Pre-aligned downwind rotor for a 13.2 MW wind turbine

Abstract

Abstract While there is continued demand for larger wind turbines with cheaper cost of energy, conventional upwind blade design may be reaching a size limit stemming from blade failure at extreme wind conditions. For turbines rated above 10 MW, decreasing the structural loads to more manageable levels may be achieved by better aligning the forces along the rotor blade to reduce ultimate bending moments and fatigue loadings. To achieve such moment reduction, a downwind configuration with a coning angle prescribed to allow load alignment for critical conditions could be used. Such a configuration also increases the rated clearance distance between the rotor and the tower since wind loads push the blades further from the tower. This concept is explored herein for a 13.2 MW rated downwind design compared to a conventional upwind three-bladed rotor design that uses the Sandia SNL100-02 blades. The simulation results show in Class IIB winds that the two-bladed downwind pre-aligned rotor with 15° coning, decreases the blade damage equivalent loads by 19.0%, and decreases rotor blade mass by 27.4%, compared with the unmodified conventional upwind three-bladed rotor. However, further design optimization is needed to ensure annual energy production is preserved with this concept.