Historically, the first stationary unit using wind energy was windmill, which was manually guided by the wind. Its main working body was a multi-bladed wheel with a horizontal axis of rotation, installed in the direction of the wind. Such wind turbines were widely used in the Middle Ages and later for grinding grain, lifting and pumping water, as well as for driving some industries. Large factory-made windmills at high wind speeds could develop power up to 60 kW. In the 19th century, the number of windmills in Russia exceeded 200 thousand, their total capacity was approximately 1.3 million kW, and in 1930 there were more than 800 thousand of them in the USSR.
Wind wheels of impeller wind turbines: 1 - multi-bladed, 2 - three-bladed, 3 - two-bladed, 4 - single-bladed with a counterweight
Currently known many different types of windmills - wind turbines(). Wind turbines with winged wind wheels and a horizontal axis of rotation are widely used. Among them, two- and three-bladed wind turbines have received the greatest development. The torque of the wind wheel is created by the lifting force generated when the air flow flows around the profile of the blades. As a result, the kinetic energy of the air flow within the area swept by the blades is converted into mechanical energy of rotation of the wind wheel.
windmills
windmills
The power developed on the axis of the wind wheel is proportional to the square of its diameter and the cube of the wind speed. According to the classical theory of N.E. Zhukovsky for an ideal wind wheel, the wind energy utilization factor £ = 0.593. That is, an ideal one (with an infinite number of blades) can extract 59.3% of the energy passing through its cross section. In reality, in practice, for the best high-speed wheels, the maximum value of the wind energy utilization factor reaches 0.45-0.48, and for low-speed wheels, up to 0.36-0.38.
An important characteristic of the wind wheel is its speed Z, which is the ratio of the speed of the end of the blade to the speed of the wind flow. The end of the blade usually moves in the plane of the wind wheel at a speed that is several times higher than the wind speed. The optimal speed values for a two-blade wheel are 5-7, for a three-blade one - 4-5, for a six-blade one - 2.5-3.5. windmills
Of the design characteristics, the power of a wind wheel is mainly influenced by its diameter, as well as the shape and profile of the blades. Power depends little on the number of blades. The frequency of rotation of the wind wheel is proportional to the speed and speed of the wind and inversely proportional to the diameter. The height of the center of the wheel also affects the amount of power, since the wind speed depends on the height.
Power, as noted, is proportional to wind speed to the third power. At the design wind speed and above, the operation of the wind turbine with rated power is ensured. At wind speeds below the design capacity of a wind turbine, it can be 20–30% of the nominal value or less.
Under such operating conditions, large energy losses occur in generators due to their low efficiency. at low loads, and in asynchronous generators, in addition, large reactive currents occur, which must be compensated. To eliminate this shortcoming, some wind turbines use 2 generators with a rated power of 100 and 20 - 30% of the rated power of the wind turbine. In light winds, the first generator is switched off. In some wind turbines, a small generator also makes it possible to operate the plant at low wind speeds at low speeds with a high wind energy utilization factor. windmills
Installation of a wind wheel in the wind, i.e. perpendicular to the direction of the wind, is produced in units of very low power with the help of a tail (tail), in units of small and medium power - by means of a windrose mechanism, and in modern large installations - by a special orientation system that receives a control impulse from a wind direction sensor (weather vane) installed at the top of the wind turbine nacelle. The windrose mechanism is one or two small windwheels, the plane of rotation of which is perpendicular to the plane of rotation of the main wheel, working to drive the worm that turns the platform of the wind turbine head until the windroses lie in a plane parallel to the direction of the wind.
Winged with a horizontal axis of rotation can be located in front of the tower and behind it. In the latter case, the blade is subjected to constant repeated action of variable forces while passing through the shadow of the tower, which at the same time significantly increases the noise level. A number of methods are used to control the power and limit the speed of rotation of the wind wheel, including the rotation of the blades or parts of them around their longitudinal axis, as well as flaps, valves on the blades, and other methods. windmills
The main advantages of wind turbines with a horizontal axis of rotation of the wind wheel is that the conditions for the flow of air around the blades are constant, do not change when the wind wheel turns, but are determined only by the wind speed. Due to this, as well as the rather high value of the wind energy utilization factor, vane-type wind turbines are currently the most widely used.
Savonius rotor: a) two-bladed, b) four-bladedAnother type of wind turbine is the Savonius rotor.
