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## PowerPedia:Turbine

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A turbine is a rotary engine that extracts energy from a fluid flow. Claude Burdin coined the term from the Latin turbinis, or vortex, during an 1828 engineering competition. 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. Turbines operating in reverse are called compressors. It converts mechanical energy to pressurized fluid flow.

#### Introduction

Gas, steam, and water turbines usually have a casing around the blades that focuses and controls the fluid. The casing and blades may have variable geometry that allows efficient operation for a range of fluid-flow conditions. A working fluid contains potential energy (pressure head) and kinetic energy (velocity head). The fluid may be compressible or incompressible.

##### Principles

Several physical principles are employed by turbines to collect this energy:

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Impulse 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. The impulse of a force is the product of the force and the time during which it acts. Although momentum is conserved within a closed system, individual parts of a system can undergo changes in momentum. Impulse has the same units and dimensions as momentum (kg m/s or N·s). The impulse of a time-varying force is calculated as the integral of force with respect to time. Impulse is the force applied in a unit of time. Force multiplied by time which equates to change in momentum.

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Reaction 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 efficiently harness the expanding gas. Newton's third law describes the transfer of energy for reaction turbines. A reaction is usually any response caused by some other action.

Turbine designs will use both these concepts to varying degrees whenever possible. Wind turbines use a airfoil to generate lift from the moving fluid and impart it to the rotor (this is a form of reaction), they 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. Gas turbines with multiple stages have the first stage reacting to impulse of the gas flow (because it is inefficient to increase the velocity when it is almost at the speed of sound) and later stages being designed for reaction in the decreasing velocity flow. Blades in many stages being arranged to be reaction over some parts (of their length) and impulse over the rest.

##### Mathematical theory

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. Formulas 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:

\Delta\H = U\cdot \Delta\Vw/g

Whence:

\left (\frac{\Delta\H}{T}\right) = \left(\frac{U}{\sqrt{T}}\right)\cdot\left(\frac{\Delta\Vw}{g\cdot\sqrt{T}}\right)

where:

g =\, acceleration of gravity

\Delta\H = enthalpy drop across stage

T =\, turbine entry total (or stagnation) temperature

U =\, turbine rotor peripheral velocity

\Delta\,Vw = delta whirl velocity

The turbine pressure ratio is a function of \left(\frac{\Delta\H}{T}\right) and the turbine efficiecy. 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.

#### Utilization

Almost all electrical power on Earth is produced with a turbine of some type. The exceptions being solar panels, fuel cells, and diesel generators which are commonly use in small isolated towns (this practice is very common in Alaska for instance). Very high thermal efficiencies (Power Production Efficiency = [Electrical energy Output/Thermal Energy Input]) are achievable in gas turbine power generation facilities (60% or greater when using combined cycles).

Most jet engines (excluding scramjet and ramjet engines) rely on turbines to supply mechanical work from their working fluid and fuel as do all nuclear warships 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. Reciprocating engine Piston engines, especially for aircraft, 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 incredible power density (with respect to volume and weight). 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).

##### Steam turbine

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A There was an error working with the wiki: Code[16] is a mechanical device that extracts thermal energy from pressurized steam, and converts it into useful mechanical work. It has 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. Also, because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator — it doesn't require a linkage mechanism to convert reciprocating to rotary motion. 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 (as opposed to the one stage in the Watt engine), which results in a closer approach to the ideal reversible process.

used for ship propulsion.]]

The first steam engine was little more than a toy, the classic Aeolipile made by Heron of Alexandria. Another steam turbine device was created by Italian Giovanni Branca in year 1629. The modern steam turbine was invented by an Anglo Irishman, Charles A. Parsons, in 1884 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.

##### Gas turbine engines

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These devices 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. 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 released when air is mixed with fuel and ignited in the combustor. A common mistake is that combustion increases the pressure of the gasses flowing through a turbine. In fact the heat addition stage of a gas turbine cycle incurs a slight pressure drop to facilitate flow through the engine. For all intents and purposes, however, the combustion process can be considered as occuring at constant pressure, with an increasing volume to accommodate the temperature rise, as explained by the ideal gas law. This in turn results in an increase in the velocity of the gas flow (see gas laws). This is directed over the turbine's blades, spinning the turbine and powering the compressor, and finally is passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure. 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.

