The Coanda effect; explaining how a wing works: from fizzics.org
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- Опубликовано: 13 сен 2024
- The Coanda effect is a convincing explanation for the lift of an aircraft wing. It is the tendency for a stream of fluid, such as air or water, to cling to nearby surfaces. The effect is sometimes wrongly used to explain some phenomena. The video combines examples and logical explanations. Notes on the Coanda Effect are here:
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Wow the simple video with a simple example blows every other video out there that tried to complicate the explanation. The demonstration succinctly proves the fluid being deflected downwards and thus creating lift due to the opposite and equal reaction.
Roger,
I think you have done a very good job here in several of your explanations, However I have a slightly different spin (excuse the pun) on some of this. Please consider the following.
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First, in my discussions with some in aerodynamics, Coanda defined this effect for a forced jet, or sheet of air along a convex curve - just as shown with the straw and can. However, while it looks very similar and may even be explained with similar words, it was not defined as the "ordinary" flow over a surface moving through air --- only for the forced stream condition. This may seem pedantic, but a definition is a definition. Given this understanding, I could consider the upper airflow to be "Coanda-Like".
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The blown paper is spot on.
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I can explain the "action - reaction" concepts with these two reversed. While I do not dispute that the lift force and downwash momentum change are indeed necessary and comply with Newton's Third Law, I maintain that the common explanation as you show here is reversed. The downward moving air can not be responsible for an upward force on the wing --- It must be a RESULT. The pressure differences around the wing that are caused by the shape moving through air must also be pushing down on the air. Because the downwash has been left behind the wing to continue downward due to its inertia, it can no longer have an effect on the wing that has moved forward. The pressure differences around the wing, in effect, are the air pushing up on the wing. If the air is pushing up on the wing, the wing must be pushing down on this continuous bulk of air.
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I use this analogy. I push on a wall. We know quite well that the wall pushes back. The minute spring action allows us to understand this better. Newton's Third Law leads us to believe these are two "different" forces (though equal and opposite) and I sometimes call Newton's #3 "The Law Of Pared Forces". However, another way to look at it is that this is only one force and any and all forces act in TWO opposite directions at once. [this is somewhat analogous to fluid pressure at a point acting in all directions].
Now, we must certainly agree that MY PUSHING on the wall is what instigated this shoving match in the first place. The wall certainly did not show any aggression towards me before I pushed first. Therefore, my push is the cause and the wall's pushback is a result. I liken my push to the pressure difference lift force and the wall's push-reaction to the downwash' sreaction. I also point out that had the wall been free to move, such as a friend on ice skates, it would have moved in accordance with with the force of my push and his mass and that his movement is directly equivalent to the downwash movement.
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The water suspended ball and the water spoon I will not discuss due to the air-water fluid and flow pattern differences.
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For the air suspended ball, the Action-Reaction is explained as I have above, with the decreased pressure on one side caused by the increased length of the curved air path on one side. This pressure reduction then allows the atmospheric pressure further from the ball to push the air around the ball further around the back which results in the increased momentum change in the opposite direction from the lowered pressure. This air then leaves the ball where it no longer can exert any force on the ball. Its momentum change was due to the pressures around the ball, not the cause of them. The lowered pressure on one side allows the not-as-much-lowered -pressure-due-to less-curved-flow-on-the-other-side to push the ball back inward. Thus the "turned air stream" behind the ball.is the result of the pressure difference, not the cause of the force on the ball.
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I hope you follow these descriptions and comment.
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Cheers ScienceAdvisorSteve
www.challengerillinois.org/
I agree. I think Coanda efect cannot explain lift. There is a different premise. On Coanda efect there is a relative speed between the jet and the surounding air. This is not the case when a wing moves through the air.
