Plasma Laminar-Separation-Bubble Control over Airfoil at Low Reynolds Numbers

Abstract

An experimental study of the active flow control over an elliptic airfoil is performed using an Alternating Current Single Dielectric Barrier Discharge (AC-SDBD) plasma actuator combined with the duty-cycle technique. The purpose is to eliminate or decrease the nonlinearities of the lift curve at the range of small angles of attack for low Reynolds number. The tests are carried out in a low-turbulence low-speed wind tunnel. The Reynolds number based on the chord of the airfoil is from 1.0 to 2.2 × 10. The pressure distributions and lift curve with and without plasma actuation over the airfoil are investigated. The results consist of three different controls modes: plasma-off, steady plasma actuation, and duty-cycle plasma actuation. To explain how the plasma actuation effects the laminar separation over the airfoil, the impact of the boundary layer trip strip is explored and the surface oil flow measurement is made. The results show that the AC-SDBD plasma actuator would re-energy the boundary layer, thereby delay the trailing-edge laminar boundary layer separation and results in the enhancement of the lift when the laminar boundary layer separation occurs in the trailing-edge region of the airfoil without laminar separation bubble. When the laminar separation bubble occurs at trailingor leading edge region of the airfoil, the AC-SDBD plasma actuator can eliminate or decrease the bubble like a transition trip strip, in this case, the extra lift supplied by the bubble is eliminate or decrease, so it leads to a reduction in the airfoil lift. The linear proportional control of the lift is achieved with the enhancement and reduction lift changes by using plasma actuation.