Modeling of discharges in flowing plasmas.

摘要

Plasmas with electron densities significantly elevated with respect to their chemical equilibrium values are of use in a wide range of applications. However the practicality of these uses critically depends on the ability to generate these super-ionized plasmas at low temperatures with the minimum possible power input. Electron heating by means of electric discharges has been shown to be an efficient method to produce these super-ionized plasmas. In order to devise power reduction strategies it is important to understand the chemical mechanisms of ionization and recombination in air plasmas with energetic electrons. It is also vital to have an understanding of the discharge physics. This is possible only by detailed numerical simulation of these current carrying plasmas.; In this dissertation, a new computational tool has been developed to simulate DC and pulsed discharges in flowing atmospheric plasmas. The state of the plasma is represented with eleven chemical species, a mass-averaged vibration-electronic temperature, an electron translational temperature and a mass-averaged translational temperature for the heavy particles. This model incorporates a self-consistent multicomponent, multitemperature diffusion model and a two-temperature chemical kinetics model to represent the nonequilibrium thermochemistry of the plasma. The equations for the gas model are then solved numerically using a new semi-implicit finite volume time marching technique. This method significantly reduces the cost of solution compared to an explicit method.; The numerical method has been tested against nonequilibrium plasma experiments conducted at Stanford University. The calculated temperatures were compared to the experimentally predicted values. The computations were in excellent agreement with the experiments. The results showed that it is necessary to include multicomponent diffusion to simulate these flows. The numerical method was then tested against DC and pulsed discharge experiments. The calculated temperatures and the peak electron number density for the DC discharge were compared to the measurements. The computed temporal decay of electron number density for a combined DC/pulsed discharge was compared to the experimentally measured decay. Again, the simulations are in good agreement with the experiments. These results show that the current numerical simulation model is capable of treating DC and pulsed discharges in flowing plasmas.