CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

realizableKE hanging and then exploding

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   April 19, 2011, 01:49
Default realizableKE hanging and then exploding
  #1
Senior Member
 
Join Date: Feb 2010
Posts: 213
Rep Power: 8
vaina74 is on a distinguished road
Hi foamers,

I have some problems with the k-epsilon realizable turbulent model. I already used it for other cases without troubles, so I'm not able to understand what's wrong or what I can improve.

The simulation starts bad, hanging for several minutes, but then it seems to run:
Code:
Time = 1

smoothSolver:  Solving for Ux, Initial residual = 0.470174, Final residual = 0.00400859, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 1, Final residual = 0.00600497, No Iterations 4
smoothSolver:  Solving for Uz, Initial residual = 1, Final residual = 0.00335194, No Iterations 4
GAMG:  Solving for p, Initial residual = 1, Final residual = 2.767, No Iterations 1000
time step continuity errors : sum local = 0.00166243, global = 9.18302e-06, cumulative = 9.18302e-06
smoothSolver:  Solving for epsilon, Initial residual = 0.000497916, Final residual = 1.88216e-06, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 1, Final residual = 0.00867952, No Iterations 4
ExecutionTime = 751.02 s  ClockTime = 751 s
Anyway, after some hundreds iterations, the computation explode:
Code:
Time = 398

smoothSolver:  Solving for Ux, Initial residual = 0.288734, Final residual = 0.000692462, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.288723, Final residual = 0.00069192, No Iterations 4
smoothSolver:  Solving for Uz, Initial residual = 0.288259, Final residual = 0.000668387, No Iterations 4
GAMG:  Solving for p, Initial residual = 2.92554e-10, Final residual = 2.92554e-10, No Iterations 0
time step continuity errors : sum local = 5.31272e+87, global = -2.8754e+74, cumulative = -1.25563e+76
smoothSolver:  Solving for epsilon, Initial residual = 0.0914353, Final residual = 8.60873e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 6.30816e-14, Final residual = 6.30816e-14, No Iterations 0
ExecutionTime = 7035.03 s  ClockTime = 7035 s

GGI pair (stitch_in, stitch_out) : 1.71408e+78 1.71091e+78 Diff = 7.54614e+74 or 0.0440244 %
Cyclic GGI pair (cyclic_1, cyclic_2) : 9.55415e+76 9.5507e+76 Diff = -1.62343e+73 or 0.0169919 %
Cyclic GGI pair (symmetry_1, symmetry_2) : 6.86082e+76 6.86082e+76 Diff = 1.06058e+62 or 1.54585e-13 %
I think I can edit something in fvSolution (or fvSchemes?), but I don't know how. Any suggestion? I report both files.

fvSolution
Code:
solvers
{
    p GAMG
    {
        tolerance             1e-8;
        relTol                0.01;
        smoother              GaussSeidel;
        cacheAgglomeration    true;
        nCellsInCoarsestLevel 20;
        agglomerator          faceAreaPair;
        mergeLevels           1;
    };

    U smoothSolver
    {
        smoother              GaussSeidel;
        nSweeps               2;
        tolerance             1e-7;
        relTol                0.01;
    };

    k smoothSolver
    {
        smoother              GaussSeidel;
        nSweeps               2;
        tolerance             1e-7;
        relTol                0.01;
    };

    epsilon smoothSolver
    {
        smoother              GaussSeidel;
        nSweeps               2;
        tolerance             1e-7;
        relTol                0.01;
    };
}

SIMPLE
{
    nNonOrthogonalCorrectors  0;
    pRefCell                  0;
    pRefValue                 0;
}

relaxationFactors
{
    p                 	      0.3;
    U               	      0.5;
    k                         0.5;
    epsilon                   0.5;
}
fvSchemes
Code:
ddtSchemes
{
    default                       steadyState;
}

gradSchemes
{
    default                       faceMDLimited Gauss linear 0.5;
}

divSchemes
{
    default                       none;
    div(phi,U)                    Gauss GammaV 0.2;
    div(phi,k)                    Gauss upwind;
    div(phi,epsilon)              Gauss upwind;
    div(phi,tau)                  Gauss limitedLinear 1;
    div(phi,omega)                Gauss upwind;
    div(phi,nuTilda)              Gauss limitedLinear 1;
    div((nuEff*dev(grad(U).T()))) Gauss linear;
}

laplacianSchemes
{
    default                       Gauss linear limited 0.5;
    laplacian(DomegaEff,omega)    Gauss linear limited 0.33;
//    laplacian(DepsilonEff,epsilon) Gauss linear corrected;
}

interpolationSchemes
{
    default                       linear;
}

snGradSchemes
{
    default                       limited 0.6;
}

fluxRequired
{
    default                       no;
    p;
}
vaina74 is offline   Reply With Quote

Old   April 19, 2011, 05:48
Default
  #2
Senior Member
 
stephane sanchi
Join Date: Mar 2009
Posts: 300
Rep Power: 9
openfoam_user is on a distinguished road
Hi,

I have used realizableKE turbulence model for external aerodynamics with the following settings.

fvSchemes:

ddtSchemes
{
default steadyState;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
grad(U) Gauss linear;
}

divSchemes
{
default none;
div(phi,U) Gauss SFCD;
div(phi,k) Gauss SFCD;
div(phi,epsilon) Gauss SFCD;
div((nuEff*dev(grad(U).T()))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
interpolate(U) linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p;
}

fvSolution:
solvers
{
p
{
solver GAMG;
tolerance 1e-7;
relTol 0.1;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration on;
agglomerator faceAreaPair;
nCellsInCoarsestLevel 10;
mergeLevels 1;
};

U
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-5;
relTol 0.1;
};

k
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-5;
relTol 0.1;
};

epsilon
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-5;
relTol 0.1;
};
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
}

relaxationFactors
{
p 0.3;
U 0.7;
k 0.7;
epsilon 0.7;
}

Best regards,

Stephane.
openfoam_user is offline   Reply With Quote

Old   April 20, 2011, 05:45
Default
  #3
Senior Member
 
Join Date: Feb 2010
Posts: 213
Rep Power: 8
vaina74 is on a distinguished road
Thank you very much for your help, I'll try to test your fvSolution file.
vaina74 is offline   Reply With Quote

Old   May 2, 2011, 09:00
Default
  #4
Senior Member
 
Join Date: Feb 2010
Posts: 213
Rep Power: 8
vaina74 is on a distinguished road
I also tried the fvSchemes and fvSolution settings suggested by Stephane, but I still have bounding epsilon problems - I can see epsilon and evaluated forces getting higher and higher.
Can you explain that? I already used k-epsilon realizable turbulent model without such problems, does it depend on the geometry? I tried to change relaxion factors till 0.2 without success (values get a little lower but always too big). What could I improve in my fvSolution and fvSchemes files?
Thanks for your help, regards.
vaina74 is offline   Reply With Quote

Old   January 10, 2013, 09:54
Default realizableKE problem with OF1.71
  #5
New Member
 
Zinedine
Join Date: Sep 2010
Posts: 11
Rep Power: 6
Zinedine is on a distinguished road
Hi
I am trying to use Rke turbulence model in a case which runs OK
using standard ke.
Am I missing something when using Rke ?
Has anybody has an example of what needs to be initialise when using Rke please ?
When using ke I initialise k,e,R using standard tools as explained ijn OF user guide etc ?
Do I need to add something elsewhen using Rke please ?

Thanks for your help


Regards

Z.
Zinedine is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 20:45.