[Jad.L.]

Dear Foamers,

I am using openFoam v.6 and the solver sonicFoam for k-omega SST simulation.
My simulation stops after few loop due to a negative temperature (in Kelvin ). I think I have a trouble with my parameters. Could someone please check it?

About the simulation :
A cylinder of 100 mm length and with a 50 mm diameter. There is one inlet and one outlet at each part of the cylinder. This cylinder is under vacuum 0.1 Pa. The inlet will release 1.5e7 Pa (150 bar) and the outlet does nothing for now.

alphat


alphat = thermal conductivity / heat capacity

For H2 , alphat = 0.18/14300 = 1.2587e-5

internalField   uniform 0.000012587;

boundaryField
{
    Inlet
    {
        type            calculated;
        value           uniform 0.000012587;
    }
    Outlet
    {
        type            calculated;
        value           uniform 0.000012587;
    }
    
    Pipe
    {
        type            compressible::alphatWallFunction;
        value           uniform 0.000012587;
    }
 }

k
For the kinematic energy k, I found 4.14e-22 ( I used k=3/2*Boltzman cst* Temperature ) But this result seems weird.

I assume to have supersonic flow, I should have a velocity around U=750 m.s-1

Then I used the formula k = 3/2 (U*I) from CFD wiki . k = 16537



Is it correct to assume U= 750 and sound Velocity = 300 for my case ?

internalField   uniform 1;

boundaryField
{
    Inlet
    {
        type            fixedValue;
        value           uniform 16537;
    }
    Outlet
    {
        type            inletOutlet;
        inletValue      uniform 1;
        value           uniform 1;
    }
    Pipe
    {
        type            kqRWallFunction;
        value           uniform 1;
    }
 }

nut

 internalField   uniform 0;

boundaryField
{
    Inlet
    {
        type            calculated;
        value           uniform 0;
    }
    Outlet
    {
        type            calculated;
        value           uniform 0;
    }
    Pipe
    {
        type            nutkWallFunction;
        value           uniform 0;
    }
 }

omega


from the formula given in CFD wiki, omega =128/1.9e-4 =0.024

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

internalField   uniform 0.024;

boundaryField
{
    Inlet
    {
        type            fixedValue;
        value           uniform 0.024;
    }
    Outlet
    {
        type            inletOutlet;
        inletValue      uniform 0.024;
        value           uniform 0.024;
    }
    Pipe
    {
        type            omegaWallFunction;
        value           uniform 0.024;
    }
 }

p

internalField   uniform 0.1;

boundaryField
{
    Inlet
    {
        type            fixedValue;
        value           uniform 15000000;
    }

    Outlet
    {
        type            waveTransmissive;
        field           p;
        psi             thermo:psi;
        gamma           1.3;
        fieldInf        0.1;
        lInf            1;
        value           uniform 0.1;
    }
    Pipe
    {
        type            zeroGradient;
    }
 }

T

internalField   uniform 20;

boundaryField
{
    Inlet
    {
        type            fixedValue;
        value           uniform 20;
    }

    Outlet
    {
        type            inletOutlet;
        inletValue      uniform 20;
        value           uniform 20;
    }
    Pipe
    {
        type            zeroGradient;
    }
 }

U

internalField   uniform (0 0 0);

boundaryField
{
    Inlet
    {
        type            fixedValue;
        value           uniform (750 0 0);
    }

    Outlet
    {
        type            inletOutlet;
        inletValue      uniform (0 0 0);
        value           uniform (0 0 0);
    }
    Pipe
    {
        type            noSlip;
    }
}