Reduced-order model for robust aeroelastic control

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The objective of aeroelastic control, i.e., aeroservoelasticity, is either suppression of instability, such as flutter, or impeding the effect of external excitation, e.g., due to a gust. In the present work, a robust active feedback controller for a NACA64A010 airfoil model under sub- and transonic flow conditions is designed to impede flutter. The airfoilmodel has an elastic heave and pitch suspension and is equipped with an active aerodynamic control surface. The control design is based on linear reduced-order models (ROM) derived from a coupled computational fluid dynamics (CFD)-computational structural mechanics (CSM) simulation environment. Because the control design should be robust across a range of flow conditions, a collection of ROMs, which span the desired operational envelope, is considered. For each condition, the stability region for a three-term controller is determined with a parameter space approach. Building the intersection area for certain flow regimes allows determining the area of robust stability. The possibility of shifting the flutter boundary with a robust controller compared to adaptive control designs is discussed. To determine finally a set of control parameters chosen from within the stabilizing area, an optimization approach is used. Comparisons of the response of the investigated airfoil model under control between ROM and CFD–CSM shows that the linear ROM is able to predict the response very accurately, despite nonlinearities due to shocks in the flow field.