Trailing edge noise prediction for rotating serrated blades

Abstract

Serrations have been widely studied in the case of stationary blades, as an efficient method for reducing trailing edge noise. However, most of the problems involving trailing edge noise are related to rotating blades and it is not known how rotation affects the efficiency of serrations. This paper tackles this problem using an efficient analytical model for predicting trailing edge noise radiation for rotating serrated blades. The model combines Howe's low Mach number isolated airfoil theory with Amiet's rotating airfoil technique. The paper also outlines a theory that generalizes Amiet's stationary airfoil the- ory to serrated trailing edges. Three different types of serrations - sinusoidal, sawtooth and slitted-sawtooth - are investigated for a model wind turbine blade element. The inuence of the serrations width, depth, and slits, on noise radiation is compared to known results valid for stationary blades. The best serrations are narrow (relative to the boundary layer thickness) and deep. Rotation has been found to have little impact on the performance of serrations at low Mach numbers.