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CFD time stepping: CFL vs implicit

Posted Sep 2, 2010, 7:48 a.m. EDT Fluid & Heat, Computational Fluid Dynamics (CFD) 2 Replies

Kai Herbrig
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Hi,

i'm struggling on which time stepping method for transient fluid-thermal-interaction i should use. (Comsol V3.5a)

The default setting for the stepping for the transient solver is the following:

Time steps taken by solver: "Manual"
Time Step: "5*dt_cfl_g1_chns"

So the time stepping is explicit based on the Courant Number. This results - in my case - to a time step size of about 0.0033s which is fairly low.

On the other hand, you can select time steps taken by the solver: "Free". This means implicit time stepping (?). This runs quite well and i get convergence.

So my question is: what is best: Time stepping based on "5*dt_cfl_g1_chns" or "Free"?

Any ideas? Suggestions? Doubts? Experience?

Thanks in advance!







2 Replies Last Post Sep 7, 2010, 7:31 a.m. EDT
Danial Tz
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Posted: 1 decade ago Sep 5, 2010, 4:42 p.m. EDT
Hi,

It depends on what you're looking for. If you don't want to miss any detail of the flow (as mush as possible), you should stick to CFL. An example is vortex streets. If you set your time solver to Free it will jump over the vortexes and you won't see them forming. If it is just a simple heat transfer, then free should do it.
Hi, It depends on what you're looking for. If you don't want to miss any detail of the flow (as mush as possible), you should stick to CFL. An example is vortex streets. If you set your time solver to Free it will jump over the vortexes and you won't see them forming. If it is just a simple heat transfer, then free should do it.
Kai Herbrig
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Posted: 1 decade ago Sep 7, 2010, 7:31 a.m. EDT
Hi Danial,

thanks for replying.

I think you're right! :) Right now, I'm using "Free".


Best regards
Hi Danial, thanks for replying. I think you're right! :) Right now, I'm using "Free". Best regards

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