## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

#### Volume blocking in porous media

• student_18
Subscriber

Hello,

I need to simulate an electrolyte filling process of a tank in ANSYS Fluent. In the tank there is a porous medium and I use VOF for a two phase flow. In my case not only the flow resistance is point of interest, but also the mass distribution. As I understood, the option ‘porous media model’ in ANSYS Fluent does not model the volume blockage. For me it is important to get the correct total mass of the flow – is there any way in Fluent to model the volume blocking?
So that only the void volume can be filled with fluid, not the volume of the hollow body.

Thanks for a short response and best regards.

• DrAmine
Ansys Employee

Hi,

in Fluent we have the superficial and physical velocity formulation. Within the superficial velocity formulation the porosity is indirectly accounted for due to your input of inertial and viscous losses but the volume is still 100% open. This lead to a conservation of the superficial velocity or volumetric flux (no jump in the velocity). With the physical velocity formulation the porosity will enter into your momentum conservation. This is more accurate but might suffer from stability issues. The User's Guide in Fluent does cover both formulation with a lot of details.

A.

• student_18
Subscriber

Hi,

In my case the mass distribution in the porous zone is important. To be sure that I understood you correctly: With the physical velocity formulation the volume is e.g. only 20% open for fluid for a porosity of 0.2.
As an example: A 1 liter tank can only be filled with 0.2 liter fluid using physical velocity, for superficial velocity the tank can be filled with 1 liter fluid, is this correct?

Best regards

• Rob
Ansys Employee

Not quite. In both cases you'll be able to add 1l into your domain, but the velocity field may become very unstable as it tries to accelerate to account for the porosity.

If you need to fully model where the liquid goes within the system the porous media may not be the best model: it's a lumped parameter model used to simplify things. For an exact distribution you may need to rethink your set up.

Please can you put a couple of diagrams up and the community may be able to offer greater assistance. Note, as ANSYS staff abenhadj and I can only offer limited assistance.

• Dino
Subscriber

I have a similar issue. How can I calculate the mass fraction of a species only in the volume of voids?

I am writing a UDF for a mass sink of a species and want to apply this sink only within the volume of voids. Please help. Thank you!

• DrAmine
Ansys Employee

User defined sources need to be scaled with porosity function.

• Dino
Subscriber

Thank you so much. So, all I need is to multiply the source by the porosity or (1 - porosity)?