CFD Online Discussion Forums

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   OpenFOAM Post-Processing (https://www.cfd-online.com/Forums/openfoam-post-processing/)
-   -   Compressible model producing unknown "boundary" near patch interfaces (https://www.cfd-online.com/Forums/openfoam-post-processing/225363-compressible-model-producing-unknown-boundary-near-patch-interfaces.html)

PeterStrbik March 24, 2020 14:19
Compressible model producing unknown "boundary" near patch interfaces
 
3 Attachment(s)
Hi all,

I have been attempting to model high-speed compressible lubrication in a bearing but have been struggling to get viable results. The model is simplified to a wedge geometry where the inlet is twice the height of the outlet. I have been able to get an incompressible model working using icoFoam, and have attached an image of it to show the approximate results for pressure I am aiming to achieve with a compressible model. (Flow is from left to right)

The problem comes when trying to model the case with a compressible solver. I chose rhoCentralFoam to use in my case. After running the simulation with boundary conditions that mimic the incompressible case, I arrived at results where the boundary conditions were not necessarily satisfied. I have attached 2 images showing the pressure solution for the compressible case. I am unsure as to why those pressure jumps are occurring near the patch boundaries (especially near the outlet) when the boundary condition for those patches is that they should be at a fixed value of the ambient pressure.

Any insight as to why this is occurring would be much appreciated. Thanks!

PeterStrbik March 24, 2020 14:32
Initial Conditions
 
Here are the initial T, U, and p files for the compressible simulation:

T:
Code:
internalField  uniform 400;

boundaryField
{
    top
    {
        type            fixedGradient;
        gradient        uniform 100;
    }

    inlet
    {
        type            fixedValue;
        value          uniform 400;
    }

    outlet
    {
        type            zeroGradient;
    }

    bottom
    {
        type            fixedGradient;
        gradient        uniform 100;
    }

    frontAndBack
    {
        type            zeroGradient;
    }
}
U:
Code:
internalField  uniform (0 0 0);

boundaryField
{
    top
    {
        type            noSlip;
    }

    inlet
    {
        type            zeroGradient;
    }

    outlet
    {
        type            zeroGradient;
    }

    bottom
    {
        type            movingWallVelocity;
        value                uniform (170 0 0);
    }

    frontAndBack
    {
        type            zeroGradient;
    }
}
p:
Code:
internalField  uniform 100000;

boundaryField
{
    top
    {
        type            zeroGradient;
    }

    inlet
    {
        type            fixedValue;
        value          uniform 100000;
    }

    outlet
    {
        type            fixedValue;
        value                uniform 100000;
    }

    bottom
    {
        type            zeroGradient;
    }

    frontAndBack
    {
        type            fixedValue;
        value                uniform 100000;
    }
}


All times are GMT -4. The time now is 00:50.