DDDs in 2010

[BreezyRacer]

Lots of great info in this thread, vey well illustrated by that McL floor pic.

I find it so irritating that the OWG's work resulted in massive car changes & costs to the teams, and much less visually appealing wings (they are NOT growing on me) - only to all be undone by their overlooking of this one detail. The result was a total failure to improve passing in F1. But if the FIA were to declare DDD's illegal for 2010, the OWG's work would not have been wasted. Instead it is.

Next - narrower front tires to reduce front grip, one year after the OWG mandated the snowplow front wings to increase front grip. I hope there's some logic in all of this that I'm missing.

The reality of things is that F1 is first and foremost a competition. When groups like the OWG are formed you have to realize that there will be subtle attempts to carve out an advantage for yourself. I very much feel like F1 needs an effort like the OWG but sadly I also believe it should be managed by an outside group and handled at arm's reach via the FIA. We almost made it last year but it was the structure of the OWG that brought us this failure. Influence is everywhere in this world and it's difficult to isolate it out.

[ISLAMATRON]

Lots of great info in this thread, vey well illustrated by that McL floor pic.

I find it so irritating that the OWG's work resulted in massive car changes & costs to the teams, and much less visually appealing wings (they are NOT growing on me) - only to all be undone by their overlooking of this one detail. The result was a total failure to improve passing in F1. But if the FIA were to declare DDD's illegal for 2010, the OWG's work would not have been wasted. Instead it is.

Next - narrower front tires to reduce front grip, one year after the OWG mandated the snowplow front wings to increase front grip. I hope there's some logic in all of this that I'm missing.

The "snow plow" front wings were not instituted to increase front grip, overall they produce less downforce than the 2008 Front wings... the 2009 Front wings were introduced to not lose as much front DF when following another car as the 2008 Front wings.

But yes the DDD's pretty much undid all the OWG's work, But it is not the FIA's place to declare them illigal. Regardless of what the uninformed posters on this board will have you believe it is the teams and not the FIA that make the rules, it is the teams who make up the members of the OWG and every other technical group. And it would have to be the teams that declare them illigal, especially as the 2010 rules are less than a year away, so therefore any rules changes would have to be agreed upon unanimously by the teams.

[allstaruk08]

[Richard]

It is a real gem and I can't imagine the McL designers team were pleased to see their secret paraded for all to see.

Why? Floor-défilé is a mandatory practice this year

You have pics from other teams?

Islamatron - [-X please can we keep this a politics free thread! This is about what the DDD will look like in 2010, now the rules that allowed it to came into existence.

[BreezyRacer]

Whether you would use a double deck or triple deck depends on whether it adds any efficiencies. The only reason for this new diffuser design is because of a loophole in how the rules were written. Ideally the entire diffuser (or now you could call them tunnels) would be open to the bottom of the car, without any ports. Adding ports adds drag and turbulence. It's only thru careful design that this loophole added increased downforce.

So could your triple deck design work? Yes, but if you could do it with just a double deck it would likely be more efficient. Also I would refer you to the pic earlier in this thread. The port size is huge. Trying to add an add'l port would likely reduce the efficiency of that port, if you could find the room to do it. Also exiting the port at the center of the rear of the car is pretty important because that's where the maximum wake is, thus maximum "pull" thru the port.

[Richard]

...

I'm not sure how placing that on top of the floor would help downforce? The aim is to reduce the pressure under the floor?

[BreezyRacer]

...

I'm not sure how placing that on top of the floor would help downforce? The aim is to reduce the pressure under the floor?

Opps! Yes, you are right Richard. I assumed that the ports would be open to the undertray. If they are not this just adds drag and reduces airflow to the lower wing area.

[allstaruk08]

im no expert on aerodynamics but i thought the top level of the diffuser could be used like a wing as i thought having four holes instead of 2 or making the 2 holes bigger under the floor to get the air into the top level of the diffuser would disturb the air too much for the bottom level of the diffuser and not help with downforce. does that makes sense =S lol

[speedsense]

I started this as reply in a McL thread, but realised the topic is much more general than just one car, hence a new thread.

We saw most teams struggle to get their DDDs working on this years cars, so how will that feature evolve over this winter?

Some have suggested triple deck diffusers but my perspective is that we have two decks only because the rules require a surface at a set level. Also the loophole requires the supply to the upper part to come from a different source. AFAIK the split doesn't give a performance advantage in itself compared to a single diffuser of the same volume. The split could conceivably make them less efficient?

I can see that a third deck might be required if the teams tap into a third source for the air supply. Spatial reasons might require a separate deck to route the flow around an obstruction, ie suspension, drive train, crash structure etc.

Other factors will limit the development of the DDD. they need to be solved before the diffuser can significantly bigger. Brawn commented about the use of the DDD being more than just the diffuser - sorry ciro no ref, but is was a BBC interview at the track when McL jumped in performance.

Firstly, the DDD is an air exit route, so it needs a balanced air supply route. Then you can't change the under car air flow without having to rebalance the over car (and side) airflow. This results in a significant extra aero downforce on the rear which must surely mean you need to rearrange the other down and lateral forces to keep things in balance. That all requires the mechanical grip to be rebalanced, so that changes the suspension geometry and drive characteristics.

