sound barrier

Sound barrier

a phenomenon that occurs during the flight of an aircraft or rocket at the moment of transition from subsonic to supersonic flight speed in the atmosphere. When the aircraft speed approaches the speed of sound (1200 km/h), a thin area appears in the air in front of it, in which there is a sharp increase in pressure and air density. This compaction of air in front of a flying aircraft is called a shock wave. On the ground, the passage of a shock wave is perceived as a pop, similar to the sound of a shot. Having exceeded , the aircraft passes through this area of ​​increased air density, as if piercing it - it overcomes the sound barrier. For a long time, breaking the sound barrier was considered a serious problem in the development of aviation. To solve it, it was necessary to change the profile and shape of the aircraft wing (it became thinner and swept), to make the front of the fuselage more pointed and to equip the aircraft with jet engines. For the first time, the speed of sound was exceeded in 1947 by C. Yeager on an X-1 aircraft (USA) with a liquid-propellant rocket engine launched from a B-29 aircraft. In Russia, the first to overcome the sound barrier in 1948 was O. V. Sokolovsky on an experimental La-176 aircraft with a turbojet engine.

Encyclopedia "Technology". - M.: Rosman. 2006 .

sound barrier

a sharp increase in the drag of an aerodynamic aircraft at flight Mach numbers M(∞) slightly exceeding the critical number M*. The reason is that at numbers M(∞) > M* comes, accompanied by the appearance of wave resistance. The wave drag coefficient of aircraft increases very rapidly with increasing number M, starting from M(∞) = M*.
The presence of Z. b. makes it difficult to achieve a flight speed equal to the speed of sound, and the subsequent transition to supersonic flight. For this, it turned out to be necessary to create aircraft with thin swept wings, which made it possible to significantly reduce resistance, and jet engines, in which thrust increases with increasing speed.
In the USSR, a speed equal to the speed of sound was first achieved on the La-176 aircraft in 1948.

Aviation: Encyclopedia. - M.: Great Russian Encyclopedia. Chief editor G.P. Svishchev. 1994 .

See what a "sound barrier" is in other dictionaries:

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The sound barrier in aerodynamics is the name of a number of phenomena that accompany the movement of an aircraft (for example, a supersonic aircraft, rocket) at speeds close to or exceeding the speed of sound. Contents 1 Shock wave, ... ... Wikipedia

SOUND BARRIER, the cause of difficulties in aviation when increasing the speed of flight above the speed of sound (SUPERSONIC SPEED). Approaching the speed of sound, the aircraft experiences an unexpected increase in drag and a loss of aerodynamic LIFT ... ... Scientific and technical encyclopedic dictionary

sound barrier- garso barjeras statusas T sritis fizika atitikmenys: engl. sonic barrier; sound barrier vok. Schallbarriere, f; Schallmauer, f rus. sound barrier, m pranc. barrière sonique, f; frontiere sonique, f; mur de son, m … Fizikos terminų žodynas

sound barrier- garso barjeras statusas T sritis Energetika apibrėžtis Staigus aerodinaminio pasipriešinimo padidėjimas, kai orlaivio greitis tampa garso greičiu (viršijama kritinė Macho skaičiaus vertė). Aiškinamas bangų krize dėl staiga padidėjusio… … Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas

A sharp increase in aerodynamic drag when the aircraft flight speed approaches the speed of sound (the critical value of the Mach number of flight is exceeded). It is explained by a wave crisis, accompanied by an increase in wave resistance. Overcome 3.… … Big encyclopedic polytechnic dictionary

sound barrier- a sharp increase in the resistance of the air environment to the movement of the aircraft at. approach to speeds close to the speed of sound propagation. Overcoming 3. b. made possible by improving the aerodynamic forms of aircraft and the use of powerful ... ... Dictionary of military terms

sound barrier- sound barrier - a sharp increase in the resistance of an aerodynamic aircraft at Mach flight numbers M∞, slightly exceeding the critical number M*. The reason is that for numbers M∞ > Encyclopedia "Aviation"

sound barrier- sound barrier - a sharp increase in the resistance of an aerodynamic aircraft at Mach flight numbers M∞, slightly exceeding the critical number M*. The reason is that at numbers M∞ > M* a wave crisis sets in,… … Encyclopedia "Aviation"

