An experimental investigation of the unsteady counter-flow generated by a DBD plasma actuator for flow control

Surface dielectric barrier discharge has been well-known as an active flow control device during recent years. In this paper, an experimental investigation has been performed on the flow control capacity of a surface DBD, placed over the pressure side of a NACA 0015 airfoil at the trailing edge. The induced wall jet is opposed to the free stream, operated in both steady and unsteady modes. The power spectral density of the total pressure signals, measured by the Hot Wire Anemometry in the still air, illustrated the ability of the unsteady plasma in generating the reverse flow structures at the pulse frequency and some of its harmonics. The strength of these vortices decreased at higher distances above the surface. The aerodynamic experiments focusing on evaluating the flow control capability of the unsteady counter-flow jet, were performed at low Reynolds number of 52,791\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{52,791}$$\end{document}. It was inferred from the results that modulation of the counter-flow jet in both actuation modes leads to lift enhancement at pre-stall and post-stall angles of attack up to 8% and 17%, respectively. Surface pressure measurements revealed that the upper surface pressure distribution is influenced by the effect of the lower surface counter-flow jet, especially at small angles of attack. It can be explained by the suction effect intensification, resulted by the plasma stimulated vortical flow. It was also found that the counter-flow jet actuated in the unsteady mode is considerably efficient at post-stall angles of attack, capable of increasing Cl\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${C}_{l}$$\end{document} more than16% greater than that of the co-flow one.