[saidc.]

Hi,

I am trying to define a heat flux polynomial equation as a function of height on the wall. So far, I haven't been successful with the attempts I've made. First, I used the codedMixed boundary condition, and my 0/T file is as follows:

heatFluxWall
{
	type            codedMixed;
	value           uniform 865; // Initial value
	refValue        uniform 0;   // Reference value (not used in this case)
	refGradient     uniform 0;   // Reference gradient
	valueFraction   uniform 0;   // Fraction of the value that is fixed
	name            sscHeatFlux;
	
	code
	#{
		const fvPatch& boundaryPatch = patch();
		const fvBoundaryMesh& boundaryMesh = boundaryPatch.boundaryMesh();
		const fvMesh& mesh = boundaryMesh.mesh();
		
		const vectorField& Cf = boundaryPatch.Cf();
		scalarField& field = *this;
		
		const vectorField& faceAreas = mesh.Sf();
		const scalarField faceMagnitudes = mag(faceAreas);
		
		this->valueFraction() = 0.0;
		this->refValue() = 0.0;
		scalarField& refGradField = this->refGrad(); // Access refGrad as a scalarField
		
		// Coefficients for thermal conductivity kappa(T) 
		scalar kappaCoeffsArray[] = {myKappa(T)polynomial};
		const scalarField kappaCoeffs(8, kappaCoeffsArray);

		auto evaluateKappa = [&](scalar T) {
			scalar kappa = 0.0;
			scalar T_power = 1.0;
			for (int j = 0; j < kappaCoeffs.size(); ++j)
			{
				kappa += kappaCoeffs[j] * T_power;
				T_power *= T;
			}
			return kappa;
		};

		forAll(field, i)
		{
			scalar yValue1 = Cf[i].y();
			scalar T = field[i]; // Assuming field[i] gives the temperature at the face
			scalar kappa = evaluateKappa(T);
			
			scalar heatFlux = myEquation;
							  
			refGradField[i] = heatFlux / kappa; // Divide by thermal conductivity kappa
		}
	#};
}

Secondly, I used the groovyBC boundary condition, but I couldn't get a result from that either. It is as follows:

heatFluxWallgroovy
{
	type            groovyBC;
	valueExpression "T"; // Initial value
	variables "
		kappa=myKappa(T)polynomial; //I guess this is wrong. I should access to k on ith face and then use that value?
                yVal=pos().y;
                heatFlux=myEquation(yVal)";
	gradientExpression "heatFlux / kappa";
	valueFraction   uniform 0;
}

I think I am making a mistake while trying to define the heat flux as a gradient on the boundary.

I thought I could define the dT/dx gradient using the Fourier law q = -k dT/dx.

dT/dx = -q/k

If there is a more accurate method or if you identify the error, I would appreciate it if you could share it.

Kind regards,
said

[saidc.]

Hi,

When I compared the heat flux values obtained on the wall using the boundary condition I defined with groovyBC, leveraging Fourier's Law with a constant k, to my existing data, I encountered significantly overestimated values. Therefore, I used the externalWallHeatFluxTemperature boundary condition as shown below instead of groovyBC and achieved accurate results. I'm sharing this as a snippet for anyone who encounters a similar issue.

HFregion
{
	type            externalWallHeatFluxTemperature;
	mode            flux;
	q
	{
		type        coded;
		code
		#{
			auto sscQ = tmp<scalarField>::New(patch_.size(), 10000.0);
			auto& qq = sscQ.ref();
			const vectorField& sscCF = patch_.faceCentres();
			forAll(qq, i)
			{
				scalar yy = sscCF[i].y();
				qq[i] = myPolynomial_Equation;
			}
			return sscQ;
		#};
	}
	kappaMethod     solidThermo;
	value           $internalField;
}

Regards,
said