- (French barriere outpost). 1) gates in fortresses. 2) in arenas and circuses, a fence, a log, a pole through which a horse jumps. 3) a sign that fighters reach in a duel. 4) railing, grating. Dictionary of foreign words included in ... ... Dictionary of foreign words of the Russian language

BARRIER, husband. 1. An obstacle (type of wall, crossbar) placed on the way (during jumps, running). Take b. (get over it). 2. Fence, fence. B. lodges, balconies. 3. trans. An obstacle, an obstacle to something. River natural b. for… … Explanatory dictionary of Ozhegov

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Why is an airplane breaking the sound barrier accompanied by an explosive pop? And what is a "sound barrier"?

There is a misunderstanding with "cotton" caused by a misunderstanding of the term "sound barrier". This "clap" is properly called "sonic boom". An aircraft moving at supersonic speed creates shock waves, air pressure surges, in the surrounding air. Simplistically, these waves can be imagined as a cone accompanying the flight of an aircraft, with a vertex, as it were, tied to the nose of the fuselage, and generators directed against the movement of the aircraft and propagating quite far, for example, to the surface of the earth.

When the boundary of this imaginary cone, denoting the front of the main sound wave, reaches the human ear, then a sharp pressure jump is perceived by ear as a pop. The sonic boom, like a tethered one, accompanies the entire flight of the aircraft, provided that the aircraft is moving fast enough, albeit at a constant speed. Cotton, on the other hand, seems to be the passage of the main sound shock wave over a fixed point on the earth's surface, where, for example, the listener is located.

In other words, if a supersonic aircraft with a constant but supersonic speed began to fly back and forth over the listener, then the clap would be heard every time, some time after the aircraft flew over the listener at a fairly close distance.

A “sound barrier” in aerodynamics is called a sharp jump in air resistance that occurs when an aircraft reaches a certain boundary speed close to the speed of sound. When this speed is reached, the nature of the air flow around the aircraft changes dramatically, which at one time made it very difficult to achieve supersonic speeds. A conventional, subsonic aircraft is not capable of sustainably flying faster than sound, no matter how it is accelerated - it will simply lose control and fall apart.

To overcome the sound barrier, scientists had to develop a wing with a special aerodynamic profile and come up with other tricks. It is interesting that the pilot of a modern supersonic aircraft feels well the “overcoming” of the sound barrier by his aircraft: when switching to a supersonic flow, an “aerodynamic impact” and characteristic “jumps” in controllability are felt. But these processes are not directly related to the “pops” on the ground.

Before the plane breaks the sound barrier, an unusual cloud may form, the origin of which is still not clear. According to the most popular hypothesis, there is a pressure drop near the aircraft and a so-called Prandtl-Glauert singularity followed by condensation of water droplets from humid air. Actually, you can see the condensate in the pictures below ...

Click on the picture to enlarge it.

Passed the sound barrier :-) ...

Before jumping into conversations on the topic, let's bring some clarity to the question of the accuracy of concepts (what I like :-)). There are two terms in common use today: sound barrier and supersonic barrier. They sound similar, but still not the same. However, there is no point in diluting it with particular rigor: in fact, this is one and the same thing. The definition of the sound barrier is used most often by people who are more knowledgeable and closer to aviation. And the second definition is usually all the rest.

I think that from the point of view of physics (and the Russian language :-)) it is more correct to say the sound barrier. There is simple logic here. After all, there is the concept of the speed of sound, but there is no fixed concept of the speed of supersonic, strictly speaking. Looking ahead a little, I’ll say that when an aircraft flies at supersonic, it has already passed this barrier, and when it passes (overcomes) it, then it passes a certain threshold value of speed equal to the speed of sound (and not supersonic).

Something like that:-). Moreover, the first concept is used much less frequently than the second. This is apparently because the word supersonic sounds more exotic and attractive. And in supersonic flight, the exotic is certainly present and, of course, attracts many. However, not all people who savor the words " supersonic barrier' really understand what it is. More than once I was convinced of this, looking at the forums, reading articles, even watching TV.

