High Mach Number Leading-Edge Flow Separation Control Using AC DBD Plasma Actuators

Abstract

Wind tunnel experiments were conducted to quantify the e↵ectiveness of alternating current dielectric barrier discharge flow control actuators to suppress leading-edge stall on a NASA energy e cient transport airfoil at compressible freestream speeds. The objective of this research was to increase lift, reduce drag, and improve the stall characteristics of the supercritical airfoil near stall by flow reattachment at relatively high Mach and Reynolds numbers. In addition, the e↵ect of unsteady (or duty cycle) operation on these aerodynamic quantities was also investigated. The experiments were conducted at the University of Notre Dame Mach 0.6 Wind Tunnel for a range of Mach numbers between 0.1 and 0.4 with an airfoil model of chord 30.48 cm at atmospheric conditions corresponding to a Reynolds number range of 560, 000 through 2, 260, 000. Lift and drag forces, as well as the quarter chord moments were measured directly by a sting which reacted on load cells and torque sensors on the outside of the 0.91⇥0.91 m wind tunnel test section. Two leading-edges of the airfoil were fabricated. The first was covered in a Kapton dielectric film of 0.127 mm and had a 7 μm copper electrode, and the second was a thick-dielectric Macor with a copper tape exposed (76 μm thick) electrode. A high voltage AC signal was applied to electrodes for the flow control case. The results show that the plasma actuators were e↵ective at reattaching the leading-edge separated flow as evidenced by the increase in maximum lift coe cient and stall angle. In the post stalled regime, the lift was dramatically increased, by as much as 90%. Drag in the stalled regime was reduced by as much as 28% and the nose down pitching moment was reduced by as much as 40%. Pressure taps on the suction surface confirmed flow reattachment as evidenced by the return of a pressure peak near the leading-edge and better pressure recovery aft of the leading-edge when the active flow control was enabled. Time-averaged PIV confirmed the airflow following the airfoil surface closely. The experiment also showed that lift was increased the most in deep stall when the plasma actuator was operated unsteady with a reduced frequency of unity, whereas in light stall steady operation was preferred. Overall, both AC DBD plasma actuator designs were able to increase the maximum lift coe cient and stall angle of attack for the full range of Mach numbers, with the thick-dielectric Macor leading-edge performing better at Mach 0.4.