GB2110768A

GB2110768A - Fixings for stator vanes

Info

Publication number: GB2110768A
Application number: GB08136229A
Authority: GB
Inventors: David Nigel Crapper; Michael John Holroyd
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1981-12-01
Filing date: 1981-12-01
Publication date: 1983-06-22

Abstract

Stator vanes 19, 21, 23 of a multi-stage axial flow compressor, e.g. for a gas turbine engine, are fixed in compressor casing 31 by "dovetail" shaped ends 25, 27, 29 or similar which mate with similarly profiled channels 33, 35, 37 in the casing 31. At their radially inner ends the stator vanes are fixed to shroud rings 47, 49, etc., which in turn seal against portions 15, 17 of the compressor rotor drum. In order to exert satisfactory torsional restraint on the stator vanes and also to damp vibrations, fixing of the stator vanes to the shroud rings is by means of one or more flanges such as 59, 61 projecting from the inner ends of the stator vanes into elastomer-lined channels in the shroud rings. The shroud ring channels may be defined between upstanding flanges such as 63-66 and the elastomer linings 67 are bonded to the walls of the channels and to the flanges 59, 61 on the stator vanes. <IMAGE>

Description

SPECIFICATION Stator assembly for axial flow compressor The present invention relates to a stator vane assembly for an axial flow compressor, and in particular to a stator vane assembly including novel fixing means for the stator vane.

In one type of multi-stage axial flow compressor, used in gas turbine aeroengines, the stator vanes in each ring of such vanes before and after successive stages of rotor blading, are fixed in static structure at both their radially inner and their radially outer ends. At their outer ends they are held in a casing which forms the radially outer wall of the compressor flow annulus, whilst at their inner ends they are held in an annular ring member. This ring member is in fact held concentric with the rotor by the vanes themselves, and has no other support. Its function is to secure the radially inner ends of the vanes in fixed relationship to each other and to provide a seal against flow of the compressor air around the radially inner ends of the vanes.

This seal is formed with the vanes on the radially outer side of the ring member and with the compressor rotor on the radially inner side of the ring member.

The stator vanes may be held in the compressor casing and the ring member by means of the well-known "dovetail" or 'T'-slot shaped fixings, the casing or ring being provided with channels having these shapes in which are received complementary shaped features on the radially outer and inner ends of the vanes. One problem which can arise with this type of fixing is fretting between the channels and the mating features on the vanes. The fretting is caused by twisting of the vanes in their seatings due to aerodynamic forces, and by vibration.

The present invention seeks to reduce fretting by providing the stator vanes with fixing means exerting torsional restraint and at the same time providing damping of the vibrations.

According to the present invention a stator vane assembly for an axial flow compressor comprises a compressor casing, a ring member spaced radially inwards from the compressor casing, and stator vanes extending between the compressor casing and the ring member, wherein the vanes are: a) fixed to the compressor casing by means of features on the radially outer ends of the vanes which features mate with a channel provided in the compressor casing, said channel having a radial cross-section with a reentrant profile and said features on the radially outer ends of the vanes engaging said reentrant profile;; b) fixed to the ring member by means of at least one flange projecting substantially radially inwardly from the radially inner end of each vane and extending substantially circumferentially of the ring member, which flange projects into a corresponding channel in the ring member and is bonded thereto through an elastomeric material interposed between the flange and the internal surfaces of the channel. Preferably there are at least two such flanges projecting into respective channels in the ring member and similarly bonded thereto through the elastomeric material.

Preferably the elastomeric material in the channels in the ring member comprises extrusions or mouldings conforming to the shape of the channels and adapted to receive the flanges on the radially inner ends of the vanes, the elastomeric material being bonded to the flanges and the channels. The extrusions or mouldings are preferably sized such that they are radially compressed by the flanges against the bottoms of the channels.

Bonding to the channels and flanges may be means of a cureable adhesive, and in order to maintain a constant bond thickness of adhesive the extrusions or mouldings can be provided with raised lands or ribs on those portions of their surfaces which are bonded to the channels and flanges. The elastomeric material may be a silicone rubber.

The channels in the ring member are preferably defined by pairs of upstanding flanges thereon, and the ring member preferably comprises a rolled or an extruded member.

The invention also comprises a stator vane, a ring member, or an elastomeric extrusion or moulding adapted to be incorporated in a stator vane assembly as described above.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a sectional side elevation of part of an axial flow compressor to which the invention has been applied; Figure 2 is a scrap view on section line A-A in Fig. 1; and Figure 3 is an enlarged view of area B in Fig. 2.

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The drawings are not to scale and the embodiments are described by way of example only.

Referring to Fig. 1, there is shown several stages of a multi-stage axial flow compressor 1, such as would form part of a gas turbine aeroengine. The compressor 1 comprises several stages 3, 5, 7, 9 of rotor blading, which rotor blades are mounted in known manner on respective rotor discs, the middle two of the discs being indicated at 11 and 1 3. The rotor discs are joined together by bridging rings 15, 17, thereby creating a rotor drum.

