Title: Stabilized Finite Element Modeling of Plasma Flow Instabilities

Speaker: Juan Pablo Trelles, University of Minnesota

Date/Time: Thursday, December 7, 2006, 10:00am – 11:00am

Location: CSRI Building/Room 90

Brief Abstract: The further development of thermal plasma technologies, from plasma spraying and cutting to toxic waste treatment and nanoparticle synthesis, has been limited by our lack of fundamental understanding of the flow inside plasma torches. This complex flow is susceptible to fluid-dynamic and electromagnetic instabilities, which drive it through a series of bifurcations as the operating conditions are varied. The extreme conditions inside the torch (i.e. temperatures above 20kK) make numerical simulation the only alternative for its analysis. This talk describes our attempts to model this inherently unsteady, three-dimensional, strongly nonlinear, and multiscale flow.

The plasma flow is described by a set of fluid and electromagnetic equations, which are discretized in a fully coupled approach by a stabilized finite element method. To add robustness to the formulation, a discontinuity-capturing operator has been implemented.
The global discrete system of equations is advanced in time by a predictor multi-corrector alpha-method combined with a globalized Newton-GMRES solver. To obtain reasonable convergence rates, different pre-conditioning strategies have been investigated, from ILU factorizations and Schwarz methods, to element-by-element techniques.

The effectiveness of these methods is demonstrated in simulations of a commercial plasma torch. The modeling of this flow stresses the need for robust numerical methods for the solution of multiphysics and multiscale problems.