Abstract

A keypoint in modeling the transport of substances in water is the simulation of mixing processes due to dispersion. Solution of the transport equation must be achieved numerically in 2 and 3 dimensional cases, causing a false diffusion or numerical dispersion. In this technical note, results of a numerical experiment are presented to evaluate the numerical dispersion produced by different discretization schemes used in the finite volumes method. The experiment consisted in solving the pure advective bidimensional transport for a concentration bell of a conservative substance. The problem was solved on two different grids, namely a structured rectangular grid and an unstructured triangular one. Solutions obtained for different velocity fields representing natural situations are compared on the base of the numerical dispersion. The results show that the false diffusion associated with the Quick discretization scheme is practically negligible. Other schemes like Upwind or Hybrid produce a numerical dispersion of the order of magnitud of the physical dispersion, introducing much error in the calculations. The implemented spatial discretization schemes did not affect the numerical dispersion significantly.