Pore-scale simulation of dispersion

Tracer dispersion has been simulated in three-dimensional models of regular and random sphere packings for a range of Peclet numbers. A random-walk pa rticle-tracking (PT) method was used to simulate tracer movement within por e-scale flow fields computed with the lattice-Boltzmann (LB) method. The si mulation results illustrate the time evolution of dispersion, and they corr oborate a number of theoretical and empirical results for the scaling of as ymptotic longitudinal and transverse dispersion with Peclet number. Compari sons with nuclear magnetic resonance (NMR) spectroscopy experiments show ag reement on transient, as well as asymptotic, dispersion rates. These result s support both NMR findings that longitudinal dispersion rates are signific antly lower than reported in earlier experimental literature, as well as th e fact that asymptotic rates are observed in relatively short times by tech niques that employ a uniform initial distribution of tracers, like NMR. (C) 2000 American Institute of Physics. [S1070-6631(00)02308-4].