3D MHD modelling of low current – high voltage DC plasma torch under restrike mode

We present in this paper a MHD modelling of the gliding arc behaviour of a DC plasma torch operating with air under low current and high voltage conditions. The low current leads to instabilities and difficulties to simulate the process because the magnetic field is not sufficient to constrict the arc. The model is 3D, time-dependent and the MHD equations are solved in using CFD software Code_Saturne ® . Although the arc is definitively non-LTE, the LTE assumption is considered as a first approach. The injection of air is tangential. A hot gas channel reattachment model has been used to simulate the restriking process of the arc root. After the description of the model, the most appropriate electrical voltage breakdown parameter has been selected in comparing with experimental results. A typical operating point is then studied in details and shows the helical shape of the arc discharge in the nozzle. Finally, the mass flow rate and the current have been varied in the range 0.16 – 0.5 gs -1 and 100 – 300 mA, respectively, corresponding to typical glidarc operating points of our experimental plasma torch. The model shows good consistency with experimental data in terms of: global behaviour, arc length, mean voltage and glidarc frequency.