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Luise August 10, 2010 12:45

freestreamPressure & freestream BCs

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



Luise August 19, 2010 10:20

2 Attachment(s)

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...


Bertrand November 26, 2010 08:18

About freestream/freestreamPressure
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 :)



yongxiang October 15, 2015 05:54

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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