Where to change CFL number in CFX

trump · July 22, 2015, 16:35

Hi everybody ,

I' m want to change the CFL number in CFX , both in a case for steady and a case for unsteady conditions.
I wanted to ask where I can find the option to change the Courant number. Or I can maybe just change the deltat and the velocity ?
Thank yoy

ghorrocks · July 22, 2015, 19:27

CFX uses physical variables, so adjust the time step size to adjust the CFL number.

Martin_Sz · July 23, 2015, 07:10

on the expert parameters??

ghorrocks · July 23, 2015, 07:12

No, there is no expert parameter for CFL. As I said, you adjust the CFL by setting the time step size.

You can use adaptive time stepping to home in on a Courant number. You can also define a CEL expression for the CFL number and use that to set the time step if you like.

trump · July 23, 2015, 09:24

Thank you for your answers , but if I am working in steady (so no time step to choose) how can I change the deltat ? Should I change the time scalefactor ? In which way ?
Thanks ,

Trump

ghorrocks · July 23, 2015, 18:36

If you are doing a steady state simulation then CFL does not apply.

But CFX uses a psuedo-transient approach to steady state convergence. So you still define a physical time step size. Local time scale factor is another approach CFX can do, but that is not generally recommended for most applications.

July 22, 2015, 16:35	Where to change CFL number in CFX	#1
trump New Member Join Date: Jul 2015 Posts: 9 Rep Power: 10	Hi everybody , I' m want to change the CFL number in CFX , both in a case for steady and a case for unsteady conditions. I wanted to ask where I can find the option to change the Courant number. Or I can maybe just change the deltat and the velocity ? Thank yoy

July 23, 2015, 07:10		#3
Martin_Sz Senior Member Marcin Join Date: May 2014 Location: Poland, Swiebodzin Posts: 232 Rep Power: 12	on the expert parameters?? __________________ Quick Tips and Tricks, Tutorials FLuent/ CFX (CFD) https://howtooansys.blogspot.com/

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July 22, 2015, 19:27		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	CFX uses physical variables, so adjust the time step size to adjust the CFL number.

July 23, 2015, 07:12		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	No, there is no expert parameter for CFL. As I said, you adjust the CFL by setting the time step size. You can use adaptive time stepping to home in on a Courant number. You can also define a CEL expression for the CFL number and use that to set the time step if you like.

July 23, 2015, 09:24		#5
trump New Member Join Date: Jul 2015 Posts: 9 Rep Power: 10	Thank you for your answers , but if I am working in steady (so no time step to choose) how can I change the deltat ? Should I change the time scalefactor ? In which way ? Thanks , Trump

July 23, 2015, 18:36		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If you are doing a steady state simulation then CFL does not apply. But CFX uses a psuedo-transient approach to steady state convergence. So you still define a physical time step size. Local time scale factor is another approach CFX can do, but that is not generally recommended for most applications.