Concepts for Adaptive Wind Turbine Blades

Bend-twist coupling in wind turbine blades has been shown to reduce both fatigue and extreme operating loads, especially when applied in conjunction with a pitch-controlled rotor. This type of coupling has been used in other industries, implemented either through biased lay-ups of fiber-reinforced materials, or with swept wings. The critical issues restricting the widespread implementation of this technology to wind turbines lies in the detailed design, manufacturing, and durability of the bend-twist-coupled blades. A series of industry contracts were initiated to evaluate/study these issues. The results of three of these studies are summarized in this paper. Global Energy Concepts (GEC) studied design issues from the perspective of traditional wind turbine blade conceptual design. Wichita State University investigated the use of braided composites with a multi-cellular blade structure. Finally, MDZ Consulting studied the possibilities of using sweep alone to achieve the desired bend-twist coupling. A common result of all the studies is that a higher stiffness fiber, such as carbon, has tremendous benefits in this application.