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Unconventional wind turbines are those that differ significantly from the most common types in use. , the most common type of wind turbine is the three-bladed upwind horizontal-axis wind turbine (HAWT), where the turbine rotor is at the front of the nacelle and facing the wind upstream of its supporting turbine tower. A second major unit type is also classified by its axis: the vertical-axis wind turbine (VAWT), with blades extending upwards that are supported by a rotating framework. Due to the large growth of the wind power industry and the length of its historical development dating back to windmills, many different wind turbine designs exist, are in current development, or have been proposed due to their unique features. The wide variety of designs reflects ongoing commercial, technological, and inventive interests in harvesting wind resources both more efficiently and to the greatest extent possible, with costs that may be either lower or greater than conventional three-bladed HAWT designs. Some turbine designs that differ from the standard type have had limited commercial use, while others have only been demonstrated or are only theoretical concepts with no practical applications. Such unconventional designs cover a wide gamut of innovations, including different rotor types, basic functionalities, supporting structures and form-factors. == Modified horizontal == ; Twin-bladed rotor: Nearly all modern wind turbines uses rotors with three blades, but some use only two blades. This was the type used at Kaiser-Wilhelm-Koog, Germany, where a large experimental two-bladed unit—the GROWIAN, or ''Große Windkraftanlage'' (big wind turbine)—operated from 1983 to 1987. Other prototypes and several wind turbine types were also manufactured by NedWind. The Eemmeerdijk Wind Park in Zeewolde, Netherlands uses only two-bladed turbines. Wind turbines with two blades are manufactured by Nordic Windpower,〔(NedWind Rhenen bV NW 43/500 (Turbine) ), Nedwind website. Retrieved 27 January 2013.〕 such as model # N 1000, and by GC China Turbine Corp.〔(Why 2-Blade? ), GC China Turbine Corporation website. Retrieved 27 January 2013. 〕 The NASA wind turbines (1975-1996) each had 2-blade rotors, producing the same energy at lower cost than three-blade rotor designs. ; Downwind rotor: Nearly all wind turbines are of an upwind design, meaning the rotor is in front of the nacelle when the wind is blowing. Some turbines are of a downwind design, meaning the rotor is behind the nacelle when the wind is blowing. ; Ducted rotor: Still something of a research project,〔(Uni-Stuttgart.de website ) 〕 the ducted rotor consists of a turbine inside a duct that flares out at the back. They are also referred as Diffuser-Augmented Wind Turbines (i.e. DAWT). The main advantage of the ducted rotor is that it can operate in a wide range of winds and generate a higher power per unit of rotor area. Another advantage is that the generator operates at a high rotation rate, so it doesn't require a bulky gearbox, allowing the mechanical portion to be smaller and lighter. A disadvantage is that (apart from the gearbox) it is more complicated than the unducted rotor and the duct is usually quite heavy, which puts an added load on the tower. The Éolienne Bollée is an example of a DAWT. ; Co-axial, multi-rotor: Two or more rotors may be mounted to the same driveshaft, with their combined co-rotation together turning the same generator: fresh wind is brought to each rotor by sufficient spacing between rotors combined with an offset angle (alpha) from the wind direction. Wake vorticity is recovered as the top of a wake hits the bottom of the next rotor. Power has been multiplied several times using co-axial, multiple rotors in testing conducted by inventor and researcher Douglas Selsam, for the California Energy Commission in 2004. The first commercially available co-axial multi-rotor turbine is the patented dual-rotor American Twin Superturbine from Selsam Innovations in California, with 2 propellers separated by 12 feet. It is the most powerful turbine available, due to this extra rotor. In 2015, Iowa State University aerospace engineers Hui Hu and Anupam Sharma were optimizing designs of multi-rotor systems, including a horizontal-axis co-axial dual-rotor model. In addition to a conventional three-blade rotor, it has a smaller secondary three-blade rotor, covering the near-axis region usually inefficiently harvested. They were considering the overall efficiency of the wind farm, and checking many variations beyond the one mentioned. Preliminary results indicated 10-20% gains, less efficient than is claimed by existing counter-rotating designs but those are complex.〔(Iowa State engineers study the benefits of adding a second, smaller rotor to wind turbines. )〕 ; Counter-rotating horizontal-axis: When a system expels or accelerates mass in one direction, the accelerated mass causes a proportional but opposite force on that system. The spinning blade of a single rotor wind turbine causes a significant amount of tangential or rotational air flow. The energy of this tangential air flow is wasted in a single-rotor propeller design. To use this wasted effort, the placement of a second rotor behind the first takes advantage of the disturbed airflow. Contra-rotation wind energy collection with two rotors, one behind the other, can gain up to 40% more energy from a given swept area as compared with a single rotor. Much work has been done recently on this in the United States. A patent application dated 1992 exists based on work done with the Trimblemill.〔((WO1992012343) Wind Turbine ), Patentscope website, 1992.〕 :Other advantages of contra-rotation include no gear boxes and auto-centering on the wind (no yaw motors/mechanism required). Counter-rotating turbines can be used to increase the rotation speed of the electrical generator. As of 2005, no large practical counter-rotating HAWTs are commercially sold. When the counter-rotating turbines are on the same side of the tower, the blades in front are angled forwards slightly so as to avoid hitting the rear ones. If the turbine blades are on opposite sides of the tower, it is best that the blades at the back be smaller than the blades at the front and set to stall at a higher wind speed. This allows the generator to function at a wider wind speed range than a single-turbine generator for a given tower. To reduce sympathetic vibrations, the two turbines should turn at speeds with few common multiples, for example 7:3 speed ratio. Overall, this is a more complicated design than the single-turbine wind generator, but it taps more of the wind's energy at a wider range of wind speeds. ; Furling tail and twisting blades: In addition to variable pitch blades, furling tails and twisting blades are other improvements on wind turbines. Similar to the variable pitch blades, they may also greatly increase the efficiency of the turbine and be used in "do-it-yourself" construction〔(Furling tail windturbines ) (page 18) PDF〕 ; Wind-mill style: De Nolet is a wind turbine in Rotterdam disguised as a windmill. ; Ducted 2-Blade HAWT: Looking similar to the standard 2-blade or three-blade horizontal-axis wind turbine (HAWT)—the most used types—the British experimented with this type in the early 1950s. As the wind turns the blades, it draws air from near the bottom of the turbine's large hollow mast, and through turbines that spin an electrical generator. Air expels at the tip of the blades. The engineers of this design believed it saved cost by not requiring a linkage and transmission for the generator, and being of lighter weight because the generator was near the bottom of the mast rather than the top. One was built and tested near St Albans, Hertfordshire, England.〔("Power from the Winds." ) ''Popular Mechanics'', June 1954, pp. 124-125.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Unconventional wind turbines」の詳細全文を読む スポンサード リンク
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