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Old   July 14, 2010, 16:37
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For NACA 6 series you will find experimental data in Abbott's book or in his original NACA report 824 (if I remember correctly).

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Old   July 16, 2010, 01:40
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You are right, I downloaded NACA report 824 and there are expeimental results for NACA 6 series airfoils.
Thank you.
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Old   August 9, 2010, 08:31
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Hi all!

I'm trying to use the TransitionSST for my thesis case. I have a wind vertical asxis turbine. I'm using a NACA 0012 85.8mm for the cord, blunt. Reynolds I'm trying 360.000, so 61.3 m/s x velocity. It's quite high I suppose but it's only the first attempt. I found that there is, for alfa=0, a good corrispondence with the physics but now I would like to see if I'm modelling well the mesh. How I can see the point of transition? I have a y+ almost equal to 1 over the profile. But this is only for the first layer? I read that I have to create about 50 nodes till the number y+ reach 30, to read well the boundary layer. The question are:

how to see after convergence where y+ reach 30 in the fluid?
how to see where transition occurs?
there are experimental data that I can compare?
for example I found that cd for this case it should be 0.0079 from here http://www.cyberiad.net/library/airf...ta/n0012cd.htm there are other references?

I tried to use Xfoil to know before where exactly this point is but I didn't manage it yet.
I tried the other transition model... it oscillates around 0.0075, good value but it's not converging. with SST I reached 0.0078, but very slowly(16000 iterations, ok I have 109k elements but in the end I modelled the entire wind tunnel. I attach some images about the mesh near the profile. done with ICEM.

please if anyone can help me I would be very grateful
thank all
best regards

baggiovive
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Old   September 4, 2010, 10:39
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It is trivial to get the transition point in Xfoil for your problem. Just search Google for "Xfoil tutorials" and you will find a bunch of indications of how you can solve this problem.

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Old   September 4, 2010, 11:41
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Hi friends,
I got a question,
I have to study the head loss along a 1 km 8" pipe and to do so, I would face the problem by dividing the pipe into several parts and the result of one section pipe will be the input of the next one and so on till getting the final head loss.

Could anybody tell me how to take those results and use them as an input of the next section pipe?

every section pipe is stored into a different file.

thanks
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Old   September 14, 2010, 12:34
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Hi Do,
it's not so trivial to get the right transition point.. X-foil works as a e^n method and the transition point depends on the number of n. N itself depends on the freestream turbulence. Likewise it's the same problem with menter. I've the sandia references for the naca 0012.. but there's no informations about the level of turbulence in the wind tunnel. I cannot explain better. I would onl know if someone has found the same difficulty to reach the theoric value of Cd. Write me soon.
bye

baggiovive
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Old   September 14, 2010, 21:50
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If you have an experimental Cd for an airfoil at moderate Mach and a reasonable Reynolds number you can "guess" the correct N by ... trial and error. First try with the default N=9 and see the relative error of the experimental Cd vs the calculated one and so on ...

Once you have the good Cd for a certain N (say less then 8% relative error), you can look at the transition point, you can assume the code has correctly placed the transition.

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Old   July 21, 2013, 21:45
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Quote:
Originally Posted by galtmann View Post
I'm trying to model forced transition with a trip strip on a 2D airfoil in fluent 12.1. I did not think about trying to split the entire domain into two zones, so I'll try that, but the original way I wanted to model it was with the transition SST model in fluent 12. In this model, they supply an area to insert a user defined function (UDF) to fix the point of transition. The only problem is the example UDF they supply is as follows:


#include "udf.h"

DEFINE_TRANS_FLENGTH(user_Flength, c, t)
{
real Flength = 31.468;

return Flength;
}



I am not sure what this does. I origionally thought it was a fixed distance from the stagnation point, but I applied the distance of the trip strip to Flength, and it did not change the solution at all. Am I doing something wrong?

Thanks for your input!
Hi Galtman. I was reading your message on FLENGTH and I would like to know if you meanwhile solved your problem. How is FLENGTH defined? From Where is it measured? Is it a dimensional quantity?

Thanks a lot,

Best

Roberto
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