@@urdearadu9451 Good observation and correct.. However, It is confusingly similar. The Coanda effect has continuous entrainment at it's boundary with the still air; but it does not flow along the convex surface _because of_ the Coanda effect. Air will follow a convex surface because air pressure is pushing it there; unless it is so fast that it can't make the turn. Air does not "stick" to that surface because it is 'sticky', it is constantly pushed against it by the air pressure all around that many people forget is there. We live in a pressurized atmosphere and the air will do its very best to flow in all around anything moving.
Coanda also produces a lower pressure along a convex surface.
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Air having inertia, "wants to" go straight (Newton's First Law). Because it is held against the the curve by atmospheric pressure it is like being on a playground merry-go-round --- it 'swings outward", the centiipetal effect. This lowers the pressure near the surface. A curved flow indicates a lower pressure toward the center of curvature - higher on the outside.
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The curved flow is the cause of the lowered pressure as the air maintains contact, but the centrifugal effect lowers it.
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These pressure changes are very small, hence large wings. For a light plane, the most change from ambient is about 0.6% decrease above the wing.
For commercial jets it is about 6% at low altitude and 23% in the much thinner air at 35.000 feet altitude.
@@urdearadu9451
Where did you learn that there is no relative speed between the jet and the surrounding air on a wing? So wrong bro! Even if the paper would've been blown from both the upper and lower surface and it would stand at a given average camber due to it's mass, and suddenly more airflow speed is added to the upper The Coanda's effect is actually the most accurate definition for lift. If you only like the obsolete Bernoulli, it's your choice to never understand lift!
@@Observ45er
Sorry, but it makes no sense what you've been saying in here and in your first post where you were referring to an "increased length of the curved air path" before replying to this fella who says that there is no relative airflow speed between the upper and lower surface on the wing..., just forget that guy, he doesn't know what he's talking! Now..., when you say that the surrounding pressure ("that everyone forgets about") that has the effect of "bending" the airflow towards the curved surface..., is this how you explain the Coanda effect?
It is indeed the stickiness between the air and the solid surface which actually reduces the pressure. The reduced pressure instantly introduces the Newton's third law between the airflow cone over the paper and the paper, regardless if of the atmosphere around. Try to get that. Yes, it's there..., but even if it wouldn't be there (absent surrounding pressure and having only a tube of air over the paper), the interaction between the airflow stream and the paper would be the same, even if at a different magnitude only due to the absence of the surrounding atmosphere. That's it. That's all the difference.
How it works:
1. As the airflow meets the curved surface, it will try to stick to it (YES, it will literally stick to it, like it or not) and the pressure will reduce itself according to the speed and turn radius that the airflow must follow, but due to it's inertia and momentum, the airflow cone will tend to go as straight as it possibly can.
2. Due to the developed lower pressure on the side of airflow against the convex shape, the paper is pushed up by the higher pressure beneath.
3. Due to the upward movement of the paper and higher radius turn that the airflow cone must meet, the curving of the airflow and the straightening of the paper are now settled at a value which depends on factors such as Reynolds (including viscosity, temperatures, geometric references and speeds) and paper weight. Yes..., the surrounding pressure which now is higher than the one developed between the airflow cone and the curved surface of the paper that it sticks to and tries to follow will bend the airflow cone more than if the surrounding pressure wouldn't exist (let's say..., as if the airflow cone and the paper would be separated from the outside air by a wall or being within a tube), so that would only affect how much the airflow cone would bend and also affect how much the paper would also straighten up, but it's not as if only the surrounding atmospheric air is the one generating the transversal (downward in this case) momentum of the airflow cone.
You've earned my subscription sir...
It is not a case of using the Coanda effect to explain lift but we need to explain the reason for the Coanda effect.
All the effects allotted to Bernoulli, Newton and Coanda, owe their activity to Fluid mass being accelerated in a straight line or around a curved surface. Fluid has a viscosity (elasticity) and small volumes can be subjected to compression or to tension, resulting in the associated pressures or forces. If the viscosity holds, the tension, then we have laminar flow, if it does not, turbulent states exist.