Between successive stages of rotor blades 3, 5, 7 and 9 are provided stator vanes 19, 21, 23. The vanes are provided with "dovetail" shaped radially outer ends 25, 27, 29 respectively by means of which the vanes are fixed to compressor casing 31. These dovetail shaped ends 25, 27 and 29 mate with respective channels 33, 35, 37 provided in compressor casing 31, these channels also having "dovetail" shape complementary to that of the ends of the vanes so that the ends of the vanes can engage the profiles of the channels. Although the ends of the vanes and the profiles of the radial cross-sections of the channels have been described as "dovetail" shaped, other shapes adapted to retain the ends of the vanes in the casing are possible, such as T-shapes.Genetically, the profiles of suitably shaped channels may be termed effectively "reentrant", the radially outer ends of the vanes having features thereon which can engage the reentrant profile so as to positively retain the vanes to the casing.

As can be seen in Fig. 1, the radially outer shrouds of the vanes 19, 21, 23 are formed by the radially inner surfaces 39, 41, 43 respectively of the dovetail shaped ends of the vanes, these surfaces being contiguous with the inner surface 45 of the compressor casing when the vanes are assembled into the casing.

At their radially inner ends, the vanes 19, 21 and 23 are held fixed to respective annular ring members 47, 49, 51, known as shroud rings. Their function is to secure the radially inner ends of the vanes in fixed relationship to each other and to provide a seal against flow of the compressor air around the radially inner ends of the vanes, the seal being made against the inner ends of the vanes on outer sides of the shroud rings 47, 49 and 51, and against annular ribs 53 of the compressor drum on the inner sides of the shroud rings. The shroud rings have annular recesses on their inner sides, these recesses being filled by an abradeable material 55 so that during differential expansion and contraction of the compressor drum with respect to the shroud rings, ribs 53 can wear grooves in the abradeable material, thereby maintaining the seal.

Guide vanes 19, 21 and 23 differ from each other only in respect of dimensions, and are fixed to their shroud rings 47, 49 and 51 in accordance with the claimed invention. The inner fixing for guide vane 1 9 is therefore typical of the others and will now be described, together with the inner fixing of guide vane 21 in connection with Fig. 2. Features associated with the inner fixing of vane 21 are similar to features described in connection with vane 1 9 and will be similarly numbered except that a superscript 1 will be used.

From Fig. 1, it will be noted that vane 1 9 has a radially inner shroud portion 57. The underside of shroud portion 57 is substantially plain except for two axially spaced-apart flanges 59 and 61 which project radially inwards and extend parallel with each other.

They are plain and are of substantially uniform height and thickness. A side elevation of flanges 59' on vane 21 is shown in Fig. 2, where it can be seen that they are substantially coextensive in the circumferential sense with shroud portions 57'.

Flanges 59 and 61 project into respective channels in shroud ring 47, the twin channels being defined by pairs of upstanding flanges 63, 64 and 65, 66, which project radially outwards, the former pair projecting from the foremost portion of the shroud ring. and the latter pair projecting from the rearmost portion.

Flanges 59 and 61 do not directly contact any part of flanges 63 or 66, not do they contact the bottoms of the channels defined by flanges 63 to 66. Instead, an elastomeric material 67 is interposed between each flange 59 and 61 and the internal surface of the channel into which it projects. The elastomeric material 67 is bonded both to flanges 59 and 61 and to the internal surfaces of the channels, thereby forming a lining for the channels and a seating for the flanges received therein.

This configuration for the fixing of the guide vanes to their shroud rings achieves the following advantages: a) it provides good torsional restraint for the vane against aerodynamic forces by virtue of the cooperating flanges 59, 61 and 63 to 66 which are coupled together through the elastomeric material 67; b) the inclusion of the elastomeric material 67 and its bonding to all the flanges damps vibrations in the vanes and their outer fixings.

Both these factors contribute to reduction of fretting between the dovetail-shaped outer ends of the vanes and the walls of their respective channels in casing 31.

Although the drawings show two axially spaced flanges on the radially inner ends of the vanes, there is no reason why the inner fixings of the vanes should not incorporate only one flange positioned at any suitable axial position on the inner ends of the vanes.

Arrangements incorporating more than two flanges are also possible.

The elastomeric material 67 in fact comprises U-section extrusions conforming to the shape of the channels and sized internally to receive flanges 59, 61 as a snug fit. Mouldings could be utilised instead of extrusions. It will be seen from Fig. 2 that the elastomeric extrusions (or mouldings) are continuous between vanes, preferably extending around the shroud rings for up to half a circumference.

Note also that except as necessary to provide the desired degree of resilience and resistance to tearing during assembly, the thickness of the elastomeric material could be much less than that shown in the drawings.

Silicone rubber is preferred as the material 67 from which the extrusions or mouldings are made, but other types of elastomer could also be used, depending upon operating temperatures of the compressor and other envi ronmental factors.

The elastomer extrusions or mouldings are bonded to the flanges by means of a cureable adhesive, a suitable type for silicone rubber extrusions or mouldings being "SILCOSET", a silicone rubber adhesive supplied by Ambersil Limited, Daneshill, Basingstoke, Hampshire.

