[wc34071209]

Hi,

When I enable 'pseudo transient', the Courant number disappears in the Control tab.

What is the essential difference between pseudo-transient and steady-state for coupled pressure based solve in Fluent?

Thank you!

Originally Posted by LuckyTran

That's actually an under-relaxation factor for the coupled solver and hence why it is listed with the under relaxation factors in the Fluent GUI. It has no direct connection to time-stepping and the CFL number (i.e. you can use the coupled solver for steady-state problems). But the change in the solution from one iteration to the next is analogous to some change in time so that urf's can also be interpreted as local shortening/lengthening of this time-stepping and it turns out that this characteristic time-step so happens to be the cell Courant number so finally it makes sense at the end to call this something related to a courant number. Unfortunately the Fluent devs decided to simply call it courant number to make it confusing rather than something like CFL multiplier.

oj's post earlier in this thread gave a really detailed explanation of the meaning of CFL (which is actually a urf).

See also 21.4.4.2 in the Fluent Theory Guide.

A CFL of 200 is equivalent to an implicit under-realxation factor of 0.995 (not much under-relaxation). An infinite CFL is urf = 1 and CFL of 1 is urf = 0.5. The default value has changed over time from 50 to 100, I guess it is 200 now. Higher is better so you probably do not want to mess with this option until your solution diverges.