Aeroelastic Design of a 25 MW Downwind Rotor for High Efficiency and Low Weight

The advantages of continuously increasing wind turbine scales necessitate aeroelastic rotor design strategies to maximize performance. In this study, three downwind 25 MW rotors were designed with an aim of high power production with low rotor weight. To achieve this objective, the swept area was maximized by adjusting pre-cone and shaft tilt angles such that the aeroelastic orientation of an upward pointing blade was nearly vertical near rated conditions. The power coefficient was maximized by using an inverse rotor design tool in which axial induction factor and lift coefficient distributions were prescribed. To determine lift coefficient distributions, a design space was created based on a combination of maximum lift and maximum lift/drag conditions. For the flatback airfoils, empirical correlations were used to adjust for drag and maximum lift coefficient. Once the design space was created, three lift coefficient distributions were chosen which results in three rotors of small, medium, and large chords. The resulting rotors were simulated for performance and optimized for minimum mass using OpenFAST. The results indicated that the medium chord provided the best performance, producing the highest power coefficient and the lowest rotor mass. This approach can be used for other extreme-scale (upwind and downwind) turbines.