diffuser behind the rear wheels

[Meister]

Hi everyone,
i noticed an interesting postioning of the diffuser which is right behind the rearwheel without any connection to some kind of underbody tubes.
first example is the march 751 brabham:


second example is the pagani zonda r:


can anyone explain what the intension of this setting is and wheter it works out? has it something to to with the low pressure area behind a moving wheel?
kind regards
meister

[Giblet]

The whole point of a diffuser is to be fed air from upstream, then diffuse/expand it. I don't see how having a diffuser only in front of the tires will be fed much air and do to much.

Here is a shot of that car without that diffuser (or any diffuser at all) from Montreal 2010

[RacingManiac]

I can see maybe if it allows for more expansion by being fed through the under body flow from the middle....Considering the double decker idea was to get more expansion volume, going to the side might work too? The Zonda one might be like that...

[horse]

second example is the pagani zonda r:

Well, you know, the above photo might look a bit silly without the whole bodywork of the car seen here:



The rear bodywork and the spoiler help to improve the performance of the diffuser.

You don't necessarily need a source of low pressure to drive the diffuser (like the bodywork or spoiler), just its shape will induce ground effect (assuming the car is low enough)

[gato azul]

not a uncommon solution, also notice the small gurney flap on top of the diffuser extension behind the rear wheel.

[MadMatt]

There was a thread here regarding this : http://www.f1technical.net/forum/viewto ... f=5&t=5410

I am also wondering about these devices. Isn't there a REAL explanation on what they are trying to achieve with them?





And this just to remind you how cool cars low to the ground are (take this, FIA):

[wesley123]

It is just to improve downforce with the area they can work on. it might not add much but it adds a little more and the fins might even help with controlling the airflow from the rearwheel.

[Gecko]

Do not forget that the tyres are rotating when the car moves. The bottom of a rotating tyre does not really block the air upstream in a way a non rotating tyre would.

Think about it form the point of view of still air and the car driving through it. The bottom point of the tyre is stationary, so the still air in the vicinity of this point is not that much disturbed. When the tyre passes over the stationary air, it pushes the air slightly to the sides and then back together (as it effectively rolls down onto the air, then lifts again), but it does not drag the air along with the car in a way a locked tyre would. Therefore, if only the bottom part of the tyre sticks out from the underbody, the effect on the air, especially in the direction of the car movement, as compared to a situation with no tyre is much less than what it would initially appear.

[MadMatt]

Gecko, English is not my native language but despite reading your message 3 times I still don't really understand its full meaning. Correct me if I'm wrong, but (as you don't talk about these flaps behind the wheels) I assume they are there to suck the air behind the tire help help reducing the drag. My knowledge is quite limited in aero (I'm learning) but that's the hypothesis I have !