Numerical Simulation And Experimental Research Of DC Corona Streamer In Centimeter-level Air Gap

Streamer discharge is a transient process with dramatic changes temporally and spatially in a time scale of nanosecond. Even today, with ICCD ultrarapid camera, experiment means are still insufficient to record the developmental process completely; the parameters inside the streamer channel, such as charge density, electric field distribution, are still uncertain just by experiment. This paper studied the streamer discharge of centimeter-level short gap under DC conditions, using physical modeling and numerical simulation methods to analyze the characteristics of the initiation and progression of streamer discharge.Photoionization avalanche-streamer model and streamer development fluid dynamics model were proposed basing on the initiation and progression of streamer discharge. Space electric field solution method under cylindrical coordinate system was established based on Finite-Difference Time-Domain (FDTD) method and red-black ordering parallel compute method was used to improve the efficiency of the solution of the space electric field.Photoionization avalanche-streamer model was used to carry out the simulation analysis of the initial characteristics of uniform field streamer in different gap length. FD-FCT algorithm for two-dimensional cylindrical coordinate system was proposed to realize the solution of streamer development fluid dynamicsl in uniform field. Simulation study of the short gap streamer discharge was carried out to get the micro physical characteristics of the streamer space charged particles distribution, spatial distribution of electric field, the streamer channel radius, speed of streamer development and streamer discharge current. The initial conditions of streamer discharge simulation and the effects of background electric field on the physical characteristics of streamer discharge were also discussed.A quasi-one-dimensional equivalent numerical model was established to simulate the progression of streamer in non-uniform field, overcoming the shortage of non-uniform field of two-dimensional streamer simulation, whose numerical solution is complex and hard to converge. Based on the equivalent model of the streamer development, the process of positive development streamer of typical rod-plane gap was studied, getting the variation characteristics of micro-physical parameters of spatial electric field, electric potential, charge density distribution and streamer speed. The effect of streamer channel shape on the physical characteristics of streamer discharge was also discussed, determining reasonable principles on the choice of streamer channel shape. For negative streamer discharge characteristics, the model considered the physical processes of positive ions impact the cathode surface to produce the secondary electron emission specifically. And the physical processes of negative streamer trichel pulse were analyzed. The study shows negative ions weaken the cyclical of the rod electrode in head field, and take great influence on the formation and development of the trichel pulse.A humidity calculation model was proposed to carry out the study of the micro-physically characteristic effect of humidity on the initial and developing process of streamer in both uniform field and non-uniform field. The Study shows that humidity has little effect on streamer inception voltage, neither in uniform field nor non-uniform field, could even be neglected. With the increasing humidity, the attachment and composite function of electronic is enhanced, reducing the effective space ionization, leads to density decreasing of charge at positive streamer head, and plasma inside the streamer channel. The streamer head field fades, while the average field strength of the streamer channel rises. Trichel pulse current presents reductions on both amplitude and frequency with an increasing humidity.High potential current measurement system was designed to measure the streamer discharge current, centimeter-level gap discharge synchronous observation platform was established, combining with the high-potential current collection technology and high-speed photography. The characteristics of air gap discharge under different electrode structure and different clearance was studied, and compared with the simulation results of the proposed model (Photoionization avalanche-streamer model and streamer development fluid dynamics model), to verify the rationality of the physical models of streamer initiation and progression.