Reducing the drag of a two element wing through stall

[Steve S14]

im just an economist, but i believe this is what you are looking for:

the downforce is generated by the air having lower pressure below the wing, and higher pressure above it.

the highspeed, low pressure air below the wing gets disturbed by the inserted air stream, causing the air to turn turbulent and "coil" off the back of the wing, effectively changing the pressure differences between the top and bottom of the wing, causing downforce to be lost.

[cornermarker]

From the photos I've seen to this point, this isn't completely analogous to the McLaren system. The Mac system feeds the upper element, and blows air outward, from a curved, angled slot on the upper element, the kind of thing that would create vortices (vgj's or vortex generating jets). At high speed this means less drag, less downforce than uncontrolled separation.



The Sauber solution appears at first sight to just be a logical development of the old blown wing we've seen in previous seasons (BMW, Mac). A blown wing, blowing air transversely along the surface. Now, instead of just an opening in front of the wing (passive) there is a whole system dedicated to controlling the pressure coming from that main element blowing slot. Question is, does it increase or decrease that pressure, or is it both.



But according to Autosport, there is also a slot cut into the upper element???:
"It is believed that once the air is channelled through the car it is then blown out onto the main profile of the rear wing, rather than the upper element as happens with McLaren. It is not clear where the driver is able to influence the airflow.

As well as the duct, Sauber has introduced a slot gap in the middle of the upper element - in similar style to the McLaren design that was approved by the FIA."

Question is, does the fin actually feed a slot on the upper element as well? The pics I've seen don't indicate this. The research I've done suggests there are tons of things you could do with a tube of air running to or from a wing. Question is, what have Sauber decided to do with theirs. Need more pics!

Oh, even if the supposed upper element slot isn't fed, it could still have an effect on flow:

"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."

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


Kelpster

edit: bolded wrong term

[cornermarker]

Comparison of the McLaren fin/wing and the new Sauber fin/wing assembly:



Kelpster

[ringo]

I think the snorkel air works the other way round.
Normally the air from above the drivers head goes to the slot in the upper wing where it helps to keep the airflow attached to the wing giving increased downforce & drag.
When the driver blocks the hole in the pipe from the snorkel it injects air from above to divert the air from the upper wing to down the gearbox way. The upper wing airflow then separates from the rear side (stalls) reducing both downforce & drag - when running down the straights.
I think the snorkel air should be injected from the top to make the airstream take the lower route.

I was considering that as well. That could be the case, though the piping would be intricate to go up then curve back down. It would work very well though.
The logic would be the iverse.
blowing would mean not stalled and not blowing would mean stall. This suggests the wing is running at stalled angle under all circumstances, and blowing is taking place at all times as well. Stopping the blowing would cause separation and stall the wing. Sound logic.

[forty-two]

I don't think I'm going over old ground here but..

Take a look at the following image:


Notice the airbox design. It has extra scoops either side of it. Could it be that FIF1 built in a partial intake for a later "sharkfin rear-wing feed" similar to the McLaren and now Sauber? I don't recall seeing this before in the FI, but if it's been there all along, well done FI for keeping quiet about it!

If so, all they'd be missing would be a control mechanism (if one exists or is necessary!) involving a vent somewhere in the tub. In fact I think I spotted some of those on the FI in Bahrain?? Does anybody know if I'm right about the tub vents?

[Balt23]

I think the snorkel air works the other way round.
Normally the air from above the drivers head goes to the slot in the upper wing where it helps to keep the airflow attached to the wing giving increased downforce & drag.
When the driver blocks the hole in the pipe from the snorkel it injects air from above to divert the air from the upper wing to down the gearbox way. The upper wing airflow then separates from the rear side (stalls) reducing both downforce & drag - when running down the straights.
I think the snorkel air should be injected from the top to make the airstream take the lower route.

I was considering that as well. That could be the case, though the piping would be intricate to go up then curve back down. It would work very well though.
The logic would be the iverse.
blowing would mean not stalled and not blowing would mean stall. This suggests the wing is running at stalled angle under all circumstances, and blowing is taking place at all times as well. Stopping the blowing would cause separation and stall the wing. Sound logic.

