turbine

steam turbine Dictionary: steam turbine Sponsored LinksMAN TURBO Steam TurbinesCompressors and turbines for industrial processes. www.manturbo.comSteam TurbineSulzer Turbo Services: Repair, maintenance and refurbishment. www.sulzerts.com/steam_turbinesHome > Library > Literature & Language > Dictionary

n.

A turbine operated by highly pressurized steam directed against vanes on a rotor.

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A machine for generating mechanical power in rotary motion from the energy of steam at temperature and pressure above that of an available sink. By far the most widely used and most powerful turbines are those driven by steam. Until the 1960s essentially all steam used in turbine cycles was raised in boilers burning fossil fuels (coal, oil, and gas) or, in minor quantities, certain waste products. However, modern turbine technology includes nuclear steam plants as well as production of steam supplies from other sources. See also Nuclear reactor.

The illustration shows a small, simple mechanical-drive turbine of a few horsepower. It illustrates the essential parts for all steam turbines regardless of rating or complexity: (1) a casing, or shell, usually divided at the horizontal center line, with the halves bolted together for ease of assembly and disassembly; it contains the stationary blade system; (2) a rotor carrying the moving buckets (blades or vanes) either on wheels or drums, with bearing journals on the ends of the rotor; (3) a set of bearings attached to the casing to support the shaft; (4) a governor and valve system for regulating the speed and power of the turbine by controlling the steam flow, and an oil system for lubrication of the bearings and, on all but the smallest machines, for operating the control valves by a relay system connected with the governor; (5) a coupling to connect with the driven machine; and (6) pipe connections to the steam supply at the inlet and to an exhaust system at the outlet of the casing or shell.

steam turbine

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steam turbine

Cutaway of small, single-stage steam turbine. (General Electric Co.)

Steam turbines are ideal prime movers for driving machines requiring rotational mechanical input power. They can deliver constant or variable speed and are capable of close speed control. Drive applications include centrifugal pumps, compressors, ship propellers, and, most important, electric generators.

Steam turbines are classified (1) by mechanical arrangement, as single-casing, cross-compound (more than one shaft side by side), or tandem-compound (more than one casing with a single shaft); (2) by steam flow direction (axial for most, but radial for a few); (3) by steam cycle, whether condensing, noncon-densing, automatic extraction, reheat, fossil fuel, or nuclear; and (4) by number of exhaust flows of a condensing unit, as single, double, triple flow, and so on. Units with as many as eight exhaust flows are in use. See also Turbine.

Sponsored LinksSteam TurbineChina Steam Turbine Supplier. High Quality, Competitive Price. Made-In-China.comCoil Type Steam GeneratorRental, 300-1200 kg/hr, PHE's for Deluge & Process Pipework Descaling www.dutchoffshoreservices.orgWordNet: steam turbine Top Home > Library > Literature & Language > WordNetNote: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: turbine in which steam strikes blades and makes them turn

Sponsored LinksCellkraft E-SeriesHigh precision evaporation/steam generation. 1.8 to 3000 ml liq/hour www.cellkraft.seAc Power Plus dieselDiesel Engines Generator Gas Genset Yanmar Kohler John Deere Westerbeke www.acpowerplus.comWikipedia: Steam turbine Top Home > Library > Miscellaneous > Wikipedia

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A rotor of a modern steam turbine, used in a power plant

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Charles Parsons in 1884.

It has almost completely replaced the reciprocating piston steam engine (invented by Thomas Newcomen and greatly improved by James Watt) primarily because of its greater thermal efficiency and higher power-to-weight ratio. Because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator – about 80% of all electricity generation in the world is by use of steam turbines. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency through the use of multiple

stages in the expansion of the steam, which results in a closer approach to the ideal reversible process.

Contents[hide]

1 History 2 Types

o 2.1 Steam Supply and Exhaust Conditions o 2.2 Casing or Shaft Arrangements

3 Principle of Operation and Design o 3.1 Turbine Efficiency

3.1.1 Impulse Turbines 3.1.2 Reaction Turbines

o 3.2 Operation and Maintenance o 3.3 Speed regulation

4 Direct drive 5 Speed reduction 6 References 7 Further Reading 8 External link

HistoryThe first device that may be classified as a reaction steam turbine was little more than a toy, the classic Aeolipile, described in the 1st century by Hero of Alexandria in Roman Egypt.[1][2][3] A thousand years later, the first impact steam turbine with practical applications was invented in 1551 by Taqi al-Din in Ottoman Egypt, who described it as a prime mover for rotating a spit. Similar smoke jacks were later described by John Wilkins in 1648 and Samuel Pepys in 1660. Another steam turbine device was created by Italian Giovanni Branca in 1629.[4]

The modern steam turbine was invented in 1884 by the Englishman Charles A. Parsons, whose first model was connected to a dynamo that generated 7.5 kW of electricity. His patent was licensed and the turbine scaled-up shortly after by an American, George Westinghouse. A number of other variations of turbines have been developed that work effectively with steam. The de Laval turbine (invented by Gustaf de Laval) accelerated the steam to full speed before running it against a turbine blade. This was good, because the turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam. It is also, however, considerably less efficient. The Parson's turbine also turned out to be relatively easy to scale-up. Within Parson's lifetime the generating capacity of a unit was scaled-up by about 10,000 times. [5]

Parsons turbine from the Polish destroyer ORP Wicher II

TypesSteam turbines are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment, to 2,000,000 hp (1,500,000 kW) turbines used to generate electricity. There are several classifications for modern steam turbines.

Steam Supply and Exhaust Conditions

These types include condensing, noncondensing, reheat, extraction and induction.

Noncondensing or backpressure turbines are most widely used for process steam applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low pressure process steam are available.

Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser.

Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back into an intermediate pressure section of the turbine and continues its expansion.

Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boiler feedwater heaters to improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled.

Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.

Casing or Shaft Arrangements

These arrangements include single casing, tandem compound and cross compound turbines. Single casing units are the most basic style where a single casing and shaft are coupled to a generator. Tandem compound are used where two or more casings are directly coupled together to drive a single generator. A cross compound turbine arrangement features two or more shafts not in line driving two or more generators that often operate at different speeds. A cross compound turbine is typically used for many large applications.

Principle of Operation and DesignAn ideal steam turbine is considered to be an isentropic process, or constant entropy process, in which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving the turbine. No steam turbine is truly “isentropic”, however, with typical isentropic efficiencies ranging from 20%-90% based on the application of the turbine. The interior of a turbine comprises several sets of blades, or “buckets” as they are more commonly referred to. One set of stationary blades is connected to the casing and one set of rotating blades is connected to the shaft. The sets intermesh with certain minimum clearances, with the size and configuration of sets varying to efficiently exploit the expansion of steam at each stage.

Turbine Efficiency

Schematic diagram outlining the difference between an impulse and a reaction turbine

To maximize turbine efficiency, the steam is expanded, generating work, in a number of stages. These stages are characterized by how the energy is extracted from them and are known as impulse or reaction turbines. Most modern steam turbines are a combination of the reaction and impulse design. Typically, higher pressure sections are impulse type and lower pressure stages are reaction type.

Impulse Turbines

An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain significant kinetic energy, which the rotor blades, shaped like buckets, convert into shaft rotation as the steam jet changes direction. A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage.

As the steam flows through the nozzle its pressure falls from steam chest pressure to condenser pressure (or atmosphere pressure). Due to this relatively higher ratio of expansion of steam in the nozzle the steam leaves the nozzle with a very high velocity. The steam leaving the moving blades is a large portion of the maximum velocity of the steam when leaving the nozzle. The loss of energy due to this higher exit velocity is commonly called the "carry over velocity" or "leaving loss".

Reaction Turbines

In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor. Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the stator and decelerating through the rotor, with no net change in steam velocity across the stage but with a decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.

Operation and Maintenance

When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass line to allow superheated steam to slowly bypass the valve and proceed to heat up the lines in the system along with the steam turbine. Also a turning gear is engaged when there is no steam to the turbine to slowly rotate the turbine to ensure even heating to prevent uneven expansion. After first rotating the turbine by the turning gear, allowing time for the rotor to assume a straight plane (no bowing), then the turning gear is disengaged and steam is admitted to the turbine, first to the astern blades then to the ahead blades slowly rotating the turbine at 10 to 15 RPM to slowly warm the turbine.

Problems with turbines are now rare and maintenance requirements are relatively small. Any imbalance of the rotor can lead to vibration, which in extreme cases can lead to a blade letting go and punching straight through the casing. It is, however, essential that the turbine be turned with dry steam. If water gets into the steam and is blasted onto the blades (moisture carryover) rapid impingement and erosion of the blades can occur, possibly leading to imbalance and catastrophic failure. Also, water entering the blades will likely result in the destruction of the thrust bearing for the turbine shaft. To prevent this, along with controls and baffles in the boilers to ensure high quality steam, condensate drains are installed in the steam piping leading to the turbine.

Speed regulation

The control of a turbine with a governor is essential, as turbines need to be run up slowly, to prevent damage while some applications (such as the generation of alternating current electricity) require precise speed control. Uncontrolled acceleration of the turbine rotor can lead to an overspeed trip, which causes the nozzle valves that control the flow of steam to the turbine to close. If this fails then the turbine may continue accelerating until it breaks apart, often spectacularly. Turbines are expensive to make, requiring precision manufacture and special quality materials.

Direct driveElectrical power stations use large steam turbines driving electric generators to produce most (about 80%) of the world's electricity. Most of these centralised stations are of two types: fossil fuel power plants and nuclear power plants. The turbines used for electric power generation are most often directly coupled to their generators. As the generators must rotate at constant synchronous speeds according to the frequency of the electric power system, the most common speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. In installations with high steam output, as may be found in nuclear power stations, the generator sets may be arranged to operate at half these speeds, but with four-pole generators.[6]

Speed reduction

The Turbinia - the first steam turbine-powered ship

Another use of steam turbines is in ships; their small size, low maintenance, light weight, and low vibration are compelling advantages. (Steam turbine locomotives were also tested, but with limited success.) A steam turbine is only efficient when operating in the thousands of RPM range while application of the power in propulsion applications may be only in the hundreds of RPM and so requiring that expensive and precise reduction gears must be used, although several ships, such as Turbinia, had direct drive from the steam turbine to the propeller shafts. This purchase cost is offset by much lower fuel and maintenance requirements and the small size of a turbine when compared to a reciprocating engine having an equivalent power, except for diesel engines which are capable of higher efficiencies. Steam turbine efficiencies have yet to break 50% yet diesel engines routinely exceed 50%, especially in marine applications.[7] [8] [9] [10]

References

1. ̂ turbine. Encyclopedia Britannica Online 2. ̂ A new look at Heron's 'steam engine'" (1992-06-25). Archive for History of Exact

Sciences 44 (2): 107-124. 3. ̂ O'Connor, J. J.; E. E. Roberston (1999). Heron of Alexandria. MacTutor 4. ̂ Ahmad Y Hassan (1976). Taqi al-Din and Arabic Mechanical Engineering, p. 34-35.

Institute for the History of Arabic Science, University of Aleppo. 5. ̂ Parsons, Sir Charles A.. "The Steam Turbine".

http://www.history.rochester.edu/steam/parsons/part1.html. 6. ̂ Leyzerovich, Alexander (2005). Wet-steam Turbines for Nuclear Power Plants. Tulsa

OK: PennWell Books. pp. p111. ISBN 1593700326. 7. ̂ www.ansys.com/assets/testimonials/siemens.pdf 8. ̂ http://pepei.pennnet.com/display_article/152601/6/ARTCL/none/none/1/New-

Benchmarks-for-Steam-Turbine-Efficiency/ 9. ̂ http://en.wikipedia.org/wiki/Wärtsilä-Sulzer_RTA96-C 10. ̂ https://www.mhi.co.jp/technology/review/pdf/e451/e451021.pdf

Further Reading Cotton, K.C. (1998). Evaluating and Improving Steam Turbine Performance. Traupel, W. (1977) (in German). Thermische Turbomaschinen. Thurston, R. H. (1878). A History of the Growth of the Steam Engine''. D. Appleton and

Co..

