Blade Load Reduction for a 13 MW Downwind Pre-Aligned Rotor

To alleviate the mass-scaling issues associated with conventional upwind rotors of extreme-scale turbines, a downwind rotor concept is considered that uses coning and downwind curvature to align the non-circumferential loads for a given steady-state condition. This load-alignment can be pre-set to eliminate downwind blade moments for a given steady-state condition at rated wind speed and to minimize them for other conditions. The alleviation in downwind dynamic loads may enable a reduced structural blade mass as compared with a conventional upwind rotor. To examine the potential impact of this design, FAST simulations were conducted for a 13.2 MW rated turbine at steady-state conditions for two rotor configurations with similar power outputs: 1) a conventional upwind rotor with three blades and 2) a downwind pre-aligned rotor with two blades. The rotor mass was reduced by approximately 25% for the downwind pre-aligned configuration. In addition, the damage equivalent loads on the blades were reduced at all wind speed for the downwind pre-aligned configuration, with a reduction of more than 60% at the rated condition.