Producing Non-Zero Lift Coefficient for NACA 0012 at AOA=0

cagesbuild · January 11, 2020, 15:41

I have been working on validating my CFD skills with a NACA 0012 airfoil (I have tested NACA 2412 and 0015 but had incorrect results) by investigating the Cl and Cd of the airfoil at Various AOA. I achieve this by rotating the base plane associated with the airfoils imported data. Regardless this particular question focuses at AOA=0 and thus a NACA 0012 should have cl = 0. Where as in my most recent test CL=-0.099067769 and Cd =0.87579035.
The Cl would have been acceptable at with an unrefined mesh but I don't think the quantity of cells (see attached) can be deemed "unrefined". Additionally the left far field is 5 chord lengths from the leading edge and the right far field is 10.
I am using the K-W (SST) Turbulence model with default values (5% intensity and 10 ratio) at 5 m/s.
I am the Coupled pseudo-transient method with all parameters set to "Second-Order Upwind". I used the standard initialization with default reference values and iterated to 1000.
I am not sure what the issue is with either the mesh or the solver, maybe I tweaked something I shouldn't have? Any insight into what the problem is and a solution thereof would be greatly appreciated.mesh Shown.jpg

Airfoil.PNG

cagesbuild · January 14, 2020, 17:53

Solved: It seems that the voracity viscosity ratio was too high. Following
https://www.reddit.com/r/CFD/comment...ce_validation/

With validation from:
https://turbmodels.larc.nasa.gov/naca0012_val_sa.html

January 11, 2020, 15:41	Producing Non-Zero Lift Coefficient for NACA 0012 at AOA=0	#1
cagesbuild New Member Join Date: Jan 2020 Posts: 8 Rep Power: 6	I have been working on validating my CFD skills with a NACA 0012 airfoil (I have tested NACA 2412 and 0015 but had incorrect results) by investigating the Cl and Cd of the airfoil at Various AOA. I achieve this by rotating the base plane associated with the airfoils imported data. Regardless this particular question focuses at AOA=0 and thus a NACA 0012 should have cl = 0. Where as in my most recent test CL=-0.099067769 and Cd =0.87579035. The Cl would have been acceptable at with an unrefined mesh but I don't think the quantity of cells (see attached) can be deemed "unrefined". Additionally the left far field is 5 chord lengths from the leading edge and the right far field is 10. I am using the K-W (SST) Turbulence model with default values (5% intensity and 10 ratio) at 5 m/s. I am the Coupled pseudo-transient method with all parameters set to "Second-Order Upwind". I used the standard initialization with default reference values and iterated to 1000. I am not sure what the issue is with either the mesh or the solver, maybe I tweaked something I shouldn't have? Any insight into what the problem is and a solution thereof would be greatly appreciated.mesh Shown.jpg Airfoil.PNG

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January 14, 2020, 17:53		#2
cagesbuild New Member Join Date: Jan 2020 Posts: 8 Rep Power: 6	Solved: It seems that the voracity viscosity ratio was too high. Following https://www.reddit.com/r/CFD/comment...ce_validation/ With validation from: https://turbmodels.larc.nasa.gov/naca0012_val_sa.html