Art of Nature -turbulence

On July 10, 1923, Heisenburg submitted a 59 -page calculation report entitled "The stability and turbulence of fluid flow" of the 59th pages of the Munich Academy, and published it on the "Physics Magazine". This problem is a classic problem of turbulence -the accurate transition of determining the layer to turbulence is also a very difficult problem, so that only a approximate solution is provided. His degree instructor Arnold said: "I will not give this difficult subject as any other student of my papers." You must know that his students even have outstanding figures such as Wolfgang Pauli.

Figure 1 Doctoral dissertation of Heisenburg [1]

Hessonburg's powerful mathematics ability has made him great achievements in the field of quantum mechanics, but only achieved limited success in turbulence. He once said that if he allows him to ask God's two questions, it is: "Why is quantum mechanics? Why is turbulence?" It is speculated that he is convinced that God can answer the first question. This sentence may be fictional, with different versions everywhere. Nevertheless, Haysonburg has been fighting the problem of turbulence for many years. This is a fact.

Physicist Ferman also tried to study turbulence, saying in the letter to his student Monyuno Kato: "I have studied the theory of turbulence for several years, but it has not succeeded."

Figure 2 Ferman's letter to Nodoyo

In fact, people's understanding of turbulence has been long for a long time. From Da Vinci's manuscript to Van Gogh's "Starry Sky", from Ma Yuan's water map to Japan's Ukiyo -e -paint His artistic brush describes the intuitive visual image of turbulence in the same way.

Figure 3 Da Vinci Manuscript

Figure 4 "Starry Sky" -Dan Van Gogh

Figure 5 "Water Picture Volume -Wave Waves" -Ma Yuan, Southern Song Dynasty

Figure 6 "Kanagawa Surfing" -gei Kitashi, Japan, the 19th century

In nature, the most spectacular large -scale turbulence may be the sun. The sun's spots are related to the so -called sunburn (the huge arched structure that can be seen on the surface of the sun during solar eclipse). The sun is usually extended from the low -level atmosphere of the sun to the crown, and it is usually at least 10 times that of the earth. The sun is surrounded by the magnetic flux tube, and the magnetic pipe tube is arched from the surface of the sun and staggered in the sun. The bottom point of the magnetic pipe tube is constantly colliding, making the surface of the sun a height turbulence. The magnetic flux in the corona is entangled, causing the magnetic pipe tube to be cut off and re -combined. The cutting of this flux tube is realized through the local effect of turbulence in electrical halo.

The sudden release of the quality and energy of the solar surface produces the solar wind, and the quality of the release of spots through the solar system. One to two days after the outbreak of the spray, the earth will be impacted by magnetic storms.

Figure 7 (A) The crowned flux is arched from the light ball layer;

The magnetic field of the Earth makes the charged particles shot into the solar wind of the earth to deflect, which makes us avoid the influence of the solar style. But why are there many planets on the planet that have magnetic fields? The answer seems to be turbulent. Now it is generally believed that the source of these magnetic fields is the turbulence convection in the core of the planet.

Figure 8 The turbulence of the ground nucleus maintains the magnetic field of the earth: (a) the schematic diagram; (b) numerical simulation [2]

Not only the large -scale ocean and atmospheric flow on the planet are turbulent. The atmospheric flow on other planets, especially the giant giant stars, the atmospheric flow of these planets is also highly turbulent. The big red spots on Jupiter are actually a diameter of two to three times the diameter of the earth, which lasted millions of years. The sulfide in the turbulence wrapped in the air made it unique red.

Figure 9 Jupiter big erythema [3]

Of course, all kinds of engineers must face turbulence. The air power resistance on the aircraft or cars is controlled by the turbulent boundary layer. In fact, one of the main obstacles that restrict our design of better wings is the lack of understanding of turbulence. The turbulence on the triangle wing is particularly violent, and the vortex is also displayed on the upper wing surface.

Figure 10 The turbulence vortex on the surface of the triangular wing: (a) downward view; (b) the view [2]

On the other hand, the designer of the engine rely on the turbulence of fuel and gas to maximize efficiency.

Figure 11 During the combustion, the density, combustion rate and temperature image of hydrogen, methane, propane [2]

Turbine is also crucial in the environment. Urban planning must simulate the turbulence of pollutants in cigarettes and automotive engines, and architects need to predict how naturally affects the temperature distribution of the building in the building.

Figure 12 Cylinder Winding: Similar models surrounding buildings flow [2]

Even steel manufacturers and medical researchers have to worry about turbulence, because excessive turbulence in ingots can cause deterioration of metallurgy structure, and the current flowing through our throat and nostrils is usually turbulent.

"Being large and small, can be promoted and hidden; Cao Cao once described the change of dragon. In fact, this narrative very vividly portrayed the natural phenomenon of turbulence as a large -scale scale.

So, what exactly is turbulent? Unfortunately, now people cannot give the turbulence a clear and clear definition. The easiest way, when the flow speed is large to a certain extent, all the flow will produce a random, chaotic movement. People summarize these complicated flow together, call them turbulence, and notice that they have some common characteristics: • Speed ​​on changes in time showing the characteristics of random fluctuations, which are highly disorderly in space distribution;

• The initial micro -disturbance will lead to a huge change in subsequent exercise, so the flow speed is unpredictable.

So, how does turbulence produce? From the above description, you may have noticed that the production of turbulence comes from the instability of flow. The story starts with Renault's round management experiments.

Figure 13 Renault Round Management Experiment

Renault first pointed out the important role played from layer to turbulence in 1883 and the number of Renault in this transition. Renault is concerned about flowing straight and smooth pipes. He let the fluid flow through a thin pipe and inject non -color dyes into a small section of water. When the dye flows downstream to the downstream, it can be clearly seen whether the water flow is stable (stratified) or disorderly (turbulent). By adjusting the parameters in the experiment, he discovered the conditions to ensure orderly flow.

FIG. 14 Pipeline flow in the middle layer flow to turbulence transformation

He found a simple and magical number to predict what will happen. This number cleverly linked the flow -related physical quantity, called Renault numbers

In this formula, 流 is the density of water flow, U is the speed of water flow, D is the diameter of the pipeline, and the µ is the viscosity of the fluid. The viscosity of thick liquids such as honey and corn syrup is very high, and the viscosity of gas such as air is very low. These are the amount that can be measured directly.

There is no physical unit in Renault, which means that no matter which unit system is selected to measure the above physical quantities, Renault numbers are the same. Renault discovered that when the number exceeded 2300, the flow jumped from orderly to turbulent.

This shows that for low speed flows, that is, when the number of Renault is very small, the flow is basically stable. As the speed increases, it will soon reach a critical point. At this time, the system becomes unstable, causing a gradual complicated flow. Until the end, the flow becomes a complete turbulence for sufficient speed. The key point is that fluid movements are almost inherently unstable. Only when the stickiness is high enough can it suppress instability. However, the viscosity of almost all fluids is extremely low. This is the so of water, air, blood, and molten metals in the nucleus and the atmosphere of the sun. This means that turbulence is a natural state of things, and layer flow is often the exception.

references

[1] Werner Heisenberg. Über Stabilität Und Turbulenz von FlüssigkeitsströMen.annalen Der Physik, 379 (15): 577–627, 1924.

[2] Peter Alan Davidson. Turbulence: An introiduction for scientister andNGINEERS. Oxford University Press, 2015.

[3] https://www.nasa.gov/content/jupiters-great-diew-voyager-i.

(Some pictures of the article are derived from the Internet, only for science popularization for reference)

- END -