Turning to Fig. 3 of the drawings, U-shaped extrusion comprising elastomeric material 67 is provided with lands or ribs 69 on those portions of its surface which are bonded to the flanges 59, 63 and 64, this extrusion being typical of the others shown in Figs. 1 and 2. The lands 69 are provided in order to maintain a constant bond thickness of adhesive 71 before it is cured, lands 69 being somewhat compressed when the extrusion is inserted into the channel, and when flange 59 is inserted into the extrusion.

Referring again to Fig. 2, it will be noted that there is an appreciable gap between the adjacent ends of the two flanges 59'. This gap has been filled by injecting a plug 73 of cureable silicone rubber material into it in order to prevent ingress of compressor air past inner shroud 57'. This occurs after assembly of each half ring of stator vanes onto its corresponding half shroud ring, as detailed hereafter.

Production of a complete stator vane assembly, utilising vanes 1 9 as an example, involves firstly sliding two half sets of stator vanes 1 9 into the channel 33 in corresponding semi-circular halves of casing 31. The shrouding 47 also comprises two semi-circular halves. Half circular elastomeric extrustions are bonded into the channels in the two halves of the shroud ring 47, and the half rings are then pushed onto the flanges 59 and 61 of the vanes 19, incured adhesive having first been applied to the internal surfaces of the extrusions. The same procedure is followed for the other stages of stator vanes such as 21 and 23. Thereafter the two halves of casing 31 are bolted together and the adhesive and filler materials are cured by heat.

It should be noted that it is preferably to size the silicone rubber extrusions or mouldings such that they are radially compressed by the flanges such as 59, 61 and 59', 61', against the bottoms of the channels in the shroud rings when the casing halves are bolted together; This gives a small amount of radial thrust on the vanes so that they are held against their outer seatings in casings 31 and it also centralises the shroud rings.

For economy of manufacture it is preferred that the shroud rings 47, 49 and 51 (Fig. 1) be rolled (or extruded and rolled) sections, the flanges 63 to 66 etc. being formed integrally with the rest of their shroud ring.

As an alternative to the above construction for the shroud rings, it would be possible to bridge the space between flanges such as 64, 65 and 64', 65' and produce shroud rings having a box section. This would produce more rigid shroud rings and at the same time leave a small annular gap between the outer faces of the box sections and the undersides of the shrouds 57, 57' etc. This could be filled with a resilient material if more damping of vibrations were required.

Note that otherwise the larger space between the outer faces of the shroud rings and the undersides of the shrouds as shown in Fig. 1 could also be filled with a resilient material for greater damping of vibrations.

Claims

1. A stator vane assembly for an axial flow compressor, comprising a compressor casing, a ring member spaced radially inwards from the compressor casing, and stator vanes extending between the compressor casing and the ring member, wherein the vanes are: a) fixed to the compressor casing by means of features on the radially outer ends of the vanes which features mate with a channel provided in the compressor casing, said channel having a radial cross-section with a reentrant profile and said features on the radially outer ends of the vanes engaging said reentrant profile;; b) fixed to the ring member by means of at least one flange projecting substantially radially inwardly from the radially inner end of each vane and extending substantially circumferentially of the ring member, which flange projects into a corresponding channel in the ring member and is bonded thereto through an elastomeric material interposed between the flange and the internal surfaces of the channel.

2. A stator vane assembly according to claim 1 in which the elastomeric material in the channel in the ring member comprises extrusions or mouldings conforming to the shape of the channel and adapted to receive the flange on the radially inner end of each vane, the extrusions or mouldings being bonded to the flange and to the channel.

3. A stator vane assembly according to claim 2 in which the extrusions or mouldings are sized such that they are radially compressed by the flange against the bottom of the channel.

4. A stator vane assembly according to claim 2 or claim 3 in which the extrusions or mouldings are bonded to the channel and to the flange by means of a cureable adhesive.

5. A stator vane assembly according to claim 4 in which the extrusions or mouldings are provided with raised lands on those portions of their surfaces which are bonded to the channels and flanges, thereby to maintain a constant bond thickness of adhesive.

6. A stator vane assembly according to any one of claims 2 to 5 in which the elastomeric material comprises a silicone rub ber.

7. A stator vane assembly according to any one of claims 1 to 6 in which the channel in the ring member is defined by a pair of upstanding flanges thereon.

8. A stator vane assembly according to any one of claims 1 to 7 in which the ring member comprises a rolled or an extruded member.

9. A stator vane for a stator vane assembly according to any one of claims 1 to 8.

10. A ring member for a stator vane assembly according to any one of claims 1 to 8.

11. An elastomeric extrusion or moulding for a stator vane assembly according to any one of claims 2 to 8.

1 2. A stator vane assembly substantially as described in this specification with reference to and as illustrated by Fig. 1 of the accompanying drawings.

1 3. A stator vane substantially as described in this specification with reference to and as illustrated by Fig. 1 of the accompanying drawings.

14. A ring member substantially as described in this specification with reference to and as illustrated by Fig. 1 of the accompanying drawings.

1 5. An elastomeric extrusion or moulding substantially as described in this specification with reference to and as illustrated by Figs. 1, 2 and 3 of the accompanying drawings.