Importance of the diffuser?

[NormanBates]

well, I think that from time to time, and I know lots of maths and some physics, and I build machines and other stuff, but I'm pretty sure that doesn't make me an engineer

in fact, here's proof of that: I'm an economist; do you still think I'm an engineeer? thought so

[xpensive]

Tricky one that, who's an engineer or not, try ask a lawyer who's a lawyer and you get my drift.

Though I picture myself as last of the mohicans when it comes to definitions on the subject,
I have to admit Leonardo da Vinci was pretty technical without a Master's degree. Actually.

Ain't that mighty generous of me, Ciro?

[xpensive]

Either way, saying it again, I am intrigued beyond my wits with what the best F1 brains might come up within soon, all according to the new interpretation of the diffuser-rules.

[PlatinumZealot]

You have "Text book" engineers and you have "Crazy nut" engineers and some in between.

I think BMW has too much of the "Text Book" ones.

[xpensive]

Actually, when looking closer at pictures of the diffuser on the Brawn, which still seems to be the car to have in F1, it strikes my that the upper part does not seem to be as much above the "175 mm rule", as Toyota's or Williams'?

It looks, to me anyway, more like the central-section is better utilized, by channeling air from the outer parts of the floor through those "slots" further up, which could be made possible by the purpose-designed gearbox.

Would this be the explanation why it seems so difficult for the competition to quickly catch up, they need a new gearbox?

scarbs?

[scarbs]

The upper section is not much higher than 175mm, in fact 200 is the effective max height it can reach. However it can be far steeper, you will see the trailing edge of most teams upper deck is ahead of the trailing edge of the lower deck (350mm behind RWCL). This creates a more aggressive diffuser with a greater expansion ratio, it is this that aids the greater downforce as much as the extra height.

[xpensive]

I think I got the picture now scarbs, thanks.

However, when it seems difficult for the other teams to catch up just like that, it indicates, to me anyway,
that it is a little more to it than simply re-designing the floor and crash-structure?

[Conceptual]

I think I got the picture now scarbs, thanks.

However, when it seems difficult for the other teams to catch up just like that, it indicates, to me anyway,
that it is a little more to it than simply re-designing the floor and crash-structure?

It's always been about a base philosophical change. That is why Ferrari said there "were two types of cars" competing in Melbourne.

[speedsense]

Having read this post with interest, and my experience of 18 years measuring live the pressures under racecars through data acquisition, a lot of the points made do back up what has been measured in my past, some do not.
1. A diffuser is not really a diffuser in the truest since of the term. It is a diffuser by name, acts similar to a diffuser, and shaped as one (such as one in a windtunnel).
It also is not completely a ground effect tunnel either, as there isn't any venturi shape allowed in the throat of the diffuser.
It also is not an inverted wing, as there's no upper airstream to complete a construction of a wing. Though by shape and theory it should function in part as each one.
But ultimately not the reason for it's existance.
A diffuser, by it's self, is not a device that creates downforce. This can be proved by simply raising the diffuser from the ground, and turning it into a diffuser, which slows the air flow and increases high pressure and creates 0 downforce. Though move it closer to the ground and you increase it's function, which is to suck high pressure created areas,(in front of and around the sides of the diffuser (causes of lift) into the throat of the diffuser.
When you stop referring to a diffuser as a downforce producer and consider it an anti-lift device or a scavenging device (removal of high pressure), it's existance and function makes more sense.
2. The underbody in reality, on a moving race car, has an enormous amount of high pressure pockets that get sucked into the layer under the car. These are caused in part by the wake(s) of the front wings, wheels and tires , body parts and ground undulations. High pressure creates lift that works against the wings (downforce device) or the upper body surfaces (producing down ward forces)
The word downforce implies negative lift and is different than a "down ward" force that is produced for instance, on an upper body high pressure over coming a lower pressure area below. (continued)

[speedsense]

