Exhaust Blown Floor - Forward Exhaust Exit

[marekk]

Allison clearly states the vortex being formed creates low pressure. This low pressure is used to produce downforce. There is no mention of sealing. I am not sure we have ever heard a current F1 engineer state that there is a sealing effect. We also have not seen any CFD work illustrating this sealing.

Brian

FEE flow does carry some lateral momentum (up to 40kgm per side if we belive in exhaust speed od more then 200m/s). One can use this momentum to push a little against the air rushing to fill the low pressure area under the car. I think dynamic flowlines bending is more appropriate description then virtual skirt, but maybe it's just a semantic thing.

What Allison states is quite obvious - every free vortex creates pressure drop around the axis, simply because particles gain some extra speed (tangential in this case), and this means (as described by bernoulli) that static pressure decrease. If you place this vortex under the floor and keep it alive along the way, this creates described downforce.

[godlameroso]

And if the vortex is perturbed it perturbs all the way across the floor of the car, and it has to build up along the whole car to regain it's function. So it may be that the FEE gives more downforce, but is more sensitive than a regular EBD design. The places where R31 scored podiums, they had mostly constant throttle corners without walls close by. Malaysia and Melbourne specifically.

[MIKEY_!]

bernoulli, yes of course, so the vortex core is not so important after all.

godla: they were also tracks at the start of the year, before the opposition could catch up with an efficient EBD, i do believe there is a correlation however.

[hardingfv32]

Does the pressure gradient across a vortex go from ambient at the outer edge of the vortex to lowest pressure at the center?

Brian

[shelly]

@sonic59: Ok I have dp/dr=rho*u^2/r, with u being tangential velocity, given by Rankine in the core.
I have to integrate this from 0 to R(vortex core radius) to get the pressure drop

[marekk]

And if the vortex is perturbed it perturbs all the way across the floor of the car, and it has to build up along the whole car to regain it's function. So it may be that the FEE gives more downforce, but is more sensitive than a regular EBD design. The places where R31 scored podiums, they had mostly constant throttle corners without walls close by. Malaysia and Melbourne specifically.

Yeah, it's a long way and hard task to keep this vortex alive all along.
At higher car speed external flow's momentum bends exhaust flow more in centerline direction, higher pressure gradient from harder working diffuser stretches vortex cone and makes it more stable. Lower ride height means even more downforce (as clearly seen on shelly's formula).

[volarchico]

I've just spent the last few days reading through this entire thread. Wow...what a mess.

A few observations:

@ringo, a valiant effort to try to prove your point using diagrams, models, track images, and rudimentary CFD.

To summarize your opinion: The exhaust exits under the leading edge of the floor and creates a low pressure suction peak at that leading edge, but then the majority of the exhaust continues outboard of the rear tires.

@shelly, you have had extreme patience and persistence with topics such as dust not being an effective flow viz tracer particle and the vortices created by bargeboards (both of which I agree with you on). There were times when your frustrations were valid that ringo wasn't getting your point or listening. However, I can understand his frustrations because you make declarative statements about what is happening without attempting to provide any proof. A diagram, sketch, equation explaining your point could go a long way to adding some sort of validity to your claims to know what is happening.

To summarize your opinion: the exhaust strengthens the underfloor vortices created by the bargeboards and runs the majority of the length under the floor and exits the diffuser.

If this were a debate or trial, I would have to say ringo has provided the more convincing argument. I'm not saying that he is necessarily right, but just that he has actually attempted to provide a coherent argument about the physics and this is even discounting his entire CFD result since in some ways, I can agree that it is not detailed enough to provide the entire answer to a non-linear phenomenon (small perturbations can make large-scale differences in a non-linear situation).

Do the people who disagree with ringo have any sort of proof or physics-based explanation for the exhaust remaining under the floor (or turning back under since we all can visually see the initial exhaust direction is outwards). What makes you think the low pressure region of the diffuser kink has enough energy to turn the flow? What other forces would cause the flow to turn back under the floor?

