GB2280478A - Gas turbine sealing assemblies. - Google Patents

Abstract

A gas turbine rotor assembly includes two types of sealing assemblies 63, 64 which are securable between rotor discs 38, 42 and 42, 46 to act as heat shields. One type of assembly 63 comprises an array of sealing segments 66 having serrated legs 66B, 66C which engage in blade root slots in the rotor discs 38, 42. The other type of sealing assembly 64 comprises sealing segments (68) having at one end a serrated leg 68B which engages in a blade root slot in the rotor disc 42. To avoid over-stressing the blade root slots in the rotor disc 46 at the other end of the segments, the other leg 68C is provided with a spigot 68E which engages in a recess 70 in the front face of the rotor disc 46. Alternatively (Fig. 10), the latter type of segment may have a serrated leg (268B') instead of a spigot, the serrated legs being secured in complementarily shaped slots in a ring member (271) secured to a flange (272) on the face of the turbine disc (246) by means of studs (274). Specially shaped sealing plates (78, Figs. 10 and 12) may be incorporated in the assembly to prevent leakage of turbine cooling air from one side of a turbine rotor disc (42) to the other. <IMAGE>

Description

GAS TURBINE ENGINE SEALING ASSEMBLY This invention relates a gas turbine engine sealing assembly for sealing the gas flow path in a turbine of a gas turbine engine. In particular the invention relates to sealing the gas flow path in an industrial gas turbine engine.

Industrial gas turbine engines generally comprise a gas generator consisting of a compressor, a combustor in which fuel and air are mixed and burnt, a turbine which is driven by the products of combustion and which drives the compressor, and a power turbine driven by the high temperature, high velocity gases from the gas generator. The power turbine is arranged to drive a load, such as an electricity generator, or a pump for pumping oil or gas.

Heavyweight industrial gas generators are bulky and there can be large distances between the bearings of a shaft on which the compressor and turbine are mounted.

The turbine of the gas generator will comprise one or more stages of blades, each stage comprising an array of rotor blades mounted on the gas generator rotor disc, and an array of stator blades mounted from a casing of the gas generator. The high temperature, high velocity gases flow through an annular passage in which the rotor and stator blades are disposed. The radially inner boundary of the passage is partially defined by platforms on the inner ends of the stator blades. To restrict leakage of the turbine gases around the ends of the stators between their inner platforms and the rotor, the platforms are usually sealingly engaged by sealing elements secured to the rotor.

The relatively large distances between the rotor bearings, for example up to nine metres, result in large relative axial movements between the rotor and the gas generator casing due to differential thermal expansion between the rotor and the casing. Thus, any seal components providing a seal between the rotating and static components of the gas generator turbine must be able to cope with such movements.

In the case of relatively low power engines, rotating sealing elements, against which the stator inner platforms run, can be achieved by casting axially extending projections or 'wings', otherwise known as heat shields, onto the inner platforms of the rotor blades. These projections are provided on the rotor blades of adjacent stages and extend towards each other over the intervening gap so that their confronting edges abut one another.

On higher power larger engines, these wings become so long and/or the rotor speeds become so high, that the bending stresses on them are excessive. Also, when the rotor blades are cast by directional solidification techniques, the material properties of the wings are not appropriate.

The present invention seeks to provide a form of annular sealing construction which avoids the need for wings on the rotor blade platforms to provide a seal, whilst maintaining a seal along the inner boundary of the gas flow annulus.

Accordingly, the present invention provides a gas turbine engine sealing assembly comprising a plurality of sealing segments spanning a gap between a pair of adjacent turbine rotor discs, the rotor discs having rim regions comprising a plurality of turbine blade attachment locations, the sealing segments forming in combination a circumferential sealing surface, each sealing segment having attachment means attaching it to attachment locations on both of the turbine rotor discs, the attachment means on at least one side of the gap between the rotor discs being attached to a turbine blade attachment location.

Each sealing segment preferably comprises a bridge piece and a leg located at each end of the bridge piece, the leg carrying the attachment means.

The attachment locations in the rotor disc rim regions conveniently comprise slots, the attachment means on the seal segments being shaped to engage with the slots. The slots may have re-entrant geometric profiles.

In one form of the invention, the attachment means at one side of the gap between the rotor discs comprises a lip engagable with a shoulder formed on a face of one of the rotor discs in the rim region of the disc. More specifically, the attachment means may comprise a spigot engagable with a recess of the rotor disc face.

Alternatively, the attachment means at one side of the gap between the rotor discs engage attachment locations provided on a ring member extending from the rim region of a rotor disc. This ring member may be attached to a projection on the rotor disc by stud means.

Each sealing segment may include strengthening rib means extending between the legs.

In a preferred embodiment, the blade attachment locations comprise slots equi-angularly spaced around a rim region of a rotor disc, the slots being defined between outward projections of the rim region, blades being secured in the slots by root portions of the blades, wherein sealing plate means is trapped between the root portions of the blades and attachment means of the sealing segments to obturate a gap defined between radially inner platforms of the blades and the rim region of the rotor disc, the sealing plate means being formed with female replicas of the shape of the outward projections of the disc rim region, whereby the sealing plate means fits closely over the projections, the sealing plate means further being configured to fit closely against the blade platforms.

