F1technical.net

So in 2009 the cars will no longer be able to drive upsidedown lol

Ogami musashi wrote:The reason is the loss of the central section which was 800x300x400mm (L,W,H) and this is done on purpose, this is a very important feature of the new package helping to clean the wake.

It is expected the diffuser to make only 15-20% of the total downforce compared to the actual 40-45%

Yes and it was done on balance purpose to shift the local center of pressure closer to the one of the rear wing.

The move aft will make the coupling with the rear wing less efficient.

The rules specify the same rigidity requirements than now.

This central section you speak of was located under the engine I am presuming? How does removing it clean the wake? Do you have a link in regards to the diffuser only providing 15-20% of total downforce? How was that number determined?

Why would they want to move the center of pressure closer to the rear wing? and why would that make the rear wing more effiecient? Please explain this "coupling effect" I am a mechanical engineer that has focused on power production and transmission, so alot of this aero stufff in new to me, but still very interesting... thanks for the time & patience.

enkidu wrote:So in 2009 the cars will no longer be able to drive upsidedown lol

Oh they will!

We're talking peak downforce levels of around 2200kg compared with 2800kg of today. Still massive.

And smirkoff: BRILLIANT renders. Would it be possible for you to send me the model in IGES format so I can have a more detailed look at it on my CAD packages?

The williams 2009 front wing (and rear wing):


http://www.autosport.com/news/report.php/id/72093

imightbewrong wrote:The williams 2009 front wing (and rear wing):


http://www.autosport.com/news/report.php/id/72093

AHAHAHA Im going to watch something else now...

I quite like it.

Seriously the rear wing is so of putting, if only they had an option making it translucent/transparent (out of different materials)......anyways front wing looks decent.

ISLAMATRON wrote:
This central section you speak of was located under the engine I am presuming?

The central section is just below the ramp lamp

ISLAMATRON wrote: How does removing it clean the wake?

It reduces the high pressure turbulence zone just aft of the diffuser that stayed there varying with:

-Mass flow out of the diffuser
-Couping with the rear wing

ISLAMATRON wrote: Do you have a link in regards to the diffuser only providing 15-20% of total downforce?

See RCE Nov 08

ISLAMATRON wrote: How was that number determined?

After OWG wind tunnel trials of prototypes (based on F2004)

ISLAMATRON wrote: Why would they want to move the center of pressure closer to the rear wing?

Because it guarantees the the shifts or Cp will be the same for rear wing and diffuser helping to reduce the balance shift.

ISLAMATRON wrote: and why would that make the rear wing more effiecient?

Because the more the rear wing Downforce, the stronger the inwash which cleans the turbulences by pulling them above the car (it moves them away with two strong inward rotating vortex).

ISLAMATRON wrote:
Please explain this "coupling effect" I am a mechanical engineer that has focused on power production and transmission, so alot of this aero stufff in new to me, but still very interesting... thanks for the time & patience.

Diffuser (in the diffuser) slows down the air. This has as a result to accelerate the air upstream of it (under the flat bottom) because the flow there behave like in a venturi channel ,that is the total pressure can't vary so when you increase it somewhere in the tube it has to decrease at the other extremity to balance.

Thus the diffuser slows down the air accelerated. Without it the air would still accelerate (because it goes through a "tunnel" thus has less space than in free air) but the slowing down by the diffuser accelerates it even more.

Additionaly the diffuser helps recovering the air to the near ambient pressure which reduces the form drag of the car (it tries to bring the pressure to the same level than the pressure right a the front of the car which the car is encountering).

The more you slow down the air (be it the faster you slow it down or the more quantity you slow down) the more it will be accelerated underbody and thus the more downforce you have.

The problem is that you have to slow it down in a short space (the diffuser) and the produces a lot of risks of flow seperation and then stalls.
The air that slows down tends to move backward when slowed down and this triggers stall into the diffuser.

When you have a rear wing just above the diffuser, the rear wing low pressure (on the bottom side) pumps the air that exit the diffuser and thus prevent it to stall.

With that help you can extract a lot of air from the diffuser without risking to stall.

Coupling had produced so much results than in the 90's Le mans cars and F1 had the vast majority of the their downforce from the coupling.


The problem the coupling brings is that a zone of turbulence is preserved aft the car. That zone will seldom evolute because the rear wing always prevent the state to change by pumping it.
In addition since the area is a high pressure one, the upwash produces (the air that exit the diffuser tend to go toward the rear wing) is strong and it decreases the potential energy for the following's car front and rear wings.

Thus decoupling (meaning less coupling) allow first to make the diffuser less usefull then decrease the turbulence area and next by allowing the rear wing the be the most downforce producing surface in that region you create a strong inwash that sucks everything around thus cleaning the flows.

Well cleaning the flows is an image, there're still turbulence, but that reduces a bit the wake.


The topic is difficult and very complex, the thing to understand is that we speak about wake structures and that why all the discussions on "cutting downforce" have very little relevance to the probleme of overtaking (except if you cut downforce to Zero..then yes, no problem anymore).

Do not hesitate to ask questions if you have some difficulties and we are here a number of people to have knowledge in aerodynamics (i think of Gekko, Sguy, AeroGT3 and i forget many others).

That actually looks pretty damn good. The car has a very wide nose but I believe that is as low as possible for next year; many will be higher.

On the whole, I think it looks great...if a little simple (the front wing looks like a late 90's wing).

ISLAMATRON wrote:outstanding indeed... could we get a better look at the diffuser outlet in the rear? Got any underbody comparison shots 2008 vs 2009?

Here's a try:



Thank you all for your kind comments on my work!

And Scotracer, the model was made and rendered in Maya, and it's about 90% polygon mesh. I've made a test converting it to Iges and importing in other softwares, but the mesh appeared "broken", with various parts out of scale. If I have some time later I'll do some more tests to convert it.

That's okay, Smirkoff -- if it means a lot of faffing around, it doesn't matter

And bravo on your attention to detail on that model.

Ogami musashi wrote:

ISLAMATRON wrote:
This central section you speak of was located under the engine I am presuming?

The central section is just below the ramp lamp

Ok the central section is along the centerline of the car and terminates at the lamp(ok that explains why I was so confused). Is the diffuser split/ comparmentalised into 3 main sections? left right and center? or is the air allowed to freely go where it wishes under the car?

ISLAMATRON wrote:Ok the central section is along the centerline of the car and terminates at the lamp(ok that explains why I was so confused). Is the diffuser split/ comparmentalised into 3 main sections? left right and center? or is the air allowed to freely go where it wishes under the car?

What do you mean by freely? As smirkoffs picture shows, the fluid is only separated when the channels for the 3 parts of the diffuser (central tunnel and left/right). The only thing that determines where a fluid particle goes is its lateral position at the bottom of the car.

@smirkoff... thanks alot... a picture is truly worth 1000 of Ogami's words.

Honestly, just looking at it the 2009 spec looks like it would produce more downforce because of the increased ground effect flat area behind the front wheels, in front of the rear wheels & between the rear wheels. But maybe the lower diffuser area negates all of that. But then what about the front wing allowing more air under the car?

Oh yes, removing the central diffuser removes the ability to extract air from under the FIA plank and lowering the ground effect area.

Scotracer wrote:What do you mean by freely? As smirkoffs picture shows, the fluid is only separated when the channels for the 3 parts of the diffuser (central tunnel and left/right). The only thing that determines where a fluid particle goes is its lateral position at the bottom of the car.

He posted the picture while I was writing that... it is clear to me now that the central diffusers main purpose is to extract air from under the FIA plank.