This question is actually rather complicated from the point of view of physics. But we, of course, will not climb into complexity. We will just try, as usual, to clarify the situation using the principle of "explaining aerodynamics on the fingers" :-).

So, to the barrier (sonic :-))!… Aircraft in flight, acting on such an elastic medium as air, becomes a powerful source of sound waves. I think everyone knows what sound waves are in the air :-).

Sound waves (tuning fork).

This is an alternation of areas of compression and rarefaction, propagating in different directions from the sound source. Approximately like circles on the water, which are also just waves (but not sound :-)). It is these areas, acting on the eardrum, that allow us to hear all the sounds of this world, from human whispers to the roar of jet engines.

An example of sound waves.

The points of propagation of sound waves can be various nodes of the aircraft. For example, an engine (its sound is known to anyone :-)), or body parts (for example, the bow), which, condensing the air in front of it when moving, create a certain type of pressure (compression) wave running forward.

All these sound waves propagate in the air at the speed of sound we already know. That is, if the plane is subsonic, and even flies at low speed, then they seem to run away from it. As a result, when such an aircraft approaches, we first hear its sound, and then it flies itself.

I will make a reservation, however, that this is true if the plane does not fly very high. After all, the speed of sound is not the speed of light :-). Its magnitude is not so great and sound waves need time to reach the listener. Therefore, the sequence of sound appearance for the listener and the aircraft, if it flies at high altitude, may change.

And since the sound is not so fast, then with an increase in its own speed, the plane begins to catch up with the waves emitted by it. That is, if he was motionless, then the waves would diverge from him in the form concentric circles like circles on the water from a thrown stone. And since the plane is moving, then in the sector of these circles, corresponding to the direction of flight, the boundaries of the waves (their fronts) begin to approach each other.

Subsonic motion of the body.

Accordingly, the gap between the aircraft (its nose) and the front of the very first (head) wave (that is, this is the area where gradual, to a certain extent, braking oncoming flow when meeting with the nose of the aircraft (wing, tail) and, as a result, increase in pressure and temperature) begins to decrease and the faster, the greater the flight speed.

There comes a moment when this gap practically disappears (or becomes minimal), turning into a special kind of area, which is called shock wave. This happens when the flight speed reaches the speed of sound, that is, the aircraft moves at the same speed as the waves emitted by it. The Mach number in this case is equal to one (M=1).

Sound movement of the body (M=1).

shock wave, is a very narrow area of ​​the medium (of the order of 10 -4 mm), when passing through which there is no longer a gradual, but a sharp (jump-like) change in the parameters of this medium - speed, pressure, temperature, density. In our case, the speed drops, pressure, temperature and density increase. Hence the name - the shock wave.

Somewhat simplistically, I would say this about all this. It is impossible to slow down the supersonic flow sharply, but it has to be done, because there is no longer the possibility of gradual deceleration to the speed of the flow just in front of the nose of the aircraft, as at moderate subsonic speeds. It seems to stumble upon a section of subsonic in front of the nose of the aircraft (or the toe of the wing) and collapses into a narrow jump, transferring to it the great energy of movement that it possesses.

By the way, it can also be said vice versa that the aircraft transfers part of its energy to the formation of shock waves in order to slow down the supersonic flow.

Supersonic motion of the body.

There is another name for the shock wave. Moving along with the aircraft in space, it is, in fact, the front of a sharp change in the above parameters of the environment (that is, the air flow). And this is the essence of the shock wave.

shock wave and a shock wave, in general, are equal definitions, but in aerodynamics the first is more commonly used.

The shock wave (or shock wave) can be almost perpendicular to the direction of flight, in which case they take an approximately circular shape in space and are called straight lines. This usually happens in modes close to M=1.

Modes of body movement. ! - subsonic, 2 - M=1, supersonic, 4 - shock wave (shock).

At numbers M > 1, they are already at an angle to the direction of flight. That is, the plane is already overtaking its own sound. In this case, they are called oblique and in space they take the form of a cone, which, by the way, is called the Mach cone, after the scientist who studied supersonic flows (he mentioned him in one of).