The torque occurs when the Savonius rotor flows around the rotor due to the different resistance of the convex and concave parts. Savonius rotor. The wheel is simple, but has a very low wind energy utilization factor - only 0.1 - 0.15. windmills
Wind power plants () with a vertical rotor: a - F-shaped, b - L-shaped, c - with straight blades. 1 - tower (shaft), 2 - rotor, 3 - extensions, 4 - support, 5 - torque transmission
In recent years, in a number of foreign countries, especially in Canada, they began to develop a wind turbine with a Darrieus rotor, proposed in France in 1920. This Darrieus rotor has a vertical axis of rotation and consists of two to four curved blades.
The blades form a spatial structure that rotates under the action of lifting forces arising on the blades from the wind flow. In the Darrieus rotor, the wind energy utilization factor reaches values of 0.30 - 0.35. Recently, the development of a Darrieus rotary engine with straight blades has been carried out.
Windmills with vertical type
The main advantage of Darrieus wind turbines (rotors) is that they do not need a wind-orientation mechanism. They have a generator and other mechanisms placed at a slight height near the base. All this greatly simplifies the design. However, a serious organic disadvantage of these wind turbines is a significant change in the conditions of the flow around the wing during one revolution of the Darrieus rotor, which is cyclically repeated during operation.
This can cause fatigue phenomena and lead to the destruction of the elements of the Darrieus rotor and serious accidents, which must be taken into account when designing the Darrieus rotor (especially at high power wind turbines). In addition, to get started, they need to be untwisted.
Dependences of the wind energy utilization factor £, on the speed Z for various windmills shown in the figure.
Typical dependences of the wind energy utilization factor £ on the speed of the wind wheel Z: 1 - an ideal winged wind wheel; 2,3 and 4 - two-, three- and multi-bladed impeller wind turbines; 5 - Darier rotor; 6 - Savonius rotor; 7 – four-blade wind wheel of a Danish mill
It can be seen that two- and three-blade wheels with a horizontal axis of rotation have the largest value of ξ. For them, high £ is preserved in a wide range of speed Z. The latter is essential, since wind turbines have to operate at wind speeds that vary within wide limits. That is why installations of this type have received the greatest distribution in recent years.
Most types of wind turbines have been known for so long that history is silent about the names of their inventors.
Types of wind turbines:
The main types of wind turbines are shown in the figure. They are divided into two groups:
wind turbines with a horizontal axis of rotation (vane type) (2...5);
wind turbines with a vertical axis of rotation (carousel: bladed (1) and orthogonal (6)).
Types of vane wind turbines differ only in the number of blades.
winged
For vane wind turbines, the greatest efficiency of which is achieved when the air flow is perpendicular to the plane of rotation of the blades-wings, a device for automatically rotating the axis of rotation is required.
For this purpose, a stabilizer wing is used.
Carousel wind turbines have the advantage that they can work in any direction of the wind without changing their position.
Wind energy utilization factor (see fig.) of vane wind turbines is much higher than that of carousels.
At the same time, carousels have much more torque.
It is maximum for carousel bladed units, at zero relative wind speed.
The spread of winged wind turbines is explained by the magnitude of their rotation speed.
They can be directly connected to an electric current generator without a multiplier.
The rotation speed of vane wind turbines is inversely proportional to the number of wings, therefore, units with more than three blades are practically not used.
carousel
The difference in aerodynamics gives carousels an advantage over traditional windmills.
With an increase in wind speed, they quickly increase the traction force, after which the rotation speed stabilizes.
Carousel wind turbines are low-speed and this allows the use of simple electrical circuits, for example, with an asynchronous generator, without the risk of an accident in case of an accidental gust of wind.
Slowness puts forward one limiting requirement - the use of a multi-pole generator operating at low speeds.
Such generators are not widely used, and the use of multipliers (multiplier [lat. Multiplicator - multiplying] - step-up gearbox) is not effective, due to the low efficiency of the latter.
An even more important advantage of the carousel design was its ability, without additional tricks, to keep track of “where the wind is blowing from”, which is very important for surface scouring flows.
Wind turbines of this type are built in the USA, Japan, England, Germany, Canada.
Carousel bladed wind turbine is the easiest to operate. Its design provides maximum torque when starting the wind turbine and automatic self-regulation of the maximum rotation speed during operation.
With an increase in load, the rotation speed decreases and the torque increases up to a complete stop.
Orthogonal
Orthogonal wind turbines, as experts believe, are promising for large-scale energy.
Today, wind fans of orthogonal structures face certain difficulties. Among them, in particular, the launch problem.
In orthogonal installations, the same wing profile is used as in a subsonic aircraft (see Fig. 6).
The aircraft, before "leaning" on the lifting force of the wing, must run up. The same is true in the case of an orthogonal setup.
