An indicator‐based problem reduction scheme for coupled reactive transport models

Freeman, Brubeck Lee; Cleall, Peter John; Jefferson, Anthony Duncan

A number of effective models have been developed for simulating chemical transport in porous media; however, when a reactive chemical problem comprises multiple species within a substantial domain for a long period of time, the computational cost can become prohibitively expensive. This issue is addressed here by proposing a new numerical procedure to reduce the number of transport equations to be solved. This new problem reduction scheme (PRS) uses a predictor‐corrector approach, which “predicts” the transport of a set of non‐indicator species using results from a set of indicator species before “correcting” the non‐indicator concentrations using a mass balance error measure. The full chemical transport model is described along with experimental validation. The PRS is then presented together with an investigation, based on a 16‐species reaction‐advection‐diffusion problem, which determines the range of applicability of different orders of the PRS. The results of a further study are presented, in which a set of PRS simulations is compared with those from full model predictions. The application of the scheme to the intermediate‐sized problems considered in the present study showed reductions of up to 82% in CPU time, with good levels of accuracy maintained.