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Arj October 16, 2006 22:19

angle of attack CFX
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

Johnny October 17, 2006 05:29

Re: angle of attack CFX
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.

Arj October 17, 2006 06:11

Re: angle of attack CFX
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

Kir October 17, 2006 06:52

Re: angle of attack CFX
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.

Arj October 17, 2006 07:19

Re: angle of attack CFX
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

Kir October 17, 2006 07:28

Re: angle of attack CFX
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.

Arj October 17, 2006 08:23

Re: angle of attack CFX
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

Kir October 17, 2006 09:05

Re: angle of attack CFX
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.

Robin October 17, 2006 13:03

Re: angle of attack CFX
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

Arj October 17, 2006 17:18

Re: angle of attack CFX
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

Michael B October 18, 2006 02:31

Re: angle of attack CFX
I'm NOT getting on a plane if you are doing the CFD calculatons thats for sure!

Arj October 18, 2006 02:58

Re: angle of attack CFX
Cheers mate, thanks for that tip

jon October 18, 2006 04:22

Re: angle of attack CFX
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.

Arj October 18, 2006 08:06

Re: angle of attack CFX
Thanks jon,

Robin October 18, 2006 08:30

Re: angle of attack CFX
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.


jon October 18, 2006 09:19

Re: angle of attack CFX
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.

Kevin October 18, 2006 09:22

Re: angle of attack CFX
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

asap171 October 2, 2015 07:07

Hi Arj and Kir,

On the method of specifying the U, V and W velocities, I was wondering how much would my flow get affected after striking the outer domains of the setup.

I am doing 3d flow analysis of a badminton shuttlecock inside a cylindrical domain. Now when I start to think about introducing angle of attack by specifying the component wise velocities, I wonder my flow will get highly messed up due to mixing from the flow that gets reflected from walls.

My domain is around 10 times the diameter of shuttlecock skirt.


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