Coanda Effect

7/24/2019 Coanda Effect

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The Coanda- 1910, the world's first jet aircraft

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Coanda Effect

Although generally unrecognized, Romanian aerodynamics pioneer Henri Coanda was

actually the first person to build and fly a jet powered aircraft. It is commonly believed

that the first jet engines were developed during World War II. Dr. Hans Von Ohain

designed the first German jet aircraft, which made its first flight on August 27, 1939.

Unaware of Dr. Von Ohain's work, A British engineer named Sir Frank Whittle also

independently designed a jet aircraft, which first flew on May 15, 1941.

Although these two men are generally thought of as the fathers of jet aircraft, Henri

Coanda built and "flew" the first recorded jet aircraft about 30 years earlier.

In 1934 he obtained a patent in France for an effect presently named after Coanda

and was described as:

"Deviation of a plan jet of a fluid that penetrates another fluid in the vicinity of a

convex wall."

Unfortunately Coanda couldn't obtain funding to continue his research after he

wrecked his airplane, and so his contribution to jet propulsion never became

widespread. If he had been able to continue his work, France could have had a

FORZA JULES. Stay strong.

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Some useful links:

- f1technical.net, a great site

with a lot of technical

informations and

explanations. Site is updated

daily with news from F1word.

- autosport.com, This site is

a legend. A bible for racing

lovers. News from all around

the word. Unfortunately, to

get access to all news,

interviews and to open thesite completely you should be

subscribed to A utosport

magazine. Anyway, great

read.

- JA.F1site (or blog) ovned

by ITV Sport s lead

commentator on Formula 1

James Allen

-joesawardis the Joe

Saward official blog about

Formula 1 world. Joe is an

journalist, who write primarily

about politics in and around

motorsport, specifically onthe FIA Formula 1 WorldChampionship

- f1network.net, Good read.

Fans from every team can

find his team forum. For me,

like Ferrari fan, forumis the

best Ferrari forum, very

visited, with great threads.

- vitalf1.com/is another

great site for Motor Sports

fans like me. Site is relatively

new, but great fun, with

great discussion forum,

Formula 1 news and forum.

- f1.gpupdate.net , Site withfresh news from Formula 1

- planetf1, another site with

many different articles, news

and statistics. Biased toward

British teams, but anyway

good read.

- gurneyflap.com, Great

history site. You can learn a

lot from this site. Pictures,

cars and many many more.

Great.

- fia.com, La Fdration

Internationale del'Automobile, representing

the interests of motoring

organisations and motor car

users. Head organisation and

ruler in auto sport.

- wikipedia.org , I dont

believe that I have to tell you

anything about this site. It s

not about Formula 1

technology, but you can learn

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jet-powered air force before WWII began. Even though he didn't build another jet

aircraft, he did make a very important contribution to how the aircraft wings produce

lift when he discovered what is now called the Coanda Effect.

A natural question is "how the hell does the wing divert the air down?" When a moving

fluid, such as air or water, comes into contact with a curved surface it will try to follow

that surface.

Coanda Effect: A moving stream of fluid in contact with a curved surface will

tend to follow the curvature of the surface rather than continue traveling in a

straight line.

To perform a simple demonstration of this

effect, grab a spoon and find a sink. You can

easily demonstrate the Coanda effect for

yourself. Conveniently, these are often found

together in the kitchen, no need for highly

technical lab. Get a small stream of water

coming down from the sink, and then place

the bottom of the spoon next to the stream.

Dangle the spoon next to the stream coming

from the tap. I say dangle because you want

to hold it loosely enough so it can swing back

and forth a bit. It helps to attach a piece of

tape at the handle end to act as a hinge.

Move the spoon up to the edge of the stream

so it barely touches. When you do the water

will flow around the bowl of the spoon and off

the bottom deflected to the side and the

spoon will move into the stream. Spoon is

actually being pulled towards the stream of

water. Gases behave pretty much like liquids,

so when you see the water behaving strangely with the spoon, that's what the air

does with the curved paper. Just as water flowing around the spoon's curved surface

draws it into the stream, air blown over the curved paper is what causes the lift in that

common paper lift demonstration.

What is unusual about the Coanda effect is the fact that the fluid or gas flow is pulled

so strongly by a curved surface. With a tap, the water will be projected out at a

remarkable distance. The degree to which the water and the curved surface remain

attached goes beyond the expected. A concave curve will naturally push the flow, but

the fact that a convex one would react so strongly to fluid or gas is unusual.

