Invited Paper PS1-ThM10
Modeling and Simulation of Nonequilibrium Atmospheric Pressure Plasma Flows

Thursday, November 10, 2016, 11:00 am, Room 104C

Atmospheric pressure plasmas are at the core of diverse technological applications, from materials processing and chemical synthesis, to waste treatment and environmental remediation. These plasmas display high collision frequencies among electrons and heavy-species (molecules, atoms, and ions). The interaction of atmospheric pressure plasmas with the processing media, such as a gas stream, produces significant deviations from the Local Thermodynamic Equilibrium (LTE) state, manifested by dissimilar velocity distributions between electrons and heavy-species, leading the plasma to a state of thermodynamic nonequilibrium (non-LTE or NLTE). Moreover, such interactions are characterized by large variations in flow properties and complex coupling among fluid flow, heat transfer, chemical kinetics, and electromagnetic phenomena. These characteristics impose severe challenges to numerical modeling and simulation approaches, which include resolution of multiscale features, multiphysics coupling, and robustness in the presence of large solution field gradients. An overview of the modeling and simulation of nonequilibrium plasma flows using the Variational Multiscale (VMS) Finite Element Method (FEM), one of the most robust, versatile, and widely used techniques for the numerical solution of multiphysics problems, is presented. The plasma is modeled as a compressible reactive electromagnetic fluid in chemical equilibrium and thermodynamic nonequilibrium. Material properties vary in a markedly nonlinear manner and by several orders of magnitude, which severely stresses the robustness required from the numerical methods. The VMS methodology treats the plasma flow model as a coupled system of transient-advective-diffusive-reactive transport equations, which naturally allows the extension of the approach to other plasma models. Simulation results of canonical and industrially-relevant atmospheric pressure nonequilibrium plasmas, namely the plasma flow in transferred and non-transferred arc plasma torches and the free-burning arc, demonstrate the effectiveness of the method. Particularly, the simulation approach is capable to capture the complex arc dynamics inside plasma torches, including the arc re-attachment process, as well as the spontaneous formation of self-organized anode patterns in the free-burning arc. The results indicate the suitability of the VMS-FEM for its application to other types of plasma flow models and the simulation of other plasma-related processes.