As someone working with semiconductors, I think the limit should be watts instead of flops to encourage competition in this aspect too.
Can't they use a secret cloud somewhere?
The fines for cheating (unless you are Ferrari, usually) are catastrophic (for a non-works team): Lots of money and probable disqualification from the WCC
Of course they could cheat but the penalties of getting caught are severe.
The limit isn't very high, though. A single box with a few GPUs is enough to hit the limit.
also 30 teraflops of RANS simulations is a lot.
basic cfd with turbulence modelling can get you pretty close and then refine in wind tunnels.
the other techniques are LES https://en.wikipedia.org/wiki/Large_eddy_simulation
genetic algorithms and iterative optimization is leading to more organic and nature inspired shapes in the latest generations.