This blog post describes the performance gain of the Perrin Performance BRZ gurney flap on the 2013-2016 Subaru BRZ.
Slightly increased drag
Improved aerodynamic efficiency
All work was done using ANSYS software: geometry preparation was completed using SpaceClaim, meshing was done with ANSYS Meshing, setup and solution
Comparing the two figures above, the rear wake changes a significant amount. The low-velocity region moves in the positive Z direction on the gurney model. This is caused by the gurney redirecting the airflow over the factory BRZ wing. Also, note the low-velocity region in front of the gurney. This area is a higher pressure zone. The gurney acts more like an air dam than a traditional gurney.
In the figure above we note the vortex coming off of the vertical strake on the wing. These vortices are caused by pressure differentials caused by the wing and gurney interaction.
Aerodynamic Coefficient Deltas
Deltas are what really matter when dealing with simulations: whether it be CFD or wind tunnel testing. The delta is defined as the difference between the gurney flap model coefficient and the stock model coefficient. Below we can see we increased drag coefficient by 11 counts, and reduced coefficient by 55 counts.
Aerodynamic forces change with the square of velocity. That is why a solid downforce number cannot be given unless it is at a specific speed. Most OEM road vehicles create lift from the factory, and the Subaru BRZ is in that category. Notice the below graph, the factory lift from the BRZ is reduced while drag is slightly increased.
The Perrin Performance Gurney decreased lift and slightly increased drag of the BRZ. The overall aerodynamic efficiency was increased even though the drag was increased slightly. The gurney acted like a spoiler air dam more than a traditional gurney flap. This can clearly be seen in the Cp plots by looking at the higher pressure regions in front of the gurney. This high-pressure area is where most of the downforce is created. Overall, if you want to increase the aerodynamic performance of your BRZ, the Perrin Performance Gurney is a great component to install.