Can't get accurate lift and drag coefficients

Project Support
1

Hello! I am trying run incompressible simulations for a NACA 0012 airfoil at a variety of angles of attack at a speed of 15 m/s. My goal is to see how lift and drag coefficients change with angle of attack.

Here are the links to my project:
Part 1 (AOA = 0, 8, 16 degrees)
Part 2 (AOA = 24, 32 degrees)

From the force coefficients plots for each run, these are the results I have gotten:

image
image520×183 3.17 KB

However, these results do not make sense because the critical angle of attack should be somewhere around 16 degrees, so the lift coefficient should not keep increasing. Additionally, drag is supposed to increase with angle of attack, not decrease.

Could someone please help me figure out what I am doing wrong? Also, I would appreciate if you could explain things simply because I am just in high school and completely brand new to CFD ! :slight_smile:

2

Hello SayanS,

without looking too deeply into your project, I can give you the following suggestions.

#1 Meshing,
Wings are especially sensitive to the mesh settings, because for example the accuracy of the leading edge or the accuracy of the suction side, can have a huge influence due to separation points and vortices. For example, your leading edge looks very coarse.

#2 Tip vortex.
Most of the results you find online for wing profiles are so that the tip vortex is not been taken into account.
(More info on tip vortices can be found here: aerodynamics of wing vortices )

Therefore i would suggest you create a case without an open end and try to dial in the mesh so that it matches the theoretical results. Once this is achieved you can sightly change the AoA.

Best regards
Sebastian