So it is not about who has the biggest or most decked diffuser, but who is able to incorporate in it in the most imaginative way.

Isn't this limited by the inlet size? The dimensions are spec'd as to the size of the inlet and surely it is being utilized already. If they were to go to a triple, it would be with the same inlet size feeding both of the upper chambers. Can't see how that would work.....
Correct me if I'm wrong...

[BreezyRacer]

As I understand it there is no limiting inlet size. It simply states that in plan view there are no visible openings. Who knows, maybe the FIA clarified that when these were ruled legal or there is some kind of self imposed limitation by the teams. The first ones only had openings along the sides of the legality plank step. Of course now they have their own inlets protruding within the floor/plank rules. The real thing is that the more ports/inlets you have, the weaker the "pull" becomes, beyond a certain point.

I don't have the wind tunnel fired up right now so I cannot provide more specifics

[Mystery Steve]

im no expert on aerodynamics but i thought the top level of the diffuser could be used like a wing as i thought having four holes instead of 2 or making the 2 holes bigger under the floor to get the air into the top level of the diffuser would disturb the air too much for the bottom level of the diffuser and not help with downforce. does that makes sense =S lol

I really don't like the term "double-deck diffuser." If you wanted to call it what it really is, you would call it "wing interacting with venturi tunnels in the undertray," but that would lack the catchy alliteration. But here's a crash course in how the DDD works...

As the air flows around the car, the total pressure remains (for the most part) constant:



So if you increase the velocity in the undertray, the pressure will go down. This pressure differential provides the downforce. Now, the rate of mass flow will also remain relatively constant:



At these speeds, the air is not compressible, so you can assume the density remains constant, and you're left with:



With a conventional design, the flow area is decreased drastically, but once you get into the undertray the area it is maintained relatively constant by the restrictions on the width of the car and the ride height requirements, and now you're down to:



So the only way left to increase the velocity in the undertray is to physically move more air through it. This is where the second deck (i.e. the wing) comes into the picture. The wing generates a low pressure region on it's lower side, which is of a lower pressure than the flow exiting the diffuser. This pressure differential increases mass flow, which increases velocity, which increases total pressure differential, which increases overall downforce.

Now, the way you've drawn the picture, you show the "extra flow" interacting with the wing element (I think? Correct me if I'm wrong...). If that is the case, you could possibly use a converging nozzle with complex geometry to speed the flow up and feed it to the underside of the wing. That would increase the downforce from the wing alone and potentially pull more air through the undertray. At first glance, I could see this working, but I would have to sit down and run numbers to look at the feasibility. One big question (aside from legality) is the drag penalty. It would have to be determined if the increase in performance isn't offset by the drag penalty, in which case all the extra ducting would be nothing more than ballast.

[speedsense]

im no expert on aerodynamics but i thought the top level of the diffuser could be used like a wing as i thought having four holes instead of 2 or making the 2 holes bigger under the floor to get the air into the top level of the diffuser would disturb the air too much for the bottom level of the diffuser and not help with downforce. does that makes sense =S lol

I really don't like the term "double-deck diffuser." If you wanted to call it what it really is, you would call it "wing interacting with venturi tunnels in the undertray," but that would lack the catchy alliteration. But here's a crash course in how the DDD works...

As the air flows around the car, the total pressure remains (for the most part) constant:



So if you increase the velocity in the undertray, the pressure will go down. This pressure differential provides the downforce. Now, the rate of mass flow will also remain relatively constant:



At these speeds, the air is not compressible, so you can assume the density remains constant, and you're left with:



With a conventional design, the flow area is decreased drastically, but once you get into the undertray the area it is maintained relatively constant by the restrictions on the width of the car and the ride height requirements, and now you're down to:



So the only way left to increase the velocity in the undertray is to physically move more air through it. This is where the second deck (i.e. the wing) comes into the picture. The wing generates a low pressure region on it's lower side, which is of a lower pressure than the flow exiting the diffuser. This pressure differential increases mass flow, which increases velocity, which increases total pressure differential, which increases overall downforce.

Now, the way you've drawn the picture, you show the "extra flow" interacting with the wing element (I think? Correct me if I'm wrong...). If that is the case, you could possibly use a converging nozzle with complex geometry to speed the flow up and feed it to the underside of the wing. That would increase the downforce from the wing alone and potentially pull more air through the undertray. At first glance, I could see this working, but I would have to sit down and run numbers to look at the feasibility. One big question (aside from legality) is the drag penalty. It would have to be determined if the increase in performance isn't offset by the drag penalty, in which case all the extra ducting would be nothing more than ballast.

IMHO, There is a drag penalty, though it is offset by constraining the wake out the back of the diffuser, where if it was "allowed" to expand freely it was limit efficency inside the diffuser.
By carefully engineering the vortices out the back of diffuser, you increase/maintain the velocity out the back of the diffuser where it would deaccellerate without the said vertices.
If the rules allowed for it (they don't), they would simply extend the diffuser beyond the back of the car and physically built sides and top to it. The vortices are kinda like a "virtual" extension of the diffuser.

