[huhaijun]

Hi. I try to calculate the concentration in a pipe. Since the thickness of concentration boundary is much less than thickness of velocity boundary layer, the wall function cannot be applied. The low reynold number model (LaunderSharmaKE)is selected. However, the velocity and k , epsilon can be correctly calculated, but the concentration is always wrong. Some nodes' values are(>400) very large compared with those of the inner nodes(<1). The solver is a modified simpleFoam where concentration transport equation is added. the code and case are given. I don't know what is the problem and wish someone can give good advices.

[huhaijun]

solver:
\*---------------------------------------------------------------------------*/

#include "fvCFD.H"
#include "singlePhaseTransportModel.H"
#include "RASModel.H"
#include "simpleControl.H"
#include "fvIOoptionList.H"

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

int main(int argc, char *argv[])
{
#include "setRootCase.H"
#include "createTime.H"
#include "createMesh.H"
#include "createFields.H"
#include "createFvOptions.H"
#include "initContinuityErrs.H"

simpleControl simple(mesh);

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

Info<< "\nStarting time loop\n" << endl;

while (simple.loop())
{
Info<< "Time = " << runTime.timeName() << nl << endl;

p.storePrevIter();

// --- Pressure-velocity SIMPLE corrector
{
#include "UEqn.H"
#include "pEqn.H"

}


turbulence->correct();

#include "CEqn.H"

runTime.write();

Info<< "ExecutionTime = " << runTime.elapsedCpuTime() << " s"
<< " ClockTime = " << runTime.elapsedClockTime() << " s"
<< nl << endl;
}

Info<< "End\n" << endl;

return 0;
}
//===================
CEqn.H
{
dimensionedScalar DT = dimensionedScalar("D", dimensionSet(0,2,-1,0,0,0,0), 5.26e-9 ) ;

fvScalarMatrix CEqn
(
fvm::ddt(C) // <--- steady state simulation, so ddt disabled...
+
fvm::div(phi, C)
- fvm::laplacian(DT, C)
// viscous heat dissipation term
);

CEqn.relax();


CEqn.solve().initialResidual();
}
//================case ========
k:

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object k;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -2 0 0 0 0];

internalField uniform 3.84e-3;

boundaryField
{
inlet
{
type fixedValue;
value uniform 3.84e-3;
}
outlet
{
type zeroGradient;
}
wall
{
type fixedValue;
value uniform 1e-10;
}
axi_symm-f
{
type wedge;
}
axi_symm-r
{
type wedge;
}
}

epsilon:
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object epsilon;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -3 0 0 0 0];

internalField uniform 2.79e-3;

boundaryField
{
inlet
{
type fixedValue;
value uniform 2.79e-3;
}
outlet
{
type zeroGradient;
}
wall
{
type zeroGradient;
}
axi_symm-f
{
type wedge;
}
axi_symm-r
{
type wedge;
}
}

nut:

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -1 0 0 0 0];

internalField uniform 0;

boundaryField
{
inlet
{
type calculated;
value uniform 0;
}
outlet
{
type calculated;
value uniform 0;
}
axi_symm-f
{
type wedge;
}
axi_symm-r
{
type wedge;
}
wall
{
// type nutUSpaldingWallFunction;
// value uniform 0;

// type nutkWallFunction;
// value uniform 0;

// type fixedValue;
// value uniform 0;

// type zeroGradient;
type nutLowReWallFunction;
value uniform 0;
}
defaultFaces
{
type empty;
}
}

C:

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object C;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 -3 0 0 1 0 0]; //*** kg, m,s,K,kmol,A,cd *** mol/l or kmol/m3 *****//

internalField uniform 1;

boundaryField
{



inlet
{
type fixedValue;
value uniform 1;
}
outlet
{
type fixedValue;
value uniform 0;
}
wall
{
type fixedValue;
value uniform 0;
}
axi_symm-f
{
type wedge;
}
axi_symm-r
{
type wedge;
}


}