External link Steam Turbines: A Book of Instruction for the Adjustment and Operation of the Principal

Types of this Class of Prime Movers by Hubert E. Collins.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

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wind turbine

 Dictionary: wind turbine   (wĭnd) Sponsored LinksUsed Steam TurbinesEurope's largest provider of used Steam Turbines & Power Plants www.lohrmann.comSiemens answers:Efficient energy supply with Offshore Windparks. www.Siemens.com/AnswersHome > Library > Literature & Language > Dictionaryn.

A turbine that is powered by the wind.

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Background

A wind turbine is a machine that converts the wind's kinetic energy into rotary mechanical energy, which is then used to do work. In more advanced models, the rotational energy is converted into electricity, the most versatile form of energy, by using a generator.

For thousands of years people have used windmills to pump water or grind grain. Even into the twentieth century tall, slender, multi-vaned wind turbines made entirely of metal were used in American homes and ranches to pump water into the house's plumbing system or into the cattle's watering trough. After World War I, work was begun to develop wind turbines that could produce electricity. Marcellus Jacobs invented a prototype in 1927 that could provide power for a radio and a few lamps but little else. When demand for electricity increased later, Jacobs's small, inadequate wind turbines fell out of use.

The first large-scale wind turbine built in the United States was conceived by Palmer Cosslett Putnam in 1934; he completed it in 1941. The machine was huge. The tower was 36.6 yards (33.5 meters) high, and its two stainless steel blades had diameters of 58 yards (53 meters). Putnam's wind turbine could produce 1,250 kilowatts of electricity, or enough to meet the needs of a small town. It was, however, abandoned in 1945 because of mechanical failure.

With the 1970s oil embargo, the United States began once more to consider the feasibility of producing cheap electricity from wind turbines. In 1975 the prototype Mod-O was in operation. This was a 100 kilowatt turbine with two 21-yard (19-meter) blades. More prototypes followed

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w ind turbine

(Mod-OA, Mod-1, Mod-2, etc.), each larger and more powerful than the one before. Currently, the United States Department of Energy is aiming to go beyond 3,200 kilowatts per machine.

Many different models of wind turbines exist, the most striking being the vertical-axis Darrieus, which is shaped like an egg beater. The model most supported by commercial manufacturers, however, is a horizontal-axis turbine, with a capacity of around 100 kilowatts and three blades not more than 33 yards (30 meters) in length. Wind turbines with three blades spin more smoothly and are easier to balance than those with two blades. Also, while larger wind turbines produce more energy, the smaller models are less likely to undergo major mechanical failure, and thus are more economical to maintain.

Wind farms have sprung up all over the United States, most notably in California. Wind farms are huge arrays of wind turbines set in areas of favorable wind production. The great number of interconnected wind turbines is necessary in order to produce enough electricity to meet the needs of a sizable population. Currently, 17,000 wind turbines on wind farms owned by several wind energy companies produce 3.7 billion kilowatt-hours of electricity annually, enough to meet the energy needs of 500,000 homes.

Raw Materials

A wind turbine consists of three basic parts: the tower, the nacelle, and the rotor blades. The tower is either a steel lattice tower similar to electrical towers or a steel tubular tower with an inside ladder to the nacelle. Most towers do not have guys, which are cables used for support, and most are made of steel that has been coated with a zinc alloy for protection, though some are painted instead. The tower of a typical American-made turbine is approximately 80 feet tall and weighs about 19,000 pounds.

The nacelle is a strong, hollow shell that contains the inner workings of the wind turbine. Usually made of fiberglass, the nacelle contains the main drive shaft and the gearbox. It also contains the blade pitch control, a hydraulic system that controls the angle of the blades, and the yaw drive, which controls the position of the turbine relative to the wind. The generator and electronic controls are standard equipment whose main components are steel and copper. A typical nacelle for a current turbine weighs approximately 22,000 pounds.

The most diverse use of materials and the most experimentation with new materials occur with the blades. Although the most dominant material used for the blades in commercial wind turbines is fiberglass with a hollow core, other materials in use include lightweight woods and aluminum. Wooden blades are solid, but most blades consist of a skin surrounding a core that is either hollow or filled with a lightweight substance such as plastic foam or honeycomb, or balsa wood. A typical fiberglass blade is about 15 meters in length and weighs approximately 2,500 pounds.

Wind turbines also include a utility box, which converts the wind energy into electricity and which is located at the base of the tower. Various cables connect the utility box to the nacelle, while others connect the whole turbine to nearby turbines and to a transformer.

The ManufacturingProcess

Before consideration can be given to the construction of individual wind turbines, manufacturers must determine a proper area for the siting of wind farms. Winds must be consistent, and their speed must be regularly over 15.5 miles per hour (25 kilometers per hour). If the winds are stronger during certain seasons, it is preferred that they be greatest during periods of maximum electricity use. In California's Altamont Pass, for instance, site of the world's largest wind farm, wind speed peaks in the summer when demand is high. In some areas of New England where wind farms are being considered, winds are strongest in the winter, when the need for heating increases the consumption of electrical power. Wind farms work best in open areas of slightly rolling land surrounded by mountains. These areas are preferred because the wind turbines can be placed on ridges and remain unobstructed by trees and buildings, and the mountains concentrate the air flow, creating a natural wind tunnel of stronger, faster winds. Wind farms must also be placed near utility lines to facilitate the transfer of the electricity to the local power plant.

Preparing the site

Wherever a wind farm is to be built, the roads are cut to make way for transporting parts. At each wind turbine location, the land is graded and the pad area is leveled. A concrete foundation is then laid into the ground, followed by the installation of the underground cables. These cables connect the wind turbines to each other in series, and also connect all of them to the remote control center, where the wind farm is monitored and the electricity is sent to the power company.

Erecting the tower

Although the tower's steel parts are manufactured off site in a factory, they are usually assembled on site. The parts are bolted together before erection, and the tower is kept horizontal until placement. A crane lifts the tower into position, all bolts are tightened, and stability is tested upon completion.

Nacelle

The fiberglass nacelle, like the tower, is manufactured off site in a factory. Unlike the tower, however, it is also put together in the factory. Its inner workings—main drive shaft, gearbox, and blade pitch and yaw controls—are assembled and then mounted onto a base frame. The nacelle is then bolted around the equipment. At the site, the nacelle is lifted onto the completed tower and bolted into place.

Rotary blades

Aluminum blades are created by bolting sheets of aluminum together, while wooden blades are carved to form an aerodynamic propeller similar in cross-section to an airplane wing.

By far the greatest number of blades, however, are formed from fiberglass. The manufacture of fiberglass is a painstaking operation. First, a mold that is in two halves like a clam shell, yet shaped like a blade, is prepared. Next, a fiberglass-resin composite mixture is applied to the inner surfaces of the mold, which is then closed. The fiberglass mixture must then dry for several hours; while it does, an air-filled bladder within the mold helps the blade keep its shape. After the fiberglass is dry, the mold is then opened and the bladder is removed. Final preparation of the blade involves cleaning, sanding, sealing the two halves, and painting.

The blades are usually bolted onto the nacelle after it has been placed onto the tower. Because assembly is easier to accomplish on the ground, occasionally a three-pronged blade has two blades bolted onto the nacelle before it is lifted, and the third blade is bolted on after the nacelle is in place.

Installation of control systems

The utility box for each wind turbine and the electrical communication system for the wind farm is installed simultaneously with the placement of the nacelle and blades. Cables run from the nacelle to the utility box and from the utility box to the remote control center.

Quality Control

Unlike most manufacturing processes, production of wind turbines involves very little concern with quality control. Because mass production of wind turbines is fairly new, no standards have been set. Efforts are now being made in this area on the part of both the government and manufacturers.

While wind turbines on duty are counted on to work 90 percent of the time, many structural flaws are still encountered, particularly with the blades. Cracks sometimes appear soon after manufacture. Mechanical failure because of alignment and assembly errors is common. Electrical sensors frequently fail because of power surges. Non-hydraulic brakes tend to be reliable, but hydraulic braking systems often cause problems. Plans are being developed to use existing technology to solve these difficulties.

Wind turbines do have regular maintenance schedules in order to minimize failure. Every three months they undergo inspection, and every six months a major maintenance checkup is scheduled. This usually involves lubricating the moving parts and checking the oil level in the gearbox. It is also possible for a worker to test the electrical system on site and note any problems with the generator or hookups.

Environmental Benefitsand Drawbacks

A wind turbine that produces electricity from inexhaustible winds creates no pollution. By comparison, coal, oil, and natural gas produce one to two pounds of carbon dioxide (an emission that contributes to the greenhouse effect and global warming) per kilowatt-hour produced. When wind energy is used for electrical needs, dependence on fossil fuels for this purpose is reduced. The current annual production of electricity by wind turbines (3.7 billion kilowatt-hours) is equivalent to four million barrels of oil or one million tons of coal.

Wind turbines are not completely free of environmental drawbacks. Many people consider them to be unaesthetic, especially when huge wind farms are built near pristine wilderness areas. Bird kills have been documented, and the whirring blades do produce quite a bit of noise. Efforts to reduce these effects include selecting sites that do not coincide with wilderness areas or bird migration routes and researching ways to reduce noise.

The Future

The future can only get better for wind turbines. The potential for wind energy is largely untapped. The United States Department of Energy estimates that ten times the amount of electricity currently being produced can be achieved by 1995. By 2005, seventy times current production is possible. If this is accomplished, wind turbines would account for 10 percent of the United States' electricity production.

Research is now being done to increase the knowledge of wind resources. This involves the testing of more and more areas for the possibility of placing wind farms where the wind is reliable and strong. Plans are in effect to increase the life span of the machine from five years to 20 to 30 years, improve the efficiency of the blades, provide better controls, develop drive trains that last longer, and allow for better surge protection and grounding. The United States Department of Energy has recently set up a schedule to implement the latest research in order to build wind turbines with a higher efficiency rating than is now possible. (The efficiency of an ideal wind turbine is 59.3 percent. That is, 59.3 percent of the wind's energy can be captured. Turbines in actual use are about 30 percent efficient.) The United States Department of Energy has also contracted with three corporations to research ways to reduce mechanical failure. This project began in the spring of 1992 and will extend to the end of the century.

Wind turbines will become more prevalent in upcoming years. The largest manufacturer of wind turbines in the world, U.S. Windpower, plans to expand from 420 megawatt capacity (4,200 machines) to 800 megawatts (8,000 machines) by 1995. They plan to have 2,000 megawatts (20,000 machines) by the year 2000. Other wind turbine manufacturers also plan to increase the numbers produced. International committees composed of several industrialized nations have formed to discuss the potential of wind turbines. Efforts are also being made to provide developing countries with small wind turbines similar to those Marcellus Jacobs built in the 1920s. Denmark, which already produces 70 percent to 80 percent of Europe's wind power, is developing plans to expand manufacture of wind turbines. The turn of the century should see wind turbines that are properly placed, efficient, durable, and numerous.

Where To Learn More

Books

Assessment of Research Needs for Wind Turbine Rotor Materials Technology. National Academy Press, 1991.

Eggleston, David M. Wind Turbine Engineering Design. Van Nostrand Reinhold, 1987.

Hunt, Daniel V. Windpower: A Handbook on Wind Energy Conversion Systems. Van Nostrand Reinhold, 1981.

Kovarik, Tom, Charles Pupher, and John Hurst. Wind Energy. Domus Books, 1979.

Park, Jack. The Wind Power Book. Cheshire Books, 1981.

Putnam, Palmer Cosslett. Power from the Wind. Van Nostrand Company, 1948.

Periodicals

Frank, Deborah. "Blowing in the Wind," Popular Mechanics, August, 1991, pp. 40-43+.

Mohs, Mayo. "Blowin' in the Wind," Discover. June, 1986, pp. 68-74.

Moretti, Peter M. and Louis V. Divone. "Modern Windmills," Scientific American. June, 1986, pp. 110-118.

Price, Marshall. "Basement-Built Wind Generator," Mother Earth News. July-August, 1986, p. 103.

Stefanides, E. J. "Hydraulic Yaw Control Upgrades Wind Turbine," Design News. March 3, 1986, p. 240.

Vogel, Shawna. "Wind Power," Discover. May, 1989, pp. 46-49.

[Article by: Rose Secrest]

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Top Home > Library > Miscellaneous > WikipediaWind turbines

HistoryDesign

ManufacturersUnconventional

Wind farm in the North Sea off Belgium

Wind turbines near Aalborg, Denmark

A wind turbine is a rotating machine which converts the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill. If the mechanical energy is then converted to electricity, the machine is called a wind generator, wind turbine, wind power unit (WPU), wind energy converter (WEC), or aerogenerator.

