CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > Siemens > STAR-CCM+

Utility of providing the CFL and the time-step simultaneously

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 29, 2017, 17:09
Default Utility of providing the CFL and the time-step simultaneously
  #1
New Member
 
Lise Amaniou
Join Date: Jan 2017
Location: France
Posts: 1
Rep Power: 0
Lise is on a distinguished road
NOTE: sorry in advance if my english isn't perfect, I swear I do my best

Hi everyone!

I'm working on the Von Karman Vortex Street appearing behind a cylinder put in an airflow.

Used parameters :
- Unsteady flow (implicit scheme + second order scheme)
- Ideal gas
- Turbulent k-omega SST model
- Coupled flow

I'm wondering why I have to enter the time-step AND the CFL, since the velocity is calculated and the dx is provided with the mesh.
Why doesn't the time-step set the CFL?

Moreover, I thought an implicit scheme implied no CFL condition (always stable), why is there one in this case?

Last question: my best results come with a CFL = 40, and the solution fully diverges when CFL=1, I would have think the opposite would occur (by definition of the CFL). Can someone give me a clue about the reason for that?

Thanks in advance!
Lise is offline   Reply With Quote

Old   January 31, 2017, 09:22
Default
  #2
Senior Member
 
Ping
Join Date: Mar 2009
Posts: 555
Rep Power: 17
ping is on a distinguished road
for unsteady the cfl sets the pseudo time step for the inner iterations within the outer time steps - see the user guide under pseudo time step
ping is offline   Reply With Quote

Reply

Tags
cfl, star ccm+, time-step

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 13:22.