Linearized solutions to two phase flow in porous media solved by Finite Elements

In subsurface hydrology numerical modeling of multiphase flow processes in porous media is a commonly used tool to gain a better understanding and make predictions of the migration of organic contaminants in the saturated and unsaturated ground zone. For a reliable description of these complex processes, detailed computational grids are needed with the major computational effort consisting of the repeated solution to linear systems within the linearization procedure. The efficiency of the solution scheme appears to be the key factor to improve the performance of the multiphase flow simulators. The paper discusses the performance of the Bi-CGTSAB solver for two global schemes based on a different nodal ordering of the unknowns and a scheme (called SPLIT) where a substitution of a group of unknowns is preliminary made. It is shown that SPLIT is between two and three time faster than the global schemes.