This article discusses electric power generation machinery. The Windmill article discusses machines used for grain-grinding, water pumping, etc. The article on wind power describes turbine placement, economics and public concerns. The wind energy section of that article describes the distribution of wind energy over time, and how that affects wind-turbine design. See environmental concerns with electricity generation for discussion of environmental problems with wind-energy production.

Contents[hide]

1 History 2 Resources 3 Types of wind turbines

o 3.1 Horizontal axis 3.1.1 HAWT Subtypes 3.1.2 HAWT advantages 3.1.3 HAWT disadvantages 3.1.4 Cyclic stresses and vibration

o 3.2 Vertical axis 3.2.1 VAWT subtypes 3.2.2 VAWT advantages 3.2.3 VAWT disadvantages

4 Turbine design and construction 5 Low temperature 6 Unconventional wind turbines 7 Small wind turbines 8 Record-holding turbines 9 Criticisms 10 See also 11 References 12 Further reading 13 External links

HistoryMain article: History of wind power

The world's first automatically operated wind turbine was built in Cleveland in 1888 by Charles F. Brush. It was 60 feet tall, weighed four tons and had 12kW turbine.[1]

Wind machines were used in Persia as early as 200 B.C.[2] This type of machine was introduced into the Roman Empire by 250 A.D. However, the first practical windmills were built in Sistan, Iran, from the 7th century. These were vertical axle windmills, which had long vertical driveshafts with rectangle shaped blades.[3] Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind corn and draw up water, and were used in the gristmilling and sugarcane industries.[4]

By the 14th century, Dutch windmills were in use to drain areas of the Rhine River delta. In Denmark by 1900 there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The first known electricity generating windmill operated was a battery charging machine installed in 1887 by James Blyth in Scotland, UK[citation needed]. The first windmill for electricity production in the United States was built in Cleveland, Ohio by Charles F Brush in 1888, and in 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, most for water-pumping.[5] By the 1930s windmills for electricity were common on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high-tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers.

A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual capacity factor of 32 per cent, not much different from current wind machines.[6]

The first utility grid-connected wind turbine operated in the UK was built by the John Brown Company in 1954 in the Orkney Islands. It had an 18 meter diameter, three-bladed rotor and a rated output of 100 kW.

ResourcesMain article: Wind power

Wind turbines require locations with constantly high wind speeds. With a wind resource assessment it is possible to estimate the amount of energy the wind turbine will produce.

A yardstick frequently used to determine good locations is referred to as Wind Power Density (WPD.) It is a calculation relating to the effective force of the wind at a particular location, frequently expressed in terms of the elevation above ground level over a period of time. It takes into account wind velocity and mass. Color coded maps are prepared for a particular area described, for example, as "Mean Annual Power Density at 50 Meters." The results of the above calculation are included in an index developed by the National Renewable Energy Lab and referred to as "NREL CLASS." The larger the WPD calculation, the higher it is rated by class.[7]

Types of wind turbines

Wind turbines can be separated into two types based by the axis in which the turbine rotates. Turbines that rotate around a horizontal axis are more common. Vertical-axis turbines are less frequently used.

Horizontal axis

Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position

Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.[8]

Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted up a small amount.

Downwind machines have been built, despite the problem of turbulence, because they don't need an additional mechanism for keeping them in line with the wind, and because in high winds, the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Since turbulence leads to fatigue failures, and reliability is so important, most HAWTs are upwind machines.

HAWT Subtypes

Doesburger windmill, Ede, The Netherlands.12th-century windmills

These squat structures, typically (at least) four bladed, usually with wooden shutters or fabric sails, were developed in Europe. These windmills were pointed into the wind manually or via a tail-fan and were typically used to grind grain. In the Netherlands they were also used to pump water from low-lying land, and were instrumental in keeping its polders dry.

In Schiedam, the Netherlands, a traditional style windmill (the Noletmolen) was built in 2005 to generate electricity.[9] The mill is one of the tallest Tower mills in the world, being some 42.5 metres (139 ft) tall.

19th-century windmills

The Eclipse windmill factory was set up around 1866 in Beloit, Wisconsin and soon became successful building mills for pumping water on farms and for filling railroad tanks. Other firms like Star, Dempster, and Aeromotor also entered the market. Hundreds of thousands of these mills were produced before rural electrification and small numbers continue to be made.[5] They typically had many blades, operated at tip speed ratios (defined below) not better than one, and had good starting torque. Some had small direct-current generators used to charge storage batteries, to provide power to lights, or to operate a radio receiver. The American rural electrification connected many farms to centrally-generated power and replaced individual windmills as a primary source of farm power by the 1950s. They were also produced in other countries like South Africa and Australia (where an American design was copied in 1876[10]). Such devices are still used in locations where it is too costly to bring in commercial power.

Modern wind turbines

Three bladed wind turbine

Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. These have high tip speeds of up to six times the wind speed, high efficiency, and low torque ripple, which contribute to good reliability. The blades are usually colored light gray to blend in with the clouds and range in length from 20 to 40 metres (65 to 130 ft) or more. The tubular steel towers range from 200 to 300 feet (60 to 90 metres) tall. The blades rotate at 10-22 revolutions per minute.[11][12] A gear box is commonly used to step up the speed of the generator, although designs may also use direct drive of an annular generator. Some models operate at constant speed, but more energy can be

collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system. All turbines are equipped with shut-down features to avoid damage at high wind speeds.

HAWT advantages

Variable blade pitch, which gives the turbine blades the optimum angle of attack. Allowing the angle of attack to be remotely adjusted gives greater control, so the turbine collects the maximum amount of wind energy for the time of day and season.

The tall tower base allows access to stronger wind in sites with wind shear. In some wind shear sites, every ten meters up, the wind speed can increase by 20% and the power output by 34%.

High efficiency, since the blades always move perpendicularly to the wind, receiving power through the whole rotation. In contrast, all vertical axis wind turbines, and most proposed airborne wind turbine designs, involve various types of reciprocating actions, requiring airfoil surfaces to backtrack against the wind for part of the cycle. Backtracking against the wind leads to inherently lower efficiency.

HAWT disadvantages

Turbine blade convoy passing through Edenfield in the UK

The tall towers and blades up to 90 meters long are difficult to transport. Transportation can now cost 20% of equipment costs.

Tall HAWTs are difficult to install, needing very tall and expensive cranes and skilled operators.

Massive tower construction is required to support the heavy blades, gearbox, and generator.

Reflections from tall HAWTs may affect side lobes of radar installations creating signal clutter, although filtering can suppress it.

Their height makes them obtrusively visible across large areas, disrupting the appearance of the landscape and sometimes creating local opposition.

Downwind variants suffer from fatigue and structural failure caused by turbulence when a blade passes through the tower's wind shadow (for this reason, the majority of HAWTs use an upwind design, with the rotor facing the wind in front of the tower).

HAWTs require an additional yaw control mechanism to turn the blades toward the wind.

Cyclic stresses and vibration

Cyclic stresses fatigue the blade, axle and bearing; material failures were a major cause of turbine failure for many years. Because wind velocity often increases at higher altitudes, the backward force and torque on a horizontal-axis wind turbine (HAWT) blade peaks as it turns through the highest point in its circle. The tower hinders the airflow at the lowest point in the circle, which produces a local dip in force and torque. These effects produce a cyclic twist on the main bearings of a HAWT. The combined twist is worst in machines with an even number of blades, where one is straight up when another is straight down. To improve reliability, teetering hubs have been used which allow the main shaft to rock through a few degrees, so that the main bearings do not have to resist the torque peaks.

When the turbine turns to face the wind, the rotating blades act like a gyroscope. As it pivots, gyroscopic precession tries to twist the turbine into a forward or backward somersault. For each blade on a wind generator's turbine, precessive force is at a minimum when the blade is horizontal and at a maximum when the blade is vertical. This cyclic twisting can quickly fatigue and crack the blade roots, hub and axle of the turbines.

Vertical axis

Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable. VAWTs can utilize winds from varying directions.

With a vertical axis, the generator and gearbox can be placed near the ground, so the tower doesn't need to support it, and it is more accessible for maintenance. Drawbacks are that some designs produce pulsating torque. Drag may be created when the blade rotates into the wind.

It is difficult to mount vertical-axis turbines on towers, meaning they are often installed nearer to the base on which they rest, such as the ground or a building rooftop. The wind speed is slower at a lower altitude, so less wind energy is available for a given size turbine. Air flow near the ground and other objects can create turbulent flow, which can introduce issues of vibration, including noise and bearing wear which may increase the maintenance or shorten the service life. However, when a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double the wind speed at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence.

VAWT subtypes

30 m Darrieus wind turbine in the Magdalen IslandsDarrieus wind turbine 

"Eggbeater" turbines. They have good efficiency, but produce large torque ripple and cyclic stress on the tower, which contributes to poor reliability. Also, they generally require some external power source, or an additional Savonius rotor, to start turning, because the starting torque is very low. The torque ripple is reduced by using three or more blades which results in a higher solidity for the rotor. Solidity is measured by blade area over the rotor area. Newer Darrieus type turbines are not held up by guy-wires but have an external superstructure connected to the top bearing.

A helical twisted VAWT.Giromill

A subtype of Darrieus turbine with straight, as opposed to curved, blades. The cycloturbine variety has variable pitch to reduce the torque pulsation and is self-starting.[13] The advantages of variable pitch are: high starting torque; a wide, relatively flat torque curve; a lower blade speed ratio; a higher coefficient of performance; more efficient operation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V, or curved blades may be used.

12 m Windmill with rotational sails in Osijek, CroatiaSavonius wind turbine 

These are drag-type devices with two (or more) scoops that are used in anemometers, Flettner vents (commonly seen on bus and van roofs), and in some high-reliability low-efficiency power turbines. They are always self-starting if there are at least three scoops. They sometimes have long helical scoops to give a smooth torque.

VAWT advantages

A massive tower structure is less frequently used, as VAWTs are more frequently mounted with the lower bearing mounted near the ground.

Designs without yaw mechanisms are possible with fixed pitch rotor designs. A VAWT can be located nearer the ground, making it easier to maintain the moving

parts. VAWTs have lower wind startup speeds than HAWTs. Typically, they start creating

electricity at 6 m.p.h. (10 km/h). VAWTs may be built at locations where taller structures are prohibited. VAWTs situated close to the ground can take advantage of locations where mesas,

hilltops, ridgelines, and passes funnel the wind and increase wind velocity. VAWTs may have a lower noise signature.

VAWT disadvantages

Most VAWTs produce energy at only 50% of the efficiency of HAWTs in large part because of the additional drag that they have as their blades rotate into the wind. Versions that reduce drag produce more energy, especially those that funnel wind into the collector area[citation needed].

A VAWT that uses guy-wires to hold it in place puts stress on the bottom bearing as all the weight of the rotor is on the bearing. Guy wires attached to the top bearing increase downward thrust in wind gusts. Solving this problem requires a superstructure to hold a top bearing in place to eliminate the downward thrusts of gust events in guy wired models.

While VAWTs' parts are located on the ground, they are also located under the weight of the structure above it, which can make changing out parts nearly impossible without dismantling the structure if not designed properly.

Having rotors located close to the ground where wind speeds are lower due to wind shear, VAWTs may not produce as much energy at a given site as a HAWT with the same footprint or height.

Because VAWTs are not commonly deployed due mainly to the serious disadvantages mentioned above, they appear novel to those not familiar with the wind industry. This has often made them the subject of wild claims and investment scams over the last 50 years.[14][15]

Turbine design and construction

Components of a horizontal-axis wind turbineMain article: Wind turbine design

Wind turbines are designed to exploit the wind energy that exists at a location. Aerodynamic modeling is used to determine the optimum tower height, control systems, number of blades, and blade shape.

