Prediction of spark paths in a point / two-rod gap in air

Abstract

Three-dimensional images had been obtained of some 400 positive point/plane sparks in air during previous work and analysis showed that on average each section of the spark was related to the previous one. However there was a large random perturbation (within a probability distribution) which accounted for the tortuous shapes of the spark paths. Simulations based on these findings gave satisfactory agreement in terms of, for example, appearance and fractal dimension. A more fundamental test of this analysis and simulation method has been tried by attempting to simulate a significantly different electrode system: the grounded plane electrode was replaced by two parallel grounded rods. The simulation is then used, firstly to predict the general shape of the spark paths; and secondly to predict how many of the sparks will be between the point electrode and one of the two rods, and how many between it and the other rod. By moving the point electrode in a direction at right angles to the axes of the rods, but at the same height above them, this ratio could be varied. In order to get reasonable consistency it was necessary to run 1000 trials in the simulation for each point electrode position. Different ratios were obtained for different assumptions as to the magnitude of the random element in the section-by-section prediction. A series of experiments with an analogous electrode system gave good agreement in terms of the percentage strikes to a given rod versus the position of the point electrode.