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-   -   How is the thermal conductivity calculated? (https://www.cfd-online.com/Forums/openfoam-programming-development/172223-how-thermal-conductivity-calculated.html)

pupo May 26, 2016 07:21
How is the thermal conductivity calculated?
 
Hello Foamers

I'm trying to figure out how does openFoam calculate the thermal diffusivity in BuyoantSimpleFoam. So far all the answers I've found online only go as deep as saying that alpha = nu / prandtl, but how is Prandtl calculated?

In other words, how does OpenFoam goes from a Pressure Field, Temperature Field and the properties listed below to alphaEff?

Code:
thermoType
{
    type            heRhoThermo;
    mixture        pureMixture;
    transport      sutherland;
    thermo          hConst;
    equationOfState perfectGas;
    specie          specie;
    energy          sensibleEnthalpy;
}

pRef            101325;

mixture
{
    specie
    {
        nMoles          1;
        molWeight      28.96;
    }
    thermodynamics
    {
        Cp              1006;
        Hf              0;
    }
    transport
    {
        As          1.458e-06;
        Ts          110.555;
    }
}
Best Regards

anishtain4 May 27, 2016 10:05
Looking at EEqn you'll see turbulence->alphaEff, then searching for turbulence you'll figure out it's been defined in createFields.H by autoPtr<compressible::turbulenceModel> turbulence, so you gotta look into documents to find Foam::compressible::turbulenceModel. However as thermo is mentioned in the turbulence model you can guess right here it's coming from thermo. It's again defined at createFields.H.
(following turbulence model gets you to phase fraction alpha which I doubt is what you want).

checking rhoThermo which is defined at very first lines of createField.H you find this:
http://openfoam.com/documentation/cp...ml/a02284.html
there you can follow up the alphaEff definition.

pupo May 29, 2016 14:33
Thank you for your answer,

As expected, alpha seems to be calculated from kappa [Thermal conductivity] and Cp.

I've found kappa being calculated in the sutherland transport model

however, this thread seems to hint that this kappa() is not used at all.

Can someone who knows a bit more about these models shed some light? I've been in a wild goose chase for some days, and I can't figure this one out :(


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