question about unsteady run and swirl number

a_cucen · March 9, 2011, 03:49

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.

March 9, 2011, 03:49	question about unsteady run and swirl number	#1
a_cucen Member Ahmet Join Date: Mar 2011 Location: Ankara/ Turkey Posts: 37 Rep Power: 15	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.

March 14, 2011, 04:00		#2
alastormoody11 Senior Member Join Date: Jun 2009 Posts: 100 Rep Power: 17	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.