Blowing the Wing - what is it?

[Cam]

With all the talk around the different systems teams are using, understanding the fundamentals of why, blowing the wing (or other components) through slots and holes, is beneficial. This should help us all better understand the technology and give us insights into why and where the teams use it. Please join in with what you know as this is certainly a dark art.

I'll lead off with this cracker from The Ministry of Technology. Enjoy.

Exploratory Investigation of the Effects of Blowing from the Leading Edge of a Delta Wing

The characteristic features of the flow over highly swept delta wings are produced by a pair of powerful vortices where spanwise location varies with sweepback and incidence x. These vortices give rise to large non-linear lift increments and from theoretical considerations Kiichemann and Maskell suggested that additional lift may be available if the vortex strength could be artificially increased. With this end in view, they proposed that high energy air should be ejected from the leading edge.

http://naca.central.cranfield.ac.uk/rep ... m/3518.pdf

[gato azul]

if this is aimed to understand what may and may not is used by F1 teams, then I think, it would be better to select a example (aviation or aerospace) which is close to an F1 (or race car in general) application.
In this context choosing leading edge blowing of an deltawing is maybe not the best example to choose - but nice graphs.

[Just_a_fan]

THe idea was to introduce and understand the principles of blowing and why it is beneficial. That means looking at all aspects of the science, not just the bits that relate to F1 cars. I think it's a great idea - but instead of having a dig at Cam (apparently a follow on from a dig elsewhere...), how about you bringing something that you think is relevant?

[gato azul]

THe idea was to introduce and understand the principles of blowing and why it is beneficial. That means looking at all aspects of the science, not just the bits that relate to F1 cars. I think it's a great idea - but instead of having a dig at Cam (apparently a follow on from a dig elsewhere...), how about you bringing something that you think is relevant?

Sorry, I thought, that this is implied in the name of the forum and the subsection of it --> Formula One --> Aerodynamics, chassis & tyres.
And as far as I can tell, he stated that his aim was:

This should help us all better understand the technology and give us insights into why and where the teams use it

Therefore, just posting any random paper which uses the words wing & blowing, may does not to achieve the stated objective.

And you are mistaken, it's not a dig at Cam (I like and respect him a lot), and it's not a follow on from any other thread or discussion.
But it seems that all his admirable enthusiasm get's the better of him at times.
So while this paper is a worthwhile read, as are the other papers he linked to, they are maybe not of the greatest relevance to the subsection of this forum and the topic he would like to understand.
It's easy to arrive at the wrong conclusions if you don't state the "problem" you would like to investigate clearly and define the boundary conditions (nothing to do with boundary layer etc.) you think will apply for your application.
There are perhaps different objectives as to what one would like to achieve by blowing an aircraft wing in a variety of conditions, to what the teams try to achieve on there cars.

Otherwise this thread could get very voluminous, very quickly, if you would like to consider every perceivable combination of sub-, trans- or supersonic flow, wing shapes, angle of attacks, Re numbers etc. etc. etc. - but that's just fine with me.

I just would like to see, that he reads the papers, comments on the specific points of interest and what they mean to the application he has in mind, rather then turn it into a "who can post the most voluminous papers and coolest pictures/diagrams/photos" event.

[hardingfv32]

I think a little narrowing of the subject is helpful. Why concern ourselves with pressurized systems that are clearly not possible in F1. I have found most airplane systems to be a pressurized design.

Brian

[Cam]

I guess I was trying to open discussion and learning around the factors and benefits of blowing air through slots, on or around wings. Like the Merc front wing, which has slots in there, where air is pumped through to reduce drag. What is the actual science behind it? How much air is required to be effective? How has it migrated from aviation to F1? When did it first appear?How far can we push this technology? Where else on the the F1 car can we utilise this? Etc.

If anyone has any actually stats and science from an F1 team, I'd love to see it. I can't find any. Again, I am showing science which is similar so that we can take those parts relevant and try to form some kind of real data.

[olefud]

Aircraft wing theory can be useful as a basis for grasping the basics of any wing. For instance, the discussion at http://www.regenpress.com does a pretty god job of explaining how any wing functions. But a blown wing, or other aero device, is a bit more esoteric. It appears that the F-1 use is more a guiding and containing of the slipstream than with only lesser effects of increased mass flow from the blown airstream.

And doesn’t the exhaust flow constitute a pressurized system?

[hardingfv32]

I gueLike the Merc front wing, which has slots in there, where air is pumped through to reduce drag. What is the actual science behind it? How much air is required to be effective? How has it migrated from aviation to F1? When did it first appear?

