Cd and Cl coefficients

shift8650 · February 5, 2020, 12:14

Good day,

I am trying to get Cl and Cd coefficients in post result expression tab, by writting formulas:

Fy=force_y()@Airfoil
Fx=force_x()@Airfoil
Lift =cos(AOA)*Fy-sin(AOA)*Fx
Drag =cos(AOA)*Fx +sin(AOA)*Fy
Denom=0.5*massFlowAve(Density)@Inlet*Uinf^2*Area
cL=Lift/Denom
cD=Drag/Denom

Im struggling with the Area part, because I dont know what formula to use for calculating airfoil area. Im researching NACA0012 airfoil with angle of attack of 0.

Any help would be really appreciated because I want to validate my CFX results with XFOIL calculations of Cl and Cd

ghorrocks · February 5, 2020, 17:07

You need to read the papers you are comparing against because CL and CD definitions vary depending on what you are doing.

For most bodies CL and CD are based on frontal area. But for airfoils the area is the planform area. If you are doing NACA0012 work it is almost certainly planform area, but check first.

shift8650 · February 5, 2020, 17:12

Hi,

Thank you for the reply. Could you tell me how can I calculate the planform area? Is there a formula for it regarding the airfoil?

ghorrocks · February 5, 2020, 17:20

Refer to: https://lmgtfy.com/?q=planform+area

February 5, 2020, 12:14	Cd and Cl coefficients	#1
shift8650 New Member Join Date: Feb 2020 Posts: 2 Rep Power: 0	Good day, I am trying to get Cl and Cd coefficients in post result expression tab, by writting formulas: Fy=force_y()@Airfoil Fx=force_x()@Airfoil Lift =cos(AOA)Fy-sin(AOA)Fx Drag =cos(AOA)Fx +sin(AOA)Fy Denom=0.5massFlowAve(Density)@InletUinf^2*Area cL=Lift/Denom cD=Drag/Denom Im struggling with the Area part, because I dont know what formula to use for calculating airfoil area. Im researching NACA0012 airfoil with angle of attack of 0. Any help would be really appreciated because I want to validate my CFX results with XFOIL calculations of Cl and Cd

February 5, 2020, 17:07		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	You need to read the papers you are comparing against because CL and CD definitions vary depending on what you are doing. For most bodies CL and CD are based on frontal area. But for airfoils the area is the planform area. If you are doing NACA0012 work it is almost certainly planform area, but check first. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

February 5, 2020, 17:20		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	Refer to: https://lmgtfy.com/?q=planform+area __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

February 5, 2020, 17:12		#3
shift8650 New Member Join Date: Feb 2020 Posts: 2 Rep Power: 0	Hi, Thank you for the reply. Could you tell me how can I calculate the planform area? Is there a formula for it regarding the airfoil?