The direction of the air flowing away is almost right underneath, so the work of bending the flow of A and B is roughly the same, but it is considered to be about the same.

However, since the distance from the fulcrum to the point of action is very different, the drawing paper is pulled to the left by the principle of "lever". 　

Red arrows indicate the image of force acting on the drawing paper, and the direction and position are not always accurate.

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By the way, it has been confirmed that the flow on the upper surface of the wing is faster than that on the lower surface, and that the air pressure on the upper surface of the wing is lower than the air pressure on the lower surface.

In a sense, Bernoulli's theorem is actually very very useful for explaining the lift generated on the wing.

① Speed difference that the flow on the upper surface of the wing is faster than the flow on the lower surface

② Applying Bernoulli's theorem, the pressure difference on the upper surface of the wing is lower than that on the lower surface

③ Lifting force

It seems that there is no contradiction with this.

That is why it is easy to make mistakes.

The truth is, as you can see from my experimental results,

"There is no lower air pressure than a faster air flow than a slower air flow. This means that Bernoulli's theorem cannot be used to explain the pressure difference between the upper and lower surfaces of the wing. "

My experimental results suggest what Dr. Anderson and Dr. Eberhardt say that

"The air pressure on the upper surface of the wing does not decrease because the flow is fast, but the air pressure on the upper surface causes the flow velocity to increase."

In other words, which one comes first, "difference in flow velocity" or "difference in atmospheric pressure"?

It's just the relationship between chickens and eggs,

According to "Circulation and Bernoulli's Theorem", "difference in flow velocity" comes first, and as a result, "difference in atmospheric pressure" is created.

According to "Coanda effect and action reaction theory", "difference in atmospheric pressure" comes first, and as a result, "difference in flow velocity" is created.

That! ? We confirmed it at the river flow! ‥

"The velocity and direction of the air depends on the pressure gradient", we confirmed !!

Next

Coanda effect and reaction theory

Theory of Dr. Anderson and Dr. Eberhardt of USA.

The lift generation mechanism of this theory is as follows.

① The air flow on the upper surface of the wing is bent downward due to the Coanda effect

② Upward force (lift force) acts on the wing due to the reaction of the force that bends the flow downward

I forgot how I knew about this theory, but I felt that the things I had been swayed up to that point were blown away, and at that time, I was really feeling "the scales drop from my eyes."

However, although I generally agreed with this theory, there were still some doubts.

Question 3: Can the airplane be lifted just by the Coanda effect?

The concept that "mass x downward acceleration" when the air is bent and downwashed becomes the lift of the airplane is a story of a world in which only wings and air exist, so Newton's third law (action reaction) , I think it should be.

F=ma (F: lift, m: mass, a: downward acceleration).

In other words, it is understandable that this relationship occurs when we consider the entire air that is bent downward across the wing. (However, it does not matter if the whole lift is estimated)

It is a fact that it is hard to understand because the opponent, which is the point of action of Newton's third law, is not the individual but the air (gas) above the wing, so it literally seems to catch a cloud. is

And, it is natural for Dr. Anderson and Dr. Everhart to pay attention to the Coanda effect, that emphasizes only the upper surface of the wing and does not stick to the lower surface at all.

However, I think that the work of the lower surface of the wing should be large enough like the upper surface.

Videos showing the face coming out of the window of a car running at high speed and the soft cheeks dented by the wind, and a sandy beach rippling, throwing a round board on the water and jumping on it immediately and sliding.

Looking at it, I'm convinced that not only the lower surface of the wing can be ignored, but also the large force that pushes up the wing from the bottom should be working, just like the upper surface.

And in the world of architectural engineering, the concept of "wind pressure" in which the wind hits a building and exerts a force has been established and is being utilized in the design of buildings.

About Problems common to both theories

Question 4: Can air be treated as incompressible?

Even if it is not stated explicitly in the commentary, when we quote Bernoulli's theorem, we consider air to be incompressible.

Dr. Anderson and Dr. Eberhardt, as well as anyone else's commentary on "The Circulation and Bernoulli's Theorem", to be clear perhaps everyone but me treats air as "incompressible" when describing lift.

Why do they do that?

・In “Bernoulli's theorem theory”, the pressure is lower where the flow is faster than for the slower flow, that is, the Bernoulli's theorem is applied to form a direct mechanism of lift generation.

Bernoulli's theorem was premised on an ideal gas (incompressible, inviscid).

On the other hand,

・Dr. Anderson and Dr. Eberhardt's "Coanda effect and action reaction theory" ,says the reason why the flow velocity on the upper surface of the wing is faster is because the air pressure on the upper surface of the wing is low. Thus, the pressure of the air is reduced and the flow is accelerated on the upper surface of the wing."

Dr. Anderson and Dr. Eberhardt explain the boating "water and oar" relationship that most of us have experienced, for the sake of clarity.

