Reducing the drag of a two element wing through stall

[wesley123]

pretty stupid as if im correct stalling the diffuser would add drag, reduce downforce and make the whole floor instable, ideal conditions for an take off.

[The FOZ]

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

I'm no aerodynamicist, but perhaps there's a way to overload the diffuser, result in reduced downforce and...greater top end speed!

Granted, that's a stretch. If it's even possible. Most likely just a crazy idea of mine.

I was more trying to make the point that misinformation can be a powerful tactic in F1. Red Bull's sticker exhaust outlets are another fine example. They wouldn't do it if it wasn't worth doing. There's dozens of other examples, and probably dozens more that nobody has noticed.

WB - Do you know that it exits at the rear wing? All I see is an inlet in one location, and what appears to be an outlet elsewhere. Nobody has proven that the two are connected in any way. Or maybe stalling the rear wing is a valid concept. But maybe piping the air to the diffuser is a more effective concept, and McLaren has thrown everybody off the trail by making them think it's going to the rear wing.

wesley123 - I hesitate to reply to you, since your reply is somewhat disrespectful, but you might be incorrect. While the diffuser does add to downforce, it isn't the only downforce generating element - the front and rear wing are a significant part of the puzzle, too. Overloading the diffuser would reduce downforce, but wouldn't even come close to causing the car to "take off" (I'm assuming you mean literally leave the ground). Your comment about making the floor unstable, however, might be accurate.

Anyhow, I'm sure that 99 times out of a hundred, this is a ridiculous concept. But who knows? I can't be bothered to try and run a CFD sim of this at the moment. Anybody else can have at 'er...

[wesley123]

well, why would you run an timeconsuming, expensive CFD run on something that is known not working?

[PlatinumZealot]

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

I'm no aerodynamicist, but perhaps there's a way to overload the diffuser, result in reduced downforce and...greater top end speed!

I think I understand where you are coming from. It is becaue people usually equate drag and down-force and this is not the truth. It really depends on the shape of the object and the properties of the air around the object. Even though the floor adds a lot of downforce, the floor is almost horizontal so It barely impedes the air which is also flowing horizontally. So it does not add much drag.

A wing is different as you know, since they are usually angled into the air stream, they impede the air. So people can usually guess that a high angled wing (which makes much downforce) has much drag. So that is why some people follow the notion that down-force brings drag, which is not the whole story.

[The FOZ]

I think I understand where you are coming from. It is becaue people usually equate drag and down-force and this is not the truth. It really depends on the shape of the object and the properties of the air around the object. Even though the floor adds a lot of downforce, the floor is almost horizontal so It barely impedes the air which is also flowing horizontally. So it does not add much drag.

My reasoning was slightly different. As downforce increases, the car is pushed (or pulled) downwards. Proximity to the ground affects the aerodynamics of the car. Less downforce should mean less pull/push downwards on the suspension, so the car is higher off the ground, which should result in less drag. Or am I completely backwards on that one? Hrm...apparently being closer to the ground minimizes the formation of wingtip vortices...

I may be backwards on this one. Or am I?

[wesley123]

I think I understand where you are coming from. It is becaue people usually equate drag and down-force and this is not the truth. It really depends on the shape of the object and the properties of the air around the object. Even though the floor adds a lot of downforce, the floor is almost horizontal so It barely impedes the air which is also flowing horizontally. So it does not add much drag.

My reasoning was slightly different. As downforce increases, the car is pushed (or pulled) downwards. Proximity to the ground affects the aerodynamics of the car. Less downforce should mean less pull/push downwards on the suspension, so the car is higher off the ground, which should result in less drag. Or am I completely backwards on that one? Hrm...apparently being closer to the ground minimizes the formation of wingtip vortices...

I may be backwards on this one. Or am I?

What do ou think that happens when the diffuser stalls?
The Pressure under there will differ completely, air will heap up etc. count it up to each other and you have an completely instable car, the car would have probably taken off with the way hamilton hit Massa, it will simply make the car so instable

[99cent]

I think I understand where you are coming from. It is becaue people usually equate drag and down-force and this is not the truth. It really depends on the shape of the object and the properties of the air around the object. Even though the floor adds a lot of downforce, the floor is almost horizontal so It barely impedes the air which is also flowing horizontally. So it does not add much drag.

A wing is different as you know, since they are usually angled into the air stream, they impede the air. So people can usually guess that a high angled wing (which makes much downforce) has much drag. So that is why some people follow the notion that down-force brings drag, which is not the whole story.

Where:
D is downforce in newtons
WS is wingspan in metres
H is height in metres
AoA is angle of attack
F is drag coefficient
ρ is air density in kg/m³
V is velocity in m/s

Edit: For the front and rear wing....Is the measurement for the angle of attack adjusted for every corner? How is the optimal down force determined for the entire circuit?

[PlatinumZealot]

Well, I am saying that the way the diffuser makes drag is different from the wings. I am not too sure that the diffuser stalls similar to a wing. But I can see where:

1. It can bottom out, by coming down to the slow moving boundary layer.
2. If it has a bad curvature, it can cause some turbulence in the "cone" at low speeds.
3. Excessive air can enter under the floor and blow the car off the track.