This is more in line with common Active Flow Control methods that have been in use on airplane wings and studied in many wind tunnel and CFD simulations in research facilities since the 80's. Blowing air over a wing to PREVENT separation is much more logical than blowing air to create separation.

also think of it from a driver actuation standpoint, cornering or braking at 5G's, you arent going to be thinking about closing a hole with your knee (its been reported multiple times on jamesallenonf1.com that it is a hole in the cockpit closed with the drivers knee) you're going to be using that left foot and leg to actuate your braking. So, if they need to close the slot to induce stall, than when its open, it must be NOT stalled to create necessary downforce for cornering and braking.

[ringo]

Yes that is the danger with the wing element being normally stalled and dependent on the blown slot to produce down-force.

Even with figuring out the fin's chamber, there is still the nature of the wing element itself to consider. What angle does a second element on a multi element wing stall. I have a feeling it is more than 90* relative to the horizontal, ie an obtuse angle.
Second elements on multi element wings are very diffult to stall becuase of the already steep incident angle of the air coming from through the slot from the first element.

[forty-two]

Not sure if this has been commented upon before or not, but taking a look at this image:



You can see right through the airbox, but annoyingly, you can't see through the top section of it. Looks like the ductwork behind the airbox was not fitted when this picture was taken.

[cornermarker]

This is more in line with common Active Flow Control methods that have been in use on airplane wings and studied in many wind tunnel and CFD simulations in research facilities since the 80's. Blowing air over a wing to PREVENT separation is much more logical than blowing air to create separation.

This is how I feel. One technique would require brute force and high pressures, while the other is an elegant and safe engineering solution.



The wing on the left was the kind used in Aus 09. The one n the right, while it may create a lot of df at low speed, is gonna experience separation--and therefor drag--much more easily at high speed, basically turning itself into an air brake. (There's a reason you don't see something like this at Monza.) You make this change in design philosophy because you can eliminate a lot of the drag it creates with the new technology.

As for the duct, I like to imagine things are as simple as they could be made and, as someone mentioned, it's just a hole. The only ducting there would be is to put the outlet in line with the pedals (or over/beside the knee), for the sake of ergonomics. And I'm thinking that whether it's covered or not influences the relative pressure of the cockpit to the air around it, and this is for some reason important. Normally, (and in the 25 when the hole is covered) the pressure surrounding the cockpit is quite a bit lower than the cockpit, creating a partial vacuum. Faster it goes, the higher the pressure differential. When the hole is left open, the effect is decreased. I'm guessing this change in relative pressure alone is the mechanism by which the the slot is "turned" off or on. It's just another air flow conditioner, much like a winglet/flick up, but one whose angle of attack you can change. The change it affects is flow to one of the openings above the driver's head.

Would explain helmet roulette and a certain driver's spending a whole day of testing getting his larger body "comfortable" in the car.

Another thing to consider: If the duct is just for air flow conditioning, there's the possibility air is always coming out of those slots. Covering the hole just increases or decreases the slot pressure. Lower pressure, smaller vortices. Higher pressure, larger vortices.

Could someone explain to me normal flow around the cockpit and helmet in an f1 car at high speed? What happens when you change the pressure of the cockpit?

Kelpster.

[DaveKillens]

I think the snorkel air works the other way round.
Normally the air from above the drivers head goes to the slot in the upper wing where it helps to keep the airflow attached to the wing giving increased downforce & drag.
When the driver blocks the hole in the pipe from the snorkel it injects air from above to divert the air from the upper wing to down the gearbox way. The upper wing airflow then separates from the rear side (stalls) reducing both downforce & drag - when running down the straights.
I think the snorkel air should be injected from the top to make the airstream take the lower route.

I was considering that as well. That could be the case, though the piping would be intricate to go up then curve back down. It would work very well though.
The logic would be the iverse.
blowing would mean not stalled and not blowing would mean stall. This suggests the wing is running at stalled angle under all circumstances, and blowing is taking place at all times as well. Stopping the blowing would cause separation and stall the wing. Sound logic.