Wind turbines convert wind energy to electricity for distribution. The turbine can be divided into three components. The rotor component, which is approximately 20% of the wind turbine cost, includes the blades for converting wind energy to low speed rotational energy. The generator component, which is approximately 34% of the wind turbine cost, includes the electrical generator, the control electronics, and most likely a gearbox component for converting the low speed incoming rotation to high speed rotation suitable for generating electricity. The structural support component, which is approximately 15% of the wind turbine cost, includes the tower and rotor pointing mechanism.[16]

Low temperatureUtility-scale wind turbine generators have minimum temperature operating limits which apply in areas that experience temperatures below –20 °C. Wind turbines must be protected from ice accumulation, which can make anemometer readings inaccurate and which can cause high

structure loads and damage. Some turbine manufacturers offer low-temperature packages at a few percent extra cost, which include internal heaters, different lubricants, and different alloys for structural elements. If the low-temperature interval is combined with a low-wind condition, the wind turbine will require an external supply of power, equivalent to a few percent of its rated power, for internal heating. For example, the St. Leon, Manitoba project has a total rating of 99 MW and is estimated to need up to 3 MW (around 3% of capacity) of station service power a few days a year for temperatures down to –30 °C. This factor affects the economics of wind turbine operation in cold climates.

Unconventional wind turbinesMain article: Unconventional wind turbines

One E-66 wind turbine at Windpark Holtriem, Germany, carries an observation deck, open for visitors. Another turbine of the same type, with an observation deck, is located in Swaffham, England.

A series of lighter-than-air wind turbines are in development in Canada by Magenn Power. They deliver power to the ground by a tether system.[17]

Wind turbines may also be used in conjunction with a large vertical solar updraft tower to extract the energy due to air heated by the sun. Or as part of wave powered generators where air displaced by waves drives turbines.[18]

Small wind turbines

A small wind turbine being used at the Riverina Environmental Education Centre near Wagga Wagga, New South Wales, AustraliaMain article: Small wind turbine

Small wind turbines may be as small as a fifty-watt generator for boat or caravan use. Small units often have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind. Larger, more costly turbines generally have geared power

trains, alternating current output, flaps and are actively pointed into the wind. Direct drive generators and aeroelastic blades for large wind turbines are being researched.

Record-holding turbinesThe world's largest turbines are manufactured by the Northern German companies Enercon and REpower. The Enercon E-126 delivers up to 6 MW, has an overall height of 198 m (650 ft) and a diameter of 126 meters (413 ft). The Repower 5M delivers up to 5 MW, has an overall height of 183 m (600 ft) and has a diameter of 126 m (413 ft).

The turbine closest to the North Pole is a Nordex N-80 in Havøygavlen near Hammerfest, Norway. The turbines currently operating closest to the South Pole are two Enercon E-30 in Antarctica, used to power the Australian Research Division's Mawson Station,[19] although a modified HR3 turbine from Northern Power Systems operated at the Amundsen-Scott South Pole Station in 1997 and 1998.[20]

Matilda was a wind turbine located on Gotland, Sweden. It produced a total of 61.4 GW·h in the 15 years it was active. That is more renewable energy than any other single wind power turbine had ever produced to that date. It was demolished on June 6, 2008.

The world's highest wind turbine of company DeWind is located in the Andes/Argentina to 4,100 metres (13,000 ft) above sea level. Turbine type D8.2 - 2000 kW / 50 Hz was used for that site. This turbine has a new drive train concept with a special torque converter (WinDrive) of the company Voith and a synchronous generator. The WKA was put into operation in December 2007 and has supplied the local gold mine with electricity since then.[21][22]

CriticismsMain article: Environmental effects of wind power

While wind turbines in operation can generate electricity without the emission of greenhouse gases or the consumption of fuel, they have significant disadvantages over conventional generation.

One disadvantage is that wind power is an intermittent power source. The production from a wind turbine may increase or decrease dramatically over a short period of time with little or no warning. In the absence of large scale energy storage, the balance of the grid must be able to quickly compensate for this change.

The economics of wind turbines can be challenging as well. With high quality wind resources often located in areas inhospitable to people, logistics and transmission capacity can introduce significant obstacles to new installations.

The impact of wind turbines on wildlife has often been cited as a disadvantage of wind installations. Wind turbines can pose a danger to birds and bats, though the magnitude and

gravity of this danger is much less than more ubiquitous threats such as house cats or plate glass. In fact, less than one bird is killed per 10,000 wind turbines annually.[23]

Wind turbines are certainly not without critics, but may have much more favorable life cycle impacts than conventional generation technologies.

See also

Sustainable development portal

Airborne wind turbine American Wind Energy Association Atmospheric icing Darrieus wind turbine Electrical generator Éolienne Bollée Floating wind turbine Green energy Hybrid power source

List of wind turbine manufacturers Microgeneration Renewable energy Savonius wind turbine Thomas O. Perry Wind power Wind turbines (UK domestic) Windmill

References1. ̂ A Wind Energy Pioneer: Charles F. Brush, Danish Wind Industry Association,

http://www.windpower.org/en/pictures/brush.htm, retrieved on 2008-12-28 2. ̂ "Part 1 — Early History Through 1875". http://www.telosnet.com/wind/early.html.

Retrieved on 2008-07-31. 3. ̂ Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology: An illustrated

history, p. 54. Cambridge University Press. ISBN 0-521-42239-6. 4. ̂ Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific

American, May 1991, p. 64-69. (cf. Donald Routledge Hill, Mechanical Engineering) 5. ^ a b Quirky old-style contraptions make water from wind on the mesas of West Texas 6. ̂ Alan Wyatt: Electric Power: Challenges and Choices. Book Press Ltd., Toronto 1986,

ISBN 0-920650-00-7 7. ̂ Kansas Wind Energy Project, Affiliated Atlantic & Western Group Inc, 5250 W 94th

Terrace, Prairie Village, Kansas 66207 8. ̂ http://www.windpower.org/en/tour/wtrb/comp/index.htm Wind turbine components

retrieved November 8, 2008 9. ̂ Molendatabase Dutch text 10. ̂ Extract from Triumph of the Griffiths Family,

http://au.geocities.com/ozwindmills/SouthernCross.htm, Bruce Millett, 1984, accessed January 26, 2008

11. ̂ 1.5 MW Wind Turbine Technical Specifications 12. ̂ Size specifications of common industrial wind turbines 13. ̂ http://www.awea.org/faq/vawt.html

14. ̂ http://www.rebelwolf.com/essn/ESSN-Aug2005.pdf 15. ̂ http://www.motherearthnews.com/Renewable-Energy/2008-02-01/Wind-Power-

Horizontal-and-Vertical-Axis-Wind-Turbines.aspx 16. ̂ "Wind Turbine Design Cost and Scaling Model," Technical Report NREL/TP-500-

40566, December, 2006, page 35,36. http://www.nrel.gov/docs/fy07osti/40566.pdf 17. ̂ Magenn Power Inc. - Technology 18. ̂ see http://www.bwea.com/marine/devices.html and scroll down to SPERBOY™, 19. ̂ Mawson Station Electrical Energy - Australian Antarctic Division 20. ̂ Bill Spindler, The first Pole wind turbine. 21. ̂ http://www.youtube.com/watch?v=VxYm2bWUdjo 22. ̂ http://www.voithturbo.com/vt_en_pua_windrive_project-report_2008.htm 23. ̂ www.awea.org/pubs/factsheets/MythsvsFacts-FactSheet.pdf

Further reading BBC News,"Wind farms 'must take root in UK",

http://news.bbc.co.uk/2/hi/science/nature/4560139.stm, BBC News, Copyright 2007 Tony Burton, David Sharpe, Nick Jenkins, Ervin Bossanyi: Wind Energy Handbook,

John Wiley & Sons, 1st edition (2001), ISBN 0-471-48997-2 Darrell, Dodge, Early History Through 1875, TeloNet Web Development,

http://telosnet.com/wind/early.html, Copyright 1996-2001 David, Macaulay, New Way Things Work, Houghton Mifflin Company, Boston,

Copyright 1994-1999, pg.41-42 www.awea.org/pubs/factsheets/MythsvsFacts-FactSheet.pdf

External links

Wikimedia Commons has media related to: Wind turbine

Photo journal and tutorial for 1.5kw residential wind turbine Domestic Wind Turbine installation and videos Wind Projects Guided tour on wind energy Wind Energy Technology World Wind Energy Association Wind turbine simulation, National Geographic Domestic and Commercial wind turbine directory and information wiki,

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n.

An internal-combustion engine consisting essentially of an air compressor, combustion chamber, and turbine wheel that is turned by the expanding products of combustion.

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One of a class of heat engines which use fuel energy to produce mechanical output power, either as torque through a rotating shaft (industrial gas turbines) or as jet power in the form of velocity through an exhaust nozzle (aircraft jet engines). The fuel energy is added to the working substance, which is gaseous in form and most often air, either by direct internal combustion or indirectly through a heat exchanger. The heated working substance, air co-mixed with combustion products in the usual case of internal combustion, acts on a continuously rotating turbine to produce power. The gas turbine is thus distinguished from heat engine types where the working substance produces mechanical power by acting intermittently on an enclosed piston, and from steam turbine engines where the working substance is water in liquid and vapor form. See also Internal combustion engine; Steam turbine.

Gas turbine engines depend on the principle of the air cycle, where, ambient air is first compressed to a maximum pressure level, at which point fuel heat energy is added to raise its temperature, also to a maximum level. The air is then expanded from high to low pressure through a turbine. The expansion process through the turbine extracts energy from the air, while the compression process requires energy input.

As the air moves through the engine, the turbine continuously provides energy sufficient to drive the compressor. In addition, because the turbine expansion process starts from a high temperature that comes from the fuel energy released by combustion, surplus energy beyond that

gas turbine

0

gas turbine

required for compression can be extracted from the air by further expansion. At the point where the turbine has provided sufficient energy to power the compressor, the air pressure remains higher than the outside ambient level. This higher pressure represents available energy in the air that can be turned into useful output power by a final expansion process that returns the air pressure to ambient. The exhaust air leaves the engine with pressure equal to the outside, but at a higher temperature. As with any heat engine, the high exhaust temperature represents wasted energy that will dissipate into the outside atmosphere. See also Compressor.

From an energy accounting standpoint, the sequence of processes acting on the air from front to rear constitutes a full cycle. It starts with the outside air entering at its initial state, and is completed when the air returns again to both ambient pressure and temperature levels. The series of cycle processes includes the final outside dissipation of the wasted exhaust energy, inevitable for every heat engine according to Carnot's principle. The ideal version of the gas turbine cycle is known as the Brayton cycle. See also Brayton cycle; Carnot cycle.

For any completed cycle, the total energy added from the fuel sources will always be equal to the sum of the useful output energy and the wasted exhaust energy. The thermal efficiency, which is the ratio of net output energy to fuel input energy for the cycle, measures the engine's ability to minimize wasted energy. A thermal efficiency of 60% means that for every 100 units of added energy 60 units will be available as useful output while 40 units will leave the engine as high-temperature exhaust.

Another performance measure is the specific power, which is the ratio of output power to quantity of working substance mass flow rate. Gas turbine engines, in comparison with other types of heat engines, are characterized not only by high levels of efficiency but also by very high levels of specific power. They are especially useful for applications that need compact power.

By far the most common mechanical arrangement for the gas turbine is an in-line axial flow positioning of all components (see illustration). In the ground-based engine, the inlet at the front guides the incoming air into the compressor, which in turn delivers high-pressure air into the combustor section. The combustor burns the injected fuel at a high reaction temperature, using some of the air itself as an oxygen source. The combustion products in the combustor mix with the remaining unused air to reach a uniform equilibrium temperature, still high but diluted down from the reaction temperature. The hot, high-pressure combustor exit air enters the compressor drive turbine, where it expands down in pressure toward, but stays higher than, ambient level. This expansion process results in output shaft power that can be delivered directly to the compressor through a connecting rotating shaft. Starting from the exit of the compressor drive turbine, net output power remains available. This power can be realized through the process of further pressure expansion completely down to the ambient level. For ground-based applications, the final expansion takes place through a power turbine whose output shaft is connected to the external load. In the single-spool arrangement the power turbine and compressor drive turbine are indistinguishably combined into one unit which, together with the compressor and the output load, is connected to a common shaft. For aircraft applications, either a power turbine extracts useful power to drive a propeller through a separate shaft (turboprop), or the expansion process

takes place through a nozzle which acts to convert some of the thermal energy into velocity energy to be used for jet propulsion. See also Aircraft engine; Jet propulsion.

Simple gas turbine component arrangements.

