# LES flow through time?

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 March 28, 2008, 09:46 LES flow through time? #1 kasim Guest   Posts: n/a Hi I am running a LES case on a duct with repeated obstcales inside. I have initialised my case with RANS model. I was wondering how many flow through times (residence time) would I need to obtain converged statistics. What excatly would indiacte that my flow has achieved stability and I do not need to run it any longer. I know its a very basic question but I dont wanna get it wrong. Thank you kasim

 March 28, 2008, 22:07 Re: LES flow through time? #2 Tedy Guest   Posts: n/a Hello Kasim, Typically you need about 5-10 flow-through time to obtain a good initial LES solution, then you should run a similar time to accumulate you data for LES statistics. This will give you statistically converged LES results. Success! Ted

 March 29, 2008, 08:33 Re: LES flow through time? #3 kasim Guest   Posts: n/a Thank you Ted for your answer. I am collecting statistics in my current run. Do you mean I should disable these statistics and then run the problem with new statistics for 5-10 flow through times. Kasim

 March 29, 2008, 14:31 Re: LES flow through time? #4 kasim Guest   Posts: n/a One more thing, when I re-start the simulation should I interpolate the existing solution on new run OR should I continue running existing solution and only remove the history from old statistics. Thank you kasim

 March 29, 2008, 15:11 Re: LES flow through time? #5 Ted Guest   Posts: n/a Hello Kasim, Yes, you should first run to obtain a statistically converged LES solution (5-10 flow through is an empirical value based on experimenting), THEN you should start accumulating your statistics, that is if you want to look say at your flow mean and turbulent quantities, ex: Ui_av, Ui'_rms, Ui'Uj'_av, etc. Best, Ted

 March 29, 2008, 16:06 Re: LES flow through time? #6 kasim Guest   Posts: n/a Thank you Ted. In order to collect new statistics should I just disable my current statistics and continue with the LES run OR should I interpolate my existing solution on new run to collect new statistics? kasim

 March 29, 2008, 16:31 Re: LES flow through time? #7 Ted Guest   Posts: n/a Kasim, Just continue your LES run, and when you consider that your initial LES solution is ok (5-10 flow through's), start accumulating LES statistics. Before you LES becomes fully statistically converged, the statistics you accumulate are more-or-less meaningless. Good luck! Ted

 March 29, 2008, 19:41 Re: LES flow through time? #8 kasim Guest   Posts: n/a Thanks Ted. Have a nice week end. Kasim