Yaw Dynamics of Horizontal Axis Wind Turbines, Final Report

Designers of a horizontal axis wind turbine yaw mechanism are faced with a difficult decision. They know that if they elect to use a yaw-controlIed rotor then the system will suffer increased initial cost and increased inherent maintenance and reliability problems. On the other hand, if they elect to allow the rotor to freely yaw they know they will have to account for unknown and random, thoughbounded, yaw rates. They will have a higher-risk design to trade-off against the potential for cost savings and; reliability improvement. The risk of a yaw-free system could be minimized if methods were available for analyzing and understanding yaw behavior. The complexity of yaw behavior has, until recently, discouraged engineers from developing a complete yaw analysis method. The objectives ofthis work are to (1) provide a fundemantal understanding of free-yaw mechanics and the design concepts most effective at eliminating yaw problems, and (2) provide tested design tools and guidelines for use by free-yaw wind systems manufacturers. The emphasis here is on developing practical and sufficiently accurate design methods.