##### Transonic turbine

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The gasflow in most turbines employed in gas turbine engines remains subsonic throughout the expansion process. In a There was an error working with the wiki: Code[17] 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.

##### Contrarotating turbines

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Some efficiency advantage can be obtained if a downstream turbine rotates in the opposite direction to an upstream unit. This is taken advantage of in the There was an error working with the wiki: Code[18]s. However, the complication may be contraproductive.

##### 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 There was an error working with the wiki: Code[19] 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

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Most turbine blades (and vanes) are made from nickel alloy and often require intricate air-cooling passages to prevent the metal from melting. In recent years, experimental ceramic blades have been manufactured and tested in gas There was an error working with the wiki: Code[20]s, with a view to increasing Rotor Inlet Temperatures and/or, possibly, eliminating aircooling. Unfortunately, like china cups, ceramic blades are very brittle and cannot withstand sudden shock. Ways of overcoming this problem are being investigated.

##### Shrouded and shroudedless turbines

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There was an error working with the wiki: Code[21] rotor blades have a shroud at the top, which interlocks with that of adjacent blades, to increase damping and thereby reduce blade flutter. Modern There was an error working with the wiki: Code[22] practise has innovated the practice where possible, to eliminate the rotor shroud, thus reducing the centrifugal load on the blade and the cooling requirements.

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The There was an error working with the wiki: Code[23] uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine. The Tesla turbine is a bladeless turbine design patented by Nikola Tesla in 1913. It is referred to as a bladeless turbine because it uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine. The Tesla turbine is also known as the boundary layer turbine, cohesion-type turbine, and Prandtl layer turbine (after Ludwig Prandtl). It is one of the few turbomachines that can be simply manufactured in primitive machine shops. One of Tesla’s desire for implementation of this turbine was for geothermal power, which was described in "Our Future Motive Power".

's Turbine]]

If a similar set of disks and a housing with an involute shape (versus circular for the turbine) are used, the device can be used as a pump. In this configuration a motor is attached to the shaft. The fluid enters near the center, is given energy by the disks, then exits at the periphery. The Tesla turbine does not use friction in the conventional sense precisely, it avoids it, and uses adhesion (the Coand? effect) and viscosity instead. It utilizes the boundary layer effect on the disc blades. This is an important point of this invention. Smooth rotor disks were originally proposed, but these gave poor starting torque. Tesla subsequently discovered that smooth rotor disks with small washers bridging the disks in ~12–24 places around the perimeter of a 10? disk and a second ring of 6–12 washers at a sub-diameter made for a significant improvement in starting torque, without compromising efficiency.

##### Water turbine

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There was an error working with the wiki: Code[24]s have a thermodynamic cycle that is part of weather. A water turbine is a rotary engine that takes energy from moving water. Water turbines were developed in the nineteenth century and were widely used for industrial power prior to electrical grids. Now they are mostly used for electric power generation. They harness a clean and renewable energy source.

Water wheels have been used for thousands of years for industrial power. Their main shortcoming is size, which limits the flow rate and head that can harnessed. The migration from water wheels to modern turbines took about one hundred years. Development occurred during the Industrial revolution, using scientific principles and methods. They also made extensive use of new materials and manufacturing methods developed at the time. The word turbine was coined by the French engineer Claude Bourdin in the early 19th century and is derived from the Latin word for "whirling" or a "vortex". The main difference between early water turbines and water wheels is a swirl component of the water which passes energy to a spinning rotor. This additional component of motion allowed the turbine to be smaller than a water wheel of the same power. They could process more water by spinning faster and could harness much greater heads. (Later, impulse turbines were developed which didn't use swirl).

