GB2434414A

GB2434414A - Stator blade assembly

Info

Publication number: GB2434414A
Application number: GB0701109A
Authority: GB
Inventors: Mark Harvey Tothill
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2006-01-24
Filing date: 2007-01-22
Publication date: 2007-07-25
Anticipated expiration: 2027-01-22
Also published as: GB0601359D0; GB0701109D0; GB2434414B

Abstract

A bayoneted stator blade assembly or diaphragm that can be fitted in an axial fluid flow turbine with an unsplit outer casing 6. The stator blade assembly includes a one-piece stator blade ring 24 having an annular row of stator blades 26 (sometimes called stator vanes or nozzles) and at least one engagement projection or "bayonet" 32. A mounting ring 16 is assembled between two annular rows of rotor blades 12 and 36 mounted to disc-type rotors. The mounting ring 16 includes an engagement wall 18 with at least one recess 18a that is configured to receive the engagement projection 32. The stator blade ring 24 is secured to the mounting ring 16 by moving the stator blade ring axially past the engagement wall 18 in such a way that the at least one engagement projection 32 passes through the at least one recess 18a in the engagement wall. The mounting ring 16 is then indexed or rotated relative to the stator blade ring 24 so that the engagement projection 32 is axially secured in an annular channel 22 between the engagement wall 18 and a supporting wall 20. A pin (34, figure 4) may be inserted to lock the blade ring 24 in place on the mounting ring 16.

Description

TURBINE ASSEMBLIES

Field of the Invention

The present invention relates to assemblies having stator blades (otherwise called fixed blades, vanes or nozzles) for use in axial flow turbines, and in particular for use in such turbines having an unsplit outer casing.

Background of the Invention

A stage of an axial flow turbomachine, such as a gas turbine, typically includes an annular row of rotor blades (otherwise called moving blades) mounted to a disc-type rotor inside an outer casing. The stage also includes a stator blade assembly or diaphragm, which is immediately upstream of the rotor blades, having an annular row of stator blades.

It is generally preferred that the stator blade assembly or diaphragm is formed in one piece because it enables the clearance between the rotating and stationary parts of the turbine stage to be minimised. However, assembly problems can arise if the outer casing of the turbine is formed in a single piece instead of being split horizontally into two generally semi-circular pieces. For example, it can be impossible to fit a one-piece stator blade assembly into a turbine sub-assembly consisting of an unsplit outer casing and a welded rotor blade sub-assembly having two turbine rotor stages in axial succession. One solution is to form the stator blade assembly as a segmented ring but this can lead to unacceptably large clearances between the' rotating and stationary parts.

Accordingly, there is a need for an improved stator blade assembly that can be formed in one-piece and fitted in a turbine having an unsplit outer casing.

Summary of the Invention

The present invention provides a stator blade assembly comprising: a stator blade ring including a plurality of stator blades and at least one engagement projection; and a mounting ring having a radially extending engagement wall with at least one recess configured to receive the at least one engagement projection, whereby the stator blade ring and the mounting ring can be secured together prior to use by axial movement of the stator blade ring to pass the at least one engagement projection through the at least one recess in the engagement wall, the mounting ring being indexable relative to the stator blade ring to take the at least one engagement projection out of angular alignment with the at least one recess.

The stator blade assembly is therefore secured to the mounting ring using a bayonet-type fixing method.

The mounting ring preferably further includes a radially extending supporting wall axially spaced apart from the engagement wall by an annular channel and wherein the at least one engagement projection (or "bayonet") of the stator blade ring is located in the annular channel in use. After the mounting ring has been indexed relative to the stator blade ring it will be understood that the stator blade ring cannot be moved axially past either of the engagement wall and the supporting wall.

The at least one engagement projection and the at least one recess can have any suitable shape or profile.

The stator blade ring is preferably formed in one-piece so that when it is secured to the mounting ring the complete stator blade assembly does not suffer from the clearance problems mentioned above. The use of the bayonet-type fixing method enables a one-piece stator blade ring to be fitted inside a turbine having an unsplit casing.

