# Effect of iterations on result

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 August 5, 2011, 15:53 Effect of iterations on result #1 Member   sheth roh Join Date: Jul 2011 Posts: 56 Rep Power: 5 Hi folks I was wondering what is the effect of iterations on the result. Does increasing iteration increase accuracy of result?

 August 8, 2011, 19:59 #2 Senior Member   cfdnewbie Join Date: Mar 2010 Posts: 551 Rep Power: 11 generally:no! why should it? exception: implicit code, where your matrix inversion has not converged yet.... what kind of iteration (physical / computational) did you mean?

 August 9, 2011, 08:25 #3 Member   Join Date: Mar 2009 Posts: 85 Rep Power: 8 Hi, Could you let me ask what the physical iteration is?

 August 9, 2011, 14:56 #4 Member     Omid Seyedashraf Join Date: May 2010 Location: Iran Posts: 41 Rep Power: 7 if you know how to make the whole system and the results to converge yes more iterations could bring better results but you may also consider the time/cost of the accuracy

August 9, 2011, 17:20
#5
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cfdnewbie
Join Date: Mar 2010
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Quote:
 Originally Posted by husker Hi, Could you let me ask what the physical iteration is?
I was sloppy with my language there. What I meant was a physical time step in your iteration, i.e. a delta t.

 August 10, 2011, 16:07 #6 Member     Join Date: Mar 2009 Posts: 72 Rep Power: 8 Do you run a transient or steady state solver? If the convergence is well behaved then more iterations will generally lead to lower residuals. This is a good thing (to a point) in a steady state solver, but it might not be necessary within a transient solver. I would suggest that you put an iteration number so that you will reach convergence for your variables within most of the time-steps. __________________ "Trying is the first step to failure." - Homer Simpson

 August 15, 2011, 12:49 #7 Member   sheth roh Join Date: Jul 2011 Posts: 56 Rep Power: 5 Thanks for answers everyone.

August 20, 2011, 18:40
#8
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Ertan Karaismail
Join Date: Apr 2009
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Quote:
 Originally Posted by Ford Prefect Do you run a transient or steady state solver? If the convergence is well behaved then more iterations will generally lead to lower residuals. This is a good thing (to a point) in a steady state solver, but it might not be necessary within a transient solver. I would suggest that you put an iteration number so that you will reach convergence for your variables within most of the time-steps.

If I am wrong please correct me.
If you set an "iteration number" (I guess, you meant maximum iteration) and the solution does not converge to a desired value within a time step, then iteration error will start accumulating. Unless those errors are convected out with the flow, and the solution starts converging to the desired value, your simulation will have high iteration error. For an accurate simulation, generally the minimum number of (non-linear) iterations is set.

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