Lotus E20 VD

[gato azul]

What exactly is the FloViz indicating in the center of the bottom of the main element (wedge shape)?
Is this indicating a lack of flow or increased flow inside the wedge region?

It's the exit plume of the jets in the center pillar ( what bhallg2k calls vent 2).
It indicates that the normal circular flow around the wing is disturbed in this region.
in simpler words the flow viz which gets applied to the leading edge of the wing is "blown off" in this area
by the flow exiting the jets/slots (vent 2)

As for the diffuser question, but bhallg2k is the man to answer this, if I understand his line of thought, he would need
some sort of velocity dependent discharge rate through Vent 1, to keep the pressure inside the plenum (volume under the engine cover) constant ( or better as close to constant as is possible).
With an defined exit area (vent 1 & vent 2) you cannot compensate for the increase in flow rate coming in via the "ears", with increasing car speed, so after some point, you will build up pressure in the plenum, and the pressure will increase with car speed. (this explanation assumes that you discharge into ambient pressure, that the pressure on the other sides of the vents is constant, independent from car speed).
If you find a way to modify the pressure into which the vents discharge, you are able to affect the flow rate through the vents and thereby the pressure built up in the plenum.

I guess, this is where the diffuser enters the picture.

otherwise, you would need to alter the inlet or exit area of the ducts in relation to car speed, but I think the FIA would not like this solution too much.

[amc]

When in doubt, draw a diagram:
(All of the figures are based on rough estimates, but the idea stands.)
https://skydrive.live.com/embed?cid=E2C ... 6AHm6QgVUU
Sorry if the link doesn't work. Will try again later if not. To summarise, the 'critical point' is a point between the pylon splitting from the main duct, and the lower exit. I have estimated flow speed at the inlet as 50m/s, and at exit 1 as about 58m/s.

At the 'critical point', and this is what Bhallg2k is trying to explain, the duct is reducing in cross sectional area. This is increasing the flow speed, increasing the dynamic pressure, and therefore decreasing static pressure. At the actual exit, marked 'exit 1', the pressure conditions are defined by the diffuser that has been added. (In this case all it serves to do is reduce static pressure). I have estimated a dynamic pressure value at this point, which is probably way off.

Here's the important bit though: When the dynamic (and therefore static) pressure at the 'critical point' equals the dynamic (and therefore static) pressure at exit 1, there will be no further flow through exit 1.
At this point, all of the intake air is vented out of the slits at exit 2.

By changing the diffuser behind exit 1 (and Lotus did - they removed the middle 150mm of the beam wing during Hungary practice) they can change the flow speed and pressure conditions at exit 2, changing the speed at which the static and dynamic pressures at the critical point and exit 1 become equal.

Up until the critical speed, a small amount of air is vented underneath the rear wing, but it serves to reduce both downforce and drag, meaning the team can simply increase the angle of attack for a normal setup.

@ Bhallg2k: Awesome work... Oh, and have you ever considered stand-up?

[bhall]

So why is a diffuser required for this purpose instead of say a larger duct opening?

[...]

Brian, I want you to pay very close attention to what I'm about to say. To assist you, I'm going to make the print a bit larger than normal, because I don't want you to miss it, ok?

We can do this. We can have a conversation.

That said, the system's diffuser is necessary to this end, because Exit 1 would be overwhelmed without it if the vent is appropriately sized. Remember, this system must accumulate pressure before it begins to work. That means Exit 1 must be large enough to never be overwhelmed, but small enough to allow pressure to escape from Exit 2. If Exit 1 is too large, the VD can't accumulate enough useful pressure. If Exit 1 is too small, the VD can't release enough pressure to prevent the duct from becoming completely pressurized and choking. This is the pain-in-ass tuning part, getting the sizes of the inlets and exits just right.

This is called an answer. Specifically, this is the answer to your question. In fact, this is just one instance of the three times in which the answer was provided for the benefit of knowledge.

You are, of course, entitled to accept this answer any way you desire. If you do not like it, you're free to say as much. If you do like it, by all means, please share your pleasure with the rest of us. If you do not understand it, tell us which part you don't understand. You might even find it helpful to tell us which part you do understand. If you disagree, tell us why. Further, tell us what you think the answer could be. These are all acceptable responses to an answer you solicited.

But, please, for the love of God, do not ask this question again. Advance the conversation.

Be the diffuser. Keep things moving.

[hardingfv32]

If you do not understand it, tell us which part you don't understand.

New statement......

...Assuming a desired flow rate that meets the requirement of your proposed theory....

Why not just use a larger E1 opening that meets your flow requirements instead of a diffuser style E1 opening? IF either design can achieve the desired flow requirement, then why has Lotus used a diffuser? I feel it is a choice the has unknown significance to us.

