Modeling and three dimensional simulation of the neutral dynamics in an air discharge confined in a microcavity. II. Analysis of the wall and geometry effects

This article is devoted to the analysis of the confinement effects of the n eutral dynamics generated by a short-gap (0.5 mm) discharge inside three di fferent microcavity geometries (cylinder, cube, and bricklike) filled with air at atmospheric pressure (760 Torr) and ambient temperature (293 K). The discharge is modelled by two mathematical functions representing the Joule heating and the momentum transfer between charged and neutral particles. T heir spatio-temporal evolution an taken from experimental results with 470 ns for the duration and 13.5 W for the maximum injected power. The neutral gas evolution is described by the classical transport equations and solved by a powerful numerical monotonic upstream-centered scheme for conversion l aws, Because of the microcavity dimensions considered, particular care has been used in the analysis of the thermal and hydrodynamics boundary layers which condition the gas-solid interaction in terms of viscous slip effects and thermal exchanges. The results presented show the microcavity geometry effects on the distribution of the initial cylindrical pressure wave as soo n as it reaches the lateral walls. They show the specificity of the cube an d bricklike microcavities due to the delayed reflections on the corners lea ding to a more heterogeneous gas behavior than in the case of the cylindric al microcavity. We also discuss the specific gas behaviors near the wall re sulting from heat exchange and viscous stress. (C) 1998 American Institute of Physics. [S0021-8979(98)00921-9].