Development of a passive‐adaptive slat for a wind turbine airfoil

A passive‐adaptive slat concept was designed to avoid separation in the root region of a horizontal‐axis wind turbine blade. This concept incorporates an autonomously moveable slat device only driven by the aerodynamic forces acting on it without the need for mechanical or electrical actuation. It opens at high local angles of attack to delay the stall angle and closes for small angles of attack to increase the lift to drag ratio of the blade segment. This article describes the development of a passive‐adaptive slat for a DU‐91‐W2‐250 airfoil, which is a segment of the reference rotor blade in the project SmartBlades 2.0. In the course of the passive‐adaptive slat design, the optimization of the slat and its extended position is presented. This is followed by the development of two passive‐adaptive slat kinematics, which are opening and closing the slat passively at different angles of attack. With the designed passive‐adaptive slat the stall of the airfoil is delayed by 20° in incidence and the maximum lift of the airfoil is increased by about 130% at the same time in comparison to the original airfoil. Furthermore, the DU‐91‐W2‐250 airfoil with moveable passive‐adaptive slat has in most conditions a higher climb index and therefore a better aerodynamic performance than the same airfoil with a fixed integrated slat.