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-   -   Solving pressure in anisotropic porous media (https://www.cfd-online.com/Forums/openfoam-solving/152543-solving-pressure-anisotropic-porous-media.html)

Nathanael3 May 3, 2015 10:50
Solving pressure in anisotropic porous media
 
Hi,

I am trying to solve a pressure equation in a 2D axi reacting porous medium. The permeability of the medium is highly anisotropic: the ratio between the directions is 1/5000.
The solvers runs "without problem". Yet, the computed pressure field is problematic. Artefacts appear from time to time. Then, the velocity field is wrong and species transport gets wrong too.

Here is a picture of the problem. The artefact is on the third column.

http://perso.mines-albi.fr/~vpozzobo/dl/p_artefact.png

I tried my luck with numerical schemes. Yet, it does not seem to change anything. I would like to as you for some advices.

Note: the case is transient.

Thanks,
Nath'

Nathanael3 May 5, 2015 15:23
Bump !

Nathanael.

Nathanael3 May 9, 2015 04:51
No one has a clue ?

Nath'

Nathanael3 May 12, 2015 14:14
Hi,

I am circling around the problem. In case someone is interested. It seems to have something to do with the source term in the pressure equation.

Nath'

arjun May 13, 2015 02:08
Quote:
Originally Posted by Nathanael3 (Post 546048)
Hi,

I am circling around the problem. In case someone is interested. It seems to have something to do with the source term in the pressure equation.

Nath'

It is very difficult to tell what the exact problem is.

Fluxes could be related to problem.

Nathanael3 May 13, 2015 08:06
Hi,

Thank you for your answer.
I have to admit that I am not familiar with flux correction. Could you lend me a hand on this problem, please ?
If it helps, here is how I solve the pressure equation :

Code:
    fvScalarMatrix peqn
                (
                    fvm::ddt(Poro * M / R / T, p)
                    - fvm::laplacian(Kappa * Rho_g / Mu, p)   
                    ==
                    MassSource
                );
    peqn.relax();
    peqn.solve();
    p.relax();
With Poro = porosity, M = gas molar mass, R = ideal gas constant, p = pressure, Kappa = permability tensor, Rho_g = gas density, Mu = viscosity, MassSource = pressure source term.

Relaxation factors are set to 1.

Then I compute the velocity using Darcy's law :

Code:
  U = - Kappa & fvc::grad(p) / Mu;
  phiF = linearInterpolate(U) & mesh.Sf();
Thank for your help,
Nath'

arjun May 14, 2015 02:07
I am not very familiar with openFOAM, in fact never used it.

If you assume that fluxes could be the problem (very likely actually), then the only way it could happen is that the Rhie Chow part adds some spurious flux that it shall not be adding.

In this scenario the origin would be anisotropy in Ap variable for momentum that is used in Rhie Chow flux. I understand that in case of porous flow this Ap var could vary too much and thus some cells could see too much spurious flux coming or going out of them.

One way to handle that problem is to limit the amount of Rhie Chow flux allowed. Say for example shall be no more than physical flux (computed by interpolating velocity on face center)

Note that in many simulations, Rhie Chow flux is more than physical flux and is necessary for coupling of equations (v-p)

Nathanael3 May 16, 2015 07:42
Hi,

Alright. Thank you for the advice. I am currently looking into it. I will come back to you once I am done.

Thanks again,
Nathanaël.

Nathanael3 July 1, 2015 04:14
Hi dear Foamers,

After a review of literature and with the help of arjun, I have been able to conclude that this problem is a state of the art problem. There is currently no way to solve it.

Nathanaël.

arjun July 1, 2015 16:44
Quote:
Originally Posted by Nathanael3 (Post 552812)
Hi dear Foamers,

After a review of literature and with the help of arjun, I have been able to conclude that this problem is a state of the art problem. There is currently no way to solve it.

Nathanaël.
If you have access to other software do try it with them too. For example if you have starccm then try this with and without delta-v dissipation.

Also it would be interesting to see how fluent does this.
My guess is that both of these softwares would do it.


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