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-   -   Problems with BC (http://www.cfd-online.com/Forums/openfoam/65131-problems-bc.html)

sven June 4, 2009 15:18

Problems with BC
 
Hi everyone,

I am trying to simulate a simple 2D-Channel Flow with the icoFoam solver. Unfortunatelly I do not reach a steady solution after more than 150 seconds. Strange things are happening at the In- and Outflow (I get some kind of detachment/displacement at the outflow). I think these troubles are caused by the BCs. So, I wanted to change my Outlet BC to "calculated". I tried it like this:

Outlet
{
type calculated;
}

for the U file in the folder 0. But if I want to solve this I always get an error saying:

gradientInternalCoeffs cannot be called for a calculatedFvPatchField
on patch Outlet of field U in file "/home/sven/OpenFOAM/sven-1.5/run/Case1-laminarChannelFlow/Subcase1/0/U"
You are probably trying to solve for a field with a default boundary condition.

From function calculatedFvPatchField<Type>::gradientInternalCoef fs() const
in file fields/fvPatchFields/basic/calculated/calculatedFvPatchField.C at line 187.

Does somebody know what the problem is? Tanks.

wolle1982 June 10, 2009 06:07

hi,

why not use a simple pressure outlet?? please post your BC files so people can have a look on it.

sven June 10, 2009 13:14

here are my boundary conditions:

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0.0;

boundaryField
{
upperWall
{
type zeroGradient;
}

lowerWall
{
type zeroGradient;
}

frontAndBack
{
type empty;
}

Inlet
{
type zeroGradient;
}

Outlet
{
type fixedValue;
value uniform 0.0;
}

}

// ************************************************** *********************** //

What do you mean by using a simple pressure outlet?? Tanks for your help!

leonardo.morita June 11, 2009 03:28

I think he meant a fixedValue 0.0 for pressure at the outlet, like you used.
But you should put here the velocity BC as well. A priori, a zeroGradient for U at the outlet should work...
By the way, have you checked if your flow is really laminar?


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