SimpleFoam Boundary Conditions
 

Hi

I have a question about the boundary conditions in simpleFoam. I want to modify the pitzDaily Tutorial with other boundary conditions.

I want a static low pressure at the outlet. My p file looks like this:

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.5 |
| \\ / A nd | Web: http://www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions [0 2 -2 0 0 0 0];
internalField uniform 0;
boundaryField
{
inlet
{
type zeroGradient;
}
outlet
{
type fixedValue;
value uniform -5000;
}
upperWall
{
type zeroGradient;
}
lowerWall
{
type zeroGradient;
}
frontAndBack
{
type empty;
}
}
// ************************************************** *********************** //

And I don´t want to have a fixed magnitude. My solution would be a velocity profile. My U file looks like this:

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.5 |
| \\ / A nd | Web: http://www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions [0 1 -1 0 0 0 0];
internalField uniform (0 0 0);
boundaryField
{
inlet
{
type zeroGradient;
}
outlet
{
type zeroGradient;
}
upperWall
{
type fixedValue;
value uniform (0 0 0);
}
lowerWall
{
type fixedValue;
value uniform (0 0 0);
}
frontAndBack
{
type empty;
}
}
// ************************************************** *********************** //

The Problem is that I have not a right solution. I think the U file is not correct.

Thanks for your help

Johannes

Hi,
simpleFoam solves incompressible. For this kind of simulation normally you set for the inlet condition:
pressure: zerogradient
velocity: fixedValues (Ux Uy Uz)

and for outlet condition:
pressure: fixedValue
velocity: zeroGradient

Regards Thomas

I wouldn't use zeroGradient for both velocity and pressure at the inlet... one of them should have a value. If not, the problem is not well described.

By the way, do you really need to use negative pressures?

You haven't set enough conditions. The problem as you described it could simply be solved by making the pressure -5000 everywhere and having no flow. Or it could pick just about any flow and calculate the pressure to meet it.

You need to define a pressure or velocity somewhere else, probably the inlet.