Reducing the drag of a two element wing through stall

[autogyro]

At low vehicle speed there would be insufficient wing area within the regulations to produce enough lift for DF using a suitable angle of incidence for maximum lift force only.
This is why the 'wing' section is near vertical.
At low speed the 'drag' created is sufficient to convert to DF.
At higher speed the drag increases to unwanted levels that reduce top speed and increase fuel consumption.
However at these higher speeds and flow rates, it becomes possible to bleed air to the rear boundary layer and attatch the rear flow, negating most of the drag but maintaining a reasonable DF resultant.

[TheMinister]

Here is a close-up view of the air under the secondary flap. Note that as the air injection is increased, flow remains better attached to the profile.

Image 1 - No air injection
Image 2 - 1.5x free stream velocity injected
Image 3 - 2x free stream velocity injected

[img=http://lh6.ggpht.com/_dmpizYAOtJw/S4QbE ... p.gif=/img]

(image taken out not to clutter thread)

=D> brilliant.

thats the sort of flow diagrams I would expect with a blow a flap.

As was the problem with ringo's CFDs, that's not got a diffuser underneath it. It does show the principal of the coanda effect nicely.

If you cant be bothered to model the entire base of the car, maybe just stick another wing a bit underneath it to try and give a flow of air up in the right place. A bit of guesswork, but it should help for showing the concept.


Anyway the question I really wanted to ask is: what effect would stalling the rear wing (either just the top element, the whole thing, whatever- seperate the flow wherever) have on the wingtip vortices? Would it reduce them? Could that contribute to a reduction in drag?

[horse]

I think the direction which these pitot tubes are orientated would also indicate that they are expecting flow about the wing to be attached rather than stalled. (In the case of the MP25)

Anyway the question I really wanted to ask is: what effect would stalling the rear wing (either just the top element, the whole thing, whatever- seperate the flow wherever) have on the wingtip vortices? Would it reduce them? Could that contribute to a reduction in drag?

I think if the wing was properly in stall then there would be no tip vortices, or at least not ones that you would recognise. Instead, you'll get large eddys pealing off the back of the entire wing. Which are worse than tip vortices.

[tok-tokkie]

http://images.google.co.uk/imgres?imgur ... s%3Disch:1

Where the Mustang Naca duct originated.

Although that aircraft does have a cooler inlet under the mid fuselage similar to the P-51 they bear no resemblance to a NACA duct. Quote from Wike (emphasis added):

The design was originally called a "submerged inlet," since it consists of a shallow ramp with curved walls recessed into the exposed surface of a streamlined body, such as an aircraft. It is especially favored in racing car design.

Full Wiki here.

[MaF1td]

Ducting air onto the rear wing in a controlled fashion, (i.e. mechanical valve) thereby stalling the wing at high speed presumeably reduces downforce. Usefull on the straights??
Could that work?, more to the point is it legal?

[autogyro]

Agreed and I agree with the Wiki description which is for the accepted definition of a Naca duct. However the term originated with the Mustang radiator in general terminolgy for surface layer ducting.

[autogyro]

I think the direction which these pitot tubes are orientated would also indicate that they are expecting flow about the wing to be attached rather than stalled. (In the case of the MP25)

Anyway the question I really wanted to ask is: what effect would stalling the rear wing (either just the top element, the whole thing, whatever- seperate the flow wherever) have on the wingtip vortices? Would it reduce them? Could that contribute to a reduction in drag?

I think if the wing was properly in stall then there would be no tip vortices, or at least not ones that you would recognise. Instead, you'll get large eddys pealing off the back of the entire wing. Which are worse than tip vortices.

The pitot tubes are measuring the high pressure flow on the front of the wing segment. That flow will be unstalled. The underside/rear flow will be stalled at low speed and until the surface is blown. This will not have much effect on tip vortices.

[autogyro]

It also explains the cut outs in the very rearmost tops of the side fins.
This will be to allow the vortices to propogate without upsetting the rear flow at blown high speed.

[horse]

The pitot tubes are measuring the high pressure flow on the front of the wing segment. That flow will be unstalled. The underside/rear flow will be stalled at low speed and until the surface is blown.

Oh, it appeared to me as if the strake of tubes straddles both the front and rear of the flap element. They go pretty low.

This will not have much effect on tip vortices.

Can you explain why this is true? My impression was that although the pressure deficit is now greater, the vortex sheet leaving the trailing edge will be less well defined in stall and thus the vorticity more distributed rather than concentrated.

