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Mapped boundary condition mass flow rate behavior

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Old   August 4, 2020, 11:05
Question Mapped boundary condition mass flow rate behavior
  #1
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Dear Foamers,


I am working on a case where I have to use a smaller geometry by achieving fully developed condition at the inlet (due to its complexity simulating a bigger geometry takes way too long)...


To do so, I imposed the following boundary condition on U:

Code:
    outlet
    {
        type                 zeroGradient;
        value               uniform (0 0 0);
    }
    inlet
    {
        type                 mapped;
        interpolationScheme cell;
        value               uniform (0 0 -0.4021);
        setAverage   false;
    }
My intention is to achieve 1.65 kg/s of mass flow rate. My calculation shows it is equivalent to 0.4021 m/s. So I conducted the simulations and the mass flow rate is changing in the range 3 to 4 kg/s (!)


Here is my main question: So I made a change and imposed "setAverage" as follows:

Code:
    outlet
    {
        type                 zeroGradient;
        value               uniform (0 0 0);
    }
    inlet
    {
        type                  mapped;
        interpolationScheme cell;
        value                uniform (0 0 -0.4021);
        setAverage    true;
        average           (0 0 -0.4021);
    }
Now what I see in the console is that the mass flow rate goes from roughly 1.65 to roughly -1.65 kg/s successively. So for even iterations it is positive while for odd iterations it is negative. Any ideas guys? Please help.


Cheers,
MJ
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Old   September 18, 2020, 03:52
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Ran Yi
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Hi MJ,

1. What is your inlet setting in polyMesh/boundary?
2. What does your geometry look like? I noticed the velocity in Z-direction is negative.

BTW, have you solved this issue?

Best,
Ran
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Old   November 5, 2020, 11:32
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Quote:
Originally Posted by lizzy View Post
Hi MJ,

1. What is your inlet setting in polyMesh/boundary?
2. What does your geometry look like? I noticed the velocity in Z-direction is negative.

BTW, have you solved this issue?

Best,
Ran

Hi Ran,


Thanks a lot for the reply and please accept my apologies for responding rather late...


1. The inlet boundary type is "patch"
2. It is a vertical geometry (in z-direction) where the fluid enters the domain from the bottom. Unfortunately I cannot share the geometry


I really appreciate your thoughts on this.

Regards,
MJ
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Old   November 5, 2020, 12:35
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Adhiraj
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When I use this boundary condition I have to set the inlet boundary type to
mappedPatch. This is in OpenFOAM 2.3.1.

Here is an example from my constant/polyMesh/boundary file:
Code:
inAir
{
    type            mappedPatch;
    inGroups        1(mappedPatch);
    nFaces          16000;
    startFace       16759500;
    sampleMode      nearestCell;
    sampleRegion    region0;
    samplePatch    none;
    offsetMode     uniform;
    offset    (0 0 0.04);
}
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Old   November 5, 2020, 14:57
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Quote:
Originally Posted by adhiraj View Post
When I use this boundary condition I have to set the inlet boundary type to
mappedPatch. This is in OpenFOAM 2.3.1.

Here is an example from my constant/polyMesh/boundary file:
Code:
inAir
{
    type            mappedPatch;
    inGroups        1(mappedPatch);
    nFaces          16000;
    startFace       16759500;
    sampleMode      nearestCell;
    sampleRegion    region0;
    samplePatch    none;
    offsetMode     uniform;
    offset    (0 0 0.04);
}
Dear Adhiraj,

Thank you very much for your prompt response.

I tried this with OpenFOAM 1812 and (unfoirtunately) "mappedPatch" is not recognized as a valid boundary condition:

Code:
--> FOAM FATAL IO ERROR:
Unknown patchField type mappedPatch for patch type mappedPatch
Regards,
MJ
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