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.

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.