Feedback Control and Parameter Estimation for Lift Maximization of a Pitching Airfoil

A study investigates feedback control and parameter estimation for lift maximization of a pitching airfoil. It demonstrates a technical approach to regulate the pitching rate of an airfoil using feedback control to visit the high-lift regions of the GK-model state space accessible only to unsteady pitch angles. Using experimental towing tank data, the dynamic stall properties of an airfoil are captured via a parameter fit. By designing state and, eventually, output feedback controls, the researchers remove the explicit time dependence of an open-loop sinusoidal input, which allows us to formally characterize the oscillations as a stable limit cycle of the dynamics. They analyze the closed-loop system using tools from bifurcation analysis and airfoil theory. Numerical results show that oscillating-pitch solutions boost the performance of the time-averaged lift by 40% over the optimal steady-pitch solution and by 65% over pre-stall conditions.