First, you need to bring energy to it - spin it up and bring it to certain aerodynamic parameters, and only then, it will switch from engine mode to generator mode.
Power take-off starts when the wind speed is about 5 m/s, and the rated power is reached at a speed of 14...16 m/s.
Preliminary calculations of wind turbines provide for their use in the range from 50 to 20,000 kW.
In a realistic installation with a power of 2000 kW, the diameter of the ring along which the wings move will be about 80 meters.
The powerful wind turbine has large dimensions. However, you can get by with small ones - take a number, not a size.
By supplying each electric generator with a separate converter, it is possible to sum up the output power generated by the generators.
In this case, the reliability and survivability of the wind turbine increases.
WIND POWER
a device that converts wind energy into rotational energy. The main working body of a wind turbine is a rotating unit - a wheel driven by the wind and rigidly connected to the shaft, the rotation of which drives the equipment that performs useful work. The shaft is installed horizontally or vertically. Wind turbines are usually used to generate energy consumed periodically: when pumping water into tanks, grinding grain, in temporary, emergency and local power networks.
History reference. Although surface winds do not always blow, change their direction and their strength is not constant, the wind turbine is one of the oldest machines for obtaining energy from natural sources. Due to the dubious reliability of ancient written reports about wind turbines, it is not entirely clear when and where such machines first appeared. But, judging by some records, they already existed before the 7th century. AD It is known that they were used in Persia in the 10th century, and in Western Europe the first devices of this type appeared at the end of the 12th century. During the 16th century the tent type of the Dutch windmill was finally formed. No special changes were observed in their design until the beginning of the 20th century, when, as a result of research, the shapes and coatings of the wings of mills were significantly improved. Since low-speed machines are bulky, in the second half of the 20th century. began to build high-speed wind turbines, i.e. those whose wind wheels can make a large number of revolutions per minute with a high coefficient of utilization of wind energy.
Modern types of wind turbines. Currently, three main types of wind turbines are used - drum, vane (screw type) and rotary (with an S-shaped repeller profile).
Drum and winged. Although the drum-type wind wheel has the lowest wind energy utilization rate compared to other modern repellers, it is the most widely used. On many farms, it is used to pump water if for some reason there is no mains electricity. A typical shape of such a wheel with sheet metal blades is shown in fig. 1. Drum and vane wind wheels rotate on a horizontal shaft, so they must be turned into the wind to get the best performance. To do this, they are given a rudder - a blade located in a vertical plane, which ensures the turn of the wind wheel to the wind. The wheel diameter of the world's largest vane-type wind turbine is 53 m, the maximum width of its blade is 4.9 m. The wind wheel is directly connected to an electric generator with a capacity of 1000 kW, which develops at a wind speed of at least 48 km/h. Its blades are adjusted in such a way that the rotation speed of the wind wheel remains constant and equal to 30 rpm in the wind speed range from 24 to 112 km/h. Due to the fact that the winds blow quite often in the area where such wind turbines are located, the wind turbine usually generates WIND 50% of maximum power and feeds the public power grid. Vane wind turbines are widely used in remote rural areas to provide electricity to farms, including charging the batteries of radio communication systems. They are also used in the onboard power plants of aircraft and guided missiles.
S-shaped rotor. The S-shaped rotor mounted on a vertical shaft (Fig. 2) is good because a wind turbine with such a repeller does not need to be brought into the wind. Although the torque on its shaft changes from a minimum to one-third of its maximum value in half a turn, it does not depend on the direction of the wind. When a smooth circular cylinder rotates under the influence of wind, a force perpendicular to the direction of the wind acts on the body of the cylinder. This phenomenon is called the Magnus effect, after the German physicist who studied it (1852). In 1920-1930, A. Flettner used rotating cylinders (Flettner rotors) and S-shaped rotors instead of bladed wind wheels, and also as propellers for a ship that made the transition from Europe to America and back.
Wind energy utilization factor. The power received from the wind is usually small - less than 4 kW is developed by an outdated type of Dutch windmill at a wind speed of 32 km / h. The power of the wind flow that can be used is formed from the kinetic energy of air masses moving per unit time perpendicular to the area of a given size. In a wind turbine, this area is determined by the windward surface of the repeller. When taking into account the height above sea level, air pressure on it and its temperature, the available power N (in kW) per unit area is determined by the equation N = 0.0000446 V3 (m/s). The coefficient of wind energy utilization is usually defined as the ratio of the power developed on the wind turbine shaft to the available power of the wind flow acting on the windward surface of the wind wheel. This coefficient becomes maximum at a certain ratio between the speed of the outer edge of the wind wheel blade w and the wind speed u; the value of this ratio w/u depends on the type of wind turbine. The wind energy utilization factor depends on the type of wind wheel and ranges from 5-10% (Dutch mill with flat wings, w/u = 2.5) to 35-40% (profiled vane repeller, 5 Ј w/u Ј 10).