If a mass of air has a velocity vector, it tends to try to keep going straight on, if at a later stage it flows near a surface that curves away , the air mass tends to keep going straight and if the sheet " edges" of air flow " seals" themselves, around the curved surface, then the fluid between the sheet of air and the curve, is tensioned and so this is what pulls the moving air to the curve due to the lower pressure effectively. (The upper surface of a wing).
If it happens that moving air hits a surface as the lower surface of a wing, then the fluid particles under the wing are in compression and so they accelerate the air downwards. Those above the wing are in tension and so they accelerate the mass of air downwards.
Bernoulli, Newton, Coanda effects are due to ACCEPERATION FORCES applied to the mass flow of the fluid.
A hairdryer ad brought me here 😂
Except for the illustration at 3:15 everything is physically well defined. At 3:15 however, the ball's center is to the right of the streamlines that are splitting and doesn't make any sense to have more streamlines on the right. It would make sense for the Coanda effect and the Newton's third law which is otherwise the complete global lift explanation if the ball's center would've been to the left of the streams splitting position. If the ball would be moving from left to right as in that illustration and when the center of the ball would have passed the splitting point of the streamlines and there would still remain more and concentrated streamlines on the right side towards where the ball is going, then this would represent an unstable motion behavior and the ball wouldn't ever reenter the airflow stream cone again. It would simply be accelerated outwards from the airflow cone. Again, that illustration would be correct if having the ball's center to the right of the streamlines splitting point and more streamlines would be illustrated on the left side of the ball meaning that now a lower pressure is on the left side of the ball, decelerating it from going out of the airflow cone and thus stabilizing it to remain within the cone, or..., by illustrating the ball's center still being on the left side of the streams splitting point and leaving the streamlines illustrations as they are.
For as we are learning and understanding things closer to reality everyday, we must understand and take it as a fact that the Bernoulli effect was proposed as an early explanation to why does the pressure decreases when the airflow speed increases along with it's subsequent math model regarding the total pressure as a sum between the dynamic and static pressure.
Nowadays we are more correctly understanding that the Bernoulli's effect should mostly be limited to airflows along inside of tubes, except at the entrance and exiting of that tube where Bernoulli expects the opposite of what actually and physically happens or otherwise in conditions where there is no interaction between separate airflows (such as what happens in the atmosphere or at the interface between two airflows (like two layers) with relative speed between them).
If someone wants to explain the lift by using Bernoulli..., heh..., he's up for a great blind ride with no end, simply because the things don't add up!
Interesting video on lift force! I like how you emphasize the stream of fluid or air sticking closely to a nearby surface and being deflected downwards, resulting in a change of momentum, which generates an equal and opposite force pushing the object upwards, thus creating lift.
The explanation provided in the video may not be entirely accurate or universally accepted. While you mentioned the Coanda Effect as an explanation for lift force in some cases, it's one of the common misconceptions. The Coanda Effect is based on fluid entrainment into a jet flow, which doesn't occur around an airfoil. Consider discussing pressure differences and air acceleration around an airfoil, which would contribute to a more comprehensive explanation of lift.
Keep up the excellent work, and I look forward to seeing more educational content from your channel!
Pressure itself is a sacalar quantity, it has only magnitude which is perpendicular to surface and no any direction. Lift is a vector sum of the pressure acting on the entire surface. Lift is directly related to change in momentum of airflow. You may change the direction of airflow in any direction and you will get a force in opposite direction as per action reaction pair.
I have basically zero knowledge in
fluid and aerodynamics, and would love to know why the top air stream “hugs” the wing, and how it causes a difference in pressure. Could someone please explain it to me? (In simple terms since I don’t know much about this)
Fantastic explanation, do you know of any videos explaining in depth why water sticks to surfaces?
I don't but it is to do the the fact that the size/charge of the oxygen atom dwarfs the two hydrogen and therefore the molecule is polarised.
@@fizzicsorg ok, thanks
its because surface tension of water is high
Aerospace engineering major here, second year. My book explicity says this is true but not the source of lift rather a product of it. And that lift can solely be explained by pressure distributions nothing else.
