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SimpleFoam divergence because of rare outlet behaviour

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Old   November 3, 2016, 08:04
Default SimpleFoam divergence because of rare outlet behaviour
  #1
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Katrin
Join Date: Jul 2016
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Dear all,

I set up a simple foam case, where I expect laminar behaviour (Re max. 30).
However I don't reach a steady state solution because my outlet i showing rare behavior: I have inflow even though I gave an InletOutlet Velocity boundary condition there.

Any thoughts as to where could be the error?

Thanks in advance,
highpressuretube

PS: My U-file:
Code:
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
inlet
{
        type            fixedValue; 
        value           uniform (9.4314 0.000000 0.000000);
}
outlet
{
	type            inletOutlet;
	inletValue	uniform (7.79455 0. 0.); 
        value           uniform (7.79455 0. 0.);
}
walls
{
        type            fixedValue; 
        value           uniform (0. 0. 0.);
}
side1
{
        type            symmetryPlane;
}
side2
{
	type            symmetryPlane;
}
}
My p-File:
Code:
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{
inlet
{
       type            zeroGradient;
}
outlet
{
        type            fixedValue; 
        value           uniform 0;
}
walls
{
        type            zeroGradient;
}
side1
{
        type            symmetryPlane;
}
side2
{
	type            symmetryPlane;
}
}
Attached Images
File Type: png AfterSimpleFoamFirstSteps-Backflow_trotzInletOutlet.png (124.3 KB, 10 views)
File Type: png Divergence.png (23.6 KB, 4 views)
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Old   November 3, 2016, 11:49
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  #2
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Sudheer Reddy B
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Location: San Antonio, Texas
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Hello,

If you don't need any inflow your inlet value should be (0 0 0). Try with that.

Code:
outlet
{
	type            inletOutlet;
	inletValue      uniform (0 0 0);         // (7.79455 0. 0.); 
        value           uniform (7.79455 0. 0.);
}
This is from the documentation:
Code:
inletOutlet
This boundary condition provides a generic outflow condition, with specified inflow for the case of return flow
HTH

-Sudheer
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Old   November 8, 2016, 10:50
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Katrin
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It's been the mesh :-(. I assumed that it would be ok to have global and local coordinate system differently as I am used to from FE calculations. blockMesh told me otherwise. When local and global coordinate system is equal for all cells, the calculations shows no more abnormal behavious and also checkMesh does not continue to complain.

Sorry for bugging.
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