So you have cooling air flowing into the engine compartment, through the radiators etc.
Then where does it go?
It can't flow in if it cant flow out right. That's like you trying to blow through a snorkel or something with your hand over the other end.
Well usually its exit is out underneath the car.
And that's where this paper comes in.
Basically it says that when you put in your smooth under-body panels you want to leave an exit vent that flows that air out backwards under the car, not downwards.
The where and how big the vent should be I'll leave to the paper. and you all to discuss as it's... well; advanced aerodynamics and well above my pay grade.
https://sci-hub.ru/https://www.scien...89430497000647
Perhaps side vents are a better option? Or that aero shaping behind the wheel well story?
I will add that the Meredith Effect is interesting: (thrust from radiators/heat)
https://en.wikipedia.org/wiki/Meredith_effect
Here's another paper on all this:
https://sci-hub.ru/https://www.jstor...table/44745485
(Sci-Hub 'frees' paywalled papers to us tax paying citizens , but many ISPs seem to have been bribed or something into flagging Sci-Hub as a malicious site:
If you run the URLs through VirusTotal (and others) it isnt.
https://www.virustotal.com/gui/home/upload
If you're having trouble; say, and we can get into bypassing their BS)