Development of Efficient and accurate CFD Technologies for Wind Turbine Unsteady Aerodynamics

This paper focuses on novel unsteady and low-speed algorithmic developments of a structured explicit Euler solver and an unstructured implicit Euler/RANS solver for wind turbine CFD. The central topics are a) a discussion on the definition of optimal low-speed preconditioning for explicit solvers featuring state-of-the-art convergence acceleration methods, b) the presentation of a simple optimal mixed preconditioning strategy, and c) the novel implementation in the implicit unstructured code of a preconditioning method which thus far has only been used for steady problems. These technologies are thoroughly validated by considering a low-speed vortex convection problem and the low-speed flow field past a pitching wind turbine airfoil. The excellent computational performance of the implicit approach is also demonstrated by computing the stalled flow past the same airfoil. All results demonstrate the accuracy and computational efficiency of these algorithms.