Reducing the drag of a two element wing through stall

[jason.parker.86]

Cant see how they can do all this testing, data gathering over the past few weeks and now slap a new floor onto it? Looking for more air!

Ive got a sneek preview from a spy in the pit lane who says this is what mclaren are using to feed that diffuser, and the reason behind that snorkel on the nose...

[TheMinister]

Aha- I knew it! There was a bump there last season, but it seems to have changed sides:


Could it be cooling for whatever caused the bump?

Is that rotary inertial damper still there? Could that need extra cooling?

[Sikthskies]

It has the function of vibrating and sending air towards the rear wing as was initially suggested. I was told by a guy who works for McLaren

[autogyro]

Any improvement to the boundary flow at the rear of the wing section by blowing will reduce both form and induced drag.
All it needs is good flow diagrams to prove it.

[Pup]

Actually, since induced drag is a function of the wing's force vector, it would be increased if the wing is made more effective.

[autogyro]

Your right pup, so increased drag from better lift would reduce downforce at higher speeds with smoother flow.At least the induced component of it.
Reducing form drag by blowing will also reduce the DF component of that drag.
Over all result, reduced drag and reduced DF when blowing at higher speeds.

[SoftBatch]

Form drag does not produce down force unless the airflow is being directed towards the ground.

[cornermarker]

So, it seems to be active flow separation control using vortices created by a skewed vortex generating jet.

http://adsabs.harvard.edu/abs/1992PhDT........50L

"Surface static pressure measurements and oil-flow visualization results from the wind tunnel tests indicated that transverse grooves, longitudinal grooves, submerged vortex generators, vortex generator jets (VGJ's), Viets' fluidic flappers, elongated arches at (+)alpha (positive angle of attack), and large-eddy breakup devices (LEBUS's) at (+)alpha placed near the baseline separation location reduce flow separation and increase pressure recovery"

This is a first-generation flow/wake/whatever-control device, and so has likely been kept simple. No really high pressures involved, No angled nozzle, just a flow of air, either straight out, or straight in.

There have been a few other suspicious changes to the rear wing. The change in element gap design since last year. Notice how the gap widens at the edges, where the first element seems to flatten out, whereas the middle is steeper, and the gap smaller. Note the proximity of the slot to the gap in elements. And the fact that the slot reflects somewhat the shape of the gap between elements.



http://resources.metapress.com/pdf-prev ... ze=largest
"Results indicate that flow-separation control can be accomplished, with the level of control achieved being a function of jet speed, jet orientation (with respect to the free-stream direction), and jet location (distance from the separation region in the free-stream direction). Compared to slot (flap) blowing, jet vortex generators can provide an equivalent level of flow control over a larger spanwise region (for constant jet flow area and speed)."

Also note the angle of the slot to free stream during most of its length.

http://www.springerlink.com/content/jvhmh5um403x4312/
"First results show that the optimal skew angle is about β = 15° for the slot actuator."

Because of the above, it seems that the slot is there to act on the flow of air coming from the gap (primarily), and first element to create longitudinal (upward propagating) vortices. The air from the slot meets the free stream, and the two roll up forming a vortex which stays attached to the surface, unlike the uninterupted free stream.



The primary benefit, aside from preventing flow detachment, is a reduction in drag permitting an increase in speed.
"Air-jet vortex generators, unlike passive vane vortex generators, do not induce a large increase in drag and they can be actively operated and controlled."
http://pdf.aiaa.org/jaPreview/AIAAJ/2009/PVJA41986.pdf

Because the vortices aren't very strong, I'm guessing they break up quickly on contact with flow from the high pressure side of the wing. It's unclear to me how they would interact with flow from the diffuser, but it can't be a bad thing to have a low pressure zone above a diffuser, all contained within large end plates.

Kelpster

[autogyro]

Form drag does not produce down force unless the airflow is being directed towards the ground.

Near vertical wing element creates form drag in the reverse direction to the cars motion.
This force results in DF because it works on the car through the moment between the center of form drag and the wing mounting point which is fixed.

[SoftBatch]

Form drag does not produce down force unless the airflow is being directed towards the ground.

Near vertical wing element creates form drag in the reverse direction to the cars motion.
This force results in DF because it works on the car through the moment between the center of form drag and the wing mounting point which is fixed.

A moment like that would create a force on both the front and rear wheels about the center of pressure of the car if the moment is caused by the forces on the rear wing then then it would create a downforce on the rearwheels while creating a lifting force on the front wheels.

[delacf]

Regards to all, forgive my English. I'm sorry.

It vibrates (flexes) laterally at high frequency, acting as fan that directs more air on the rear wing than it would naturally get there.

Hi, manchild. So, why many teams have resorted to fixing the "shark fin"? Its function will be to reduce the turbulence that are formed when fin flexed? I do not think fin flex provide more air to rear wing, I think it will create a vortex street. The problem can be solved by fixing the fin. I think the goal of the "shark fin" is to reduce turbulence when flows between both sides of the car meet. So the air that reaches the rear spoiler has higher pressure. If you avoid the two streams meet, you avoid causing turbulence. It is my opinion...

Greetings

[autogyro]

Yes but the main force is down on the rear wheels, the lifting force on the front is reduced by the wheel base to rear wing mount/form drag center ratio.

[tok-tokkie]

Form drag does not produce down force unless the airflow is being directed towards the ground.

Near vertical wing element creates form drag in the reverse direction to the cars motion.
This force results in DF because it works on the car through the moment between the center of form drag and the wing mounting point which is fixed.

That is very true. I had only considered the aero forces as on an aircraft but here the mechanical leverage you are talking about is very much part of the whole.

[autogyro]

Form drag does not produce down force unless the airflow is being directed towards the ground.

Near vertical wing element creates form drag in the reverse direction to the cars motion.
This force results in DF because it works on the car through the moment between the center of form drag and the wing mounting point which is fixed.

That is very true. I had only considered the aero forces as on an aircraft but here the mechanical leverage you are talking about is very much part of the whole.

If the wing only worked to produce lift (negative) there would be no reason to have such a steep angle of attack. Useless on an aircraft.

[horse]

If the wing only worked to produce lift (negative) there would be no reason to have such a steep angle of attack

I think you're forgetting that the flap element also effects the main element. Having the flap element improves the down force generated by the main element.

I'm not sure a moment about the rear wheels is that desirable anyway. If you push the back down then you will lift the front at the same time.

Useless on an aircraft.

Flap angles get pretty steep, but the wings are not stalling.