Turbine on display at
U.S. Space & Rocket Center •
Steam turbines are used to drive electrical generators in thermal power plants which use
coal,
fuel oil or
nuclear fuel. They were once used to directly drive mechanical devices such as ships'
propellers (for example the
Turbinia, the first turbine-powered
steam launch), 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. Turbo electric ship machinery was particularly popular in the period immediately before and during
World War II, primarily due to a lack of sufficient gear-cutting facilities in US and UK shipyards. • Aircraft
gas turbine engines are sometimes referred to as turbine engines to distinguish them from piston engines. •
Transonic turbine. The gas flow in most turbines employed in gas turbine engines remains subsonic throughout the expansion process. In a transonic turbine the gas flow 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. •
Contra-rotating turbines. With
axial turbines, some efficiency advantage can be obtained if a downstream turbine rotates in the opposite direction to an upstream unit. However, the complication can be counter-productive. A contra-rotating steam turbine, usually known as the Ljungström turbine, was originally invented by Swedish Engineer
Fredrik Ljungström (1875–1964) in Stockholm, and in partnership with his brother Birger Ljungström he obtained a patent in 1894. The design is essentially a multi-stage
radial turbine (or pair of 'nested' turbine rotors) offering great efficiency, four times as large heat drop per stage as in the reaction (Parsons) turbine, extremely compact design and the type met particular success in back pressure power plants. However, contrary to other designs, large steam volumes are handled with difficulty and only a combination with axial flow turbines (DUREX) admits the turbine to be built for power greater than ca 50 MW. In marine applications only about 50 turbo-electric units were ordered (of which a considerable number were finally sold to land plants) during 1917–19, and during 1920–22 a few turbo-mechanic not very successful units were sold. Only a few turbo-electric marine plants were still in use in the late 1960s (ss Ragne, ss Regin) while most land plants remain in use 2010. •
Statorless turbine. Multi-stage turbines have a set of static (meaning stationary) inlet guide vanes that direct the gas flow onto the rotating rotor blades. In a stator-less turbine the gas flow 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 based alloys and often use intricate internal air-cooling passages to prevent the metal from overheating. 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 air cooling. Ceramic blades are more brittle than their metallic counterparts, and carry a greater risk of catastrophic blade failure. This has tended to limit their use in jet engines and gas turbines to the stator (stationary) blades. •
Ducted fan (shrouded) turbine. Many turbine rotor blades have shrouding at the top, which interlocks with that of adjacent blades, to increase damping and thereby reduce blade flutter. In large land-based electricity generation steam turbines, the shrouding is often complemented, especially in the long blades of a low-pressure turbine, with lacing wires. These wires pass through holes drilled in the blades at suitable distances from the blade root and are usually brazed to the blades at the point where they pass through. Lacing wires reduce blade flutter in the central part of the blades. The introduction of lacing wires substantially reduces the instances of blade failure in large or low-pressure turbines. •
Propfan (shroudless turbine). Modern practice is, wherever possible, to eliminate the rotor shrouding, thus reducing the
centrifugal load on the blade and the cooling requirements. •
Tesla turbine, or bladeless turbine, uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine. •
Water turbines: •
Pelton wheel, a type of impulse water turbine. •
Francis turbine, a type of widely used water turbine. •
Kaplan turbine, a variation of the Francis Turbine. •
Turgo turbine, a modified form of the Pelton wheel. •
Tyson turbine, a conical water turbine with helical blades emerging partway down from the apex gradually increasing in radial dimension and decreasing in pitch as they spiral towards the base of the cone. •
Cross-flow turbine, also known as Banki-Michell turbine, or Ossberger 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. • 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 blade rows, as in the Parsons or de Laval, typically up to ten compared with up to a hundred stages of a Parsons design. The overall efficiency of a Curtis design is less than that of either the Parsons or de Laval designs, but it can be satisfactorily operated through a much wider range of speeds, including successful operation at low speeds and at lower pressures, which made it ideal for use in ships' powerplant. In a Curtis arrangement, the entire heat drop in the steam takes place in the initial nozzle row and both the subsequent moving blade rows and stationary blade rows merely change the direction of the steam. Use of a small section of a Curtis arrangement, typically one nozzle section and two or three rows of moving blades, is usually termed a Curtis 'Wheel' and in this form, the Curtis found widespread use at sea as a 'governing stage' on many reaction and impulse turbines and turbine sets. This practice is still commonplace today in marine steam plant. •
Pressure compound multi-stage impulse, or "Rateau", after its French inventor,
Auguste 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. •
Mercury vapour turbines used
mercury as the working fluid, to improve the efficiency of fossil-fuelled generating stations. Although a few power plants were built with combined mercury vapour and conventional steam turbines, the toxicity of the metal mercury was quickly apparent. •
Screw turbine is a
water turbine which uses the principle of the
Archimedean screw to convert the
potential energy of water on an upstream level into
kinetic energy. == Uses ==