Stability analysis of wind turbines with bend-twist coupled blades

Over the last years, bend-twist coupling (BTC) has become one of the most important passive load reduction techniques in wind turbine blades. The kind and amount of BTC is often decided on the basis of the load reduction, often forgetting the related stability implications. In this work we perform the stability analysis of a very large wind turbine, where the BTC is obtained by rotating the fibers of the spar caps. The study focuses first on the isolated blade, and then on the complete wind turbine. The findings show that this BTC leaves some modes unaffected, but reduces the damping of the collective edgewise mode.