Gas turbines characteristically produce smooth and linear throttle response over their entire operating range. Rotor speeds normally vary continuously over this range without the need for the gear shifting and clutch mechanisms found in piston engines. The governing fuel control senses rotor speeds, pressures, and temperatures to maintain stable, steady power or thrust output and, when needed, ensure rapid accelerations and decelerations. The control is programmed, normally by electronic input, to guard against harming the engine during throttle changes by governing the appropriate fuel input rate. Most important, during throttle transients the control functions to prevent turbine overheating, burner blowout, and compressor surge.

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The noun has one meaning:

Meaning #1: turbine that converts the chemical energy of a liquid fuel into mechanical energy by internal combustion; gaseous products of the fuel (which is burned in compressed air) are expanded through a turbine

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This machine has a single-stage radial compressor and turbine, a recuperator, and foil bearings.

A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.)

Energy is added to the gas stream in the combustor, where air is mixed with fuel and ignited. Combustion increases the temperature, velocity and volume of the gas flow. This is directed through a nozzle over the turbine's blades, spinning the turbine and powering the compressor.

Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks.

Contents[hide]

1 History

2 Theory of operation 3 Types of gas turbines

o 3.1 Aeroderivatives and jet engines o 3.2 Amateur gas turbines o 3.3 Auxiliary power units o 3.4 Industrial gas turbines for electrical generation

3.4.1 Compressed air energy storage o 3.5 Turboshaft engines o 3.6 Radial gas turbines o 3.7 Scale jet engines o 3.8 Microturbines

4 External combustion 5 Gas turbines in vehicles

o 5.1 Tank use o 5.2 Naval use o 5.3 Commercial use

6 Advances in technology 7 Advantages and disadvantages of gas turbine engines

o 7.1 Advantages of gas turbine engines o 7.2 Disadvantages of gas turbine engines

8 See also 9 References 10 Further reading 11 External links

History

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150: Hero's Engine (aeolipile) - apparently Hero's steam engine was taken to be no more than a toy, and thus its full potential not realized for centuries.

1500: The "Chimney Jack" was drawn by Leonardo da Vinci which was turning a roasting spit. Hot air from a fire rose through a series of fans which connect and turn the roasting spit.

1551: Taqi al-Din invented a steam turbine, which he used to power a self-rotating spit.[1] 1629: Jets of steam rotated a turbine that then rotated driven machinery allowed a

stamping mill to be developed by Giovanni Branca. 1678: Ferdinand Verbeist built a model carriage relying on a steam jet for power. 1791: A patent was given to John Barber, an Englishman, for the first true gas turbine.

His invention had most of the elements present in the modern day gas turbines. The turbine was designed to power a horseless carriage.

1872: The first true gas turbine engine was designed by Dr Franz Stolze, but the engine never ran under its own power.

1894: Sir Charles Parsons patented the idea of propelling a ship with a steam turbine, and built a demonstration vessel (the Turbinia). This principle of propulsion is still of some use.

1895: Three 4-ton 100 kW Parsons radial flow generators were installed in Cambridge Power Station, and used to power the first electric street lighting scheme in the city.

1903: A Norwegian, Ægidius Elling, was able to build the first gas turbine that was able to produce more power than needed to run its own components, which was considered an achievement in a time when knowledge about aerodynamics was limited. Using rotary compressors and turbines it produced 11 hp (massive for those days). His work was later used by Sir Frank Whittle.

1913: Nikola Tesla patents the Tesla turbine based on the Boundary layer effect. 1914: Application for a gas turbine engine filed by Charles Curtis. 1918: One of the leading gas turbine manufacturers of today, General Electric, started

their gas turbine division. 1920: The practical theory of gas flow through passages was developed into the more

formal (and applicable to turbines) theory of gas flow past airfoils by Dr A. A. Griffith. 1930: Sir Frank Whittle patented the design for a gas turbine for jet propulsion. His work

on gas propulsion relied on the work from all those who had previously worked in the same field and he has himself stated that his invention would be hard to achieve without the works of Ægidius Elling. The first successful use of his engine was in April 1937.

1934: Raúl Pateras de Pescara patented the free-piston engine as a gas generator for gas turbines.

1936: Hans von Ohain and Max Hahn in Germany developed their own patented engine design at the same time that Sir Frank Whittle was developing his design in England.

Theory of operationGas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isentropically, combustion occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure.

In practice, friction, and turbulence cause:

1. non-isentropic compression: for a given overall pressure ratio, the compressor delivery temperature is higher than ideal.

2. non-isentropic expansion: although the turbine temperature drop necessary to drive the compressor is unaffected, the associated pressure ratio is greater, which decreases the expansion available to provide useful work.

3. pressure losses in the air intake, combustor and exhaust: reduces the expansion available to provide useful work.

Brayton cycle

As with all cyclic heat engines, higher combustion temperature means greater efficiency. The limiting factor is the ability of the steel, nickel, ceramic, or other materials that make up the engine to withstand heat and pressure. Considerable engineering goes into keeping the turbine parts cool. Most turbines also try to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchangers that pass exhaust heat to the compressed air, prior to combustion. Combined cycle designs pass waste heat to steam turbine systems. And combined heat and power (co-generation) uses waste heat for hot water production.

Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple turbines might have one moving part: the shaft/compressor/turbine/alternative-rotor assembly (see image above), not counting the fuel system.

More sophisticated turbines (such as those found in modern jet engines) may have multiple shafts (spools), hundreds of turbine blades, movable stator blades, and a vast system of complex piping, combustors and heat exchangers.

As a general rule, the smaller the engine the higher the rotation rate of the shaft(s) needs to be to maintain top speed. Turbine blade top speed determines the maximum pressure that can be gained,this produces the maximum power possible independent of the size of the engine. Jet engines operate around 10,000 rpm and micro turbines around 100,000 rpm.

Thrust bearings and journal bearings are a critical part of design. Traditionally, they have been hydrodynamic oil bearings, or oil-cooled ball bearings. These bearings are being surpassed by foil bearings, which have been successfully used in micro turbines and auxiliary power units.

Types of gas turbines

Aeroderivatives and jet engines

Diagram of a gas turbine jet engine

Airbreathing jet engines are gas turbines optimized to produce thrust from the exhaust gases, or from ducted fans connected to the gas turbines. Jet engines that produce thrust primarily from the direct impulse of exhaust gases are often called turbojets, whereas those that generate most of their thrust from the action of a ducted fan are often called turbofans or (rarely) fan-jets.

Gas turbines are also used in many liquid propellant rockets, the gas turbines are used to power a turbopump to permit the use of lightweight, low pressure tanks, which saves considerable dry mass.

Diagram of a high-pressure turbine blade

Aeroderivatives are also used in electrical power generation due to their ability to startup, shut down, and handle load changes more quickly than industrial machines. They are also used in the marine industry to reduce weight. The GE LM2500 and LM6000 are two common models of this type of machine.

Amateur gas turbines

Increasing numbers of gas turbines are being used or even constructed by amateurs.

In its most straightforward form, these are commercial turbines acquired through military surplus or scrapyard sales, then operated for display as part of the hobby of engine collecting.[2][3] In its most extreme form, amateurs have even rebuilt engines beyond professional repair and then used them to compete for the Land Speed Record.

The simplest form of self-constructed gas turbine recycles the turbine wheel and compressor from an automotive turbocharger. A single separate combustion chamber is fabricated and plumbed between the compressor and turbine.[4]

More sophisticated turbojets are also built, where their thrust and light weight are sufficient to power large model aircraft.[5] The Schreckling design[5] constructs the entire engine from raw materials, including the fabrication of a centrifugal compressor wheel from plywood, epoxy and wrapped carbon fibre strands.

Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. Several small companies now manufacture small turbines and parts for the amateur. Most turbojet-powered model aircraft are now using these commercial and semi-commercial microturbines, rather than a Schreckling-like home-build.[6]

Auxiliary power units

Auxiliary power units (APUs) are small gas turbines designed for auxiliary power of larger machines, such as those inside an aircraft. They supply compressed air for aircraft ventilation (with an appropriate compressor design), start-up power for larger jet engines, and electrical and hydraulic power.

Industrial gas turbines for electrical generation

GE H series power generation gas turbine. This 480-megawatt unit has a rated thermal efficiency of 60% in combined cycle configurations.

Industrial gas turbines differ from aeroderivatave in that the frames, bearings, and blading is of heavier construction. Industrial gas turbines range in size from truck-mounted mobile plants to enormous, complex systems. They can be particularly efficient—up to 60%—when waste heat from the gas turbine is recovered by a heat recovery steam generator to power a conventional steam turbine in a combined cycle configuration. They can also be run in a cogeneration configuration: the exhaust is used for space or water heating, or drives an absorption chiller for cooling or refrigeration. A cogeneration configuration can be over 90% efficient. The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated enclosure, both to protect the engine from the elements and the operators from the noise.

Simple cycle gas turbines in the power industry require smaller capital investment than either coal or nuclear power plants and can be scaled to generate small or large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for base load power plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Because they are less efficient than combined cycle plants, they are usually used as peaking power plants, which operate anywhere from several hours per day to a couple dozen hours per year, depending on the electricity demand and the generating capacity of the region. In areas with a shortage of base load and load following power plant capacity, a gas turbine power plant may regularly operate during most hours of the day and even into the evening. A typical large simple cycle gas turbine may produce 100 to 300 megawatts of power and have 35–40% thermal efficiency. The most efficient turbines have reached 46% efficiency.[7]

Compressed air energy storage

Main article: Compressed air energy storage

One modern development seeks to improve efficiency in another way, by separating the compressor and the turbine with a compressed air store. In a conventional turbine, up to half the generated power is used driving the compressor. In a compressed air energy storage configuration, power, perhaps from a wind farm or bought on the open market at a time of low demand and low price, is used to drive the compressor, and the compressed air released to operate the turbine when required.

Turboshaft engines

Turboshaft engines are often used to drive compression trains (for example in gas pumping stations or natural gas liquefaction plants) and are used to power almost all modern helicopters. The first shaft bears the compressor and the high speed turbine (often referred to as "Gas Generator" or "N1"), while the second shaft bears the low speed turbine (or "Power Turbine" or "N2"). This arrangement is used to increase speed and power output flexibility.

Radial gas turbines

Main article: Radial turbine

1963, Norway, Jan Mowill initiated the development at Kongsberg Våpenfabrikk. Various successors have made good progress in the refinement of this mechanism. Owing to a configuration that keeps heat away from certain bearings the durability of the machine is improved while the radial turbine is well matched in speed requirement

Scale jet engines

Scale jet engines are scaled down versions of this early full scale engine

Also known as miniature gas turbines or micro-jets.

Many model engineers relish the challenge of re-creating the grand engineering feats of today as tiny working models. Naturally, the idea of re-creating a powerful engine such as the jet, fascinated hobbyists since the very first full size engines were powered up by Hans von Ohain and Frank Whittle back in the 1930s.

Recreating machines such as engines to a different scale is not easy. Because of the square-cube law, the behaviour of many machines does not always scale up or down at the same rate as the machine's size (and often not even in a linear way), usually at best causing a dramatic loss of power or efficiency, and at worst causing them not to work at all. An automobile engine, for example, will not work if reproduced in the same shape at the size of a human hand.

With this in mind the pioneer of modern Micro-Jets, Kurt Schreckling, produced one of the world's first Micro-Turbines, the FD3/67.[8] This engine can produce up to 22 newtons of thrust, and can be built by most mechanically minded people with basic engineering tools, such as a metal lathe. Its radial compressor, which is cold, is small and the hot axial turbine is large

experiencing more centrifugal forces, meaning that this design is limited by Mach number. Guiding vanes are used to hold the starter, after the compressor impeller and before the turbine. No bypass within the engine is used.

Microturbines

A micro turbine designed for DARPA by M-Dot

Also known as:

Turbo alternators MicroTurbine (registered trademark of Capstone Turbine Corporation) Turbogenerator (registered tradename of Honeywell Power Systems, Inc.)

Microturbines are becoming widespread for distributed power and combined heat and power applications. They are one of the most promising technologies for powering hybrid electric vehicles. They range from hand held units producing less than a kilowatt, to commercial sized systems that produce tens or hundreds of kilowatts.

Part of their success is due to advances in electronics, which allows unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows the generator to be integrated with the turbine shaft, and to double as the starter motor.

Microturbine systems have many advantages over reciprocating engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. Microturbines also have the advantage of having the majority of their waste heat contained in their relatively high temperature exhaust, whereas the waste heat of recriprocating engines is split between its exhaust and cooling system.[9] However, reciprocating engine generators are quicker to respond to changes in output power requirement and are usually slightly more efficient, although the efficiency of microturbines is increasing. Microturbines also lose more efficiency at low power levels than reciprocating engines.

