CFD Online Discussion Forums - Phase depending absorption & emission model properties

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Phase depending absorption & emission model properties

Hello,

I am trying to model laser melting using OpenFOAM1912, with the icoReactingMultiphaseInterFoam solver. This solver has the radiation model laserDTRM built in.

I have managed to solve simple problems nicely, but the optical properties are significantly different in the gas (almost completely transmissive)/liquid(highly absorbing)/solid phases(highly absorbing and reflective).

Is it possible to set the absorptivity/emissivity/E to different values in different phases? Does any of the built in models support this?

I have tried looking around in the source code, but I do not quite follow the radiation models.

Any help on the topic is greatly appreciated.

EDIT: It seems that localDensityAbsorptionEmission does the trick, and it does more or less what I would expect.

Best regards
Hektor

Attachments:

radiationProperties

Code:

radiation       on;

radiationModel  laserDTRM;

solverFreq 3;



absorptionEmissionModel constantAbsorptionEmission;

    mode    "Gaussian";

    nTheta    20;

    nr     100;

    opd    0.4425;

    focalLaserPosition constant     (.0002 .00020 0.0002);

    laserDirection constant     (0 -1 0);

    focalLaserRadius         0.000025;

    laserPower            200;

    sigma                25e-6;

    //qualityBeamLaser        1.0;

    absorptivity    absorptivity    [0 -1 0 0 0 0 0] 1e5;

    emissivity      emissivity      [0 -1 0 0 0 0 0] 0.04;

    E               E               [1 -1 -3 0 0 0 0] 0;



scatterModel    none;

sootModel       none;

transmissivityModel none;

Included absorptionEmissionModels

Quote:

binaryAbsorptionEmission
constantAbsorptionEmission
greyMeanAbsorptionEmission
greyMeanSolidAbsorptionEmission
localDensityAbsorptionEmission
multiBandAbsorptioEmission
multiBandZoneAbsorptionEmission
none
wideBandAbsorptionEmission

Hi Hektor,

I am also trying to work with LaserDTRM for laser melting. Unfortunately, I don't know much about your problem, but I wonder if it is connected to a problem I am having. I also have three phases set up (gas, liquid, solid), however, the laser source will not travel through the gas phase and into the solid phase. I have attached quick snapshots from paraview. I use a simple blockmesh and then initialize the phases using setFields.

Have you also encountered this problem?

Cheers

My solution has been to use the "localDensityAbsorptionEmission" absorption/emission model, there you can set the absorptivity/emissivity/E of the different phases.

The value can be set to 0 for the gas, and metals typically have around 10^8 1/m. Find good values for your material at (https://refractiveindex.info/).

The other option is to to skip the gas phase and use a boundary condition to model the laser. This will work if you have a high absorptivity and a simple geometry.

Hi Hektor,

Thanks for your quick reply. I'm glad you were able to figure your problem out. I'm trying to incorporate your comments, but I don't know how exactly to code in the coefficients. Here's what I have:

localDensityAbsorptionEmissionCoeffs
{
alphaNames alpha.gas;
absorptivity absorptivity [0 -1 0 0 0 0 0] 0;
emissivity emissivity [0 -1 0 0 0 0 0] 0;
E E [1 -1 -3 0 0 0 0] 0;

alphaNames alpha.liquid;
absorptivity absorptivity [0 -1 0 0 0 0 0] 0;
emissivity emissivity [0 -1 0 0 0 0 0] 0;
E E [1 -1 -3 0 0 0 0] 0;

alphaNames alpha.solid;
absorptivity absorptivity [0 -1 0 0 0 0 0] 0;
emissivity emissivity [0 -1 0 0 0 0 0] 0;
E E [1 -1 -3 0 0 0 0] 0;
}

Any insight?
Thanks in advance!

I think I was able to figure it out after trial and error. For anyone else interested, here's what ended up working for me:

localDensityAbsorptionEmissionCoeffs
{
alphaNames (alpha.gas alpha.liquid alpha.solid);
aCoeff (0 1e3 1e10);
eCoeff (0 0.5 0.5);
ECoeff (0 0.5 0.5);
}

Please let me know if I made any errors or left something out.

Thanks!

Yes this looks correct.