And finally, even if ringo is completely wrong about the location of the exhaust gases when it passes the rear tires, I think it would be hard to argue that the actual majority of functionality of the exhaust does exist at the leading edge of the floor and no where else based on the energy dissipation the exhaust would experience after only a few exhaust diameter from its exit.

EDIT: Moved the blue summaries to make them stand out. Let me know if I got either one of them wrong. I just felt it was useful to contain a summary of each side so we can really see what is at odds between the two "camps".

[MIKEY_!]

Thats a great help, actually just what this forum needed. =D>

[ringo]

You know i could not have worded such a good post. It's pretty good!


For all the talk about vortices though, i think they are helping but too much credence is given to them.

As mentioned earlier, in one of the images posted. There is an ejector effect at the front of the floor as well, this is before any vortex is formed.

WHat this means is that there is a high speed high energy expanding flow that pulls vacuum. This creates a pressure drop behind the nozzle of the high speed flow.
Ejectors are used in water treatment facilities to pull chlorine into water.

They pull really strong vacuums.

here is an example:

[youtube]http://www.youtube.com/watch?v=8MvHplOIQCI[/youtube]

the reason why there was such a low pressure drop in one of the CFD images under the splitter, upstream of the exhausts was because of the exhausts behaving like an ejector.
This is one aspect of downfroce creation Allison didn't mention. It may be very pitch sensitive i think.
Just used the video and imagine the nozzle as the exhaust and the splitter upstream as the inlet stream. This should make sense to those who were wondering what the heck i was banging on about ejectors.

I hope the video is of help with understanding one aspect of the design. It's not all vortices.

And before anyone gets any bright ideas, there is no relation to this diffuser and the diffuser on the car. It's not technically interlinked. As the effect is just in the little frontal region near the exhausts.

[hardingfv32]

Ok, then please define what parts of the car mimic this ejector example. For instance what do you consider to be the chamber and inlet port?

Could it be Allison doesn't mention it because the theory is not valid?

Brian

[MIKEY_!]

Interesting. Think a similar pump like system could be used to suck air though the radiators? With the red steam being exhaust and the blue being radiator air. Radiators placed in the area between the 'inlet' and the 'suction chamber'.

[zorog]

from Ferrari 150° Italia thread

Was used in Spain
Barcelona:


And Valencia:

[ringo]

Ok, then please define what parts of the car mimic this ejector example. For instance what do you consider to be the chamber and inlet port?

Could it be Allison doesn't mention it because the theory is not valid?

Brian

Sometimes i wonder why .. never mind.

Put it this way; everything you accept right now from ALlison about the FEE as fact, which was proposed in this thread from april, was seen as invalid. Why? Because it wasn't on some F1 website with a big name to it.
F1T was the only site with the theory.

Allison is not saying everything. What someone chooses not to say cannot be scientific proof that something is not happening.

The CFD is not lying, and it's still holding unchallenged. Evidence of the floor pressure suggested that the ejector effect was occurring under the splitter.

Having a lower pressure under the car at the front directly benefits the pressure at the diffuser as well, as the net pressure under the floor itself is less.

The only thing left to do now is direct comparisson between FEE and EBD.
Quantitative comparison.

[ringo]

Interesting. Think a similar pump like system could be used to suck air though the radiators? With the red steam being exhaust and the blue being radiator air. Radiators placed in the area between the 'inlet' and the 'suction chamber'.

Yep.

It's really old technology. Just not well known in the general public.
Most water treatment chlorinators have ejectors.

[shelly]

I appreciate volarchico's post, but I see that ringo, you have started over again with the same attitude, which has lead to a long and sometimes inconclusive thread.
I'll try not to misbehave myself, so I will start trying to point out what I think without putting it like it's falling from the skies.

My first point is this: a home made cfd with limited computing resources does not give reliable results when we are trying to discern exhaust trajctories in a f1 car. Who does agree/disagree/ need explaination about this?