Locking means can be provided to prevent the mounting ring from being indexed relative to the stator blade ring once the at least one engagement projection is out of angular alignment with the at least one recess. The locking means can be a pin, dowel, bolt or the like that is inserted in corresponding apertures provided in the at least one engagement projection and the engagement wall of the mounting ring.

Preferably three or more pins are used and they can be equally spaced around the circumference of the stator blade assembly. However, it will be readily appreciated that the actual number of pins (and also the selection of an appropriate type of locking means) will depend on the design and operating requirements of the turbine. For additional strength and rigidity, the pin may also extend into or through a corresponding aperture in the supporting wall.

The stator blade ring preferably includes a plurality of engagement projections and the engagement wall of the mounting ring preferably includes a corresponding plurality of recesses. It will be readily appreciated that the engagement projections and recesses must have the same circumferential spacing so that they are all radially aligned at the same time. Otherwise, the stator blade ring will be prevented from moving axially past the engagement wall.

The mounting ring is preferably split into two substantially semi-circular pieces that are secured (for example, bolted) together.

The stator blade assembly can be fitted into a turbine sub-assembly. The present invention therefore further provides a turbine sub-assembly comprising: an outer casing; a first plurality of rotor blades mounted to a first rotor disc; a second plurality of rotor blades mounted to a second rotor disc; and a stator blade assembly as described above and axially located between the first and second rotor blades.

The turbine sub-assembly preferably further comprises a substantially cylindrical sealing diaphragm extending between the first and second rotor discs and including at least one sealing land, and the mounting ring of the stator blade assembly is preferably axially aligned with the at least one sealing land. In use, the mounting ring will "float" on the sealing land. In other words, the mounting ring is not secured to the sealing diaphragm and a very small gap is maintained between the radially inner surface of the mounting ring and the at least one sealing land to reduce the leakage flow past the stator blade assembly.

The stator blade assembly may further comprise means for securing the stator blade ring to the outer casing. The securing means may, for example, take the form of one or more hooks that are received in slots formed on the inside of the outer casing.

Other ways of securing the stator blade assembly to the outer casing or to any other structural component of the turbine sub-assembly may be used.

The present invention further provides a method of assembling a stator blade assembly comprising the steps of: providing a stator blade ring including a plurality of stator blades and at least one engagement projection; providing a mounting ring having a radially extending engagement wall with at least one recess that is configured to receive the at least one engagement projection; axially moving the stator blade ring to pass the at least one engagement projection through the at least one recess in the engagement wall; and indexing the mounting ring relative to the stator blade ring to take the at least one engagement projection out of angular alignment with the at least one recess to secure the stator blade ring and the mounting ring together.

The mounting ring may further include a radially extending supporting wall axially spaced apart from the engagement wall by an annular channel and in this case the method preferably further comprises the steps of locating the at least one engagement projection of the stator blade ring in the annular channel before indexing the mounting ring relative to the stator blade ring to take the at least one engagement projection out of angular alignment with the at least one recess, whereby the stator blade ring cannot be moved axially past the engagement wall or the supporting wall.

The method preferably further comprises the step of preventing the mounting ring from being indexed relative to the stator blade ring once the at least one engagement projection is out of angular alignment with the at least one recess. This can be achieved using a locking means.

The mounting ring can be split into two substantially semi-circular pieces and in this case the method preferably further comprises the step of secured the pieces together before the stator blade ring is secured to the mounting ring.

Brief Description of the Drawings

Exemplary embodiments of the invention will now be described, with reference to the accompanying drawings, in which: Figure 1 is a radial cross section view showing a first stage in the assembly of a turbine sub-assembly according to the present invention; Figure 2 is a radial cross section view showing a second stage in the assembly of the turbine sub-assembly of Figure 1; Figure 3 is a radial cross section view showing a third stage in the assembly of the turbine sub-assembly of Figure 1; and Figure 4 is a radial cross section view showing a final stage in the assembly of the turbine sub-assembly of Figure 1;

Detailed Description of the Preferred Embodiments

With reference to Figure 1, a gas turbine sub-assembly 1 includes a first disc-type rotor 2 and a second disc-type rotor 4 located inside an unsplit or one-piece outer casing 6. A cylindrical sealing diaphragm 8 extends between the first and second disc-type rotors 2 and 4 and includes a number of sealing lands 10.

