sven 
August 6, 2009 20:33 
Problems with Courant number (LaunderGibsonTurbulence Model)
Hey,
I am calculating a turbulent channel flow using the LaunderGibsonRSTM Model to account for turbulence. After starting the calculation with the "turbFoam" solver, everything seems to be normal, but after some time or iterations, respectively, my courant number suddenly starts to explode within a few itertations. This can be seen by having a look at the log file:
Code:
Time = 0.0875
Courant Number mean: 9122.99 max: 4.06223e+07
DILUPBiCG: Solving for Ux, Initial residual = 0.00407551, Final residual = 1.89596, No Iterations 1001
DILUPBiCG: Solving for Uy, Initial residual = 0.03075, Final residual = 11.7948, No Iterations 1001
DICPCG: Solving for p, Initial residual = 0.998609, Final residual = 3.99957, No Iterations 1001
time step continuity errors : sum local = 1.61145e+17, global = 1.30081e+07, cumulative = 1.30081e+07
DICPCG: Solving for p, Initial residual = 0.988565, Final residual = 0.0414409, No Iterations 1001
time step continuity errors : sum local = 5.72657e+17, global = 1.74464e+10, cumulative = 1.74595e+10
DILUPBiCG: Solving for epsilon, Initial residual = 1, Final residual = 1.47062, No Iterations 1001
bounding epsilon, min: 3.17508e+37 max: 4.88268e+29 average: 1.58754e+33
DILUPBiCG: Solving for Rxx, Initial residual = 2.48129e11, Final residual = 2.48129e11, No Iterations 0
DILUPBiCG: Solving for Rxy, Initial residual = 0.90075, Final residual = 3.6413e13, No Iterations 1
DILUPBiCG: Solving for Ryy, Initial residual = 4.78801e10, Final residual = 4.78801e10, No Iterations 0
DILUPBiCG: Solving for Rzz, Initial residual = 1.18566e10, Final residual = 1.18566e10, No Iterations 0
ExecutionTime = 219.83 s ClockTime = 229 s
Time = 0.088
Courant Number mean: 4.40528e+18 max: 1.49104e+21
DILUPBiCG: Solving for Ux, Initial residual = 0.999991, Final residual = 2.18406, No Iterations 1001
DILUPBiCG: Solving for Uy, Initial residual = 0.999902, Final residual = 0.431004, No Iterations 1001
DICPCG: Solving for p, Initial residual = 1, Final residual = 428.858, No Iterations 1001
time step continuity errors : sum local = 3.71337e+39, global = 6.60944e+30, cumulative = 6.60944e+30
DICPCG: Solving for p, Initial residual = 0.99985, Final residual = 6.04153e07, No Iterations 6
time step continuity errors : sum local = 2.58801e+44, global = 6.17492e+31, cumulative = 5.51398e+31
DILUPBiCG: Solving for epsilon, Initial residual = 3.69884e06, Final residual = 3.69884e06, No Iterations 0
bounding epsilon, min: 1.82392e20 max: 4.88268e+29 average: 2.5136e+25
DILUPBiCG: Solving for Rxx, Initial residual = 0.65553, Final residual = 5.73954e06, No Iterations 27
DILUPBiCG: Solving for Rxy, Initial residual = 0.578075, Final residual = 3.79017e06, No Iterations 7
DILUPBiCG: Solving for Ryy, Initial residual = 0.99998, Final residual = 2.08634e06, No Iterations 7
DILUPBiCG: Solving for Rzz, Initial residual = 0.983104, Final residual = 2.01267e06, No Iterations 27
ExecutionTime = 228.81 s ClockTime = 238 s
Time = 0.0885
Courant Number mean: 1.25453e+44 max: 1.21128e+48
DILUPBiCG: Solving for Ux, Initial residual = 0.995264, Final residual = 0.995264, No Iterations 1001
DILUPBiCG: Solving for Uy, Initial residual = 0.998526, Final residual = 58.4614, No Iterations 1001
DICPCG: Solving for p, Initial residual = 1, Final residual = 8.85047, No Iterations 1001
time step continuity errors : sum local = 1.2145e+82, global = 1.27702e+64, cumulative = 1.27702e+64
DICPCG: Solving for p, Initial residual = 1, Final residual = 6.97309e16, No Iterations 2
time step continuity errors : sum local = 1.99448e+90, global = 1.40764e+72, cumulative = 1.40764e+72
As long as I can judge this, it is because of the epsilon. The line with bounding epsilon only appears in the last few iterations before the Courant number explodes. At this moment the solver also stops displaying these error messages:
Code:
#0 Foam::error::printStack(Foam::Ostream&) in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libOpenFOAM.so"
#1 Foam::sigFpe::sigFpeHandler(int) in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libOpenFOAM.so"
#2 Uninterpreted: [0xb802b400]
#3 Foam::DILUPreconditioner::calcReciprocalD(Foam::Field<double>&, Foam::lduMatrix const&) in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libOpenFOAM.so"
#4 Foam::DILUPreconditioner::DILUPreconditioner(Foam::lduMatrix::solver const&, Foam::Istream&) in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libOpenFOAM.so"
#5 Foam::lduMatrix::preconditioner::addasymMatrixConstructorToTable<Foam::DILUPreconditioner>::New(Foam::lduMatrix::solver const&, Foam::Istream&) in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libOpenFOAM.so"
#6 Foam::lduMatrix::preconditioner::New(Foam::lduMatrix::solver const&, Foam::Istream&) in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libOpenFOAM.so"
#7 Foam::PBiCG::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libOpenFOAM.so"
#8 Foam::fvMatrix<double>::solve(Foam::Istream&) in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libfiniteVolume.so"
#9 Foam::lduMatrix::solverPerformance Foam::solve<double>(Foam::tmp<Foam::fvMatrix<double> > const&) in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libincompressibleRASModels.so"
#10 Foam::incompressible::RASModels::LaunderGibsonModified::correct() in "/home/sven/OpenFOAM/OpenFOAM1.5/lib/linuxGccDPOpt/libincompressibleRASModels.so"
#11 main in "/home/sven/OpenFOAM/OpenFOAM1.5/applications/bin/linuxGccDPOpt/turbFoam"
#12 __libc_start_main in "/lib/tls/i686/cmov/libc.so.6"
#13 _start in "/home/sven/OpenFOAM/OpenFOAM1.5/applications/bin/linuxGccDPOpt/turbFoam"
zsh: floating point exception turbFoam > log
turbFoam > log 230,31s user 7,14s system 96% cpu 4:07,20 total
I already tried to decrease the time step and tried different values for epsilon, but none of it helps in any way. Does anyone has an idea what else could cause the Courant number to explode?? Thanks a lot!
