Lift improvements using duty-cycled plasma actuation at low Reynolds numbers

Abstract

An experimental study on active flow control over an elliptic airfoil is performed using an alternating-current dielectric-barrier-discharge (AC-DBD) plasma actuator combined with the duty-cycled technique. This study aims to eliminate or decrease the nonlinearities of the lift curves within a range of small angles of attack at low Reynolds numbers. The results of plasma actuator characterization in the quiescent air show that the duty-cycled plasma actuation can generate periodic sustained vortices with strengthened vorticity and streamwise momentum in comparison of steady-on mode. The wind tunnel test results show that the baseline airfoil exhibits the clearer nonlinear behavior at small AOA for lower Reynolds numbers. With duty-cycled plasma actuation, a rigidly linear proportional control of the lift that varies with the AOA is achieved with the reduced frequency f+=1. The surface oil-flow measurement shows the plasma actuator can delay the separation and result in an enhanced lift when the laminar boundary layer separation occurs without reattachment. When the long laminar separation bubble appears in the trailing edge region, the plasma actuator can eliminate the bubble. In this case, the extra lift supplied by the bubble is eliminated, leading to a reduced airfoil lift. The linear proportional control of the lift can be achieved by the appropriate enhanced and reduced lift changes which can be supplied by the duty-cycled plasma actuation.