Ján Andrej Segner developed a reactive water turbine in the mid-1700s. It had a horizontal axis and was a precursor to modern water turbines. It is a very simple machine that is still produced today for use in small hydro sites. Segner worked with Euler on some of the early mathematical theories of turbine design. In 1820, Jean-Victor Poncelet developed an inward-flow turbine. In 1826 Benoit Fourneyron developed an outward-flow turbine. This was an efficient machine (~80%) that sent water through a runner with blades curved in one dimension. The stationary outlet also had curved guides. In 1844 Uriah A. Boyden developed an outward flow turbine that improved on the performance of the Fourneyron turbine. Its runner shape was similar to that of a Francis turbine. In 1849, James B. Francis improved the inward flow reaction turbine to over 90% efficiency. He also conducted sophisticated tests and developed engineering methods for water turbine design. The Francis turbine, named for him, is the first modern water turbine. It is still the most widely used water turbine in the world today.

Inward flow water turbines have a better mechanical arrangement and all modern reaction water turbines are of this design. Also, as the swirling mass of water spins into a tighter rotation, it tries to speed up to conserve energy. This property acts on the runner, in addition to the water's falling weight and swirling motion. Water pressure decreases to zero as it passes through the turbine blades and gives up its energy. Around 1890, the modern fluid bearing was invented, now universally used to support heavy water turbine spindles. As of 2002, fluid bearings appear to have a mean time between failures of more than 1300 years. Around 1913, Victor Kaplan created the Kaplan turbine, a propeller-type machine. It was an evolution of the Francis turbine but revolutionized the ability to develop low-head hydro sites.

All common water machines until the late 19th century (including water wheels) were reaction machines water's pressure head acted on the machine and produced work. A reaction turbine needs to fully contain the water during energy transfer. In 1866, California millwright Samuel Knight invented a machine that worked off a completely different concept. Inspired by the high pressure jet systems used in hydraulic mining in the gold fields, Knight developed a bucketed wheel which captured the energy of a free jet, which had converted a high head (hundreds of vertical feet in a pipe or penstock) of water to kinetic energy. This is called an impulse or tangential turbine. The water's velocity, roughly twice the velocity of the bucket periphery, does a u-turn in the bucket and drops out of the runner at 0 velocity. In 1879, Lester Pelton, experimenting with a Knight Wheel, developed a double bucket design, which exhausted the water to the side, eliminating some energy loss of the Knight wheel which exhausted some water back against the center of the wheel. In about 1895, William Doble improved on Pelton's half-cylindrical bucket form with an elliptical bucket that included a cut in it to allow the jet a cleaner bucket entry. This is the modern form of the Pelton turbine which today achieves up to 92% efficiency. Pelton had been quite an effective promoter of his design and although Doble took over the Pelton company he did not change the name to Doble because it had brand name recognition. Turgo and Crossflow turbines were later impulse designs.

: See Directory:Tidal and River Turbine by University of Southampton for a minimalist design in a tidal generator.

##### Wind turbine

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These normally operate as a single stage without nozzle and interstage guide vanes. Wind Turbines have a thermodynamic cycle that is part of weather. A wind turbine is a machine for converting 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. This article discusses the conversion machinery. See the broader article on wind power for more on turbine placement and controversy, and in particular see the wind energy section of that article for an understanding of the temporal distribution of wind energy and how that affects wind turbine design. For a machine that generates wind, see wind machine. For an unusual way to induce a voltage using an aerosol of ionised water, see vaneless ion wind generator.

Wind turbines can be separated into two general types based on the axis about which the turbine rotates. Turbines that rotate around a horizontal axis are most common. Vertical axis turbines are less frequently used. Wind turbines can also be classified by the location in which they are to be used. Onshore, offshore, or even aerial wind turbines have unique design characteristics which are explained in more detail in the section on Turbine design and construction. Wind turbines may also be used in conjunction with a solar collector to extract the energy due to air heated by the Sun and rising through a large vertical Solar updraft tower.

Horizontal Axis Wind Turbines (HAWTs) have the main rotor shaft and generator at the top of a tower, and must be pointed into the wind by some means. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servomotor. Most have a gearbox too, which turns the slow rotation of the blades into a quicker rotation that is more suitable for generating electricity. 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. Because turbulence leads to fatigue failures and reliability is so important, most HAWTs are upwind machines.

