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time step in unsteady combustion process

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Old   July 24, 2007, 02:44
Default time step in unsteady combustion process
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FRANK LEE
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hey,everybody i am facing a problem in simulating a unsteady combustion process.i found that when time step is varied,the maximum of temperature varied ,too. in detail,when i specify time step to 0.01s,the maximum is 1700K, while when time step is 0.0001s, the maximum would be 2100k.So, what is the proper time step? i also have another question.user's guide tell us that 15-20 iterations per time step is proper.however,radiation equation(DO model) is included in my case.it's really hard to converge within 20 iterations. can anybody help? sincerely FRANK
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Old   July 24, 2007, 05:53
Default Re: time step in unsteady combustion process
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Joe
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The proper time step is the one that results in unchaging values.

Use as many iterations as needed to ensure convergence in each time step.
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Old   July 25, 2007, 04:51
Default Re: time step in unsteady combustion process
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FRANK LEE
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thank you for your help.but i'm still not clear. solutions in each time step are converged,but the teperature profile is different under different time steps.i wonder why it happens. what influence does time step bringļ¼Ÿ is there a way to caculate the proper time step? and what is the basis? any suggestions? regards FRANK
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