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suitable boundary condition for scavenging process?

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Old   January 24, 2013, 18:38
Default suitable boundary condition for scavenging process?
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Ehsan
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I have found the cause of errors in my simulation.its at scavenging process.
there is a tube that is filled with
internalField: U=0,T=400K,p=250000pa
and suddenly one side of it become open to environment.the environment has

BC: p0=100000pa and T=288K.
I have set various set of BC's for it but I have not obtain correct answer yet.a divergence in e calculation is occured because of decreasing T below 200K.
I have examined these sets so far:
1)p:waveTransmissive T and U:zeroGradient
Code:
type            waveTransmissive;
        field           p;
        phi             phi;
        rho             rho;
        psi             psi;
        gamma           1.4;
        fieldInf        100000;
        lInf            .1;
        value           uniform 100000;
problem: physically incorrect situation with continously increasing pressure return of decreasing.
2)p:totalPressure T and U:zeroGradient
Code:
type totalPressure;
            p0 uniform 100000;
            gamma 1.4;
            rho rho;
            psi none;
problem: physically incorrect situation with reaching high pressure around 200000 return of outside pressure(100000).
3)p:fixedValue T and U:zeroGradient
Code:
type fixedValue;
      value uniform 100000;
problem: physically incorrect situation with a very low temperature and divergence due to e value.
4)p:fixedValue T:fixedValue U:zeroGradient
T:
Code:
type fixedValue;
      value uniform 288;
p:
Code:
type fixedValue;
      value uniform 100000;
problem:like above(3)
why this simple phenomenon has these difficulties?
could anyone give me any help?
thanks.

Last edited by immortality; January 25, 2013 at 06:34.
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Old   January 25, 2013, 02:11
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any guidance or idea?just a small tube with higher pressure fluid than outside.what's wrong with the modelling?what BC is appropriate? can be linear schemes unstable?
Any thought is appreciated.
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Old   January 25, 2013, 07:48
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fvSchemes:
Code:
fluxScheme      Kurganov;

ddtSchemes
{
    default         Euler;
    ddt(rho)        Euler;
    ddt(rhoU)       Euler;
    ddt(rhoE)       Euler;
    ddt(rho,U)      Euler;
    ddt(rho,e)      Euler; 
    ddt(rho,omega)  Euler;
    ddt(rho,k)      Euler;
}

gradSchemes
{
    default         none;
    grad(U) Gauss linear;
    grad(rho) Gauss linear;
    grad(rhoU) Gauss linear;
    grad((1|psi)) Gauss linear;
    grad(e) Gauss linear;
    grad(sqrt(((Cp|Cv)*(1|psi)))) Gauss linear;
   // grad(c) Gauss linear;
    grad(T) Gauss linear;
    grad(omega) Gauss linear;
    grad(k) Gauss linear; 
}

divSchemes
{
    default none;
    div(tauMC) Gauss linear;

    div(phi) Gauss linear;
    div(phi,omega) Gauss linear;
    div(phi,k) Gauss linear;
    //div(phiEp) Gauss linaer;
    //div(phiUp) Gauss linear;
    //div(sigmaDotU) Gauss linear;
}

laplacianSchemes
{
    default         none;
    laplacian(muEff,U) Gauss linear corrected;
    laplacian(alphaEff,e) Gauss linear corrected;
    laplacian(alpha,e) Gauss linear corrected;
    laplacian(k,T) Gauss linear corrected;
    laplacian(DepsilonEff,omega) Gauss linear corrected;
    laplacian(DkEff,k) Gauss linear corrected;
    laplacian(DomegaEff,omega) Gauss linear corrected;
}

interpolationSchemes
{
    default none;
    reconstruct(rho) vanLeer;
    reconstruct(U) vanLeerV;
    reconstruct(T) vanLeer;

    interpolate(rho) linear;
    interpolate(U) linear;
    //interpolate(T) linear;
    //interpolate(e) linear;
    //interpolate(c) linear;
    interpolate(rhoU) linear;
    //interpolate(rPsi) linear;
    interpolate(muEff) linear;
    interpolate(tauMC) linear;
}

snGradSchemes
{
    default none;

    snGrad(U) corrected;

}
fvSolution:
Code:
solvers
{
    "(rho|rhoU|rhoE)"
    {
        solver          diagonal;
    }

    U
    {
        solver          smoothSolver;
        smoother        DICGaussSeidel;
        nSweeps         4;
        tolerance       1e-11;
        relTol          0;
        maxIter        2000;
    }

    h
    {
        $U;
        tolerance       1e-12;
        relTol          0;
        maxIter         2000;
    }

   e
   {
   $U;
   tolerance 1e-12;
   relTol 0;
   maxIter 5000;
   }

   "(k|omega)"
   {
   solver smoothSolver;
   smoother GaussSeidel;
   nSweeps 3;
   tolerance 1e-11;
   relTol 0;
   maxIter         2000;
   }
}
I have attached files of my case:
Attached Files
File Type: gz scavenging_1.tar.gz (5.1 KB, 0 views)
File Type: gz scavenging_2.tar.gz (5.0 KB, 0 views)
File Type: gz scavenging_3-p.tar.gz (5.0 KB, 0 views)
File Type: gz scavenging_3-p_InletOutlet.tar.gz (5.0 KB, 0 views)
File Type: gz scavenging_3_p_T.tar.gz (5.0 KB, 0 views)
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Old   January 25, 2013, 20:10
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does someone know any experiment result of pressures at a scavenging process of a suddenly opened tube to surroundings?
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