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

ywem · June 9, 2020, 03:42

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?

sourav90 · June 15, 2020, 05:03

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

Courant Number

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

ywem · June 15, 2020, 19:03

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.

June 9, 2020, 03:42	Why the convergence of a steady problem also need several time evolution steps	#1
ywem Member Wenming Yang Join Date: Jun 2018 Posts: 42 Rep Power: 7	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?

June 15, 2020, 05:03	transient and steady-state: 2 & 1 time consideration respectively	#2
sourav90 Member Sourav Mandal Join Date: Jul 2019 Posts: 55 Rep Power: 6	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 Courant Number PS: I am new to CFD simulation, experienced users don't hesitate to correct me if I am unclear / wrong.

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June 15, 2020, 19:03		#3
ywem Member Wenming Yang Join Date: Jun 2018 Posts: 42 Rep Power: 7	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.