Pore-scale network modeling of sharp and diffuse ...

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XVI International Conference on Computational Methods in Water Resources (CMWR-XVI) Ingeniørhuset

Pore-scale network modeling of sharp and diffuse infiltration fronts through the addition of viscous effects
Author:David DiCarlo <ddicarlo@ars.usda.gov> (USDA-ARS National Sedimentation Laboratory)
Presenter:David DiCarlo <ddicarlo@ars.usda.gov> (USDA-ARS National Sedimentation Laboratory)
Date: 2006-06-18     Track: Special Sessions     Session: Pore-Scale Modelling: New Developments And Applications

Most infiltrations of a wetting phase have an imbibition front that is diffuse at the pore-scale, allowing the common use of continuum formulations to model the macroscopic flow. But for macroscopic flow phenomena such as preferential flow, this continuum approach fails as the imbibition water front is sharp at the pore- scale. Pore-scale network models are ideal for handling sharp fronts due to their inherent discreteness, but many models produce only sharp fronts contrary to observations. Here we modify the physically-based static network model of Valvatne and Blunt to add viscous effects in a quasi-static manner. We find that at low imbibition velocities, that the imbibing front is diffuse due to flow within the layers of the model, and the majority of the elements filling through snap-off. At high imbibition velocities, the front becomes sharp at the pore-scale due to the viscous forces enhancing collective piston-like pore filling. The width of the transition between diffuse and sharp fronts in terms of velocity matches well what is observed in experimental measurements. We discuss how the initial layer conductivity, pore-size distribution, and the wetting properties of the media control the absolute magnitude of the transition.