Flow separation control over an airfoil using dual excitation of DBD plasma actuators

This paper investigates flow separation control over an airfoil using dual excitation of DBD plasma actuators as a novel approach. Large eddy simulation is adopted to capture vortical structures within the airfoil wake. Power spectral density and dynamic mode decomposition analyses have been utilized to identify local and global oscillatory behavior associated with flow structures of the wake. Three controlled cases are considered in the present study. In the first case, the wake mode frequency (i.e., the frequency of natural vortex shedding) is used to excite separated shear layers at both the upper surface and the trailing edge of the airfoil, simultaneously. In the second case, the excitation frequency of the trailing edge actuator is increased to sixth multiples of the wake mode, while the other actuator excites the flow same as the first case. In the third case, excitation with frequency of the wake mode is only applied to the upper surface separated shear layer and no excitation is exerted at the trailing edge. According to the results, actuations manipulate the shear layers instabilities and modify the wake patterns remarkably. In all controlled cases, breakdown of the upper surface shear layer takes place closer to the separation point and also less strong vortices shed from the trailing edge compared to the baseline flow. It is revealed that the coherency of vortices within the wake region is not quite the same for all cases and the least coherency of vortical structures is observed in the first case. The maximum values of lift-to-drag ratio and lift coefficient is achieved in the first and second cases, respectively. (C) 2018 Elsevier Masson SAS. All rights reserved.