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Method for calculating nonstationary aerodynamic derivatives of H - type Darrieus turbine working blades under conditions of harmonic changes in kinematic parameters.
New Manual for Vertical Axis Wind Turbines
+ - usage of wind energy; - - resistance to rotation, negative work; 0 - no resistance to rotation.
Calculations for three type blade wind turbine
http://www.cal-epower.com/ - Already proven effectiveness and profitability
New technology for collecting and concentrating wind energy to effectively increase the power of wind turbines without changing their designs.
Currently, wind turbine designers are actively working to improve the design of wind turbines to increase their capacity. However, these studies have not yet led to a large increase in the power factor of wind turbines. This is because the volume of air that passes through the turbine is limited in accordance with Betz’s law. In other words, the turbine can use no more than 59% of the air volume, which corresponds to the turbine inlet area. Therefore, to increase power, designers have only one option - to increase the size of the turbine rotor in order to increase the incoming air volume into the turbine (air flow through the turbine). Creating a large diameter rotor is very expensive. There is an alternative way to increase the air flow through the turbine without changing the size of the turbine. For its implementation, it is necessary to increase the wind speed in front of the turbine. To increase the wind speed in front of the turbine, it is necessary to create a device that "collects" the wind over a large area and directs it to the turbine (by analogy with hydroelectric power stations). Since the turbine power is directly proportional to the wind speed in the cube, this method is very effective. Currently, many devices have been invented and patented to perform this function, but they all have low efficiency, so they are practically not used. This is due to the fact that any design in front of the turbine creates additional aerodynamic drag, which reduces the air flow through the turbine. There is also a method of increasing the speed of atmospheric wind using a natural topography (mountains, hills or residential buildings). But all of these devices are not designed to effectively increase wind speed. Therefore, they are not suitable for increasing the power of wind turbines. The idea of devices that “collect” wind from a large area and direct it to a small turbine is often patented in various versions. However, the authors of these patents do not provide evidence of the effectiveness of the proposed devices. Therefore, at present, these patented devices are not used in practice. The reason for this is the reluctance of air to penetrate into the "wind energy concentrators" that the inventors unreasonably offer. All wind amplifiers such as a mechanical confuser (narrowing channel with solid walls) in front of the turbine do not increase wind speed, as they create a lot of additional resistance and reduce air flow through the turbine. This is because in the free (open) flow, the amount of air that enters the turbine decreases when the total resistance of the turbine increases (Betz's law). The air flow through a mechanical confuser in an open stream is inversely proportional to the hydraulic resistance of the confuser. The terminology “accelerator plates”, “flow rotation devices”, “vortex generator that accelerates the flow”, “turbulizers”, “casings”, “mechanical wind concentrators”, “air flow reflectors” and others have nothing to do with devices that collect and accelerate the flow of atmospheric wind. This is due to the fact that all these devices violate the laws of motion of an open air flow and are applicable only in closed ducts.
Therefore, the evaluation of the efficiency of devices for increasing wind speed can be performed only on the basis of the laws of mechanics of liquids and gases. Unreasonable reasoning is not permissible.
In order to practically realize the idea of collecting and concentrating wind energy, it is necessary to create the following conditions for the movement of an open air stream in the conditions of proximity of the earth's screen. Far from the turbine, the air stream that enters the turbine should have a cross-sectional area larger than the turbine rotor area. Then, as it approaches the turbine, this jet should narrow and the air velocity will increase. At the same time (which is very important), the rate of increase in speed should be the same as in a tapering closed pipe. Behind the turbine, the air stream must expand and the pressure increase to atmospheric. This effect is called the venturi effect. In other words, the air flow in this jet must be constant. A device that implements the Venturi effect in an open stream will be called a wind amplifier or a device for collecting and concentrating wind energy on a turbine rotor. The ratio of the cross-sectional area of the jet far from the turbine to the area of entry into the turbine will be called the degree of confusion of the Venturi effect. This degree of confusion determines how much the wind speed increases at the entrance to the turbine and, therefore, how much the turbine power increases compared to the nominal value.
Such a device can only be designed subject to the laws of wind movement. Otherwise, such a device will create resistance to the movement of air, and air will pass by this device. For this, it is necessary to develop a simulation model of air movement. Using this model, determine the flow velocity field and design the wind amplifier so as to obtain the planned increase in power at the minimum cost of building a wind amplifier. The development of such a model for each type and size of the turbine is done individually and is based on the theory of conformal transformations of potential flows. This mathematical apparatus is very complex, as a result of which the proposed technology is still not implemented in practice. For this reason, wind turbines operate at low efficiency.
The proposed technology differs from existing similar technologies in that it allows for the first time to create the Venturi effect in an open stream, without losing energy, to compress the jet in front of the turbine. In other words, the technology differs from the modern level of similar technologies in that it allows you to increase the wind speed in front of the turbine and at the same time increase the air flow through the turbine. This is a fundamental difference from existing technologies, which reduce the air flow through the turbine due to energy losses when the jet in front of the turbine is forced to compress. In other words, the proposed technology implements the confuser effect in front of the turbine (collects and accelerates the wind) and the diffuser effect in the back of the turbine (organizes the correct air outlet) for free air flow without additional energy losses. The proposed technology creates a Venturi effect in an open stream, which works the same as in closed pipelines (changing the degree of confusion does not change the air flow through the amplifier).
Using this technology, it is shown for the first time how to build a structure that creates a confuser - diffuser effect in an open wind stream in order to collect and concentrate wind energy. This problem in wind energy has not yet been resolved. For this reason, unlike hydroturbines, wind turbines have low efficiency. Solving this problem will significantly increase the contribution of wind energy to the total amount of energy produced in the world. The proposed technology opens up a new direction in the development of wind energy installations - to create such installations that are installed together with wind amplifiers. Such installations can be significantly simpler and smaller than existing ones.
To implement this technology, 16 variants of amplifiers have been developed, each of which requires a unique method of aerodynamic design. The accuracy of the results is guaranteed by the rigorous mathematical apparatus underlying this design. The developed methods allow:
• Choose the type of amplifier;
• Perform design parametric design analysis;
• Optimize the design at the cost of manufacturing costs;
• Design a wind amplifier so as to realize the planned increase in power of a particular turbine;
• Calculate the power of a particular turbine installed with an amplifier.
• Conduct research on the development of new devices for collecting and concentrating wind energy.
Theoretical calculations show that it is possible to create a wind amplifier that increases the turbine power by 70 times (by 7000%). Depending on the complexity of the design, this efficiency can be obtained in the range of 450% ... 7000%. The graph shows an example of calculating the increase in turbine power in percent (along the ordinate) depending on the relative diameter of the turbine rotor (squared on the graph field) and from
a parameter characterizing the efficiency of the amplifier (abscissa).
Professor V. Sannikov