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Nico A. January 28, 2013 05:51

Residuals in buoyantBoussinesqSimpleFoam
 
4 Attachment(s)
Dear FOAMers,

I am simulating a (laminar) natural convection boundary layer in 2D with the above-named solver. So my domain has a uniformly heated wall at the left and atmospheric inlet and outlet conditions at the top, bottom and right respectivly. The domain is attached.

The case is already running with the following BCs for T, U, p_rgh:

0/T
Code:

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

dimensions      [ 0 0 0 1 0 0 0 ];

internalField  uniform 288.15;

boundaryField
{
    heatedWall
    {
        type            fixedValue;
        value          uniform 298.15;
    }
    right
    {
        type            inletOutlet;
        inletValue      uniform 288.15;
        value          uniform 288.15;
    }
 
    frontAndBack
    {
        type            empty;
    }
    inlet
    {
        type            inletOutlet;
        inletValue      uniform 288.15;
        value          uniform 288.15;
    }
    outlet
    {
        type            zeroGradient;
    }
}


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

0/U
Code:

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

dimensions      [ 0 1 -1 0 0 0 0 ];

internalField  uniform ( 0 0 0 );

boundaryField
{
    heatedWall
    {
        type            fixedValue;
        value          uniform ( 0 0 0 );
    }
   
    right
    {
        type            pressureDirectedInletVelocity;
    value        uniform (0 0 0);
    inletDirection  uniform (-1 0 0);
    }
   
    frontAndBack
    {
        type            empty;
    }
   
    inlet
    {
        type            pressureInletOutletVelocity;
    value        uniform (0 0 0);
    }
   
    outlet
    {
        type            inletOutlet;
        inletValue      uniform ( 0 0 0 );
        value          uniform ( 0 0 0 );       
    }
}

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

0/p_rgh
Code:

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

dimensions      [ 1 -1 -2 0 0 0 0 ];

internalField  uniform 0;

boundaryField
{
    heatedWall
    {
        type            buoyantPressure;
    rho        rhok;
        value          uniform 0;
    }
   
    right
    {
        type            totalPressure;
        U              U;
        phi            phi;
        rho            rhok;
        psi            none;
        gamma          1.4;
        p0              uniform 0;
    }
   
    frontAndBack
    {
        type            empty;
    }
   
    inlet
    {
        type            totalPressure;
        U              U;
        phi            phi;
        rho            rhok;
        psi            none;
        gamma          1.4;
        p0              uniform 0;
    }
   
    outlet
    {
    type            buoyantPressure;
    rho        rhok;
        value          uniform 0; 
    }
}

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

For the temperature difference of 10K and other flow parameters, the Rayleigh number is Ra=10^6, so a laminar boundary layer will develop, as you can see in the attached pictures for the Uz and T distribution at the vertical wall. The results seem to be physically correct.

But when I look at the residuals, they are oscillating (see attached picture). Normally they should fall due to given tolerances/ convergence criterions of 10^-08. The results are nearly the same for upwind and linear div-schemes.

I appreciate any suggestion regarding this case.

Best regards,
Nico


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