  Plasma jets produced by direct-current (DC) non-transferred arc plasma
torches, at the core of technologies ranging from spray coating to pyrolysis,
present intricate dynamics due to the coupled interaction of fluid flow,
thermal, and electromagnetic phenomena. The flow dynamics from an arc discharge
plasma jet are investigated using time-dependent three-dimensional simulations
encompassing the dynamics of the arc inside the torch, the evolution of the jet
through the discharge environment, and the subsequent impingement of the jet
over a flat substrate. The plasma is described by a chemical equilibrium and
thermodynamic nonequilibrium (two-temperature) model. The numerical formulation
of the physical model is based on a monolithic and fully-coupled treatment of
the fluid and electromagnetic equations using a Variational Multiscale Finite
Element Method. Simulation results uncover distinct aspects of the flow
dynamics, including the jet forcing due to the movement of the electric arc,
the prevalence of deviations between heavy-species and electron temperatures in
the plasma fringes, the development of shear flow instabilities around the jet,
the occurrence of localized regions with high electric fields far from the arc,
and the formation and evolution of coherent flow structures.
