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-   -   Criteria for transition ? (http://www.cfd-online.com/Forums/main/6618-criteria-transition.html)

Jarmo Monttinen September 25, 2003 18:54

Criteria for transition ?
 
I am currently calculating flow over a low Reynolds number airfoil, an Eppler 387 to be exact (chosen as there are plenty of experimental results available). Re = 100,000. The experiments show a separation bubble at about 45 % chord to about 85 % chord, my laminar computation shows separation from 47 % on. So, in order to match the location of the re-attachment, I need to use a turbulence model, I've chosen the Spalart-Allmaras model. The question is though, when to trip the model? Based on the data I have from experiments, I can vary the location of my trip and get a good agreement, but this is useless unless I can justify the location where I trip, and successfully use it with other airfoils (for which the bubble location is not documented) I am really only interested in a reasonable match of CL & CD, but those cannot be achieved unless the separation is captured correctly.

I know some people have used the Abu-Ghannam&Shaw criteria, but is there something newer and perhaps better available?

Thanks! -- Jarmo

Nicola September 26, 2003 11:31

Re: Criteria for transition ?
 
Hi,

Abu-Ghannam&Shaw model with some corrections by Mayle is the most used model to predict transition, and it works well.

So far, many efforts have been made to avoid using empirical correlations, but it seems a lot of work is left to be done yet.

If you want something newer then read "Predicting Transition Without Empiricism or DNS", Mark W. Johnson, 2002-GT-30188: it doesn't contain the solution, but it shows research activity at present.

Good luck,

Nicola


Jarmo Monttinen September 26, 2003 11:57

Re: Criteria for transition ?
 
Thanks.

I will look that one up!

-- Jarmo


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