Learning Forum

[helen.durand]

Hello and thank you for taking the time to look at my questions. They are relating to understanding the porous zone calculations undertaken by Fluent during a simulation. 

1). When Fluent calculates the variable Y_i in calculations involving a porous zone (such as in the species transport equation 7-1 in the Fluent theory guide), is Y_i calculated as (mass of species i)/(mass of fluid) or is it related to a total mass that includes the mass of the fluid and solid in the porous zone?

2). How does the momentum source term in equation 6-1 (from the user's guide) play a role in Fluent's calculations? I notice that a source term S_i is included in the species transport equation (equation 7-1 in the theory guide), but I do not see any source term in the momentum equation (equation 1-3 in the theory guide). Where exactly is equation 6-1 used in Fluent? 

3). For equation 6-12 in the user's guide, why is it helpful to multiple rho and Yi by the porosity in the time derivative?  That appears to put the equation in terms of the derivative of the (mass of i per total volume) with respect to time, but why is that more helpful than having the equation be in terms of the (mass of i per volume of fluid)?  I do not believe that I fully understand what the porous zone model is trying to achieve, and would appreciate any help in describing that.

Again, I really appreciate the help. Please let me know if something I have written needs clarification. 

[Rob]

Porous zones are used to provide a pressure resistance, and don't provide any blockage in the domain. If you've added in porosity that can effect heat transfer and (if set) surface area for reactions.

[helen.durand]

Thank you for the reply, rwoolhou. I have thought about what you have written and reread the Fluent manual, and I have another question. 

 

In section 6.2.3.6 in the Fluent User's Guide (Effect of Porosity on Transient Scalar Equations), it says that fluent accounts for the porosity by modifying the time derivative term to include the porosity. 

Equation 7-1 in the Fluent Theory guide is the species transport equation. From what I understand, Fluent is not taking the porosity into account in this equation.

I have included snips of these sections at the end of this post for reference.

 

My question: How is equation 7-1 modified to account for porosity? Does Fluent include gamma in every term, just the time-derivative term, or only some of the terms? I have included two of these options below:

Thanks!

 

 

 

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[DrAmine]

Use physical velocity formulation and the blockage effect on convective field and on diffusion fluxes is taken into account. That is Option 2.

[helen.durand]

Thank you Amine. I have one clarification to ask of you.

If every term is multiplied by a constant porosity, as is done in option 2:

... then wouldn't the porosity terms cancel?