GB2049054A

GB2049054A - Gas turbine engines

Info

Publication number: GB2049054A
Application number: GB8014278A
Authority: GB
Original assignee: Alstom Power UK Holdings Ltd
Current assignee: Alstom Power UK Holdings Ltd
Priority date: 1979-05-04
Filing date: 1980-04-30
Publication date: 1980-12-17
Also published as: GB2049054B

Abstract

A gas turbine engine has a gas generator section including a compressor and a compressor turbine on one shaft, and a power turbine on another shaft axially aligned. The two shafts or the end turbine rotors are adapted for the fitment of a flexible coupling between them to convert the twin-shaft engine into a single shaft engine. Thus two quite different markets can be supplied with a single engine type merely by incorporating a flexible coupling or omitting it.

Description

SPECIFICATION Gas turbine engines This invention relates to gas turbine engines of the single and twin-shaft variety. A single-shaft engine is shown diagrammatically in Figure 1 of the accompanying drawings (reproduced, with Figure 2, as typical examples, from the August 78 edition of "Engineering", with kind permission).

The engine of Figure 1 comprises an air compressor 52, a combustion chamber 55 and a turbine 53, the latter providing the power output from the engine and also driving the compressor 52 by way of the single shaft on which they are both mounted. The single shaft may, of course, comprise individual shafts rigidly coupled together as shown at 54. The combustion chamber 55 is supplied with air from the compressor 52 and fuel from a supply 56 and provides exhaust gas to the turbine 53.

A twin-shaft engine is shown in Figure 2, this comprising a gas generator section 50 and a power turbine section 51. The gas generator section is basically a single shaft engine with an exhaust gas output but no mechanical output. The exhaust gas output is fed to the power turbine section 51, there being no mechanical coupling between the two.

The two types of engine have quite different characteristics. Thus, in a twin-shaft type, the gas generator section is allowed to find its own running speed to suit load demand, independently from the power turbine shaft. The sudden application of load will slow down the power turbine but not the whole plant, and the power turbine will develop increased torque, so accelerating to reach its normal governed speed as the governing system provides an increased fuel supply. The single-shaft engine, in contrast, is more suited to electrical load generation, where frequency control is required. On a change of 'impedance' in the driven load, there may be a 'shock' thrown back through the single shaft. If the singie-shaft engine is synchronised with the mains bus-bar frequency, with a phase difference between the two, a shock torque will be transmitted through the shaft.A shock torque will also occur on the shprt-cirnuking of the phases of the driven machine. The inertia of the rigid rotating assemblies in a single-shaft engine is greater than that of the power turbine alone, and it acts like a massive flywheel to give steady running.

It is therefore generally impossible to provide one gas turbine engine which will satisfy both kinds of application. One object of the present invention is to provide a gas turbine engine which can be converted quickly and easily, either by the customer or by the manufacturer prior to delivery, between single and twin-shaft operation.

According to the invention, in a gas turbine engine having a gas generator section and a power turbine section having respective coaxial shafts, the gas generator section including a compressor, a compressor turbine, and a combustion chamber supplied with fuel and with air from said compressor, the two sections being driven by exhaust gas from the combustion chamber, said coaxial shafts or members fixed to said shafts are adapted to be coupled together by a flexible coupling to provide a choice of single or twin-shaft Qperation.

Preferably the two sections of the gas turbine engine have individual casings which entrain the working fluid, these casings being adapted for the mounting therebetween of an annular interduct adapted to be rigidly attached to the individual casings to interconnect them for passage of the working fluid and provide relative location of each with respect to the other. The interduct may be split along a longitudinal diametral plane, one half of the interduct providing said relative location and the other half being removably fixed to the first half. This arrangement provides access to the flexible coupling, which may be circumferentially enclosed in an air-cooled and pressurised coupling housing.

The coaxial shafts may be disposed in an axially spaced arrangement or one of them may be hollow and embrace the other one. An end most rotor of the compressor turbine and an endmost rotor of the power turbine, facing each other, may be provided with projections at fixed radii on thier opposing faces for the mounting of the flexible coupling.

One embodiment of a gas turbine engine in accordance with the invention will now be described with reference to the accompanying drawings in which Figure 1 shows a sectional elevation of a generator section of an already proposed singleshaft gas turbine engine, Figure 2 is a diagram of an already proposed twin-shaft gas turbine engine, and Figure 3 is a sectional elevation of a gas turbine engine in accordance with the invention, the elevation being on a plane containing the shaft axis, and the coupled ends of the compressor turbine and the power turbine.

Referring to Figure 3, on one shaft is mounted a compressor (not shown) and a compressor turbine. The righthand endmost rotor of the compressor turbine is shown in outline, referenced 1. On the other shaft is mounted a power turbine the lefthand endmost rotor 6f which is referenced 2. The two shafts have a common axis 3. The two rotors 1 and 2 are formed with annular projections 4 and 5 on which can be mounted, as shown, a standard flexible coupling 6.

