Modeling of material bend-twist coupling on wind turbine blades

Material bend-twist coupling (BTC) as a mean to passively alleviate wind turbine blade loads is assessed. It is accomplished by introducing an offset angle on the plies of the uni-directional material over the spar caps of the blade. At first, the ability of the multibody, FEM, aeroelastic tool hGAST to consistently predict deflections of BTC beam structures is proved through comparisons against existing measured data and numerical predictions. Next, the effect of the plies offset angle and the spanwise position wherefrom offset of the plies starts on maximum attainable tip torsion deflection is assessed. Bend-twist coupling coefficient distributions along the blade span are generated and associated with the corresponding ply offset angles. Finally, the potential of the material BTC method to alleviate blade loads is demonstrated through aeroelastic analyses based on IEC design load cases. Blade root flapwise bending fatigue (7-10%) and ultimate (6-8%) load reduction is possible by means of moderate ply offset angles of 9-12.5°.