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-   -   question about unsteady run and swirl number (http://www.cfd-online.com/Forums/star-ccm/85882-question-about-unsteady-run-swirl-number.html)

a_cucen March 9, 2011 03:49

question about unsteady run and swirl number
 
i have a case about unsteady flow. mesh has approximately 750.000 cells. but i don' t know what the time step must be? how can i calculate the time step? What is the relation between time step and cells. and second question: how can i calculate swirl number; i found that SN= G_theta/R.G_x. but i could not find how to calculate G_theta and G_x.

best regards,
Ahmet.

alastormoody11 March 14, 2011 04:00

A general rule of thumb is to use a time step which is 1/100 th of the approximate time required for the flow to traverse the entirety of the CV.

If you see that the solution is taking a large number of iterations to converge you might consider using half of the initial time step and so on.


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