[Natalie2210]

Hi!

I'm trying to simulate the flow of water through two layers of porous media where the permeability of the layers is different (see attached pictures). At the inlet on the left side, the water is injected with a certain pressure, and at the outlet, I have less pressure, thus, the water flows through due to a pressure gradient.
Naturally, the water flows faster through the more permeable layer than through the other one and thus, a significant through-thickness flow is established. This through thickness flow should help to penetrate the lower permeable layer faster than it would be the case if this layer were just infiltrated due to the pressure gradient between inlet and outlet.

Basically, the simulation shows this behaviour, however, it is seen in the attached picture that the lower permeable layer is not fully penetrated - close to the wall, I still have a significant amount of air which is not transported to the outlet. This is unphysical - in a corresponding experiment, it is shown that indeed the lower permeable layer is fully penetrated by water, without air entrapments. So I believe that this behaviour in the simulation is due to the boundary conditions - so far, I've tried the BCs "wall" and "symmetry". I think it is not possible to use "axis" in this context since, although it is a simple geometry, the setting is not axisymmetric. I'm using the VOF-model - but I have also tried the "mixture"-model, and I encounter the same problem.

I'd be grateful for any suggestions,
thanks,
Natalie