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Contents 1 transonic turbine 2 re-write 3 Quasiturbine 4 removed material 5 betz limit and efficiency of turbines in air 5.1 Turbine operating in reverse 5.2 Useful image

[edit] transonic turbine

This bit says that near supersonic speeds the turbine has a reduced efficiency. Are the rear turbines in a jet engine just inefficient, as the air is certainly supersonic in some of them? Or can turbines become more efficient at completly supersonic speeds? cc 24.137.78.34 00:22, 3 March 2006 (UTC)

"Turbine" is also a mathematical term: http://mathworld.wolfram.com/Turbine.html

-Todd

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[edit] re-write

I re-wrote this page. Some of the material was already covered in Gas turbine or Steam turbine. And some of the material I moved to Steam turbine.

Also; organized, added theory, added sections and added external links. Pud 03:11, 17 Jun 2004 (UTC)

[edit] Quasiturbine

I removed the recent Quasiturbine entries, it belongs here about as much as rotary engine. Duk 06:25, 9 Dec 2004 (UTC)

[edit] removed material

I removed the following material since its un-organized and doesn't really belong on this page. Some of it would be better at gas turbine or jet engines;

• cooled turbine

Modern gas turbine engines often feature one, or more, air-cooled turbine stages. Relatively cool air, bled-off the compression system, is piped around the combustor and fed into the hollow turbine rotor blades and/or vanes, to prevent them melting in the hot gas stream. The used cooling air is dumped, eventually, into the main gas stream.

• high pressure turbine

In a multi-shaft gas turbine, the first turbine downstream of the combustor is usually called the high pressure (i.e. HP) turbine. Normally the HPT is a one or 2 stage unit, the latter usually being more efficient.

• intermediate pressure turbine

In 3 shaft gas turbine engines, (e.g. Rolls-Royce Trent), the middle unit in the turbine expansion system is often called the intermediate pressure (i.e. IP) turbine. The IPT is usually a single stage unit (i.e. a single row of stators, followed by a row of rotor blades).

• low pressure turbine

In a multi-shaft gas turbine, the last unit in the turbine expansion system, is usually called the low pressure (i.e. LP) turbine. Number of stages in an LPT can range from one to 7, or even more, depending on the load imposed.

• power turbine

In turboprop and turboshaft engines, the LP turbine is often called the power turbine

• transonic turbine

In most of the turbines employed in gas turbine engines, the flow exiting the nozzle guide vanes (NGV's) is at a high subsonic Mach number (e.g. 0.85). In a transonic turbine, the flow exits the NGV's at supersonic velocity, increasing the work capacity of the unit, albeit with a penalty on efficiency.

• statorless turbine

Most turbines have a set of stators or NGV's to direct the gas onto the turbine rotor blades. In a statorless turbine,(e.g. GE YF120 variable cycle engine) the exit swirl in the gasflow from a preceding turbine rotor is directed onto another contra-rotating rotor stage, situated immediately downstream. The work capacity of the statorless unit is, however, somewhat lower than normal.

• rotating stator turbine

Usually, being 'earthed' to the engine frame, the stators of a turbine are stationary. However, in the GE36 (UDF) propfan demonstrator engine, the 7 stage power turbine drives a set of contra-rotating propfan blades. The turbine rotors drive one set of propfan blades, whilst the 'unearthed' stators drive the other set of blades, in the opposite direction!

• shrouded turbine

Most turbine rotor blades have a shroud at the tip, which incorporates a seal, to minimize overtip leakage from the high pressure at inlet to the low pressure, downstream. One disadvantage of the shroud is that the extra mass imposes additional centrifugal stress on the aerofoil and the disc which holds the rotor blades. Another disadvantage is the shroud has to be cooled.

• unshrouded turbine

Today, some turbine rotor blades are unshrouded. However, careful design is required to prevent the tips of the blades suffering a 'haircut' (i.e. tip rub) under extreme conditions (e.g. high 'g' maneuver).

• ram air turbine

Modern aircraft are often fitted with a ram air turbine, which provides emergency electrical power, should the normal source of this power (i.e. offtake from the propulsion system) be lost. With unducted rotor blades, the unit behaves like a small windmill, extracting power from the external airstream. The unit is normally stowed within the airframe, to minimize drag, but automatically pops-out into the airstream if there is a power emergency.

• turbopump

Turbine driven fuel (or oxidizer) pump used in rocket motors and ramjet engines. Rockets often use a highly reactive chemical process to generate hot gases to drive the turbine, whereas ramjets usually use ram air.