To prove out the downforce production theories, or lack of downforce production, take a winged car and add a diffuser to it. Note the added increase of downforce. Now remove the wings, and you will find that a high percentage of the "added" downforce has all but disappeared. The reason is that the device does not produce downforce, ie: negative lift- but simply helps remove the lift causing high pressure areas that develope undercar and grant the wings more downforce. Even on the "removed wing car", the device helps remove the high pressures thus granting the car less lift, but the increased effectiveness of the wings is the major difference for the seemily increase in downforce.
It isn't completely correct to say a diffuser device, creates downforce by way of the device its self, but rather a removal device of high pressure accumalation by creation of a (high/low combined) lower pressure area (than the rest of the floor) at the leading edge of the diffuser. This lower pressure area "attracts" the high pressure pockets, and uses the increased volume of the diffuser to dispell of them. Witness this low pressure area in the CFD images provided in the thread, and that the low pressure is lower than the areas directly proceeding the opening. I believe these images are of a car without a moving ground underneath it or wheels turning in front of it, as there's no accumalation of high pressure (pocket) areas present.

IMHO- A diffuser is not a downforce device, but an anti-lift device.

[speedsense]

In reference to the DDD or two tier diffusers.... the removal of the rear wing location by the '09 rules, has created a change in how the lower extremeties of the wing, that produced a wake and in turn helped extract air from the diffuser. The wing's current location has little to no effect on the diffuser.
The DD Defuser, has a channel above the diffuser that is creating vortices to replace the loss of diffuser extraction properties by the new location of the wing. The more air that is added to this channel, the larger and number of vortices that can be created.
These vortices vary in strength depending on how much air can be funnelled into this channel. The slot openings allow more air to proceed into this channel and create larger and stronger vortices, extracting more air out of the diffuser.
IMHO

[Conceptual]

I tend to think of the Splitter/Stepped floor/Diffusor as a single element. Inlet, throat, and exhaust. As in any system, the more synergized the components, the better and more efficiently they behave.

I have read Comp. Car D-force, and I understand the low pressure area and such, but it is the complete underbody system that leads to the desired effect, not a single part of the system.

Each part can be optimized, but the optimum of the system is more important than the optimum of the individual parts.

I love the "out-of-the-box" thinking that lead to the DDD, and I continue to hope that the same thinking will be turned loose on the 2010 "Cap Regs".

It would be nice to see F1 take a technological leap forward. It has been a LONG time since that has happened!

[Conceptual]

dp

[speedsense]

The poster that referenced what the shape of the diffuser should be to be most effective. The most effective shape would a ground effect tunnel, starting at the leading edge of the side pod and ending, beyond the rear wheels. With one or two strakes seperating the tunnel into channels. Both sides would need to be sealed to the ground to be most effective and would resemble the bottom of a wing.
This design would have the least amount of pitch sensitivity.

The short design of the diffuser, mandated by the 09 rules, causes high pitch sensitivity as the pressure areas shift easily with angle change. A small chassis movement makes a large change in the "center of pressures" (difference between high and low pressure point) as compared to the longer tunnel.

[RideRate]

To prove out the downforce production theories, or lack of downforce production, take a winged car and add a diffuser to it. Note the added increase of downforce. Now remove the wings, and you will find that a high percentage of the "added" downforce has all but disappeared. The reason is that the device does not produce downforce, ie: negative lift- but simply helps remove the lift causing high pressure areas that develope undercar and grant the wings more downforce. ......

IMHO- A diffuser is not a downforce device, but an anti-lift device.

Speedsense,
I, and I think many others here, would disagree with you. I don't like referring to the diffuser itself as a downforce making device, but the underbody as a system sure is a downforce making device. The diffuser is just the most visible part of the underbody so it gets a fair amount of attention.

Whether you call it anti-lift or downforce is just semantics. It's the same thing. Any force in the downward direction, even if it only partially cancels a net upwards force, is downforce. Underbodys can generate significant amount of net downforce both with and without wings. However a diffuser/underbody designed to work with a rear wing should not be the same as a diffuser/underbody designed to work with no wings. Just removing a wing from an underbody setup built to work with a wing isn't proving much of anything.

My point is, with and without wings the underbody is a giant source of net downforce. With a winged car the wings create yet more downforce individually, further help drive the diffusers effectiveness, and most importantly tune aero balance.