(sometimes more than one, depending on the shape of the body). The photo shows shock waves generated at the tip of the fuselage of the model, on the leading and trailing edges of the wing and at the rear end of the model.
At the front of a shock wave (sometimes also called a shock wave), which has a very small thickness (fractions of a mm), cardinal changes in the properties of the flow occur almost abruptly - its velocity relative to the body decreases and becomes subsonic, the pressure in the flow and the temperature of the gas increase abruptly. Part of the kinetic energy of the flow is converted into the internal energy of the gas. All these changes are greater, the higher the speed of the supersonic flow. At hypersonic speeds(Mach 5 and above), the gas temperature reaches several thousand degrees, which creates serious problems for vehicles moving at such speeds (for example, the Columbia shuttle collapsed on February 1, 2003 due to damage to the thermal protective shell that occurred during the flight).
The shock wave front, as it moves away from the apparatus, gradually takes on an almost regular conical shape, the pressure drop across it decreases with increasing distance from the top of the cone, and the shock wave turns into a sound wave. The angle between the axis and the generatrix of the cone is related to the Mach number by the relation:
When this wave reaches an observer, who is, for example, on Earth, he hears a loud sound, similar to an explosion. A common misconception is that this is a consequence of the aircraft reaching the speed of sound, or "breaking the sound barrier". In fact, at this moment, a shock wave passes by the observer, which constantly accompanies the aircraft moving at supersonic speed. Usually, immediately after the "pop", the observer can hear the hum of the aircraft's engines, which is not heard before the passage of the shock wave, since the aircraft is moving faster than the sounds made by it. A very similar observation takes place during subsonic flight - an aircraft flying above an observer at a high altitude (more than 1 km) is not heard, or rather, we hear it with a delay: the direction to the sound source does not coincide with the direction to the visible aircraft for the observer from the ground.
wave crisis
Wave crisis - a change in the nature of the flow aircraft air flow when the flight speed approaches the speed of sound, accompanied, as a rule, by a deterioration in the aerodynamic characteristics of the apparatus - an increase in drag, a decrease in lift, the appearance of vibrations, etc.
Already during the Second World War, the speed of fighters began to approach the speed of sound. At the same time, pilots sometimes began to observe incomprehensible at that time and threatening phenomena that occur with their cars when flying at top speeds. The emotional report of the US Air Force pilot to his commander, General Arnold, has been preserved:
“Sir, our planes are already very strict now. If there are cars with even higher speeds, we will not be able to fly them. Last week I dived on Me-109 in my Mustang. My plane shook like a pneumatic hammer, and stopped obeying the rudders. I couldn't bring him out of his dive. Just three hundred meters from the ground, I hardly leveled the car ... ".
After the war, when many aircraft designers and test pilots made persistent attempts to achieve a psychologically significant mark - the speed of sound, these incomprehensible phenomena became the norm, and many of these attempts ended tragically. This gave rise to the not-so-mystical expression “sound barrier” (fr. mur du son, German Schallmauer- sound wall). Pessimists argued that it was impossible to exceed this limit, although enthusiasts, risking their lives, repeatedly tried to do this. The development of scientific ideas about the supersonic motion of gas made it possible not only to explain the nature of the "sound barrier", but also to find means to overcome it.
With subsonic flow around the fuselage, wing and tail of the aircraft, zones of local flow acceleration appear on the convex sections of their contours. When the flight speed of an aircraft approaches the sound speed, the local air speed in the flow acceleration zones may slightly exceed the speed of sound (Fig. 1a). Having passed the acceleration zone, the flow slows down, with the inevitable formation of a shock wave (this is the property of supersonic flows: the transition from supersonic to subsonic speed always occurs discontinuously - with the formation of a shock wave). The intensity of these shock waves is low - the pressure drop on their fronts is small, but they arise immediately in a multitude, at different points on the surface of the apparatus, and together they sharply change the nature of its flow, with a deterioration in its flight characteristics: the wing lift drops, air rudders and the ailerons lose their effectiveness, the apparatus becomes uncontrollable, and all this is extremely unstable, there is a strong vibration. This phenomenon has been named wave crisis. When the velocity of the apparatus becomes supersonic ( > 1), the flow again becomes stable, although its character changes fundamentally (Fig. 1b).
