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Old   October 1, 2010, 08:24
Default UDS convergence problem
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I am using a passive user defined scalar and I am having a convergence problem. The flow field is already solved and I am simply solving the UDS equation so simulate a pathogen release in a room.

The residuals seem to be converging and the solution looks good, but if the solver carries on then the residuals come right back up again and the solution is junk.

Any ideas please?

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Old   October 1, 2010, 16:01
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If I follow you right, you're iterating to convergence without the UDS being solved (ie its transport equation is turned off), and once the solution is converged, you're turning on the transport equation, and the solution diverges. Is that right?

You might try lowering under-relaxation factors for any terms that the UDS equation affects. I've noticed that UDS equations tend to diverge without under-relaxation.
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