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Gerrit February 19, 2016 03:00
Pressure definitions for buoyantSimpleFoam
 
1 Attachment(s)
Hi,

I am solving a case with buoyantSimpleFoam. It is a small heated wire in a pipe that is laying horizontal (see picture attached). So inlet and outlet are on the same level.
Although my simulations run, I am still not sure about the pressure definitions.

1. As far as I know the pressures are related by this:
PHP Code:
p = p_rgh + rho*g*z 
I am simulating a gas and my pipe is only 6 mm in diameter, wouldn't that lead to:
PHP Code:
p=p_rgh 
2. How do I handle this if I have a pressure of for example 2 bar at outlet?

What I did until now is to define my p file like always:

Code:
 
  dimensions      [1 -1 -2 0 0 0 0];

 internalField  uniform 2e5;

  inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value          uniform 2e5;
    }
    "(wall1|wall2|wire)"
    {
        type            zeroGradient;
    }
    "(bottom|top)"
    {
        type            empty;
    }
and the p_rgh like this:

Code:
dimensions      [1 -1 -2 0 0 0 0];   

internalField  uniform 2e5;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value          uniform 2e5;
    }

    "(wall1|wall2|wire)"
    {
        type            fixedFluxPressure;
        gradient        uniform 0;
        value          uniform 2e5;
    }

    "(bottom|top)"
    {
        type            empty;
    }
}
Especially in the p_rgh I am not sure, if my definitions are correct. Does it make sense to use zeroGradient at inlet for this?

Can someone give a comment on this please?

Thank you!

Best
Gerrit

Gerrit February 21, 2016 05:19
Hi,

I continued on the case and found a tutorial called circuitBoardCooling. I copied the boundaries from there it now I think it makes somehow sense:

p:
Code:
dimensions      [1 -1 -2 0 0 0 0];

internalField  uniform 237233.6;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value          uniform 237233.6;
    }
    "(wall1|wall2|wire)"
    {
        type            zeroGradient;
    }
    "(bottom|top)"
    {
        type            empty;
    }

}
and p_rgh
Code:
dimensions      [1 -1 -2 0 0 0 0];   

internalField  uniform 237233.6;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value          uniform 237233.6;
    }

    "(wall1|wall2|wire)"
    {
        type            fixedFluxPressure;
        gradient        uniform 0;
        value          uniform 237233.6;
    }

    "(bottom|top)"
    {
        type            empty;
    }
}
I am still a little bit uncertain about the value itself. From my point of view it should be similar to the incompressible cases, where the pressure p is the static pressure. From that point of view I could set it to 0, right?

Best


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