Why the convergence of a steady problem also need several time evolution steps
 

Dear Foamers,

I found that if we solve a steady problem such as that using "simpleFoam", whereas the convergence of it also need several time steps. I am not sure if this is a general conclusion. I checked this using the tutorials of "incompressible/simpleFoam/airFoil2D" in OpenFOAM.

If this is true, is it mean that we have to use two times when solving a transient problem, one is for the evolution within another time step. I am confused about this. Dose anyone has some ideas?

transient and steady-state: 2 & 1 time consideration respectively
 

Hi,

You are right, there are 2 different times to be considered in transient problem. Whereas for any steady-state only one.

I have never run in the transient simulation, only have worked with steady-state problems so far. As far as I know, this stems from courant number consideration, which is important for transient but need not be considered for steady-state. I can share some links that might be useful:

https://en.wikipedia.org/wiki/Couran...Lewy_condition

https://www.cfd-online.com/Forums/cf...nt-number.html

PS: I am new to CFD simulation, experienced users don't hesitate to correct me if I am unclear / wrong.

Dear Sourav,
Thank you for your reply.
I am not sure with this. But there is no second time in some transients solver such as pisoFoam in OpenFOAM.