Brian

[bhall]

Try again. This time with effort.

(Hint: By definition, altering the size of the inlet after reaching the desired, balanced flow rate will alter the flow rate and ruin the balance. You need something else.)

[hardingfv32]

It indicates that the normal circular flow around the wing is disturbed in this region.
in simpler words the flow viz which gets applied to the leading edge of the wing is "blown off" in this area
by the flow exiting the jets/slots (vent 2)

Look closely at the FloViz along the rib in the center of the 'wedge section'. Why is it flowing back into the center of the 'wedge section'? Why not just flow parallel to the rib, pushed along by the flow from the slot? What does this indicate about the 'wedge section'?

Brian

[gato azul]

don't know for sure - you tell me.
If you look, close to the exit slit, there is no flowviz or it's pushed parallel to the rib.
what you describe/see starts when the rib changes (the main pillar ends) and you have only a 10-15 mm high separation
from the left to the right side of the wing.
The momentum of the plume will decrease with distance from the exit jet, and due to the surface friction on the rib, the
exit plume is not total symmetric.
As the effect you describe starts a distance from the exit, I think it's fair to say, that the momentum of the plume has allready
diminished somewhat, and it is more prone, to be affected by other flows, such as possibly the upwash from the diffuser deck
around vent 1, as well as the plume from the slits on both sides of the pillar spilling across and mixing, because they are not
longer separated by the pillar.

[Cam]

EDIT: I don't like who I am here. So, I'm going to stop now. It's just not worth it.

On a lighter note.

@bhallg2k - I've been thinking about this and have some observations.

From what I can see of that opening, it's really being spread quite wide. Theres a lot of force being applied into that vent. I mean it's really ramming it in there. With all that constant ramming, that pressure is going to build up. Trying to contain that plume past the pressure peak is pointless and it needs to be released. On release, the plume is certain to go everywhere, I mean all over the place, sometimes it's difficult to direct that plume. I imagine there'll be some leakage of flow from that vent after the fact, and that's completely normal and to be expected.

This kind of behaviour definitely leads to VD, so I think you're on the right track mate.

[Dragonfly]

I am following the discussion but somehow missed the definition of the VD abbreviation. Would be grateful if someone enlightens me or even better - place the term in the thread title for everyone to see.

Also, it may have been touched already, is the position of the moving flap of the RW influencing the function of the system by the changes it causes to flows in the RW region?

[Gaara]

On British broadcaster Sky’s ‘F1 Show’, television pundit Ted Kravitz explained that – unlike Mercedes’ pioneering device – the Lotus version is in fact not attached to the rear wing DRS.

http://www.f1zone.net/news/lotus-pushin ... spa/15244/

[Dragonfly]

Yes, but when the flap is open we have air flowing between it and the main element which changes the pressures and the streams behind the wing. I don't know how exactly, but definitely there's a change. Which I thought might affect the system's operation.

As bhallg2k kindly explained to me VD = Vee Duct

[Huntresa]

Yeah but the good part is that its legal until 2014 when they are removing beam wings monkey seats, which means the middle 15cm will prob go away aswell.

[superdread]

Yeah but the good part is that its legal until 2014 when they are removing beam wings monkey seats, which means the middle 15cm will prob go away aswell.

Do you mean the radius rule exclusion of the middle 15cm of the main wing? So no more pylons to the wing.
Then they could try to stall the wing from the enplates, but getting high energy flow in there could be hard.

[Huntresa]

Yeah but the good part is that its legal until 2014 when they are removing beam wings monkey seats, which means the middle 15cm will prob go away aswell.

Do you mean the radius rule exclusion of the middle 15cm of the main wing? So no more pylons to the wing.
Then they could try to stall the wing from the enplates, but getting high energy flow in there could be hard.

Well i dont know but they want to remove the Beam Wing and Monkey Seat, and i think the 15cm rule is the thing that makes Monkey Seats legal.

[N12ck]

Yeah but the good part is that its legal until 2014 when they are removing beam wings monkey seats, which means the middle 15cm will prob go away aswell.

Do you mean the radius rule exclusion of the middle 15cm of the main wing? So no more pylons to the wing.
Then they could try to stall the wing from the enplates, but getting high energy flow in there could be hard.

Well i dont know but they want to remove the Beam Wing and Monkey Seat, and i think the 15cm rule is the thing that makes Monkey Seats legal.

I have been following the 2014 regs, and I have seen nothing to suggest the central 15cm rule doesn't exist anymore in 2014, and the 15cm rule is the thing that allows the monkey seats, it exists to allow wing supports (which was the intention I guess)