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Source Term on Scalar Transport Equation

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Old   January 27, 2011, 12:59
Default Source Term on Scalar Transport Equation
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Alex
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Hi,

I have to add a transport scalar equation on the variable "C" but the problem is how to add the source term.

Using for instance SimpleFoam and modifying the solver I obtain the following equation for C "Ceqn.H":

solve
(
fvm::ddt(C)
+fvm::div(phi, C)
-fvm::laplacian(nu, C)
);

This is without source term and it works after I tested, including all the changes I have to do in the NewSimpleFoam.C and in createFields.H

Suppose that I want to add the sorce term with the following expression ST=C*(1-C), considering that I have to respect the dimensions in the solving, how can I set this ?

thanks in advance

alex
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Old   January 28, 2011, 06:20
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Jose Luis Santos
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Hi,

You can just include your source term as 'C*(1-C)' in the Ceqn.H equation. In this way it will be defined explicitly. I am not sure if you can work out the dimensions of this source term so it is consistent with the other terms.

Probably you want the source term to be implicit for better convergence stability, so you need to include it as: 'fvm::Sp(k,C)', where k is a constant that is to be multiplied by C.

Regards,
Jose
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Old   January 28, 2011, 06:32
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Hi, thanks for the reply. If I consider the second option, implicit ST, and I write the fvm::Sp(k,C) to the Ceqn.H, do you think I should also declare the k in the createFields.H? regards alex
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Old   January 28, 2011, 06:56
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Alex,

k is a placeholder for the constants that are multiplied by C in your source term.

Hence, if your source term is 2*C, it is defined implicitly as: fvm::Sp(2,C). The Programmers Guide that comes with OpenFOAM has more information on this.

Regards,
Jose
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Old   January 28, 2011, 08:01
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thanks a lot! I will try to fix it.

cheers,

alex
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Old   January 31, 2011, 04:49
Default re: Source Term on Scalar Transport Equation
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Hi I setted the equation as follows, but everytime there is an error. Do you know how can I solve it?

Actually, considering I need a source term dimensioned as [00-10000] I wrote the equation in this was, but I still don't get the error. Regards. alex


-----------------------------------

/*{CEqn.H}*\

solve
(
fvm::ddt(C)
+fvm::div(phi, C)
-fvm::laplacian(nu, C)==
fvm::ddt(C*(1-C))
);



Making dependency list for source file SourceFanzySimple.C
SOURCE=SourceFanzySimple.C ; g++ -m64 -Dlinux64 -DWM_DP -Wall -Wextra -Wno-unused-parameter -Wold-style-cast -Wnon-virtual-dtor -O3 -DNoRepository -ftemplate-depth-40 -I/cvos/shared/apps/OpenFOAM/OpenFOAM-1.7.1/src/turbulenceModels -I/cvos/shared/apps/OpenFOAM/OpenFOAM-1.7.1/src/turbulenceModels/incompressible/RAS/RASModel -I/cvos/shared/apps/OpenFOAM/OpenFOAM-1.7.1/src/transportModels -I/cvos/shared/apps/OpenFOAM/OpenFOAM-1.7.1/src/transportModels/incompressible/singlePhaseTransportModel -I/cvos/shared/apps/OpenFOAM/OpenFOAM-1.7.1/src/finiteVolume/lnInclude -IlnInclude -I. -I/cvos/shared/apps/OpenFOAM/OpenFOAM-1.7.1/src/OpenFOAM/lnInclude -I/cvos/shared/apps/OpenFOAM/OpenFOAM-1.7.1/src/OSspecific/POSIX/lnInclude -fPIC -c $SOURCE -o Make/linux64GccDPOpt/SourceFanzySimple.o
In file included from SourceFanzySimple.C:63:
Ceqn.H: In function ‚int main(int, char**)‚:
Ceqn.H:6: error: no matching function for call to ‚ddt(Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> >)‚
/cvos/shared/apps/OpenFOAM/OpenFOAM-1.7.1/src/finiteVolume/lnInclude/readSIMPLEControls.H:6: warning: unused variable ‚momentumPredictor‚
/cvos/shared/apps/OpenFOAM/OpenFOAM-1.7.1/src/finiteVolume/lnInclude/readSIMPLEControls.H:9: warning: unused variable ‚transonic‚
make: *** [Make/linux64GccDPOpt/SourceFanzySimple.o] Error 1
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Old   January 31, 2011, 05:52
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Hi,

I am not sure you can include your source term like that, ddt should be in the form ddt(C) or ddt(rho,C).

If you need: (C*(1-C))/dt, then try:

solve
(
fvm::ddt(C)
+fvm::div(phi, C)
-fvm::laplacian(nu, C)==
fvm::Sp(1-C,C)/runTime.deltaT()
);

The source term is not fully implicit, as 1-C is defined explicitly. Maybe someone else knows how to define the whole term implicit.

Regards,
Jose
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Old   January 31, 2011, 06:04
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Thanks Josť!

I have also another way, just I want you to give me an opinion about it:

if I write explicitly the ST as (C*a*(1-C)) where "a" has the dimension of [1/time] to keep the dimension in the parabolic equation, setted in the transportproperties, do you think is it reasonable?
cheers,alex
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Old   January 31, 2011, 06:19
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Actually I have used in the past a 'quick and dirty' trick that allows you to do just that:
sourceTerm = (1-C)*C*runTime.deltaT().value()/runTime.deltaT();

Therefore, you get the correct dimension, without needing to care about the deltat value.

Regards,
Jose
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Old   January 31, 2011, 08:56
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thanks again for the reply!

regards,

Alex
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