Spectacular photographs of fighter jets in a dense cone of water vapor are often claimed to represent the aircraft breaking the sound barrier. But this is a mistake. We will tell you about the true reason for the phenomenon.
This spectacular phenomenon has been repeatedly captured by photographers and videographers. A military jet passes over the ground 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.
The imaginative captions under such photographs often claim that this is visual evidence of a sonic boom when an aircraft reaches supersonic speed.
In fact, this is not entirely true. We are observing the so-called Prandtl-Glauert effect - a physical phenomenon that occurs when an aircraft approaches the speed of sound. It has nothing to do with breaking the sound barrier.
As aircraft manufacturing 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 bulkier predecessors were not capable of.
The mysterious shock waves that form around low-flying aircraft as they approach and then break the sound barrier suggest that air behaves in strange ways at such speeds.
So what are these mysterious clouds of condensation?
The Prandtl-Gloert effect is most pronounced when flying in a warm, humid atmosphere.
According to Rod Irwin, chairman of the aerodynamics group at the Royal Aeronautical Society, the conditions under which a cone of steam occurs immediately precede an aircraft breaking the sound barrier. However, this phenomenon is usually photographed at speeds slightly less than the speed of sound.
The surface layers of air are denser than the atmosphere at high altitudes. When flying at low altitudes, increased friction and drag occur.
By the way, pilots are prohibited from breaking the sound barrier over land. “You can go supersonic over the ocean, but not over a solid surface,” explains Irwin. “By the way, this circumstance was a problem for the supersonic passenger liner Concorde - 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.
To photograph 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 the shock wave.
When air pressure changes, the air temperature drops and the moisture it contains turns into condensation.
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) formed around the model.
During blowing, no cones of condensation are created around the models, since the air used in wind tunnels is pre-dried.
Water vapor cones are associated with shock waves (of which there are several) that form around the aircraft as it gains 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 hold moisture, and condensation forms in the shape of a cone, as in this video:
“The visible vapor cone is caused by a shock wave, which creates a difference in pressure and temperature in the air surrounding the aircraft,” Irwin says.
Many of the best photographs of the phenomenon are of US Navy aircraft - not surprising, given that warm, moist air near the sea's surface tends to make the Prandtl-Glauert effect more pronounced.
Such stunts are often performed by F/A-18 Hornet fighter-bombers, the main type of carrier-based aircraft in American naval aviation.
The shock when an aircraft reaches supersonic speed is difficult to detect with the naked eye.
The same combat vehicles are used by members of the US Navy Blue Angels aerobatic team, who skillfully perform maneuvers in which a condensation cloud forms around the aircraft.
Because of 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 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 with 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 speeds, and partially at subsonic speeds.
“The plane is not necessarily flying at supersonic speed, but the air flows over the upper surface of the wing at a higher speed than the lower surface, which leads to a local shock wave,” says Irwin.
According to him, for the Prandtl-Glauert effect to occur, certain climatic conditions are necessary (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 plane was captured surrounded by a spectacular cloud of water vapor, which many of us mistakenly take as a sign of reaching supersonic speed.
Stephen Dowling
An amazing sight is a cone of steam appearing around an airplane flying at transonic speed. This amazing effect, known as the Prandtl-Gloert effect, causes the eyes to open wide and the jaw to drop. But what is its essence?
(Total 12 photos)
1. Contrary to popular belief, this effect does not appear when the plane breaks the sound barrier. The Prandtl-Gloert effect is also often associated with supersonic bang, which is also not true. Ultra-high bypass aircraft engines can create this effect at takeoff speed because the engine inlet is low pressure and the fan blades themselves operate at transonic speed.
2. The reason for its occurrence is that an airplane flying at high speed creates an area of high air pressure in front of it and an area of low pressure behind it. After the plane passes, the area of low pressure begins to fill with ambient air. In this case, due to the sufficiently high inertia of air masses, first the entire low pressure area is filled with air from nearby areas adjacent to the low pressure area.
3. Imagine an object moving at transonic speed. Transonic speed is different from the speed of sound. The sound barrier is broken at a speed of 1235 km/h. Transonic speed is below, above or near the speed of sound and can vary from 965 to 1448 km/h. Therefore, this effect can occur when the aircraft is moving at a speed less than or equal to the speed of sound.
4. And yet it’s all about the sound - the “visibility” of this steam cone behind the plane depends on it. The cone shape is created by the force of sound (in the case of airplanes) moving faster than the sound waves it produces. The Prandtl-Gloert effect arises as a result of the wave nature of sounds.
