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immortality January 24, 2013 18:38

suitable boundary condition for scavenging process?
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

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

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

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

type fixedValue;
      value uniform 288;


type fixedValue;
      value uniform 100000;

problem:like above(3)
why this simple phenomenon has these difficulties?
could anyone give me any help?

immortality January 25, 2013 02:11

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.

immortality January 25, 2013 07:48

5 Attachment(s)

fluxScheme      Kurganov;

    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;

    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;

    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;

    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;

    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;

    default none;

    snGrad(U) corrected;



        solver          diagonal;

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

        tolerance      1e-12;
        relTol          0;
        maxIter        2000;

  tolerance 1e-12;
  relTol 0;
  maxIter 5000;

  solver smoothSolver;
  smoother GaussSeidel;
  nSweeps 3;
  tolerance 1e-11;
  relTol 0;
  maxIter        2000;

I have attached files of my case:

immortality January 25, 2013 20:10

does someone know any experiment result of pressures at a scavenging process of a suddenly opened tube to surroundings?

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