Large Eddy Simulation of a Free-Burning Arc Discharge in Argon with a Turbulent Cross Flow and External Field

In most of the numerical approaches proposed for modeling high-intensity plasma-arcs, the effects of turbulence on the arc structure are often excluded because of the intricate physics originating from the interaction of turbulent scales, high-temperature gas dynamics, magnetohydrodynamics (MHD) and chemical kinetics. The goal of this study is threefold: to develop a generic turbulent MHD model to simulate free-burning arc discharges, to validate the code with available experimental data, and to investigate the effect of an external field and turbulent cross flow on the free-burning arc configuration. The governing equations are solved in conservative form using a hybrid scheme that combines a high-order monotonic upwind scheme with a second-order central scheme. The fluid and MHD turbulence are resolved using a large eddy simulation (LES) approach with a recently developed sub-grid closure model. An implicit scheme is used to compute the magnetic diffusion term appearing in the magnetic induction equation to alleviate the severe time-step constraint. The comparison of the model prediction with experimental data for Argon arcs at different current intensities shows generally good agreement. When an external field is applied, the overall shape of the free-burning arc drastically changes. The straightening of the arc indicates the potential for stabilization of a free-burning arc by magnetic forces. Even though the turbulence is significantly attenuated as a result of the thermal expansion near the cathode, it adds an unsteady characteristic to the arc and, in general, has a negative impact on the stabilization of the electrical discharge.