Setting up additional convergence criteria: output parameters are ‘constant’
 

Typically there are two convergence criteria

1. Residuals drop to enough low value
2. Output parameters (the parameters we care about in the simulations results) don’t change anymore with more simulation iterations

It seems that we can only set up the 1st criteria in Fluent and CFX. Regarding the second one, we need to either monitor by eyes or setup to run absolutely enough iterations number to make sure the simulations satisfy it. Both of these two ways are costly.

Anyone has a better way to set up the second criteria?

You could use a scheme file alongside your UDF as described on this page (first Google search result..).

After you have created your monitors (surface monitors or volume monitors) you can then specify convergence monitors. This will allow you to specify absolute convergence criteria to any existing monitors. In the GUI, the convergence monitors are on the monitors panel at the bottom, below surface and volume monitors.

Fluent User's Guide Section 28.16 goes over the convergence manager. This was added in either 14.0 or 14.5, so you might not have it if you're using an older version.