[autogyro]

The high pressure smooth flow over the front of the wing segment will leave the tips and create a vortice. The 'stalled' low pressure air from the rear will not.
At higher speeds the blown rear will attach the boundary layer and the spill from the tips will add to the tip vortices. Space being available for rapid decay through the rear top fin cut outs.
Anyway what do I know, I dont do fluid dynamics.

[Raptor22]

I think the direction which these pitot tubes are orientated would also indicate that they are expecting flow about the wing to be attached rather than stalled. (In the case of the MP25)

Anyway the question I really wanted to ask is: what effect would stalling the rear wing (either just the top element, the whole thing, whatever- seperate the flow wherever) have on the wingtip vortices? Would it reduce them? Could that contribute to a reduction in drag?

I think if the wing was properly in stall then there would be no tip vortices, or at least not ones that you would recognise. Instead, you'll get large eddys pealing off the back of the entire wing. Which are worse than tip vortices.

The pitot tubes are measuring the high pressure flow on the front of the wing segment. That flow will be unstalled. The underside/rear flow will be stalled at low speed and until the surface is blown. This will not have much effect on tip vortices.

Stalled flow at low speed....?? Yes perhaps at 60-80km/hr in the pitlane, but here mechanical grip is more important anyways.
where the wings need to efficient is from around 140km/hr to +300km/hr since this is the zone where the aerodynamics really needs to work at it best. Most f1 type wings will have uncoupled flow or stagnated flow at low speeds. However the McLaren wing will not be stalled until the blowing kicks in. The blowing is there to delay the stall till beyond the speed that the car is geared to be capable of for a given circuit. the wing will still function like any other well designed wing.

[horse]

The high pressure smooth flow over the front of the wing segment will leave the tips and create a vortice. The 'stalled' low pressure air from the rear will not.

Frankly, that is plain fantasy. The tip vortices are a consequence of the wing operating correctly, not in stall. Particularly with blanked ends you need a concentrated vortex sheet leaving the trailing edge to witness this phenomenon.

[Pup]

Stalled flow at low speed....?? Yes perhaps at 60-80km/hr in the pitlane, but here mechanical grip is more important anyways.
where the wings need to efficient is from around 140km/hr to +300km/hr since this is the zone where the aerodynamics really needs to work at it best. Most f1 type wings will have uncoupled flow or stagnated flow at low speeds. However the McLaren wing will not be stalled until the blowing kicks in. The blowing is there to delay the stall till beyond the speed that the car is geared to be capable of for a given circuit. the wing will still function like any other well designed wing.

No offense intended, but I think you have a fundamental misunderstanding about how the setup is supposed to work. The blowing prevents the stall - it does not cause it. And if the wing is supposed to stall on the straight, at high speed, then it certainly would be stalled at lower speeds. So the blowing/sucking/whatever (it's blowing) would prevent that, and then it is cut off or disrupted somehow along the straight.

That, of course, is if you believe the wing is supposed to stall on the straight. If you don't, then the theory is the same, but the wing is blown constantly, never stalls, except perhaps at very low speeds, and the benefit is simply greater downforce and/or less drag.

[ringo]

Before we jump to conclude on the blowing. There has to be an indication that the upper element is much steeper than the end of 09 upper element.
If we consider that the angle of attack does not change, stalling is not an issue if the element is at an angle where it is optimal, which could be similar to the 09 wing.

Stalling at low speed becomes an issue because the element is fixed in a position where it is inherently stalled, meaning it is always stalled no matter what and blowing is it's only means for operating optimally. Remember the wing is fixed.
This suggests that as the blowing speed falls, or if it so happens that there are moments when there is not jet blown, the wing would be stalled. We have to ask if the team will deliberately risk using an inherently stalled wing.

I would call this the "normally open" theory, where the blowing is what "turns on" the wing.
In this case the wing is always stalled and requires that it is blown to operate normally.

The base bleeding concept is the "normally closed" theory, where the wing is "turned off" by blowing the jet. In this case the wing is normally not stalled and only stalled at high speeds.

The normally open theory is what seems to be the accepted theory here , which suggests that if anything were to happen to that jet , the wing will stall. This seems to be very risky.

In the normally closed theory, the one that I and SLC have not thrown away as yet, suggests if the jet stops blowing, the wing will be in no danger of stalling because it is normally in an optimal position.

You all see what i am getting at?

[ringo]

I am going to make some amendments to my wing and get the flow attached with a bridged wing.
The FIA regs should have some insight to the maximum thicknesses of the wing profiles, and i will work from there.
I will through in something like a diffuser as well.
I will repeat the experiment and see what happens.