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-   -   Get coordinates of airfoil from picture (http://www.cfd-online.com/Forums/main/13132-get-coordinates-airfoil-picture.html)

Ben March 14, 2007 00:46

Get coordinates of airfoil from picture
 
Hi,

This is not directly related to CFD but I think someone here may have encountered this problem before.

Suppose I have a picture of an airfoil (in jpg,gif etc). How can I get its coordinates? I need them to draw an outline to build my mesh. Is there any software which can help?

thank you

Charles March 14, 2007 02:36

Re: Get coordinates of airfoil from picture
 
http://digitizer.sourceforge.net


Praveen. C March 14, 2007 03:31

Re: Get coordinates of airfoil from picture
 
While you could use some software like digitizer, it will not give you a good airfoil definition. I would not take such an approach to get my airfoil shape.

Charles March 14, 2007 03:47

Re: Get coordinates of airfoil from picture
 
Something that you could try (given the total absence of actual coordinates) is to digitize it, and then to take those coordinates into an airfoil design program like XFoil to smooth them, before doing a CFD mesh. Working with the raw digitized coordinates is likely to produce an extremely lumpy pressure distribution. It is amazing how sensitive airfoils are to small unevenness. Having said all that, If you can't get the actual coordinates, they are probably proprietary, and you shouldn't be doing this work!


Jules March 14, 2007 11:13

Re: Get coordinates of airfoil from picture
 
Just find out the properites of your aerofoil and use Xfoil or Javafoil to generate it. Alternatively look it up and get a complete list of co-ords say from a database of NACA aerofoils.

buch March 14, 2007 14:19

Re: Get coordinates of airfoil from picture
 
Hi,

Just keep in mind that in many publications, pictures do not always have the good aspect ratio. This can be done intentionally or not, but you may have problems if you just trust a picture.

Regards


Ben March 14, 2007 21:08

Re: Get coordinates of airfoil from picture
 
Thanks everyone. Teh digitizer works although it's quite difficult to get a smooth airfoil.

I've found a program called profili which seems to be able to take an image and get the approx coordinates. However, this feature seems to work only in the registered version :(

Anton Lyaskin March 16, 2007 05:51

Re: Get coordinates of airfoil from picture
 
If the airfoil comes from some paper, usually its name is stated. Or you can contact the authors about it. If it's from aircraft, you can also try to find it here

http://www.ae.uiuc.edu/m-selig/ads/aircraft.html

George March 16, 2007 09:56

Re: Get coordinates of airfoil from picture
 
You can also draw it yourself. You can use the Joukowski transformation algorithm and if you know the chord length and some other geometrical values you can use this transformation and with a few different configurations (and maybe many different tries) you can get analytically the coordinates.


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