# maximum number of iterations

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 April 22, 2003, 15:44 maximum number of iterations #1 solomon Guest   Posts: n/a Hello! What is the maximum number of iterations one should expect to reach convergency. I tried up to 5000 but not reached to convergency. Is there any guide line one can follow to determine the number of iterations one can tray to see if convergency can be achieved.

 April 22, 2003, 16:37 Re: maximum number of iterations #2 Alex Munoz Guest   Posts: n/a Hi Your question is too broad, keep in mind that the itertion number is different for each case and also it depends of the turbulence model selected, relaxation factors, discretization and grid type. You should provide more infromation about your case!! Regards Alex Munoz

 April 22, 2003, 19:03 Re: maximum number of iterations #3 solomon Guest   Posts: n/a Dear Munoz I agree with you. But I just wonder rougly under extreme cenario what the case could be. I am enquiring not problem specific answer. I am traying to get a guide line so that I can get a feeling to say well this is too much iteration attempt let me do some adjustemnt. You can even tell me from your previous experience the highest number of iteration which leads to convergence in CFD analysis you encountered.

 April 22, 2003, 20:16 Re: maximum number of iterations #4 ap Guest   Posts: n/a It's difficult to give general guidelines because the number of iteration you need to obtain a converged solution depends on a lot of factors (models, boundary and initial conditions). FLUENT considers a solution converged if all scaled residuals reduce of three order of magnitude (six for energy). But if you set a good initial solution for your problem, you couldn't notice such a reduction because you're already close to the converged solution. However, for steady calculations I think you should stay around 1000-2000 iterations. While for unsteady calculation, the manual suggests 20 iteration per time step, but sometimes I had to increase to 30-40 at the beginning of the calculation. 5000 iterations seem too much, maybe your problem is ill posed. Check boundary conditions. Or maybe you're initial solution is extremly good, so you can't have a big reduction of residuals. Check their behaviour to understand that (are they stable/reducing or they vary a lot?). Hi and good work ap

 April 23, 2003, 07:42 Re: maximum number of iterations #6 ap Guest   Posts: n/a Thanks for compliments Alex. Hi ap

 April 24, 2003, 15:42 Re: maximum number of iterations #7 shewaferaw solomon Guest   Posts: n/a Alex Munoz and ap thank you for your valuable explanation on the subject. Solomon

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