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Epsilon and mixing length value for airfoil simulation

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Old   January 29, 2009, 07:50
Default Hi all, I'm trying to simulat
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Gianluca VZ
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Hi all,
I'm trying to simulate a turbulent flow around an airfoil. I have some difficulties in evaluating the correct value for epsilon.
In particular I don't know which value of the mixing length I should use.
The domain is 3 meters long and 2 high.
The airfoil is located at 1 meter from the inlet and in the middle of the height, the chord length is 0.1 m, the speed is 100 m/s, Re=1e6.
Thank you in advance for your suggestions.

Bye
Gianluca
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Old   January 29, 2009, 09:33
Default Hi, this is what I obtained so
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Gianluca VZ
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Hi, this is what I obtained so far.
I attach the directory of the case and a screenshot.
Thanks again.



airfoil_simulation.zip

Gianluca
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Old   January 29, 2009, 12:32
Default hi, your U value seams to b
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Wolfgang Heydlauff
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hi,

your U value seams to be 10m/s instead of 100. you also will have to raise the size of your mesh to 40-100 times the chordlength.
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Old   January 29, 2009, 15:17
Default Actually, Gianluca and I tried
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antonio segalini
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Actually, Gianluca and I tried to do a different simulation with the k and epsilon of a simulation of prof.Jasak on a naca 0012. with the same chord length and the same distance. but you see the result (it is embarassing :-) )
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Old   January 30, 2009, 17:32
Default Hello Antonio and Gianluca,
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Maruthamuthu Venkatraman
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Hello Antonio and Gianluca,
Try to keep y+ approx 1 to 5 and use sst k-w model. You shall check the best practise guidelines in ERCOFTAC for such flow.

Naca profile example is there in it... May be it helps you.

good luck
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Old   January 31, 2009, 14:15
Default Mmmm, the k-Omega SST coded
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Ivan Flaminio Cozza
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Mmmm,
the k-Omega SST coded in OF is based on a wall functions approach, so it should be necessary to use an y+ of about 30...
egards, Ivan
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Old   February 1, 2009, 04:55
Default thanks Ivan and Maruthamuthu.
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antonio segalini
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thanks Ivan and Maruthamuthu. We find out our bug :-). In the boundary file we did not specify that the profile surface was of wall type. There are other types in OpenFOAM (inlet, outlet, etc...)

Is it so important to specify the other types (apart wall of course)?
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