| callumso |
September 30, 2013 10:24 |
Omega goes infinity
Hi dear foamers,
I am running simulations for a complex geometry, mesh size around 5 million. I use k-omega SST model and wall function. From the residuals it seems all the equations converge all right. But omega is just always extremely large and goes to infinity in the orifice where mixing of flow occurs and is of interest. Consequently k goes to almost zero in this region where turbulence should be really high. Strangely even omega equation seems to converge.
Have anyone encountered something like this? below is the boundary condition I used for k and omega:
Code:
dimensions [0 2 -2 0 0 0 0];
internalField uniform 0.00027;
boundaryField
{
PILOT
{
type compressible::kqRWallFunction;
value uniform 0.00027;
}
PLENUM
{
type zeroGradient;
}
INLET
{
type fixedValue;
value uniform 0.00027;
}
OUTLET
{
type zeroGradient;
}
DUCT
{
type compressible::kqRWallFunction;
value uniform 0.00027;
}
VANES
{
type compressible::kqRWallFunction;
value uniform 0.00027;
}
PASSAGE
{
type compressible::kqRWallFunction;
value uniform 0.00027;
}
BELLMOUTH
{
type compressible::kqRWallFunction;
value uniform 0.00027;
}
}
Code:
dimensions [0 0 -1 0 0 0 0];
internalField uniform 2.6;
boundaryField
{
PILOT
{
type compressible::omegaWallFunction;
Cmu 0.09;
kappa 0.41;
E 9.8;
value uniform 0.00027;
}
PLENUM
{
type zeroGradient;
}
INLET
{
type fixedValue;
value uniform 0.1813;
}
OUTLET
{
type zeroGradient;
}
DUCT
{
type compressible::omegaWallFunction;
Cmu 0.09;
kappa 0.41;
E 9.8;
value uniform 0.00027;
}
VANES
{
type compressible::omegaWallFunction;
Cmu 0.09;
kappa 0.41;
E 9.8;
value uniform 0.00027;
}
PASSAGE
{
type compressible::omegaWallFunction;
Cmu 0.09;
kappa 0.41;
E 9.8;
value uniform 0.00027;
}
BELLMOUTH
{
type compressible::omegaWallFunction;
Cmu 0.09;
kappa 0.41;
E 9.8;
value uniform 0.00027;
}
}
The numerical schems look like below:
Code:
ddtSchemes
{
default Euler;
}
gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
}
divSchemes
{
default none;
div(phi,U) Gauss limitedLinearV 1;
div(phid,p) Gauss limitedLinear 1;
div(phi,K) Gauss linear;
div(phi,h) Gauss upwind;
div(phi,k) Gauss limitedLinear 1;
div(phi,epsilon) Gauss limitedLinear 1;
div(phi,R) Gauss upwind;
div(phi,omega) Gauss limitedLinear 1;
div((rho*R)) Gauss linear;
div(R) Gauss linear;
div(U) Gauss linear;
div((muEff*dev2(T(grad(U))))) Gauss linear;
}
laplacianSchemes
{
default none;
laplacian(muEff,U) Gauss linear corrected;
laplacian(mut,U) Gauss linear corrected;
laplacian(DkEff,k) Gauss linear corrected;
laplacian(DepsilonEff,epsilon) Gauss linear corrected;
laplacian(DREff,R) Gauss linear corrected;
laplacian(DomegaEff,omega) Gauss linear corrected;
laplacian((rho*(1|A(U))),p) Gauss linear corrected;
laplacian(alphaEff,h) Gauss linear corrected;
}
interpolationSchemes
{
default linear;
}
snGradSchemes
{
default corrected;
}
fluxRequired
{
default no;
p ;
}
Code:
solvers
{
p
{
solver PCG;
preconditioner DIC;
tolerance 1e-08;
relTol 0.01;
}
pFinal
{
$p;
tolerance 1e-08;
relTol 0;
}
"(rho|U|h|k|epsilon|omega)"
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-08;
relTol 0.01;
}
"(rho|U|h|k|epsilon|omega)Final"
{
$U;
tolerance 1e-08;
relTol 0;
}
}
PIMPLE
{
momentumPredictor yes;
nOuterCorrectors 4;
nCorrectors 2;
nNonOrthogonalCorrectors 1;
rhoMin rhoMin [ 1 -3 0 0 0 ] 0.5;
rhoMax rhoMax [ 1 -3 0 0 0 ] 2.0;
residualControl
{
"(U|k|epsilon)"
{
relTol 0;
tolerance 0.000001;
}
}
}
relaxationFactors
{
fields
{
"p.*" 0.7;
"rho.*" 0.9;
}
equations
{
"(U|h|k|epsilon|omega).*" 0.7;
}
}
I fiddled with the numerical scheme a bit (e.g. use upwind scheme, use very low relaxation factors, etc). But nothing changed. I am still getting this weird infinite omega. Below is the residual trace:
Quote:
Courant Number mean: 0.002384836 max: 10.06362
deltaT = 4.105397e-05
Time = 0.001018885
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
PIMPLE: iteration 1
DILUPBiCG: Solving for Ux, Initial residual = 0.009422393, Final residual = 1.336213e-08, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.005013185, Final residual = 1.673009e-06, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.004954721, Final residual = 1.658077e-06, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 0.008704607, Final residual = 1.068494e-08, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.02191301, Final residual = 8.992473e-05, No Iterations 4
DICPCG: Solving for p, Initial residual = 0.0001136703, Final residual = 1.065346e-06, No Iterations 17
