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Fluid flow in porous media using image-based modelling to parametrize Richards' equation
L J Cooper1, K R Daly1, P D Hallett2
1Bioengineering Sciences Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton, UK.
Proceedings. Mathematical, Physical, and Engineering Sciences
|December 12, 2017
Summary
Image-based modeling reveals how soil pore structure influences Richards
Area of Science:
- Soil physics
- Porous media flow
- Computational modeling
Background:
- Richards' equation parameters are typically derived from experimental soil-water characteristic curves and saturated hydraulic conductivity.
- Complex pore structures, hysteresis, and tortuosity in porous media complicate traditional parameter estimation.
- Image-based modeling offers an alternative to indirect measurements for understanding pore structure-parameter relationships.
Purpose of the Study:
- To investigate the direct relationship between porous media's intricate pore structure and the parameters of Richards' equation.
- To utilize advanced imaging and computational fluid dynamics to bypass traditional indirect parameterization methods.
- To assess the impact of varying contact angles on the soil-water retention curve and Richards' equation parameters.
Main Methods:
- A 3D X-ray computed tomography image stack of a soil sample was used to generate a computational mesh.
- The Cahn-Hilliard-Stokes equations for two-fluid flow (water and air) were solved using the finite-element method.
- Upscaled parameters for Richards' equation were derived through homogenization, with contact angle variations explored.
Main Results:
- The study demonstrates that the pore structure significantly influences large-scale flow properties.
- Different contact angles (0°, 20°, 60°) were shown to alter the effective parameters of Richards' equation.
- Image-based modeling provides a direct link between micro-scale pore geometry and macro-scale flow behavior.
Conclusions:
- Pore structure is a critical determinant of Richards' equation parameters, challenging traditional estimation methods.
- Contact angle variations introduce significant changes to soil hydraulic properties, impacting model parameters.
- Image-based computational fluid dynamics is a powerful tool for characterizing porous media flow and parameterization.
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