Same situation apply to the wing. Since air behaves exactly like any fluid, Bernoullis

principleapplies. Any time the wind is blowing or a fan blows air, the pressure of the

moving air becomes less than it would be if the air wasn't moving. As an aside, this

characteristic plays a huge role in how weather systems work! If you can cause air to

move faster on one side of a surface than the other, the pressure on that side of the

surface will be less than the pressure on its other side.

a lot about that too.

- carbibles.com, a great site

for normal car users. Here

you can find explanations ofalmost everything about your

car and how it works.

Technical reviews and

explanations of some in-car

gadgets.

- The F1 Links Pageis a

database for all relevant F1

links. All visitors have a more

powerful search engine thanever before on this site.


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One of the most widely used applications of Bernoulli's principle is in the airplanewing. Wings are shaped so that the top side of the wing is curved while the bottom

side is relatively flat. In motion, the front edge of the wing hits the air, and some of

the air moves downward below the wing, while some moves upward over the top.

Since the top of the wing is curved, the air above the wing must move up and down to

follow the curve around the wing and stay attached to it (Coanda effect), while the air

below the wing moves very little. The air moving on the top of the curved wing must

travel farther before it reaches the back of the wing; consequently it must travel faster

than the air moving under the wing, to reach the back edge at the more or less same

time. The air pressure on the top of the wing is therefore less than that on the bottom

of the wing, according to Bernoullis principle. The higher pressure air on the bottom

of the wing pushes up on the wing with more force than the lower pressure air above

the wing pushes down. This result in a net force acting upwards called lift. Lift pushes

the wings upwards and keeps the airplane in the air.

Though Bernoulli's principle is a major source of lift in an aircraft wing, Coanda effect

plays an even larger role in producing lift.

If the wing is curved, the airflow will follow the curvature of the wing. In order to use

this to produce lift, we need to understand something called angle of attack. This gives

the angle between the wing and the direction of the air flow, as shown in the following

picture.

The angle of attack indicates how tilted the wing is with respect to the oncoming air.

In order to produce lift, or downforce acting on the wing, Newton's third law says that

there must be equal force acting in the opposite direction. If we can exert a force on

the air so that it is directed down, the air will exert an upward force back on the wing.

Look at how the Coanda effect directs the airflow for different angles of attack in the

diagrams below.

This diagram shows that

increasing the angle of

attack increases how

much the air is deflected

downwards. If the angle

of attack is too high, the

air flow will no longer

follow the curve of the

wing (Coanda effect is

loosing the power). As

shown in the bottom of

the diagram, this

creates a small vacuum

just behind the wing.

We can say that wing is

stalled. As the air

rushes in to fill this

space, called

cavitations, it causes

heavy vibrations on the

wing and greatly decreases the efficiency of the wing. For this reason, aircraft wings

are generally angled like the middle wing in the diagram. This wing efficiently directs

the airflow downward, which in turn pushes up on the wing, producing lift. If you turn

this wings on upper picture up side down, you get formula 1 or any wing in use in auto

sport. This configuration of the wing, with longer lower part of the wing will produce

opposite force, called downforce. But we can apply same rules.

To get around air stream


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separation problem in airplane

wing construction and in

Formula 1, and increase the

Coanda effect on wings, dual or

more element or slot-gap wings

are used, these allow for some

of the high pressure flow from

(in Formula 1 case) the upper

surface of the wing to bleed to

the lower surface of the next

flap energizing the flow. Thisincreases the speed of the flow

under the wing, increasing

downforceand reducing the boundaryflow separation. If you look at a F1 rear wing

few years ago on picture above, you can see this concept taken to the extreme, with

multi-element wings creating huge amounts of downforce and little air stream

separation even on the flaps with extremely high angle of attack.

The Coanda effect has important applications in various high-lift or high downforce

devices on aircraft, or in our area of interest, on the racing car wing, where air moving

over the wing can be "bent" using flaps over the curved surface of the top of the wing.

The bending of the flow results in its acceleration and as a result of Bernoulli's

principle pressure is decreased; aerodynamic lift or downforce is increased.

Notice how unlikely is to have a wing in flight with air flow only on one side. TheCoanda effect only works in specific conditions where an isolated jet of fluid (or air)

flows across a surface, a situation which is usually man-made. You don't find it much

in nature. Just so you know, there is no Coanda lift on an airfoil. Coanda effect helps

airstream to stay attached to the wing surface, but Bernoulli principle and difference in

pressures are the reason why we have a lift or downforce.

