Reducing the drag of a two element wing through stall

[casper]

ferrari's seemingly passive system. It has the shrouded pipe on the bridge wing as well.

As against the blown wing concept, this picture illustrates the blown engine concept., I guess.

[raymondu999]

Interesting... blow the right bank eh? Hmmm...

[ringo]

ferrari's seemingly passive system. It has the shrouded pipe on the bridge wing as well.

As against the blown wing concept, this picture illustrates the blown engine concept., I guess.

Oh i get you

[ringo]

Any shots or clips of the stalled wing working in the rain in China?
I hear the trails could be seen to move in the upwash as the f duct is activated and deactivated.
pm me the clips if you have.

[cornermarker]

I think the opposite was true, actually, and it may have been another big piece of the puzzle. It looked like activation of the slot resulted in a reduction in wingtip vortices from the rwep's, and this would make sense, as they're a large component of induced drag.

Watching the race a couple times, paying particular attention to the long straight, between 13 and 14, all the cars at one time or another had visible wing tip vortices (visible because of condensation in the low pressure at the center of the vortices in these conditions) coming off the tips of the rwep's. The 25 was more succeptible than the other cars, sometimes creating them when other cars weren't, and showing stronger, more clearly defined ones when other cars developed them too (under same atmospheric conditions). I think this is just because of the nature of the 25's wing. It's less slippery, higher df as the slot device allows it to be. Key thing is, they were the same type of vortex, nothing special. The Redbulls and Renaults also had a lot of condensation in the tip vortices.

Usually the only time down the straight when vortices were formed was immediately after hitting the brakes in the braking zone for turn 14. This was usually the only time we saw a combination of sufficient speed and deactivation of the device. This happens lap after lap. No tip vortices, hit brakes, tip vortices. The best illustration though was in more humid conditions, later in the race 53 laps in, JB and LH racing to the finish, both form visible vortices through and out of turn 13. As soon as the car straightens out, the vortices are gone. As soon as they brake for 14, they're back. That really was a thing of beauty.

Lap 12, Sutil Vettel and Lewis are racing down the straight to turn 14, and only the Red Bull is forming visible vortices (Perhaps the FI was running low wing?). As Lewis hits the brakes, vortices form, then die down as he slows. Vettel's vortices die at the same rate.

But under the safety car on lap 22, Jenson is warming up his tires, swerving at low speed, and there are well-formed tip vortices. This is the only time that the 25 formed visible tip vortices in the middle of the straight. It seems like a side effect of the slots, if not the primary function, is to interfere with the formation of tip vortices, which can be a large source of drag.

So tip vortices form when two volumes of air meet going in different directions (and speeds) at the trailing edge/wing tip. Rear wing endplates are designed to take this effect away from the wing itself, making it more efficient. But the endplates themselves still create vortices. Air on the outside of the wing is travelling basically back and slightly upward, while air on the inside is traveling sharply upward and back at different speed because of the wing. When they meet, you get the out-back-down-in vortices we saw from all the cars in China.

I think they could be eliminated by the same method I proposed earlier, form vortices on wing surface by passing air through the slots. But do this in way that also changes the direction and speed of the air exiting between the endplates, making it match more closely the speed and direction of free stream air on the outside that it will encounter. There will still be vortices, of course, but smaller ones.

Up until yesterday I didn't think it would be a laminar bubble, but that seems to be what would help reduce tip vortices at the endplate, and at the same time it would effectively change the profile of the wing, making it's rear profile very round and slippery.

Overall effect, again less drag so you can crank on more wing without sacrificing too much top speed.

Kelpster

[raymondu999]

Hey all. Just a thought here. When the drag is gone... wouldn't that also save fuel, and mean that the McLarens have to use less fuel at the start of the race?

[hollus]

No, it wouldn't save much fuel. You go full throttle and use the same fuel to achieve greater speed. Well, maybe the car is at full throttle for some tenths of a second less, since the straights last less at the higher speed, but I doubt will will add up to much. And running more wing adds extra drag in the corners.

[ringo]

Merc passive system:

http://www.formula1.com/news/technical/ ... 7/740.html

they say it uses pressure sensors, however i don't know how is this a form of control. Maybe it's for data collecting purposes.