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| Rice. 1a. Aerowing in close to sound flow. | Rice. 1b. Aerowing in supersonic flow. |
For wings with a relatively thick profile, under conditions of a wave crisis, the center of pressure shifts sharply back and the nose of the aircraft "gets heavier". Pilots of piston fighters with such a wing, who tried to develop maximum speed in a dive from a great height to maximum power, when approaching the "sonic barrier" they became victims of a wave crisis - once in it, it was impossible to get out of a dive without extinguishing speed, which in turn is very difficult to do in a dive. The most famous case of diving into a dive from horizontal flight in the history of Russian aviation is the Bakhchivandzhi disaster during the test of the BI-1 missile at maximum speed. The best straight-wing fighters of World War II, such as the P-51 Mustang or the Me-109, had a wave crisis at high altitudes at speeds of 700-750 km/h. At the same time, the jet Messerschmitt Me.262 and Me.163 of the same period had a swept wing, thanks to which they developed speeds of over 800 km / h without problems. It should also be noted that an aircraft with a traditional propeller in level flight cannot achieve speeds close to the speed of sound, since the propeller blades enter the zone of wave crisis and lose efficiency much earlier than the aircraft. Supersonic propellers with saber blades can solve this problem, but on this moment such screws turn out to be too technically complex and very noisy, which is why they are not used in practice.
Modern subsonic aircraft with a cruising flight speed close enough to the sonic speed (over 800 km/h) are usually carried out with swept wings and empennage with thin profiles, which makes it possible to shift the speed at which a wave crisis begins towards higher values. Supersonic aircraft, which have to go through a section of a wave crisis when gaining supersonic speed, have structural differences from subsonic ones, associated both with the features of the supersonic flow of the air medium and with the need to withstand the loads that arise during supersonic flight and wave crisis, in particular - triangular in plan, a wing with a diamond-shaped or triangular profile.
- at subsonic flight speeds, speeds at which a wave crisis begins should be avoided (these speeds depend on the aerodynamic characteristics of the aircraft and on the flight altitude);
- the transition from subsonic to supersonic speed by jet aircraft should be carried out as quickly as possible, using engine afterburner, to avoid a long flight in the wave crisis zone.
Term wave crisis also applies to watercraft moving at speeds close to the speed of waves on the surface of the water. The development of a wave crisis makes it difficult to increase the speed. Overcoming the wave crisis by the ship means entering the gliding mode (sliding the hull on the surface of the water).
Historical facts
- The first pilot to achieve supersonic speed in controlled flight was the American test pilot Chuck Yeager on the Bell X-1 experimental aircraft (with a straight wing and rocket engine XLR-11) reaching M=1.06 in a gentle dive. It happened on October 14, 1947.
- In the USSR, the sound barrier was first overcome on December 26, 1948 by Sokolovsky, and then by Fedorov, in flights with a decrease in an experimental La-176 fighter.
- The first civilian aircraft to break the sound barrier was the Douglas DC-8 passenger liner. On August 21, 1961, it reached a speed of 1.012 Mach or 1262 km/h during a controlled dive from a height of 12496 m. The flight was undertaken in order to collect data for the design of new wing leading edges.
- On October 15, 1997, 50 years after breaking the sound barrier on an airplane, Englishman Andy Green broke the sound barrier in a Thrust SSC car.
- On October 14, 2012, Felix Baumgartner became the first person to break the sound barrier without the aid of any motorized vehicle, in free fall while jumping from a height of 39 kilometers. In free fall, he reached a speed of 1342.8 kilometers per hour.
see also
- Thermal barrier (problems in the development of hypersonic aircraft)
Notes
Links
- Theoretical and Engineering Foundations of Aerospace Engineering.
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See what "Sound Barrier" is in other dictionaries:
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
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 ... ... Encyclopedia of technology
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
What do we think of when we hear the expression "sound barrier"? A certain limit and which can seriously affect hearing and well-being. Usually the sound barrier is correlated with the conquest of airspace and
Overcoming this barrier can provoke the development of chronic diseases, pain syndromes and allergic reactions. Are these perceptions correct or are they stereotypes? Do they have a factual basis? What is a sound barrier? How and why does it occur? All this and some additional nuances, as well as historical facts related to this concept, we will try to find out in this article.
This mysterious science is aerodynamics
In the science of aerodynamics, designed to explain the phenomena that accompany the movement
aircraft, there is the concept of "sound barrier". This is a series of phenomena that occur during the movement of supersonic aircraft or rockets that move at speeds close to the speed of sound or greater.
What is a shock wave?
In the process of supersonic flow around the apparatus, a shock wave arises in the wind tunnel. Its traces can be seen even with the naked eye. On the ground they are marked with a yellow line. Outside the cone of the shock wave, in front of the yellow line, on the ground, the plane is not even audible. At a speed exceeding the sound, the bodies are subjected to a flow around the sound stream, which entails a shock wave. It may not be alone, depending on the shape of the body.
Shock wave transformation
The shock wave front, which is sometimes called a shock wave, has a rather small thickness, which, nevertheless, makes it possible to track abrupt changes in the properties of the flow, a decrease in its velocity relative to the body, and a corresponding increase in the pressure and temperature of the gas in the flow. In this case, the kinetic energy is partially converted into the internal energy of the gas. The number of these changes directly depends on the speed of the supersonic flow. As the shock wave moves away from the apparatus, the pressure drops decrease and the shock wave is converted into sound. She can reach an outside observer who will hear a characteristic sound resembling an explosion. There is an opinion that this indicates that the device has reached the speed of sound, when the sound barrier is left behind by the plane.
