Hi @smittag,
Like Jousef mentioned, there should be an option to adjust the relaxation factors under the numerics tab.
As for how the relaxation factor affects the simulation, this was a post from awhile back by Hannes from SimScale.
Apply under-relaxation
Under-relaxation is a simple yet effective technique for updating the fields between iterations. The default way to update the field values in a new iteration would be to simply ignore the old value and replace it with the new values. Imagine you’re starting a simulation and have made an estimation for initial conditions. Most likely, this will be far off the final results, so you hope that the iterations will gradually change the values to make them converge to the final result. But what if the new field values are actually worse than the old ones? And what if the values for the next iteration will be even worse? This will lead to divergence.
The standard way to deal with this is called under-relaxation and is very effective. Instead of replacing the field values with the new result, it gets updated with a weighted average between the old and the new values. An under-relaxation factor of 1 corresponds to fully accepting the new result (hence no under-relaxation at all) while an under-relaxation factor of 0 corresponds to completely ignoring the new result (hence no updating with subsequent iterations). Values between 0 and 1 are used to stabilize the convergence process. Typically, we suggest starting with
- 0.7 for velocity
- 0.3 for pressure and other scalar fields
If the simulation diverges, try using lower relaxation factors (say 0.3 for velocity and 0.1 for pressure).
That is condensed explanation of how relaxation works. More detailed and in depth information such as the mathematics behind it can surely be found with a quick google search.
Hope this helps.
Cheers.
Regards,
Barry