Coanda effect is a balancing act between many factors, among them speed of fluids

stream, pressure, molecular attraction, and a centrifugal effect if the surface is

curved.

Main trouble of the Coanda effect is the airstream becoming turbulent and detaching

from the surface, that's how a wing stalls. Pull of surrounding air causes turbulence,

dragfrom the surface and from the ambient air. It's a goal to pull as much as possible

ambient air into the airstream, but the drag caused by the difference in velocity

between the airstream and the surface is just a loss of energy. If the airstream gets

turbulent and stops following the curved surface, there's no more low air pressure, nomore thrust.

Since all applications of a Coanda effect involve a fluid object flowing over a solid one,

the science behind this effect is known as fluid dynamics. Fluid dynamics represents

and study the motion of liquids or gases. Studying this science can lead to many

consequential discoveries like the Coanda effect.

The Coanda effect is used on a modern Formula 1 car everywhere sometime to

generate downforce, but sometime not for generating downforce directly, but for

guiding and conditioning airflow in one place, as a means of maximizing downforce on

other. For example, the rear of a modern Formula 1 car is tightly tapered between the

rear wheels, like the neck and shoulders of a coke-bottle. By means of the Coanda

effect, the air flowing along the flanks of the sidepods adheres to the contours at the

rear, and the airflow here is accelerated, creating lower pressure. In itself, this

tranverse pressure differential on either side of the car cancels out, and creates no netforce. However, the accelerated airflow between the rear wheels and over the top of

the diffuserdoes raise the velocity of the air exiting the diffuser. In addition, bending

air away from the rear tirescontribute to reducing drag.

The Coanda effect is also used by the bargeboards, aerodynamic appendages typically

sited between the trailing edge of the front wheels and the leading edge of the

sidepods. Bargeboards are used to guide turbulent air from the front wing wake, away

from the vital airflow underneath the car. In addition, the lower trailing edge of a

bargeboard creates a vortexwhich travels down the outer lower edge of the sidepod,

acting as a skirt, helping to seal the lower pressure area under the car.

On the end of 2011 exhaust blown diffusers where prohibited by the FIA. Stringent

requirements have been placed on the location of the exhaustexit, and engine


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mappingrestrictions are imposed to eliminate off-throttlepumpingof the exhaust jet.

In short, these move the exhaust exit to at least 500mm in front of the rear axle line,

and 250mm above the reference plane underneath the car. The exhaust exit must also

be angled upwards by at least 10 degrees. Hence, it will no longer be possible to blow

the exhaust directlybetween the outer edge of the diffuser and inner face of the

rotating rear wheel. Moreover, it will be illegal to place any sprung bodywork in a

cone-shaped region, aligned with the exhaust exit, diverging at 3 degrees, and

terminating at the rear axle line.

New positioning of the exhaust pipes exits and limitations are shown on picture below.

Exits of the pipe can be positioned inside green box with exhaust tailpipe pointed

upwards.

But this was not sufficient to eliminate exhaust-blown diffusers. Well, the first thing to

note is that it is not possible to point the exhaust exit down at the diffuser in same

way as before, this will not necessarily prevent the exhaust jet itself from blowing in

that direction. When an exhaust jet exits into a cross-stream of fresh air, the exhaust

jet bend with the air stream, effect called "Downwash".

Picture from paper published by F. L. Parra and K.Kontis in their 2006 ,

Aerodynamic effectiveness of the flow of exhaust gases in a generic

formula one car configuration

If the exhaust exit is placed flush in the rearward face of sidepods sweepingdownwards at a fairly steep angle, then the free stream airflow could deflect the

exhaust jet downwards in direction of the diffuser. The degree to which the jet is

deflected is determined by the ratio between the velocity of the jet and the velocity of

the cross-stream flow. The smaller the ratio, the more the jet is deflected. This effect

is well documented and often termed jet in cross flow.

After that, coanda effect will take over and "glue", now energized air stream (mixed

with exhaust jet) to the bodywork. Of course, secret is to design this part of the

bodywork and bodywork in front of the exhaust exit in the way to optimize this effect

and give a proper and exact route for gasses to flow downward in diffuser direction.

Effect of diffuser blowing is not as strong as before, but with clever design and

optimization you can get few percent more of download. With this set up the exhaust

plume is curved downwards by both the shape of the bodywork aft of the tailpipe


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(coanda) and by the airflow passing over the sidepod (downwash). To learn more

about Exhaust Blown Diffuser check my article here.

Coanda Effect

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