A Coupled CFD-CSD Method for Predicting HAWT Rotor Blade Performance

Abstract

In the present study, a coupled CFD-CSD method has been developed to predict the aerodynamic loads and the elastic deformation of horizontal-axis wind turbine rotor blades. The blade aerodynamic loads were obtained by a Navier-Stokes CFD flow solver based on unstructured meshes. The blade elastic deformation was calculated by using a FEM-based comprehensive CSD solver employing a nonlinear coupled flap-lag-torsion beam theory. The coupling of the CFD and CSD solvers was accomplished in a loosely coupled manner by exchanging the information between the two solvers at infrequent intervals. At first, the present CFD-CSD coupled method was applied to the NREL 5MW reference wind turbine rotor under steady axial flow conditions, and the mean rotor loads and the static blade deformation were compared with other predicted results. The blade aeroelastic deformation effects on the rotor performance were also investigated by comparing the results with those of CFD-only rigid blade calculations. Then, the unsteady blade aerodynamic loads and the dynamic blade response due to the rotor shaft tilt and the tower interference were investigated, along with the influence of the gravitational force. It was found that due to the aeroelastic blade deformations, the unsteady blade aerodynamic loads are significantly reduced, particularly by the blade torsional deflection. From the observation of the tower interference, it was also found that the aerodynamic loads are abruptly reduced as the blades pass by the tower, resulting in oscillatory blade deformations, particularly in the flapwise bending.