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
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daily with news from F1word.
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magazine. Anyway, great
read.
- JA.F1site (or blog) ovned
by ITV Sport s lead
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- vitalf1.com/is another
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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.
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- 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
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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.