But talking about drag, the main thing is this:

The nature of a diffuser is that it creates a gradual increase in pressure from the the throat up to the pressure at the exit. This is inherent in the shape of the diffuser.

The majority of the drag from the diffuser comes from this pressure at its exit vs the pressure at the front of the car. This pressure at the exit is just whatever pressure is behind the car.
So no matter what you do under the car, the shape of the diffuser will try to bring the pressure up to whatever pressure is at it's exit.


So to say the duct is stalling the diffuser.... Maybe you can say that the duct is just reducing the pressure behind the diffuser and behind the car in general.

[hecti]

Well, I am saying that the way the diffuser makes drag is different from the wings. I am not too sure that the diffuser stalls similar to a wing. But I can see where:

1. It can bottom out, by coming down to the slow moving boundary layer.
2. If it has a bad curvature, it can cause some turbulence in the "cone" at low speeds.
3. Excessive air can enter under the floor and blow the car off the track.

But talking about drag, the main thing is this:

The nature of a diffuser is that it creates a gradual increase in pressure from the the throat up to the pressure at the exit. This is inherent in the shape of the diffuser.

The majority of the drag from the diffuser comes from this pressure at its exit vs the pressure at the front of the car. This pressure at the exit is just whatever pressure is behind the car.
So no matter what you do under the car, the shape of the diffuser will try to bring the pressure up to whatever pressure is at it's exit.


So to say the duct is stalling the diffuser.... Maybe you can say that the duct is just reducing the pressure behind the diffuser and behind the car in general.

Are you sure? The diffuser creates an area of low pressure, thus increasing the velocity of the air flowing under the car (gradually) and also reducing the density of the air under the car, so the decrease in pressure and density sucks the car to the ground. I dont know how effective stalling a diffuser would be (could be catastrophic failure, who knows) but you would basically have to keep the pressure constant under the car to stall the diffuser, and i dont think thats very feasible.

[ringo]

A diffuser increases pressure, it transitions the pressure from the throat to a higher pressure behind the car. People always get it the other way around.
The fact it increases pressure is the trick why the pressure at the throat is so low, following what I am saying?

Lets say pressure at end of diffuser is 1atmosphere (the end condition is not variable).

So logically for the throat pressure to be increased it has to be less than 1atm. Since it's less than 1 atmosphere, that's your floor suction right there.



1:2 is a hypothetical ratio.
The nozzle is the opposite. It decreases pressure.

[hollus]

Ringo, thanks for the drawings. That second scheme is so counterintuitive that I even made a post challenging it... only to remove it 2 minutes later. Common sense says that the pressure must increase at the chocking point, but analyzing it bit by bit, the exit must be at 1 atm, and there is air bieng fed from the left so the pressure must be higher in the middle section to keep new air that cannot exit from coming in, and of course the pressure must change gradually. So it must be right.
I am enjoying this whole discussion so much, and just when I though I had understood pretty much the whole thing, the second scheme makes me realize how little I really understand.
It still feels wrong, and yet it must be right and it withstands detailed analysis. No wonder aero is so difficult to understand for all but the ones working on it! =D>

[LegendaryM]

If mclaren were using a fluidic valve, what would the cross sectional area of the control tube have to be?

[forty-two]

Further to earlier comments about the F-Duct system when running in the rain (cockpit filling up with rainwater through the front duct), could it be that McLaren had the F-Duct covered/partly covered during the Malaysian GP for fear of this being a problem. Or could this perhaps be why they were so keen to stay in the garage during qualifying?

[Asphalt_World]

OK, can anyone say if the air flow is being activated on the straights or through corners?

It strikes me that they would want to reduce the drag in corners.

My thinking is as follows.

An F1 wing is like an upturned aeroplane wing.

So, when a plane (of the large variety) comes in to land at slow speed, the flaps move to create a hole to appear along the length of the wing allowing air to flow up through it. This is used to reduce the effect of stall when the plane is going slower as required when landing. Without this happening there would not be enough uplift from the wing for the plane to land at such speeds.

Therefore, turn this situation upside down and a car going slow round corners would not create much down force because the airspeed over the wing is slower. Allowing extra air to pass through the middle of the wing or behind it in some other way would reduce 'stall' and make the wing more efficient, thus pushing the car down on the ground more.

So, Macca run a setup with less wing giving them a straight line speed advantage but due to this anti stall system create as much down force as a higher wing setting on a normal rear wing system.

[avatar]

Therefore, turn this situation upside down and a car going slow round corners would not create much down force because the airspeed over the wing is slower. Allowing extra air to pass through the middle of the wing or behind it in some other way would reduce 'stall' and make the wing more efficient, thus pushing the car down on the ground more.

So, Macca run a setup with less wing giving them a straight line speed advantage but due to this anti stall system create as much down force as a higher wing setting on a normal rear wing system.

This is how Sauber have used the blown wing in the past (to prevent airflow separation from the wing) - lets them run a steeper wing angle, thus more downforce.

But the theory (as I understand it) is that McLaren have found an additional effect; by overloading the blowing of the wing, causing the airflow to separate & reducing drag - thus more straight line speed.