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how to make a scalar transport equation to be conserved?

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Old   May 5, 2013, 07:33
Default how to make a scalar transport equation to be conserved?
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Ehsan
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hello
I run a solver that has a scalar transport equation scalar but value is not between 0 and 1 as the snapshot.
how to resolve?
this is the equation I modified solver by:
Code:
// --- Scalar Transport
    tmp<fvScalarMatrix> gasEqn
    (
     fvm::ddt(rho,gas) 
             + fvm::div(phi, gas)
                -fvm::Sp(fvc::div(phi), gas)
                      - fvm::laplacian(turbulence->muEff(), gas)     
    );
    
    gasEqn().relax();
    
    gasEqn().solve(mesh.solver("gas"));
how to make it conseved so that gas(a scalar transport variable)be between 0(internalField value) and 1(inlet value)?(outlet zeroGradient.one inlet and one outlet only)
thanks.
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Old   May 5, 2013, 08:01
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Hi Ehsan,

A few questions:
  1. Are you using a compressible or incompressible solver?
    1. Which solver are you using as base?
  2. What are the base fluid properties?
Best regards,
Bruno
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Old   May 5, 2013, 08:04
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hi Bruno
compressible.viscous.in both rhoCentralFoam and rhoPimpleFoam it occurs.
I had sent you the modified solvers and a case before.I think its because scalar transport equation is not conserved.maybe a term is excess or in lack!
I use janafThermo and sutherland
Code:
//thermoType      hePsiThermo<pureMixture<sutherland<janaf<perfectGas<specie>>,sensibleEnthalpy>>>;
thermoType
{
    type            hePsiThermo;
    mixture         pureMixture;
    transport       sutherland;
    thermo          janaf;
    equationOfState perfectGas;
    specie          specie;
    energy          sensibleEnthalpy;
}
mixture
{
    specie
    {
        nMoles          1;
        molWeight       28.96;
    }
    thermodynamics
    {
     Tlow 200;
     Thigh 6000;
     Tcommon 1000;
     highCpCoeffs (3.129672277499967 1.211766752750042e-3 -4.04761109000018e-7 6.409571300000324e-11 -3.780447620000211e-15 -.996955811e3 5.257756413);
     lowCpCoeffs  (3.593868050000014 -8.419292810001117e-4 2.08457592775033e-6 -5.938441825004294e-10 -2.456771699998039e-13 -1.0512181e3 3.140021718);
        /*Cp              1040;
        Hf              2.544e+06;*/
    }
    transport
    {
       As 1.4584e-6;
       Ts 110.4;
        /*mu              1.84e-05;
        Pr              0.75;*/
    }
}


// ************************************************************************* //
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Old   May 5, 2013, 08:11
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OK, then for comparison, adapt the solver pimpleFoam as well and compare the results.
Because as I wrote before in the same thread you mentioned, this way it'll make it easier to diagnose which component is making the scalar diffuse too much!
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