Horizontal Axis Wind Turbine VS Vertical Axis Wind Turbine
The features of structure:
As to the Horizontal axis wind turbine, during the process of one circle of rotation of the blades, the blades receive the combined effects of inertial force and gravity, the direction of the inertial force is subject to change, while that of the gravity is stable ever, so that the blades suffer an alternating load, which is very detrimental to the fatigue strength of the blades. Besides, the generator of the Horizontal axis wind turbine is about tens of meters far away from the ground, which brings a lot of troubles to repair and maintain the generator.
As to the Vertical axis wind turbine, during the process of rotation of the blades, the condition of receiving effects is better than that of the Horizontal axis wind turbine, because the directions of the inertial force and gravity keep stable ever. Therefore, the blades receive a fixed load, and accordingly the fatigue longevity is longer than the Horizontal axis wind turbine. At the same time, the generator of the Vertical axis wind turbine is often placed under the rotor or on the ground, and so it is easy for repair and maintenance.
The starting wind speed:
It is commonly admitted that the Horizontal axis wind turbine enjoys a good starting performance. But according to the gas-hole experiment practiced by China Aerodynamics Research and Development Centre (CARDC) on the small-sized Horizontal axis wind turbine, the starting wind speed is usually in the range of 4~5 m/s, and the maximum has been up to 5.9 m/s. this starting performance obviously can't be satisfactory.
In the field of wind turbines, it is also commonly said that the Vertical axis wind turbine suffers a bad starting performance, especially the Ф structure of Darrieus wind turbine, which has no initial starting ability to speak of. This is also an obstacle on the way of the development of the Vertical axis wind turbine. Nevertheless, as for the H structure of Darrieus wind turbine, it has an opposite conclusion. As long as the airfoil and installing angle are selected appropriately, the wind turbine can gain quite satisfactorily starting performance. Considering the air-hole test, the H structure of Darrieus wind turbine can start at a wind speed of 2m/s, which is undoubtedly preferable than the Horizontal axis wind turbine.
The environmental problems:
Although the wind is called as the clean energy, and can be friendly to the environment, with more and more large-scale wind power farms being built, some environmental problems caused by the wind turbines have been also prominent. These problems are mainly reflected in two aspects: first, the noise problem; second, the negative impact on the local ecological environment.
The tip speed ratio of the Horizontal axis wind turbine is generally about 5 to 7, and at such a high speed, the blades cutting the air flow will produce loud aerodynamic noise, and meanwhile many birds through such high-speed blade are difficult to escape.
The tip speed ratio of the Vertical axis wind turbine is usually 1.5 to 2, which is much lower than that of the Horizontal model. Such low rotating speed basically can't produce aerodynamic noise, and completely mute the noise. The benefits of muteness are apparent, because it solved the difficult that in the past the wind turbine couldn't be erected in some circumstances, such as urban public facilities, residential areas, etc. With this regard, it can be got that the Vertical model will enjoy a wider field of application than the Horizontal model.
The benefits brought by the low tip speed ratio are not only the environmental advantages, but also beneficial to the overall performance of the wind turbines. Based on the aerodynamic analysis, the faster the object, the greater the impact of the shape of outlook on the flow field. When the wind turbine runs in the outdoors, the blades are inevitably contaminated by the pollution, and the pollution can actually change the shape of the blades. In terms of the Horizontal model, even if this kind of change to the blades is trivial, it can also reduce the energy utilization. But as for the Vertical model, its rotating speed is quite low, so it is not so sensitive to the change of the shape, which means that the contamination to the blades has no effect on the aerodynamic performance of the wind turbine.
The comparative parameters:
