element Theory

This paper presents the results of a blade optimization to reduce propeller tonal noise, using the Blade Element Momentum Theory for aerodynamics and a spherical harmonics expansion for acoustic field prediction. For each blade pass frequency, accurate far-field results can be obtained by keeping only a few terms in the expansion. The optimization is performed by finding the spanwise chord distribution that minimizes the objective function, which is a weighted sum of mechanical and loading noise power, for a fixed value of thrust. Results are presented for different angular speeds and weights of the objective function.