Study on fatigue life of bend-twist coupling wind turbine blade based on anisotropic beam model and stress-based fatigue analysis method

Abstract

Bend-twist coupling (BTC), also called aeroelastic tailoring or passive pitch control method, is often utilized to reduce the fatigue loading on wind turbine blades. With BTC, the blade can twist as it bends, this alleviates the aerodynamic force due to the decrease in the angle of attack when the load is increased suddenly. In this research, the stress-based method is employed to investigate the fatigue load due to the BTC effect under different wake conditions. To begin with, the one-dimensional anisotropic beam model is adopted in aeroelastic simulation. Next the static and modal analyses for the NREL 5 MW wind turbine blade with different fiber orientations are performed to verify the anisotropic beam model. Finally, the stress history of each element on each cross section is reconstructed using DTU BECAS. The fatigue life of different materials in each cross section under different wake conditions has been analysed. The results show that the predicted fatigue life of NREL 5 MW wind turbine blade (26.0187 years) is very close to the design life (20 years). The fatigue effect has an impact on the life of wind turbine blades, which can be affected by the layout of wind turbines and alleviated by BTC effect.