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Dimensions in ScalarTransportFoam

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Old   November 26, 2017, 09:15
Default Dimensions in ScalarTransportFoam
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Dan
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Hi,

I have an simple question. I'm referring to OF 4.1.

There is the definition of the equation:
fvScalarMatrix TEqn
(
fvm::ddt(T)
+ fvm::div(phi, T)
- fvm::laplacian(DT, T)
==
fvOptions(T)
);

So, this means: \frac{\partial T}{\partial t} +\nabla\cdot{(\phi T)}-\nabla(\Gamma \nabla T)=0.

For incompressible fluids phi means: U \cdot A. I don't get the dimensions right here. For the first term it's obviously \frac{K}{s}. But for the second term phi has to be U, to get the right dimension.

I looked up phi and it says: surfaceScalarField phi

(
IOobject
(
"phi",
runTime.timeName(),
mesh,
IOobject::READ_IF_PRESENT,
IOobject::AUTO_WRITE
),
fvc::flux(U)
);

So what exactly is meant with flux(U), is this without the area? I couldn't find the code definition of flux(U).

I hope someone can help me to clarify this topic.

Best regards

Gesetzt
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Old   November 27, 2017, 03:55
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Quote:
Originally Posted by Gesetzt View Post
So what exactly is meant with flux(U), is this without the area? I couldn't find the code definition of flux(U).
Hi,
please have a look at src/finiteVolume/finiteVolume/fvc/fvcFlux.C where the volVectorField is U in your case! Makes things clearer ?
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Old   December 3, 2017, 05:48
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Dan
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Hey,

Thanks. I think it's clear now. Part of the problem was, that I didn't thought about the fact we are using FVM, so for the discretisation over all faces we need the area.

Best Regards,

Gesetzt
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Old   February 16, 2018, 02:27
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Ramana
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Quote:
Originally Posted by Gesetzt View Post
Hi,

I have an simple question. I'm referring to OF 4.1.

There is the definition of the equation:
fvScalarMatrix TEqn
(
fvm::ddt(T)
+ fvm::div(phi, T)
- fvm::laplacian(DT, T)
==
fvOptions(T)
);

So, this means: \frac{\partial T}{\partial t} +\nabla\cdot{(\phi T)}-\nabla(\Gamma \nabla T)=0.

For incompressible fluids phi means: U \cdot A. I don't get the dimensions right here. For the first term it's obviously \frac{K}{s}. But for the second term phi has to be U, to get the right dimension.

I looked up phi and it says: surfaceScalarField phi

(
IOobject
(
"phi",
runTime.timeName(),
mesh,
IOobject::READ_IF_PRESENT,
IOobject::AUTO_WRITE
),
fvc::flux(U)
);

So what exactly is meant with flux(U), is this without the area? I couldn't find the code definition of flux(U).

I hope someone can help me to clarify this topic.

Best regards

Gesetzt
HI,
i have question about TEqn. can this be valid for porous simple foam also.
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