Consider this explanation. The coanda effect causes the surrounding air not part of the flow to push inward on the flow due to a friction with the object interupting the flow. This push also simultaneously constricts the flow similar to how a nozzle would. This constriction leads to an increase in speed, this is because when flow is constricted the air is doing work on the air in front of it, ie pressure energy is converted to kinetic energy. This drop in pressure due to A combination of the Coanda effect + Nozzle flow. WIll drop the static pressure of the air flow above the wing. Then Since the flow below the wing is parallel to air flow no constriction occurs thus it's pressure remains unchainged. This leads to a net force upward! What do you think.
Pressure itself is a scalar quantity it has only magnitude but no any direction. Lift is a vector sum of the pressure acting over the entire surface. You may change the direction of the incoming airflow in one direction and lift will be created in the opposite direction as per action reaction pair
Can you please explained why the air traveler faster on the upper surface than bottom surface of the wing ? Or more like why the air above the wing is rather lower pressure compared the bottom of the wing
Thank you
@@aviationbird1962 I would love to know this too
Because of the angle of attack. As you can see, the wing nose tilted upwards. This generated a air speed difference between the upper and bottom surface.
The same Coanda effect explains it pretty well!
For the speed increase, the explanation first comes due to the lower pressure being developed first. You'll probably say: "WHAT? Then if the speed increases, the pressure should further decrease?" And the answer is: NO! Once the speed has increased as a response to the pressure decrease, this increase in airspeed will be a result. If you would force more airspeed over a diverging curved surface (upper of the wing at positive AoA), then the result would be that the pressure lowers, and especially over the lower radius of the curve (such as it happens closer to the leading edge of a wing), but the resultant reduced pressure won't further affect the airspeed, such as if they would self-amplify each-other. No, only one is the result of the other and..., if you really want to, you can either reduce the pressure on the top of a wing at positive AoA, which will result in an acceleration of airflow over that lower pressure area and if you can... at the same time you can add more airflow speed over that upper surface and even further decrease the pressure over that area. And guess what..., this is exactly what happens with an aircraft, when, for example it pulls higher positive AoA on it's wings and at the same time, the airspeed of the whole aircraft gets higher. Now..., when increasing the AoA, or..., when increasing the camber of the wing or local airfoil such as when deploying leading edge krueger flaps and slats or trailing edge flaps with or without also increasing the whole AoA of the wing, you effectively start benefiting from the Coanda effect which implies a pressure reduction over that diverging curvature of the wing and also wherever the airflow must turn in order to continue following the solid surface..., THE PRESSURE WILL DECREASE. Coanda effectively took place. Now..., let's say that the above happens but at the same time, your plane is also speeding up, such as when you dive upside-down or in a downward spiral and although you may have great drag due to flaps/slats and great AoA..., the combined engines thrust + gravity thrust component is greater than the drag and you still increase your speed. Now..., the already low pressure will get even lower as you forcibly increase the airflow speed over the lower pressure area. And now you have a complete explanation of how lift varies with both the decrease in pressure due to AoA and flight control devices which lower pressure accelerates the flow up to a given amount and they all (pressure and airflow speed) settle at that a value, as well as increasing the airflow speed alone which on it's side also decreases the pressure on a diverging surface. And to make it complete also for the higher pressure side..., exactly the opposite happens as for what I've depicted above. The higher the pressure (such as flaps deployed) on the lower surface of a wing will reduce the airflow..., will brake it down, and of course..., at the same time, the higher airflow speed, the higher the pressure. And again, these won't resonate on each other, but only one affecting the other one. Hope I didn't complicate it by trying to get into tiny more details. If you understand it as a whole..., it will be easier to make sense of what happens deeper.
For short..., the curved airflow..., either due to the curved surface or due to the angle of attack AoA, which has a momentum (the air has it's own inertia as it tries to follow a surface) which creates a lower pressure zone along it's curve, also generates a higher airflow rate (the airflow isn't pulled by the lower pressure, but rather accelerated along the streamlines by the higher pressure ahead of the wing) over the lower pressure area on the wing.
