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-   -   How should I set these boundary conditions? (http://www.cfd-online.com/Forums/openfoam-pre-processing/93548-how-should-i-set-these-boundary-conditions.html)

CNT9 October 18, 2011 20:06

How should I set these boundary conditions?
 
Hi, I am trying to set up a very simple problem with
three inlets coming from left and one outlet going out (to right).
I want the inlets to have certain pressure values & speed.
For simplicity, I ran it with potentialFoam solver.
However, after running the code, it seems like the flow is not going through
the outlet; instead, it seems like the flow is flowing from motive inlet and
exiting to suction inlets.
Can someone help me how should I fix these boundary conditions?
Thank you in advance!

(suctiontop & suctionbottom & motive are inlets.)

For U:


FoamFile
{
version 2.0;
format ascii;
class volVectorField;
location "0";
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform (0 0 0);


boundaryField
{
down
{
type symmetryPlane;
}
outlet
{
type zeroGradient;
}
top
{
type symmetryPlane;
}
motive
{
type fixedValue;
value uniform (0 0 0);
}
suctiontop
{
type fixedValue;
value uniform (0 0 0);
}
suctionbottom
{
type fixedValue;
value uniform (0 0 0);
}
defaultFaces
{
type empty;
}
}


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



For P:


FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0;

boundaryField
{
down
{
type symmetryPlane;
}

top
{
type symmetryPlane; // zeroGradient; //symmetryPlane;
}


motive
{
type fixedValue ;
value uniform 5;
}

suctionbottom
{
type fixedValue ;
value uniform 1;
}

suctiontop
{
type fixedValue ; //zeroGradient;
value uniform 1;
}


outlet
{
type zeroGradient
}

defaultFaces
{
type empty;
}
}

stevenvanharen October 19, 2011 02:56

Why do you want to have inlets with a fixed pressure? I assume u solve for incompressible flow.

To me it is not strange that the fluid is moving from the high pressure inlet to the low pressure inlets.

I think the standard combination is fixedValue U/zeroGradient p for inlets and zeroGradient U/fixedValue p for outlets.

romant October 19, 2011 05:13

if you want pressure driven flows you should take a look at the appropriate boundary conditions,

pressureInletOutletVelocity
pressureInletUniformVelocity


and some of the others that have to do with pressure velocities, those will set your velocity due to a set pressure.

you can find the different boundary conditions under

/opt/openfoam201/src/finiteVolume/fields/fvPatchFields/derived


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