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-   -   Very high courant number, time step continuity errors and bounding epsilon (http://www.cfd-online.com/Forums/openfoam-solving/86211-very-high-courant-number-time-step-continuity-errors-bounding-epsilon.html)

erncyc March 17, 2011 03:33

Very high courant number, time step continuity errors and bounding epsilon
 
1 Attachment(s)
Hi all,

I am simulating flow in a double cylinder on cone cyclone and so far the iterations are wildly diverging. I am getting very high courant number, time step continuity errors and bounding epsilon. I don't know whether this is problem with my BC's. My mesh has over 600,000 cells. The flow is turbulent and I am applying the LaunderGibson turbulent model (RSM) given that the flow is strongly 3-dimensional. The checkMesh result is shown below. I have also included below the contents of the fvSchemes and fvSolution. Also attached is the BC's file for the 0 time folder. Please help thanks.


/*---------------------------------------------------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.7.x |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
Build : 1.7.x-131caa989cd3
Exec : checkMesh
Date : Mar 17 2011
Time : 10:18:11
Host : ernest-desktop
PID : 18833
Case : /home/ernest/OpenFOAM-1.7.1/novel-cyc-scaled/test2-dense
nProcs : 1
SigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
points: 116586
faces: 1253437
internal faces: 1203775
cells: 614303
boundary patches: 7
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 0
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 614303
polyhedra: 0

Checking topology...
Boundary definition OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
Patch Faces Points Surface topology
inlet1 284 167 ok (non-closed singly connected)
inlet2 485 291 ok (non-closed singly connected)
inlet3 259 148 ok (non-closed singly connected)
outlet1 208 124 ok (non-closed singly connected)
outlet2 312 176 ok (non-closed singly connected)
outlet3 173 105 ok (non-closed singly connected)
wall 47941 24117 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-0.61425 -0.61425 0) (0.61425 1.28388 3.04395)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (8.23856e-20 1.03745e-19 -1.27393e-19) OK.
Max cell openness = 1.70191e-16 OK.
Max aspect ratio = 8.32182 OK.
Minumum face area = 5.8284e-06. Maximum face area = 0.00236657. Face area magnitudes OK.
Min volume = 8.02989e-09. Max volume = 3.07651e-05. Total volume = 2.27731. Cell volumes OK.
Mesh non-orthogonality Max: 54.2817 average: 15.0228
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 0.742671 OK.

Mesh OK.



/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.7.1 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
default steadyState;
}

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

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

laplacianSchemes
{
default none;
laplacian(nuEff,U) Gauss linear limited 0.333; //Gauss linear corrected;
laplacian((1|A(U)),p) Gauss linear limited 0.333; //Gauss upwind corrected;
laplacian(DkEff,k) Gauss linear limited 0.333; //Gauss upwind corrected;
laplacian(DepsilonEff,epsilon) Gauss linear limited 0.333; //Gauss upwind corrected;
laplacian(DREff,R) Gauss linear limited 0.333; //Gauss upwind corrected;
laplacian(DnuTildaEff,nuTilda) Gauss linear limited 0.333; //Gauss upwind corrected;
}

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

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p ;
}


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


/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.7.1 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
p
{
solver PCG;
preconditioner DIC;
tolerance 1e-06;
relTol 0.01;
}


pFinal
{
solver PCG;
preconditioner DIC;
tolerance 1e-06;
relTol 0.01;
}

U
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}

k
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}

epsilon
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}

R
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}

nuTilda
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}
}

/*SIMPLE
{
nNonOrthogonalCorrectors 5;
}*/

PISO
{
nNonOrthogonalCorrectors 5;
nCorrectors 5;
}

relaxationFactors
{
p 0.3;
U 0.5;
k 0.1;
epsilon 0.1;
R 0.3;
nuTilda 0.3;
}


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

McCarra March 24, 2011 12:00

Try reducing the timestep (deltaT in system/controlDict) and see if the divergence takes place later in the simulation. If it does so, reduce the timestep until there is no divergence.

If it does not work reducing the time step, reduce the velocity of the fluid if it is possible.

Good luck


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