Response of stall‐controlled,teetered, free‐yaw downwind turbines

Stall‐controlled, teetered, free‐yaw downwind turbines have historically experienced higher than desired peak loads due to occasional large teeter excursions when the blades are stalled. Understanding of the causes of these excursions and the potential solution have been the subject of much research in the past. This article contributes to this study in three areas. One is the development of the equations of motion for a teetered rotor with a delta‐3 angle. The solution of these equations leads to an improved understanding of the mechanics of these types of rotors and to a theory concerning how the rotor responds to different overall aerodynamic moments. A second contribution is a set of test cases to confirm the theories developed and to show how wind speed and different delta‐3 angles affect the restoring moments on the rotor and nacelle. A final contribution is an ADAMS^® analysis of the fatigue loading of the AWT‐27 under high turbulent wind speeds with different delta‐3 angles and the comparison with results of a field testing programme. Both the predictions and the field data point to the more benign response of a hub having a negative delta‐3 angle. This contradicts previous opinions but is consistent with the criteria presented in this article. Copyright © 1999 John Wiley & Sons, Ltd.