Robust Aerodynamic Design of Variable Speed Wind Turbine Rotors

This study focuses on the robust aerodynamic design of the bladed rotor of small horizontal axis wind turbines. The optimization process also considers the effects of manufacturing and assembly tolerances on the yearly energy production. The aerodynamic performance of the rotors so designed has reduced sensitivity to manufacturing and assembly errors. The geometric uncertainty affecting the rotor shape is represented by normal distributions of the pitch angle of the blades, and the twist angle and chord of their airfoils. The aerodynamic module is a blade-element momentum theory code. Both Monte Carlo-based and the Univariate Reduced Quadrature technique, a novel deterministic uncertainty propagation method, are used. The performance of the two approaches is assessed both in terms of accuracy and computational speed. The adopted optimization method is based on a hybrid multi-objective evolutionary strategy. The presented results highlight that the sensitivity of the yearly energy production to geometric uncertainties can be reduced by reducing the rotational speed and increasing the aerodynamic blade loads.