5. Again, think of the plane as the source and the sound as the crest of the wave. These sound wave crests are a series or shell of overlapping circles. When the waves overlap each other, a cone shape is created, and the tip is the source of the sound. So far invisible.
6. For the effect to become visible to the human eye, one more thing is needed - humidity. When the humidity is high enough, the air around the cone condenses and forms the cloud we see. As soon as the air pressure returns to normal, the cloud disappears. The effect almost always occurs on planes flying over the ocean in the summer - the combination of water and heat gives the desired level of humidity.
7. Here you can destroy another one. Some believe that the Prandtl-Gloert effect occurs as a result of fuel combustion.
8. You can probably understand if you think that this effect is a contrail, that is, an unnatural cloud appearing from condensed water vapor produced by engine exhaust. However, this is not the same thing. The water vapor is already there - it's already in the air before the plane even passes through it.
9. Air pressure is also worth mentioning. When an airplane is moving at transonic speed, the air pressure around it is called an N-wave because when pressure varies with time, the result is similar to the letter N.
10. If we could slow down the blast wave passing through us, we would see the leading compression component. This is the beginning of the N. The horizontal stick occurs when the pressure drops, and when the normal atmospheric pressure returns to the final point, the letter N is created.
11. The effect is named after two outstanding scientists who discovered this phenomenon. Ludwig Prandtl (1875 – 1953) was a German scientist who studied the development of systematic mathematical analysis in aerodynamics. Hermann Glauert (1892 – 1934) was a British aerodynamicist.
12. Believe it or not, you can create this effect yourself. You only need two things: a whip and a day with high humidity. If you can whip a whip like Indiana Jones, you'll see a similar effect. Although, you shouldn't try this at home.
MOSCOW, April 15 - RIA Novosti, Tatyana Pichugina. Aromatherapy is not part of the arsenal of modern medicine; it is reserved for beauty salons and massage rooms. Nevertheless, scientists are trying to understand how smell affects human behavior, mood, and physiology. RIA Novosti talks about what the science of fragrances has achieved.
Psychologists in Stavropol began to use aromatherapy in their work in the colonyIn women's correctional colony No. 7 in the Stavropol Territory, specialists help women relieve emotional stress with the help of aromatherapy and teach them to work on their psycho-emotional state.Vegetable essential oils in Ancient China were burned to fumigate rooms, the Egyptians added them to solutions for embalming the dead, and the Romans took them with them to thermal baths. But science started doing this relatively recently. The term "aromatherapy" was coined in the 1920s by French chemist Rene-Maurice Gattefosse.
Plants certainly contain beneficial substances. For example, willow bark has been chewed since ancient times to treat inflammation, and then acetylsalicylic acid, now known as aspirin, was discovered in it. But it’s one thing to take medicine in tablets, and quite another to inhale it. How can you confirm that a scent has a therapeutic effect? What is the physical mechanism of action? In aromatherapy, only subjective descriptions are given that cannot be verified. For example, the smell of rosemary is reported to clear the mind and improve memory, while lavender calms and relieves stress, anxiety, depression, and treats insomnia. In general, juniper oil has 17 beneficial effects: from an aphrodisiac to a sedative.
The Science of Fragrance
Since the 1980s, a new scientific direction has been developing - aromacology, that is, the study of how odors affect physiology and health. In 2007, American scientists analyzed all articles that published data on the healing effects of odors. Only 18 of them were considered accessible for scientific analysis, and even then with certain reservations. Conducting such studies is difficult because there is a lot of subjective stuff in them, it is unclear how the experimental technique affects the result, and, most importantly, it is not known what the mechanism of the effect of odor on the body is.
Perhaps the aroma molecules directly affect the olfactory neurons and then the brain or the endocrine system. Or chemical substances enter the blood through the nose or the mucous membrane of the lungs and then spread throughout the body. This is confirmed by experiments on rodents, in which molecules of inhaled essential oils were found in the blood. In other experiments, rats were calmed by inhaling cedrol, a component of cedar, even though their sense of smell was damaged. Of course, treatment with odors would be convenient, because the effect after inhalation is immediate, and the dose of the substance required is much less than when taking tablets. But to develop scientifically based aromatherapy, we need to understand the mechanism of action of smell, and this is still a long way off.
