2D Computational Fluid Dynamics simulation for our 818R - APR GTC-300 Rear Wing

[SixStar]

We had Zebulon Motorsports Consulting run some CFD on the APR GTC-300 wing to see what AOA (angle of attack) we should start with given our down force and top speed goals. They found out that an AOA of ~5-10 degrees would be ideal on our 818R since it has no windscreen or roof. The suggested starting point of the GTC-300 should even be set much lower than APR suggests given the design of the wing. Even at a 0 AOA there will still be separation on the sides since the wing isn't flat and exhibits flow closer to 15 AOA on the sides at a 0 AOA.

All simulations are at 100 mph. Vector traces are scaled
from 0 to 350 mph as seen on photo scales.

0 Degrees AOA
0AOA.jpg

15 Degrees AOA
15AOA.jpg

25.5 Degrees AOA
25.5AOA.jpg

From these simulations we can draw some interesting conclusions about the wing design.
First, remember that this is a twisted wing. As such, when they have the wings at 0 degrees
AoA, APR expects that the effective flow-based AoA is ~15 degrees. This can be derived
from the ~15 degree twist built into the wing. When the center is at 0 degrees AoA, the
outer edges are at 15 degrees. This makes the 0 degree simulation null, except in the case of
cars without windshields – like the 818R. At 0 AoA, you can see the extreme camber of the
wing is detrimental; the airflow cannot compensate and separates off the top. This is not
extremely bad, but it does limit the wing.

At 15 degrees AoA, or what the center section would effectively be at on a sedan, and
what the outer ends are at to start, the wing already separates off the back. In 3d, this would
not be as pronounced, but with this degree of separation it would still exist to some extent
and be highly detrimental to performance.

Hope this helps some folks when setting up their aero. Remember, tuning is a science and takes time and patience but having a good starting point never hurts!