97. High performance shrouded wind turbine, "Wind-lens" turbine
Statement:
The fraction of wind energy against the total of worldwide energy supply can grow up to 10 percent by 2050. To contribute a continuous and smooth transition without losing momentum, our research team at RIAM considers the following problems as the opportunities for the innovative solution we provide. Problem 1: Conventional wind power farms require strong wind (6 meter/second or greater) in order to economically provide stable supply of electricity. And there are many areas in the world where the average annual wind speed is less than this. Problem 2: Wind turbine causes acoustic noise that is harmful to people and animals, especially when the generator is set up in or near the urban or the residential areas, or the farm areas near animals. Problem 3: Bird strikes. Currently the number of birds killed by wind turbines is not huge. But this is expected to grow as more wind power generators will be installed. Bird strikes may also damage the turbines.
Summary:
In the previous section, we presented the following problems associated with the conventional wind power generators: 1) Conventional wind power farms require strong wind (6 meter/second or greater) in order to economically provide stable supply of electricity. 2) Wind turbine causes acoustic noise that is harmful to people and animals, especially when the generator is set up in or near the urban or the residential areas, or the farm areas near animals. 3) Bird strikes. The innovative solution we propose is the technology named “Wind Lens”, which was developed at Kyushu University of Japan. It is a device designed to concentrate wind energy locally resulting output power augmentation of wind turbine. Wind power generation is proportional to the wind speed cubed. Therefore, a large increase in the output is brought about if there is even a small increase in the velocity of the approaching wind to a wind turbine. Also, this wind speed acceleration allows wind turbines to be operated with lower cut-in wind speed. And for this we created a diffuser-type structure that is capable of collecting and accelerating the approaching wind. Namely, we have devised a diffuser shroud with a large brim that is able to increase the wind speed from approaching wind substantially by utilizing various flow characteristics, e.g., the generation of low pressure region by vortex formation, flow entrainment by vortices, etc. of the inner or peripheral flows of the diffuser shroud equipped with a brim. Although the idea of power augmentation by a diffuser is not new, what makes our method different from (and superior to) the others is a large brim attached at the exit of diffuser shroud. We started calling this device “Wind Lens”. Our first prototype 500W Wind-lens turbine had relatively large diffuser and brim. It demonstrated a remarkable increase in the output power of approximately 4 to 5 times that of a conventional wind turbine, which was achieved in a field experiment. For the practical small to mid size wind turbine application, we have developed a compact-size brimmed diffuser. Reducing the size of the brimmed diffuser usually means sacrificing its power augmentation. However, our newest ring-like model still accelerates approaching wind by 30 percent near the outer tips of blades, resulting 2.5 fold output power augmentation. Corresponding power coefficient is about 0.54, which is remarkably close to the theoretical limit called “Betz limit”. This high power coefficient makes Wind-lens turbine one of the most effective turbines worldwide. The largest Wind-lens turbine with this design built at this moment is 100kW turbine installed at Ito campus of Kyushu University. Also, small Wind-lens turbines such as 1kW and 3kW/5kW models have been commercialized. The cut-in speed of these turbines is around 3 meters/second, which is near the lowest end among currently available wind turbines. One of the important features of the Wind-lens turbine is the significant reduction in wind turbine noise. Since the vortices generated from the blade tips are greatly suppressed through the interference with the boundary layer within the diffuser shroud, the aerodynamic noise is reduced substantially. A number of field tests with 3kW wind-lens turbines demonstrated almost no recognizable difference between noise levels when the turbine is in operation and not in operation in both weak and strong wind conditions. This low noise feature allows Wind-lens turbines to be installed in or near urban or residential areas, or farm areas near animals. Reduction of bird strikes can also be achieved by the diffuser. There have been more than 50 Wind-lens turbines installed worldwide in the past 5 years, and no bird/bat mortality has been reported. Some of the turbines are installed in a habitat/path of large number of migratory birds. Wind Lens is easily recognizable by birds. Research team has witnessed many birds rested on the Wind-lens structure while the turbines were in operation. Because of the ring structure of the Wind Lens, it is easy to install protective mesh across the inlet and outlet of the Lens, if necessary. This mesh installation will have very little negative impact on the output performance of the turbine. Other features of Wind Lens turbine include:  Improved safety: The wind turbine, rotating at a high speed, is shrouded by a covering structure, which also prevents damage from broken blades.  Brim-based yaw control: The brim at the exit of the diffuser makes wind turbines rotate like a weathercock, following the change in the wind direction. As a result, the wind turbine automatically turns to face the incoming wind.
Why it should be recognized:
Wind-lens turbine is simple, yet effective and innovative. It is superior to conventional turbines because of the following.  Unprecedented high power coefficient of 0.54, achieving 2.5 fold increase in turbine output power in small to mid size turbines.  Reduction of blade tip vortices resulting very quiet wind turbine (TIME Magazine, 2006). This low noise feature allows Wind-lens turbines to be installed in or near the urban or the residential areas, or the farm areas near animals.  Brim-based yaw control: The brim at the exit of the diffuser makes wind turbines rotate like a weathercock, following the change in the wind direction. As a result, the wind turbine automatically turns to face the incoming wind.  Reduction of bird strikes: No bird strikes have been reported from the 50 turbines installed worldwide in the past 5 years.  Improved safety: The wind turbine, rotating at a high speed, is shrouded by a covering structure, which also prevents damage from broken blades.  Easy installation of lightning rod: A rod or rods can be easily installed on top of the Wind-lens diffuser that prevents direct lightning hit on the nacelle of the turbine. Our first prototype 500W Wind-lens turbine had relatively large diffuser and brim. But our latest technology can be best applied to crate small to mid size (sub-MW scale) turbines. We do not believe there are many other wind turbines that offer all the above advantages.
1 comment:
On Apr 15, 2013 marianna.grossman said: This is an important innovation to catalyze rapid adoption of this important source of renewable power.
Submitted: Jan 31, 2013
Author: Tomoyuki Nagai
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URL: http://www.riam.kyushu-u.ac.jp/windeng/en_index.php