They accept most commercial fuels, such as gasoline, natural gas, propane, diesel, and kerosene as well as renewable fuels such as E85, biodiesel and biogas.

Microturbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator. Recuperators are difficult to design and manufacture because they

operate under high pressure and temperature differentials. Exhaust heat can be used for water heating, space heating, drying processes or absorption chillers, which create cold for air conditioning from heat energy instead of electric energy.

Typical microturbine efficiencies are 25 to 35%. When in a combined heat and power cogeneration system, efficiencies of greater than 80% are commonly achieved.

MIT started its millimeter size turbine engine project in the middle of the 1990s when Professor of Aeronautics and Astronautics Alan H. Epstein considered the possibility of creating a personal turbine which will be able to meet all the demands of a modern person's electrical needs, just like a large turbine can meet the electricity demands of a small city. Problems have occurred with heat dissipation in these new microturbines. According to Professor Epstein current commercial Li-ion rechargeable batteries deliver about 120-150 Wh/kg. MIT's millimeter size turbine will deliver 500-700 Wh/kg in the near term, rising to 1200-1500 Wh/kg in the longer term.[10]

External combustionMost gas turbines are internal combustion engines but it is also possible to build an external combustion gas turbine which is, effectively, a turbine version of a hot air engine.

External combustion has been used for the purpose of using pulverized coal or finely ground biomass (such as sawdust) as a fuel. External combustion gas has been used both directly and indirectly. In the direct system, the combustion products travel through the power turbine. In the indirect system, a heat exchanger is used and clean air travels through the power turbine. The thermal efficiency is lower in the indirect type of external combustion, however the blades are not subjected to combustion products.

Gas turbines in vehicles

The 1950 Rover JET1

The 1967 STP Oil Treatment Special on display at the Indianapolis Motor Speedway Hall of Fame Museum, with the Pratt & Whitney gas turbine shown.

A 1968 Howmet TX, the only turbine-powered race car to have achieved victory.

Gas turbines are used on ships, locomotives, helicopters, and in tanks. A number of experiments have been conducted with gas turbine powered automobiles.

In 1950, designer F.R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car, and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum.

Rover and the British Racing Motors (BRM) Formula One team joined forces to produce the Rover-BRM, a gas turbine powered coupe, which entered the 1963 24 Hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km/h) and had a top speed of 142 mph (229 km/h). American Ray Heppenstall joined Howmet Corporation and McKee Engineering together to develop their own gas turbine sports car in 1968, the Howmet TX, which ran several American and European events, including two wins, and also participated in the 1968 24 Hours of Le Mans. The cars used Continental gas turbines, which eventually set six FIA land speed records for turbine-powered cars.[11]

For open wheel racing, 1967's revolutionary STP Oil Treatment Special four-wheel drive turbine-powered special fielded by racing and entrepreneurial legend Andy Granatelli and driven by Parnelli Jones nearly won the Indianapolis 500; the STP Pratt & Whitney powered turbine car was almost a lap ahead of the second place car when a gearbox bearing failed just three laps from the finish line. In 1971 Lotus principal Colin Chapman introduced the Lotus 56B F1 car, powered by a Pratt & Whitney gas turbine. Chapman had a reputation of building radical championship-winning cars, but had to abandon the project because there were too many problems with turbo lag.

The original General Motors Firebird was a series of concept cars developed for the 1953, 1956 and 1959 Motorama auto shows, powered by gas turbines.

American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. Chrysler built fifty Chrysler Turbine Cars in 1963 and conducted the only consumer trial of gas turbine-powered cars.[12] Their turbines employed unique rotating recuperator that significantly increased efficiency.

Japanese car manufacturer Toyota demonstrated several gas turbine powered prototype vehicles such as the Century gas turbine hybrid in 1975, the Sports 800 Gas Turbine Hybrid in 1977 and the GTV in 1985. No production vehicles were made.

The fictional Batmobile is often said to be powered by a gas turbine or a jet engine. In fact, in 1989s filmed Batman, the production department built a working turbine vehicle for the Batmobile prop.[13] Its fuel capacity, however, was reportedly only enough for 15 seconds of use at a time.

In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1 series hybrid. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator. Later on in 2006 GM went into the EcoJet concept car project with Jay Leno.

The arrival of the Capstone Microturbine has led to several hybrid bus designs, starting with HEV-1 by AVS of Chattanooga, Tennessee in 1999, and closely followed by Ebus and ISE Research in California, and Designline in New Zealand. AVS turbine hybrids were plagued with reliability and quality control problems, resulting in liquidation of AVS in 2003. The most successful design by Designline is now operated in 5 cities in 6 countries, with over 30 buses in operation worldwide.

A key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important.

Gas turbines offer a high-powered engine in a very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of RPMs and powers needed in vehicle applications. In hybrids, gas turbines reduce the responsiveness problem, and the emergence of the continuously variable transmission may also help alleviate this.

Turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small gas turbine engines are rarities; but turbines are mass produced in the closely related form of the turbocharger.

The MTT Turbine SUPERBIKE appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a turbine engine - specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 283 kW (380 bhp). Speed-tested to 365 km/h or 227 mph (according to some stories, the testing team ran out of road during the test), it holds the Guinness World Records for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000.

Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See gas turbine-electric locomotive for more information.

Tank use

The first use of a gas turbine in an armoured fighting vehicle was in 1954 when a unit, PU2979, specifically developed for tanks by C. A. Parsons & Co., was installed and trialled in a British Conqueror tank.[14] Since then, gas turbine engines have been used as auxiliary power units (APUs) in some tanks and as main powerplants in Soviet/Russian T-80s and U.S. M1 Abrams tanks, among others. They are lighter and smaller than diesels at the same sustained power output but the models installed to date are less fuel efficient than the equivalent diesel, especially at idle, requiring more fuel to achieve the same combat range. Successive models of M1 have addressed this problem with battery packs or secondary generators to power the tank's systems while stationary, saving fuel by reducing the need to idle the main turbine. T-80s can mount three large external fuel drums to extend their range. Russia has stopped production of the T-80 in favour of the diesel-powered T-90 (based on the T-72), while Ukraine has developed the diesel-powered T-80UD and T-84 with nearly the power of the gas-turbine tank.

A turbine is theoretically more reliable and easier to maintain than a piston engine, since it has a simpler construction with fewer moving parts but in practice turbine parts experience a higher wear rate due to their higher working speeds. The turbine blades are highly sensitive to dust and fine sand, so that in desert operations air filters have to be fitted and changed several times daily. An improperly fitted filter, or a bullet or shell fragment that punctures the filter can damage the engine. Piston engines also need well-maintained filters, but they are more resilient if the filter does fail.

Like most modern diesel engines used in tanks, gas turbines are usually multi-fuel engines.

Naval use

Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly.

The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. Metrovick developed the "Beryl" engine equipping an existing F2/3 jet engine with a power turbine. As the test was successful, the Fast Patrol Boats Bold Pioneer and Bold Pathfinder built in 1953 were the first ships created specifically for gas turbine propulsion.[15]

The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti ) was commissioned in 1961.

The Germany Navy launched the first Köln class frigate in 1961 with 2 GTs from BBC in the worlds first combined diesel and gas propulsion system.

The Swedish Navy produced 6 Spica class torpedoboats between 1966 and 1967 powered by 3 Bristol Siddeley Proteus 1282, each delivering 4300 hp. They were later joined by 12 upgraded Norrköping class ships, still with the same engines. With their aft torpedo tubes replaced by antishipping missiles they served as missile boats until the last was retired in 2005.[16]

The Finnish Navy issued two Turunmaa class corvettes, Turunmaa and Karjala, in 1968. They were equipped with one 16 000 shp Rolls-Royce Olympus TMB3 gas turbine and two Wärtsilä marine diesels for slower speeds. Before the waterjet-propulsion Helsinki class missile boats, they were the fastest vessels in the Finnish Navy; they regularly achieved 37 knot speeds, but they are known to have achieved 45 knots when the restriction mechanism of the turbine was geared off. The Turunmaas were paid off in 2002. Karjala is today a museum ship in Turku, and Turunmaa serves as a flotating machine shop and training ship for Satakunta Polytechnical College.

The next series of major naval vessels were the four Canadian Iroquois class helicopter carrying destroyers first commissioned in 1972. They used 2 ft-4 main propulsion engines, 2 ft-12 cruise engines and 3 Solar Saturn 750 kW generators.

The first U.S. gas-turbine powered ships were the U.S. Coast Guard's Hamilton -class High Endurance Cutters the first of which (USCGC Hamilton ) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry -class frigates , Spruance -class and Arleigh Burke -class destroyers, and Ticonderoga -class guided missile cruisers . USS Makin Island , a modified Wasp - class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines. The marine gas turbine operates in a more corrosive atmosphere due to presence of sea salt in air and fuel and use of cheaper fuels.

Commercial use

There have been a number of experiments in which gas turbines were used to power seagoing commercial vessels. The earliest of these experiments may have been the oil tanker "Auris" (Anglo Saxon Petroleum) - circa 1949.

The United States Maritime Commission were looking for options to update WWII Liberty ships and heavy duty gas turbines were one of those selected. In 1956 The "John Sergeant" was lenghened and installed with a General Electric 6600 SHP HD gas turbine, reduction gearing and a variable pitch propeller. It operated for 9700 hours using residual fuel for 7000 hours. The success of this trial opened the way for more development by GE on the use of HD gas turbines for marine use with heavy fuels. The "John Sergeant" was scrapped in 1972 at Portsmouth PA.

Between 1970 and 1982, Seatrain Container Lines operated a scheduled container service across the North Atlantic with four 26,000 tonne dwt. container ships. Those ships were powered by twin Pratt & Whitney gas turbines of the FT 4 series. The four ships in the class were named "Euroliner", "Eurofreighter", "Asialiner" and "Asiafreighter". They operated a transatlantic container service between ports on the eastern seaboard of the United States and ports in north west Europe. Following the dramatic OPEC price increases of the mid-nineteen seventies, operations were constrained by rising fuel costs. Some modification of the engine systems on those ships was undertaken to permit the burning of a lower grade of fuel (i.e. marine diesel). The modifications were partially successful. It was proved that particular fuel could be used in a marine gas turbine but, savings made were less than anticipated due to increased maintenance requirements. After 1982 the ships were sold, then re-engined with more economical diesel

engines. Because the new engines were much larger, there was a consequential loss of some cargo space.

The first passenger ferry to use a gas turbine was the GTS Finnjet , built in 1977 and powered with two Pratt & Whitney FT 4C-1 DLF turbines, generating 55000 kW and propelling the ship to a speed of 31 knots. However, the Finnjet also illustrated the shortcomings of gas turbine propulsion in commercial craft, as high fuel prices made operating her unprofitable. After just four years of service additional diesel engines were installed on the ship to allow less costly operations during off-season. Another example of commercial usage of gas turbines in a passenger ship are Stena Line's HSS class fastcraft ferries. HSS 1500-class Stena Explorer, Stena Voyager and Stena Discovery vessels use combined gas and gas (COGAG) setups of twin GE LM2500 plus GE LM1600 power for a total of 68,000 kW. The slightly smaller HSS 900-class Stena Charisma, uses twin ABB–STAL GT35 turbines rated at 34,000 kW gross. The Stena Discovery was withdrawn from service in 2007, another victim of too high fuel costs.

In July 2000, the Millennium became the first cruise ship to be propelled by gas turbines, in a Combined Gas and Steam Turbine configuration. The RMS Queen Mary 2 uses a Combined Diesel and Gas Turbine configuration.[17]

Advances in technologyGas turbine technology has steadily advanced since its inception and continues to evolve; research is active in producing ever smaller gas turbines. Computer design, specifically CFD and finite element analysis along with material advances, has allowed higher compression ratios and temperatures, more efficient combustion and better cooling of engine parts. On the emissions side, the challenge in technology is increasing turbine inlet temperature while reducing peak flame temperature to achieve lower NOx emissions to cope with the latest regulations. Additionally, compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system.

On another front, microelectronics and power switching technology have enabled commercially viable micro turbines for distributed and vehicle power.

