Learning Forum

[manelaero2020]

Hi friends ;

How can we control CFL number when we use a pressure-based solver in Fluent?

I can't find it in the solver controls

Thank you ?

[Rob]

If you've got pseudo transient option on it's the time scale factor. Otherwise you adjust the time step. Without knowing if you're running transient or steady I can't say which to look at.

[manelaero2020]

Ok thank you, Rob, I am running a steady computation so I think it isn't possible to adjust the CFL number because the physics is established, and no longer depends on the time

[DrAmine]

There is some CFL number based under relaxation used by coupled solvers ( pressure and density based steady and unsteady) which does not really have anything to do with the transient CFL number we usually learn in the CFD lectures

[manelaero2020]

Does the user can modify this parameter in that case? If yes, what do you think about the impact on the computation?

[DrAmine]

In which case? I will not change default values as a beginner. For steady state problems use pseudo transient coupled solver

[Rob]

Default Courant Number is 200 in steady, try using 25-50 if the solution isn't converging. It'll mean you need more iterations to reach convergence, but you've a better chance of getting there. For pseudo transient, the time scale factor is 1, dropping that to 0.1 can help stabilise the solution.