Discussion Forum

As you may know, there is a NACA 0012 model in application library which tries to validate the lift coefficient and pressure coefficient (with respect to angle of attack) against existing data in the literature.

The lift force is obtained by integrating either of the following equations over the airfoil:

• (Eq.1): (spf.T_stressx * sin(alpha * pi/180)-spf.T_stressy * cos(alpha * pi/180))

• (Eq.2): p * (spf.nymesh * cos(alpha * pi/180)-spf.nxmesh * sin(alpha * pi/180))

Now if I want to calculate the drag force (and then the drag coefficient), I should theoretically rewrite (Eq.1) as in

• (Eq.3): (-spf.T_stressx * cos(alpha * pi/180)-spf.T_stressy * sin(alpha * pi/180))

However, the obtained results are not consistent with the data in the literature. For example, at 14 degrees, my cd (coefficient of drag) is 0.027 whereas Ladson's data (Ref.1 which was used to validate lift coefficients), mentiones a value of 0.01625. The discrepancy at lower angles (up to 5 degrees) is acceptable.

Is the NACA 0012 model in the application library suitable for obtaining drag coefficient at all? I mean the utilized SST physics, which does not use a wall function, can predict drag coefficient data? Or the equation for obtaining drag force/coefficient can be rewritten differently?

Ref.1: 1. C.L. Ladson, “Effects of Independent Variation of Mach and Reynolds Numbers on the Low-Speed Aerodynamic Characteristics of the NACA 0012 Airfoil Section,” NASA TM 4074, 1988.