Diffuser vs. Rear Wing

[explosiva]

My first post!

I read somewhere this year that diffusers are better than rear wings in creating downforce vs creating wake turbulence. So why not make the diffusers larger and rear wing much less efficient? Will this help in allowing cars to follow closers and overtake more frequently?

Is this question too simplistic?

[Ogami musashi]

Because this is not true.

First, it is important not to confuse Diffusers and Venturis.

Diffusers are much more aggressive than Venturis and by design they are also more constrained. This forces teams to use quite a bit of vortex flows to seal and glue the boundary layer and surroundings from this things.

Next the problem is that when the turbulence from diffusers exits, it goes into mixing with the ground boundary layer and stay on the ground very long.

This phenomenon is worsened by a rear wing coupling: The rear wing pumps the air under the diffuser which enables the diffuser to slow down more volume of air without stalling: that means you get the same turbulence factor but times a bigger mass flow= more turbulence.


The rear wing does create turbulence but the counter rotation vortex of the rear wing tend to create an upwash that cleans the wake.



In the early 2k's, Nasa patented a natural trailing vortex annulation technic by forcing the two trailing vortex to encounter each other; This reduced to distance of wake from 7km to 5km on large planes like 747's.

in addition some new technics involve pulsed jets to clean out the wake.

As said by paddy lowe, the simple fraction of downforce influence on turbulence (for a given turbulence factor, the more downforce you produce/rely on, the more you'll be disturbed ) has its limits.

Since a racing car can't go as fast as an F1 car without downforce (and no viable solution is available for now) we can't go too low with downforce and by anyway it requires redesign to ensure the turbulence factor is not increased.

So the solution will probably come from novel technics.

My own opinion is that the problem is very much related to the imprint:

When a front wing encounters clean air, the air is moved with a certain pattern that is modified by the later elements (diffuser/rear wing, body etc..).

If the following car is of the same geometry, it will lose less downforce.

That why, i think, in spec series, while the designs are close to F1, there's not so much problem.

[Mystery Steve]

The underbody/diffuser combination does generate a large percentage of the downforce on an F1 car, but simply making the diffusers larger does not equate to more downforce. The downforce is generated by air moving faster under the car than on top, so the underbody downforce is limited by the mass flow under the body. The actual diffuser section of the underbody slows this flow down, and increases the pressure of the flow closer to the ambient pressure behind the car. Decreasing the pressure differential reduces the drag.

To generate the same downforce levels that these cars have right now without the use of wings, you would probably have to lift the ban on side skirts and ground effect aero. Generating the same downforce with the underbody alone would also mean that you would have a relatively lower pressure in the underbody and that would have to be diffused back to atmospheric conditions. If the rear diffuser doesn't slow the flow down enough you will still get unwanted vorticity, which increases drag and makes it harder for a car to follow.

Unfortunately, when a system is optimized to the point that modern F1 cars are, dramatic improvements to one aspect of the car often means trading off performance in another area. Now, if the goal was reduce the level of downforce, thus increasing overtaking, then that would be a different story... Something tells me that might be a controversial decision, though.

[PaulS]

Hello to everyone. I cross this forum in the beginning of this year, when I tried to find information about the double diffusor. And now my first post in this forum.

Is this question too simplistic?

I don´t think so

As complicatet as aerodynamics are, the basic physical differents in function between diffusors and a wings could maybe explain as follows:

-The wing (on the upperside of the car) push the air in the sky. So you get the downforce from the impulse (actio = reactio). This air deflection creates fortexes. More downforce = more vortex.

-The diffusor or underbodywing takes the downforce with the effect of Bernoulli (pressure = density/2*velocity^2). The target is to increase the velocity of the air under the car, compared to the velocity of the car. This reducese the pressure under the car and the static pressure of the atmosphere push the car down. This means, you don´t produce a vortex. Additional, no vortex means no drag.

In fact in formula1 this both effects are quite mixed.

So I think it is also proven in the past, that cars with more underbody downforce can follow closer. So basically a good idea from the thread starter.

The "drawback" of the Bernoulli effect is the highly combination of downforce and distance car/ground. This means, when you hit a curb and the car jumps a little bit, the Bernulli effect is destroyed and the downforce decreases massively. The wing will turn up the air furthermore. So probably the groundeffect is not very calculabel for the drivers.

[kilcoo316]

My first post!

Welcome!