This is more in line with common Active Flow Control methods that have been in use on airplane wings and studied in many wind tunnel and CFD simulations in research facilities since the 80's. Blowing air over a wing to PREVENT separation is much more logical than blowing air to create separation.

also think of it from a driver actuation standpoint, cornering or braking at 5G's, you arent going to be thinking about closing a hole with your knee (its been reported multiple times on jamesallenonf1.com that it is a hole in the cockpit closed with the drivers knee) you're going to be using that left foot and leg to actuate your braking. So, if they need to close the slot to induce stall, than when its open, it must be NOT stalled to create necessary downforce for cornering and braking.

There are important criteria that must be recognized in order to understand this mechanism better.

First and foremost, the system has to be fail-safe so that under normal conditions without any input from the driver, it is in it's high drag, high downforce mode. if this system failed, the last thing anyone would want is low downforce entering Parabolica. And with a low downforce wing, lap times would be embarrasing, to say the least.

The system has to be designed so that under "normal" driving conditions the driver cannot activate the low drag/low downforce mode. Imagine the driver's left knee somehow activating the system into a low downforce configuration in the middle of some fast esses, such as at Maggots.

But the system has to be incredibly simple for the driver to use. The only time this mode would be activated was in a straight. Under these circumstances, it is folly to ask any driver to take his hands off the wheel at high speeds. His right foot is busy pressing the gas, but the left foot is idle, and doing nothing until the next braking point is reached. So it comes down to the left foot or leg, the driver has to move it to cover a hole to pressurize the control circuit, switching the rear wing into the low drag/low downforce configuration.

The picture above is close, but in reverse. Under "normal" circumstances the input air designated for the rear wing is directed up towards the wing, and only by input from the pressurized air controls would it switch flow away from there, depriving the blown slot air, and thus reducing drag and downforce.

[ringo]

Yes, i would prescribe to the normally attached flow theory.

The pic i have above is just investigating the feasibility. It can be modified to do the opposite. As long as I change the end conditions. The fin duct is mostly figured out, it's the wing that is the enigma.

The real question is if the jet of air is to force a separation to stall it. Or the lack of the jet is what stalls it. I am not sure which one it is. The latter is the typical blown wing and the first is the opposite.
It would be nice if a journalist would ask an F1 engineer what is actually happening in that respect.
It's too difficult for fans, especially half the world away to get a word in.

[cornermarker]

The real question is if the jet of air is to force a separation to stall it. Or the lack of the jet is what stalls it.

That's actually the easiest question to answer. The engineers and aerodynamicists have already done the research, so we don't need to guess. We just have to find the papers, which I have. Unless air is coming out of the slots at tremendous pressure, they will form vortices when encountering the free stream. Vortices stay attached when air might otherwise separate.

It's all laid out in the last page of the fin and engine cover thread

Only possible question is, what if the air is at tremendous pressure? 1. not sure, but wouldn't someone notice? 2. would that be something a team would risk?

Kelpster

[The FOZ]

I heard McLaren call it the SH duct... meaning $hit h0t?! I do not know why Macca are being all "secretiv" about its bloody name!

It's a very common practice in F1 to use deceptive names for new developments. I believe the "J-damper" is another such instance. Everyone in your garage knows what you're talking about, and it's juust confusing enough to potentially lead other teams in the wrong direction.

For all we know, that duct is stalling the diffuser, not the rear wing...

[wesley123]

I heard McLaren call it the SH duct... meaning $hit h0t?! I do not know why Macca are being all "secretiv" about its bloody name!

It's a very common practice in F1 to use deceptive names for new developments. I believe the "J-damper" is another such instance. Everyone in your garage knows what you're talking about, and it's juust confusing enough to potentially lead other teams in the wrong direction.

For all we know, that duct is stalling the diffuser, not the rear wing...

why would it stall the diffuser? and part 2, how you know that? you are the first person to say that

[WhiteBlue]

For all we know, that duct is stalling the diffuser, not the rear wing...

Great balls of fire! I thought they would have to locate it where the stalling is supposed to happen? So how can it stall the diffusor when it exits at the rear wing?