LITERATURE
Wind power. M., 1982 Yaras L. et al. Wind energy. M., 1982
Collier Encyclopedia. - Open Society. 2000 .
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The content of the article
wind turbine, a device that converts wind energy into rotational energy. The main working body of a wind turbine is a rotating unit - a wheel driven by the wind and rigidly connected to the shaft, the rotation of which drives equipment that performs useful work. The shaft is installed horizontally or vertically. Wind turbines are usually used to generate energy consumed periodically: when pumping water into tanks, grinding grain, in temporary, emergency and local power networks.
History reference.
Although surface winds do not always blow, change their direction and their strength is not constant, the wind turbine is one of the oldest machines for obtaining energy from natural sources. Due to the dubious reliability of ancient written reports about wind turbines, it is not entirely clear when and where such machines first appeared. But, judging by some records, they already existed before the 7th century. AD It is known that they were used in Persia in the 10th century, and in Western Europe the first devices of this type appeared at the end of the 12th century. During the 16th century the tent type of the Dutch windmill was finally formed. No special changes were observed in their design until the beginning of the 20th century, when, as a result of research, the shapes and coatings of the wings of mills were significantly improved. Since low-speed machines are bulky, in the second half of the 20th century. began to build high-speed wind turbines, i.e. those whose wind wheels can make a large number of revolutions per minute with a high coefficient of utilization of wind energy.
Modern types of wind turbines.
Currently, three main types of wind turbines are used - drum, vane (screw type) and rotary (with an S-shaped repeller profile).
Drum and winged.
Although the drum-type wind wheel has the lowest wind energy utilization rate compared to other modern repellers, it is the most widely used. On many farms with it pump water if for any reason there is no mains electricity. A typical shape of such a wheel with sheet metal blades is shown in fig. 1. Drum and vane wind wheels rotate on a horizontal shaft, so they must be turned into the wind to get the best performance. To do this, they are given a rudder - a blade located in a vertical plane, which ensures the turn of the wind wheel to the wind. The wheel diameter of the world's largest vane-type wind turbine is 53 m, the maximum width of its blade is 4.9 m. The wind wheel is directly connected to an electric generator with a capacity of 1000 kW, which develops at a wind speed of at least 48 km/h. Its blades are adjusted in such a way that the rotation speed of the wind wheel remains constant and equal to 30 rpm in the wind speed range from 24 to 112 km/h. Due to the fact that the winds blow quite often in the area where such wind turbines are located, the wind turbine usually generates ~ 50% of the maximum power and feeds the public power grid. Vane wind turbines are widely used in remote rural areas to provide electricity to farms, including charging the batteries of radio communication systems. They are also used in the onboard power plants of aircraft and guided missiles.
S-shaped rotor.
The S-shaped rotor mounted on a vertical shaft (Fig. 2) is good because a wind turbine with such a repeller does not need to be brought into the wind. Although the torque on its shaft changes from a minimum to one-third of its maximum value in half a turn, it does not depend on the direction of the wind. When a smooth circular cylinder rotates under the influence of wind, a force perpendicular to the direction of the wind acts on the body of the cylinder. This phenomenon is called the Magnus effect, after the German physicist who studied it (1852). In 1920–1930, A. Flettner used rotating cylinders (Flettner rotors) and S-shaped rotors instead of bladed wind wheels, and also as propellers for a ship that made the transition from Europe to America and back.
Wind energy utilization factor.
The power received from the wind is usually small - less than 4 kW is developed by an outdated type of Dutch windmill at a wind speed of 32 km / h. The power of the wind flow that can be used is formed from the kinetic energy of air masses moving per unit time perpendicular to the area of a given size. In a wind turbine, this area is determined by the windward surface of the repeller. When taking into account the height above sea level, air pressure on it and its temperature, the available power N(in kW) per unit area is given by the equation
N\u003d 0.0000446 V 3 (m / s).
