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CFL and CFL_ADAPT with Unsteady Simulations

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Old   April 11, 2019, 01:51
Question CFL and CFL_ADAPT with Unsteady Simulations
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Tim Jim
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Hi,

I have a few questions on the Unsteady implementation.

1. Are unsteady simulations affected by CFL and CFL_ADAPT flags?

2. If running UNST_TIMESTEP=TIME_STEPPING (not 2nd order), are UNST_TIME and UNST_INT_ITER ignored?

Thanks and regards,
Tim
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Old   April 11, 2019, 03:41
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Hi,




I never run unsteady simulation on SU2 but I am very used to unsteady simulations.


SU2 uses dual-time step algorithm as used in Fluent. There are two time levels in one total iteration. First one takes place in pseudo time which is converged in few iterations (generally 5 to 30) according to your real time step, CFL etc. The second one is marching in time simply.


So I think this is your answer. CFL is important for pseudo time level.


I strongly recommend to look at Blazek book, chapter 6, temporal discretization.
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Old   April 11, 2019, 03:51
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Tim Jim
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Hi,

Thanks for your reply and tip. Sorry, I was actually asking about the implementation in SU2 for single time stepping (not dual-time stepping) - I wanted to find out which flags are ignored and which are used when the UNSTEADY flags are given.

Kind regards,
Tim
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Old   April 11, 2019, 04:02
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Hi,


In single time step, I think it uses only real time step (not cfl etc.) and march in time explicitly. I hope, someone can clear this subject.


Nevertheless, I can say if time accuracy is not important for you, use dual time stepping method. You can go with larger time steps that speed up your run.


Best regards.
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