[frossi]

I am conducting a study of the effects caused by changing the winglet cant angle. In particular, I am observing how drag, lift, and L/D of the whole wing change as the winglet cant angle is changed.

Wing
My wing has a dihedral of 6 deg, and thus I consider the winglet to be "flat" (0 cant angle) when it has an angle of 6 deg from the horizontal.

Winglet
The winglet cant angle is changed from 0 cant angle (same deflection as wing dihedral) to 60 deg, at increments of 3 deg.

Conditions
My wing (as seen in the picture) has an angle of attack of 7.5 deg, a velocity of Mach 0.392. The ambient conditions are those at 3,000 m altitude.

As you can see from my graphs:
1) The values before 42 deg winglet angle seem to oscillate

2) There is a huge jump in both lift and drag from 42 deg winglet deflection to 45 deg winglet deflection. How can a 3 deg change give this much of a difference?

3) The pattern after 45 deg winglet seem more stable and reasonable. Why is this?

It looks like when the winglet is at 45 deg (39 deg from the horizonatal) something changes, either in the physics or the math, so that my results change drastically. I thought it may be an error in the way in which the software calculates lift, or maybe the force components, due to the fact that the winglet is inclined compared to the wing, but I cant figure it out.
I also thought it may be the way in which I define the force components, but they look right.

I define lift as:
x-component: -sin(7.5)
y-component: cos(7.5)

I define drag as:
x-component: cos(7.5)
y-component: sin(7.5)

What could be the cause of my results? should I define lift and drag differently for the wing? Could it be that Fluent is not resolving the components on the winglet because it is angled? Is it a geometry problem or a physics problem?

Thank you all for your help.