Mach cone.

The shape of this cone (its “slimness”, so to speak) just depends on the number M and is related to it by the relation: M = 1 / sin α, where α is the angle between the axis of the cone and its generatrix. And the conical surface touches the fronts of all sound waves, the source of which was the aircraft, and which it “overtook”, reaching supersonic speed.

Besides shock waves may also be affiliated, when they are adjacent to the surface of a body moving at supersonic speed or retreated if they do not touch the body.

Types of shock waves in supersonic flow around bodies of various shapes.

Usually, shocks become attached if the supersonic flow flows around any pointed surfaces. For an aircraft, for example, this can be a pointed nose, a PVD, a sharp edge of an air intake. At the same time, they say “jump sits”, for example, on the nose.

And the receding shock can be obtained when flowing around rounded surfaces, for example, the front rounded edge of a thick aerodynamic wing profile.

Various components of the aircraft body create a rather complex shock wave system in flight. However, the most intense of them are two. One head on the bow and the second tail on the elements of the tail unit. At some distance from the aircraft, the intermediate jumps either overtake the head one and merge with it, or the tail one overtakes them.

The shock waves on the aircraft model when blowing in a wind tunnel (M=2).

As a result, two jumps remain, which, in general, are perceived by the earthly observer as one due to the small size of the aircraft compared to the flight altitude and, accordingly, a short time interval between them.

The intensity (in other words, energy) of the shock wave (compression shock) depends on various parameters (the speed of the aircraft, its design features, environmental conditions, etc.) and is determined by the pressure drop at its front.

As the distance from the top of the Mach cone, that is, from the aircraft, as a source of perturbations, the shock wave weakens, gradually turns into an ordinary sound wave and eventually completely disappears.

And on what degree of intensity it will have shock wave(or shockwave) that reaches the ground depends on the effect it can produce there. It's no secret that the well-known Concorde flew supersonic only over the Atlantic, and military supersonic aircraft go supersonic at high altitudes or in areas where there are no settlements (at least it seems like they should do it :-)).

These restrictions are very justified. For me, for example, the very definition of a shock wave is associated with an explosion. And the things that a sufficiently intense shock wave can do may well be up to it. At least the glass from the windows can fly out easily. There is enough evidence of this (especially in the history of Soviet aviation, when it was quite numerous and the flights were intense). But you can do worse things. You just have to fly lower :-) ...

However, for the most part, what remains of shock waves when they reach the ground is no longer dangerous. Just an outside observer on the ground can at the same time hear a sound similar to a roar or explosion. It is with this fact that one common and rather persistent misconception is associated.

People who are not too experienced in aviation science, hearing such a sound, say that this plane overcame sound barrier (supersonic barrier). Actually it is not. This statement has nothing to do with reality for at least two reasons.

Shock wave (compression shock).

Firstly, if a person on the ground hears a booming roar high in the sky, then this only means (I repeat :-)) that his ears have reached shock wave front(or shock wave) from an airplane flying somewhere. This plane is already flying at supersonic speed, and not just switched to it.

And if the same person could suddenly be a few kilometers ahead of the aircraft, then he would again hear the same sound from the same aircraft, because he would be affected by the same shock wave moving along with the aircraft.

It moves at supersonic speeds, and therefore approaches silently. And after it has had its not always pleasant effect on the eardrums (well, when only on them :-)) and safely passes on, the rumble of running engines becomes audible.

Approximate aircraft flight pattern for various values ​​of the M number on the example of the Saab 35 "Draken" fighter. The language, unfortunately, is German, but the scheme is generally understandable.

Moreover, the transition to supersonic itself is not accompanied by any one-time “booms”, pops, explosions, etc. On a modern supersonic aircraft, the pilot most often learns about such a transition only from the readings of the instruments. In this case, however, a certain process occurs, but it is practically not noticeable to him, subject to certain piloting rules.

But that's not all :-). I'll say more. in the form of just some kind of tangible, heavy, difficult-to-cross obstacle, against which the plane rests and which needs to be “pierced” (I have heard such judgments :-)) does not exist.

