# intermittency factor for transitional flow over an airfoil

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

 March 22, 2011, 21:41 intermittency factor for transitional flow over an airfoil #1 Senior Member   Nick Join Date: Nov 2010 Posts: 121 Rep Power: 6 Hi all, I'd like to simulate flow over an airfoil at Rey 120,000. From the literature I understand that the flow has both laminar and turbulent portions, therefore a transition model may be the most reliable option in CFX. How can I use the Gamma Theta's intermittency factor for this purpose? The documentation says it is a measure of the probability that a point lies in the turbulent region. What does this mean practically and what information do I need to set it reasonably? I can make some prediction using XFOIL regarding the transition point. Thanks for your attention. Nick

 March 22, 2011, 22:31 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 11,080 Rep Power: 86 0 means laminar and 1 means turbulent. Generally it will transition quickly from 0 to 1 and so you won't get much flow between these values. So then it simply tells you where the flow is laminar and where turbulent. So for an airfoil flow set intermittency to 0 at the inlet and let it work it out from there. It will naturally increase at the airfoil and hopefully automatically work out the transition location.

 March 23, 2011, 23:10 #3 Senior Member   Nick Join Date: Nov 2010 Posts: 121 Rep Power: 6 Thanks Glenn. I changed it for the domain to 0 and the residuals osculated dramatically, the same happened with 0.5. This behaviour wasn't observed when transition was not turned on ie the solution converged but still it's a fully turbulent solution on the foil. Perhaps I should try the other transition models (Gamma-theta). Just wondering whether I can get some information about setting those parameters.

 March 24, 2011, 21:29 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 11,080 Rep Power: 86 You should use 0 as the initial value and inlet value. It is a complex model and you need to know what it all means before you change models or constants. Read the published literature references about the model - they are listed in the references section of the documentation. Even better do an advanced turbulence modelling course from CFX so you know how the model works.

 March 25, 2011, 03:36 #5 Senior Member   Nick Join Date: Nov 2010 Posts: 121 Rep Power: 6 Thanks for the suggestions. However, I can't find the setting for intermittency in inlet. It's only available for the fluid settings. What am I missing?

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post andrenonaka CFX 6 December 4, 2014 04:57 CD adapco Group Marketing CD-adapco 3 June 21, 2011 08:33 guess Main CFD Forum 8 March 20, 2010 14:54 Dave Main CFD Forum 3 April 24, 2008 17:11 Quarkz Main CFD Forum 2 January 6, 2006 11:56

All times are GMT -4. The time now is 15:26.