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-   -   courant number explodes with pisoFoam solver (http://www.cfd-online.com/Forums/openfoam-solving/95137-courant-number-explodes-pisofoam-solver.html)

tol24 December 7, 2011 08:23

courant number explodes with pisoFoam solver
 
2 Attachment(s)
Hi,

I'm trying to simulate the unsteady flow arround a cylinder with a velocity inlet of 17 m/s. I'm using a pisoFoam solver with a RAS kEpsilon turbulent model. When I run the simulation the courant numbre explodes.

Time = 5e-05

Courant Number mean: 4.53303e+07 max: 1.0204e+12
DILUPBiCG: Solving for Ux, Initial residual = 0.985101, Final residual = 9.2599e-06, No Iterations 389
DILUPBiCG: Solving for Uy, Initial residual = 0.735666, Final residual = 0.188579, No Iterations 1001
DICPCG: Solving for p, Initial residual = 1, Final residual = 12.4404, No Iterations 1001
time step continuity errors : sum local = 4.28628e+29, global = -1.82086e+27, cumulative = -1.82086e+27
DICPCG: Solving for p, Initial residual = 0.582249, Final residual = 18.1122, No Iterations 1001
time step continuity errors : sum local = 2.2474e+41, global = -6.08311e+32, cumulative = -6.08312e+32
DICPCG: Solving for p, Initial residual = 0.940306, Final residual = 3.70065, No Iterations 1001
time step continuity errors : sum local = 1.08796e+43, global = 1.37468e+36, cumulative = 1.37407e+36
#0 Foam::error::printStack(Foam::Ostream&) in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/lib/libOpenFOAM.so"
#1 Foam::sigFpe::sigHandler(int) in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/lib/libOpenFOAM.so"
#2 __restore_rt at sigaction.c:0
#3 Foam::LimitedScheme<double, Foam::limitedLinearLimiter<Foam::NVDTVD>, Foam::limitFuncs::magSqr>::limiter(Foam::Geometric Field<double, Foam::fvPatchField, Foam::volMesh> const&) const in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/lib/libfiniteVolume.so"
#4 Foam::limitedSurfaceInterpolationScheme<double>::w eights(Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) const in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/lib/libfiniteVolume.so"
#5 Foam::fv::gaussConvectionScheme<double>::fvmDiv(Fo am::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) const in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/lib/libfiniteVolume.so"
#6 Foam::tmp<Foam::fvMatrix<double> > Foam::fvm::div<double>(Foam::GeometricField<double , Foam::fvsPatchField, Foam::surfaceMesh> const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&, Foam::word const&) in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/lib/libincompressibleRASModels.so"
#7 Foam::tmp<Foam::fvMatrix<double> > Foam::fvm::div<double>(Foam::GeometricField<double , Foam::fvsPatchField, Foam::surfaceMesh> const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/lib/libincompressibleRASModels.so"
#8 Foam::incompressible::RASModels::kEpsilon::correct () in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/lib/libincompressibleRASModels.so"
#9 main in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/bin/pisoFoam"
#10 __libc_start_main in "/lib64/libc.so.6"
#11 Foam::UOPstream::write(char) in "/apl/OpenFOAM/OpenFOAM-2.0.0/platforms/linux64Gcc45DPOpt/bin/pisoFoam"
Floating exception


I've tried to decrease the deltaT but it doesn't work. I also changed the nNonOrthogonalCorrectors and the ddtSchemes

If I run the simulation without a turbulent model it works.

I tried to modify the boundaryField but i cannot find out the problem. I'm just learning to use openfoam so it may be a basic problem that i cannot see.

I couldn't upload the geometry files since it's too large.

Thanks for your help

Best regards

kumar December 8, 2011 04:53

HI ,
Just a suggestion run a checkMesh and see if your aspect ratio and Non-orthogonality checks are ok.

It may also be caused due to the non-appropriate boundary conditions. So if you give some details about the boundary conditions.

May be some one can help.

regards
K.SUresh kumar

robbirobocop December 8, 2011 05:32

@kumar: He attached his case in a .zip file ;)

@tol24:
By having a quick look at your files I assume that your BC's for the symmetryPlane are wrong. The wallfunctions might not be the problem. But having a look at your "U" file you can see that you assigned 17 m/s on your symmetryPlane. So even if you treat your symmetryPlane like a wall this is not correct!

If the "fix(es)" don't help maybe you should give simpleFoam a try.

tol24 December 9, 2011 07:57

Thanks, for helping!

@kumar: I did check mesh and it was ok

@robbirobocop: yes, I thought it could be that, but actually I want to simulate the cylinder in a freestream and not between two walls. How could I do that?
If I fix the velocity to zero it will generate a boundary layer arround the limits, doesn't it?

mxylondon August 19, 2013 04:19

I have the nearly exactly same trouble now.


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