A flexible turbine blade for passive blade pitch control in wind turbines

Abstract

We present a flexible wind turbine blade that effectively pitches itself according to variable wind loading. In contrast to rigid turbine blades, where active controls are often required to pitch blades, the flexible or morphing blade adjusts its geometry passively, eliminating the need for costly electromechanical systems. We analyze the airfoil using a robust and accurate fluid-structure interaction routine, and introduce two morphing scenarios: one where rigid and flexible blade are identical when unloaded, and one where they are identical at the stall angle. We choose a single Reynolds number and a flexible airfoil material for a case study, and simulate over a range of attack angles, noting the lift and drag coefficients as well as the attack angle change through passive pitching of the flexible airfoil. It was found that the flexible airfoil can delay stall as well as significantly increase lift/drag ratios compared to the rigid blade. In addition, negligible increases in drag and large increases in lift were realized. This suggests that flexibility can be used as a design parameter for wind turbine blades, and would likely increase the operational range and/or part- or over-load efficiencies significantly.