Dynamic Stall Control Using a Model-Based Observer

Dynamic stall control is of interest for its potential to enhance the performance of rotorcraft. The experiments described used pulsed vortex generator jets, shown previously to prevent separation on steady wings and airfoils, to delay dynamic stall on a rapidly pitching airfoil. In tests performed on a NACA-0012 airfoil at low Reynolds numbers, the jets yielded a 25–35% increase in the lift coefficient achievable without moment stall. Next, a differential equation model of the dynamic stall process was derived and experimentally validated. Models of this form enable the application of well-known control theory to the design of flow control systems. In the final round of experiments, a state observer based on the mathematical model detected incipient dynamic stall. A controller used the stall prediction to operate the pulsed jets only when needed to prevent stall. The controller turned the jets off for the remainder of the oscillation cycle. The controller only operated the jets for about 25% of the pitch cycle, so that the best lift increases of the early experiments could be achieved with only 25% of the air mass flow.