Aeroelastic Research Programme EFP-99

The project constitutes a continuously running 5 years research program in aeroelasticity and the main part of the project has been concentrated to obtain results on six specific milestones. A few important results will briefly be described below. Further details can be found in the summary report where a thorough list of published material from the project can be found. Within the period from July 1999 to June 2000 the project has contained the following milestones: 1) Wind tunnel measurements on a NACA 63-415 airfoil with a modified leading edge. 2) Detailed verification of 3D Computational Fluids Dynamics (CFD) computations with the code EllipSys3D on National Research Energy Laboratory's (NREL's) 10 m rotor. 3) Development of a model for simulation of airfoil roughness. 4) Aeroelastic modelling of a rotor with flexible blades. 5) Aeroacoustic modelling of noise emission from an airfoil section. A NACA63-415 with a modified leading edge has been tested in a wind tunnel together with a standard NACA 63-415 airfoil. The tests did show more stable stall characteristics of the modified airfoil and double stall was not observed during the tests on this airfoil. Further the modified airfoil had other improved characteristics: higher lift/drag ratio, less sensitivity to roughness and better aerodynamic damping characteristics in the chordwise direction. To start a detailed verification of 3D rotor simulations with the EllipSys3D code a number of 3D rotor simulations on NREL's 10 m rotor has been performed. Wind Tunnel tests on this rotor was carried out by NREL in the NASA Ames 24x36 m rotor in the spring 2000. When these detailed wind tunnel data become available a comparison with the simulations will be carried out. In order to simulate the influence from roughness on the airfoil characteristics a sub model for roughness has been developed and build into the EllipSys2D CFD code. Also a simplified model for vortex generators was developed and coupled to EllipSys2D. Results from both models has been compared with experiments and in general a good correlation was found. Flutter instability has been computed with a simplified 2D model as well as with full aeroelastic simulations. The main result is that flutter probably is not a problem with the present blade designs but it should be taken into account in future designs, particularly if e.g. the tip speed is increased for off shore applications. The correlation between fatigue loads and different control strategies for normal operation as well as situations with failure in the pitch system has been investigated with aeroelastic simulations. At high wind speeds the pitch regulated turbine is generally lower loaded than the stall and active stall regulated turbine. Operation with failure in the pitch system gives high fatigue loads on the blades whereas tower loads and tilt/yaw loads are only marginally increased except for the pitch regulated turbine where some increase in tilt and yaw loads are found