Limitations of lift correction models for thick airfoils in wind turbine roots

Abstract

The flow in wind turbine blade root sections has proven to be challenging to predict for two main reasons; the use of thick airfoils (relative thickness greater than 40%) and three-dimensional effects including a strong radial flow. Several lift correction models have addressed these 3D effects acting on the inner part of rotating blades, however, they are derived for thinner airfoils in a stall-delay context, which changes significantly in thick airfoils, as found in modern wind turbines. This study numerically evaluates the performance of a 10 MW reference rotor in realistic operational conditions, as well as analytical rotors, in 3D and 2D CFD computations. It is found that, for thick airfoils, traditional lift correction models under-predict the lift coefficient by more than 1, depending on the operational conditions. But for non-thick airfoils, the difference between predicted and real lift coefficient is typically less than 0.5. Furthermore, a new correction term is proposed, which considers the effects introduced by thick airfoils and brings the overall error to the same level as for non-thick sections.