Investigation of Stability Issues for an Adaptive Trailing Edge System

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This work presents a method to determine ∞utter and divergence instability limits for a 2D airfoil section fltted with an actively controlled trailing edge ∞ap. This ∞ap consists of a deformable trailing edge, which deformation is governed by control algorithms based on measurements of either heave displacement or local angle of attack. The purpose of the controlled deformable ∞ap is to reduce ∞uctuations in the aerodynamic forces on the airfoil, which according to recent studies have a signiflcant potential for fatigue load alleviation. The structural model of the airfoil section contains three degrees of freedom: heave translation, pitch rotation and ∞ap de∞ection. A potential ∞ow model provides the aerodynamic forces and their distribution. The unsteady aerodynamics are described using an indicial function approximation. Stability of the full aeroservoelastic system is determined through eigenvalue analysis by state-space formulation of the indicial approximation. Validation is carried out against an implementation of the recursive method by Theodorsen and Garrick for ‘∞exure-torsion-aileron’ ∞utter. The implemented stability tool is then applied to an airfoil section representative of a wind turbine blade with active ∞ap control. It is thereby observed that the airfoil stability limits are signiflcantly modifled by the presence of the ∞ap, and they depend on several parameters: ∞ap structural characteristics, type of control, control gain factors and time lag.