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-   -   porousInterFoam - problem setting correct bcs (https://www.cfd-online.com/Forums/openfoam-solving/124559-porousinterfoam-problem-setting-correct-bcs.html)

Natalie2210 October 8, 2013 07:07
porousInterFoam - problem setting correct bcs
 
2 Attachment(s)
Dear all,

I'm working with the porousInterFoam solver. Currently, I'm trying to simulate two porous layers which have the same porosity but differ in their permeability. The fluid is injected laterally.
I expect the fluid to move through the layers at different velocities, resulting in an asymmetric flow front (see attachments, both pictures depict the volume fraction alpha1 at t=10 s. ). Additional, I have a kind of "leakage flow" where fluid leaks from the higher permeable layer into the other one.

Basically, the simulation performs as expected. However, the flow front lead lag I find is much greater than expected, and having a close look at the simulation (see Problem2.jpg) it becomes clear that the fluid does not arrive at the bottom of the lower permeable layer as it should. Since this phenomenon only affects the last layer of cells regardless how many volume elements I have in "thickness" direction, I assume that this problem is due to the applied boundary conditions.

Presently, I set the following boundary conditions:

HTML Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.1.1                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      volScalarField;
    object      alpha;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions      [0 0 0 0 0 0 0];
internalField  uniform 0;
boundaryField
{
    wall
    {
        type            zeroGradient;
    }
    outflow
    {
        type            inletOutlet;
        inletValue      uniform 0;
        value          uniform 0;
    }
  inflow
  {
      type    fixedValue;
      value  1; 
  }
}
// ************************************************************************* //
HTML Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.1.1                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions      [1 -1 -2 0 0 0 0];
internalField  uniform 0;
boundaryField
{
    wall
    {
        type            zeroGradient;
    }
    inflow
    {
        type            fixedValue;
        value          3.5e4;
    }
    outflow
    {
        type            fixedValue;
        value          $internalField;
    }
}
// ************************************************************************* //
HTML Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.1.1                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions      [0 1 -1 0 0 0 0];
internalField  uniform (0 0 0);
boundaryField
{
    wall
    {
        type            slip;
        value          uniform (0 0 0);
    }
    inflow
    {
        type            pressureInletUniformVelocity;
        phi            phi;
        rho            rho;
        value          uniform (0 0 0);
    }
    outflow
    {
        type            pressureInletOutletVelocity;
        phi            phi;
        value          uniform (0 0 0);
    }
}
// ************************************************************************* //
Do you have any idea how to change the boundary conditions in order to avoid this problem?
I have no idea what the bc "symmetry plane" does, is it of use here?

Thank you,
Natalie

Natalie2210 October 10, 2013 05:42
1 Attachment(s)
Hi everybody,

I think I can now state the problem differently:

Basically, in my setup as described in the previous post, I have two layers of material. The fluid flows faster through the upper material since it presents less resistance than the lower material layer due to different permeability values specified for each.

So, the fluid flows fast through the upper layer and leaks into the lower layer. This leakage flow in thickness (z-) direction is considerable and almost fills the lower layer completely. Due to this differences in velocities, I also obtain a non-constant pressure profile - basically, the pressure should drop in direction of the lower permeable layer.

The attached plot shows that this is actually the case. However, in the lower permeable layer at z=0, a nearly constant pressure profile is present. Therefore, there is no driving force to force the fluid from the top to actually the very bottom of the simulation domain, which results in the problem stated in the previous thread.

I believe that the pressure profile in thickness direction is heavily influenced by the boundary condition I pose, namely, I pose a zeroGradient boundary condition on the pressure. However, what I really want is the linear continuation of my pressure profile at the boundary.
Is there a boundary condition in OpenFoam which can do this?

Thank you for patiently reading my post,
Natalie

Natalie2210 December 2, 2013 05:26
No one here has any thoughts on this? I'd still be interested, you know..


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