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intermittency factor for transitional flow over an airfoil

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Old   March 22, 2011, 21:41
Default intermittency factor for transitional flow over an airfoil
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Nick
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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.
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Old   March 22, 2011, 22:31
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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.
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Old   March 23, 2011, 23:10
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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.
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Old   March 24, 2011, 21:29
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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.
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Old   March 25, 2011, 03:36
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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?
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