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Convergence problem of the energy equation

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Old   May 12, 2008, 21:00
Default Convergence problem of the energy equation
Woo Meng Wai
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Dear all,

I am running a 3D simulation of a vessel. The turbulence model used is RSM. In the solution process, I monitor the scaled residuals, outlet surface averaged temperature and outlet surface averaged velocity magnitude.

I have no problem getting a converged and stable solution of the turbulence quantitites and outlet velocity. The problem is getting the energy equation to converge. The outlet temeprature just seems to oscillate towards the end of the solution process. The residuals then plateau out at around 4E-6 (convergence criteria is 1E-6 default). Hope someone can help me.

I have tried the following but failed:

1. Solve the flow and energy equations separately. And then recombine 2. Put all the relaxation factors to 0.1 or 0.2 or 0.3. 3. Use a smaller mesh

Anyone who has any suggestion, do kindly let me know. Thank you.

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Old   May 12, 2008, 23:20
Default Re: Convergence problem of the energy equation
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Are you tried with coupled solver. Try with second order discretization scheme and don't reduce the energy relaxation factor below 0.99. It is not advisable.

If you are solving in steady state, then use FMG initialization to get the good converged solution.

Finally check the total heat transfer convergence. If it is acceptable, then you can consider the solution is converged.

Hope it will help you

with regards, JSM
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Old   May 13, 2008, 03:06
Default Re: Convergence problem of the energy equation
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May be mesh boundaryes is to close to vessel?
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