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Old   January 14, 2010, 09:09
Default 2D gambit and fluent
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Chih Fang
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Hello.. I need help here.. Im doing a project which requires me to do turbulence modelling for an airfoil. Im a beginner in this field, just learn gambit and fluent.

As my 1st task, i was ask by my supervisor to compare the best mesh for my airfoil. Use fluent to get the Cl vs alpha and also the required contours. However, after running analysis using fluent for 3 different meshes, i realize that my data is very different from experimental data which i obtained from internet.

Im doing Naca 0012, so from internet, the stall angle for 2x10^6 is around 10-15 deg. However, for my mesh, i run the analysis until 25 deg, but the Cl is still not decreasing.

Can anyone help me and tell me what is wrong with my mesh? Thanx alot..
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Old   January 16, 2010, 14:55
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USMAN
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hi ,,
you have not mentioned your mesh size and type of mesh.Anyhow your problem is simple and the reason for not stalling the airfoil is not dependent upon mesh.you should make sure that your airfoil vortex data was correct in Gambit and proper domain and boundary conditions were given in Fluent.I will suggest a circular domain with "pressure far field" boundary condition.
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Old   January 17, 2010, 22:20
Default Will try..
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hi ,,
you have not mentioned your mesh size and type of mesh.Anyhow your problem is simple and the reason for not stalling the airfoil is not dependent upon mesh.you should make sure that your airfoil vortex data was correct in Gambit and proper domain and boundary conditions were given in Fluent.I will suggest a circular domain with "pressure far field" boundary condition.

Thanks for the comment.. Well, im trying with 3 different meshes, structured, unstructured and also with boundary layer.. I also tried coarse, medium and fine for all the meshes. But for my boundary layer, when i reach 10 deg, my fluent data is not converge, but fluent gives me a repetitive 'mountain shape data. /\../\ something like i show here..
i am using a circular arc to put my airfoil and a rectangular at the back of airfoil.. then boundary condition i used for the arc is velocity inlet. perhaps i will try pressure far field and see whether i get the correct result or not.. Thanks again..
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Old   January 18, 2010, 03:28
Default no problem..
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no need to say thanks,,,

wish you all the best for your project !
by the way you even dont need boundary profile at this stage,,,
simply make an airfoil with circular domain,and tri paved mesh,,
you will find good results..
increase the difficulty gradually...
good luck
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Old   January 18, 2010, 03:54
Default Trouble..
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Im trying to use pressure far field at the arc of my mesh (means the front part, however i still cant get the desired values.. i get a very high value for my cl. I got 4.2 for my angle of attack 5 deg. last time, i used velocity inlet at the arc. Im not that familiar with fluent, but time is kinda limited for me to explore everything.
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Old   January 18, 2010, 04:02
Default haha..
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I set the wrong gauge pressure... hahaha..
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Old   January 18, 2010, 05:14
Default Still cant..
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I still cant get the satisfying results although i used pressure far field.. i dont know wats wrong..
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