Flemming Rasmussen

On the Dynamics of a Teeter Hinge with Delta3 Angle on a Two Bladed Multi MW Wind Turbine

This study analyses the effect of delta-3 on a 5 MW turbine using a simple analytical model of the teeter system in combination with time simulations on the same turbine with the aeroelastic code HAWC2. The analysis shows that the delta 3 angle changes both the eigen-frequency and the damping of the teeter system. The effect is strongly dependent on the lock number which further seems to change with the up-scaling of the turbines. For a modern turbine the lock number is typically above 20 and the teeter motion is strongly damped and the influence of the delta-3 is small. However, a reduction of the out-of plane movement of the blade tip can be obtained using a positive delta-3 angle. Also the influence on flapwise moment and the yaw moment is discussed. The most used wind turbine concept of today is the three blade upwind turbine, but the two teetering bladed downwind turbine could be a rival for the off-shore market. The major problems with two bladed turbines are the increased noise 1 from the blade passing the tower and the visually impact of the two blade concept, but for off-shore this will not be a problem. The blade cost and the tower top mass of a two bladed turbine will be reduced compare to the traditionally three bladed design, and the teeter mechanism of the two bladed turbine reduce the blade loads. The teeter motion dynamics can be changed by including a �3 angle, which couples the teeter motion to a pitching of the blade. However, as described in a recent paper by Malcolm 2 the role of the delta-3 angle has been shrouded in some mystery and there seems not to be clear guide-lines in the literature about how to choose the optimal delta-3 for a specific turbine configuration and what the main effects are on the teeter dynamics. In the present paper a simple analytical model, suggested by Anderson 1, is used to study and characterize the dynamics of a two-bladed teetering rotor with a delta 3 angle. The results of the analytical model are compared with numerical results from simulations with the aeroelastic model HAWC2, developed at Risoe National Laboratory.