1 Risø National Laboratory for Sustainable Energy, Technical University of Denmark2 Department of Wind Energy, Technical University of Denmark
In the Energy Research Project ”Program for Research in Applied Aeroelasticity” (EFP2005), Risø National Laboratory (Risø) and the Technical University of Denmark (DTU) have applied and further developed the tools in the aeroelastic design complex. Themain results from the project are: Adding a winglet to a wind turbine blade for minimizing the induced drag of the blade led to the biggest increase in power of 1.4%. Transient wind loads during pitch motion are determined using CFD. Compared to theNREL/NASA Ames test, reasonably good agreement is seen. A general method was developed for the determination of 3D angle of attack for rotating blades from either measurements or numerical computations using CFD. A model of the far wake behind windturbines was developed for stability studies of the tip vortices in the far wake. Investigating the blade root region showed that the power efficiency, CP, locally can be increased significantly beyond the Betz limit, but that the global CP for the rotorcannot exceed the Betz limit. When including tip losses and a minimum blade drag coefficient, a maximum rotor CP in the range of 0.51-0.52 was obtained. A new airfoil family was designed and a 3D airfoil design tool was developed. Compared to the Risø-B1family, the new airfoil family showed similar or improved aerodynamic and structural characteristics. Four different airfoils were analyzed to reveal the differences between 2D and 3D CFD. The major conclusions are the dependency of computational resultsto transition modelling, and the ability of 3D DES calculations to realistically simulate the turbulent wake of an airfoil in stall. ?The capability of a theory for simulation of Gaussian turbulence driven gust events was demonstrated by emulating aviolent shear gust event from a complex site. An asymptotic model for the PDF of the largest excursion from the mean level, during an arbitrary recurrence period, has been derived for a stochastic wind speed process driven by atmospheric turbulence. Thesimulation of an offshore monopile foundation with HAWC2 showed a reduction of the first tower frequency with app. 5%. The influence of hydrodynamics showed only minor influence on the tower frequency and damping. An increase in external water velocityleads to a noticeable increase in damping. A new anisotropic beam element has been implemented. This provides the basis for giving more confidence in flutter estimation and the ability to analyze the reduction of fatigue loads by aeroelastic tailoring offuture blades.