[Richard]

http://twitpic.com/rv9fq



Seems that they are using some air coming in from above the floor to speed up the DDD exit air flow? Like one of those artist sprays where you blow across the supply tube to draw up ink from a bottle?

[PlatinumZealot]

im no expert on aerodynamics but i thought the top level of the diffuser could be used like a wing as i thought having four holes instead of 2 or making the 2 holes bigger under the floor to get the air into the top level of the diffuser would disturb the air too much for the bottom level of the diffuser and not help with downforce. does that makes sense =S lol

I really don't like the term "double-deck diffuser." If you wanted to call it what it really is, you would call it "wing interacting with venturi tunnels in the undertray," but that would lack the catchy alliteration. But here's a crash course in how the DDD works...

As the air flows around the car, the total pressure remains (for the most part) constant:



So if you increase the velocity in the undertray, the pressure will go down. This pressure differential provides the downforce. Now, the rate of mass flow will also remain relatively constant:



At these speeds, the air is not compressible, so you can assume the density remains constant, and you're left with:



With a conventional design, the flow area is decreased drastically, but once you get into the undertray the area it is maintained relatively constant by the restrictions on the width of the car and the ride height requirements, and now you're down to:



So the only way left to increase the velocity in the undertray is to physically move more air through it. This is where the second deck (i.e. the wing) comes into the picture. The wing generates a low pressure region on it's lower side, which is of a lower pressure than the flow exiting the diffuser. This pressure differential increases mass flow, which increases velocity, which increases total pressure differential, which increases overall downforce.

Now, the way you've drawn the picture, you show the "extra flow" interacting with the wing element (I think? Correct me if I'm wrong...). If that is the case, you could possibly use a converging nozzle with complex geometry to speed the flow up and feed it to the underside of the wing. That would increase the downforce from the wing alone and potentially pull more air through the undertray. At first glance, I could see this working, but I would have to sit down and run numbers to look at the feasibility. One big question (aside from legality) is the drag penalty. It would have to be determined if the increase in performance isn't offset by the drag penalty, in which case all the extra ducting would be nothing more than ballast.

I think there is a slight mix up with the mass flow part. Choose a control volume first. All the air that goes through it has mass flow M.' The front splitter redirects some of the mass m1 under the car, the rest m2 goes on top of the car. m1+m2 = M right.

You can only increase m1 from taking away from m2. Assume the car is driving at a fixed speed, you can not simply increase m1 by just increasing the velocity under the car which you can do by decreasing A (or doing work) and or keeping the pressure at the back of the car lower. The mass flow m1 will not increase from when it entered just by increasing the air velocity under the car. Because the velocity under the car does change at many points but the mass can not magically increase at theses points (Conservation of mass). You have to take mass from some where else. What the equation is really saying is that when the mass is constant the Rho,V or A change to depending on each other. You said Rho is constant so you should work with the V and the A.

The actual proper way of increasing the mass flow taking some air from m2 works but as said by a poster in the "floor thread." To help with the downforce You do it for the upward sloping part of the diffuser. The extra air flow at the roof of the diffuser can help to draw out air from the throat of it. You can't take the air from the top middle of the car where you need it to press the car down. So they take it from the top back where the wing is there.

I found this picture really interesting, because the upper diffuser roof is actually two pieces. There is a gap that alows air from the top side of the car to enter the diffuser and flow along the ceiling of it. I think this adds energy to the boundary of the air in the diffuser and helps to pull it along. I never seen this before, though some say it was used in Abu Dhabi.

Renault at Jerez test. taken from pre season Test thread

edit: sorry again, hehe link to image on twitter!

http://twitpic.com/rv9fq

But the main thing I am saying is that before the equations are applied I look on how the system is set up first. In this case the addition of mass is possible by taking air from above the car, but you can not add mass magically to the original amount that was at the front entrance of the floor (assume car is driving at a certain speed). I notice that they take mass from above only when the air underneath is going through a type of diffuser and needs to be energised. (Like the back underside of the front wings, via endplate holes and the top ceiling of the rear diffuser). It is usually in a way so that the extra incoming air does not impinge on the main stream, but runs along side it, creating like an "inducing" effect. So is usually in an area that is sloping away from the air stream. This is just my observation though.

[xpensive]

I did some draft calculations om another thread last summer, just to get a feel for what we are talking about:

...a draft calculation based on Bernoulli calculations with different air-speeds on the two sides of a horizontal plane:

Resulting vertical force will be: Area * Density * (Speed2^2 - Speed1^2)/2.

With a realistic scenario, let's say a car with an underbody area of 2 m^2, is moving at 144 km/h(40 m/s) through
a corner with an air-speed underneath of 70 m/s, resulting downforce is 4000N.

A 7% higher speed under thar car, 75m/s, would increase downforce with 20% to 4800 N, with virtually no drag-penalty
to carry for the coming straight, unbeatable.

No wonder the teams are bickering over the interpretation of diffuser-rules.