could anyone explain double deck diffuser?

[Scania]

I can't understand how the air flow can make down force from in the diffuser is from the upper side of chssis.....

[TheChad]

There are gaps in the floor.

So the opening of the upper deck receives air from under the floor.

[alexbarwell]

Can anyone clarify, but is the factor that was so hotly debated that this additional diffusing element was formed in some part on the tail of the gearbox/rear crash zone, making a mandated safety design/required part have a positive aero effect. I know the aero design presents a complex boundaried volume in which to work and that the rule books are something that is more useful to a weightlifter than an engineer. I have not dug up any pics of 'with' and 'without' diffusers.
We have seen though, that a number of elements in a space can be more effective than just one bigger one, if this could be a factor, but to a limit only. (like multi-elemented front wings as we are seeing developed again)

[RacingManiac]

The rule is suppose to limit the volume of the diffuser by assigning it a set dimension with some boundary. The double decker diffuser is basically creating a way of creating a secondary(or tertiary(sp?) in some cases) diffuser volume, by having some gap at the bottom of the car to allow the air into those extra volume, which technically in the rule are not viewed as part of the diffuser, thus not really limited by the book. Since diffuser works by allowing the air flowing through the bottom of the car to expand to merge with regular flow, the volume is important to its effectiveness. The DDD is a way to regain the lost volume that the 2009 rule was intended to cut(the "spirit" of the rule). Since there are no real good pic of the actual gap in the floor and how they are formed it is hard to speculate the exact packaging.....

[xpensive]

Perhaps this thread could be useful on the subject?

viewtopic.php?f=6&t=6545

[NormanBates]

the diffuser "sucks" air from below the car
this makes the air travel faster under the car
faster moving air has lower pressure (bernouilli's principle: the one that makes planes fly)
so pressure is higher above the car than below the car, and the car gets pushed down

for a more technical discussion, go to xpensive's thread

[BiTXBoi]

Could they make the upper deck of the diffuser more effective if they could join it with the engine cover (not the anvil one), using a slot on the upper deck for that purpose? That way they could feed the diffuser with more air, I guess.

I know each diffuser has its own design, so for some it would be easier than others to aply the solution, but I see it particularly 'easy' to do it on the Renault.

Any ideas?

[RacingManiac]

diffuser doesn't just use more or less air by itself, it needs to get the air from the underside because it is an aid to the underbody, not an aerodynamic device by itself like a wing...

[BiTXBoi]

yes, but you still need to 'feed' it with air somehow, don't you? Being it from the underbody or from somewhere else (exhaust gases were used before they were banned)

[RacingManiac]

You feed it with extra "free air" doesn't help its function though. It functions by making the underside work better because it lets more air expand from the underside of the car thus draws more flow throung the underbody and make more downforce. Shoving more air from the top doesn't help that cause. Exhaust gases was used because it is energized air, being from the expanding combustion hot gases.....

I think of the diffuser as basically a severely limited version of the venturi of the ground effect car of the yore. If they used to run sealed side skirts to prevent outside air from going into the tunnel, it should have the same requirement for the current car.