Vritual gurney flap

[manchild]

Here I go again…

Something I came up with last night.

Imagine duct at outer side of each endplate feeding the upper blade of the wing assembly with air. That upper blade has transversal/full width aperture on top.

My question is: - would the air fed in by duct exiting under pressure on top of the blade at 90 degrees act as virtual gurney flap relative to main air stream hitting the top of the blade? If so, wouldn’t such solution increase downforce and decrease drag (relative to conventional gurney flap) as well and narrow stream at the rear end of the car?



In addition, while I was thinking about it, it came to me that upper blade should be hollow all the way but with divider in the middle of it. This divider would prevent decrease of pressure in turns and naturally put pressure (more downforce) on same side of the wing as the specific turn (more grip to side of the car with tendecy to go up). Duct would also increase stability because side wind would have less effect on endplate. Also, the aperture could be shaped in a way that air exits only at certain spots (more exiting near the endplate to increase aero efficiency and downforce).

Any comment is welcomed.

[zac510]

hmm, I'm not sure the problem is that they need more air on the upper side of the wing.

Wouldn't this enhance the end plate vortex that teams have spent much time trying to control/minimise?

[NickT]

I don't think so, the gurney flap creates a vortex at its trailing edge that extends the point at which the wing will stall by helping the flow under the wing remain attached for longer, allowing a more agressive angle of attack or slightly more down force for at the same angle of attack. However there is a small drag penalty.

What I think your idea will do is bleed a little air off the upper surface and alter the vortexs at the ends of rear of the wing, in a similar way the teams are already doing with the cut outs in the endplate just ahead of the rear wing. Unfortunately I cant find any good pictures at the moment, but I will try later.

[scarbs]

I see what you are trying to achieve, I don’t think the outlet slot needs to be at right angles to the flap, instead if it were inline with the flaps trailing edge the effect would be similar to gurney in the sense that the flow would add some velocity to the stalling flow under the flap, Additionally as NickT pointed out the lower pressure on the outside face of the end plate would reduce the drag induced by the tip vortices.
The management of the flow from the inlet duct to the slot would need to be carefully managed to get a consistent distribution of pressure across the trailing edge

This seems a useful solution, one wonders if there's a precedent set somewhere else, possibly in aviation where flow through slots is used more often?

[kilcoo316]

Just trying to understand this.

The endplate duct feeds the inside of the wing? Which then has a slot at the trailing edge?


Trailing edge blowing has been investigated for turbofan blades, mostly as a means of reducing the boundary layer wake to reduce tonal engine noise. From what I know, I'd guesstimate at a minimum blown mass flow rate of 0.15 kg to fill the boundary layer wake of the rear wing. Would you be able to get that much from a couple of small thin ducts in the rear wing endplate?


To actually vector the flow you tend to need a much higher pressure ratio (of blown to ambient) - between 5 to 10, how do you pressurise this air in the rear wing? You'd need some sort of pump. This is easier to achieve on a turbine engine for aircraft as it has a massive pump as part of the design.

[manchild]

Thanks for replies. Yes, kilcoo you understood it right (sorry for my bad technical English).

To actually vector the flow you tend to need a much higher pressure ratio (of blown to ambient) - between 5 to 10, how do you pressurise this air in the rear wing? You'd need some sort of pump. This is easier to achieve on a turbine engine for aircraft as it has a massive pump as part of the design.

Well, if the inlet (duct) is bigger than the outlet (slot) than it would pressurise inside the wing because air would enter it in greater amount than it would exit, right? Duct feeding more air in than what slot is capable of letting out. That's what I had in mind from the beginning.

...

BTW, what about this? Same duct inlet but different position of outlet (slot). Would this instead of creating virtual gurney flap act like some sort of stretched wing (virtually again).

[kilcoo316]

Well, if the inlet (duct) is bigger than the outlet (slot) than it would pressurise inside the wing because air would enter it in greater amount than it would exit, right? Duct feeding more air in than what slot is capable of letting out. That's what I had in mind from the beginning.

Yes, but at the low speeds an F1 car does, I think the maximum theoretical pressure ratio you can achieve is 2 [the air is virtually incompressible]. I'd think that you'd have serious trouble getting close to that as it is a stagnation point.

[Cp = (1 + Sin theta)] From invisicd flow IIRC

BTW, what about this? Same duct inlet but different position of outlet (slot). Would this instead of creating virtual gurney flap act like some sort of stretched wing (virtually again).

I don't think so it would depend on whether the pressure perturbations from the circulatory system (sometimes called the bound vortex) transmit through it - and since the flow is strictly subsonic, it would do so unhindered. It would reduce the boundary layer wake, thus reducing form drag, but it wouldn't increase the downforce produced I think.... unless, if the wing was running virtually stalled, the energised air from the slot may keep the lower surface moving through entrainment - but it would be very sensitive and no F1 team would like to run that close to the stall margin I feel.

[zac510]

That image looks almost the identical manchild. I think I understand the effect you are trying to create. Is it not unlike when the teams place a third element at the above and forward of the standard two elements (as shown in your picture)?

[manchild]

That image looks almost the identical manchild. I think I understand the effect you are trying to create. Is it not unlike when the teams place a third element at the above and forward of the standard two elements (as shown in your picture)?

Yes those two on my pic are standard two elements.

In general this is what I based that idea on:

[zac510]

Is that a standard NACA duct in your original diagram?

[manchild]

Is that a standard NACA duct in your original diagram?

Yes it is, but I'm not insisting on it, just used it as most recongnisable/suitable for understanding of sketch I made.

[Ciro Pabón]

Well, really interesting Manchild. You are an original thinker.

I used to be a model aircraft constructor when I was a child. I remember an older guy that tried once to imitate an externally blown flap. I googled a little and I found that you may have a very good idea, but the exit of the air should be located at the leading edge.

As a source of compressed (if hot!) air I offer the engine exhaust. You could bleed a little air, not the full exhaust, and cool it with an interchager if needed, or use the hot air from the exhaust to "draw" cool air. Sort of a "turbocharged wing"...

For some references on the mechanism at work (prevention of stagnation of the boundary layer) you can take a look at the Wikipedia article here.

I quote: "In general, blown flaps can improve the lift of a wing by two to three times. Whereas a complex triple-slotted flap system on a Boeing 767 delivers a coefficient of lift of about 2.8, external blowing improves this to about 7, and internal blowing to 9".

Internal blown flaps were discarded because of maintenance problems (clogging with dirt and other problems).

[manchild]

Thanks Ciro (for compliment and link)

I made adittional sketches to clear out what I suggested





Would anyone dare suggesting directing some of the exhaust to blow into wing or feeding the wing with pressure from sidepods?

[Ciro Pabón]

Would anyone dare suggesting directing some of the exhaust to blow into wing or feeding the wing with pressure from sidepods?

I think I did.. But I think the idea is something like this:



Now, invert the image, substitute the jet engine for the exhaust of the car engine and make the exit of the first element of the wing blow on a new second element on your drawing. What you want is to blow air over the surface of the second wing to "fool" the wing into "believing" its moving at a higher speed.

I would love somebody to run the figures to see if the effect is as promisory as the sources mention.

Oh, and by the way, I wouldn't call it the "whatever flap", but the Manchild flap, of course.

[manchild]

I get it... hold on I'll make more sketches