|
[Sponsors] |
Error in turbulentHeatFluxTemperatureFvPatchScalarField v1.6 |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
September 16, 2009, 08:06 |
Error in turbulentHeatFluxTemperatureFvPatchScalarField v1.6
|
#1 |
Senior Member
|
I noticed an error in turbulentHeatFluxTemperatureFvPatchScalarField class for temperature gradient calculation:
Code:
00146 void turbulentHeatFluxTemperatureFvPatchScalarField::updateCoeffs() 00147 { 00148 if (updated()) 00149 { 00150 return; 00151 } 00152 00153 const scalarField& alphaEffp = 00154 patch().lookupPatchField<volScalarField, scalar>(alphaEffName_); 00155 00156 const scalarField& Cpp = 00157 patch().lookupPatchField<volScalarField, scalar>(CpName_); 00158 00159 gradient() = q_/(Cpp*alphaEffp); 00160 00161 fixedGradientFvPatchScalarField::updateCoeffs(); 00162 } 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!
__________________
Best regards, Dr. Alexander VAKHRUSHEV Christian Doppler Laboratory for "Metallurgical Applications of Magnetohydrodynamics" Simulation and Modelling of Metallurgical Processes Department of Metallurgy University of Leoben http://smmp.unileoben.ac.at Last edited by makaveli_lcf; September 17, 2009 at 08:47. |
|
September 17, 2009, 02:36 |
|
#2 | |
Senior Member
Mark Olesen
Join Date: Mar 2009
Location: https://olesenm.github.io/
Posts: 1,684
Rep Power: 40 |
Quote:
They are formulated somewhat differently and the incompressible formulation will obviously not have rho in it. |
||
September 17, 2009, 03:32 |
|
#3 |
Senior Member
|
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 00054 : 00055 public fixedGradientFvPatchScalarField 00056 { 00057 // Private data 00058 00059 //- Heat flux [W/m2] 00060 scalarField q_; 00061 00062 //- Name of effective thermal diffusivity field 00063 word alphaEffName_; 00064 00065 //- Name of specific heat capacity field 00066 word CpName_; 00067 [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.
__________________
Best regards, Dr. Alexander VAKHRUSHEV Christian Doppler Laboratory for "Metallurgical Applications of Magnetohydrodynamics" Simulation and Modelling of Metallurgical Processes Department of Metallurgy University of Leoben http://smmp.unileoben.ac.at Last edited by makaveli_lcf; September 17, 2009 at 08:48. |
|
September 17, 2009, 09:54 |
|
#4 |
New Member
Yi Wang
Join Date: Mar 2009
Posts: 17
Rep Power: 17 |
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. |
|
September 17, 2009, 10:28 |
|
#5 |
Senior Member
|
Thank you, Yi!
Following your guidance I found in basicThermo_8H_source.html: Code:
00077 //- Laminar thermal diffusuvity [kg/m/s] 00078 volScalarField alpha_;
__________________
Best regards, Dr. Alexander VAKHRUSHEV Christian Doppler Laboratory for "Metallurgical Applications of Magnetohydrodynamics" Simulation and Modelling of Metallurgical Processes Department of Metallurgy University of Leoben http://smmp.unileoben.ac.at |
|
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Forces in V1.6 | terrybarnaby | OpenFOAM Post-Processing | 72 | September 2, 2015 16:49 |
installing v1.6 and keeping v1.5 | Gavin | OpenFOAM | 9 | October 23, 2009 04:16 |
nutRoughWallFunction v1.6 | Schag | OpenFOAM | 2 | October 1, 2009 16:28 |
icoDyMFoam v1.6 | shyam | OpenFOAM Bugs | 1 | September 5, 2009 04:22 |
Postprocessing and uniformDensityHydrostaticPressure in v1.6 | Schag | OpenFOAM Bugs | 2 | July 28, 2009 13:41 |