Program for research in applied aeroelasticity

The project 'Program for Research in Applied Aeroelasticity was carried out from 1. April 2005 to 31. March 2006. The partners in the project were Risø National Laboratory (Risø) and the Technical University of Denmark (DTU). The results from the project were obtained by focusing or several pre-defined milestones, but other topics and problems have as well been investigated and published separately. The results are described below. Advanced rotor aerodynamics - tip and root aerodynamics: Several specific issues concerning rotor aerodynamics have been investigated during the present project: 1) An aerodynamic investigation of adding a winglet to the wind turbine blade showing an increase in power of 1.4%, 2) Modelling of transient wind loads during pitch motion computations were compared to the NRE/NASA Ames test and reasonably good agreement was seen, 3) A method for determination of 3D angle of attack for rotating blades was developed, 4) A model of the far wake behind wind turbines was developed. It forms the basis for stability investigations of the tip vortices in the far wake, 5) An investigation of an aerodynamically more efficient root regior showed that the local CP can be increased significantly beyond the Betz limit, but that the global CP for the rotor did not exceed the Betz limit. New airfoil series - optimal weighting between aerodynamic and structural characteristics: A new airfoil family for MWsize wind turbines with variable speed and pitch control was designed. Compared to the Risø-B1 family, the aerodynamic characteristics are improved and structurally around 5% more stiffness around the chord line was obtained. The design tool was extended to 3D so that the complete blade shape, including the compatibility between the airfoil sections, and the rotor flow were taken into account. 2D airfoil catalogue based on 3D DES computations: Based on the Wind Turbine Airfoil Catalogue (EFP-2000/2001) the original two-dimensional results were compared with three-dimensional calculations. The two major conclusions of this work were the dependency of computational results to transition modelling, and the ability of 3D DES calculations to realistically simulate the turbulent wake of an airfoil in stall. Aeroelastic response from MW turbines in extreme wind conditions: A 'gust generator' was used to demonstrate the importance of considering stochastic gust events as an alternative to today's stylized deterministic coherent gust specifications. Also, a consistent statistical extreme value model for the simplest possible gust type was developed. Integrated hydroelastic and aeroelastic computation on offshore turbine: An offshore monopile foundation was investigated using HAWC2. The boundary conditions of the soil and the flexibility of the pile mainly reduced the first tower frequency with app. 5%. The effective damping on the 1st tower bending frequency was not affected by the hydrodynamics, but slightly on the higher frequencies. An increase in external water velocity led to a noticeable increase in damping. Torsional properties for large wind turbine blades: A new anisotropic beam element based on the program VABS has been implemented. This provides the basis for giving more confidence in flutter estimation and also the ability to analyze the reduction of fatigue loads by aeroelastic tailoring of future blades