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July 4, 2012, 09:57 |
How to achieve the forced transition in CFX?
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#1 |
New Member
Fukun Zhang
Join Date: Jul 2012
Posts: 3
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How to achieve the forced transition in CFX?
I want to simulate Vortical Flow of wing ,and achieve the forced transition in the wing location where I just set. In the CFX how to achieve the forced transition in CFX? |
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July 5, 2012, 00:24 |
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#2 |
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Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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Do you mean laminar to turbulent flow transition?
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July 5, 2012, 02:07 |
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#3 |
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Alex
Join Date: Jun 2012
Location: Germany
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Apart from grid-induced separation in a Detatched Eddy Simulation (which is rather a modeling error) i can't think of of a "pre-built" solution for this purpose in CFX.
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July 5, 2012, 02:35 |
Transition
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#4 |
New Member
Fukun Zhang
Join Date: Jul 2012
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We all konw that in the laminar flow the separation is earlier than in the turblence flow. Indeed the turblence separation is promoted more area than the laminar.
In my study,my problem is that the separation is promoted earlier, and I think the laminar flow has an efficient effect on my study. Because the experient results show that the separation should occur downstream. So I would like to set the boundary between laminar and turblence , I called it forced transition. Could I achieve it? |
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July 5, 2012, 04:09 |
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#5 | |
Super Moderator
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Quote:
1. We all know that laminar flow is more prone to separation than turbulent flow. 2. Separation is not a good effect. What type of geometry you are modelling? 3. It is known fact that, all RANS model assume the fully turbulent flow unless the separate equations are solved for the transition mechanism. One such example is gamma theta transition model, which does not model the transition physics, rather it uses the correlation to properly model the different type of transitions such as bypass, natural and separation induce transition. http://www.cfd-online.com/Forums/flu...ent-flows.html 4. LES and DNS are the methods which solve the transition in real sense. 5. There is a trip term in SA model http://turbmodels.larc.nasa.gov/spalart.htmlwhich forces the transition from laminar to turbulent at prescribed location. But this term is abandoned in commercial codes. http://courses.washington.edu/mengr5...our-report.pdf So if you still do not want to use the transition model and/or LES/DNS then you can make two fluids. For one use the laminar model and for other use the turbulence model. I used this in Fluent http://hpce.iitm.ac.in/website/Manua...ug/node267.htm and I believe there should be no difficulty using this combination in CFX as well. http://www.cfd-online.com/Forums/flu...same-time.html https://www.sharcnet.ca/Software/Flu...e231.htm#36737 This should work for CFX http://www.kxcad.net/ansys/ansys_cfx.../i1324236.html http://www.dept.aoe.vt.edu/~cjroy/Jo...icles/jsr1.pdf one of the old post: http://www.cfd-online.com/Forums/cfx...turbulent.html |
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July 5, 2012, 07:03 |
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#6 |
Super Moderator
Glenn Horrocks
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Location: Sydney, Australia
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Yes. The turbulence transition model in CFX has an option where you can specify which regions of the flow are turbulent and which are laminar. You can use this to specify the lam-turb transition point. This has been used to model things like turbulence trip wires and similar things.
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July 5, 2012, 07:11 |
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#7 | |
Super Moderator
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This is the quote from one of the above references: http://www.kxcad.net/ansys/ansys_cfx.../i1324236.html
Quote:
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July 8, 2012, 22:07 |
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#8 | |
New Member
Fukun Zhang
Join Date: Jul 2012
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Quote:
Your suggestion is a great favor for me. Thank you! Now I am simulating the delta_wing based on VFE-2 geometry. When I calculate delta_wing in the condition of medium leading_edge (round leading_edge ) and in the Ma=0.4, Re=3 Million , angle of attack 13 degree, my calculation did not fit the experiment data very well. I found that in my study the onset of the main primary separation was in more upstream position compared with the experimental separation point. Result: http://www.imageuploading.com/ims/pi...2z5nL&i=137831 Last edited by seraphzfk; July 8, 2012 at 23:00. |
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July 9, 2012, 06:31 |
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#9 | |
Super Moderator
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I
Quote:
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