Transforming wind energy is one way to get cheap electricity. There are many designs of wind turbines. Some of them are designed for maximum efficiency, others are unpretentious in use. The second group includes the Savonius rotor, created about 100 years ago, it is still successfully used to solve various technical problems.
History of Creation
Sigurd Johannes Savonius (1884 - 1931) - inventor from Finland, gained fame for his work in physics related to the study of wind energy. During his life, he received several patents that are used not only to create wind turbines, but also in shipbuilding, as well as in ventilation systems of modern railway cars and buses.
Another inventor from Germany - Anton Flettner (1888 - 1861) at the beginning of the last century came up with an alternative to the classic sail, creating the so-called Flettner rotor. The essence of the inventionwas reduced to the following: a rotating cylinder, blown by the wind, received a force directed in the horizontal direction, exceeding 50 times the force of the air flow. Thanks to this discovery, several ships were built that use the power of the wind to move. Unlike conventional sailboats, these vessels were not completely energy independent. Motors were needed to spin the rotor.
Thinking about Flettner's sail, Savonius came to the conclusion that wind energy could also be used to spin it. In 1926, he developed and patented the design of an open cylinder with oppositely directed blades inside.
A bit of physics
First, a little theory. Everyone noticed that when riding a bicycle, the air creates a significant resistance to movement. And the higher the speed, the higher this value. The second factor affecting resistance is the cross-sectional area of the body affected by the air flow. But there is a third quantity, which is related to the geometry of the body. This is exactly what car body designers are trying to reduce when it comes to aerodynamics.
For example, we can say that three plates with the same cross-sectional area, but having different shapes: concave, straight and convex, will have a very different drag coefficient. For a convex shape, it will be 0.34, for a straight one - 1.1, for a concave one - 1.33. It was the concave shape that was taken for the blades of the Savonius rotor. It is recognized as the most effective hostwind energy.
The principle of operation of the Savonius rotor
Unlike Flettner's sail, Savonius proposed to divide the cylinder into two halves and move them relative to each other to get the blades and the space between them. The essence of Savonius's idea was that the air flow hitting one blade did not just go to the side after that, but, passing through the axial gap, was redirected to the second blade, which significantly increased the effect of the wind.
This principle of operation allows the Savonius rotor to work even in light wind.
There are several profile options:
- The blades are fixed on the axis in such a way that there is no air gap between them. This is the simplest version of the many descriptions of the Savonius rotor.
- The base of one blade is inserted into the base of the other. A significant gap remains along the axis line. This option allows the wind from one half of the rotor to move to the other. More efficient profile.
- Same as the second option, only the area of the blades is increased by adding a straight plate on the inside.
Scope of application
In the 60s of the last century, Savonius rotors were used in railway ventilation systems. They were installed on the roofs of the wagons. During the movement, the rotor began to spin up and pump air from the street into the room. Similar systems were also installed on buses.
Today, the main application of the rotor is invertical axis wind turbines. There are a number of similar designs that combine two factors:
- vertical axis of rotation;
- unpretentiousness to the direction of the wind flow.
In addition to vertical wind turbines, there are devices with a horizontal axis. They are distinguished by a large return with the same wind force. Structurally, they resemble the blades of aircraft propellers, located on a horizontal axis and having a guide tail for alignment with the wind.
Advantages of the Savonius Wind Turbine
Despite the fact that vertical axial rotors of wind turbines lose in efficiency to horizontal axial rotors, they still have a number of undeniable advantages:
- Work in any climate zone. Due to their small transverse area, they are not afraid of hurricane winds.
- Do not require additional devices for their launch. Due to the concave shape of the blades, the launch occurs at minimum wind values - 0.3 m / s. The generator reaches optimal values at an air flow speed of 5 m/s.
- Due to the low noise level of up to 20 dB, the windmill can be installed in close proximity to housing, which is important for low-power electricity generation and loss of current in the wires.
- Do not require a specific wind direction. They start working from the air flow going at any angle.
- Simple design reduces maintenance costs.
- Not dangerous for birds that perceive the structure as a whole and do not try to fly through the blades.
The disadvantages of vertical wind turbines include relatively low efficiency, higher costs for building materials, large sizes required to achieve the required power.
How to make a wind turbine with your own hands
To make a device that would provide a country house completely with electricity seems unlikely. However, making a small windmill to generate free electricity that ensures the operation of low-power devices (irrigation pump, street lighting in front of the house, opening automatic gates) is within the power of any craftsman. For this you will need:
- 3 aluminum sheets with a side length of 33cm, about 1mm thick;
- drainpipe 15 cm in diameter and 60 cm long;
- 4 cm water pipe;
- electric generator (car can be used);
- fittings (steel angles, self-tapping screws, nuts, bolts).
To make a simple Savonius rotor you need:
- Cut out 3 discs with a diameter of 33 cm from aluminum sheets.
- Cut a water pipe with a diameter of 15 cm along the axis to make 2 blanks for the blades. Then cut each piece across the middle. Thus, you get 4 identical blades, 30 cm long.
- Drill a hole in the center of the disks through which a 4 cm water pipe can be inserted.
- Connect all three disks with a pipe, and between theminsert blades. Two between two disks. The blades must be oriented so that the angle between their axes is 90 degrees. This will allow even a slight wind to spin the generator.
- Use corners and self-tapping screws to fix the blades on aluminum rims.
- Press the generator shaft into the lower part of the pipe, which is the axis.
The wind generator is ready. It remains only to choose an installation site that is sufficiently open to air currents. If there is not enough wind, then you can make a high mast, on top of which place the generator.
Factory-made vertical wind turbines
With the development of alternative energy, there is an increasing demand for autonomous power supply products. Currently, there are Russian-made wind turbines on the market, the price of which starts from 60 thousand rubles.
These units can be used in the private sector, meeting electricity needs from 250 W to 250 kW.