An annular row of rotor blades 12 is mounted to the first disc-type rotor 2 using a well known "fir tree" root type of blade fixing. However, it will be readily appreciated that any other suitable type of root fixing could be used. A substantially cylindrical static shroud 14 is hooked into the inside of the outer casing 6 to reduce the leakage flow past the tips of the rotor blades 12.

The way in which a stator blade assembly or diaphragm is fitted to the turbine sub-assembly I will now be explained with reference to Figures 2 to 4. First of all, a mounting ring 16 is assembled around the sealing diaphragm 8 between the first and second disc-type rotors 2 and 4 as shown in Figure 2. The mounting ring 16 is formed in two parts, being horizontally split into two semi-circular pieces. Once the pieces have been located on the sealing lands 10, they are bolted together through flanges (not shown) on the horizontal split line. The mounting ring 16 is not fixed to the sealing diaphragm 8 and when the turbine sub-assembly is in use the mounting ring will "float" on the sealing lands 10 in such a way that any leakage flow between the radially inner surface of the mounting ring and the sealing lands is minimised.

An engagement wall 18 extends all of the way around the radially outer periphery of the mounting ring 16. When viewed in the axial direction, the engagement wall 18 has a generally castellated appearance with a number of radially extending recesses or slots separated by a number of securing lands. The cross section of Figure 2 is taken through a recess 1 8a of the engagement wall 18 and the circumferentially adjacent securing land I 8b can also be seen. A supporting wall 20 also extends all of the way around the radially outer periphery of the mounting ring 16 and is axially spaced from the engagement wall 18 by an annular channel 22.

Figure 2 shows a one-piece or non-segmented stator blade ring 24 before it is secured to the mounting ring 16. The stator blade ring 24 includes an annular row of stator blades 26 (sometimes called stator vanes or nozzles) extending between a radially inner cylindrical platform 28 and a radially outer frusto-conical shroud 30. The shroud 30 includes a pair of hooks 30a so that it can be hooked into the inside of the outer casing 6 in the same way as the shroud 14. A number of engagement projections 32 (or "bayonets") extend radially inwardly from the platform 28. The number of engagement projections 32 is the same as the number of recesses I 8a provided in the engagement wall 18 and the engagement projections and the recesses have the same circumferential spacing.

The stator blade ring 24 is secured to the mounting ring 16 by locating it adjacent the mounting ring in an orientation where the engagement projections 32 are angularly aligned with the corresponding recesses 18a in the engagement wall 18. The stator blade ring 24 can then be moved in an axial direction towards the annular row of rotor blades 12 and past the engagement wall 18 until the engagement projections 32 are located in the annular channel 22 as shown in Figure 3. During this axial movement, the engagement projections 32 will pass through the corresponding recesses I 8a and the hooks 30a are slidably received in slots 6a (see Figure 2) provided in the inside of the outer casing 6.

Once the engagement projections 32 are securely located in the annular channel 22, the mounting ring 18 is indexed or rotated relative to the stator blade ring 24 by half a pitch of the securing lands I 8b so that the engagement projections are no longer angularly aligned with the corresponding recesses 18 provided in the engagement wall 18 but are instead at least partially angularly aligned with the securing lands. The stator blade ring 24 is therefore unable to move in the axial direction because it is trapped in the annular channel 22 between the supporting wall 20 and the securing lands I 8b of the engagement wall 18.

In a final step, three or four pins 34 are inserted through matching holes (not shown) provided in the securing lands 18b and the engagement projections 32 (and optionally also through the supporting wall 20) to retain the relative positions of the stator blade ring 24 and the mounting ring 16. The pins 34 also centralise the stator blade ring 24 and the mounting ring 16 on the sealing diaphragm 8 to maintain concentricity during operation of the turbine sub-assembly. The pins 34 are spaced at equal distances around the circumference of the stator blade ring 24. A second annular row of rotor blades 36 is then mounted to the second disc-type rotor 4 using a "fir tree" root type of blade fixing as shown in Figure 4. The rotor blades 12 and 36 are axially retained in their respective disc-type rotor using well known means, such as lock plates (not shown).

