The difference between the design methods of horizontal axis generators and vertical axis generators:
The blade design of horizontal axis wind turbines currently generally adopts the motion blade theory. The main methods include the Glauert and Wilson method. Loi et al. However, because the blade element theory ignores the flow interference between each blade element, and at the same time, the resistance of the airfoil is ignored when designing blades using the blade element theory, this simplification inevitably leads to imprecision in the results, the literature [1] It is emphasized that this simplification has little impact on the design of the shape of the blade, but has a greater impact on the use of energy wind turbine by the wind wheel. At the same time, the interference between the blades of the wind wheel is also very strong, and the entire flow isvery complex. It is impossible to obtain accurate results based on blade element theory alone.
The blade design of vertical axis wind turbines was previously designed based on the horizontal axis method and was based on blade element theory. Since the flow of vertical axis wind turbine is more complex than that of horizontal axis, it is a typical large separation unsteady flow and is not suitable for analysis and design using blade element theory. This is also an important reason for the vertical axis. The wind turbine has not been developed for a long time. With the continuous development of computer technology, computational fluid dynamics (Computational Fluid Dynamics) has made great progress. From the initial small disturbance velocity equation to the more complex Euler equation and N-S equation, Current CFD technology can simulateer complex flows entirely. in complex forms. For vertical axis wind turbine blades, CFD methods can already be used to design them, which is arguably much more accurate than blade element theory. However, there is no way to apply the CFD method to the design of horizontal axis blades, which is mainly determined by the two types of wind turbine structures. Horizontal axis blades have different twist angles, chord lengths and tip speed ratios for each section. If you want to use CFD simulation, you must use a three-dimensional model. In this way, at least 1 million calculation grids will be used. the total amount of calculation will be huge. Intuitively speaking, to simulate a working condition, on a personal computer equipped with a P4 3.0G processor, the calculation time takes about 7 to 10 days. If you design a wind turbine, thisIt can take several years, or even more than ten years. a price is very high in the industry, it is difficult to accept in terms of design. The vertical axis is completely different (only for Darrieus type H wind turbines). Each cross section of the blade is the same, which can be simplified to a two-dimensional situation. The number of grids is greatly reduced, and the number of grids is greatly reduced. the amount of calculation is also reduced. Typically, simulating a working condition only takes 4 hours. In terms of design methods, vertical axis wind turbines are much more advanced than horizontal axis wind turbines.
The difference between the wind energy utilization rate of horizontal axis generators and vertical axis generators:
At present, the utilization rate Wind power of large horizontal axis wind turbines is mainly calculated per blade. the creators. Lhe revenues are generally above 40%. As mentioned earlier, due to flaws in the design method itself, the accuracy of wind energy usage calculated in this way is highly questionable. Of course, wind turbines in wind power plants will plot wind power curves based on the measured wind speed and power output, but the wind speed at that moment is measured at the back of the wind wheel. The speed of the wind measured by the wind instrument is lower than the speed of the incoming wind, the measured wind power curve is therefore too high and must be corrected. After correction according to the literature correction method, the wind energy utilization rate of the horizontal axis will be reduced by about 30% to 50%. Regarding the wind energy utilization rate of small horizontal axis wind turbines, the China Aerodynamic Research and Development Center has conducted experimentsrelevant in the wind tunnel, and the measured utilization rate is around 23 to 29%.
Since leaf element theory has been used in the past to calculate the wind energy utilization rate of vertical axis wind turbines, it was concluded that the rate of utilization is not as good as that of horizontal axis wind turbines. However, according to the author's CFD simulation results, the wind energy utilization rate of vertical axis wind turbines is not lower than that of horizontal axis. Some foreign institutions have also conducted experiments showing that the vertical axis wind energy utilization rate. vertical axis wind turbine is more than 40%. In addition, in the actual environment, the wind direction changes frequently, and the windward side of the horizontal axis wind rotor cannot always face the wind, resulting in "wind loss". This problem does not exist with the axis wind rotorvertical, so considering After taking into account the wind loss, it is entirely possible that the wind energy utilization rate of the vertical axis wind rotor exceeds that of the horizontal axis wind rotor.