: See Directory:High-Efficiency Horizontal Axis Wind Turbines for HAWTs

Vertical Axis Wind Turbines (or VAWTs) have the main rotor shaft running vertically. The advantages of this arrangement are that the generator and/or gearbox can be placed at the bottom, near the ground, so the tower doesn't need to support it, and that the turbine doesn't need to be pointed into the wind. Drawbacks are usually the pulsating torque produced during each revolution, and the difficulty of mounting vertical axis turbines on towers, meaning they must operate in the slower, more turbulent air flow near the ground, with lower energy extraction efficiency.

: See Directory:Vertical Axis Wind Turbines for VAWTs

Offshore wind turbines are considered to be less obtrusive than turbines on land, as their apparent size and noise can be mitigated by distance. Because water has less surface roughness than land, the average wind speed is usually higher over open water. This allows offshore turbines to use shorter towers, making them less visible. In stormy areas with extended shallow continental shelves (such as Denmark), turbines are practical to install, and give good service - Denmark's wind generation provides about 25-30% of total electricity demand in the country, with many offshore windfarms. Denmark plans to increase wind energy's contribution to as much as half of its electrical supply.

The offshore environment is, however, more expensive. Offshore towers are generally taller than onshore towers once one includes the submerged height, and offshore foundations are generally more difficult to build and more expensive as well. Power transmission from offshore turbines is generally through undersea cable, which is more expensive to install than cables on land, and may use high voltage direct current operation if significant distance is to be covered -- which then requires yet more equipment. The offshore environment is also corrosive and abrasive. Repairs and maintenance are much more difficult, and much more costly than on onshore turbines. Offshore wind turbines are outfitted with extensive corrosion protection measures like coatings and cathodic protection. While there is a significant market for small land-based windmills, offshore wind turbines have recently been and will probably continue to be the largest wind turbines in operation, because larger turbines reduce the marginal cost of many of the difficulties of offshore operation. There are some conceptual designs that might make use of the unique offshore environment. For example, a floating turbine might orient itself downwind of its anchor, and thus avoid the need for a yawing mechanism. One concept for offshore turbines has them generate rain, instead of electricity. The turbines would create a fine aerosol, which is envisioned to increase evaporation and induce rainfall, hopefully on land.

Airborne wind turbines have been suggested to be flown in high speed winds at high altitude taking advantage of the steadier winds at high altitudes. No such systems currently exist in the marketplace. The idea of airborne wind turbines reappears in the industry every few years, and seldom (if ever) gets off the drawing board.

: See Directory:Home Generation:Wind Turbine for wind turbine systems for home power generation.

: See Directory:AE Wind Turbine Plans for a place for feedback and input regarding AE Wind Turbine Plans.

#### Related articles

PowerPedia:Viktor Schauberger

#### External articles and references

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Turbine introductory math

American Wind Energy Association

California Wind Energy Collaborative (CWEC)

National Wind Watch -- US coalition opposed to industrial wind energy development.

European Wind Energy Association (EWEA)

British Wind Energy Association

Danish Wind Industry Association

Wind and Hydro Power, turbine basics+principle of operation

How does it work? -- Danish Wind Industry Organisation.

Vertical axis turbines at the American Wind Energy Association Web site

Floating, tilting, co-axial multi-rotor turbines

W. A. Doble, The Tangential Water Wheel, Transactions of the American Institute of Mining Engineers, Vol. XXIX, 1899.

W. F. Durrand, The Pelton Water Wheel, Stanford University, Mechanical Engineering, 1939.

There was an error working with the wiki: Code[1], Wikipedia: The Free Encyclopedia. Wikimedia Foundation.

Impluse Turbine

Introductory turbine math

Alstom Hydro Turbines

Voith Siemens Hydro Turbines

GE Hydro Turbines

European Union publication, Layman's hydropower handbook,12MB pdf

Selecting Hydraulic Reaction Turbines

Cline, Roger, "Mechanical Overhaul Procedures for Hydroelectric Units (Facilities Instructions, Standards, and Techniques, Volume 2-7)", United States Department of the Interior Bureau of Reclamation, Denver, Colorado, July 1994 (800KB pdf).

United States Department of the Interior Bureau of Reclamation, Duncan, William (revised April 1989), "Turbine Repair (Facilities Instructions, Standards & Techniques, Volume 2-5)" (1.5MB pdf).

Australian Wind Energy Association

Residential Wind Power Q&A

Windustry -- "How to" wind energy information