Experimental Study On Atmospheric Pressure Volume Discharges

The use of plasma for active flow control is a combination of classical fluid mechanics and electrodynamics of the new flow control technology. Having recently gained much attention, the new active flow control is expected to provide new ideas for the development and engineering applications of the flow control. In this paper, for better practical application of the active flow control, it is necessary to understand the coupling mechanisms of the plasma and high-speed airflow in detail. This paper focuses on the discharge characteristics of plasma in airflow to meet the needs of the flow control.In order to carry out the experiment in airflow, we had designed and built a test bench to meet the basic requirements. Intermittent noise and electromagnetic radiation could be produced when nanosecond pulse voltage was applied in the breakdown gap, and made a lot of interference to real signal. Therefore this paper analyzed the sources of noise and implemented a series of strict screening measures to construct a complete measurement system that could accurately measure the applied voltage, discharge current and optical signal. The main contents and conclusions are as follows:1) On different time scale, there were two completely different concepts of uniform discharge, which were ’instantaneous uniformity’ and ’superimposed uniformity’. When the airflow was introduced into the discharge gap, not only more discharge channels would establish, but the discharge would become more uniform. Due to the presence of metastable particles, the later streamer would follow the same path and propagated faster. The effect of the airflow could damage the ’memory effect’ in filamentary discharge, which could make the metastable particles distribute more evenly, as a consequence the discharge more uniform.2) The boundaries of the discharge starting characteristics were experimentally explored at different voltage. The results showed that, when the amplitude of the applied voltage was low, it was necessary to increase the frequency to start the discharge with the increasing velocity of the airflow.3) Increasing the airflow velocity introduced into the discharge gap gradually, the discharge characteristics would change significantly, transforming from filamentary discharge mode to the uniform and stable diffuse discharge mode. Furthermore, the discharge intensity was diminishing.If you increased the amplitude of the applied voltage, the discharge mode would change at a higher velocity of the airflow. Moreover, the airflow also effected the number and the amplitude of the discharge current.4) When the discharge was excitated by nanosecond pulse, the airflow would have larger effect on the negative discharge current than the positive discharge current. The secondary discharge current peak slightly decreased at low flow velocity and gradually increased with the increasing velocity of airflow. When the velocity reached a certain value, the secondary discharge current reached a peak and remained unchanged. In the same condition, the higher repetition rate were applied, the smaller discharge current would be. When the amplitude of the applied voltage was up to 23 k V, the discharge excitated by repetitive nanosecond pulse with multiple current pulses would occur.