Question about sharper saturation front in two-phase flow simulation (step-21)

[aibike nagyz]

Dear all,

I am currently working on a simulation of two-phase flow in porous media, based on the step-21 tutorial of deal.II.

I noticed a curious difference when changing the viscosity of the wetting phase.

With wetting phase viscosity = 0.001 Pa.s and non-wetting phase viscosity = 0.004473 Pa.s, the saturation front appears smooth and expected.

When I change the wetting phase viscosity to 0.1 Pa.s and apply a higher inlet pressure, the saturation front becomes noticeably sharper.

I wanted to ask:

Could this behavior be due to neglecting capillary pressure or gravity effects in the simulation? Or are there other possible explanations for the sharper front?

Any insights or suggestions would be greatly appreciated!

Best wishes,
Aibike

[Wolfgang Bangerth]

On 5/29/25 02:19, aibike nagyz wrote:
> I noticed a curious difference when changing the viscosity of the wetting phase.
>

> With *wetting phase viscosity = 0.001 Pa.s* and *non-wetting phase viscosity =
> 0.004473 Pa.s*, the *saturation front appears smooth and expected*.
>
> When I change the *wetting phase viscosity to 0.1 Pa.s* and apply a *higher
> inlet pressure*, the *saturation front becomes noticeably sharper*.
>
> I wanted to ask:
>
> Could this behavior be due to neglecting *capillary pressure* or *gravity
> effects* in the simulation? Or are there other possible explanations for the

> sharper front?
>
> Any insights or suggestions would be greatly appreciated!

Aibike:
This is a modeling question, which I don't know the answer of. In the end, the
ratio of viscosities matters whether you have a straight front or observe a
"fingering instability" as you see in your second picture. I imagine that the
literature on two-phase flow has more to offer on this.

Best
W.

--
------------------------------------------------------------------------
Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/