Examples of numerical simulations of two- dimensional unsaturated flow with VS2DI code using different interblock conductivity averaging schemes

摘要

Flow in unsaturated porous media is commonly described by the Richards equation. This equation is strongly nonlineardue to interrelationships between water pressure head (negative in unsaturated conditions), water content and hydrau-lic conductivity. The accuracy of numerical solution of the Richards equation often depends on the method used toestimate average hydraulic conductivity between neighbouring nodes or cells of the numerical grid. The present paperdiscusses application of the computer simulation code VS2DI to three test problems concerning infiltration into an ini-tially dry medium, using various methods for inter-cell conductivity calculation (arithmetic mean, geometric mean andupstream weighting). It is shown that the influence of the averaging method can be very large for coarse grid, but thatit diminishes as cell size decreases. Overall, the arithmetic average produced the most reliable results for coarse grids.Moreover, the difference between results obtained with various methods is a convenient indicator of the adequacy ofgrid refinement.