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-   -   CEL expression for projected area? (http://www.cfd-online.com/Forums/cfx/94190-cel-expression-projected-area.html)

k.vimalakanthan November 8, 2011 15:45

CEL expression for projected area?
 
Hi Guys,

Could anyone please help with the exact CEL expression to compute the projected area (normal to x axis)of an Iso clip (3D surface)?

I have tried:

area()@IsoClip1 = seems to give me a very large value
area_x()@IsoClip1 = Seems to give me a smaller value than expected (in the order of 10)

Lastly I was told to try

IsoClip1.area_x()@IsoClip1

Which gives an error message as such:

"ERROR
The following unrecognised name was referenced: IsoClip1.area_x."

Any help is greatly appreciated,
Thanks in advance. :)

ghorrocks November 8, 2011 17:35

If your iso clip is wrinkly it will have a massive area. The area_x function will not give you the projected area if it is a folded or wrinkly surface.

I would try to define a new iso clip surface which is flat and the area of that should not be a problem.

k.vimalakanthan November 8, 2011 17:47

Quote:

Originally Posted by ghorrocks (Post 331268)
If your iso clip is wrinkly it will have a massive area. The area_x function will not give you the projected area if it is a folded or wrinkly surface.

I would try to define a new iso clip surface which is flat and the area of that should not be a problem.

Thanks ghorrocks,

Basically I'm trying to calculate force operating (projected) area of the small span wise section of a turbine blade (iso clip), which is fairly smooth in this case. This will help me to calculate the coefficient of thrust and torque value for this annulus element.

Do you have any other CEL expressions that I could use to preform this area calculation?

Thanks in advance

ghorrocks November 8, 2011 17:50

If you want the force then use the force_x/y/z functions.

k.vimalakanthan November 8, 2011 20:00

Quote:

Originally Posted by ghorrocks (Post 331278)
If you want the force then use the force_x/y/z functions.

Well CFX Post calculates the forces and moments (thrust and torque) on the iso clip fine, but I'm trying to calculate the non dimensional torque and thrust* for this anulus element. This require the force operating area (projected area).

i.e. Ct = Thrust / (q*dA)

so Ct = force_x()@IsoClip1/(DynH*dA)

I need to find the exact 'dA' that this force (force_x()@IsoClip1) was calculated on.

ghorrocks November 8, 2011 23:22

The area() and area_x() functions should work. Can you give more details as to why it is wrong? Can you show and image of what you are doing?

k.vimalakanthan November 9, 2011 12:13

Quote:

Originally Posted by ghorrocks (Post 331300)
The area() and area_x() functions should work. Can you give more details as to why it is wrong? Can you show and image of what you are doing?

Hi ghorrocks,

Unfortunately, I'm not in a position to display the image of the geometry, however I have found this in the CFX manual:

"area
The area function is used to calculate the area of a 2-D location"

and

"An error is raised if the location specified is not a 2-D Object"

Does this mean that, the projected area of a 3D surface cannot be computed in CFX Post?
I have tried using TecPlot but had no luck too :(

ghorrocks November 9, 2011 19:17

The area function returns the area of a surface body. The surface can be twisted in space, it will return the surface area of the whole body. The error shows you are giving it a point, line or solid body and you cannot use the area function on them.

I do not know off hand how to get projected areas but it should be possible. You will probably have to do some playing around to get it.


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