The coefficient of wind energy utilization is usually defined as the ratio of the power developed on the wind turbine shaft to the available power of the wind flow acting on the windward surface of the wind wheel. This coefficient becomes maximum at a certain ratio between the speed of the outer edge of the wind turbine blade w and wind speed u; the meaning of this ratio w/u depends on the type of wind turbine. The wind energy utilization factor depends on the type of wind wheel and ranges from 5–10% (Dutch mill with flat wings, w/u= 2.5) up to 35–40% (profiled vane repeller, 5 J w/u£10).
a device that converts wind energy into rotational energy. The main working body of a wind turbine is a rotating unit - a wheel driven by the wind and rigidly connected to the shaft, the rotation of which drives the equipment that performs useful work. The shaft is installed horizontally or vertically. Wind turbines are usually used to generate energy consumed periodically: when pumping water into tanks, grinding grain, in temporary, emergency and local power networks.
History reference. Although surface winds do not always blow, change their direction and their strength is not constant, the wind turbine is one of the oldest machines for obtaining energy from natural sources. Due to the dubious reliability of ancient written reports about wind turbines, it is not entirely clear when and where such machines first appeared. But, judging by some records, they already existed before the 7th century. AD It is known that they were used in Persia in the 10th century, and in Western Europe the first devices of this type appeared at the end of the 12th century. During the 16th century the tent type of the Dutch windmill was finally formed. No special changes were observed in their design until the beginning of the 20th century, when, as a result of research, the shapes and coatings of the wings of mills were significantly improved. Since low-speed machines are bulky, in the second half of the 20th century. began to build high-speed wind turbines, i.e. those whose wind wheels can make a large number of revolutions per minute with a high coefficient of utilization of wind energy.
Modern types of wind turbines. Currently, three main types of wind turbines are used - drum, vane (screw type) and rotary (with an S-shaped repeller profile).
Drum and winged. Although the drum-type wind wheel has the lowest wind energy utilization rate compared to other modern repellers, it is the most widely used. On many farms, it is used to pump water if for some reason there is no mains electricity. A typical shape of such a wheel with sheet metal blades is shown in fig. 1. Drum and vane wind wheels rotate on a horizontal shaft, so they must be turned into the wind to get the best performance. To do this, they are given a rudder - a blade located in a vertical plane, which ensures the turn of the wind wheel to the wind. The wheel diameter of the world's largest vane-type wind turbine is 53 m, the maximum width of its blade is 4.9 m. The wind wheel is directly connected to an electric generator with a capacity of 1000 kW, which develops at a wind speed of at least 48 km/h. Its blades are adjusted in such a way that the rotation speed of the wind wheel remains constant and equal to 30 rpm in the wind speed range from 24 to 112 km/h. Due to the fact that the winds blow quite often in the area where such wind turbines are located, the wind turbine usually generates WIND 50% of maximum power and feeds the public power grid. Vane wind turbines are widely used in remote rural areas to provide electricity to farms, including charging the batteries of radio communication systems. They are also used in the onboard power plants of aircraft and guided missiles.
S-shaped rotor. The S-shaped rotor mounted on a vertical shaft (Fig. 2) is good because a wind turbine with such a repeller does not need to be brought into the wind. Although the torque on its shaft changes from a minimum to one-third of its maximum value in half a turn, it does not depend on the direction of the wind. When a smooth circular cylinder rotates under the influence of wind, a force perpendicular to the direction of the wind acts on the body of the cylinder. This phenomenon is called the Magnus effect, after the German physicist who studied it (1852). In 1920-1930, A. Flettner used rotating cylinders (Flettner rotors) and S-shaped rotors instead of bladed wind wheels, and also as propellers for a ship that made the transition from Europe to America and back.
Wind energy utilization factor. The power received from the wind is usually small - less than 4 kW is developed by an outdated type of Dutch windmill at a wind speed of 32 km / h. The power of the wind flow that can be used is formed from the kinetic energy of air masses moving per unit time perpendicular to the area of a given size. In a wind turbine, this area is determined by the windward surface of the repeller. When taking into account the height above sea level, air pressure on it and its temperature, the available power N (in kW) per unit area is determined by the equation N = 0.0000446 V3 (m/s). The coefficient of wind energy utilization is usually defined as the ratio of the power developed on the wind turbine shaft to the available power of the wind flow acting on the windward surface of the wind wheel. This coefficient becomes maximum at a certain ratio between the speed of the outer edge of the wind wheel blade w and the wind speed u; the value of this ratio w/u depends on the type of wind turbine. Wind power utilization coefficient depends on the type of wind wheel and ranges from 5-10% (Dutch mill with flat wings, w/u = 2.5) to 35-40% (profiled vane repeller, 5 R€ w/u R€ 10) .
LITERATURE
Wind power. M., 1982 Yaras L. et al. Wind energy. M., 1982
