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

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#### Abstract

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<inf>∞</inf>, covering the chord Reynolds number Re from 4.4 × 10<sup>4</sup> to 7.7 × 10<sup>4</sup>. 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 × 10<sup>4</sup>. The sawtooth plasma actuator led to a delay in the stall angle α<inf>stall</inf> by 5° and an increase in the maximum lift coefficient $$C_{{{\text{L}}_{ \text{max} } }}$$CLmax by about 9 %. On the other hand, at the same input power, the traditional DBD plasma actuator managed a delay in α<inf>stall</inf> by only 3° and an increase in $$C_{{{\text{L}}_{ \text{max} } }}$$CLmax by about 3 %. Secondly, the convergence time t<inf>c</inf> of the lift force F<inf>L</inf> at Re from 4.4 × 10<sup>4</sup> to 7.7 × 10<sup>4</sup> was investigated for two closed-loop systems. It has been demonstrated that the t<inf>c</inf> 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 × 10<sup>4</sup>. The reduction in t<inf>c</inf> 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.

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Wu, Z., Wong, C. W., Wang, L., Lu, Z., Zhu, Y., & Zhou, Y. (2015). A rapidly settled closed-loop control for airfoil aerodynamics based on plasma actuation. Experiments in Fluids, 56(8). https://doi.org/10.1007/s00348-015-2032-5

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