# Appropriate time step

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 August 24, 2014, 02:03 Appropriate time step #1 Senior Member   Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 9 Hi all, How is it possible to calculate overall mean value of convective Courant number with a given time step. I want to set the overall mean value of convective courant number around 1, but I don t know how to choose the appropriate time step. Thanks

 August 24, 2014, 08:45 #2 Senior Member   Ping Join Date: Mar 2009 Posts: 314 Rep Power: 12 create report ot type mean for cfl then use this in a field function formula calculate the required timestep and use this as the timestep however this is maybe not a good idea depending on your flow since an important area of the flow might have cfl much higher than one and so is being poorly modelled

 August 25, 2014, 04:44 #3 Senior Member   Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 9 thanks ping, would you give me an example of what you name "an important are"? and, based on what you said it must be more rational to use maximum CFL report instead of the average, rights?

 August 25, 2014, 05:59 #4 Senior Member   Ping Join Date: Mar 2009 Posts: 314 Rep Power: 12 an important area is somewhere where capturing the flow accurately is important ie there are areas in most cases where it is less important to have a fine mesh or a reasonable cfl number yes based on max cfl is much safer but could be too conservative if some spurous cells have large values for a silly reason

September 4, 2017, 16:54
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Quote:
 Originally Posted by ping an important area is somewhere where capturing the flow accurately is important ie there are areas in most cases where it is less important to have a fine mesh or a reasonable cfl number yes based on max cfl is much safer but could be too conservative if some spurous cells have large values for a silly reason
Dear Ping,

I created a report of Volume average and select convective courant number as a scalar function. Is this correct or should i create a report of surface average?

Then how can i obtain deltax to calculate my suitable time step?

Regards

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