Streamer Propagation And Pressure Waves Produced By A Nanosecond Pulsed Surface Sliding Discharge: Effect Of The High-Voltage Electrode Shape

This paper aims at better understanding nanosecond sliding discharges based on a three-electrode geometry and at studying the effect of the shape of the pulsed high-voltage electrode on their electrical, optical and mechanical properties. Three different electrode shapes are considered: a typical planar electrode with a straight edge, a planar electrode with a sawtooth edge, and a wire electrode. First, we verified that the sliding discharge starts to appear when the potential difference between both air-exposed electrodes exceeds about 25 kV, corresponding to a mean electric strength (potential difference divided by the gap) a little bit higher than 6 kV cm(-1), but this value differs slightly depending on the shape of the electrode. Secondly, we highlighted that the current with the wire-based discharge is slightly higher compared to the two others because the streamers are more numerous and they are more uniformly distributed along the wire. Moreover, whatever the electrode shape, intensified charge-coupled device visualizations showed that many streamers initiate from the pulsed high-voltage electrode edge and propagate on the dielectric surface toward the DC voltage electrode at a mean velocity of about 1 mm ns(-1). However, the streamer trajectory depends strongly on the electrode shape. Visualizations of the pressure waves induced by the different plasma actuators have been realized with a shadowgraph system. In the presence of a sliding discharge, every streamer is at the origin of three different pressure waves. The first hemispherical pressure wave results from streamer ignition at the edge of the pulsed high-voltage electrode, the head of the streamer acting as a point heat source. The second hemispherical pressure wave is due to the corona-type discharge that ignites from the negative DC high-voltage electrode when the streamer head gets closer. Finally, the third wave is a semi-cylindrical wave as each streamer acts as a line source of heat. To conclude, pressure measurements highlighted that the peak value of the pressure is nearly constant along the spanwise direction of the wire electrode as it presents high fluctuations with the sawtooth electrode, the maximum pressure being measured above the tips, where streamers are localized.