PLASMA-BASED FLOW CONTROL ON PITCHING AIRFOIL AT LOW REYNOLDS NUMBER

To improve the poor aerodynamic performance of pitching airfoils at low Reynolds number, the paper developed a control strategy based on the dielectric barrier discharge (DBD) plasma control. The 2D quasi direct numerical simulation method was applied to solve the unsteady incompressible Navier-Stokes equations around an oscillating NACA0012 airfoil at low Reynolds number. Equations for plasma flow control are added to the momentum equations in the Openfoam solver as a source term. The effects of steady DBD plasma actuation on the aerodynamic force characteristics of an oscillating NACA0012 airfoil are investigated. The DBD plasma actuators are located at the leading edge and trailing edge of the upper and lower airfoil surfaces, respectively. And four open-loop control strategies for the actuators were proposed. The flow control effects of these control strategies with different Reynold numbers, reduced frequency and the positions of plasma actuators are compared. The mechanisms of plasma flow control is analyzed by the flow field structures and dynamic pressure distribution. Results indicate the effect of control strategy B (switch on actuator located on the upper surface at negative angle of attack, and switch on actuator located on the lower surface at positive angle of attack) is best when the plasma actuators located at leading edge of airfoil, and control strategy C (switch on actuator mounted on the upper surface during counterclockwise rotation stage, switch on actuator mounted on the lower surface during clockwise rotation stage) has best effect when the plasma actuators located at the trailing edge of airfoil. When the plasma actuators located at leading edge, the flow control effect will decrease as the reduced frequency increases, and it also increase airfoil's drag. For the trailing edge plasma cases, the pressure drag may decrease, which is better than the leading edge plasma cases. Meanwhile, the trailing edge DBD plasma control has good effect of enhancing lift and reducing drag for all the calculated reduced frequency ranges (5.01~11.82). The lift enhancement effects of DBD flow control are good at different Reynolds numbers. However, due to the flow viscosity effect enhancement, the drag reduction effects of DBD flow control become worse with decreasing Reynolds numbers.