Dynamic Loads and Wake Prediction for Large Wind Turbines Based on Free Wake Method

With large scale wind turbines, the issue of aerodynamic elastic response is even more significant on dynamic behaviour of the system. Unsteady free vortex wake method is proposed to calculate the shape of wake and aerodynamic load. Considering the effect of aerodynamic load, inertial load and gravity load, the decoupling dynamic equations are established by using finite element method in conjunction of the modal method and equations are solved numerically by Newmark approach. Finally, the numerical simulation of a large scale wind turbine is performed through coupling the free vortex wake modelling with structural modelling.The results show that this coupling model can predict the flexible wind turbine dynamic characteristics effectively and efficiently. Under the influence of the gravitational force, the dynamic response of flapwise direction contributes to the dynamic behavior of edgewise direction under the operational condition of steady wind speed. The difference in dynamic response between the flexible and rigid wind turbines manifests when the aerodynamics/structure coupling effect is of significance in both wind turbine design and performance calculation.