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 llbai@hotmail.com May 25, 2010 04:53

I had a look at the fluent tutorials at http://courses.cit.cornell.edu/fluent/airfoil/index.htm. I noticed that AOA 1.2° instead of 2° were used to calculate the actual AOA 2°. It was explained as a 2d adjustment. ("Note that 1.2° is used as our angle of attack instead of 2° to adjust for the error caused by assuming the airfoil to be 2D instead of 3D.").

Could someone tell me how the 0.8° offset is decided? Is there any theory to support this?

 mct90 May 13, 2013 06:53

Quote:
 Originally Posted by llbai@hotmail.com (Post 260094) I had a look at the fluent tutorials at http://courses.cit.cornell.edu/fluent/airfoil/index.htm. I noticed that AOA 1.2° instead of 2° were used to calculate the actual AOA 2°. It was explained as a 2d adjustment. ("Note that 1.2° is used as our angle of attack instead of 2° to adjust for the error caused by assuming the airfoil to be 2D instead of 3D."). Could someone tell me how the 0.8° offset is decided? Is there any theory to support this? Thanks in advance. Your reply is really appreciated.
I want to ask the same question. I am searching but i couldn't find yet. For example ,If angle of attack is 4°, which degree must be use?

 oj.bulmer May 13, 2013 08:46

The 2D simulation of airfoil assumes that the width of airfoil wing in thierd direction is infinite, and the flow in the third direction is zero. While, in 3D (and reality) the width is finite and there is a finite flow in 3rd direction. Hence, for same inlet velocities, the lift for 2D will be always higher than ones from 3D and hence to realize the same effect of 2deg on 3D wing, the 2D wing uses smaller angle.

There is some explanation provided here to estimate how these different values of angle of attack are related.

http://www.mh-aerotools.de/airfoils/hdi_aoawing.htm

OJ

 mct90 May 13, 2013 15:50

Quote:
 Originally Posted by oj.bulmer (Post 427180) The 2D simulation of airfoil assumes that the width of airfoil wing in thierd direction is infinite, and the flow in the third direction is zero. While, in 3D (and reality) the width is finite and there is a finite flow in 3rd direction. Hence, for same inlet velocities, the lift for 2D will be always higher than ones from 3D and hence to realize the same effect of 2deg on 3D wing, the 2D wing uses smaller angle. There is some explanation provided here to estimate how these different values of angle of attack are related. http://www.mh-aerotools.de/airfoils/hdi_aoawing.htm OJ
Thank you for the response. It was very helpful.

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