It seems that the air must be incompressible like water in order for resistance to occur.

Water flows into the back of the oar from the surroundings in a blink of an eye, but since the mass of water is large (about 770 times that of air), the movement is dull and it looks quite different from the movement of air.

In other words, it is easy to think that there is resistance to the creation of a vacuum because water is incompressible.

However, I believe that air has great compressibility, but resists the creation of a vacuum just like water does. The reason is that if there is a region where the atmospheric pressure is low even in the air, the air will flow in from the surroundings with a force of 1 atmospheric pressure. Even though the flow velocities are very different, this movement should be exactly the same as for water.

In other words, even if you move the oar in the air, the air moves exactly like the movement of water in water, but the air is invisible and the mass is very small, which is 1/770 of water, I feel that it is different from.

This interpretation is one of the important points in my opinion.

Water and air are the same fluid, with the only difference being their viscosity and mass. The air moves just like the movement of water when you take a bath and move your palm in the water.

Both doctors had to make air incompressible, just like water, to explain that there is resistance to creating a vacuum even in air.

They also says, "In this way, the air is accelerated on the upper surface of the wing by decreasing the pressure." However, decreasing the pressure of the gas is nothing but expansion of the gas.

Perhaps there must have been a contradiction in this regard.

In other words, the proponents of both theories had to tentatively define air as incompressible in order to make each theory valid. We must have been well aware that air is a compressible gas.

When talking about lift, air should be argued as a very compressible substance as it is, let alone bend the physical properties and discuss under conditions different from the truth (go in the wrong direction) I think.

Certainly, if you can't feel that the compressibility of air is "very high," that's right.

In our daily lives, about 10 tons of force is applied to 1 ㎡, but the air weighs 1 ㎥ and weighs only 1.3 kg.

Some people may say, "Oh, is it so light?", while others might say, "Eh? Is it so heavy? I didn't think there was weight!"

No, since it is a substance, there is always weight (mass x gravity). However, it is about 1/770 of water.

Because of this very large atmospheric pressure and very small mass, the "wraparound" of the air that fills the space passed by the object is so quick that we do not notice this "wraparound" itself.

If you do not fill the tires with air or inflate the bladder, you will not be able to feel the compressibility and you will not feel any dust such as the mass of air.

"I didn't think there was any weight!" is not unreasonable. For example, when we move our limbs, there is always a very rapid “wraparound” of air with compressibility of air called compression on the front side and expansion on the back side, but that kind of thing I can not be aware of it at all. You can't see it, and it's so light that it's natural.

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Digression

Air flows from high pressure to low pressure, just as water flows from high position to low pressure. It means that if there is no difference in atmospheric pressure, no flow will occur.

No, it would be a little different to say this. Air also flows from a high position to a low position. In other words, as long as air is a substance with a mass, it is pulled by the attractive force of the earth and flows to a low position. In fact, human beings live at the bottom of the air, which is attracted by the attractive force and stagnates in a low position.

At the same time that warmed air rises because heat expands and the density becomes smaller and becomes lighter and rises.

At the same time, cold air with a high density of surrounding air flows to a low place due to attractive force, so warm air with a low density It can be said that is struck out upward.

In other words, if we discuss the flow at the same positional height like a wing, we can say that "air does not flow unless there is a difference in atmospheric pressure".

I mean, that means!

”The air flow around the wing is actually guided by the difference in atmospheric pressure first, so it moves!”

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Let's try to see the wraparound with the eyes of your mind

The quick “wraparound” of the air is invisible to the naked eye and hard to be aware of, but it is possible to associate the “wraparound” situation with the events we once experienced.

Everyone has seen the smoke drifting from a bonfire. It's the same if you've seen it in movies or on TV.

Now, let's associate a person running in a place where smoke is drifting.

From the front of the running person, you can imagine how the smoke instantly circulates from the front to the back (back), and then the smoke moves in a complicated manner.

At this time, the air is compressed on the front side of the person to increase the atmospheric pressure, and on the rear side, the air expands and the atmospheric pressure decreases.

Air flows from high pressure to low pressure. In other words, the air instantly flows from the front to the back.

After a person runs away, the inertia of the movement of the air when it wraps around makes a complex wobble for a while. In this way, a series of movements of the air can be associated with movements of smoke, that is, can be seen with the eyes of your mind.

I remember that this kind of association was very important for the experimenter to read the results. Because it was necessary to immediately judge the correctness of the collected data.

What I want to say is "Don't define air as incompressible, and quick wraparound with compressibility is a very important point to consider when considering lift as a characteristic of air.

If you define air as incompressible, you will not be able to see this important event in reality, and you will miss an important point !!!

Continue to "Mechanism of lift generation" in home

2020.07

Lifting force and flow separation

Questions about conventional theories of lift generation