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April 13, 2010, 17:27 
wallHeatTransfer & Neumann BC

#1 
New Member
stefano zinna
Join Date: Mar 2009
Posts: 14
Rep Power: 8 
Dear All.
Can someone tell me how to use wallHeatTranfser type to setup Neumann boundary condition for unsteady diffusion equation? Can someone post a case for that? thank you in advance. Stefano 

June 3, 2010, 07:35 
wallHeatTransfer, Neumann or Newton boundary condition for the temperature in OF1.6

#2 
New Member
Peter Naamansen
Join Date: Mar 2010
Location: Denmark
Posts: 6
Rep Power: 7 
Dear all
I do not yet know how to the BC wallHeatTransfer should be set in OF1.6. I am trying to find out how I should make OF1.6 use the BC wallHeatTransfer on the Tfield for my solver called forchFoam. I can compile and run my solver with this BC, but it does not produce the correct results on the Tfield . The way I have set it in the 0/Tfile is: ..... leftWall { type wallHeatTransfer; alphaWall uniform 20; Tinf uniform 400; value uniform 300; } ....... I have included the file thermophysicalProperties under constant/. This file contains: ..... FoamFile { version 2.0; format ascii; class dictionary; location "constant"; object thermophysicalProperties; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // thermoType hPsiThermo<pureMixture<constTransport <specieThermo<hConstThermo<perfectGas>>>>>; mixture air 1 28.9 1000 0 1.8e05 0.7; pRef 100000; ....... Instead of hPsiThermo, I have also tried using ePsiThermo or hRhoThermo, which works just as well (that is; it runs but does not give the correct results). The file createFields.H in the solverdirectory contains the following extra lines: ........ Info<< "Reading thermophysical properties\n" << endl; autoPtr<basicPsiThermo> pThermo ( basicPsiThermo::New(mesh) ); basicPsiThermo& thermo = pThermo(); ....... My file forchFoam.C in the solverdirectory contains the following included files: ...... #include "fvCFD.H" #include "volFields.H" #include "basicPsiThermo.H" #include "basicThermo.H" #include "fixedGradientFvPatchFields.H" ...... and my Make/options contains: EXE_INC = \ I$(LIB_SRC)/thermophysicalModels/basic/lnInclude \ I$(LIB_SRC)/thermophysicalModels/specie/lnInclude \ I$(LIB_SRC)/finiteVolume/cfdTools \ I$(LIB_SRC)/finiteVolume/lnInclude EXE_LIBS = \ lbasicThermophysicalModels \ lspecie \ lmeshTools \ lfiniteVolume As I said, I can compile and run everything without errormessages, but the BC wallHeatTransfer does not produce correct results on T. What I have done in the files createFields.H and in thermopysicalProperties is done in order to make the solver forchFoam run, but what is written there has nothing to do with my actual fluid. I know that the thermophysical model has its own pressure, temperature, viscosity, thermal diffusivity, enthalpy, etc.. built in, so what I am trying to do is essentially nonsense, but somehow I feel it should be possible to use the BC wallHeatTransfer without having to specify an entire model for the thermodynamics. Am I wrong about that ? I need to do something that will allow me to run and correctly include the BC. As far I can tell, I need to write autoPtr<... in createFields.H and include some thermostuff written in thermopysicalProperties or a similar dictionary. Does any of you have any idea, what I should write in createFields.H and in thermopysicalProperties or a similar dictionary instead, in order to make wallHeatTransfer work correctly? Peter 

June 3, 2010, 08:11 

#3 
Member

Can you give a brief description of your model (what you want it to calculate, how it works, phases, etc)? At which part it gives wrong results?


June 3, 2010, 08:49 
wallHeatTransfer, Neumann or Newton boundary condition for temperature in OF1.6

#4 
New Member
Peter Naamansen
Join Date: Mar 2010
Location: Denmark
Posts: 6
Rep Power: 7 
Dear All
I am trying to make a CFDmodel with OF1.6, which can simulate drying of corn by the use of forced convection of hot air through this fixed porous material. I am at the beginning phase of the project and I am testing the various components (the BC's of course play an important role) that should be part of the OF1.6files. My final CFDmodel will contain fields of air, vapor, pressure, velocity, temperature and huimidity of the solid phase. Although the density of the gases may vary somewhat, the flow is essentially incompressible (no compressibility effects). I have not yet come so far as to implement all these fields since I am now testing the BC's for the temperature. I can define BC's for T on walls that are adiabatic (zeroGradient BC) or with a fixed rate of heat inflow or outflow (fixedGradient BC), but I have not been able to define a Newton (also called Neumann) BC, where flux = const*(TT0). The BC wallHeatTransfer in OF1.6 should do exactly that. It is part of the thermodynamical models in OF1.6 but I have not yet been able to understand the full use of these and I feel it should be possible to use wallHeatTransfer separately without having to specify a full and sophisticated thermodynamic model. Peter Last edited by PeterNaa; June 3, 2010 at 10:23. 

June 4, 2010, 11:58 

#5 
Senior Member
Nishant
Join Date: Mar 2009
Location: Glasgow, UK
Posts: 165
Rep Power: 8 
Hi peter,
Now I am getting the problem. Can you tell me from which version of the openFoam you started you forchFoam solver? It doesn't look like the OF1.6 version. or may be it is icoFoam solver. is it? your solver is asking for the thermophysicalPreoperty file in the constant folder, which might have initiated because of the wallHeatTranfer BC. you should look for some other solver for this purpose, where the solver read the thermophysicalproperty file. regards, Nishant 

August 26, 2010, 09:51 
groovyBC

#6 
New Member
Peter Naamansen
Join Date: Mar 2010
Location: Denmark
Posts: 6
Rep Power: 7 
Dear all
Installing groovyBC does the same job as wallHeatTransfer ( http://www.cfdonline.com/Forums/openfoam/74593mixedbcheattransferlaplacianfoam.html). Peter 

Tags 
newton boundary condition, wallheattransfer 
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