[JoeFriend]

Hi, I've been reading the script code of the file turbulentTemperatureRadCoupledMixedFvPatch.C and I can't understand how the radiation term is transmitted from a solid to a fluid region...I believe it's in this part of the code:

scalarField Qr(Tp.size(), 0.0);
if (QrName_ != "none")
{
Qr = patch().lookupPatchField<volScalarField, scalar>(QrName_);
}

scalarField QrNbr(Tp.size(), 0.0);
if (QrNbrName_ != "none")
{
QrNbr = nbrPatch.lookupPatchField<volScalarField, scalar>(QrNbrName_);
mpp.distribute(QrNbr);
}

scalarField alpha(KDeltaNbr - (Qr + QrNbr)/Tp);

I also can't understand the meaning of "alpha".

I would appreciate any help.

[chriss85]

I suggest that you look at the analytical solution of the 1D heat conduction equation for three nodes (two boundaries with fixed value, one center node, two different, constant heat conductivities). You can easily solve it analytically and will find the value for the temperature at the patch using the temperatures of the cells.
You can then expand it with the condition that all heat fluxes (thermal and radiative) must be equal on both sides of the patch.
You also need to keep in mind that the patch values in mixedValueFvPatchFields are determined like this:
Value=valueFraction()*refValue()+(1-valueFraction())(Value_cell+refGrad()/deltaCoeffs())
deltaCoeffs equals 1/dx in the one dimensional case, i.e. it's more or less the inverse patch-cell centre distance.
I recently checked the code of this boundary condition and found that it matches with this derivation.