Response of stall-controlled, Teetered, Free-yaw Downwind Turbines

摘要

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 researeh 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 undeistand- ing 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 aHect the restoring moments on the rotor and nacelle. A final contribution is an ADAMSR 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 held testing programme. Both the predictions and the held data point to the more benign response of a hub having a negative delta-3 angle. This contradicts previous opinions but is con- sistent with the criteria presented in this article.