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Old   July 26, 2005, 06:17
Default New to Fluent with 2 questions
  #1
Akin
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Hello All I am new to Fluent,using it to study external flows. When I ask for 1000 iterations (steady state) it stops at 200 or so, I don't like this because I don't think the fluid is gone through the domain, how can I make it go through all my iterations ? Secondly, I will like to use my steady state results to start a transient simulation, how is this done finally how do I request an out put for use in Fielview or Ensight ? Cheers !
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Old   July 26, 2005, 07:21
Default Re: New to Fluent with 2 questions
  #2
CFD-novice
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Does it say anything when it stops?
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Old   July 26, 2005, 07:22
Default Re: New to Fluent with 2 questions
  #3
Akin
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Nothing
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Old   July 26, 2005, 07:34
Default Re: New to Fluent with 2 questions
  #4
CFD-novice
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Hmm, I almost can't believe it. I never had such a case. My FLUENT always talks to me.

I would have expected something like 'Solution has converged' but you certainly would have mentioned that.
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Old   July 26, 2005, 09:39
Default Re: New to Fluent with 2 questions
  #5
Swarup
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Well, the first part of your "problem" is baffling. It will invariably complete the number of iterations you aked it to perform or will stop once convergence is obtained. I will only say that check carefully once again. About second part; you should save your steady state calculation data file using write option. Then make the calculation unsteady and now save the case file. Now, the job is to initialize your calculation. So, read the data file of steady state calculation and start calculations without initialization in the unsteady case. Hope some of the problem is solved.

Swarup.
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Old   July 26, 2005, 10:51
Default Re: New to Fluent with 2 questions
  #6
Akin
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Swarup, I think you are probably right about it converging, since the Cd, Cl and Cm are pretty settled. Now regarding restarting a transient run with steady state, I presume I should save the steady state once its completed, right ?
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Old   July 26, 2005, 15:24
Default Re: New to Fluent with 2 questions
  #7
tucker
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How are you executing your case file (e.g. live interaction, by submitting a job to a supercomputer, etc.)? I ask this because, even though I may set in my case file the number of iterations I want Fluent to perform, I often have to respecify this in the input file or else Fluent will "reset" to default values. Perhaps this is what's happening.

Also, when you run your case file, there should be a way to print out an error report to see if your case file is exiting prematurely. I just think it's dangerous to assume convergence without Fluent confirming that.

Tucker
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Old   July 27, 2005, 00:44
Default Re: New to Fluent with 2 questions
  #8
Swarup
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Yeah. You should save your steady state case and data files. Your case file will change once you make changes to make it unsteady. Data file for steady state results is to be used in unsteady case file. if you keep two separate case files for steady and un-steady problems, then you will be able to use them whenever needed. the output data file of steady state case will be input for unsteady case which will again produce its own data file.

Swarup
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Old   July 27, 2005, 12:26
Default Re: New to Fluent with 2 questions
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Akin
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Tucker, I am doing it by live interaction, what do you mean Fluent will reset to default value, please explain.
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Old   July 27, 2005, 16:14
Default Large eddy simulation
  #10
Randheer Yadav
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hi, I am doing LES of submerged jet having the jet diameter of 2mm discharging into a rectangular tank. I have two doubts 1) how to decide the timestep for LES 2) how we can judge the coinvergence of a LES simulation and decide that our simulation is converged (Since the residue convergence is not always reliable). Thanks in advance, bye
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Old   July 27, 2005, 17:51
Default Re: New to Fluent with 2 questions
  #11
tucker
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If you're running the iterations directly rather than by submitting a job file, then nevermind. I was finding simetimes in my experiments that, if I didn't restate certain solution controls in my job file, that Fluent would use default values (such as number of time-steps, number of iterations per time step, data-sampling options, etc.). This doesn't sound like it applies to you.
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