Strictly speaking, there is no barrier at all. Once upon a time, at the dawn of the development of high speeds in aviation, this concept was formed rather as a psychological belief about the difficulty of switching to supersonic speed and flying at it. There were even statements that it was impossible at all, especially since the prerequisites for such beliefs and statements were quite specific.

However, first things first…

In aerodynamics, there is another term that quite accurately describes the process of interaction with the air flow of a body moving in this flow and striving to switch to supersonic. it wave crisis. It is he who does some of the bad things that are traditionally associated with the concept sound barrier.

So something about the crisis :-). Any aircraft consists of parts, the air flow around which in flight may not be the same. Take, for example, a wing, or rather an ordinary classic subsonic profile.

From the basics of knowledge about how the lifting force is formed, we are well aware that the flow velocity in the adjacent layer of the upper curved surface of the profile is different. Where the profile is more convex it is greater than the total flow velocity, then when the profile flattens it decreases.

When the wing moves in the flow at speeds close to the speed of sound, there may come a moment when, for example, in such a convex region, the speed of the air layer, which is already greater than the total flow speed, becomes sonic and even supersonic.

Local shock that occurs on transonic during a wave crisis.

Further along the profile, this speed decreases and at some point again becomes subsonic. But, as we said above, the supersonic flow cannot quickly slow down, so the occurrence of shock wave.

Such shocks appear in different parts of the streamlined surfaces, and initially they are rather weak, but their number can be large, and with an increase in the total flow velocity, supersonic zones increase, the shocks “strengthen” and move towards the trailing edge of the airfoil. Later, the same shock waves appear on the bottom surface of the profile.

Full supersonic flow around the wing airfoil.

What is the risk of all this? But what. First- is significant increase in aerodynamic drag in the range of transonic speeds (about M=1, more or less). This resistance grows due to a sharp increase in one of its components - wave resistance. The same one that we did not take into account when considering flights at subsonic speeds.

For the formation of numerous shock waves (or shock waves) during the deceleration of a supersonic flow, as I said above, energy is spent, and it is taken from the kinetic energy of the aircraft. That is, the plane simply slows down (and very noticeably!). That's what it is wave resistance.

Moreover, shock waves, due to the sharp deceleration of the flow in them, contribute to the separation of the boundary layer after itself and its transformation from laminar to turbulent. This further increases the aerodynamic drag.

Airfoil flow at various M numbers. Shocks, local supersonic zones, turbulent zones.

Second. Due to the appearance of local supersonic zones on the wing profile and their further shift to the tail section of the profile with an increase in the flow velocity and, thereby, a change in the pressure distribution pattern on the profile, the point of application of aerodynamic forces (pressure center) also shifts to the trailing edge. As a result, there appears diving moment relative to the center of mass of the aircraft, causing it to lower its nose.

What does all this result in ... Due to the rather sharp increase in aerodynamic drag, the aircraft needs a significant engine power reserve to overcome the transonic zone and reach, so to speak, real supersonic.

A sharp increase in aerodynamic drag on transonic (wave crisis) due to an increase in wave drag. Cd is the drag coefficient.

Further. Due to the occurrence of a diving moment, difficulties arise in pitch control. In addition, due to the disorder and unevenness of the processes associated with the emergence of local supersonic zones with shock waves, too difficult to manage. For example, on a roll, due to different processes on the left and right planes.

Yes, plus the occurrence of vibrations, often quite strong due to local turbulence.

In general, a complete set of pleasures, which bears the name wave crisis. But, true, all of them take place (there were, specific :-)) when using typical subsonic aircraft (with a thick profile of a straight wing) in order to achieve supersonic speeds.

Initially, when there was not enough knowledge yet, and the processes of reaching supersonics were not comprehensively studied, this very set was considered almost fatally insurmountable and was called sound barrier(or supersonic barrier, if you want to:-)).

When trying to overcome the speed of sound on conventional piston aircraft, there were many tragic cases. Strong vibration sometimes led to the destruction of the structure. The aircraft did not have enough power for the required acceleration. In level flight, it was impossible due to an effect of the same nature as wave crisis.

