Porous Media models in commercial CFD
What porous model is in Fluent? We have been using another commercial CFD code with Brinkman model and it is pretty bad in many circumstances. Of the results it produces are 100% off!

Re: Porous Media models in commercial CFD
FLUENT uses an extra sink term on the momentum equation to account for the extra resistance. The sink term has the form: (mu x v / alpha) + (C2 x 1/2 x rho x abs(v) x v) where mu is viscosity, v is superficial velocity alpha is a permeability factor, C2 is an inertial resistance factor and rho is density.
We have benchmarked singlephase gas flow using this model and gotten decent results. It doesn't work for multiphase or phase change, because you are limited to single entries for alpha and C2. It can also use a powerlaw function of the velocity magnitude, but I'm not very familiar with that approach. 
Re: Porous Media models in commercial CFD
You can easily write a udf to compute this term or use another term that you prefer. In this case, you can then use more complex relations since you don't need to rely on the assumptions used by Fluent.
Greg 
Re: Porous Media models in commercial CFD
Thanks, Evan. What you described is the Brinkman's model. As I mentioned, I completely fails in some circumstances, such as when the inflow is very nonuniform and at an angle, while the media's resistance is not very high.

Re: Porous Media models in commercial CFD
Could you explain what's udf? thanks.

Re: Porous Media models in commercial CFD
Simple models like that will also fail when turbulence dependent phenomena like dispersion (thermal, species) become important. Porous media need a specific turbulence model below porosities of say 0.8 to account for the pseudovortices around particles and size limited interstitial vortices between particles.

Re: Porous Media models in commercial CFD
Have you tried any in particular?
What about the granular model of Fluent4? It has some turbulence models for the mutliphase flow, but I'm not aware if they account for dispersion as you point out. Do you know? Regards Greg 
Re: Porous Media models in commercial CFD
I am very unfamiliar with Fluent 4, but I'd guess that in a granular model Fluent it is assumed that the solids also flow. So Fluent offers a primary and secondary turbulence option to account for that. Maybe there's a way to modify it for porous media flow, I dunno.
I have not yet tried other turbulence models, since in our cases dispersion effects etc. have not yet been important. I did find two literature articles describing such models: 1) Turbulence model for flow thorugh porous media  T.Matsuoka  Int. J. Heat Mass Transfer  Vol.39, No.13, pp28032809 2) A general twoequation macroscopic turbulence model for incompressible flow in porous media  B. Antohe  Int. J. Heat Mass Transfer  Vol.40, No.13, pp30133024 
Re: Porous Media models in commercial CFD
Thanks  you can turn off the solids flow in Fluent 4 if you like.
Greg 
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