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freestreamPressure & freestream BCs

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Old   August 10, 2010, 13:45
Default freestreamPressure & freestream BCs
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i'm still wondering, what freestreamPressure and freestream Boundary Conditions do. I studied the sourcecode, but I think I'm missing something...

What is the difference between

U freestream (derived from inletOutletFvPatchField<Type>)
p freestreamPressure (derived from zeroGradientFvPatchScalarField)


U inletOutlet
p zeroGradient


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Old   August 19, 2010, 11:20
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i finally ran a simple case to compare the two settings.

The case is a 2d-flow over a cirular cylinder with a Reynolds-number of 5, thus stationary. I used the icoFoam solver for that. The outer boundary patch is also circular and goes coherently around the whole domain, so the boundary conditions are not seperatly defined for inflow and outflow.

The attached graph is a plot of Ux on the outer boundary patch. A difference is clearly visible.

I guess, after reading the sourcecode, that the two settings entail a different schedule for the evaluation of the inletOutlet member functions.

Can anybody confirm that? Other explanations are welcome! Maybe somebody has a deeper knowledge of the code and can give a more elaborate reasoning...

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File Type: png BCcomparision.png (19.6 KB, 535 views)
File Type: png patch_inout_U.png (60.6 KB, 398 views)
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Old   November 26, 2010, 08:18
Default About freestream/freestreamPressure
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Bertrand Delvaux
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Hello Luise,

Sorry I can't bring any elaborated explanation on the difference, but I am very interested in this topics. Did you find any further information?

I am running a case with a shaped tube ending with a radiating hemisphere.

I have an inlet with U defined, p zeroGradient, and the outlet I hesitate with U inletOutlet and p zeroGradient, or U freestream, p freestreamPressure... It's supposed to be an open atmosphere outlet.

If you have any advice, it would be more than welcome


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Old   October 15, 2015, 06:54
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Hi Bertrand,
I am also confused with these boundary conditions, do you have now a clear understanding of the difference between zerogradient pressure and freestreamPressure?
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