The difference in wind startup speed between horizontal axis generators and vertical axis generators
There is a consensus that the startup performance of horizontal axis wind turbines horizontal are good, but according to China Aerodynamics Analysis of Small Research and Development Center According to wind tunnel experiments conducted on horizontal axis wind turbines, the starting wind speed is generally between 4 and 5 meters/second, and the maximum reaches 5.9 meters/second. Such startup performance is obviously unsatisfactory.
Poor start-up performance of vertical axis wind turbines is also an industry consensus. Particularly for wind turbinesDarrieus type Ф, there is no auto-start capability. This is also a limiting reason. the application of vertical axis wind turbines. However, there is an opposite conclusion for the Darrieus type H wind wheel (see Figure 3). According to the author's research, as long as the aerodynamic profile and installation angle are selected appropriately, fairly good starting performance can be achieved. Linfeng P- Judging from the wind tunnel experience of 200 vertical axis wind turbines, the starting wind speed of this Darrieus type H-shaped wind turbine only needs 2 meters/second, which is without no doubt much better than the horizontal axis wind turbines mentioned above. .
The difference between the structural characteristics of horizontal axis generators and vertical axis generators:
The blades of horizontal axis wind turbines are affected by the combined effects of wind force. inertiaand gravity during a rotation. . , the direction of the inertial force changes at any time, while the direction of gravity always remains unchanged, so that the blade is subjected to an alternating load, which is very detrimental to the fatigue resistance of the blade. pale. In addition, horizontal axis generators are placed at an altitude of tens of meters, which brings a lot of inconvenience to the installation, maintenance and repair of generators.
The blades of wind turbines with a vertical axis are much more stressed during rotation than those with a horizontal axis. Since the directions of the force of inertia and gravity remain unchanged, they are subjected to a constant load . The lifespan is therefore constant. longer than that of the horizontal axis. At the same time, the vertical axis generator can be placed under the wind wheel or on the ground for easy installation and maintenance.
Horizontal axis generator andvertical axis generatorDifferences in environmental protection
Although wind energy is also known as clean energy and can play a very good role in environmental protection , with the establishment of more and more large-scale wind farms, some environmental protection problems have been caused by wind turbines Problems have also been pointed out. These problems are mainly reflected in two aspects: one is the noise problem and the other is the impact on the local ecological environment.
The peak speed ratio of the horizontal axis wind rotor is generally around 5 to 7. At such a high speed, the blades cutting off the airflow will produce a lot of aerodynamic noise at the same time , many birds. will also suffer under high speed blades. Barely spared.
The peak speed ratio of the vertical axis wind wheel is much smallerthan that of the horizontal axis, generally between 1.5 and 2. Such a low speed basically produces no aerodynamic noise and achieves a completely silent effect. . The benefits of being noise-free are obvious. In places where wind turbines could not be used in the past due to noise problems (such as urban public facilities, residential buildings, etc.), vertical axis wind turbines can now be used to solve the problem. Therefore, vertical axis wind turbines are more The horizontal axis has a wider range of applications.
The benefits of a low tip speed ratio are not only environmentally friendly, but also very beneficial to the overall performance of the fan. According to aerodynamic analysis, the faster the object moves, the greater influence its shape has on the flow field. When wind turbines operateWhen used outdoors, the blades are inevitably contaminated, and this pollution even modifies the shape of the blades. For horizontal axis wind rotors, although this shape change is very small, it significantly reduces the wind energy utilization of the wind rotor. Vertical axis wind rotors are not so sensitive to shape changes due to their low rotational speed. blades Pollution basically has no effect on the aerodynamic performance of the wind turbine.
Summary:
Horizontal axis and vertical axis wind turbines are compared in many aspects. From the comparison, it can be seen that compared to traditional horizontal axis wind turbines, vertical axis wind turbines. Axial wind turbines have many advantages such as advanced design methods, high wind energy utilization, low start-up wind speed and no noise.
Yes!
Reason:small hydroelectric generators are generally synchronous generators and the quality of power generation is consistent with the power grid; as long as the generator is connected to the grid, the generator will run automatically and power from the water; will be transmitted based on the output. Dynamic energy is converted into electrical energy and sent to the grid, without voltage instability caused by changes in load and water flow.