[me3840]

Hello all,


I'm trying to make a case with solar loading. Only some of my surfaces are attached to solids, the rest are adiabatic. All surfaces (except for the outer domain walls) are opaqueDiffusive. This setup is very similar to the simpleCarSolarPanel tutorial.


That tutorial looks to have reasonable interactions with the surfaces; the opaque surfaces, even though they're adiabatic, provide shade for other surfaces behind them. This can be seen by looking at the qr field.


However my case (with a similar setup) has very strange shading interactions. Sometimes opaque surfaces provide shade, sometimes they don't, and qr is only nonzero on the surfaces which attach to solids; the other adiabatic surfaces always show qr=0, which doesn't make sense. Can anyone see errors in my setup here? Attached is an image from a test case with the sun pointing straight down (-z). From this perspective, only the cap and the top vane should see any direct sun at all, and the others should be almost completely shaded, but clearly that's not the case.


Images here:
https://imgur.com/a/Q3DbIYG


boundaryRadiationProperties:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant";
    object      boundaryRadiationProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

"domain_inlet"
{
    type        transparent;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        emissivity      (1 1);
        absorptivity    (0 0);
    }
}

"domain_outlet"
{
    type        transparent;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        emissivity      (1 1);
        absorptivity    (0 0);
    }
}

"domain_left"
{
    type        transparent;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        emissivity      (1 1);
        absorptivity    (0 0);
    }
}

"domain_right"
{
    type        transparent;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        emissivity      (1 1);
        absorptivity    (0 0);
    }
}

"domain_top"
{
    type        transparent;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        emissivity      (1 1);
        absorptivity    (0 0);
    }
}

"domain_ground"
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.6 0.6);
        emissivity      (0.98 0.98);
    };
}

bottom_plate
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.3 0.3);
        emissivity      (0.8 0.8);
    };
}

chassis_poles
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.3 0.3);
        emissivity      (0.8 0.8);
    };
}

raspi_zero_w
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.7 0.7);
        emissivity      (0.8 0.8);
    };
}

sensor_mount
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.3 0.3);
        emissivity      (0.8 0.8);
    };
}

sensor_support
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.3 0.3);
        emissivity      (0.8 0.8);
    };
}

vanes
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.3 0.3);
        emissivity      (0.8 0.8);
    };
}

cap
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.3 0.3);
        emissivity      (0.8 0.8);
    };
}

hardware_plate
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.3 0.3);
        emissivity      (0.8 0.8);
    };
}

sensor
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.7 0.7);
        emissivity      (0.8 0.8);
    };
}

top_plate
{
    type       opaqueDiffusive;
    wallAbsorptionEmissionModel
    {
        type            multiBandAbsorption;
        absorptivity    (0.3 0.3);
        emissivity      (0.8 0.8);
    };
}
// ************************************************************************* //

radiationProperties:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant";
    object      radiationProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

radiation       on;

radiationModel  solarLoad;

solarLoadCoeffs
{

    // Sun direction ray model. Give the sunDirection or calculated using the
    // (solar calculator)
    sunDirectionModel   sunDirConstant; //sunDirTracking

        // Time interval to update Sun position (sec)
        sunTrackingUpdateInterval 800;

        sunDirection        (0 0 -1);

        localStandardMeridian   -5;      // GMT offset (hours)
        startDay                204;    // day of the year
        startTime               15.0;     // time of the day (hours decimal)
        longitude               -80.917; // longitude (degrees)
        latitude                28.453; // latitude (degrees)


        // Grid orientation
        gridUp                  (0 0 1);
        gridEast                (1 0 0);

    // Energy spectrum
    spectralDistribution (2 1);

    // Solar model:

        // sunLoadConstant-sunLoadFairWeatherConditions-SunLoadTheoreticalMaximum;
        sunLoadModel sunLoadConstant;

        // Sun load constant model
        directSolarRad  500;    // [w/m2]
        diffuseSolarRad 0;     // [w/m2]

        // Fair Weather Conditions Model Constants.
        // Calculate beta from the Solar calculator or input
        A       500;        // Apparent solar irradiation at air mass m = 0
        B       0.142;      // Atmospheric extinction coefficient
        //beta    45;         // Solar altitude (in degrees) above the horizontal

        // Theoretical maximum model constants
        Setrn       10;
        SunPrime    1;

        // Ground reflectivity
        groundReflectivity 0.2;

        // Solar diffusivity constants
        C   0.058;  // Model constant

    // Radiative flux coupling flags
    solidCoupled    true;  //Couple through qr the solid regions (default true)
    wallCoupled     false; //Couple through qr wall patches (default false)

    // Reflecting rays
        useReflectedRays true;
        reflecting
        {
            nPhi        10;
            nTheta      10;
        }

    absorptionEmissionModel none;
    scatterModel            none;
    sootModel               none;

}


viewFactorCoeffs
{
    smoothing true; //Smooth view factor matrix (use when in a close surface
                    //to force Sum(Fij = 1)
    constantEmissivity true; //constant emissivity on surfaces.

    nBands    2;

    useSolarLoad       true;
}

// Number of flow iterations per radiation iteration
solverFreq 1;

absorptionEmissionModel none;

scatterModel    none;

sootModel       none;

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

[me3840]

I may have found the solution to this.


In faceShading.C, the start and end points of the rays used to calculate face intersections are computed using the face center of a given face and a vector d.


Vector d is calculated as:

scalar maxBounding = 5.0*mag(mesh_.bounds().max() - mesh_.bounds().min());

const vector d(direction_*maxBounding);

where direction_ is the direction specified in the solar load. So essentially we scale the direction_ by a geometric size which is proportional to the length of the diagonal of the bounding box of the mesh.

The start and end points used for mesh intersection are calculated:

start.append(fc - 0.001*d);
end.append(fc - d);

This means that the start point, depending on a given face having proximity to a different face, may not be very close to the (original) face that the line intersection is being calculated on. In my case, since I have a lot of fins close together, this occurred.

One can sidestep this problem by just making the direction multiplication very small, i.e.

start.append(fc - 0.00001*d);
end.append(fc - d);

Or, you could just remove it all together, I suppose. Anyway, when I did this, I appear to at least get shading that makes sense. I have not computed any solutions using it however, yet.

[B_R_Khan]

Hi!

I'm not getting non zero qr on any surface when I trun on view factor with solar load. I do not have multiple regions, just a domain with a wall inside. I'm going to try the solution you mentioned but have one confusion: Is it necessary to have multiple regions for view factor ?