Abstract

We report results from simulations of single-phase flow through digital images of large and complex porous structures. Images correspond to sequences of snapshots captured during sedimentation of glass beads and sand particles in transparent, quasi-two-dimensional sedimentation units well above the compaction line. For the simulations, we use the lattice-Boltzmann method with a nine-speed model on a square lattice. For validation purposes, the lattice-Boltzmann method is compared against an explicit finite-difference method for incompressible flow in simpler geometries. Simulating Poiseuille flow through a two-dimensional channel and two-dimensional porous structures of intermediate complexity checked the accuracy of the lattice-Boltzmann scheme used. For the "frozen" structures in the images of sedimenting particles, we calculate permeability as a function of porosity. Vertical porosity profiles suggest that particle-sedimenting columns can be represented by a series of homogeneous layers, each with different but relatively uniform porosity. We use the lattice-Boltzmann scheme to calculate the permeability of the individual layers. The average permeability of the sedimenting columns is then calculated from the series arrays of layers. Reasonably good agreement is found when compared to the overall permeability of the sedimenting column. We find that this simply indicates that the flow through the layers is nearly linear. In addition, we find that one or two low porosity layers located at the bottom of the images control the flow and thus the permeability of the sedimenting structures. (C) 2004 Elsevier B.V. All rights reserved.