Error in turbulentHeatFluxTemperatureFvPatchScalarField v1.6
I noticed an error in turbulentHeatFluxTemperatureFvPatchScalarField class for temperature gradient calculation:
Code:
00146 void turbulentHeatFluxTemperatureFvPatchScalarField::updateCoeffs() q = lambda * grad (T) = alpha * rho * Cp * grad (T) where lambda - thermal conductivity alpha - thermal diffusivity Cp - cpecific heat capacity rho - density Thus temperature gradient should be grad (T) = q / (alpha * rho * Cp) Please correct me if I'm wrong! |
Quote:
They are formulated somewhat differently and the incompressible formulation will obviously not have rho in it. |
Mark,
I'm speaking about incompressible namespace. In any case, if not include density in heat flux calculations, left-hand and right-hand dimensions in that relationship will not meet! That is what I mean in details: Code:
00053 class turbulentHeatFluxTemperatureFvPatchScalarField [q] = W / m^2 = (J / s) / m^2 = (kg m^2 / s^3) / m^2 = kg / s^3 [lambda] = W / (m K)= (kg m^2 / s^3) / (m K) = kg m / (K s^3) [alpha = lambda / (rho Cp)] = m^2 / s [Cp] = J / (kg K) = (kg m^2 / s^2 ) / (kg K) = m^2 / (K s^2) [grad (T)] = K / m Thus q = lambda * grad (T) => [LHS] = W / m^2 equal to [RHS] = W / (m K) * K / m = W / m^2 But if we calculate grad (T) as q / (alpha Cp), then we get grad (T) = q / (alpha Cp) => [LHS] = K / m not equal to! [RHS] = kg / s^3 / (m^2 / s * m^2 / (K s^2)) = kg K / m^4 So we see that dimensions of the left-hand side (LHS) and the right-hand side (RHS) do not meet unless other than traditional units are used for thermal conductivity, thermal diffusivity, specific heat capacity etc. It is easy to check, that q = (alpha Cp rho ) grad (T) => grad (T) = q / (alpha Cp rho) gives correct result after dimensions analyzis. |
Not sure in incompressible solvers. But in compressible solvers, alphaEff and alpha defined in OF are not the same as the alpha [m^2/s] that we typically refer to.
They actually have already included rho in the definition. Basically in OpenFOAM: alpha = lambda/Cp ( not lambda/Cp/rho) You might want to check the thermoPhysicalModel to find it out. |
Thank you, Yi!
Following your guidance I found in basicThermo_8H_source.html: That is why there was ambiguity. |
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