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Old   August 17, 2005, 03:03
Default I am using simpleFoam with kEp
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ghanshyam
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I am using simpleFoam with kEpsilon model. After few iterations it looks like it stops solving equations of k and epsilon as I don't see error on my terminal. Does this mean that these equations diverged? How to make it visible all the time. I have experimented with "tolerences" as well as "relaxation factors" no improvement.

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GS
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Old   August 17, 2005, 03:07
Default Maybe the initial residual is
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liu
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Maybe the initial residual is less than tolerences, so these equations don't need to be solved. Steady state?
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Old   August 17, 2005, 03:10
Default Yes, steady state, I was guess
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Yes, steady state, I was guessing the same, but I still want to solve. How do I do that.

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Old   August 17, 2005, 05:30
Default Do you see the initial residua
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Do you see the initial residual fall? Does it drop below your convergence tolerance? Have you tried making the convergence tolerance very tight?
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Old   August 17, 2005, 05:40
Default >Do you see the initial residu
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ghanshyam
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>Do you see the initial residual fall?
Yes, initially there is reduction in residual.
>Does it drop below your convergence tolerance?
Yes
>Have you tried making the convergence tolerance very tight?
Yes

Currently I am compiling the code by making following change in "tests.C"

//converged_ = true;
converged_ = false;

Will this help?

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GS
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Old   August 17, 2005, 05:53
Default I would be able to help you mo
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I would be able to help you more if I had the answers to my questions or better still a section of the log file from just before k-epsilon stop solving to just after.
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Old   August 17, 2005, 05:55
Default Sorry, I missed the answers bu
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Sorry, I missed the answers buried there. Anyway, I would still like to see the section of log file. Have you looked the the field valeus for k-epsilon? Are they VERY large?
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Old   August 17, 2005, 08:18
Default BICCG: Solving for Ux, Initia
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ghanshyam
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BICCG: Solving for Ux, Initial residual = 0.0114222, Final residual = 0.000931753, No Iterations 1
BICCG: Solving for Uy, Initial residual = 0.0227955, Final residual = 0.00190204, No Iterations 1
BICCG: Solving for Uz, Initial residual = 0.00691902, Final residual = 0.000593082, No Iterations 1
ICCG: Solving for p, Initial residual = 0.0216008, Final residual = 0.000214944, No Iterations 116
time step continuity errors : sum local = 0.00871451, global = 0.000437168, cumulative = 0.0171293
BICCG: Solving for epsilon, Initial residual = 0.021943, Final residual = 2.2619e-08, No Iterations 1
BICCG: Solving for k, Initial residual = 1.78372e-05, Final residual = 1.1457e-06, No Iterations 1

ExecutionTime = 201 s


Time = 257
BICCG: Solving for Ux, Initial residual = 0.0114393, Final residual = 0.000938528, No Iterations 1
BICCG: Solving for Uy, Initial residual = 0.0228175, Final residual = 0.0019204, No Iterations 1
BICCG: Solving for Uz, Initial residual = 0.00691351, Final residual = 0.00059707, No Iterations 1
ICCG: Solving for p, Initial residual = 0.0229688, Final residual = 0.000222948, No Iterations 115
time step continuity errors : sum local = 0.00902571, global = 0.000449829, cumulative = 0.0175791
BICCG: Solving for epsilon, Initial residual = 0.0225105, Final residual = 2.18334e-08, No Iterations 1
bounding epsilon, min: -3.5104e-12 max: 822122 average: 4651.92

ExecutionTime = 205.23 s


Time = 258
BICCG: Solving for Ux, Initial residual = 0.0114469, Final residual = 0.00095594, No Iterations 1
BICCG: Solving for Uy, Initial residual = 0.0226974, Final residual = 0.00194632, No Iterations 1
BICCG: Solving for Uz, Initial residual = 0.00688176, Final residual = 0.000596608, No Iterations 1
ICCG: Solving for p, Initial residual = 0.0220571, Final residual = 0.00021926, No Iterations 118
time step continuity errors : sum local = 0.00883914, global = 0.000396233, cumulative = 0.0179754

Will this help to clarify myself? You can see after Time(iteration) # 257, k and epsilon disappears forever.

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GS
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Old   August 17, 2005, 08:27
Default What convergence tolerance hav
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What convergence tolerance have you set for k and epsilon?
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Old   August 17, 2005, 08:31
Default For both 1e-5(Tolerance), 0.1(
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For both 1e-5(Tolerance), 0.1(RelativeTolerance)
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Old   August 17, 2005, 08:35
Default For cases will wall-functions
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For cases will wall-functions I use 1e-8.
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Old   August 17, 2005, 08:38
Default Now I am running with 1e-15 an
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ghanshyam
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Now I am running with 1e-15 and 0.1 for both. It appears again. This way what is the lower tolerence limit?

Thanks and regards
GS
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Old   August 17, 2005, 08:43
Default Check the k and epsilon fields
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Check the k and epsilon fields, it sounds like they are becoming VERY large which affecting the residual normalisation.
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Old   August 17, 2005, 09:03
Default Max epsilon is 676404.2 m^2/s^
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ghanshyam
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Max epsilon is 676404.2 m^2/s^3 and k is 72 m^/s^2, which is not too large value.

It has disappeared again even after giving tolerance 1e-15 for both k and epsilon.

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GS
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Old   August 17, 2005, 09:08
Default It appears k and epsilon have
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It appears k and epsilon have converged for your case.
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Old   August 17, 2005, 09:12
Default But I do not want it to stop s
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ghanshyam
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But I do not want it to stop solving k and epsilon, as flow field is still developing. How do I do that?

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GS
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Old   August 17, 2005, 09:19
Default For some reason, probably due
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For some reason, probably due to something in your setup/BCs, the k-epsilon system has converged and nothing you do to the tolerances will make it converge further. You need to find out what is wrong with your setup.

We would be happy to check and correct your case as part of your support contract with OpenCFD.
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