Advantages and disadvantages of gas turbine engines

Advantages of gas turbine engines

[18]

Very high power-to-weight ratio, compared to reciprocating engines; Smaller than most reciprocating engines of the same power rating. Moves in one direction only, with far less vibration than a reciprocating engine. Fewer moving parts than reciprocating engines. Low operating pressures.

High operation speeds. Low lubricating oil cost and consumption.

Disadvantages of gas turbine engines

Cost is much greater than for a similar-sized reciprocating engine since the materials must be stronger and more heat resistant. Machining operations are also more complex;

Usually less efficient than reciprocating engines, especially at idle. Delayed response to changes in power settings.

These disadvantages explain why road vehicles, which are smaller, cheaper and follow a less regular pattern of use than tanks, helicopters, large boats and so on, do not use gas turbine engines, regardless of the size and power advantages imminently available.

See also Gas turbine locomotive Gas turbine-electric locomotive Gas turbine modular helium reactor Distributed Energy Resources

References1. ̂ Hassan, Ahmad Y. "Taqi al-Din and the First Steam Turbine". History of Science and

Technology in Islam. http://www.history-science-technology.com/Notes/Notes%201.htm. Retrieved on 2008-03-29.

2. ̂ "Vulcan APU startup" (video). http://www.vb.n00bunlimited.net/vBTube.php?do=view&vidid=5iQRdBE3IS0.

3. ̂ "Bristol Siddeley Proteus". Internal Fire Museum of Power. 1999. http://www.internalfire.com/modules.php?name=Content&pa=showpage&pid=136.

4. ̂ "UK TV series, " Scrapheap Challenge ", "Jet Racer" episode". 2003. http://www.channel4.com/science/microsites/S/scrapheap2003/challenges/jet_racer/.

5. ^ a b Schreckling, Kurt (1994). Gas Turbines for Model Aircraft. ISBN 0951058916. 6. ̂ Kamps, Thomas (2005). Model Jet Engines. Traplet Publications. ISBN 190037191X. 7. ̂ Mechanical Engineering "Power & Energy," June 2004 - "A Year of Turbulence,"

Feature Article 8. ̂ Gas Turbine Engines for Model Aircraft by Kurt Schreckling, ISBN 0-9510589-1-6

Traplet Publications 9. ̂ Prime Movers in CHP - Steam Turbines, Gas Turbines, Reciprocating Engines, Spark

Ignition 10. ̂ Engine on a Chip - TFOT 11. ̂ "The history of the Howmet TX turbine car of 1968, still the world's only turbine

powered race winner". Pete Stowe Motorsport History. June 2006. http://website.lineone.net/~pete.stowe/pete_howmet.htm. Retrieved on 2008-01-31.

12. ̂ Chrysler turbine information

13. ̂ 1989 Batmobile Turbine 14. ̂ Richard M Ogorkiewicz, Jane's - The Technology of Tanks, Jane's Information Group,

p.259 15. ̂ The first marine gas turbine, 1947 16. ̂ Fast missile boat 17. ̂ GE - Aviation: GE Goes from Installation to Optimized Reliability for Cruise Ship Gas

Turbine Installations 18. ̂ how stuff works

Further reading "Aircraft Gas Turbine Technology" by Irwin E. Treager, Professor Emeritus Purdue

University, McGraw-Hill, Glencoe Division, 1979, ISBN 0070651582. "Gas Turbine Theory" by H.I.H. Saravanamuttoo, G.F.C. Rogers and H. Cohen, Pearson

Education, 2001, 5th ed., ISBN 0-13-015847-X. R. M. "Fred" Klaass and Christopher DellaCorte, "The Quest for Oil-Free Gas Turbine

Engines," SAE Technical Papers, No. 2006-01-3055, available at: http://www.sae.org/technical/papers/2006-01-3055.

"Model Jet Engines" by Thomas Kamps ISBN 0 9510589 9 1 Traplet Publications Aircraft Engines and Gas Turbines, Second Edition" by Jack L. Kerrebrock, The MIT

Press, 1992, ISBN 0262111624.

External links

Wikimedia Commons has media related to: Gas turbine

Gas turbine at the Open Directory Project Technology Speed of Civil Jet Engines MIT Gas Turbine Laboratory MIT Microturbine research California Distributed Energy Resource guide - Microturbine generators First Marine Gas Turbine 1947 Introduction to how a gas turbine works from "how stuff works.com" Aircraft gas turbine simulator for interactive learning"

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turbine Dictionary: tur·bine   (tûr'bĭn, -bīn') Sponsored LinksTurbine EnginesWe Have Units Available For Immediate Delivery. Call Us Today! www.petersonpower.comSiemens answers:Efficient energy supply The world's largest gas turbine. www.Siemens.com/AnswersHome > Library > Literature & Language > Dictionaryn.

Any of various machines in which the kinetic energy of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with a series of buckets, paddles, or blades arrayed about the circumference of a wheel or cylinder.

[French, from Latin turbō, turbin-, spinning top, perhaps from Greek turbē, turmoil.]

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Any of various devices that convert the energy in a stream of fluid into mechanical energy by passing the stream through a system of fixed and moving fanlike blades and causing the latter to rotate. A turbine looks like a large wheel with many small radiating blades around its rim. There are four broad classes of turbine: water (hydraulic), steam, wind, and gas. The most important application of the first three is the generation of electricity; gas turbines are most often used in aircraft.

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Home wind turbines3kW to 20kW wind turbine kits Free energy from wind turbines www.Joliet-europe.comDirect Drive PM GeneratorBrushless alternators for Wind Turbines from 200W up to 100KW www.alxion.comColumbia Encyclopedia: turbine Top Home > Library > Miscellaneous > Columbia Encyclopediaturbine, rotary engine that uses a continuous stream of fluid (gas or liquid) to turn a shaft that can drive machinery.

A water, or hydraulic, turbine is used to drive electric generators in hydroelectric power stations. The first such station was built in Wisconsin in 1882. In a hydraulic turbine falling water strikes a series of blades or buckets attached around a shaft, causing the shaft to rotate, this motion in turn being used to drive the rotor of an electric generator. The three most common types of hydraulic turbine are the Pelton wheel, the Francis turbine, and the Kaplan turbine. Toward the end of the 19th cent. two engineers, Sir Charles A. Parsons of Great Britain and Carl G. P. de Laval of Sweden, were pioneers in the building of steam turbines. Continual improvements of their basic machines have caused steam turbines to become the principal power sources used to drive most large electric generators and the propellers of most large ships.

A steam turbine typically consists of a roughly conical, steel shell enclosing a central shaft along which a series of bladed disks are spaced like washers. The blades are curved and extend radially outward from the rim of each disk. In some steam turbines the shaft is surrounded by a drum to which the rows of blades are attached. Between each pair of disks is a row of stationary vanes attached to the steel shell and extending radially inward. Each set of stationary vanes and the bladed disk immediately next to it constitutes a stage of the turbine; most steam turbines are multistage engines.

At the inlet end of the turbine high-pressure steam enters from a boiler and moves through the turbine parallel to the shaft, first striking a row of stationary vanes that directs the steam against the first bladed disk at an optimum speed and angle. The steam then passes through the remaining stages, forcing the disks and the shaft to rotate. At one end of the turbine the shaft sticks out and can be attached to machinery. A large steam turbine unit may actually be composed of several turbines that are all using the same shaft and steam. Such a unit might consist of a small, high-pressure turbine, connected to a larger, intermediate-pressure turbine, connected to a still larger, low-pressure turbine. After the steam leaves the turbine, it is sent to a condenser where it is converted back into water before being returned to the boiler.

Gas turbines are used mainly as aircraft engines. Some are used to drive electric generators, as in a gas turbine–electric locomotive, and high-speed tools. The term gas turbine is usually applied to a unit whose essential components are a compressor, a combustion chamber, and a turbine that resembles a steam turbine. The turbine drives the compressor, which feeds high-pressure air into the combustion chamber; there it is mixed with a fuel and burned, providing high-pressure gases to drive the turbine, the gases expanding until their pressure drops to atmospheric pressure. In a

turboprop engine the turbine is used to turn a propeller as well as the compressor. In a turbojet engine only a small pressure drop is used to drive the turbine, the majority of the pressure drop occurring as the gases are expelled directly out of the engine. A variation of the turbojet is known as the turbofan engine.

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Turbines are devices that spin in the presence of a moving fluid. The difference between water wheels or windmills and turbines is largely one of emphasis and degree. During the 18th and 19th centuries, much progress was made toward extracting the kinetic energy of flowing water by devising water turbines. Leonhard Euler, applying fluid mechanics, developed a water turbine as early as 1750. During the 18th century several engineers, such as Benôit Fourneyron, succeeded in building water turbines that by far outstripped conventional water wheels by giving the blades special shapes. The term "turbine" was coined by Fourneyron's professor Claude Burdin; he derived the term from turbo, a spinning object.

The most useful turbines for many purposes are those that can be propelled with energy from heat. A typical turbine based on heat is the steam turbine. The idea of a steam turbine is much older than the steam engine itself. Around 60 BCE the Alexandrian Greek Heron (a.k.a. Hero) used jets of steam to turn a kettle. In 1629 the Italian engineer Giovanni Branca depicted in his machine book Le Machine a steam turbine in which a jet of steam is directed at the vanes of the same sort of apparatus as a water wheel. No doubt others observed that escaping steam is like the rushing wind and could be used to push mills just as the wind powers windmills.

When practical steam engines were built at the start of the 18th century, however, they moved a cylinder back and forth (reciprocating motion) instead of pushing a wheel around, although they could be made to turn wheels with various ingenious mechanisms. Reciprocating steam engines were bulky, had slow rotation speeds, and wasted much energy in the machine itself to move the heavy pistons back and forth. When first used to drive electric generators, reciprocating steam engines proved difficult to maintain at a fixed rotation speed as the load on the generator changed.

Turbines are as simple as reciprocating engines are complex. Because they have essentially only one moving part, they are sometimes called the perfect engines, almost directly turning heat into rotary motion.

The first to build a steam turbine was the British engineer Charles Algernon Parsons. In 1884 he completed a small turbine that rotated at 18,000 revolutions per minute and that delivered 10 horsepower. The Swedish engineer Carl Gustav de Laval, experimenting with steam turbines, achieved greater power and higher rotation rates. In 1890 he built a turbine consisting of a 30-cm (12-in.) disk with 200 blades mounted on a flexible axis. The steam was admitted to the blades by special nozzles (Laval nozzles) that accelerated the steam to very high velocities, thus transferring the energy of the steam in the form of kinetic energy to the blades.

The design of steam turbines developed into a science near the end of the 19th century. Better materials allowed the construction of turbine blades that are resistant to corrosion. Charles Curtis developed the multistage turbine in which the blades and disks become progressively larger when the steam expands. Parsons developed in 1894 the ship turbine engine. The slow-revolving turbine consisted of several sections of increasing diameter. High-pressure steam is admitted to the turbine and pressure differences in each section drive the turbine blades. The first ship to be equipped with such a steam turbine, the Turbinia, immediately established a speed record with 31 knots (57.5 km or 35.7 mi per hour). During the early years of the 20th century, most reciprocating steam engines were replaced by steam turbines (or by diesels). Steam turbines can deliver much more power than reciprocating engines and need less maintenance. Steam turbines also supplanted marine steam engines on ships.

A similar evolution took place for large internal combustion engines, mainly driven by the need for lightweight and powerful airplane engines. Most large modern airplanes are now powered by either turboprop or turbojet engines. These turbines are spun by the expansion of jet fuel instead of by the expansion of water into steam.

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IN BRIEF: Rotary engine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a bladed rotor to rotate.

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A Siemens steam turbine with the case opened.For other uses, see Turbine (disambiguation).

A turbine is a rotary engine that extracts energy from a fluid flow. Claude Burdin (1788-1873) coined the term from the Latin turbo, or vortex, during an 1828 engineering competition. Benoit Fourneyron (1802-1867), a student of Claude Burdin, built the first practical water turbine.

The simplest turbines have one moving part, a rotor assembly, which is a shaft with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they rotate and impart energy to the rotor. Early turbine examples are windmills and water wheels.

Gas, steam, and water turbines usually have a casing around the blades that contains and controls the working fluid. Credit for invention of the modern steam turbine is given to British Engineer Sir Charles Parsons (1854 - 1931).

A device similar to a turbine but operating in reverse is a compressor or pump. The axial compressor in many gas turbine engines is a common example.

Contents[hide]

1 Theory of operation 2 Types of turbines

o 2.1 Other 3 Uses of turbines 4 Shrouded tidal turbines 5 See also 6 Notes 7 External links

Theory of operation

A working fluid contains potential energy (pressure head) and kinetic energy (velocity head). The fluid may be compressible or incompressible. Several physical principles are employed by turbines to collect this energy:

Impulse turbines  These turbines change the direction of flow of a high velocity fluid jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. There is no pressure change of the fluid in the turbine rotor blades. Before reaching the turbine the fluid's pressure head is changed to velocity head by accelerating the fluid with a nozzle. Pelton wheels and de Laval turbines use this process exclusively. Impulse turbines do not require a pressure casement around the runner since the fluid jet is

prepared by a nozzle prior to reaching turbine. Newton's second law describes the transfer of energy for impulse turbines.

Reaction turbines  These turbines develop torque by reacting to the fluid's pressure or weight. The pressure of the fluid changes as it passes through the turbine rotor blades. A pressure casement is needed to contain the working fluid as it acts on the turbine stage(s) or the turbine must be fully immersed in the fluid flow (wind turbines). The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. Francis turbines and most steam turbines use this concept. For compressible working fluids, multiple turbine stages may be used to harness the expanding gas efficiently. Newton's third law describes the transfer of energy for reaction turbines.

Turbine designs will use both these concepts to varying degrees whenever possible. Wind turbines use an airfoil to generate lift from the moving fluid and impart it to the rotor (this is a form of reaction). Wind turbines also gain some energy from the impulse of the wind, by deflecting it at an angle. Crossflow turbines are designed as an impulse machine, with a nozzle, but in low head applications maintain some efficiency through reaction, like a traditional water wheel. Turbines with multiple stages may utilize either reaction or impulse blading at high pressure. Steam Turbines were traditionally more impulse but continue to move towards reaction designs similar to those used in Gas Turbines. At low pressure the operating fluid medium expands in volume for small reductions in pressure. Under these conditions (termed Low Pressure Turbines) blading becomes strictly a reaction type design with the base of the blade solely impulse. The reason is due to the effect of the rotation speed for each blade. As the volume increases, the blade height increases, and the base of the blade spins at a slower speed relative to the tip. This change in speed forces a designer to change from impulse at the base, to a high reaction style tip.

Classical turbine design methods were developed in the mid 19th century. Vector analysis related the fluid flow with turbine shape and rotation. Graphical calculation methods were used at first. Formulae for the basic dimensions of turbine parts are well documented and a highly efficient machine can be reliably designed for any fluid flow condition. Some of the calculations are empirical or 'rule of thumb' formulae, and others are based on classical mechanics. As with most engineering calculations, simplifying assumptions were made.

Velocity triangles can be used to calculate the basic performance of a turbine stage. Gas exits the stationary turbine nozzle guide vanes at absolute velocity Va1. The rotor rotates at velocity U. Relative to the rotor, the velocity of the gas as it impinges on the rotor entrance is Vr1. The gas is turned by the rotor and exits, relative to the rotor, at velocity Vr2. However, in absolute terms the rotor exit velocity is Va2. The velocity triangles are constructed using these various velocity vectors. Velocity triangles can be constructed at any section through the blading (for example: hub , tip, midsection and so on) but are usually shown at the mean stage radius. Mean performance for the stage can be calculated from the velocity triangles, at this radius, using the Euler equation:

Typical velocity triangles for a single turbine stage

Whence:

where:

specific enthalpy drop across stage turbine entry total (or stagnation) temperature turbine rotor peripheral velocity

change in whirl velocity

The turbine pressure ratio is a function of and the turbine efficiency.

Modern turbine design carries the calculations further. Computational fluid dynamics dispenses with many of the simplifying assumptions used to derive classical formulas and computer software facilitates optimization. These tools have led to steady improvements in turbine design over the last forty years.

The primary numerical classification of a turbine is its specific speed. This number describes the speed of the turbine at its maximum efficiency with respect to the power and flow rate. The specific speed is derived to be independent of turbine size. Given the fluid flow conditions and the desired shaft output speed, the specific speed can be calculated and an appropriate turbine design selected.

The specific speed, along with some fundamental formulas can be used to reliably scale an existing design of known performance to a new size with corresponding performance.

Off-design performance is normally displayed as a turbine map or characteristic.

Types of turbines Steam turbines are used for the generation of electricity in thermal power plants, such as

plants using coal or fuel oil or nuclear power. They were once used to directly drive mechanical devices such as ship's propellors (eg the Turbinia), but most such applications now use reduction gears or an intermediate electrical step, where the turbine is used to generate electricity, which then powers an electric motor connected to the mechanical load.

Gas turbines are sometimes referred to as turbine engines. Such engines usually feature an inlet, fan, compressor, combustor and nozzle (possibly other assemblies) in addition to one or more turbines.

Transonic turbine. The gasflow in most turbines employed in gas turbine engines remains subsonic throughout the expansion process. In a transonic turbine the gasflow becomes supersonic as it exits the nozzle guide vanes, although the downstream velocities normally become subsonic. Transonic turbines operate at a higher pressure ratio than normal but are usually less efficient and uncommon. This turbine works well in creating power from water.

Contra-rotating turbines. Some efficiency advantage can be obtained if a downstream turbine rotates in the opposite direction to an upstream unit. However, the complication may be counter-productive.

Statorless turbine. Multi-stage turbines have a set of static (meaning stationary) inlet guide vanes that direct the gasflow onto the rotating rotor blades. In a statorless turbine the gasflow exiting an upstream rotor impinges onto a downstream rotor without an intermediate set of stator vanes (that rearrange the pressure/velocity energy levels of the flow) being encountered.

Ceramic turbine. Conventional high-pressure turbine blades (and vanes) are made from nickel-steel alloys and often utilise intricate internal air-cooling passages to prevent the metal from melting. In recent years, experimental ceramic blades have been manufactured and tested in gas turbines, with a view to increasing Rotor Inlet

Temperatures and/or, possibly, eliminating aircooling. Ceramic blades are more brittle than their metallic counterparts, and carry a greater risk of catastrophic blade failure.

Shrouded turbine. Many turbine rotor blades have a shroud at the top, which interlocks with that of adjacent blades, to increase damping and thereby reduce blade flutter.

Shroudless turbine . Modern practise is, where possible, to eliminate the rotor shroud, thus reducing the centrifugal load on the blade and the cooling requirements.

Bladeless turbine uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine.

Water turbines o Pelton turbine , a type of impulse water turbine. o Francis turbine , a type of widely used water turbine. o Kaplan turbine , a variation of the Francis Turbine. o Voith , water turbine.

Wind turbine . These normally operate as a single stage without nozzle and interstage guide vanes. An exception is the Éolienne Bollée, which has a stator and a rotor, thus being a true turbine.

Tide Turbine

Other

Velocity compound "Curtis". Curtis combined the de Laval and Parsons turbine by using a set of fixed nozzles on the first stage or stator and then a rank of fixed and rotating stators as in the Parsons, typically up to ten compared with up to a hundred stages, however the efficiency of the turbine was less than that of the Parsons but it operated at much lower speeds and at lower pressures which made it ideal for ships. Note that the use of a small section of a Curtis, typically one nozzle section and two rotors is termed a "Curtis Wheel"

Pressure Compund Multistage Impulse or Rateau. The Rateau employs simple Impulse rotors separated by a nozzle diaphragm. The diaphragm is essentially a partition wall in the turbine with a series of tunnels cut into it, funnel shaped with the broad end facing the previous stage and the narrow the next they are also angled to direct the steam jets onto the impulse rotor.

Uses of turbinesAlmost all electrical power on Earth is produced with a turbine of some type. Very high efficiency turbines harness about 40% of the thermal energy, with the rest exhausted as waste heat.

Most jet engines rely on turbines to supply mechanical work from their working fluid and fuel as do all nuclear ships and power plants.

Turbines are often part of a larger machine. A gas turbine, for example, may refer to an internal combustion machine that contains a turbine, ducts, compressor, combustor, heat-exchanger, fan and (in the case of one designed to produce electricity) an alternator. However, it must be noted

that the collective machine referred to as the turbine in these cases is designed to transfer energy from a fuel to the fluid passing through such an internal combustion device as a means of propulsion, and not to transfer energy from the fluid passing through the turbine to the turbine as is the case in turbines used for electricity provision etc.

Reciprocating piston engines such as aircraft engines can use a turbine powered by their exhaust to drive an intake-air compressor, a configuration known as a turbocharger (turbine supercharger) or, colloquially, a "turbo".

Turbines can have very high power density (ie the ratio of power to weight, or power to volume). This is because of their ability to operate at very high speeds. The Space Shuttle's main engines use turbopumps (machines consisting of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine's combustion chamber. The liquid hydrogen turbopump is slightly larger than an automobile engine (weighing approximately 700 lb) and produces nearly 70,000 hp (52.2 MW).

Turboexpanders are widely used as sources of refrigeration in industrial processes.

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Turbines could also be used as powering system for a remote controlled plane that creates thrust and lifts the plane of the ground. They come in different sizes and could be as small as soda can, still be strong enough to move objects with a weight of 100kg.

Shrouded tidal turbinesAn emerging renewable energy technology is the shrouded tidal turbine enclosed in a venturi shaped shroud or duct producing a sub atmosphere of low pressure behind the turbine. It is often claimed that this allows the turbine to operate at higher efficiency (than the Betz limit [1] of 59.3%) because the turbine can typically produce 3 times more power [2] than a turbine of the same size in free stream. This, however, is something of a misconception becase the area presented to the flow is that of the largest duct cross-section. If this area is used for the calculation, it will be seen that the turbine still cannot exceed the Betz limit. Further, due to frictional losses in the duct, it is unlikely that the turbine will be able to produce as much power as a free-stream turbine with the same radius as the duct.

Although situating the rotor in the throat of the duct allows the blades to be supported at their tips (thus reducing bending stress from hydrodynamic thrust) the financial impact of the large amount of steel in the duct must not be omitted from any energy cost calculations.

Asymmetric airfoil

As shown in the CFD generated figure [3] , it can be seen that a down stream low pressure (shown by the gradient lines) draws upstream flow into the inlet of the shroud from well outside the inlet of the shroud. This flow is drawn into the shroud and concentrated (as seen by the red coloured zone). This augmentation of flow velocity corresponds to a 3-4 times increase in energy available to the turbine. Therefore a turbine located in the throat of the shroud is then able to achieve higher efficiency, and an output 3-4 times the energy the turbine would be capable of if it were in open or free stream. However, as mentioned above, it is not correct to conclude that this circumvents the Betz limit. The figure shows only the near-field flow, which is accelerated through the duct. A far-field image would show a more complete picture of how the free-stream flow is affected by the obstruction.

Considerable commercial interest has been shown in recent times in shrouded tidal turbines as it allows a smaller turbine to be used at sites where large turbines are restricted. Arrayed across a seaway or in fast flowing rivers shrouded tidal turbines are easily cabled to a terrestrial base and connected to a grid or remote community. Alternatively the property of the shroud that produces an accelerated flow velocity across the turbine allows tidal flows formerly too slow for commercial use to be utilised for commercial energy production.

While the shroud may not be practical in wind, as a tidal turbine it is gaining more popularity and commercial use. A non-symmetrical shrouded tidal turbine (the type discussed above) is mono directional and constantly needs to face upstream in order to operate. It can be floated under a pontoon on a swing mooring, fixed to the seabed on a mono pile and yawed like a wind sock to continually face upstream. A shroud can also be built into a tidal fence increasing the performance of the turbines. Several companies (for example, Lunar Energy [4]) are proposing bi-directional ducts that would not be required to turn to face the oncoming tide every six hours.

Cabled to the mainland they can be grid connected or can be scaled down to provide energy to remote communities where large civil infrastructures are not viable. Similarly to tidal stream open turbines they have little if any environmental or visual amenity impact.

See also Balancing machine RMS Lusitania Rotordynamics Secondary flow in turbines Turbinia Turbo-alternator Turboshaft Vibration of Rotating Structures

Notes1. ̂ Betz Limit 2. ̂ Paper by Brian Kirke 3. ̂ Tidal Energy 4. ̂ [1]

External links Turbine introductory math Turbines jet powered 1/16 scale Airbus A330 Turbine working process

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