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

Re: Get coordinates of airfoil from picture
 

http://digitizer.sourceforge.net

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.

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!

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.

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

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 :(

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

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.