The present invention has been described above purely by way of example, and modifications can be made within the scope of the invention as claimed. The invention also consists in any individual features described or implicit herein or shown or implicit in the drawings or any combination of any such features or any generalisation of any such features or combination, which extends to equivalents thereof. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments. Each feature disclosed in the specification, including the claims and drawings, may be replaced by alternative features serving the same, equivalent or similar purposes, unless expressly stated otherwise.

Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the

field.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like, are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". -9-.

Claims

CLAIMS

I. A stator blade assembly comprising: a stator blade ring including a plurality of stator blades and at least one engagement projection; and a mounting ring having a radially extending engagement wall with at least one recess configured to receive the at least one engagement projection, whereby the stator blade ring and the mounting ring can be secured together prior to use by axial movement of the stator blade ring to pass the at least one engagement projection through the at least one recess in the engagement wall, the mounting ring being indexable relative to the stator blade ring to take the at least one engagement projection out of angular alignment with the at least one recess.

2. A stator blade assembly according to claim 1, wherein the mounting ring further includes a radially extending supporting wall axially spaced apart from the engagement wall by an annular channel and wherein the at least one engagement projection of the stator blade ring is located in the annular channel.

3. A stator blade assembly according to claim I or claim 2, further comprising locking means to prevent the mounting ring from being indexable relative to the stator blade ring once the at least one engagement projection is out of angular alignment with the at least one recess.

4. A stator blade assembly according to claim 3, wherein the locking means includes a pin that is inserted in corresponding apertures provided in the at least one engagement projection and the engagement wall of the mounting ring.

5. A stator blade assembly according to any preceding claim, wherein the stator blade ring includes a plurality of engagement projections and the engagement wall of the mounting ring includes a corresponding plurality of recesses.

6. A stator blade assembly according to any preceding claim, wherein the mounting ring is split into two substantially semi-circular pieces that are secured together.

7. A turbine sub-assembly comprising: an outer casing; a first plurality of rotor blade mounted to a first rotor disc; a second plurality of rotor blade mounted to a second rotor disc; and a stator blade assembly according to any preceding claim axially located between the first and second rotor blades.

8. A turbine sub-assembly according to claim 7, further comprising a substantially cylindrical sealing diaphragm extending between the first and second rotor discs and including at least one sealing land, and wherein the mounting ring of the stator blade assembly is axially aligned with the at least one sealing land.

9. A turbine sub-assembly according to claim 7 or claim 8, wherein the stator blade assembly further comprises means for securing the stator blade ring to the outer casing.

10. A stator blade assembly substantially as herein described and with reference to the drawings.

11. A turbine sub-assembly substantially as herein described and with reference to the drawings.

12. A method of assembling a stator blade assembly comprising the steps of: providing a stator blade ring including a plurality of stator blades and at least one engagement projection; providing a mounting ring having a radially extending engagement wall with at least one recess that is configured to receive the at least one engagement projection; axially moving the stator blade ring to pass the at least one engagement projection through the at least one recess in the engagement wall; and indexing the mounting ring relative to the stator blade ring to take the at least one engagement projection out of angular alignment with the at least one recess to secure the stator blade ring and the mounting ring together.

13. A method according to claim 12, wherein the mounting ring further includes a radially extending supporting wall axially spaced apart from the engagement wall by an annular channel and the method further comprises the steps of: locating the at least one engagement projection of the stator blade ring in the annular channel before indexing the mounting ring relative to the stator blade ring to take the at least one engagement projection out of angular alignment with the at least one recess, whereby the stator blade ring cannot be moved axially past the engagement wall or the supporting wall.

14. A method according to claim 13, further comprising the step of preventing the mounting ring from being indexed relative to the stator blade ring once the at least one engagement projection is out of angular alignment with the at least one recess.

15 A method according to any of claims 12 to 14, wherein the mounting ring is split into two substantially semi-circular pieces and the method further comprises the step of secured the pieces together before the stator blade ring is secured to the mounting ring.