UDS convergence problem

mecarlg · October 1, 2010, 08:24

Hi,

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?

Carlos.

tstorm · October 1, 2010, 16:01

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.

October 1, 2010, 08:24	UDS convergence problem	#1
mecarlg New Member Carl Join Date: Mar 2009 Location: United Kingdom Posts: 13 Rep Power: 17	Hi, 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? Carlos.

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October 1, 2010, 16:01		#2
tstorm Member Join Date: Apr 2009 Posts: 78 Rep Power: 17	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.