Basic question about the diffuser

[CescFabulous]

sorry for asking a stupid question...
why can the diffuser speed up the air below the car? could someone explain this for me in detail cos i'm always confused abt it...
besides, how does the hole in the diffuser of BGP 001 works?
is this video a correct illustration?
http://www.youtube.com/watch?v=I0sMX0UFnj0

[Just_a_fan]

The video is wrong. The diffuser isn't fed from above the floor like that.

[Sikthskies]

The interaction of the floor with the air is like squeezing a hose pipe. It increases the velocity of the air under the car. When you increase velocity, you decrease pressure. It is the difference in pressure this makes between the bottom of the car and the top of that car that produces downforce.

There is far more to it than this and there are plenty of resources and text books which can further your knowledge. But that is about as simple as I can make it

[BreezyRacer]

First, understand that there is a wake (low pressure area) behind a moving car.

Second, understand that airflow increases in speed as it is introduced to a low pressure area.

Third, understand that rapidly moving airflow creates a low pressure area.

Forth, understand that turbulent airflow is disruptive to all of these processes and adds drag.

If you understand these concepts then you will readily see that allowing the underbody airflow to smoothly flow into the wake region will speed up the airflow under the car. The resulting increased airflow creates a low pressure area under the car, interpreted as downforce.

Therefore a diffuser creates downforce via managing the blending of underbody airflow into the wake of the car.

Hope this helps.

[CescFabulous]

The video is wrong. The diffuser isn't fed from above the floor like that.

then do you mean that it's fed by the air below the floor?

[marcush.]

The video is wrong. The diffuser isn't fed from above the floor like that.

then do you mean that it's fed by the air below the floor?

my idea is:
if you are filling the diffusser with air from above the floor this could possibly help to keep the flow attached if your defusser has separation problems (because it expands to steep),but normally I´d say feeding from above would only reduce the draw from the diffusser towards the underfloor.
Opening the slots in the floor feeding a second deck is a different story altogether because this second deck is drawing air from the floor section into a separate void,so adding downforce.The trick with thee dd diffuser is to create a bigger divergence and accordingly a bigger pull on the undertray without separation in the diffuser due to the extreme expansion.

[Just_a_fan]

The video is wrong. The diffuser isn't fed from above the floor like that.

then do you mean that it's fed by the air below the floor?

Yes. The second, upper part of the diffuser is fed from air from below the floor but further forwards than the rules might be thought to allow.
http://www.formula1.com/news/technical/ ... 9/663.html
nicely shows one method of doing it.

There was a nice picture of McLaren's eventual solution on this site but having looked for it I can't now find it (the site hosting it appears to be down).

The aim of the second part of the diffuser is to pull more air through the gap between the undefloor and the tarmac. This gives greater downforce as described so ably by others here.

[CescFabulous]

The video is wrong. The diffuser isn't fed from above the floor like that.

then do you mean that it's fed by the air below the floor?

Yes. The second, upper part of the diffuser is fed from air from below the floor but further forwards than the rules might be thought to allow.
http://www.formula1.com/news/technical/ ... 9/663.html
nicely shows one method of doing it.

There was a nice picture of McLaren's eventual solution on this site but having looked for it I can't now find it (the site hosting it appears to be down).

The aim of the second part of the diffuser is to pull more air through the gap between the undefloor and the tarmac. This gives greater downforce as described so ably by others here.

thanks, i kinda get an idea now. so the RB5 diffuser design is quite similar to BGP001?

[CescFabulous]

First, understand that there is a wake (low pressure area) behind a moving car.

Second, understand that airflow increases in speed as it is introduced to a low pressure area.

Third, understand that rapidly moving airflow creates a low pressure area.

Forth, understand that turbulent airflow is disruptive to all of these processes and adds drag.

If you understand these concepts then you will readily see that allowing the underbody airflow to smoothly flow into the wake region will speed up the airflow under the car. The resulting increased airflow creates a low pressure area under the car, interpreted as downforce.

Therefore a diffuser creates downforce via managing the blending of underbody airflow into the wake of the car.

Hope this helps.

thx it helps a lot
but sry for asking a basic question again...why there is a wake (low pressure area) behind a moving car? sry i'm just a year 1 student in uni so havent learn fluid dynamics yet...it's a bit hard for me to understand...

[Just_a_fan]

thanks, i kinda get an idea now. so the RB5 diffuser design is quite similar to BGP001?

In principle, yes. In detail, no.

[CescFabulous]

thanks, i kinda get an idea now. so the RB5 diffuser design is quite similar to BGP001?

In principle, yes. In detail, no.

do u know in which part are they different? bgp001 diffuser seems to work more efficiently

[hollus]

but sry for asking a basic question again...why there is a wake (low pressure area) behind a moving car? sry i'm just a year 1 student in uni so havent learn fluid dynamics yet...it's a bit hard for me to understand...[/quote]

The car is punching a hole through stationary air, and new air can only rush in so fast to fill in the void behind the car, hence the pressure behind the car drops.

[CescFabulous]

thanks for all your reply. they're really helpful