PMFCT‐2D: A Transport Simulator for Various Grid Peclet Numbers

Abstract

Solute transport simulation using numerical models is an important and widespread tool for evaluation of clean‐up strategies as well as for prediction of future transport. Classical simulation algorithms for advective‐dispersive transport usually introduce large numerical errors where concentrations are lowest. In general, numerical errors tend to spread (disperse) the solute more than physical processes alone. For simulations where the Peclet number (Pe) is greater than about 2, numerical dispersion can be very significant and could lead to erroneous conclusions. Recent numerical techniques for simulating advective transport minimize numerical errors and provide much better solutions. One such technique, Flux‐Corrected Transport (FCT), can preserve sharp concentration fronts by virtually eliminating numerical dispersion. In general, it has been observed that as more detailed knowledge of subsurface flow fields is obtained, smaller dispersivity values are needed to match observed and simulated data. However, for many numerical codes the use of small dispersivities is not practical, because it requires fine grids to keep the grid Peclet number limited. A general purpose transport code, PMFCT‐2D, has been developed, including a fast and efficient FCT algorithm, to simulate advective‐dispersive transport in variably saturated, heterogeneous porous media, with nonuniform aquifer thickness in the third dimension. PMFCT‐2D can be used to accurately simulate high Peclet number transport, including purely advective transport (Pe =∞), resulting from transient or steady‐state flow conditions. The code is easily coupled to any flow simulator via generated velocity, saturation, and cell thickness fields.