Therefore, a dive was used for acceleration. But it could very well be fatal. The dive moment that appeared during a wave crisis made the dive protracted, and sometimes there was no way out of it. Indeed, in order to restore control and eliminate the wave crisis, it was necessary to extinguish the speed. But to do this in a dive is extremely difficult (if not impossible).

Dragging into a dive from level flight is considered one of the main causes of the disaster in the USSR on May 27, 1943 of the famous experimental BI-1 fighter with a liquid-propellant rocket engine. Tests were carried out for the maximum flight speed, and according to the designers, the speed achieved was more than 800 km / h. Then there was a delay in the peak, from which the plane did not come out.

Experimental fighter BI-1.

Nowadays wave crisis already well enough studied and overcome sound barrier(if it is required :-)) is not difficult. On aircraft that are designed to fly at sufficiently high speeds, certain design solutions and restrictions are applied to facilitate their flight operation.

As is known, the wave crisis begins at numbers M close to unity. Therefore, almost all jet subsonic liners (passenger, in particular) have a flight limitation on the number M. Usually it is in the region of 0.8-0.9M. The pilot is instructed to follow this. In addition, on many aircraft, when the limit level is reached, after which the airspeed must be reduced.

Almost all aircraft flying at speeds of at least 800 km/h and above have swept wing(at least on the leading edge :-)). It allows you to push back the start of the offensive wave crisis up to speeds corresponding to M=0.85-0.95.

Arrow wing. Fundamental action.

The reason for this effect can be explained quite simply. On a straight wing, an air flow with a speed V runs almost at a right angle, and on a swept wing (sweep angle χ) at a certain slip angle β. The velocity V can be vectorially decomposed into two streams: Vτ and Vn .

The flow Vτ does not affect the pressure distribution on the wing, but it does the flow Vn, which determines the carrying properties of the wing. And it is obviously less in magnitude of the total flow V. Therefore, on the swept wing, the onset of a wave crisis and the growth wave resistance occurs noticeably later than on a straight wing at the same freestream velocity.

Experimental fighter E-2A (the predecessor of the MIG-21). Typical swept wing.

One of the modifications of the swept wing was the wing with supercritical profile(mentioned him). It also allows you to move the beginning of the wave crisis at high speeds, in addition, it allows you to increase efficiency, which is important for passenger liners.

SuperJet 100. Supercritical swept wing.

If the aircraft is intended to transit sound barrier(passing and wave crisis too :-)) and supersonic flight, then it usually always differs in certain design features. In particular, it usually has thin profile of the wing and plumage with sharp edges(including diamond-shaped or triangular) and a certain shape of the wing in plan (for example, triangular or trapezoidal with an influx, etc.).

Supersonic MIG-21. Follower E-2A. A typical triangular wing.

MIG-25. An example of a typical aircraft designed for supersonic flight. Thin profiles of the wing and plumage, sharp edges. Trapezoidal wing. profile

Passing the notorious sound barrier, that is, such aircraft carry out the transition to supersonic speed on afterburning engine operation due to the increase in aerodynamic resistance, and, of course, in order to quickly slip through the zone wave crisis. And the very moment of this transition is most often not felt in any way (I repeat :-)) neither by the pilot (he can only reduce the sound pressure level in the cockpit), nor by an outside observer, if, of course, he could observe this :-).

However, here it is worth mentioning one more misconception, connected with outside observers. Surely many have seen this kind of photographs, the captions under which say that this is the moment of overcoming the plane sound barrier so to speak, visually.

Prandtl-Gloert effect. Not related to passing the sound barrier.

Firstly, we already know that there is no sound barrier, as such, and the transition to supersonic itself is not accompanied by anything so extraordinary (including clap or explosion).

Secondly. What we saw in the photo is the so-called Prandtl-Gloert effect. I already wrote about him. It is in no way directly related to the transition to supersonic. It’s just that at high speeds (subsonic, by the way :-)) the plane, moving a certain mass of air in front of it, creates some rarefaction area. Immediately after the passage, this area begins to fill with air from the nearby space with natural an increase in volume and a sharp drop in temperature.

