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Old   June 29, 2017, 00:35
Default Time step limitation
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Mohsin Raza
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Hello!

I am just wondering how to overcome this time step limitation due to maximum turbulence iteration?

time step limited by maximum_turbulence_iteration, recovering...
time step limit = dt_min forced by maximum_turbulence_iteration

It has slowed down my simulation speed. I have tried by changing cfl number from 0.5 to 3 and even changed the number of iterations (itmax) from 30 to 100 but still the same. I am using v2.1 and even checked the manual. I am simulating a dual fuel RCCI case.

P.S. New to Converge. Also, when time step=dt_cfld, it runs smoothly

Please have a look.

Kind regards,
Rzaa
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Old   June 29, 2017, 12:37
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Jerome Le Moine
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Rzaa,

Based on your description it seems that your initial condition in turbulence are too high or there is an event that causing the turbulence to go too high. The turbulence are getting so high so the cfl_d (diffusion) is the limiter for the timesteps. It is rare when the number of iterations for turbulence quantities should be changed, for most simulations the turbulence should converge within 5 iterations. I would recommend looking at turbulence.out which give you the volume averaged quantities for the different region and see if you can find any abnormalities like strong change in turbulence and see if it is related to any events like start of simulation, IVO, start of combustion or something else.
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Old   June 30, 2017, 11:03
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Mohsin Raza
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Thanks a lot Jerome. I am hopeful that this will be very helpful. In case I faced any problem, I will be looking forward to your help again.
Thank you.

Regards,
Rzaa
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Old   September 18, 2017, 05:44
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Mohsin Raza
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Hello!
I tried changing the initial turbulence but still the problem exists. Even I didn't notice any major abnormalities in turbulence output file. This limitation appears soon after the case starts. Can you further guide, please?

P.S. There are too many recoveries and mostly time step is limited by dt_grow and max_iteration_turbulence

Thank you.

Sincerely,
Mohsin

Last edited by MRzaa; September 18, 2017 at 06:02. Reason: Wanted to add more details
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Old   September 18, 2017, 18:38
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Mohsin,

We'll probably need to review your case setup to provide further guidance. It's possible that there's something unphysical about your initial condition that is giving the solver some trouble. Can you send your case to support@convergecfd.com?

Best regards,

Tristan
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