NoDivergence wrote:First off, you do know that underbody flow at the entrance to diffuser is definitely not at freestream velocity, right? And that a lot of volume actually comes from the side of the vehicle? This S15 is very very wide. Floor area is huge. Also, the region of low pressure behind the car is huge.
Of course, I never said otherwise. Although I do not really agree with your second sentence regarding the flow coming from the side. This will depend on a lot of factors (car geometry and aero setup). Not to mention some guys will use side skirts to block the flow from entering from the side, so what you say is not always right and you will only know once you've seen CFD or wind tunnel experiment.
NoDivergence wrote:Andrew Brilliant has a lot more experience than you do. There are lots and lots of tricks, but looking at MCA hammerhead S13, Nemo Evo, and the Scorch Racing S15, there's an obvious trend arising.
Why the critisism? I never claimed to be better than X so why are you doing it? You have no idea of who I am or what experience I have. Also experience doesn't mean you are good at something, it just means you have been doing it for a long time. Andrew didn't invent anything, he just used what Katz, Hucho, and what others discovered and applied these concepts to the car. He did it well since the results are there, but give this amount of cash to some people on this forum and they will also produce some good machines.
NoDivergence wrote:Nemo Evo downforce was 5400 lbf at 150 mph, and this was measured and confirmed on track. The S15 has much, much more.
24kN then. Some group C cars had that amount of downforce (Allard J2X for example), but achieved that WITH regulations. Also you say this was measured and confirmed, do you actually have evidence of this? This is the engineer talking, I would love to get a hot lap data that I can analyze (Motec format, PI, excel, whatever).
That streamline thing doesn't show anything, it is more of a commercial picture than else, so I will not comment on this. As for quantify downforce by looking at the upwash, well, I have no words. With your 2 last arguments, you just showed me that you don't know much and that talking about this car (or its aero designer) will just create a fanboy rant so I will leave it here. Are you related to him by the way?
EDIT: I dug in my folders and I found experiments I did on a Cooper body. I had a small wind tunnel where I experimented with ride height and diffuser angle changes, and did the same in CFD. I was able to see that there is a tipping point in the diffuser angle where you start loosing downforce (in my case 20° was the best, 25° nearly as good, but 30° a big loss). It will of course vary with speed, the shape, and tons more parameters, but more diffuser angle is not always better, that's the point I was trying to make by posting the picture.