Experimental study of stall control over an airfoil with dual excitation of separated shear layers

This paper investigates the stall control over an airfoil employing dual excitation of separated shear layers with dielectric barrier discharge plasma actuators. This novel approach is studied experimentally on the NACA 0015 airfoil at the angle of attack and Reynolds number of 14 degrees and 0.3 x 10(6), respectively. To analyze the baseline flow, Time-averaged pressure distributions on the airfoil surfaces are evaluated with 40 pressure taps. Further, the dominant natural frequencies associated with flow structures in the airfoil wake are examined utilizing a hot-wire anemometer. Two plasma actuators, one on the suction side just upstream the separation point and the other on the pressure side at the trailing edge, are exploited to control the baseline flow. Based on the active actuators, three controlled cases are considered in the present study. In the first case, the frequency of natural vortex shedding and its different harmonics are employed to excite the suction side separated shear layer. In the second case, plasma actuation is applied to the shear layer at the trailing edge. Further, in the third case, both of the actuators are utilized to excite the separated shear layers on the suction side and the trailing edge, simultaneously. The results of the pressure coefficient distributions, as well as the aerodynamic coefficients, are compared for all cases. Moreover, the actuators energy consumption is evaluated for the controlled cases and a new efficiency parameter is presented. Accordingly, the first case prevents the stall phenomenon only at the wake mode frequency and its first super-harmonic. In addition, using the plasma actuator at the trailing edge solely is an ineffective flow separation control strategy. However, dual excitation is promising for a full stall control in a wide range of excitation frequencies. Analyses of the lift-to-drag ratio and the efficiency parameter reveal that the dual excitation case is the most efficient stall control technique. (C) 2018 Elsevier Masson SAS. All rights reserved.