Experimental study on the energy deposition of an ns-DBD plasma actuator and its effect on a laminar boundary layer

An experimental study aimed at the influence of different barrier materials on the energy deposition of nanosecond pulsed dielectric barrier discharge (ns-DBD) plasma actuator was carried out. Additionally, the direct effect of the discharge of an ns-DBD plasma actuator on a low velocity laminar boundary layer was investigated. Three barrier materials were selected for this study. These were Kapton polyimide tape, silicone-rubber and fine polyamide PA2200. Schlieren imagery in quiescent conditions were conducted to visualize the effect of the thermal energy deposition. Particle Image Velocimitry (PIV) was used to obtain the induced velocity fields by a flush mounted ns-DBD plasma actuator with a two layer Kapton barrier in a laminar boundary layer. A backward-time backward-space finite difference discretization of the compressible continuity equation was proposed to quantify the density field disturbance by ns-DBD plasma actuator. Results of the barrier characterization study indicated that a thinner barrier of the same material will allow more thermal energy to be deposited to the air per discharge pulse. A comparison between disturbed density field area and electrical energy usage per pulse, showed that an ns-DBD plasma actuator with a Kapton barrier is the most efficient tested barrier for coupling electrical energy as thermal energy to the near wall volume of air. Additionally, both the structure of the density disturbance in the quiescent air and the plasma discharge structure itself (Figure 1) are strongly dependent on the barrier material. Results of the PIV tests on the effect of discharge by ns-DBD plasma actuator in a laminar boundary layer indicated the presence of small body force. This body force was directed from the grounded exposed electrode to the high voltage covered electrode. Moreover, this body force induced a vortex like disturbance in the boundary layer. Additionally, independent of the streamwise orientation of the ns-DBD plasma actuator electrodes, an increase in energy input results in a local decrease in density. A larger area of density field disturbance was observed for the results were the body force was directed opposite to the freestream flow. It can be concluded that a barrier used in an ns-DBD plasma actuator should have a low thickness, high electrical volume resistivity, low thermal capacitance and low heat capacity in order to efficiently deposit heat to the nearby air. Additionally, based on the density field disturbances in laminar boundary layer flow, the orientation of the ns-DBD plasma actuator (thus the direction of the body force) is able to enhance the impact of the thermal energy deposition through better distribution through the boundary layer.