What is really going on?
The so-called moment of overcoming the sound barrier in practice is the passage of a shock wave with a growing rumble of aircraft engines. Now the unit is ahead of the accompanying sound, so the hum of the engine will be heard after it. The approach of speed to the speed of sound became possible during the Second World War, but at the same time, pilots noted alarm signals in the operation of aircraft.
After the end of the war, many aircraft designers and pilots sought to reach the speed of sound and break the sound barrier, but many of these attempts ended tragically. Pessimistic scientists argued that this limit could not be surpassed. By no means experimental, but scientific, it was possible to explain the nature of the concept of "sound barrier" and find ways to overcome it.
Safe flights at transonic and supersonic speeds are possible if a wave crisis is avoided, the occurrence of which depends on the aerodynamic parameters of the aircraft and the altitude of the flight. Transitions from one speed level to another should be carried out as quickly as possible using afterburner, which will help to avoid a long flight in the wave crisis zone. The wave crisis as a concept came from water transport. It arose at the moment of movement of ships at a speed close to the speed of waves on the surface of the water. Getting into a wave crisis entails a difficulty in increasing the speed, and if it is as simple as possible to overcome the wave crisis, then you can enter the mode of gliding or sliding on the water surface.
History in aircraft management
The first person to achieve supersonic flight speed in an experimental aircraft is American pilot Chuck Yeager. His achievement is noted in history on October 14, 1947. On the territory of the USSR, the sound barrier was overcome on December 26, 1948 by Sokolovsky and Fedorov, who flew an experienced fighter.
Of the civilians, the passenger liner Douglas DC-8 broke the sound barrier, which on August 21, 1961 reached a speed of 1.012 Mach, or 1262 km / h. The mission was to collect data for wing design. Among the aircraft, the world record was set by a hypersonic air-to-ground aeroballistic missile, which is in service with Russian army. At an altitude of 31.2 kilometers, the rocket reached a speed of 6389 km / h.
50 years after breaking the sound barrier in the air, Englishman Andy Green made a similar achievement in a car. In free fall, the American Joe Kittinger tried to break the record, who conquered a height of 31.5 kilometers. Today, on October 14, 2012, Felix Baumgartner set a world record, without the help of a vehicle, in a free fall from a height of 39 kilometers, breaking the sound barrier. At the same time, its speed reached 1342.8 kilometers per hour.
The most unusual breaking of the sound barrier
It is strange to think, but the first invention in the world to overcome this limit was the ordinary whip, which was invented by the ancient Chinese almost 7 thousand years ago. Almost until the invention of instant photography in 1927, no one suspected that the snap of a whip was a miniature sonic boom. A sharp swing forms a loop, and the speed increases sharply, which confirms the click. The sound barrier is overcome at a speed of about 1200 km / h.
The mystery of the noisiest city
No wonder the inhabitants of small towns are shocked when they see the capital for the first time. Abundance of transport, hundreds of restaurants and entertainment centers confuse and knock out of the usual rut. The beginning of spring in the capital is usually dated April, not the rebellious blizzard March. In April, the sky is clear, streams run and buds open. People, tired of the long winter, open their windows wide towards the sun, and street noise bursts into the houses. Birds are deafeningly chirping on the street, artists are singing, cheerful students are reciting poems, not to mention the noise in traffic jams and the subway. Employees of hygiene departments note that being in a noisy city for a long time is unhealthy. The sound background of the capital consists of transport,
aviation, industrial and domestic noise. The most harmful is just car noise, as planes fly high enough, and the noise from enterprises is dissolved in their buildings. The constant hum of cars on especially busy highways exceeds all permissible norms twice. How is the sound barrier overcome in the capital? Moscow is dangerous because of the abundance of sounds, so the residents of the capital install double-glazed windows to muffle the noise.
How is the sound barrier breached?