One more important aspect:
If there is no curvature at all..., no matter how much you'd increase the airflow..., the pressure will remain EXACTLY the same. But if you can accelerate or decelerate the airflow by varying the pressure along the virtually uncurved surface.
Velocity varies around the body because of flow deflection, Pressure varies around the body because it is related to fluid momentum.
How would the Coanda effect work at supersonic speed?, would a shockwave even form in the direction of lift of a Coanda lift vehicle?
The flow of a liquid or gas following along the outside of a curved surface is the COANDA EFFECT!
is it So , denser air keeps it hung
i always wanted to know this
LEGEND!!!
Another test one can do is bend your hand and attach your palm closely to a flowing water from a faucet and the water will follow the bend of the hand
That is also the intermolecular forces and not coanda effect, like the spoon in the vid, common misconception
Six years old.. gosh what has corona done to us
The science hasn't changed in that time.
3:15 Sorry but this is not well explained. I literally didnt understand the explanation.
For example I could explain this myself easily with the low-pressure on the left side of this picture, resulting the high-pressure from the right pushing the ball back to its centre.
"The faster stream of air clings to the surface..." bla bla bla. Nothing is explained here.
And there is not "faster stream of air" This is so wrongly explained...
Is this airflow deceleration caused by the boundary layer effect?
Not sure which situation you are referring to
@@fizzicsorg the flow around a surface in the coanda effect. The slowing of the airflow closest to the surface
i was thinking so
Fuid sticks to the surface because of fluid internal friction
The explanation is weak, the pressure difference is what causes the lift of the wing, because the air is circulating slower over the wing than below the wing. Therefore the pressure over the wing is lower than that from below the wing, so it is pushed upwards by the bigger air pressure from below, which acts on the surface with a greater force.
Coandă 🇷🇴
And.... I didn't really get it😅
The "Coanda effect" is just a special case of the Bernoulli principle. They are one and the same. It's "click-bait science" to pretend otherwise. And Bernoulli is a better instructional foundation because it's tied to first principles like velocity, density, pressure, etc...
The Bernoulli Principle causes lift on an airplane wing.
It surely helps, but it doesn't cause it.
Please learn the difference between a stream and a jet. Coanda Effect applies only to jets and has no relevance to a simple airfoil where static pressure is constant across the entire fluid.
This wrong. Very wrong.
Lift over a wing, airfoil, has NOTHING to do with the Coanda Effect, nor “equal transit.” Nor, as accurately stated here, Bernoulli.
As an airfoil moves through air, the perfect vacuum at the surface of the back of it pulls air above it downward. A low pressure zone is created above the top-back of the airfoil that pulls down additional air from above. All of this “scooped up” air is accelerated down the backside, trailing edge, of the airfoil*. Opposite but equal action equals lift. Basically a plane is a horizontal rocket-horizontal ballistic flight**.
As for Bernoulli: Bernoulli involves flowing, constricted, and NON-COMPRESSIBLE fluids. Air is highly compressible, is not constricted over an airfoil, and is, relative to the airfoil, stationary, not flowing***. As air pressure differentials are involved, the Bernoulli equations approximate well enough the processes and forces involved, and so are often utilized in explaining lift.
*There are videos of planes landing where condensation in the low pressure above their wings is seen. Some even showing that air being shot down the trailing edge of the wings.
**Interestingly, looking at the energy consumption of an airplane versus a rocket it is revealed that gravity is the primary source of energy for sustained flight by an airfoil equipped aircraft. Hence unpowered glide-ratios, auto-gyros, gliders, etc.
***It is the airfoil that is “flowing” relative to the air.
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beuluia effect
This is only and explanation, NOT the proof (mathematics, science or experimental).
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I disagree. It most certainly is the coanda effect causing this behaviour.