Interesting results were obtained from the experiments of scientists from Austria with linalool, the main component of lavender oil. When it was applied to the skin of experimental participants, their systolic blood pressure (upper) dropped slightly. This can be considered as an analogue of massage, but the fact that massage itself calms and relieves tension prevents the therapeutic effect of essential oil from being recognized.
In Russia, the project “The Influence of the Odor Environment on the Physiological Status and Cognitive Processes of Humans” is supported by the Russian Science Foundation. Its participants are from the A. N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences, the Institute of Information Transmission Problems named after. A. A. Kharkevich and Oryol State University found that the smells of lavender and mint improve the memory of schoolchildren aged 10-11 years. Analysis of participants' saliva before and after the experiment showed that inhaling peppermint most strongly reduced levels of the hormone cortisol, which regulates stress. Since it is known from other studies that high levels of cortisol in the body weakens memory, scientists conclude that mint relieves stress.
Full of emotions
All observed effects can be explained differently - through psychological influence. That is, a person reacts to smell according to his experience and expectations, as well as through learning. This hypothesis is supported by the fact that people experience emotions and change behavior in accordance with whether the smell is pleasant or not. For example, visitors to a supermarket that smells good are more likely to help other shoppers. Company employees also work better and set higher goals for themselves if the room smells nice.
Another factor is preconceived notions. When 90 female students were told that a pleasant room smell was relaxing, their heart rates and skin conductance actually decreased, even though they only sprayed lavender and neroli orange oil. All students noted that their mood improved. They said the same thing after being in a room with a placebo, that is, an odorless substance.
Proponents of the psychological hypothesis believe that the chemical nature of the smell is secondary, the main thing is the mental impact. To some extent, this is evidenced by cultural, individual and even gender differences in the perception of odors. For example, men who walked through the forest for three days in a row had a decrease in the level of the hormone adrenaline. There is also evidence that aromatherapy relieves depression. In general, so far the psychological hypothesis of aromatherapy is better confirmed by experiments.
Regardless of whether aromatherapy is scientific or not, we should not forget that the components of essential oils can cause allergies, especially with prolonged exposure.
An amazing sight is a cone of steam appearing around an airplane flying at transonic speed. This amazing effect is known as the Prandtl-Gloert effect. What is its essence?
1. Contrary to popular belief, this effect does not appear when the plane breaks the sound barrier. The Prandtl-Gloert effect is also often associated with supersonic bang, which is also not true. Ultra-high bypass aircraft engines can create this effect at takeoff speed because the engine inlet is low pressure and the fan blades themselves operate at transonic speed.
2. The reason for its occurrence is that an airplane flying at high speed creates an area of high air pressure in front of it and an area of low pressure behind it. After the plane passes, the area of low pressure begins to fill with ambient air. In this case, due to the sufficiently high inertia of air masses, first the entire low pressure area is filled with air from nearby areas adjacent to the low pressure area.
3. Transonic speed is different from the speed of sound. The sound barrier is broken at a speed of 1235 km/h. Transonic speed is below, above or near the speed of sound and can vary from 965 to 1448 km/h. Therefore, this effect can occur when the aircraft is moving at a speed less than or equal to the speed of sound.
4. And yet it’s all about the sound - the “visibility” of this steam cone behind the plane depends on it. The cone shape is created by the force of sound (in the case of airplanes) moving faster than the sound waves it produces. The Prandtl-Gloert effect occurs as a result of the wave nature of sounds.
5. Again, think of the plane as the source and the sound as the crest of the wave. These sound wave crests are a series or shell of overlapping circles. When the waves overlap each other, a cone shape is created, and its tip is the source of the sound. So far invisible.
6. For the effect to become visible to the human eye, one more thing is needed - humidity. When the humidity is high enough, the air around the cone condenses and forms the cloud we see. As soon as the air pressure returns to normal, the cloud disappears. The effect almost always occurs on planes flying over the ocean in the summer - the combination of water and heat gives the desired level of humidity.
7. Here you can destroy another myth. Some believe that the Prandtl-Gloert effect occurs as a result of fuel combustion.
8. Perhaps this can be understood if we consider that this effect is a contrail, that is, an unnatural cloud appearing from condensed water vapor, which is produced by engine exhaust. However, this is not the same thing. The water vapor is already there - it's already in the air before the plane even passes through it.
9. Air pressure is also worth mentioning. When an airplane is moving at transonic speed, the air pressure around it is called an N-wave because when pressure varies with time, the result is similar to the letter N.