Until 1947, there was no actual data on the well-being of a person in the cockpit of an aircraft that flies faster than sound. As it turned out, breaking the sound barrier requires certain strength and courage. During the flight it becomes clear that there are no guarantees to survive. Even a professional pilot cannot say for sure whether the design of the aircraft will withstand the attack of the elements. In a matter of minutes, the plane can simply fall apart. What explains this? It should be noted that movement at subsonic speed creates acoustic waves that scatter like circles from a fallen stone. Supersonic speed excites shock waves, and a person standing on the ground hears a sound similar to an explosion. Without powerful computers it was difficult to solve complex ones and had to rely on blowing models in wind tunnels. Sometimes, with insufficient acceleration of the aircraft, the shock wave reaches such strength that windows fly out of the houses over which the aircraft flies. Not everyone will be able to overcome the sound barrier, because at this moment the entire structure is shaking, the fastenings of the apparatus can receive significant damage. Therefore, good health and emotional stability are so important for pilots. If the flight is smooth, and the sound barrier is overcome as quickly as possible, then neither the pilot nor possible passengers will feel particularly unpleasant sensations. Especially for the conquest of the sound barrier, a research aircraft was built in January 1946. The creation of the machine was initiated by an order from the Ministry of Defense, but instead of weapons, it was stuffed with scientific equipment that monitored the operation of mechanisms and instruments. This plane looked like a modern cruise missile with built-in rocket engine. Overcoming the sound barrier by an aircraft occurred when top speed 2736 km/h.
Verbal and material monuments to the conquest of the speed of sound
Achievements in breaking the sound barrier are highly valued today. So, the plane on which Chuck Yeager first overcame it is now on display at the National Air and Space Museum, which is located in Washington. But technical specifications this human invention would be worth little without the merit of the pilot himself. Chuck Yeager went through flight school and fought in Europe, after which he returned to England. The unfair suspension from flying did not break the spirit of Yeager, and he obtained an appointment with the commander-in-chief of the troops of Europe. In the years remaining before the end of the war, Yeager participated in 64 sorties, during which he shot down 13 aircraft. Chuck Yeager returned to his homeland with the rank of captain. His characteristics indicate phenomenal intuition, incredible composure and endurance in critical situations. More than once, Yeager set records on his plane. His later career was in the Air Force, where he trained pilots. AT last time Chuck Yeager broke the sound barrier at age 74, which was the fiftieth anniversary of his flight history and 1997.
Complex tasks of the creators of aircraft
World-famous MiG-15 aircraft began to be created at a time when the developers realized that it was impossible to be based only on breaking the sound barrier, but complex technical problems should be solved. As a result, a machine was created so successful that its modifications were adopted by different countries. Several different design bureaus entered into a kind of competitive struggle, the prize of which was a patent for the most successful and functional aircraft. Developed aircraft with swept wings, which was a revolution in their design. The ideal apparatus would have to be powerful, fast, and incredibly resistant to any external damage. The swept wings of the aircraft became an element that helped them triple the speed of sound. Further, it continued to grow, which was explained by an increase in engine power, the use of innovative materials and the optimization of aerodynamic parameters. Breaking the sound barrier has become possible and real even for a non-professional, but it does not become less dangerous because of this, so any extreme seeker should sensibly assess his strengths before deciding on such an experiment.
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 forward part 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 is well aware of 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.
Officially, the first pilot from the USA, Chuck Yeager, overcame supersonic speed. The record was set on 10/14/1957 on the Bell X-1, which was specially designed for this purpose in early 1946 by Bell Aircraft. The aircraft was manufactured by order of the military, but had nothing to do with the conduct of hostilities. The car was literally crammed with research equipment. Outwardly, the Bell X-1 resembled a modern cruise missile.
Test pilot Chuck Yeager
Pilot in 1923 February 13. After graduating from school, the young man immediately entered the flight school, after which he had to fight in Europe. At the very beginning of his flying career, the pilot managed to shoot down the Messerschmitt-109, but later he himself was defeated in the French sky and was forced to parachute.
The pilot was picked up by partisans, but counterintelligence removed him from flying. Outraged, Chuck secured an appointment with Eisenhower, who commanded allied forces. He believed the young man and, as it turned out, not in vain: the brave pilot managed to shoot down another 13 aircraft before the end of the war.
Yeager returned home with an excellent track record, characteristics, awards, in the rank of captain. This contributed to the inclusion of the pilot in a special team of testers, who at that time were selected as carefully as astronauts. Chuck's plane became the Captivating Glenys, in honor of his wife. The aircraft was equipped with one jet engine and was launched from a B-52 bomber.
On a winged car, the pilot set speed records more than once: at the end of 1947, he first broke the previous altitude record (21372 m), and in 1953 he managed to disperse the device to almost 2800 km / h, or 2.5 M (the speed of sound is measured in “max” , named after the German philosopher, engineer; 1 M is approximately equal to 1200 km / h). Yeager retired as a brigadier general in 1975, having managed to take part in the Vietnam War and the fighting in Korea.
The USSR could not stay away from attempts to overcome the sound barrier; several design bureaus at once (Lavochkin, Yakovlev, Mikoyan) participated in the preparation of an aircraft that was supposed to fly faster than sound. Such an honor fell to the La-176 aircraft, from Lavochkin's "company". The car was fully prepared for flights in 1948, in December. And on the 26th, Colonel Fedorov overcame the notorious barrier, accelerating in a dive. Later, the pilot received the title of Hero of the Soviet Union.