I read somewhere this year that diffusers are better than rear wings in creating downforce vs creating wake turbulence. So why not make the diffusers larger and rear wing much less efficient? Will this help in allowing cars to follow closers and overtake more frequently?

Yes, diffusers make less turbulence - as measured by turbulence intensity (but that is not the be all and end all - in fact, in this case it is pretty much irrelevant really).

No, increasing the diffuser size will not help the following car as it will only result in more upwash in the wake of the 1st car.


The diffuser needs to be banned, or the diffuser ramp angle absolutely decimated (down to < 5 degrees).


I had previously indicated that variable geometry front wings might fix the problem, along with drastic reductions in diffuser size. Unfortunately, it would seem I am wrong on the front wings, as a complex control algorithm would be needed to continually maintain aero balance - a control mechanism that would cost large sums of money. Which therefore makes that proposed solution somewhat non practical.

I would very much doubt I am wrong about the diffusers though. The rear wing wake is far too high to affect the front wing of the car behind.

Is this question too simplistic?

In a word, yes. (But don't let that put you off asking!!)

[hecti]

My first post!

Welcome!

I read somewhere this year that diffusers are better than rear wings in creating downforce vs creating wake turbulence. So why not make the diffusers larger and rear wing much less efficient? Will this help in allowing cars to follow closers and overtake more frequently?

Yes, diffusers make less turbulence - as measured by turbulence intensity (but that is not the be all and end all - in fact, in this case it is pretty much irrelevant really).

No, increasing the diffuser size will not help the following car as it will only result in more upwash in the wake of the 1st car.


The diffuser needs to be banned, or the diffuser ramp angle absolutely decimated (down to < 5 degrees).


I had previously indicated that variable geometry front wings might fix the problem, along with drastic reductions in diffuser size. Unfortunately, it would seem I am wrong on the front wings, as a complex control algorithm would be needed to continually maintain aero balance - a control mechanism that would cost large sums of money. Which therefore makes that proposed solution somewhat non practical.

I would very much doubt I am wrong about the diffusers though. The rear wing wake is far too high to affect the front wing of the car behind.

Is this question too simplistic?

In a word, yes. (But don't let that put you off asking!!)

Wow, why not just change the rules for front wing design, Ie: ala 2000 style, endplates just off the ground, without diffusers f1 cars will be slow as ---, not what most people have in mind when when they hear pinnacle of motorsport

[PaulS]

Yes, diffusers make less turbulence - as measured by turbulence intensity

And thats all about!

No, increasing the diffuser size will not help the following car as it will only result in more upwash in the wake of the 1st car.

Hmm... It´s just my second post here, but... The diffusor just slow the air down smoothly to ambient pressure! And when the ambient pressure is accompished and the diffusor ends, there are no more forces to generate an upwash. Thats some basics from Bernoulli shown very well in wind tunnels.

[kilcoo316]

Yes, diffusers make less turbulence - as measured by turbulence intensity

And thats all about!

Turbulence intensity is definitely not the be-all and end all.


Effective angle of attack is a serious issue. Remember the FIA lifted the front wings for the past few years. Why was that worse? Simply because there was more room under/ahead of the wing to build a positive vertical upwash component of the upstream velocity - resulting in a loss of front wing downforce.

No, increasing the diffuser size will not help the following car as it will only result in more upwash in the wake of the 1st car.

Hmm... It´s just my second post here, but... The diffusor just slow the air down smoothly to ambient pressure! And when the ambient pressure is accompished and the diffusor ends, there are no more forces to generate an upwash. Thats some basics from Bernoulli shown very well in wind tunnels.

No. The diffuser does much more than slow the air.


A diffuser on a car is not the same as a diffuser in a pipe. Do not forget, the diffuser is not axis-symmetric. There are also entrainment and momentum effects.

[Ogami musashi]

Read my post: Diffusers create a lot of turbulence.

First because they transport de upstream turbulences (coming from front part of the car) and then because teams use vortex generators inside the diffusers to seal the air volume.

As kilcoo said there's much more than turbulence intensity (related to the CL of wings); The actual geometry (of the wake) is of prime importance.


That's why we talk about Wake signature.

No to mention the geometry of the following car.

[Shrek]

I have a question
I was reading the Racecar Engineering magazine that had stuff about active suspensions and they had the Aerobytes section that they tested the diffuser and they said that the shape of the lower wing tier was better than just the straight across one that i would think would be better because its closer to the diffuser can someone/everyone help me on this?