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 1.221163e-06, global = -8.451316e-07, cumulative = -0.0001596296
rho max/min : 1.193396 1.160766
DICPCG: Solving for p, Initial residual = 0.006488465, Final residual = 2.687909e-05, No Iterations 4
DICPCG: Solving for p, Initial residual = 3.438664e-05, Final residual = 3.410989e-07, No Iterations 36
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 1.218193e-06, global = -8.500729e-07, cumulative = -0.0001604797
rho max/min : 1.193396 1.160765
PIMPLE: iteration 2
DILUPBiCG: Solving for Ux, Initial residual = 0.006534682, Final residual = 9.631645e-09, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.004523631, Final residual = 6.797623e-07, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.004480604, Final residual = 6.662678e-07, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 0.009199319, Final residual = 1.208279e-08, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.008744652, Final residual = 3.671174e-05, No Iterations 4
DICPCG: Solving for p, Initial residual = 4.807335e-05, Final residual = 4.056757e-07, No Iterations 17
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 1.218818e-06, global = -8.48645e-07, cumulative = -0.0001613283
rho max/min : 1.193396 1.160793
DICPCG: Solving for p, Initial residual = 0.002611529, Final residual = 1.103145e-05, No Iterations 4
DICPCG: Solving for p, Initial residual = 1.45108e-05, Final residual = 1.270581e-07, No Iterations 42
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 1.217819e-06, global = -8.509643e-07, cumulative = -0.0001621793
rho max/min : 1.193396 1.160792
PIMPLE: iteration 3
DILUPBiCG: Solving for Ux, Initial residual = 0.004572449, Final residual = 6.991547e-09, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.003637689, Final residual = 2.368283e-07, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.003609003, Final residual = 2.530072e-07, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 0.005076553, Final residual = 6.463705e-09, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.004023061, Final residual = 1.699759e-05, No Iterations 4
DICPCG: Solving for p, Initial residual = 2.310766e-05, Final residual = 2.116908e-07, No Iterations 17
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 1.217778e-06, global = -8.498158e-07, cumulative = -0.0001630291
rho max/min : 1.193396 1.160799
DICPCG: Solving for p, Initial residual = 0.001204748, Final residual = 5.135975e-06, No Iterations 4
DICPCG: Solving for p, Initial residual = 6.987517e-06, Final residual = 6.530037e-08, No Iterations 41
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 1.217191e-06, global = -8.507411e-07, cumulative = -0.0001638799
rho max/min : 1.193396 1.160799
PIMPLE: iteration 4
DILUPBiCG: Solving for Ux, Initial residual = 0.003182333, Final residual = 5.051115e-09, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.00280553, Final residual = 2.892812e-09, No Iterations 3
DILUPBiCG: Solving for Uz, Initial residual = 0.002785603, Final residual = 2.954405e-09, No Iterations 3
DILUPBiCG: Solving for h, Initial residual = 0.00268957, Final residual = 3.386828e-09, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.00198696, Final residual = 8.607319e-06, No Iterations 4
DICPCG: Solving for p, Initial residual = 1.217912e-05, Final residual = 1.181804e-07, No Iterations 20
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 1.217629e-06, global = -8.508334e-07, cumulative = -0.0001647307
rho max/min : 1.193396 1.160801
DICPCG: Solving for p, Initial residual = 0.0005952442, Final residual = 2.607833e-06, No Iterations 4
DICPCG: Solving for p, Initial residual = 3.687937e-06, Final residual = 9.698358e-09, No Iterations 67
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 1.217111e-06, global = -8.50822e-07, cumulative = -0.0001655815
rho max/min : 1.193396 1.160801
DILUPBiCG: Solving for omega, Initial residual = 0.1111112, Final residual = 5.200637e-19, No Iterations 1
bounding omega, min: -1.173741e+38 max: 2.166221e+50 average: 8.778702e+43
DILUPBiCG: Solving for k, Initial residual = 0.048428, Final residual = 2.335364e-18, No Iterations 1
bounding k, min: -5.711563e-06 max: 0.0734092 average: 0.0005477621
PIMPLE: not converged within 4 iterations
ExecutionTime = 185.73 s ClockTime = 187 s
|
I went through some related threads but unfortunately none of the advice really helps.
I run the same case on Fluent and there is no problem at all. I tried a finer mesh, 12million cells. But it still doesn't work on OpenFOAM. Can anyone help me out with this? Thank you in advance.
Callum |
