A rapidly settled closed-loop control for airfoil aerodynamics based on plasma actuation

This paper presents an experimental investigation on the response of the slope seeking with extended Kalman filter (EKF) deployed in a closed-loop system for airfoil aerodynamics control. A novel dielectric barrier discharge (DBD) plasma actuator was used to manipulate the flow around the NACA 0015 airfoil. Experiments were performed under different freestream velocities U _∞, covering the chord Reynolds number Re from 4.4 × 10⁴ to 7.7 × 10⁴. Firstly, the advantages of applying this DBD plasma actuator (hereafter called sawtooth plasma actuator) on the airfoil were examined in an open-loop system at Re = 7.7 × 10⁴. The sawtooth plasma actuator led to a delay in the stall angle α _stall by 5° and an increase in the maximum lift coefficient \(C_{{{\text{L}}_{ \text{max} } }}\) by about 9 %. On the other hand, at the same input power, the traditional DBD plasma actuator managed a delay in α _stall by only 3° and an increase in \(C_{{{\text{L}}_{ \text{max} } }}\) by about 3 %. Secondly, the convergence time t _c of the lift force F _L at Re from 4.4 × 10⁴ to 7.7 × 10⁴ was investigated for two closed-loop systems. It has been demonstrated that the t _c was about 70 % less under the slope seeking with EKF than that under the conventional slope seeking with high-pass (HP) and low-pass (LP) filters at Re = 7.7 × 10⁴. The reduction in t _c was also observed at a different Re. Finally, the slope seeking with EKF showed excellent robustness over a moderate Re range; that is, the voltage amplitude determined by the control algorithm promptly responded to a change in Re, much faster than that of the conventional slope seeking with HP and LP filters.