Wicking of a liquid into porous structure of a gellant
 

As shown in the picture, my media is made of entangled fibers. First, the void space between them is filled with water. Then, it is placed in oil vicinity and therefore oil pushes the water out and is wicked into the space between the fibers (due to capillary force and lipophilicity of the micro-channels).

Should I use the Eulerian model or VOF for modeling and why? how to calculate the permeability of this material for the porous media?

Thank you!

Objective
 

It depends on what you wish to achieve; what is the objective of the simulation. If the domain is very small, recommended would be to use VOF. If you are using latest version, 2019R3 or later, you may also use AIAD, which can handle regime transition and you won't have to worry about whether it is free-surface or dispersed.

Permeability can be calculated only experimentally. Do note that porous zone in Fluent does not care about permeability but about resistance coefficients and those require data about pressure drop values for various flow rates through the zone.

Thanks Vinerm, I didn't know about AIAD.

Can I use this simulation to calculate the wicking rate of oil? and how much oil can be wicked (due to capillary)?

Do I need a UDF for AIAD model? (I read here that the Eulerian model doesn't need a UDF)

Aiad
 

AIAD is a implemented within Eulerian. So, you will have all the options of Eulerian available.