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Old   November 28, 2001, 12:02
Default modelling an airfoil
  #1
Chetan Kadakia
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Hi everyone,

I tried modelling an airfoil in Gambit, and it seems Gambit is not very good with this.

I would like to use another program like AutoCAD, but how can I take the AutoCad file into Gambit?

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Old   November 28, 2001, 19:01
Default Re: modelling an airfoil
  #2
Jim Clancy
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Chetan,

Gambit can do the job easily. If you are familiar with Autocad you can export the model to gambit after you save it in the proper format like STEP but then u have to prepare the model for meshing, some times many faces and/or edges to be deleted.

I think it is easier for you to use gambit for such simple model.

Good luck
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Old   November 28, 2001, 19:04
Default Re: modelling an airfoil
  #3
Chetan Kadakia
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but the curved airfoil, is not modeled smooth in Gambit... okay I'll try it again
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Old   November 28, 2001, 23:30
Default Re: modelling an airfoil
  #4
rafat
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why dont you use NURB to connect your points. I think it looks better than stepwise lines.
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Old   November 29, 2001, 00:45
Default Re: modelling an airfoil
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Chetan Kadakia
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I think I tried that... (I'll try it again)
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Old   November 29, 2001, 06:19
Default Re: modelling an airfoil
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An Modh Coinniolach
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If you really want to use Autocad, draw out your blade and fluid domain, turn both into regions (REGION command) and then subtract the blade region from the fluid domain region. Export this to an ACIS file (*.sat) and you can import this file type into Gambit without difficulty. I assume you are not interested an anyting going on internal to the blade.
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Old   November 29, 2001, 06:46
Default Re: modelling an airfoil
  #7
Andrew Parker
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I am spending my whole final year project at uni. Researching an airfoil in a wind tunnel using Fluent 5.5.14, at the moment I am only doing 2D, but I am getting pretty good at it, feel free to direct any questions to myself as this is something I am spending a lot of time on.

I would be happy to help,

Cheers

Andy
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Old   December 2, 2001, 21:24
Default Re: modelling an airfoil
  #8
Chetan Kadakia
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How did you model your airfoil? In Gambit, or with some other program? Does you airfoil have a relatively large camber?

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Old   December 3, 2001, 04:41
Default Re: modelling an airfoil
  #9
popcool
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i have same problem , how to define a curvature accurately better than autocad
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Old   December 3, 2001, 04:53
Default Re: modelling an airfoil
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Andrew Parker
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There is a very simple way of doing this and very accurately as well. I use another program called Xfoil, it is a viscous panel method code, but it has the ability to output 280 points specifying the curvature of any NACA 4-digit airfoil, which can be modelled for camber, scaled, and so on

It would take some time to explain, so if you are using 4-digit NACA sections and this is what you are after then e-mail me back and I will fill you in, in essence all you do is output the file and import it into Gambit as vertex data and then nurb the curve.

Hope this helps

Andy
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Old   December 3, 2001, 16:17
Default Re: modelling an airfoil
  #11
Steve
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Chetan abd Andrew,

I'm interested in highly curved airfoil sections. What Airfoils are you modelling and at what Reynolds number? What do you have in the way of wind tunnel data? How do you deal with transition, I know Xfoil can handle this with its BL model, but FLUENT?

Chetan,

You said you had used NURBS to represent the airfoil. These should be contiuous by definition. I don't know Gambit but perhaps it is just an illusion that the geometry isn't smooth. Gambit probably presents the curves to the screen as a series of line sections. You may find that when the grid is generated the grid points are off the surface and in their correct mathematical locations. You can probaly crank up some sort of geometry tolerance so that the curves look smooth. Of course when you generate a grid it will be made up of linear sections but you should have many points where there is high curvature anyway. Good luck. If I am wrong then just import the curves as IGES from any CAD package.

Steve

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