Adaptive camber airfoil for load alleviation in horizontal axis wind turbines

The present study investigates analytically and numerically the concept of an airfoil, that was investigated experimentally in a preceding work. The airfoil has a leading flap, kinematically coupled to a trailing flap. The pressure distribution on the airfoil surface creates aerodynamic moments on the flaps, which are in equilibrium with an elastic restoring torque. The concept is called adaptive camber airfoil, since the flap positions have a similar effect as the camber variation of the airfoil. To analytically describe the equilibrium, the planar equations of motion of the airfoil are derived. The equations of motion are subsequently linearized and non-dimensionalized. Under the assumption of potential flow and simple harmonic oscillations, expressions for the aerodynamic moments and forces are derived by means of the thin-airfoil theory. Thereby, the steady equilibrium of the adaptive camber airfoil can be derived analytically. Furthermore, with an harmonic Ansatz for the equations of motion, the unsteady solution can be discussed in the frequency domain. For a numerical simulation in the time domain, the aerodynamic moments and forces are obtained from an unsteady panel method, coupled to non-linear equations of motion.