Jellyfish is known as one of the "world's most efficient swimmers". It can swim several meters with a slight swing, and it swims continuously in the water, and the total distance it travels in a day is as high as several kilometers. . Why can jellyfish maintain long-distance movement for such a long time?
The mystery of jellyfish "racing"
Speaking of jellyfish, an image emerged in everyone's mind: a big head, thin "hands and feet", a mushroom-shaped balloon "weakly" drifting with the waves in the vast ocean. How could such a creature be a master swimmer? In fact, the reason why the jellyfish swims very efficiently is not because of how fast it swims, but because it swims thousands of meters in a day, and it only consumes very little energy when it swims such a long distance. Sharks, dolphins and other underwater "sportsmen" consume much less oxygen and food. What is the swimming secret of jellyfish?
The swimming secrets of jellyfish are clearly visible under the lens of a scientist's high-speed camera. The jellyfish was kept in a glass water tank, and a high-speed camera recorded every detail of its swimming. When the jellyfish shrinks its bell-shaped body (the disk-shaped structure with the head like an umbrella), the water flow is drawn close to its body, and a low-pressure area is formed around it. The fluid has the characteristics of moving from the high-pressure area to the low-pressure area, so The jellyfish is pushed forward. This is not over yet. After the jellyfish moves forward, the bell-shaped body will be relaxed, and the high-pressure water behind will rush to the jellyfish. This provides the jellyfish with a second wave of forward momentum, allowing the jellyfish to swim forward for a long period of time with one contraction. distance. Moreover, due to the elastic body structure of the jellyfish, almost no energy is consumed when relaxing the bell-shaped body, so it can swim forward in a very labor-saving way.
If you are not satisfied with this speed, the jellyfish has another trick-making "doughnuts." The jellyfish will rapidly shrink in different positions to produce two underwater vortex rings with opposite rotation directions. They collide and squeeze each other, generating a new impulse to push the jellyfish forward. Under the action of this force, the swimming speed of the jellyfish increased by 41%, and the cumulative movement distance of each systole and relaxation cycle increased by 61%. Scientists have observed that there are loops of muscle tissue growing on the edge of the jellyfish’s bell-shaped body, which is the secret weapon for jellyfish to easily stir the water.
"Jellyfish" fly away from the sea
If a jellyfish makes a "doughnut" on the water, it may be able to "fly" on the sea surface. In fact, such a "doughnut" is a big driving force for the plane to fly off the ground. Before the plane took off, there was a strong squeezed mass of air between the plane and the ground. This mass of air provided the plane with reverse lift and the plane was able to take off. The two reverse "donuts" of the jellyfish collide with each other to form a vortex ring like the interaction between the wings and the ground. The jellyfish is at the center of the two vortex rings and receives forward and upward thrust.
During the Cold War, the Soviet Union showed the world a peculiar means of transportation. It looked like a plane galloping in the air, but it was close to the sea, like a ship sailing on the sea for a period of time, and then it flew up in a flash. sky. Is this an airplane or a ship? Ships do not fly, and our common airplanes all take off from land. How do airplanes take off on the soft sea?
The scientific name of this vehicle is called ground-effect aircraft. Although it is rare, people have studied it for a long time. From the first ground-effect aircraft test conducted by the French in 1897, humans’ theoretical research and research on ground-effect aircraft The practice test has a history of hundreds of years, and the principle used is the same as the "doughnut" of jellyfish. This principle is called ground effect. It refers to the aerodynamic interference of the ground on the object when the moving object moves close to the ground. Simply put, when the moving object is close to the stationary ground, it will not fall directly. On the ground, the object stirs the air, and the air between the ground and the object produces a counterforce to the object, so the object will float near the ground for a period of time. A simple little experiment can let us see the existence of the ground effect: throw a paper towel from a high altitude, and when it approaches the ground, it will float above for a period of time instead of directly falling.
Using ground effects, the aircraft can take off on soft seas. When the aircraft flies close to the ground or water surface, the aircraft accelerates, the airflow above the wings is faster and the pressure decreases, and the airflow below decelerates and the pressure increases. The pressure difference acting on the wing increased significantly, causing the lift to increase suddenly, and the aircraft was "supported".
Compared with ordinary aircraft, ground-effect aircraft has many advantages. It is not restricted by air control, is convenient to sail, and can take off and land anywhere on the water. It has good maneuverability and can reach islands that are difficult to reach by ordinary ships and aircraft. And the waters have a wide range of uses in freight, search and rescue, and investigation. However, the development of ground-effect aircraft is very difficult, and the degree of stability when navigating on the water and turning in the air for landing needs to be improved. Until now, it has not been as common as land aircraft.
After discovering the ability of jellyfish to make "doughnuts", scientists studying ground-effect aircraft may be able to learn from jellyfish how to use "doughnuts" to make the aircraft fly faster and more stable.
"Jellyfish" racing on land
Ground-effect aircraft capable of flying over the sea
Regardless of whether the ground-effect aircraft can learn from the jellyfish, at least the racing cars on land have long noticed the power of the "doughnuts". With their help, modern racing cars are continuing to develop in a faster and more stable direction.
We know that the most important thing about a car is speed. The shock brought by the extreme speed of the speed makes all the viewers amazed, and also makes the racers addicted to it and can't stop it. The racing company has thought of many ways to increase the speed of the car. The body is made into a slender streamline, the tail is turned into fins, and the front nose is greatly raised. All of these are to reduce air resistance and accelerate the speed of the car. However, the engineers soon discovered that these methods were not practical. The car made in this way was easy to roll over when turning, and it was also easy to overturn when decelerating, which caused a great threat to the driver's life and safety. This problem has puzzled the racing company. How can we increase stability while reducing drag?
The other side of the ground effect helped them. Scientists have discovered that when the height and angle of the wing are changed, the flow rate and pressure of the gas near the wing will change. If the wing is tilted downwards, that is, when the trailing edge of the wing is very close to the ground, the gas will be blocked under the wing, causing the pressure under the wing to increase, which directly increases the lift; in turn, the wing is tilted upwards and the flow When the air under the wing is reduced and the air above is pressed downward, the grip of the aircraft will increase. If such an inverted wing is mounted on a car, will it also improve the car’s grip?
In 1968, the car was fitted with an inverted wing (called tail wing in a car) for the first time. The diverted air produced downforce on the car. When the car turned again, this downforce caused the drag and turn of the car. The centrifugal force cancels each other out, greatly reducing the occurrence of rollover. In 1970, the American racing company Chevrolet applied the ground effect to the extreme. They installed two turbofans at the rear of the car to continuously extract the air under the car during operation, which maximized the pressure of the air above. Later, although this method of air extraction was banned because it would interfere with other cars, changing the height and angle of the rear wing, and changing the gas diffusion device of the car chassis has officially become a must to increase the grip of the car without affecting the speed of the car. The method is still the research focus of the major racing companies until now.
It seems that "doughnuts" are not as simple as we thought. When "doughnuts" are made in different positions, their effect on fluids will change, resulting in different effects. If we want to use "doughnuts" freely, we need to do more research.
The rear wing of the racing car helps to improve the grip
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