Most recent introduction of this type of system is probably the McLaren F-duct a few years back. Flow was exhausted onto the bottom of the main element.

AMC wrote: "By introducing more air underneath the wing at a certain speed, the static pressure behind the wing can be reduced (through a greater volume of air), which reduces the pressure delta front to back and therefore the drag, but also the differential top to bottom and therefore the downforce."

I am not sure anyone has articulated any other theory of how dumping flow into the lower surface would reduce downforce.

Brian

[superdread]

Isn't the method rather to counter the Coanda Effect?

The air is inclined to move kinetic straight, but when it is near a curved surface this would create an area of extremely low pressure so the air is sucked to the surface (that's the Conada Effect). So when said area is filled by a high pressure onto the main flow it can detach from the surface.

[hardingfv32]

Isn't the method rather to counter the Coanda Effect... So when said area is filled by a high pressure onto the main flow it can detach from the surface.

I see your point, but how would you characterize the type of drag this form of detachment would reduce: induced, form, wake, etc.? A simplistic view would seem to indicate that detachment would increase drag. I know that is not the case, but why?

Brian

[superdread]

Isn't the method rather to counter the Coanda Effect... So when said area is filled by a high pressure onto the main flow it can detach from the surface.

I see your point, but how would you characterize the type of drag this form of detachment would reduce: induced, form, wake, etc.? A simplistic view would seem to indicate that detachment would increase drag. I know that is not the case, but why?

Brian

I'm not quite sure how these different types of drag are defined, but when viewing the gas as kinetic particles:
At a normal wing downforce is created by sweeping air upwards (Newton's 3rd Law creates a pressure on the wing downwards and Conservation of Energy decreases impulse parallel the ground and again Newton's 3rd Law creates pressure on the car, holding it bag, i.e. drag).
When the wing sweeps less air (by detaching the lower flow) it creates less downforce, flow retains more impulse (parallel to ground) and as a result drag is reduced.

(I know, this considerations are very simplified.)

[Pierce89]

Isn't the method rather to counter the Coanda Effect... So when said area is filled by a high pressure onto the main flow it can detach from the surface.

I see your point, but how would you characterize the type of drag this form of detachment would reduce: induced, form, wake, etc.? A simplistic view would seem to indicate that detachment would increase drag. I know that is not the case, but why?

Brian

I would think it would reduce induced drag by increasing static pressure on the rear face of the wing.

[Dragonfly]

I see your point, but how would you characterize the type of drag this form of detachment would reduce: induced, form, wake, etc.? A simplistic view would seem to indicate that detachment would increase drag. I know that is not the case, but why?

Brian

IIRC at the time of McLaren F-Duct appearance, in the discussions was shown some experimental data that stalling a wing (airplane in that case) at high AoA and the resulting flow detachment and turbulence paradoxically enough lead to reduction in drag. One of the theories behind the F-Duct was based on that research.
I don't feel educated enough to participate more actively in the three similar threads here, just what I remember.

[olefud]

Downforce requires that airflow be diverted upward which creates drag. If the slipstream is not diverted, work is not performed and less drag results.

[gato azul]

As we have declared this thread now, to be broader then just F-Duct and VD-Duct, and to apeace Just_a_fan and
show my good will,here my two entries:

most voluminous paper award:
(caution is a 400 page PhD thesis, may contains loads of maths and includes other devices as well, not only blowing)
Technologies for High-Lift Devices on an Aircraft Wing

small essay from the paper (a teaser, so to speak):

(b) Effect of Blowing on Drag
For CL<1.7, trailing-edge blowing on the F9F-4 aircraft increased the induced drag and consequently, the total CD increased.
However, for further increments in CL, blowing air over the trailing-edge flap decreased the total CD.

as a side note, the first mentioning of using tangential blowing over a flap was by a guy called Föttinger in 1917,
which will perhaps encourage Brian to ask the question why Mercedes & Auto Union did not used it in their pre-WW2
machines. (all in good fun) - probably because the internet, google and the really smart folks in places like this forum did not exist at the time.

my entry to the "pretty picture" award: (quick read 23 pages presentation)
Active Separation Control on High-Lift Configurations


please don't come back, and say, that this does not make any sense &/or does not correlate well with conventional forum/journalist wisdom.
I never said it does/would , but this is what happens if you don't define your "problem" clearly.
Different people do things for different reasons, because they try to achieve different objectives, have different "problems" to solve in their specific application.
Anyhow, I took the trouble, and tried to select at least partly relevant/comparable aviation applications. (trailing edge flaps etc.)
Nevertheless, people who will take the trouble reading parts of the thesis, will learn something useful along the way, it won't be a complete waste of your time.
Enjoy