CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

Turbulent Cylinder Strouhal Number

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 23, 2002, 18:00
Default Turbulent Cylinder Strouhal Number
  #1
Chetan Kadakia
Guest
 
Posts: n/a
I am trying to get obtain an accurate Strouhal number for turbulent flow of 4e6 over a cylinder. If anyone has done this type of problem and has been succesful in getting the correct frequencies, please advise me of the set up. I am using LES, and when I calculate my Strouhal Number, i get 20% error (with reference to Schlictiing)
  Reply With Quote

Old   October 9, 2002, 10:03
Default Re: Turbulent Cylinder Strouhal Number
  #2
Jimmy
Guest
 
Posts: n/a
did you try to shift your Smagorinsky constant ?

if i remember well, i've seen such works where oscillations behind a cylinder were much more well computed using a CS=0.13 CS instead of the default. However, Germano dynamic model would be a great progress in fluent.
  Reply With Quote

Old   October 9, 2002, 19:43
Default Re: Turbulent Cylinder Strouhal Number
  #3
Chetan Kadakia
Guest
 
Posts: n/a
I was reading up on the Cs constant in the Smag.-Lilly sgs model. The default value of .1 is good for transition flows, but the original proposed value is .23 and I believe that might work better for my problem.

I am unfamiliar with the Germano dynamic model. What is it?

  Reply With Quote

Old   October 10, 2002, 04:31
Default Re: Turbulent Cylinder Strouhal Number
  #4
Jimmy
Guest
 
Posts: n/a
the germano uses double filtering of different size.

The problem is solved in LES using a test filter twice as large as the original including a smagorinsky model for SGS. Then the problem is solved with the usual filter (of lower size) with the same smagorinsky model BUT it makes the assumption that the SGS have the same properties for both filtering SO in the gap between the test and the normal filter you have a correspondance between the SGS model of the test and the solved scales of the normal filter. You can here make a correspondance and then evaluate a value for the CS witch is locally dependant of the flow properties.

Of course, this is a simplified approach of the original germano model but you have the key idea. many improvements were made since espaceially in the sgs modelisation.

see reference below :

@ARTICLE{GER91, author = "\textbf{Germano M., Piomelli U., Moin P., Cabot W. H.}", title = "A dynamic subgrid-scale eddy viscosity model", journal = "Physics of Fluids A", year = "1991", volume = "3", number = "7", }

for more exhaustive list you should check the papers made by Paviz Moin (AMES laboratory i think...)
  Reply With Quote

Reply

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Turbulent Schmidt Number in Ansys CFX 12.1 DiddyPablo CFX 7 May 23, 2011 12:20
strouhal number Deloat CFX 5 March 11, 2008 04:19
Questions regarding strouhal number Ben Main CFD Forum 7 January 15, 2007 20:32
About low Re number turbulent flows gorka Main CFD Forum 13 April 2, 2003 06:19


All times are GMT -4. The time now is 21:23.