If a air humidity is sufficient and the temperature falls below the dew point of the ambient air, then moisture condensation from water vapor in the form of fog, which we see. As soon as conditions are restored to the original, this fog immediately disappears. This whole process is rather short.

Such a process at high transonic speeds can be facilitated by local surges I, sometimes helping to form something similar to a gentle cone around the aircraft.

High speeds favor this phenomenon, however, if the air humidity is sufficient, then it can occur (and occurs) at rather low speeds. For example, above the surface of water bodies. By the way, most of the beautiful photos of this nature were taken from the aircraft carrier, that is, in fairly humid air.

That's how it works. The shots, of course, are cool, the spectacle is spectacular :-), but this is not at all what it is most often called. nothing to do with it (and supersonic barrier too:-)). And this is good, I think, otherwise the observers who take this kind of photo and video might not be good. shock wave, do you know:-)…

In conclusion, one video (I have already used it before), the authors of which show the effect of a shock wave from an aircraft flying at low altitude at supersonic speed. There is, of course, a certain exaggeration there :-), but the general principle is clear. And again, it's amazing :-)

And that's all for today. Thank you for reading the article to the end :-). Until we meet again…

Photos are clickable.

The sound barrier is a phenomenon that occurs during the flight of an aircraft or rocket at the moment of transition from subsonic to supersonic flight speed in the atmosphere. When the aircraft speed approaches the speed of sound (1200 km/h), a thin area appears in the air in front of it, in which there is a sharp increase in pressure and air density. This compaction of air in front of a flying aircraft is called a shock wave. On the ground, the passage of a shock wave is perceived as a pop, similar to the sound of a shot. Having exceeded the speed of sound, the aircraft passes through this area of ​​increased air density, as if piercing it - it overcomes the sound barrier. For a long time, breaking the sound barrier was considered a serious problem in the development of aviation. To solve it, it was necessary to change the profile and shape of the aircraft wing (it became thinner and swept), to make the front of the fuselage more pointed and to equip the aircraft with jet engines. For the first time, the speed of sound was exceeded in 1947 by C. Yeager on a Bell X-1 aircraft (USA) with a liquid-propellant rocket engine launched from a Boeing B-29 aircraft. In Russia, the first to overcome the sound barrier in 1948 was pilot O. V. Sokolovsky on an experimental La-176 aircraft with a turbojet engine.

Video.

Sound speed.

Speed ​​of propagation (relative to the medium) of small pressure perturbations. In a perfect gas (for example, in air at moderate temperatures and pressure) S. z. does not depend on the nature of the propagating small perturbation and is the same both for monochromatic oscillations of different frequencies () and for weak shock waves. In a perfect gas, at the considered point in space, the S. z. a depends only on the composition of the gas and its absolute temperature T:
a = (dp/d(())1/2 = ((()p/(())1/2 = ((()RT/(())1/2,
where dp/d(() is the derivative of pressure with respect to density for an isentropic process, (-) is the adiabatic exponent, R is the universal gas constant, (-) is the molecular weight (in air a 20.1T1/2 m/s. at 0 (°)C a = 332 m/s).
In a gas with physicochemical transformations, for example, in a dissociating gas, S. h. will depend on how - in equilibrium or non-equilibrium - these processes proceed in the perturbation wave. At thermodynamic equilibrium S. h. depends only on the composition of the gas, its temperature and pressure. In the nonequilibrium course of physical and chemical processes, sound dispersion takes place, that is, S. z. depends not only on the state of the medium, but also on the frequency of oscillations (). High-frequency oscillations ((tt), ()) - relaxation time) propagate from a frozen S. z. aj, low-frequency ((,) 0) - with equilibrium S. z. ae, and aj > ae. The difference between aj and ai is usually small (in air at Т = 6000(°)С and p = 105 Pa, it is about 15%). In S.'s liquids h. much higher than in gas (in water a 1500 m/s)

Image copyright SPL

Impressive photographs of jet fighters in a dense cone of water vapor are often said to be the aircraft breaking the sound barrier. But this is a mistake. The browser talks about the true cause of the phenomenon.

