[invadoria]

Hi all.
I'm solving transport equation for a scalar variable C. I want to fix this scalar variable C in a rectangular region of the computational domain during simulation to keep the variable unchanged in this region during solution. Can you tell me how I can do it? Do I have to modify the source code?

Thank you in advance..

[alexeym]

Hi,

Take a look at $FOAM_SRC/fvOptions/constraints/general/explicitSetValue. It uses fvMatrix::setValues (http://foam.sourceforge.net/docs/cpp...a6b05660da9bc2) to fix values in a cellSet.

[rapierrz]

Hi Ender,

You can use of ForAll loop and if statement for this purpose.

[invadoria]

Originally Posted by alexeym

Hi,

Take a look at $FOAM_SRC/fvOptions/constraints/general/explicitSetValue. It uses fvMatrix::setValues (http://foam.sourceforge.net/docs/cpp...a6b05660da9bc2) to fix values in a cellSet.

I used the following body in fvOptions to set the C in the cellSet named Inlet. But it gives zero value for the C when I run the code. I'm not sure that the code is correct..

scalarVariableC
{
type scalarExplicitSetValue;
active true;
timeStart 0;
duration 10;
selectionMode cellSet;
cellSet Inlet;

scalarExplicitSetValueCoeffs
{
volumeMode absolute;
injectionRate
{
C 100;
}
}
}

[alexeym]

Hi,

If you are using scalarTransportFoam, unfortunately it does not support setting values explicitly (since in fact it does not create matrix object for equation, just uses solve(...) function).

If you would like to use fvOptions with scalarTransportFoam, you need the following modification of the solver (instead of just solve call):

fvScalarMatrix TEqn
(
    fvm::ddt(T)
  + fvm::div(phi, T)
  - fvm::laplacian(DT, T)
 ==
    fvOptions(T)
);

fvOptions.constrain(TEqn);

TEqn.solve();

with this fvOptions description:

setTValue
{
   type             scalarExplicitSetValue;
   active           true;

   scalarExplicitSetValueCoeffs
   {
       timeStart        0;
       duration         10;
       selectionMode    cellSet;
       cellSet          inlet;
       injectionRate
       {
           T 100;
       }
   }
}

it works fine.

Another way is to use forAll loop, as proposed by rapierrz, something like this:

word inletPatchName("inlet");
scalar TValue = 100;
const polyPatch& inlet = mesh.boundaryMesh()[inletPatchName];
forAll(inlet, idx)
{
    label cellI = inlet.faceCells()[idx];
    T.internalField()[cellI] = TValue;
}

before solve block could do the trick. Code above sets T value in the cells adjacent to inlet patch.

[invadoria]

Originally Posted by alexeym

Hi,

If you are using scalarTransportFoam, unfortunately it does not support setting values explicitly (since in fact it does not create matrix object for equation, just uses solve(...) function).

If you would like to use fvOptions with scalarTransportFoam, you need the following modification of the solver (instead of just solve call):

fvScalarMatrix TEqn
(
    fvm::ddt(T)
  + fvm::div(phi, T)
  - fvm::laplacian(DT, T)
 ==
    fvOptions(T)
);

fvOptions.constrain(TEqn);

TEqn.solve();

with this fvOptions description:

setTValue
{
   type             scalarExplicitSetValue;
   active           true;

   scalarExplicitSetValueCoeffs
   {
       timeStart        0;
       duration         10;
       selectionMode    cellSet;
       cellSet          inlet;
       injectionRate
       {
           T 100;
       }
   }
}

it work fine.

Another way is to use forAll loop, as proposed by rapierrz, something like this:

word inletPatchName("inlet");
scalar TValue = 100;
const polyPatch& inlet = mesh.boundaryMesh()[inletPatchName];
forAll(inlet, idx)
{
    label cellI = inlet.faceCells()[idx];
    T.internalField()[cellI] = TValue;
}

before solve block could do the trick. Code above sets T value in the cells adjacent to inlet patch.

Hello Alexey;
I used the fvOptions description and it works fine. Thank you for your suggestions..