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May 21, 2012, 23:42 
Trans. SST Intermittency Factor and Viscosity Ratio

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Question:
I'm dealing with external flow simulations of objects such as airfoils/automobiles/etc moving through fluid that is static. I'm dealing with Reynolds numbers from say 500,000 to 4 million. I've heard the Transition SST model in FLUENT could be good for these simulations as it's pretty good at predicting transition. So for my velocity inlet and pressure outlet boundary conditions, I was wondering how I know what the intermittency factor and viscosity ratio should be. What I understand so far is that the turbulence intensity for a simulation of an object moving through a stagnant fluid is very low (much less than 1%, lets say 0.05 or 0.1 %). I also understand that the turbulent viscosity ratio for external flows should be between 1 and 10. Any idea how I should select the "pick a number 1 to 10" number? So basically lets say I have a 1 meter chord airfoil going through fluid at 70 m/s (about 5 million Re#). What's the viscosity ratio that I should enter for the inlet and outlets, and how do you estimate this number? Is it from experimental data? I also understand the concept of the intermittency factor. From what I understand, it's the probability that a certain point in your domain lies within turbulent flow. So 1 would be that everything is turbulent, and 0 would be that none of it is. For transitional flows (like the flow over the airfoil), upstream of the transition points have an intermittency of 0, and downstream of the transition have an intermittency of 1. So how do I estimate the intermittency factor? Do I have to know where exactly transition occurs? Isn't that the point of running a transition sst model? Side question: Can the Transition SST model be used for compressible flows? If so, do the turbulence intensity, viscosity ratio, and intermittency factors change for the compressible case? How do I know how much they change by? I'm really pretty new to the model and don't understand it very well so any (even partial) explanations of these concepts would be greatly appreciated! 

May 22, 2012, 00:44 

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Sijal Ahmed Memon (turboenginner@gmail.com)
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Search for the papers by Ralph J. Volino http://asmedl.org/getabs/servlet/Get...ifs=yes&ref=no http://asmedl.org/vsearch/servlet/Ve...TSEBV&aqs=true http://www.google.com.pk/url?sa=t&rc...L_Kkzq8UVtwUQ http://wwwg.eng.cam.ac.uk/whittle/p...TLPReview.pdf http://www.pa.uky.edu/~rplebeau/cfd/lp.html 

May 22, 2012, 07:18 

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Hey I really appreciate the reply! Thanks!


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