This spectacular phenomenon was repeatedly captured by photographers and videographers. A military jet aircraft passes over the earth at high speed, several hundred kilometers per hour.

As the fighter accelerates, a dense cone of condensation begins to form around it; it seems that the plane is inside a compact cloud.

Exciting fantasy captions under such photographs often claim that we have before us - visual evidence of a sonic boom when the aircraft reaches supersonic speed.

In fact this is not true. We observe the so-called Prandtl-Gloert effect - a physical phenomenon that occurs when an aircraft approaches the speed of sound. It has nothing to do with breaking the sound barrier.

• Other BBC Future articles in Russian

As the aircraft industry developed, aerodynamic shapes became more and more streamlined, and the speed of aircraft steadily increased - aircraft began to do things with the air around them that their slower and more bulky predecessors could not do.

The mysterious shock waves that form around low-flying aircraft as they approach the speed of sound, and then break the sound barrier, indicate that the air at such speeds behaves in a very strange way.

So what are these mysterious clouds of condensate?

According to Rod Irwin, Chairman of the Aerodynamics Group at the Royal Aeronautics Society, the conditions under which the vapor cone occurs immediately precede an aircraft breaking the sound barrier. However, this phenomenon is usually photographed at speeds slightly less than the speed of sound.

Surface layers of air are denser than the atmosphere at high altitudes. When flying at low altitudes, there is increased friction and drag.

By the way, pilots are forbidden to break the sound barrier over land. “You can go supersonic over the ocean, but not over a solid surface,” Irwin explains. “By the way, this circumstance was a problem for the Concorde supersonic passenger liner - the ban was introduced after it was put into operation, and the crew was allowed to develop supersonic speed only over water surface".

Moreover, it is extremely difficult to visually register a sonic boom when an aircraft reaches supersonic speed. It cannot be seen with the naked eye - only with the help of special equipment.

For photographing models blown at supersonic speeds in wind tunnels, special mirrors are usually used to detect the difference in light reflection caused by the formation of a shock wave.

Photographs obtained by the so-called schlieren method (or Toepler method) are used to visualize shock waves (or, as they are also called, shock waves) that form around the model.

During blowdowns, condensate cones are not created around the models, since the air used in the wind tunnels is preliminarily dried.

The cones of water vapor are associated with shock waves (and there are several of them) that form around the aircraft as it picks up speed.

When the speed of an aircraft approaches the speed of sound (about 1234 km / h at sea level), a difference in local pressure and temperature occurs in the air flowing around it.

As a result, the air loses its ability to retain moisture, and condensation forms in the form of a cone, as on this video.

"The visible cone of steam is caused by a shock wave, which creates a pressure and temperature differential around the aircraft," says Irwin.

Many of the best photographs of this phenomenon are from US Navy aircraft - not surprising, given that warm, humid air near the sea surface tends to exaggerate the Prandtl-Gloert effect.

Such stunts are often performed by F/A-18 Hornet fighter-bombers, the main carrier-based type of American naval aviation.

Members of the US Navy Blue Angels aerobatic team fly in the same combat vehicles, masterfully performing maneuvers in which a condensation cloud forms around the aircraft.

Due to the spectacular nature of the phenomenon, it is often used to popularize naval aviation. The pilots deliberately maneuver over the sea, where the conditions for the occurrence of the Prandtl-Gloert effect are the most optimal, and professional naval photographers are on duty nearby - after all, it is impossible to take a clear picture of a jet aircraft flying at a speed of 960 km / h on a regular smartphone.

Condensation clouds look most impressive in the so-called transonic flight mode, when the air partially flows around the aircraft at supersonic speed, and partially at subsonic.

“The aircraft is not necessarily flying at supersonic speeds, but the air flows around the upper surface of its wing at a higher speed than the lower one, which leads to a local shock,” says Irwin.

According to him, for the Prandtl-Gloert effect to occur, certain climatic conditions are required (namely, warm and humid air), which carrier-based fighters encounter more often than other aircraft.

All you have to do is ask a professional photographer for the service, and voila! - your aircraft was captured surrounded by a spectacular cloud of water vapor, which many of us mistakenly take as a sign of reaching supersonic.

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