Learning Forum

[vinaychandrakar11]

Hello everyone,

I am trying to replicate a porous media UDF problem given in ANSYS Fluent UDF tutorial. Link for the porous media problem which I am doing is mentioned below.

I successfully compiled the code volumetric reaction rate "rate.c". Burt still I am not getting the exact same answer mentioned in the tutorial.

I checked the mesh and I dont think its because of the mesh.

Please see the below mentioned image (Boundary Conditions and other parameters) and let me know what wrong i am doing compared to the tutorial.

[Karthik Remella]

Hello Which tutorial are you talking about? Looks like the link did not come through.
We are talking about comparing several versions (v12 vs. 2021R1). If you have the original case and data from v12, have you tried running it on the latest release to see if you are able to replicate the results? If so, you can compare the two cases side by side and figure out what might be happening with your case. Does that make sense?
Karthik

[vinaychandrakar11]

I am not having any case and data file of this porous media tutorial. I am doing it on my own and created my own mesh and case. Geometrical parameters I took it from the tutorial.
Reason I mentioned this settings (shown in the above pic) to find out the mistake compared to the tutorial.
I am not having tutorial case and data file and if you have can you share this here. It might help (any version will be fine), otherwise you can also help me by finding problem in the setting which I mentioned in the above pic. (consist boundary conditions and cell zone conditions)

[Karthik Remella]

What tutorial is this? Could you share a link?
Karthik

[vinaychandrakar11]

Link for the tutorial is mentioned below.
*Linked removed by DrAmine*
Thanks in Advance.
Regards
Vinay

[Amine Ben Hadj Ali]

That is an old UDF and you are referring to a website hosting some old help files which is not allowed. I am removing your link

[vinaychandrakar11]

Okay DrAmine.
Can I get the link for the new pdf for this problem and associated case file for the same tutorial?
If you will share it here, it will be very helpful.
Regards
Vinay

[Amine Ben Hadj Ali]

I think that tutorial has not been updated.

[Amine Ben Hadj Ali]

And what you are referring to has not been a tutorial: only a UDF showing how to check if a zone is porous and defining the Volumetric Reaction Rates.

[vinaychandrakar11]

I understand this DrAmine.
But I am trying to replicate this as it is and I would like to know how to do this. (Because if conditions are same then results must be identical)
If you can guide me it will be really helpful.
Regards
Vinay

[Karthik Remella]

Hello Let's try to understand what you are modeling. Can you explain the problem you are attempting to solve (Physically)? What are your domain, boundary conditions, initial conditions etc.? Maybe this will help understand the issue. Without this info, we will not be able to help.
Karthik

[vinaychandrakar11]

My Problem is same as mentioned in the tutorial.
In my problem combustion of methane is happening over catalyst (which I am treating as a porous media). Gas species (CH4 and O2 is coming)flows over Porous media (Ni catalyst) and kinetics has functions of mole fraction (that's the reason I am writing UDF).
figure is mentioned below.
Problems.
1) Do I have to mention chemical kinetics in the mixture template material, because I dont think its required as its going to take reaction rate from UDF. (Am I correct?)
2) I think only order of species is important as per the code(Is that right?)
3) In cell zone conditions we have to define reaction mechanism and I hope this reaction mechanism is also depends on the UDF and not on the reaction mechanism which we define in the mixture template.(Am i wrong?)

[Rob]

OK, so the UDF will remove reactants and add heat + products based on "stuff". That's part of the issue. You'll also need to account for the surface to volume ratio of the porous media.
The order of the species is used to pick these up for the UDF.
In your cell zone you'll define the mixture-template containing all species. However, exactly what is defined is entirely down to how you write the UDF.

[vinaychandrakar11]

So it means reaction mechanism defined in mixture template does not make any sense. ONLY UDF matters, right?
In my problem(shown in above figure (consider unit width)) how can I calculate the surface to volume ratio? Is it like total surface area of porous media divided by total volume of porous media or something else?

[Rob]

You have both set? In which case it's possible the two schemes are competing and confusing the result. The surface to volume ratio is defined for the porous media, it's to tell the solver how much surface is present in the volume. Ie my resistance could be a messy fibre bundle, balls, one tortuous path etc as porous media is a pressure drop correlation and the solver doesn't know what is causing the pressure loss.

[vinaychandrakar11]

Okay, Got it.
Thanks Rob
Regards
Vinay