Well said Andyman, The thing that most impresses the judges, as it should, is when aero (or any aspect of the cars design) fits well in the grand scheme of things. The problem with aero on FSAE cars is that there are quite a lot of downsides. For high downforce, wings are ideal (preferably in conjunction with a diffuser set up) however, wings create a great deal of drag, add weight, increase MoI, increase CoG height, are rideheight/pitch sensitive etc. etc. and then there's the practical issues with hitting cones. Some teams opt for a diffuser set up which has nearly none of the afore mentioned downsides other than rideheight sensitivity. If you are clever about it you can even decrease drag with the use of diffusers. However it is not likely that a large amount of downforce can be generated with diffusers alone. So in the end a team has to decide between effectiveness and efficiency, but the most important thing is whether it fits in with the teams design philosophy.
Multiple forms of testing is absolutely imperative. Each form of testing carries with it some difficult challenges but because aerodynamic devices can be so sensitive to minor changes in geometry or flow field, verification needs to be comprehensive.
Katz is a good starting point but is not particularly in-depth. SAE Papers are good if u can find the right ones. Unfortunately F1 teams don't tend to divulge their secrets either so good practical information can be hard to come by.
Playing around with 2D CFD is the best way to find a good starting point for your geometry because its quick and easy (efficient use of resources can impress the judges too) but for refining the design it needs to be 3D. Wind tunnel and on track testing are also important when some prototypes have been made. Each method is inaccurate in some way which is why it is good to have multiple methods of verification.
Anyway, I think j_types question has been answered now.
Cheers
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