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time step size too small???

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Old   September 12, 2012, 11:53
Default time step size too small???
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Dear all,

I have got a question concerning the proper choice of the time step size:
I run a simulation and after about 25 iterations my residuals look like this (this is an example showing about time step number 600):

Updating solution at time levels N and N-1.
iter continuity x-velocity y-velocity z-velocity magnevist time/iter
! 9213 solution is converged
9213 5.5898e-14 8.0432e-15 5.2701e-15 8.5588e-15 3.8219e-04 1496884126130134:11:12 1000000000000000000
! 9214 solution is converged
9214 5.5662e-14 8.0247e-15 5.2200e-15 8.5326e-15 3.8221e-04 1498709810042426:35:44 999999999999999999
step flow-time inlet lad lcx lmca_025

The Fluent manual says that ideally there should be about 5-10 iterations per time step, otherwise one should increase the time step size.
Does it have influence on the solutions if my time step size is too small and if I have few iterations therefore?
Thank you for any help!
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Old   September 15, 2012, 00:51
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If you increases the time step the number of iterations per time step increases it not should be too large approximately 0.01 s is good (be aware your solution should convergence if you increases it else you must decreases it until you get convergence) it just make your solution run faster with time.

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