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Old   April 6, 2011, 07:15
Default divergence problem with turbulence
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Hi,

when I solve my case with f.rx. simpleFoam with turbulence switched off there is no problem.
But as soon as I turn on turbulence there are divergence problems, propably due to a negative epsilon or k value because of bad itteration.
I also know that this problem can be solved by using methods with higher arrangement (order,... don't know how it is called. ax + c - ax˛ +bx +c) or by limiting the gradient.

How can I limit the gradient? -> In fvSolutions?
How can use methods with higher arrangement?

Does someone know?
Thanks for the answer!

Best Regards,
tH3f0rC3
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Old   April 6, 2011, 07:24
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Quote:
Originally Posted by tH3f0rC3 View Post
Hi,

when I solve my case with f.rx. simpleFoam with turbulence switched off there is no problem.
But as soon as I turn on turbulence there are divergence problems, propably due to a negative epsilon or k value because of bad itteration.
I also know that this problem can be solved by using methods with higher arrangement (order,... don't know how it is called. ax + c - ax˛ +bx +c) or by limiting the gradient.

How can I limit the gradient? -> In fvSolutions?
How can use methods with higher arrangement?

Does someone know?
Thanks for the answer!

Best Regards,
tH3f0rC3
Hi,
maybe this is a good thread where to start: pressure eq. "converges" after few time steps


mad
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Old   April 6, 2011, 08:29
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Hi maddalena,

"try lowering the tolerances of the linear solvers. Something in the order of 1e-12 might be appropriate."
Can you tell me where i can lower the tolerance? Is it in the fvSolution?

When I change in fvSolution the solver crashes (at time step 20) even earlier as before (time step 27).
Here is the error message:
Code:
Time = 18
DILUPBiCG:  Solving for Ux, Initial residual = 0.311333, Final residual = 0.0143 016, No Iterations 1
DILUPBiCG:  Solving for Uy, Initial residual = 0.184059, Final residual = 0.0120 39, No Iterations 1
DILUPBiCG:  Solving for Uz, Initial residual = 0.282154, Final residual = 0.0103 257, No Iterations 1
DICPCG:  Solving for p, Initial residual = 0.699041, Final residual = 0.0292449,  No Iterations 10
time step continuity errors : sum local = 6.17123e+12, global = -4.29599e+11, cu mulative = -1.38856e+12
DILUPBiCG:  Solving for epsilon, Initial residual = 0.0355234, Final residual = 0.00232541, No Iterations 1
bounding epsilon, min: -1.20957e+34 max: 2.38968e+38 average: 9.01526e+33
DILUPBiCG:  Solving for k, Initial residual = 0.249567, Final residual = 0.01152 8, No Iterations 1
bounding k, min: -9.14125e+25 max: 6.68445e+29 average: 6.57551e+26
ExecutionTime = 83 s  ClockTime = 84 s
Time = 19
DILUPBiCG:  Solving for Ux, Initial residual = 0.956852, Final residual = 0.0501 376, No Iterations 1
DILUPBiCG:  Solving for Uy, Initial residual = 0.99477, Final residual = 0.01063 42, No Iterations 2
DILUPBiCG:  Solving for Uz, Initial residual = 0.957249, Final residual = 0.0912 169, No Iterations 1
DICPCG:  Solving for p, Initial residual = 0.965656, Final residual = 0.0432162,  No Iterations 2
time step continuity errors : sum local = 5.79332e+53, global = 2.72507e+50, cum ulative = 2.72507e+50
DILUPBiCG:  Solving for epsilon, Initial residual = 1, Final residual = 0.005137 37, No Iterations 46
DILUPBiCG:  Solving for k, Initial residual = 2.50403e-13, Final residual = 2.50 403e-13, No Iterations 0
ExecutionTime = 87.22 s  ClockTime = 89 s
Time = 20
DILUPBiCG:  Solving for Ux, Initial residual = 0.605269, Final residual = 0.0264 482, No Iterations 1
DILUPBiCG:  Solving for Uy, Initial residual = 0.592722, Final residual = 0.0560 965, No Iterations 1
DILUPBiCG:  Solving for Uz, Initial residual = 0.598655, Final residual = 0.0273 214, No Iterations 2
DICPCG:  Solving for p, Initial residual = 0.136164, Final residual = 0.00529025 , No Iterations 2
time step continuity errors : sum local = 7.53995e+60, global = -4.89601e+50, cu mulative = -2.17093e+50
#0  Foam::error::printStack(Foam::Ostream&) in "/data/caehgb.za/studienarbeit-di rk/work/OpenFoam_ParaView/OpenFOAM/OpenFOAM-1.7.1/lib/linux64GccDPOpt/libOpenFOA M.so"
#1  Foam::sigFpe::sigFpeHandler(int) in "/data/caehgb.za/studienarbeit-dirk/work /OpenFoam_ParaView/OpenFOAM/OpenFOAM-1.7.1/lib/linux64GccDPOpt/libOpenFOAM.so"
#2  __restore_rt in "/lib64/tls/libc.so.6"
#3  Foam::PBiCG::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigne d char) const in "/data/caehgb.za/studienarbeit-dirk/work/OpenFoam_ParaView/Open FOAM/OpenFOAM-1.7.1/lib/linux64GccDPOpt/libOpenFOAM.so"
#4  Foam::fvMatrix<double>::solve(Foam::dictionary const&) in "/data/caehgb.za/s tudienarbeit-dirk/work/OpenFoam_ParaView/OpenFOAM/OpenFOAM-1.7.1/lib/linux64GccD POpt/libfiniteVolume.so"
#5  Foam::incompressible::RASModels::kEpsilon::correct() in "/data/caehgb.za/stu dienarbeit-dirk/work/OpenFoam_ParaView/OpenFOAM/OpenFOAM-1.7.1/lib/linux64GccDPO pt/libincompressibleRASModels.so"
#6  main in "/data/caehgb.za/studienarbeit-dirk/work/OpenFoam_ParaView/OpenFOAM/ OpenFOAM-1.7.1/applications/bin/linux64GccDPOpt/simpleFoam"
#7  __libc_start_main in "/lib64/tls/libc.so.6"
#8  Foam::regIOobject::writeObject(Foam::IOstream::streamFormat, Foam::IOstream: :versionNumber, Foam::IOstream::compressionType) const in "/data/caehgb.za/studi enarbeit-dirk/work/OpenFoam_ParaView/OpenFOAM/OpenFOAM-1.7.1/applications/bin/li nux64GccDPOpt/simpleFoam"
Floating point exception
Best Regards,
tH3f0rC3

Last edited by tH3f0rC3; April 6, 2011 at 08:45.
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Old   April 6, 2011, 10:00
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Quote:
Originally Posted by tH3f0rC3 View Post
time step continuity errors : sum local = 6.17123e+12, global = -4.29599e+11, cu mulative = -1.38856e+12

If you have such a big continuity error at time step 20, then your problem is on the BC probably...
check them once again.

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Old   April 6, 2011, 10:14
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Ok, I will check this.

Best Regards,
tH3f0rC3
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