[cramsdead]

Hello Foamers !

I would like to know how to set the porosity properties correctly.

Please someome can advise me? Explain me how to set correctly the porosity properties?

I would like a permeability of 5e-11 m²
and trying some different porosity on : like 0,3 0,5 0,8

Is it right?
into the line :

d d [0 -2 0 0 0 0 0] (X X X);
(X X X) is the porosity coefficient divided by the permeability coeff? (here the same in all directions)
Is it right?

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.2.1 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "constant";
object porosityProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
porosity1
{
type DarcyForchheimer;
active yes;
cellZone porouszone;
porosity 0.5;
permeability 5e-11;
　
DarcyForchheimerCoeffs
{
mu mu;
d d [0 -2 0 0 0 0 0] (0.1e11 0.1e11 0.1e11); //0.5/5e-11=0.1e11
f f [0 -1 0 0 0 0 0] (0 0 0);
　
//coordinateSystem
//{
// e1 (0.70710678 0.70710678 0);
// e2 (0 0 1);
//}
 
}
}
 
************************************************************************* //

I know there is an other post about this but was only fonded about suppositions. I want to be sure!

Thanks a lot for considering my post.

[cramsdead]

please anyone?

[hchen]

Hi,

D is the porous resistance coefficient.

Darcy-Freidheim formula basically says S = d*u+F*mag(U)*U.

Best regards
Hao

[cramsdead]

ok I got it :

The permeability k is generally expressed in Darcy (D). Hao, I think you mean the porous resistance coeff right?
One Darcy is the permeability of a continuous, isotropic body through which a fluid of similar viscosity to that of water at 20 ° C flowing at a speed of 1 cm · s-1 when subjected to a pressure of 1 atm, which corresponds to the dimension of a surface. 1 D = 0.97 × 10-12 m²

The term hydraulic conductivity (K or permeability coefficient) is the ratio between the permeability and the viscosity of the fluid (the fluid is usually water). More a environement is permeable, more the fluid will flow quickly.
Hydraulic conductivity is expressed in m⋅s-1

So here into the d d [0 -2 0 0 0 0 0] (X X X);
X is the "k" permeability coefficient. This is just so weird OpenFoam ask d in m^-2 and not in m²...

So my last question is : for a permeability of 5e-11 I have to set X=5e11 OR X=0,2e11?

I don´t think we need to set the porosity coefficient here. This is 2 things really different.

thank you for your reply.

[hchen]

I am sorry that I am not an expert in hydraulics, but somehow you are right that permeability is expressed as D and F. However when you consider Darcy law, you need to put it into NS equation and the additional term S should have the same dimension with original NS equation. That is why D and F has that dimension. I remember that I read some paper describing relation between D and k, but I can not remember. You can check some papers on porous media.

Porosity does not have anything to do with D and F. It does not occur in openfoam native porous media library.

Best regards
Hao

[cramsdead]

Hi Hao,

Thanks a lot for your reply, I was asking for that to be sure that "normally" porosity does have anything to do with D and F but it seems there is a little trick about it as explained in the following post :
http://www.cfd-online.com/Forums/ope...interfoam.html

So I think I´m gonna try it into my simulations.

Well, my last question is : for a permeability of 5e-11 I have to set X=5e11 OR X=0,2e11?

Because I don´t want to do an easy mistake like this.

Thank you for your reply,

Cheers