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Old   March 1, 2010, 11:53
Default simpleFoam with Launder-Sharma Model
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June
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Hello everyone,
I'm a new user with openfoam. Now i want to use simpleFoam with Launder-Sharma Low-Re Model. There's only one time step calculated. Then a erro as below is displayed.

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

Create mesh for time = 0

Reading field p

Reading field U

Reading/calculating face flux field phi

Selecting incompressible transport model Newtonian
Selecting RAS turbulence model LaunderSharmaKE
LaunderSharmaKECoeffs
{
Cmu 0.09;
C1 1.44;
C2 1.92;
sigmaEps 1.3;
}


Starting time loop

Time = 0.1

DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 0.0606568, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.995352, Final residual = 0.0222388, No Iterations 1
DICPCG: Solving for p, Initial residual = 1, Final residual = 0.00735996, No Iterations 6
DICPCG: Solving for p, Initial residual = 0.00365507, Final residual = 3.33199e-05, No Iterations 63
DICPCG: Solving for p, Initial residual = 2.37913e-05, Final residual = 8.92903e-07, No Iterations 30
time step continuity errors : sum local = 4.57548e-05, global = -4.42317e-06, cumulative = -4.42317e-06
#0 Foam::error:rintStack(Foam::Ostream&) in "/usr/local/OpenFOAM/1.6/lib/linux64GccDPOpt/libOpenFOAM.so"
#1 Foam::sigFpe::sigFpeHandler(int) in "/usr/local/OpenFOAM/1.6/lib/linux64GccDPOpt/libOpenFOAM.so"
#2 __restore_rt at sigaction.c:0
#3 Foam::divide(Foam::Field<double>&, Foam::UList<double> const&, Foam::UList<double> const&) in "/usr/local/OpenFOAM/1.6/lib/li
#4 void Foam::divide<Foam::fvPatchField, Foam::volMesh>(Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh>&, Foam::sh> const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) in "/usr/local/OpenFOAM/1.6/lib/linux64GccDPO
#5 Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam:perator/<Foam::fvPatchField, Foam::volMeshField, Foam::volMesh> > const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) in "/usr/local/OpenFOAM/1
#6 Foam::incompressible::RASModels::LaunderSharmaKE:: correct() in "/usr/local/OpenFOAM/1.6/lib/linux64GccDPOpt/libincompressible
#7 main in "/usr/local/OpenFOAM/1.6/applications/bin/linux64GccDPOpt/simpleFoam"
#8 __libc_start_main in "/lib64/libc.so.6"
#9 _start at /usr/src/packages/BUILD/glibc-2.9/csu/../sysdeps/x86_64/elf/start.S:116
Floating exception


I cann't get any useful information from the erro.
The p, U, k, nut, epsilon are gaven as boundary condition.
My question is, can simpleFoam be used with LS Model or did I do something wrong?
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Old   March 2, 2010, 04:07
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Hi,

simpleFoam is able to use LaunderSharma,

look at following posting:
low reynolds re turbulence boundary and yPlus values

You must be careful with your inlet bc's for k and epsilon.

Regards Thomas
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Old   March 2, 2010, 08:23
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Hi Thomas,
Thanks for the reply.
why cannot i set the k and epsilon not equal 0 for the boundary condition at wall? That was the problem of me.
Regards Yang

Last edited by examosty; March 2, 2010 at 12:07.
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Old   March 3, 2010, 03:35
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I think you are not allowed to divide through zero.
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Old   March 3, 2010, 03:47
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Quote:
Originally Posted by examosty View Post
Hi Thomas,
Thanks for the reply.
why cannot i set the k and epsilon not equal 0 for the boundary condition at wall? That was the problem of me.
Regards Yang
Hi Examosty,

why would you set non-zero values at solid walls for k and epsilon? Launder-Sharma turbulence model is so called "low reynolds number" closure ad its damping function, values of constants, etc. are derived on the basis of zero values for k and epsilon (at solid walls)!

I really suggest that you grab your hands on the following book David C. Wilcox, Turbulence Modelling For CFD

Cheers,
Primoz
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Old   March 3, 2010, 07:16
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Quote:
Originally Posted by ternik View Post
Hi Examosty,

why would you set non-zero values at solid walls for k and epsilon? Launder-Sharma turbulence model is so called "low reynolds number" closure ad its damping function, values of constants, etc. are derived on the basis of zero values for k and epsilon (at solid walls)!

I really suggest that you grab your hands on the following book David C. Wilcox, Turbulence Modelling For CFD

Cheers,
Primoz
Hi Primoz,
that's what i thought and what i did, set k and epsilon at solid wall equal 0. Then the error as i've replayed in the beginning occurred. As Thomas said, it's a problem of dividing through zero.
Regards,
June
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Old   March 3, 2010, 08:01
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Quote:
Originally Posted by examosty View Post
Hi Primoz,
that's what i thought and what i did, set k and epsilon at solid wall equal 0. Then the error as i've replayed in the beginning occurred. As Thomas said, it's a problem of dividing through zero.
Regards,
June
now I am getting the point! I do not know exactly how the Launder-Shrama is incorporated in OpenFoam, but "the general" theory for solid wall behaviour is (at lest I think so):
  • since there are no velocity fluctuations in a near wall region (viscous forces are predominant) the turbulence kinetic energy is 0 at solid wall
  • for dissipation of turbulence kinetic energy "low Re" closures solves "modified" equation for epsilon
epsilon_mod=epsilon-D
  • so actually, you are prescribing boundary conditions for "modified epsilon", which is zero at solid wall
Hope this helps,
Primoz
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