Flow control around an airfoil by dielectric barrier discharge plasma actuator with voltage modulation

This study performed a three-dimensional direct numerical simulation to investigate the control mechanism for the separation flow near an National Advisory Committee for Aeronautics 0015 (NACA0015) airfoil via a dielectric barrier discharge plasma actuator. The Reynolds number was 67 000 and the angle of attack was 16°. The actuator was activated by a burst frequency of 60 Hz and a duty ratio of 50%. Three conditions (no change, decrease, and increase) for the input voltage of the actuator were used to control the separation flow. For the input voltage, the induced flow from the actuator generated a positive vorticity on its actuator; however, the transition for this positive vorticity was different during the actuator on-time under each voltage condition. The positive vorticity in the case of decreasing input voltage decreased during the actuator on-time and then pulled the negative vorticity owing to the separated flow from the front edge of the airfoil toward the airfoil surface. This increased the lift coefficient by 33% compared to that in the uncontrolled case. The lift coefficient was not enhanced when increasing the input voltage. This is because the positive vorticity increased during the actuator on-time and vanished suddenly during off-time. Before the actuator off-time, the positive vorticity under constant input voltage exceeded that when the input voltage was decreased. Consequently, the lift coefficient increased by 17%. The drag coefficient remained consistent under every input voltage condition. The behavior of the positive vorticity is important for controlling the separated flow for the airfoil.