Fluid flow in porous media using image based modelling to parametrise Richards’ equation

Abstract

The parameters in Richards’ equation are usually calculated from experimentally measured values of the soil water characteristic curve and saturated hydraulic conductivity. The complex pore structures that often occur in porous media complicate such parametrisation due to hysteresis between wetting and drying and the effects of tortuosity. Rather than estimate the parameters in Richards’ equation from these indirect measurements, image based modelling is used to investigate the relationship between the pore structure and the parameters. A three dimensional, X-ray computed tomography image stack of a soil sample with voxel resolution of 6 m has been used to create a computational mesh. The Cahn-Hilliard-Stokes equations for two fluid flow, in this case water and air, were applied to this mesh and solved using the finite element method in COMSOL Multiphysics. The upscaled parameters in Richards’ equation are then obtained via homogenisation. The effect on the soil-water retention curve due to three different contact angles, 0, 20 and 60, was also investigated. The results show that the pore structure affects the properties of the flow on the large scale and different contact angles can change the parameters for Richards’ equation.

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Identifiers

ORCID for Laura Cooper: orcid.org/0000-0003-0198-7591

ORCID for Tiina Roose: orcid.org/0000-0001-8710-1063

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