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Porous Media models in commercial CFD

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Old   April 18, 2002, 12:30
Default Porous Media models in commercial CFD
  #1
Clif Upton
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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!
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Old   April 19, 2002, 13:11
Default Re: Porous Media models in commercial CFD
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Evan Rosenbaum
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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 single-phase 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 power-law function of the velocity magnitude, but I'm not very familiar with that approach.
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Old   April 20, 2002, 23:23
Default Re: Porous Media models in commercial CFD
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Greg Perkins
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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
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Old   April 22, 2002, 11:40
Default Re: Porous Media models in commercial CFD
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Clif Upton
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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 non-uniform and at an angle, while the media's resistance is not very high.
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Old   April 22, 2002, 11:41
Default Re: Porous Media models in commercial CFD
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Clif Upton
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Could you explain what's udf? thanks.
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Old   April 23, 2002, 13:56
Default Re: Porous Media models in commercial CFD
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Erwin
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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 pseudo-vortices around particles and size limited interstitial vortices between particles.
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Old   April 24, 2002, 04:04
Default Re: Porous Media models in commercial CFD
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Greg Perkins
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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
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Old   April 24, 2002, 10:48
Default Re: Porous Media models in commercial CFD
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Erwin
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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, pp2803-2809

2) A general two-equation macroscopic turbulence model for incompressible flow in porous media - B. Antohe - Int. J. Heat Mass Transfer - Vol.40, No.13, pp3013-3024
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Old   April 24, 2002, 20:49
Default Re: Porous Media models in commercial CFD
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Greg Perkins
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Thanks - you can turn off the solids flow in Fluent 4 if you like.

Greg
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