Accuracy and Computational Efficiency in 3D Dispersion via Lattice-Boltzmann: Models for Dispersion in Rough Fractures and Double-Diffusive Fingering

Harlan W. Stockman (), Robert J. Glass, Clay Cooper and Harihar Rajaram
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Harlan W. Stockman: Sandia National Laboratories, Albuquerque, NM 87185-0750, USA
Robert J. Glass: Sandia National Laboratories, Albuquerque, NM 87185-0750, USA
Clay Cooper: Desert Research Institute, P. O. Box 60220, Reno, NV 89506-0220, USA
Harihar Rajaram: Civil Engineering Department, University of Colorado, Campus Box 428, Boulder, CO 80309, USA

International Journal of Modern Physics C (IJMPC), 1998, vol. 09, issue 08, 1545-1557

Abstract: In the presence of buoyancy, multiple diffusion coefficients, and porous media, the dispersion of solutes can be remarkably complex. The lattice-Boltzmann (LB) method is ideal for modeling dispersion in flow through complex geometries; yet, LB models of solute fingers or slugs can suffer from peculiar numerical conditions (e.g., denormal generation) that degrade computational performance by factors of 6 or more. Simple code optimizations recover performance and yield simulation rates up to ~3 million site updates per second on inexpensive, single-CPU systems. Two examples illustrate limits of the methods: (1) Dispersion of solute in a thin duct is often approximated with dispersion between infinite parallel plates. However, Doshi, Daiya and Gill (DDG) showed that for a smooth-walled duct, this approximation is in error by a factor of ~8. But in the presence of wall roughness (found in all real fractures), the DDG phenomenon can be diminished. (2) Double-diffusive convection drives "salt-fingering", a process for mixing of fresh-cold and warm-salty waters in many coastal regions. Fingering experiments are typically performed in Hele-Shaw cells, and can be modeled with the 2D (pseudo-3D) LB method with velocity-proportional drag forces. However, the 2D models cannot capture Taylor–Aris dispersion from the cell walls. We compare 2D and true 3D fingering models against observations from laboratory experiments.

Keywords: Fingering; Dispersion; Lattice-Boltzmann; Efficiency; Fractures; Roughness (search for similar items in EconPapers)
Date: 1998
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DOI: 10.1142/S0129183198001394

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