Angle of Attack (AoA) adjustment for 2D / 3D

FractureProof · May 10, 2010, 09:21

Hi, I have about 20 years of structural / stress analysis experience, however I am just diving into some CFD research to create a realistic aircraft to base a training course around.

I have gone through some simple tutorials for using FLUENT from Cornell:

http://courses.cit.cornell.edu/fluent/airfoil/step4.htm

In which, the objectiv eis to model a 2D NACA airfoil section at 2 deg AOA. In the process, it states "(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.)"

I imagine this is maybe due to vortex shedding.. but I'm just guessing... Can someone detail this requirement and provide link to allow me to calculate this adjustment for arbitrary AoA. Thx.

agd · May 10, 2010, 09:39

If I remember correctly, it is actually due to the fact that in a 2D simulation, there is no third dimension for the flow to move in. In 3 dimensions the angle of attack has to be slightly higher to get the same effective momentum change for lift because some of the flow can move out along the wings. John Anderson has a good basic Aero book (whose title escapes me now). Katz and Plotkin also have a good book on low speed airfoil theory, but again the title escapes me and I am at work while my books are at home. You could also try googling low speed airfoil theory or potential theory for airfoils.

May 10, 2010, 09:21	Angle of Attack (AoA) adjustment for 2D / 3D	#1
FractureProof New Member Mitch Greenberg Join Date: May 2010 Posts: 1 Rep Power: 0	Hi, I have about 20 years of structural / stress analysis experience, however I am just diving into some CFD research to create a realistic aircraft to base a training course around. I have gone through some simple tutorials for using FLUENT from Cornell: http://courses.cit.cornell.edu/fluent/airfoil/step4.htm In which, the objectiv eis to model a 2D NACA airfoil section at 2 deg AOA. In the process, it states "(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.)" I imagine this is maybe due to vortex shedding.. but I'm just guessing... Can someone detail this requirement and provide link to allow me to calculate this adjustment for arbitrary AoA. Thx.

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May 10, 2010, 09:39		#2
agd Senior Member Join Date: Jul 2009 Posts: 358 Rep Power: 19	If I remember correctly, it is actually due to the fact that in a 2D simulation, there is no third dimension for the flow to move in. In 3 dimensions the angle of attack has to be slightly higher to get the same effective momentum change for lift because some of the flow can move out along the wings. John Anderson has a good basic Aero book (whose title escapes me now). Katz and Plotkin also have a good book on low speed airfoil theory, but again the title escapes me and I am at work while my books are at home. You could also try googling low speed airfoil theory or potential theory for airfoils.