[rich1701]

I'm commentating as someone with minimum technical knowledge... however my understanding is that GP2 cars have greater undercar downforce with a different technical approach comapared to F1 . GP2 cars are able to get much closer to each other, especially the 2005 spec car. Perhaps somebody can explain in more detail why this is and if it can be applied to F1 cars.

Also it seems to me that F1 cars were able to get closer to each other pre 1994 before the plank was introduced reducing under car downforce. At hockenhiem pre 2002, F1 cars ran with far less wing in proportion to their undercar downforce which remained the same, and this seemed to produce better racing as the cars were able to get closer to each other and dance around more easily in each others slipstreams.

So i would suggest reducing upper surface downforce and drag and increasing undercar downforce would be the right way to go to allow cars to get closer.

[PaulS]

@ kilcoo316 and Ogami musashi,

Maybe we have a misunderstanding. The thread starter was asking if less wing and more diffusor is a way to increase overtaking. And I say, more groundeffect and less wingdownforce is a solution that the cars could follow closer.

I have now seen, that this issue had allready been discussed on this forum oppositional. And I am one of the persons who is conviced that more groundeffect is the way to go. And I don´t mean, that the over all downforce should increase. Just create rules too substitute wing-downforce to ground effect downforce.

GP2 and Group-C are examples for it I guess without aerodynamik argues.

[kilcoo316]

I'm commentating as someone with minimum technical knowledge... however my understanding is that GP2 cars have greater undercar downforce with a different technical approach comapared to F1 . GP2 cars are able to get much closer to each other, especially the 2005 spec car. Perhaps somebody can explain in more detail why this is and if it can be applied to F1 cars.

The ramp angle on a GP2 car is much less aggressive than F1 - but the floor entry/exit area ratios would be similar.


The ramp angle needs to be reduced as it then reduces the upwash in the wake. I think I posted about this elsewhere on the forum, dunno where exactly though.

[wesley123]

The Diffuser is, compared to the rear wings in general much more complex, it can be used as an efficient downforce generator, but it is about how you use it. I am having a personal idea of using underbody tunnels wich startat the car scenterline and ends at the rear wheels centerline. They have long walls at the sides to stop the air flowing in from the wheels/the sides. A Middle of the car is just flat body, this flat body can extend to the very rear of the car, and also extends to the sides(so it is 'behind the tunnels') personally it is looking good, but i guess it wont work very well. Maybe i model one soon to show the idea in public, as i'm having alot more ideas. My personal idea of creating a efficient car was always the same, slim airbox and sidepods, and alot of energy put in underbody performance, much like the indycars do.

The Panoz champcar made use of the underbody to create most of the downforce of the car, and lets state this, it was a good car to overtake.

[speedsense]

The Diffuser is, compared to the rear wings in general much more complex, it can be used as an efficient downforce generator, but it is about how you use it. I am having a personal idea of using underbody tunnels wich startat the car scenterline and ends at the rear wheels centerline. They have long walls at the sides to stop the air flowing in from the wheels/the sides. A Middle of the car is just flat body, this flat body can extend to the very rear of the car, and also extends to the sides(so it is 'behind the tunnels') personally it is looking good, but i guess it wont work very well. Maybe i model one soon to show the idea in public, as i'm having alot more ideas. My personal idea of creating a efficient car was always the same, slim airbox and sidepods, and alot of energy put in underbody performance, much like the indycars do.

The Panoz champcar made use of the underbody to create most of the downforce of the car, and lets state this, it was a good car to overtake.

I read somewhere, that the most passing instances in F1 was in the era of ground effects and that was because of the smaller chord size and reduction of the angle of attack. Even the removal of front gurneys was frequent.
IMHO, it was the reduction of turbulent air getting to the tunnels that allowed the smaller wing adjustment. In some cases no front wing at all.
It seems to me the lesser dependence on the front wing resulted in more passing though it could also be that less air drag in the braking areas resulted in longer braking areas.
My thoughts are a return to body work in the nose area ahead of the wheels instead of front wings (early 70"s). This would have several effects-
1)severe reduction in rear wing downforce (just to gain aero balance),
2)less dependence on diverting air around/under the car (the nose would do that already),
3) less change of downforce numbers following in a car's wake..
4) less aero drag with effects on braking distances...
5) Chassis attitude would be more obvious to the untrained eye or first time F1 viewer
6) lastly more advertising space to get more millions to pay for the extra body work....LOL