I think the curved pipe is to turn the air downward as it exits the upper element. So it looks more like stalling than blowing.
The good thing is that this one is easier to model and investigate than mclaren's.

[cornermarker]

The answer to the purpose of the Mac device lies in the shape of the vortex formed by the slot and the free stream. Looking at the back of the wing, there was a very deliberate attempt to get a vortex of a certain shape and size. I've been having trouble visualizing it, but think it would propagate outward from the center, get larger, then break when it reaches the end of the slot. I assume that's the reason the slot doesn't reach the endplate.



Edit: alternate, probably more accurate depiction of rw vortex. Jet pressure would naturally be higher nearer the center (fin duct) + free stream is less forceful there = larger vortex.



In this scenario flow would stay attached. Haven't yet figured out how this disrupts the formation of the tip vortices. It could be the air from the bubble itself, or perhaps the bubble draws air in from the outside of the rwep through the notch so that the air on either side of the tip is similar in nature.

Edit: Or it could just be that with the laminar bubble in place, it's just plain less efficient as a wing, and thus, like the FI, isn't likely to produce tip vortices strong enough for condensation.

Merc passive system:

http://www.formula1.com/news/technical/ ... 7/740.html

they say it uses pressure sensors, however i don't know how is this a form of control. Maybe it's for data collecting purposes.

I think the curved pipe is to turn the air downward as it exits the upper element. So it looks more like stalling than blowing.
The good thing is that this one is easier to model and investigate than mclaren's.

I haven't seen the back of the new Merc wing, but I can guarantee you that device wouldn't stall a wing because of the very low pressures we're talking about. For the same reason, it's probably not a blown wing. Again, looks like the best way to use that device would be vortex generating jets. Again, I'd need to see the back of the wing, but I'd put money on it being passive air jet vortex generators. To force separation would require a great amount of energy. Why force a fluid to do what you want when you could coax it, guide it where you want it?

Kelpster

[ringo]

Vortex generation is usually used to interact with objects downstream. It's not something the team would want to increase, because it adds drag.
Vortexes are usually used for mixing. Beyond the wing it's best to reduce them, because they affect the upwash of the wing.
However I do think though that the f duct is doing some kind of wake control, so in a sense vortexes have to do with that.
The reason i say the Merc is stalling is because of the direction of the curved duct. I don't know it to be true, but it's a hunch. I have to look into it more before i can stick to any theory.

[raymondu999]

Actually, watching the race again, you can quite easily see something happening to the water right to the back of the McLaren rear wings at the start/end of the straights. Wouldn't this have already told the other teams specifically how they were achieving the f-duct stalling? It seems to me like the rain was demonstrating the aerodynamics to the f-duct blowing.

[cornermarker]

Actually, watching the race again, you can quite easily see something happening to the water right to the back of the McLaren rear wings at the start/end of the straights. Wouldn't this have already told the other teams specifically how they were achieving the f-duct stalling? It seems to me like the rain was demonstrating the aerodynamics to the f-duct blowing.

In heavy upwash (roostertail) it was difficult or impossible to see any tip vortices, so I think you may be referring to something else? What lap do you see it clearly on? Check the instances that I mentioned above, is that the same phenomenon?

Vortex generation is usually used to interact with objects downstream. It's not something the team would want to increase, because it adds drag.
Vortexes are usually used for mixing. Beyond the wing it's best to reduce them, because they affect the upwash of the wing.
However I do think though that the f duct is doing some kind of wake control, so in a sense vortexes have to do with that.
The reason i say the Merc is stalling is because of the direction of the curved duct. I don't know it to be true, but it's a hunch. I have to look into it more before i can stick to any theory.

No actually vortices are used in aerodynamics all the time to keep planes in the air: Delta wing planes form many vortices at the leading edge, which pass over the low pressure surface. Solid vortex generators are fixed to the leading edge on small planes to maintain lift at slow speeds. The same concept is used on F4 Phantoms, F15 Eagles, and Super Hornets. The point on the jagged leading edge is there solely to create a vortex that streams over the wing. Why? Better/more predictable low speed flight characteristics. A stationary laminar bubble on the back of a car wing would only creates a small amount of drag, but is preferable to flow separation, which creates more drag. Vortices shouldn't be thought of as good or bad things, they're just things. Phenomena that come with any fluid. In some cases they are to be avoided (tips) in others they are helpful (surfaces).

