Flow reversal in millimetric annular DBD plasma actuator

A four-species plasma-fluid model is used to investigate the previously unexplained reversal of flow direction that occurs when the diameter of millimetric annular dielectric barrier discharge (DBD) plasma actuators reduces. We found that the transformation from a strong outward jet to a weak inward one is induced by disproportionate reduction of the negative radial electrohydrodynamic forcing component during the positive sub-cycle. This change of forcing is due to the increased curvature of the electric field lines, which leads to a higher rate of dielectric charging and thus an increasingly intermittent discharge structure. The flow reversal also depends on the thickness of the electrode and the ambient oxygen content via similar discharging mechanisms. This study indicates that a thinner electrode or higher oxygen fraction is favorable when using DBD plasma actuators in milli/microscale flow control problems since it maintains the strong outward jet at smaller diameter and with higher efficiency.