The modelling of an SF₆ arc in a supersonic nozzle: I. Cold flow features and dc arc characteristics

The cold flow and the arc, under direct currents burning in the nozzle of the arcing device used in Benenson (1980 Final Report General Electric Co. (Schenectady, NY) Project 246-2) with fixed stagnation pressure, have been investigated computationally using five flow models; the laminar flow model, the Prandtl mixing length model, the standard k-epsilon model and its two variants, the Chen-Kim model and the renormalization group model. For the cold flow, the computational results are almost the same for the different flow models apart from in the regions close to the two electrodes. There is a bow shock in front of the downstream hollow electrode and a wake near the tip of the upstream electrode. The size of the wake and the strength and the structure of the shock differ greatly amongst the flow models. With a dc arc in the nozzle, derived voltage-current characteristics are negative for currents of less than 600 A but for higher currents the arc voltage is nearly constant.