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Old   April 14, 2010, 22:50
Default ScalarTransportFoam
  #1
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Senthil Kabilan
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Hi All,

I have a simple question regarding scalarTransportFoam. The code seems to be executing well, but out of the blues, the residual increases (see Time=0.08628 and Time=0.08629) and the starts to settle down. Do you think it has something to do with the way I have setup the problem?

Time = 0.08622
DILUPBiCG: Solving for T, Initial residual = 3.20318e-05, Final residual = 2.31572e-11, No Iterations 8

Time = 0.08623
DILUPBiCG: Solving for T, Initial residual = 3.20261e-05, Final residual = 1.51511e-10, No Iterations 7

Time = 0.08624
DILUPBiCG: Solving for T, Initial residual = 3.20143e-05, Final residual = 6.6284e-11, No Iterations 8

Time = 0.08625
DILUPBiCG: Solving for T, Initial residual = 3.20118e-05, Final residual = 2.23166e-10, No Iterations 7

Time = 0.08626
DILUPBiCG: Solving for T, Initial residual = 3.20021e-05, Final residual = 8.8872e-11, No Iterations 8

Time = 0.08627
DILUPBiCG: Solving for T, Initial residual = 3.20002e-05, Final residual = 9.56583e-10, No Iterations 5

Time = 0.08628
DILUPBiCG: Solving for T, Initial residual = 3.19916e-05, Final residual = 8897.06, No Iterations 1001

Time = 0.08629
DILUPBiCG: Solving for T, Initial residual = 0.340886, Final residual = 9.89072e-10, No Iterations 19

Time = 0.0863
DILUPBiCG: Solving for T, Initial residual = 0.170177, Final residual = 1.99834e-10, No Iterations 20

Time = 0.08631
DILUPBiCG: Solving for T, Initial residual = 0.132551, Final residual = 1.36749e-10, No Iterations 21

Time = 0.08632
DILUPBiCG: Solving for T, Initial residual = 0.112358, Final residual = 2.48292e-10, No Iterations 19

Time = 0.08633
DILUPBiCG: Solving for T, Initial residual = 0.0994847, Final residual = 7.72147e-10, No Iterations 18

Time = 0.08634
DILUPBiCG: Solving for T, Initial residual = 0.0891127, Final residual = 5.79845e-10, No Iterations 18

Time = 0.08635
DILUPBiCG: Solving for T, Initial residual = 0.0806057, Final residual = 1.00459e-10, No Iterations 19

Thanks All
Senthil
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Old   April 15, 2010, 00:55
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Alberto Passalacqua
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Hello. We cannot answer without knowing what problem you are solving.

Judging from the residuals something happens at Time = 0.08628, where the final residual is huge (8897.06 !) and the equation reaches the maximum number of iterations.

Best,
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Old   April 15, 2010, 11:34
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Senthil Kabilan
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Hi Alberto,

I am using scalarTransportFoam to to simulate diffusion of the acrolein through the rat respiratory system. The mesh is an all tetrahedral mesh with ~13 million elements. The U file in /0 is from a steady state simulation at a constant flow rate. Please let me know if you need further information.

Thanks
Senthil

Below is T file.

out1
{
type zeroGradient;
}
out2
{
type zeroGradient;
}
out3
{
type zeroGradient;
}
out4
{
type zeroGradient;
}
inlet
{
type fixedValue;
value uniform 1.38e-06;
}
Wall
{
type fixedGradient;
gradient uniform 0;
}

fvSolution file:

solvers
{
T PBiCG
{
preconditioner DILU;
tolerance 1e-09;
relTol 0;
};
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
}
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Old   April 15, 2010, 12:28
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Alberto Passalacqua
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Just a couple of general hints.

You could check the mesh quality with checkMesh and see if there are very skewed cells.

You could also try to perform 1-2 non-orthogonal correctors.

Best,
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GeekoCFD 32bit - The 32bit edition of GeekoCFD.
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