There are fluid mechanics in the starry sky?

Author:Institute of Physics of the Ch Time:2022.09.19

From ancient times to the present, the vast stars have always given unlimited reveries, and Van Gogh, a post -impressionist painter in the Netherlands. In the famous painting "Star Moon Night", he vividly depicts the starry sky full of sports and changes with exaggerated methods.

In the painting, the vortex of the constellation swept over the overnight sky, and scientists found through the research on color brightness, and the turbulence structure (Amazing) hidden in this star sky! Today, Xiaobian wants to show you the mystery of turbulence ~

What is turbulent? Is it far from our lives? When you look up at Bai Yunsi, remember that the sky is doing flow experiments for you, demonstrating a variety of turbulence (it sounds romantic).

The story must also start from Renault's circular pipe experiment in 1883. Renault found through experiments that the flow of fluids in the pipeline can show two very different diversion.

When the flow velocity is very small, the fluid flows layer, and does not mix with each other. There are not only sliding between adjacent streams, but also mixed, at this time the turbulence is formed. The phenomenon of turning from layer flow to turbulence is called turning.

In order to characterize the flow of fluids, scientists introduced the countless number of reunion. At this time, the layer flow and turbulence of the fluid can be distinguished with the size of the Renault number. Renault number (RE) reflects the ratio of the inertia and viscosity of fluid mass. Its definition is: Re =

V, 分 and μ are the flow rate, density and viscosity coefficient of fluid, respectively, and D is a feature length. The physical meaning of Renault is the ratio of inertial force to viscosity. According to the definition and physical significance of Renault, the smaller the number of Renault numbers, the smaller the inertia compared to the viscosity force, and the greater the effect of viscosity. Therefore, the fluid can maintain a stable stratum, otherwise it is turbulent.

In order to allow the little friends to further feel the beauty in the fluid flow, Xiaobian decided to bring you the magical phenomenon in fluid mechanics -Carmen Vortex Street. Not much to say, first picture first!

So, what is Carmen Vortex Street? How did it form? What does it have to do with turbulence? Let's listen to Xiaobian's detail!

Carmen Vortex Street is very common in our daily lives. For example, the water flows across the pier, and the wind blows through the tower, chimneys, and wires. When the Carmen Vortex Street is normal under certain conditions to bypass certain objects, the dual -column vortex with the opposite rotation direction and the arranged rules on both sides of the object is formed after non -linear effects. Since it is called Carmen Vortex Street, is it found by Mr. Feng Carmen, a aerodynamist? In fact, it is not, the reason why it is called Carmen Vortex Street is because Mr. von Carmen first systematically explained this phenomenon. The "vortex" is said to be staggered on both sides of the center line of the tail, just like the street lights are staggered on both sides of the road.

Kamen Vortex Street behind Yang Man Yin Island

The formation of Carmen Vortex Street is related to Renault. When RE is 50 to 300, the vortex falling from the object is periodic; when the RE & 300, the vortex starts to start with random falling; as the re continues to increase, the randomness of the vortex falls also increases the randomness of the rotation off. In the end, turbulence was formed.

Although Kamen Vortex Street is "beautiful", it has a destructive effect on the building. It can be described as a real "beautiful killer". In the 1940s, the Tagar Canyon Bridge Wind Destruction accident made people realize the important role of Kamen Vortex Street in architectural safety.

After watching the video, Xiaobian couldn't help but sigh: there is really a modern bridge that was blown down by the wind. After World War II, people studied the cause of the wind destroyed by the Taga Bridge. At the beginning, there were two perspectives. Some people represented by aviation engineers believe that the vibration of the Taca Bridge is similar to the tremor of the wing; the fluid mechanics represented by von Carmen believes that Different from streamlined wings, there are obvious vortex falling off. It should be explained by vortex resonance. In the 1960s, after calculation and experiments, the analysis of von Carmen was correct. The wind destroying accident of the Taca Bridge is a Cammen Vortex Street when the fluid flows through the side wall with a certain rate of flow; Forcing the bridge to vibrate. When the frequency of the distribution is coupled with the inherent frequency of the bridge structure, resonance will occur, causing damage.

The same thing also happened in the Humen Bridge in my country, but it was not as large as the Tagar Bridge, but it occurred more obvious jitter and jitter, mainly because the water horses were set up on the bridge deck, which changed the steel box to change the steel box. The psychic shape of Liang has nothing to do with the overload operation of the Humen Bridge for many years.

Many people think that only when fluid winding cylindrical bodies can produce Kamen Vortex Street, in fact, as long as the boundary layer is separated, the Kamen Vortex Street may occur. To form a streamlined type to avoid the damage effect of the Cammen Vortex Street.

Do you have already felt the beauty of fluid mechanics? In fact, Xiaobian just gave you some basic knowledge about turbulence, and the turbulent movement was very complicated. It is said that the well -known theoretical physicist Vana Hesenburg said before the end of his death: "When I see God, I must ask him two questions -what is the theory of relativity and what is turbulent." Defan also called turbulence as "the last important issue in classic physics." The root cause of the complexity of turbulence movement is that it is a movement of a strong non -linear system. Therefore, the mysterious veil of turbulence has not been fully revealed, and we need to continue studying the laws and mechanisms of the movement.

When looking up at the starry sky next time, remember to watch the various mobile experiments that the sky do for you ~