10. If we could slow down the blast wave passing through us, we would see the leading compression component. This is the beginning of the N. The horizontal stick occurs when the pressure drops, and when the normal atmospheric pressure returns to the final point, the letter N is created.
11. The effect is named after two outstanding scientists who discovered this phenomenon. Ludwig Prandtl (1875 - 1953) was a German scientist who studied the development of systematic mathematical analysis in aerodynamics. Hermann Glauert (1892 - 1934) was a British aerodynamicist.
12. Believe it or not, you can create this effect yourself. You only need two things: a whip and a day with high humidity. If you can whip a whip like Indiana Jones, you'll see a similar effect.
13. It is interesting that the pilot of a modern supersonic aircraft has a good sense of “overcoming” the sound barrier with his aircraft: when switching to supersonic flow, an “aerodynamic shock” and characteristic “jumps” in controllability are felt.
NEWS IN PHOTOS
Ludwig Prandtl (German Ludwig Prandtl, February 4, 1875, Freising - August 15, 1953, Göttingen) - German physicist. He made significant contributions to the fundamentals of hydrodynamics and developed the boundary layer theory. One of the similarity criteria (Prandtl number) was named in his honor, as well as a hydro-aerometric device, which became a classic air pressure receiver for many airplanes and helicopters (Prandtl tube). He defended his doctoral dissertation at the Technical University of Munich in 1900. He was a professor in Hanover and from September 1, 1904 in Göttingen.
Ludwig Prandtl was born in Freising, near Munich. His mother was often sick, so the boy spent a lot of time with his father, an engineering professor. Under his influence, he learned to observe nature and reflect on his observations. In 1894, Prandtl entered the Technical University of Munich, from which he graduated six years later with a PhD in fluid mechanics. After defending his dissertation, young Prandtl worked on improving factory equipment. In 1901, Prandtl was offered a position as professor of fluid mechanics at the Technical School of Hannover, later the University of Hannover. It was there that he wrote his main works. In 1904, he published a fundamental work - “Fluid Flow in Very Little Friction”. In his work, he first described the theory of the boundary layer and its effect on drag and stall, thus providing an explanation for the stall phenomenon. The approximate boundary layer theory proposed by Prandtl is widely used today. After the publication of this work, Prandtl was offered a chair at the University of Göttingen. In the next decade, Prandtl founded the strongest school of aerodynamics, on the basis of which the Kaiser Wilhelm Society for the Study of Liquid and Gas Flows was organized in 1925 (now it is called the Max Planck Society). Continuing research begun by Frederick Lanchester in 1902–1907, Prandtl joined forces with physicist Albert Bertz and engineer Michael Munch to study the lift of a real aerodynamic wing using mathematical apparatus. The results of the study were published in 1918-1918 and are now known as the Lanchester-Prandtl wing theory. In 1908, Prandtl and his student Theodor Mayer first proposed the theory of a supersonic shock wave. Based on the Prandtl-Mayer flow, the world's first supersonic wind tunnel was built in Göttingen in 1909. In 1929, together with Adolf Busemann, he proposed a method for designing a supersonic nozzle. Currently, all supersonic nozzles and wind tunnels are designed based on this theory. Prandtl's student Theodor von Karman developed the theory of supersonic flow. In 1922, Prandtl and mathematician Richard Edler von Mises founded GAMM (the International Association of Applied Mathematics and Mechanics). Until 1945, Prandtl collaborated with the German Reich Ministry of Aviation. Among his works: compression of liquid under high-speed flow conditions - the Prandtl-Gloert effect, works on meteorology and the theory of elasticity. Prandtl worked at the University of Göttingen until his death on August 15, 1953. He is called the father of modern aerodynamics.
Herman Glauert (in domestic scientific and educational gas-dynamic literature the form is almost exclusively used Glauert , October 4, 1892, Aldershot - August 6, 1934, Sheffield) - British scientist, specialist in the field of aerodynamics, until December 1934 - scientific director of the Royal Aeronautical Center in Farnborough, member of the Royal Society of London.
Born into the family of an industrialist and emigrant from Germany, Louis Glauert. He graduated with honors from King Edward VII's School and studied at Trinity College, Cambridge. Glauert is known for his work in the field of aerodynamics, in particular, in 1928 he was the first to publish a work containing a formula, later called the “Prandtl-Glauert formula”. Tragically died in 1934, falling under a tree torn out by the wind.
Prandtl-Gloert effect