More importantly, there's practically nothing else those slots could be used for. If air is coming out of them, vortices are being formed. It's called jet in crossflow, has been studied for decades. Only question is, what do the resultant vortices look like, and what do they do.

I think too many people are stuck on the word stall (this is why I don't use it- the term just isn't important to understanding the mechanics of what's happening), and are trying hard to make it work. Instead, look at the actual cars, the actual devices. Ask yourself what could be happening, and what effect that would have. Then find the research that applies to these things, real world physics done with real world airfoils and fluids (more reliable than programs when you don't know the parameters). I say this, of course, because I've already done all this. viewtopic.php?f=6&t=8028&p=150459#p150459

I have yet to see a paper that says a jet in crossflow is used to force separation, but I assume, as I've said before, that it would take tremendous pressure. The end effect may be called stall, who knows. But we shouldn't start with a vague term like that.

Another realization I had, Hamilton, king of the late-brakers now has an extra bit of drag to use when he finally wants to slow that sled down. I wish my broadcast had the graphic with the g-meter. The Mac braking g's must be insane with the sudden tip vortex generation.

Kelpster

[ringo]

But you are agreeing with me here. You said leading edge of the wing, so the vortices interact with the surfaces as they go downstream.
At the end plates of a wing, those are the last surfaces on the car, nothing else is downstream.
I know vortices have uses, but it's mainly for pressure mixing. Most of the time they are detrimental, so efforts are made to eliminate them if nothing is downstream.

The slots now, i am not sure about. I don't know what is happening even though i have seen the flows themselves in cfd.
They look like they cancel the vortices, that is what i would think.



On a high cambered wing like this, the pressure distribution is so strong that it's much taller than the wing element. High pressure fills up everywhere in that pocket between end plates. So much so, some of the high pressure spills over the top of the end plate. This drives the vortices as it curls over the plate. The same can be said of the low pressure area behind the car and that flowing along the endplates.
The slots are shaped in such a way, upward chanelling louvres, that the high pressure between the end plates pass through and move upward. This upward, high pressure, movement on the outside of the end plate acts to miminize the flow coming over from the top (yellow arrows).

[cornermarker]

Cool graphic, where did it come from? The one on the left is excellent for understanding the generation of tip vortices. The two bodies of air--one from the side of the end plate, the other from the rear of the wing--meeting while traveling in very different directions and pressures = strong tip vortices. As China showed us, the 2nd isn't an extremeley accurate, as all cars created vortices at one time or another. You can't eliminate them (i think), only minimize them.



I think I understand where the confusion lies: this slot does not create vortices that trail behind the car. The vortex goes where the free stream takes it, in this case up along the surface of the wing. This is a new concept in F1, to my knowledge. A car with a vortex generating jet somewhere on it. It's different from something like vortex generators on fwep's or barg boards.

Ah, good man, I think the particular cfd you're referring to did not accurately depict a real world situation. This is the only one I've seen so far on a forum that does:



One thing happens when you have two volumes of air, different trajectories, different pressures, meeting. They roll into a vortex. In this case the air moving up along the back of the wing encounters air coming out of the slot. That's all you need to form a vortex, that's why they're such a common problem. The hard part is in controlling it, and that's why we see the special shape and skew of the slot in the wing, and, as I've mentioned before, the change in McLaren rear wing design philosophy of previous years.

So, this already has a name. It's called Jet in crossflow. It forms vortices. I'll direct you again to the paper abstracts.



There is only one other possibility. That the device is activated after separation has already occurred. In turbulent air behind the wing, I don't know then what would happen. But--as on lap 53--tip vortices disappear as soon as the car comes onto the straight, then reappear the moment the driver hits the brakes. This indicates the moments the device was activated and deactivated. I doubt separation would have ocurred right out of turn 13.


Kelpster

edit: right, left, whatever
edit: disapppear, reappear

[ringo]

I drew that in paint, but i based it was what i observed.
viewtopic.php?f=6&t=285&start=330

I think i get what you are saying with the vortices thing and the slot curvature. I think the curvature also has to do with the lift distribution along the span as well. The center of the wing always tends to have more separation in the case of an F1 wing. The stronger upwash is where the wing profile meets the end-plates.