Three-dimensional finite element modeling of dynamic arc behavior in a dc plasma torch

Summary form only given. The behavior of the electric arc inside a direct current non-transferred arc plasma torch is simulated using a three-dimensional, time-dependent, thermodynamic equilibrium model. The fluid and electromagnetic equations are solved in a fully coupled approach by a variational multiscale finite element method, which implicitly accounts for the multiscale nature of the flow. Simulations of a commercial plasma spray torch operating with Ar-He under different operating conditions are presented. The obtained results show that, due to the imbalance between electromagnetic and flow drag forces, the arc is first dragged downstream by the flow and then jumps to form a new attachment, preferably at the opposite side of the original attachment, as has been observed experimentally. This is the first time that such behavior of the arc has been obtained in a numerical simulation. Furthermore, simulations of the torch operating with different total currents yields results which qualitatively reproduce the experimentally observed change of the behavior of the arc as the total current is decreased (as the arc is driven from a steady or takeover mode of operation towards a restrike mode): a decrease in the reattachment frequency and a transition of the voltage signal from periodic to a quasi-periodic with sharp fluctuations