The particular coupling shown comprises an annular cage member 7 which carries two metal annular flexible elements 11 and 12. These flexible elements float on driving bolts 1 3 spaced around the cage member 7 at 1200 intervals on each face. The flexible element 11 then floats on driving bolts 14 which are mounted in the coupling plate 1 5. This coupling plate 1 5 is, in turn, rigidly mounted on the projection 4 by means of dowel bolts 1 6.

The flexible element 12 is similarly coupled to the other coupling plate 1 7 which is rigidly mounted on the projection 5.

In operation therefore, if the power turbine is driving the compressor turbine the plate 1 7 drives the flexible element 12 which drives the cage member 7 and is consequently in circumferential tension. The cage member 7 drives the flexible element 11 which in turn drives the plate 1 5 and is similarly in circumferential tension.

In an alternative form of coupling, the flexible coupling may be fixed directly between the two shaft ends rather than between the turbine rotors.

Other types of flexible coupling suited to the required duty may be used.

The hot working fluid is conducted from the compressor turbine to the power turbine by way of an annular interduct (not shown), whose inner wall is mounted on the stator diaphragm of the power turbine and extends back to provide a partial seal with the end rotor of the compressor turbine. The outer wall is rigidly mounted between the casings of the gas generator section and power turbine section, to provide continuity of the engine casings and transfer the working gas flow therebetween. Both inner and outer walls of the interduct are split along a longitudinal diametral plane, one half of the interduct outer wall providing relative location of the individual casings, and the other half being removably fixed to the first half.

According to a feature of the invention, the flexible coupling, enclosed by this interduct, is further isolated from the working fluid within the interduct by a stationary coupling housing 20 whose inner part is shown in the drawing. This housing is of generally cylindrical form split along a horizontal diametral plane. The lower half is rigidly secured to the power turbine stator diaphragm and the upper half is removably secured to the lower half for access to the flexible coupling. The inner face of the coupling housing 20 is sealed to the rotating coupling plates 1 5 and 17 by labyrinth seals 21 and 22. The flexible coupling is then air-cooled by air bled from an intermediate compressor stage at a pressure slightly greater than the working gas pressure in the interduct.The cooling air escapes slowly through the labyrinth seal 21, into the space between the coupling housing 20 and the inner wall of the interduct, through the partial seal mentioned above between this inner wall and the compressor turbine rotor, and finally into the hot gas stream.

The alternative path for the cooling air is through the labyrinth seal 22, between the power turbine stator and rotor structures and thus into the hot gas stream.

While still being coaxial, the two shafts may be disposed one within the other, the power turbine shaft extending through the hollow shaft of the compressor and compressor turbine. The flexible coupling is then preferably mounted at the cooler inelt end of the compressor. This arrangement would enable the two turbine rotor assemblies to be located closer together, thus reducing the length of the engine. It could also avoid the need for a protective housing for the flexible coupling.

The invention provides an obvious advantage in that a single type of engine can be built and stocked to serve two widely different applications, merely by the use or the omission of a flexible coupling. It is, of course, necessary that the construction and arrangement of the two sections should be suitable for the immediate addition of the flexible coupling.

An advantage of the use of a flexible coupling is that it will accommodate any axial, radial and angular misalignments that may exist between the two rotating assemblies, caused by manufacturing tolerances, thermal distortions, non-rigid bases etc.

Claims

1. A gas turbine engine having a gas generator section and a power turbine section having respective coaxial shafts, the gas generator section including a compressor, a compressor turbine, and a combustion chamber supplied with fuel, and with air from said compressor, the two sections being driven by exhaust gas from the combustion chamber, and wherein said coaxial shafts or members fixed to said shafts are adapted to be coupled together by a flexible coupling to provide a choice of single or twin-shaft operation.

2. A gas turbine according to Claim 1, wherein the two sections of the gas turbine engine have individual casings which entrain the working fluid, these casings being adapted for the mounting therebetween of an annular interduct adapted to be rigidly attached to the individual casings to interconnect them for the passage of the working fluid and provide relative location of each with respect to the other.

3. A gas turbine engine according to Claim 2, wherein the interduct is in split form, being divided along a longitudinal diametral plane, one half of the interduct providing said relative location and the other half being removably fixed to the first half.

4. A gas turbine engine according to any preceding claim wherein said flexible coupling is circumferentially enclosed and isolated from the working fluid by a coupling housing.

5. A gas turbine engine according to Claim 4 wherein said coupling housing is in split form, being divided along a longitudinal diametral plane.

6. A gas turbine engine according to Claim 4 or Claim 5, wherein said coupling housing is adapted to receive a supply of cooling and pressurising air.

7. A gas turbine engine according to any preceding claim, wherein said coaxial shafts are disposed in an axially spaced arrangement.

8. A gas turbine engine according to Claim 1, wherein one of said coaxial shafts is hollow and embraces the other one.

9. A gas turbine engine according to Claim 1 wherein said members are rotors, an endmost rotor of the compressor turbine facing an endmost rotor of the power turbine, said endmost rotors being provided with projections at fixed radii on their opposing faces for the mounting of the flexible coupling.

10. A gas turbine engine substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.