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This article in SSSAJ

  1. Vol. 78 No. 1, p. 108-118
     
    Received: May 22, 2013
    Published: January 30, 2014


    * Corresponding author(s): Chongxuan.Liu@pnnl.gov
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doi:10.2136/sssaj2013.05.0190

A Unified Multiscale Model for Pore-ScaleFlow Simulations in Soils

  1. Xiaofan Yang *a,
  2. Chongxuan Liua,
  3. Jianying Shanga,
  4. Yilin Fanga and
  5. Vanessa L. Baileya
  1. a Pacific Northwest National Lab., Richland, WA 9935

Abstract

Pore-scale simulations have received increasing interest in subsurface sciences to provide mechanistic insights into the macroscopic phenomena of fluid flow and reactive transport processes. The application of pore-scale simulations to soils and sediments is challenging, however, because of the characterization limitation that often allows only partial resolution of pore structure and geometry. A significant proportion of the pore spaces in soils and sediments is below the spatial resolution, forming a mixed medium with pore and porous regions. The objective of this research was to develop a unified multiscale model (UMSM) that can be used to simulate fluid flow and transport in mixed media containing pore and porous regions. The UMSM modifies the classic Navier–Stokes (N-S) equations by adding a Darcy term to describe fluid momentum and uses a generalized mass balance equation for saturated and unsaturated conditions. A series of simulations of water flow in pore, porous, and mixed pore and porous regions were performed to evaluate the UMSM by comparing with other numerical approaches. A water imbibition experiment was conducted in a soil column to compare theoretical predictions with experimental measurements. The results indicated that the UMSM is numerically equivalent to the N-S equations in pore regions, becomes Darcy’s law in porous regions, and is equivalent to a model coupling the N-S and Darcy’s law in a mixed medium containing pore and porous regions. The UMSM-simulated water imbibition also matched well with experimental measurements in the soil column, with its pore structures characterized from X-ray tomography. The UMSM approach allows direct simulation of fluid flow at the voxel resolution of characterization in realistic soils and sediments under both saturated and unsaturated conditions.

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