Aerodynamics of an ultralight load-aligned rotor for extreme-scale wind turbines

To alleviate the mass-scaling issues associated with conventional upwind rotor blades of extreme-scale wind turbines (≥ 10MW), the inviscid aerodynamics of a loadaligned blade is compared to that of a conventional blade. This fluid-structure loadalignment reduces cantilever loading and has been projected to reduce blade mass by 50% for both morphing and pre-aligned configurations. This alignment also facilitates blade segmentation, so that the combined effect may lead to a 25% reduction in cost of energy. However, previous quantitative analysis has only included structural simulations. Herein, the aerodynamic performance of this concept is investigated with computational fluid dynamics (CFD). This numerical method was first validated two-dimensionally with the S809 airfoil and three-dimensionally with the Unsteady Aerodynamic Experiment (UAE). The results indicated that this inviscid method is reasonable for predicting torque and thrust when the flow is attached, i.e., with moderate angles of attack. This technique was then applied to a 10 MW wind turbine at rated wind speed for both conventional and loadaligned configurations. The aerodynamic load predictions for thrust and torque compared well with the empirically prescribed force distributions, further supporting the morphing and pre-alignment concepts. Extreme flow conditions as well as fully-coupled fluidstructure simulations are recommended to provide improved fidelity and quantification, as well as a more detailed understanding of the load relief and expected mass savings for these concepts.