Application of output feedback sliding mode control to active flutter suppression of two-dimensional airfoil

The effectiveness of the sliding mode control (SMC) method for active flutter suppression (AFS) and the issues concerning control system discretization and control input constraints were studied using a typical two-dimensional airfoil. The airfoil has a trailing-edge flap for flutter control. The aeroelastic system involves a two-degrees-of-freedom motion (pitch and plunge), and the equations were constructed by utilizing quasi-steady aerodynamic forces. The control system, designed by the output feedback SMC method, was incorporated to suppress the pitch-plunge flutter. Meanwhile, the system discretization and the flap deflection constraints were implemented. Then, a classical Runge-Kutta (RK) algorithm was utilized for numerical calculations. The results indicated that the close-loop system with the SMC system could be stable at a speed above the flutter boundary. However, when the flap deflection limits are reached, the close-loop system with the simple discretized control system loses control. Furthermore, control compensation developed by theoretical analysis was proposed to make the system stable again. The parameter perturbations and the time delay effects were also discussed in this paper.