A MOC-based scheme for the numerical analysis of advective-dispersive contaminant transport in transient water-pipeline flow

This paper presents a new model for analysing the advection-dispersion of a contaminant in a pipeline under unsteady flow conditions. Compared to other papers in the scientific literature, the analysis focuses on fast transient, rather than steady, quasi-steady or slow transient conditions. The new model uses the method of characteristics (MOC) and the Crank-Nicolson finite difference scheme, to couple flow field with contaminant advection and to model dispersion, respectively. For fast transient analysis, the developed MOC-based scheme accounts for the unsteady friction effect through a simplified acceleration based approach. Firstly, the model is tested against advection and dispersion under steady flow while compared to other numerical schemes. The model’s performance is evaluated in terms of accuracy, computation time and stability. Comparisons with benchmark models and exact solutions prove the effectiveness of the present numerical coupling methodology at preserving the shape of the concentration profile (more than 97%) and its reduced proneness to instability. The model is applied to a challenging test case under fast transient flow conditions. Therefore, numerical diffusion as well as changes in contamination profiles induced by the variation of the flow velocity is emphasized and thoroughly discussed.