[babakflame]

Dear Foamers

I am trying to simulate a swirl flame (SM1) with reactingFoam solver (LES-FSD approach).
I have made a 3D grid wich has a compression ratio of 3.5 i.e. the last cell near the outlet has a length 3.5 times to the first cell after nozzle outlet. The latest cells have length of 1.2 mm and the first cells immediately after the nozzle outlet have the length of 0.34 mm. Also, I have used immersed bounadry conditions to make the inlet flows fully developped.

My problem is that divergence symptoms appear in the result after 30 msec.
My courant number was 0.39.

I have used the zeroGradient condition for the outelet velocity.

I have attached two pics from my velocity results one showing the flowfield at 30 msec and the other identifies velocity after 33 msec.

As It is evident the divergence symptoms appear from the outlet of the doamin.

Would Somebody PLZ hint me why this happens and how can I solve it?

PS: I reduced the courant number to 0.35 and the problem still exists.

Regards
Bobi

[jherb]

What do you use as boundary condition for the pressure field? Perhaps "meanValue" instead of fixedValue does help.

[babakflame]

Greetings Joachim

These are my input files for pressure and velocity. As it is evident from the figures the disturbance comes into the domain from outlet. I have treated side (lateral boundaries) as an outlet too. detacher is the wall between inletAir and inletSwirl flows.

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

internalField   uniform 101325;

boundaryField
{
    inletFuel
    {
        type            zeroGradient;
    }
    inletAir
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value           uniform 101325;
    }
    bluffbody
    {
        type            zeroGradient;
    }
    detacher
    {
        type            zeroGradient;
    }
    side
    {
        type            fixedValue;
        value           uniform 101325;
    }
    inletSwirl
    {
        type            zeroGradient;
    }
}

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

internalField   uniform (0 20 0);

boundaryField
{
    outlet
    {
        type            zeroGradient;
    }
    side
    {
        type            zeroGradient;
    }
    bluffbody
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    detacher
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    inletAir
    {
        type          turbulentInlet;
        referenceField   uniform (0 20 0);
        fluctuationScale (0.02 0.1 0.02);  
    value            uniform (0 20 0);
    }
    inletFuel
    {
        type          turbulentInlet;
        referenceField   uniform (0 32.7 0);
        fluctuationScale (0.04 0.2 0.04);  
    value            uniform (0 32.7 0);
    }
    inletSwirl
    {
        type          swirlFlowRateInletVelocity;
        flowRate         0.0107;
        rpm              6632.42; 
    value            uniform (0 0 0);
    }
}

Would you PLZ introduce an example in tutorials that uses meanValue?

Regards
Bobi

[jherb]

I think there is not example in the tutorials for meanValue. But you can look at the documentation in the header of https://github.com/OpenFOAM/OpenFOAM...FvPatchField.H and this thread: http://www.cfd-online.com/Forums/ope...condition.html