[edit] betz limit and efficiency of turbines in air

in the solar updraft tower there are turbines ... are these turbines limited by the betz limit?

also: how efficient are turbines?--Flexme 01:55, 11 July 2006 (UTC)

[edit] Turbine operating in reverse

I claim that a turbine "operating in reverse" is not any compressor, but specifically a centrifugal compressor (also called a turbo compressor). E.g. a "reversed" piston compressor is a combustion engine (Otto cycle engine), not a turbine. The expression "operating in reverse" should probably be rephrased: A turbine operates inversely to a centrifugal compressor.--EvenT 20:40, 1 August 2006 (UTC)

How about axial compressor then? Meggar 02:34, 3 August 2006 (UTC)

An axial compressor is close to operating inversely to a turbine and could be included in the sentence. A centrifugual compressor is however closer by having curved blades like most turbines, while an axial compressor has straight blades. A reciprocating compressor or a screw compressor are far from being candidates.--EvenT 19:52, 4 August 2006 (UTC)

We disagree only on the nomenclature. I believe that the two relevant wiki articles have it about right. Axial compressor has multistage airfoil shaped rotor and stator blades, along the lines of a turbine. Centrifugal compressor uses an impeller, often only one, followed by a diffuser stage. The impeller will have fins but not discrete blades. The only question is whether “axial compressor” is a good general name for the device. It is correct in the gas-turbine field of course. The second image now in the article is actually a centrifugal impeller, unhelpfully labeled “turbine” on the source page, and should be replaced.

Meggar 04:36, 17 August 2006 (UTC)

is actually a centrifugal impeller -- no it isn't, it's a turbine wheel. Did you read the image source page at [1] ?--Duk 08:51, 21 October 2006 (UTC)

Further down on that page is an image of a differently shaped part also with a "turbine" caption. Clearly the term is used there loosely for any spinning engine part. There is nothing wrong with that on a page about a fabrication process, just so we don't let it make the wiki article less clear. Meggar 20:44, 17 November 2006 (UTC)

Both turbines and compressors may be of either radial or axial design, or somewhere in between. For example, see Image:Turbocharger.jpg - one side is a turbine and the other side is a compressor - both are a radial design. So yes, [2] labels two different designs as turbines -- not because they are applying the term loosely to any spinning part, but because turbines come in various different designs. The article could be expanded to cover this. I think an image gallery near the end showing different designs would be useful (if the images are carefully chosen). You can also get a good idea of different designs by searching for "Axial turbines" and "Radial turbines"--Duk 22:29, 17 November 2006 (UTC)

Yes, carefully chosen and well explained images later in the article. Pud's image with parts in the housing is great. An indeterminate, unexplained image at the front of the article from a source page about a fabrication process is poor. Meggar 22:52, 17 November 2006 (UTC)

Better keep your eye on that User:Pud! I originally added the image to the article because it was the best public domain image of a radial design that I came across (at the time). Considering this thread, I think having an image of a radial design is especially important. --Duk 23:03, 17 November 2006 (UTC)

While we are on the subject of nomenclature . . .
When I worked for Rotoflow (General Electric) in the 1970's they had the unique distinction of calling the turboexpander turbine the "rotor" and the compressor the "impeller".
While this may not be accurate by definition (impeller = One that impels, as a rotating device used to force a fluid in a desired direction under pressure. A rotor or rotor blade. - Yahoo Dictionary) it does show a need to define and distinguish the two applications . . . one that is driven by the fluid . . . one that drives the fluid.
Morehugh 21:53, 16 January 2007 (UTC)

[edit] Useful image

I'm not a subject expert, and the article has too many images already, but Image:Turbines impulse v reaction.png seems like a pretty informative image that should be added somewhere in this article. I don't think I could have understood the difference between impulse and reaction turbines so quickly without it. --Interiot 18:39, 10 November 2006 (UTC)

How about this:

• replace the first four images with Image:Dampfturbine Montage01.jpg in the intro.
• add the one you've noted to theory section (important to try to explain the difference between impulse and reaction turbines, but very hard to do)
• Image:Turbinengvrotor.gif should eventually be redone as an svg

I'm not opposed to a thumbnail gallery near the end if it carefully selects images to illustrate different designs (water, wind, radial, centrifugal, impulse, reaction ... ) --Duk 19:40, 10 November 2006 (UTC)