EHD Force in Dielectric Barrier Discharges Parametric Study and Influence of Negative Ions

Abstract

Surface discharges can modify the boundary layer of a flow along an airfoil and have been proposed as actuators for flow control, drag reduction, flow acceleration and flow reattachment. Two types of surface discharges have been extensively studied: corona discharges and dielectric barrier discharges (DBDs). It is well accepted that ion wind is responsible for the observed aerodynamic effects near the surface in corona discharges, but the mechanisms leading to momentum transfer to the gas in surface dielectric barrier discharges are not as clear and various names such as “paraelectric”, or ponderomotive have been used to qualify the electrohydrodynamic (EHD) force generated in these discharges. In this paper we show, with the help of a fluid model, that the force acting on the gas in dielectric barrier discharges is of the same nature as the ion wind and is due to the momentum transfer from charged particles to gas molecules during time periods between current pulses, where a unipolar ion space charge drifts above the surface. We also show that the volume above the surface where this EHD force is active depends on the charging current between current pulses, i.e. on the product of the electrode/dielectric capacitance and voltage increase rate. The simulations are performed and compared in nitrogen and air, neglecting complex chemistry, and the role of negative ions in air is analyzed.