Study on composite bend-twist coupled wind turbine blade for passive load mitigation

Abstract The wind turbine size is nowadays becoming increasingly larger as an effective approach to reduce cost of energy. Passive load control technique is introduced to alleviate the increasing loads on an upscaling wind turbine blade to improve its fatigue life. In this paper, the composite bend-twist coupled blade is investigated and utilized to mitigate the cyclic fluctuating loads in shear wind. The NREL 5-MW blade is firstly inversely redesigned of its composite layup configuration. The fiber on the spar cap is rotated away from the blade axis to implement the bend-twist coupling (BTC). An advanced aeroelastic model of the wind turbine blade is developed to conduct the study. The geometrically exact beam theory is used to account for the large deformation effects, while the tool VABS is utilized to generate the cross-section stiffness matrices. Meanwhile, the free wake lifting surface model is adopted to calculate the aerodynamic loads, which is physically more realistic than the traditionally used BEM method. Based the established model, the influences of BTC on the rotor aerodynamic performance are investigated. Load mitigation effects of the blades with various spar cap fiber angles are evaluated. The influences of coupling region and different wind speeds are also discussed.