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Old   October 16, 2006, 22:19
Default angle of attack CFX
  #1
Arj
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Hi all,

I am just investigating lift and drag characteristics of a Boeing-737 airfoil. The issue i have is, i obviously can set the fluid flow at zero (0deg) angle of attack (default) but how may i change the angle of attack? Where abouts in CFX-Pre? Do i need to change global parameters?

Cheers for your help in advance, Arj
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Old   October 17, 2006, 05:29
Default Re: angle of attack CFX
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Johnny
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Either rotate the airfoil in your geometry and remesh, or depending on how you set up your case, you might just be able to change the inlet velocity so that it enters at the angle you want.
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Old   October 17, 2006, 06:11
Default Re: angle of attack CFX
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Arj
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My airfoil geometry is referenced at the origin, with the chord running through one of the axes. So, I don't think rotating the geometry will do much, as the airfoil is referenced along the horizontal.

"you might just be able to change the inlet velocity so that it enters at the angle you want." Do you know how i may change the inlet velocity so it enters at the angle i want?

How do "expressions" or "command editor" work, i found these in CFX-Post. will i be able to change ang. of attack this way?

Cheers, Arj
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Old   October 17, 2006, 06:52
Default Re: angle of attack CFX
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Kir
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When you input the inlet boundary condition in CFX-Pre, you may not select the "Normal", you should select the "Cartesian coordinates" or others, and input the velocity component that you need.

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Old   October 17, 2006, 07:19
Default Re: angle of attack CFX
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Arj
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Therefore, are you saying I should resolve the velocity in the specific direction into its x and y components?

Also, for example, does this U, V, and W inlet velocity refer to the axis ANSYS refers to (bottom left hand corner of screen)?

sorry for all the questions, im just new with ANSYS (and CFD!!) altogether, and i am learning this stuff from scratch with no one to physically show me how to do things.

cheers, Arj
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Old   October 17, 2006, 07:28
Default Re: angle of attack CFX
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Kir
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Yes,you may specify the velocity direction,but you may think about the inlet boundary, when you change the direction,your other boundaries may also need to be modified. U, V, and W of velocity respectively represent the Velocity of X, Y, Z direction.
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Old   October 17, 2006, 08:23
Default Re: angle of attack CFX
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Arj
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I dont quite understand what your saying about the inlet velocity settings, I already have a cartesian velocity setting in my "Global Initialisation values".

Ok if velocity is 2-dimensional do i change the two velocity components with respect to the axis. So for example if my airfoil is in the Z-Y plane. Initially at 0 angle of attack U=0m/s, V=0m/s and W=30m/s.

If i wanted an angle of attack of say 30deg, does this now mean U=0 m/s, V=30sin(30) and W=30cos(30). And so i monitor the forces (in the out file) etc. with thesen new global parameters

Cheers, Arj
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Old   October 17, 2006, 09:05
Default Re: angle of attack CFX
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Kir
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Your setting of U=0 m/s, V=30sin(30) and W=30cos(30) is right, but you should modify it not noly the initialisation values, but also the inlet velocity profile.
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Old   October 17, 2006, 13:03
Default Re: angle of attack CFX
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Robin
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Hi Arj,

I think you would benefit from running a few tutorials are reading some of the documentation before diving right into your application.

Regards, Robin
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Old   October 17, 2006, 17:18
Default Re: angle of attack CFX
  #10
Arj
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Hi Robin, I appreciate the advice, however I have completed a few tutorials, which have got me thus far. It's just most of them apart from "flow over a blunt body" and "supersonic flow over a wing" don't help me very much at the specific issue at hand right now. Plus time isn't my friend exactly,

Should I be looking at CCL expressions (expression editor) or so?

Cheers, Arj
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Old   October 18, 2006, 02:31
Default Re: angle of attack CFX
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Michael B
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I'm NOT getting on a plane if you are doing the CFD calculatons thats for sure!
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Old   October 18, 2006, 02:58
Default Re: angle of attack CFX
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Arj
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Cheers mate, thanks for that tip
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Old   October 18, 2006, 04:22
Default Re: angle of attack CFX
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jon
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I would craete a mesh with the wing and boundary layers in one mesh contained within a circular section, I would then have an outer mesh that has the circular section cut out. You can then rotate the inner mesh to the angle of attack required connecting them both with a grid interface. It will make your results easier to compare and less likely to have blockage effects.

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Old   October 18, 2006, 08:06
Default Re: angle of attack CFX
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Arj
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Thanks jon,
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Old   October 18, 2006, 08:30
Default Re: angle of attack CFX
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Robin
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I think it would be much simpler to have openings on the top and bottom walls (using the static pressure entrainment condition) and specify the velocity components at the inlet.

-Robin
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Old   October 18, 2006, 09:19
Default Re: angle of attack CFX
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jon
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It is simpler, and I will agree with that. However if rotation is to be significant and without having an unecessarily large domain, the rotating mesh solution will be much cheaper and provide an easier plane for comparison.

personal opinion.
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Old   October 18, 2006, 09:22
Default Re: angle of attack CFX
  #17
Kevin
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Hi Jon,

I was wondering if you could take a look at my posting "Proper output of angle of attack in cfx post"

Thanks Kevin
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