Characterization of the ionic wind produced by a DBD actuator designed to control the laminar-to-turbulent transition

Non thermal plasma actuators have provided a novel means of studying active flow control in aerodynamic research. The ionic wind induced by such devices has the ability to couple momentum into boundary layers resulting in control of flow separation or delay of laminar-to-turbulent transition. Significant results would probably be obtained at higher Reynolds numbers if the plasma actuators were systematically operated in unsteady mode. The aim of this experimental work was to provide an understanding of how an asymmetric DBD actuator operated in steady and unsteady mode behaved in quiescent air. Recent studies have shown that the plasma morphology is not the same during the positive and the negative cycles of the AC power supply of the DBD actuator. The mechanisms of momentum addition through the ionic wind are expected to be dependent on each cycle of the high voltage. In this work, the influence of the voltage cycles on the ionic wind velocity was studied by performing time-resolved measurements of the velocity synchronized with records of the AC voltage. Velocity measurements were carried out by means of a 2CLDV system above the actuator for heights from 0,1 to 5 mm from the dielectric panel. The actuator was working with voltages of 14 to 32 kVpp and frequencies ranging from 0,5 to 1 kHz. For the unsteady mode, the pulsed frequency was fixed to 10 Hz and duty cycles of 50% and 75% were studied. First, the ionic wind was observed to be similar to a pulsed wall jet. Although operated in steady mode, it was forced by a frequency equal to the frequency of the AC power supply (0,5 to 1 kHz). When unsteadily working, the ambient air was also pulsed at 10 Hz above the actuator. Secondly, the velocity of the ionic wind was not the same according to the high voltage cycles. Both first half of the negative and positive cycles induced ionic wind however the negative one provided a velocity approximately twice higher than the positive one. According to the measurements in unsteady mode, a counter flow seemed to appear during the second half of the negative cycle. Thus, an optimal voltage wave form was suggested to prevent this inefficiency. These results must be considered carefully since up to now it was not possible to ensure if the velocities measured in quiescent air were only representative of the induced flow or also of the velocities of charged particles moving through the electric field inherent to the plasma discharge.