[last_jedi]

Hello guys, i am trying to solve a case with icoFoam in a simple tube geometry, where laminar flow is driven by pressure.

More specific pressure is implemented in a sinusoidal form. I have been facing a problem with setting the BCs correctly.

Especially for outlet in pressure file, when i use zeroGradient case runs but results are not good. When i change this BC to fixedValue 0, then after some iterations CFL goes crazy. Pls any help would be great. My BC files can be seen below:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  dev                                   |
|   \\  /    A nd           | Web:      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            uniformFixedValue;
      uniformValue    sine;
      amplitude       6.85;
      frequency       0.25;
      scale           1;
      level           0;
      refValue        uniform 0;
  }
    
    outlet 
    {
        type            fixedValue;
        value           uniform 0;
    }
    
    wall
    {
        type            zeroGradient;
    }
    
}

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

    /*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  dev                                   |
|   \\  /    A nd           | Web:      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            fixedValue;
        value           uniform (0 0 0);
    }
    
    outlet
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    
    wall
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    
}

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

[simrego]

Hi!


You should use zeroGradient for velocity on the inlet and outlet if you define the pressure there.

[last_jedi]

Originally Posted by simrego

Hi!


You should use zeroGradient for velocity on the inlet and outlet if you define the pressure there.

Hi Simrego, i have tried also with zeroGradient for velocity inlet and outlet and CFL still goes crazy after a while..

[simrego]

You should use zeroGradient, but at least not fixedValue (0 0 0).
If it's possible to post your case or at least a simplified (if your geometry is not public) one, it's easier to help you.