The sealing plate means conveniently comprises an annular array of sealing plates, a sealing plate having a circumferential angular width measurement equivalent to the angular spacing of the slots. Preferably, edges of adjacent sealing plates confront each other centrally of the blade root portions.

Embodiments of the present invention will now be more particularly described with reference to the accompanying drawings in which: Fig. 1 shows diagrammatically an industrial gas turbine engine; Fig. 2 is a more detailed cut-away view of area II in Fig.l, comprising a partial section along a plane through the axis of rotation of a gas generator turbine incorporating a known type of gas flow path sealing and interstage heat shield construction, Fig. 3 shows a similar part-sectional view of part of a gas generator turbine incorporating two types of rotating annular sealing assemblies acting as inter-stage heat shields according to the present invention; Fig. 4 is a perspective view of a segment of one of the rotating sealing assemblies illustrated in Fig. 3; Fig. 5 is a perspective view of the other form of rotating sealing assembly illustrated in Fig. 3; ; Fig. 6 shows a modified form of the sealing segment shown in Fig. 4; Fig. 7 shows a modified form of the sealing segment shown in Fig. 5; Fig. 8 is a view similar to that of Fig. 3, illustrating a gas generator turbine incorporating rotating annular sealing assemblies assembled from the segments illustrated in Figs. 6 and 7; Figs. 9A, 9B and 9C show diagrammatically three stages of assembling sealing segments, of the type shown in Fig. 5, into the turbine rotor of Fig. 3; Fig. 10 is an enlarged view of part of a construction similar to Fig. 8, but illustrating a further variation of one of the sealing segment assemblies; Fig. 11 is a perspective view on section line XI-XI in Fig. 10; and Fig. 12 is a view on section line XII-XII in Fig. 10.

Referring to the drawings, in Fig. 1 there is shown an industrial gas turbine power plant 10 comprising a gas generator 12 and a power turbine 14 arranged to drive a load 16, which can be, for example, an electricity generator or a pump. The gas generator 12 comprises, in axial flow series, a compressor 18, a combustor 20, and a turbine 22, which is mounted on a common shaft (not shown) with the compressor 18. High temperature, high velocity gas produced in the gas generator 12 by the compressor 18 and the combustor 20 drives the turbine 22, which drives the compressor 18 through the common shaft. The excess power in the turbine gases after passage through the turbine 22 is used to drive the power turbine 14.

Referring to Fig. 2, there is shown a detail of part of a known turbine 22 of a gas generator.

The static structure of the turbine 22 comprises an outer casing 24 to which are attached, via a support ring 24A, stator vanes stages 26 and 28 comprising stator vanes 30 and 32. An array of nozzle guide vanes 34 is secured between a further support ring 24B, also attached to casing 24, and a radially inner static support structure 36. The stator vanes 30 and 32, and the nozzle guide vanes 34, all have inner and outer platforms 30A, 30B, 32A, 32B and 34A, 34B respectively.

The rotating structure of the turbine 22 includes a first stage rotor disc 38, having rotor blades 40 located axially between the nozzle guide vanes 34 and the stator vanes 30, a second stage rotor disc 42 having rotor blades 44 located between the stator vanes 30 and 32, and a third stage rotor disc 46 having rotor blades 48 located downstream of the stator vanes 32. The three rotor discs 38, 42 and 46 are welded together at their abutting faces as indicated by the short diagonal lines.

The rotor blades 40,44,48 all have inner platforms 40A,44A,48A, and root portions 40C,44C,48C respectively.

To fix the blades to the discs, their root portions 40C,44C,48C have re-entrant geometric profiles comprising a serrated or "fir-tree" shape which fits into complementary-shaped slots in the disc rims, these slots being oriented essentially in the axial direction as defined by the axis of rotation of the turbine.

The outer tips of the first stage rotor blades 40 cooperate with a static sealing ring 50 held in support ring 24B, but the outer ends of the rotor blades 44 and 48 have shrouds 44B and 48B with projections which sealingly cooperate with abradable surfaces 52 and 54 on circumferential lands of the support ring 24A.

The products of combustion flow through the gas flow path annulus 60 from the combustor 20 and between the nozzle guide vanes 34 in the direction of arrow A. The radially inner boundary of the gas flow path annulus 60 is defined by the inner platforms of the stator and rotor blades and also by wing seals 59B,61A,61B,62A and 62B.

Adequate sealing of the gas flow path is achieved on its inner boundary by labyrinth seals comprising circumferentially extending sealing fins 56A,56B,58A,58B and 59 on wing seals 61A,61B,62A,62B and 59B, respectively, which cooperate with the stator inner platforms 30A,32A and 34A.

Wing seals 61A,62A extend rearwardly from the roots 40C,44C of rotor blades 40 and 44 respectively, while wing seals 59B,61B,62B extend forwardly from the roots 40C,44C and 48C of rotor blades 40, 44 and 48 respectively. Wing seals 61A,61B and 62A,62B therefore extend towards each other and their confronting edges define small axial gaps 61C,62C, to allow for thermal expansion. Circumferentially spaced webs 61D/E, 62D/E provide support to the longer wing seals 61A/B,62A/B against the effect of centrifugal forces. However, such support is not needed for the shorter, less massive wing seal 59B.The wing seals and their support webs are cast integrally with the blade roots 40C, 44C and 48C, and of course have the same circumferential extent as the blade platforms of which they form axially extending continuations.

It should be noted that the wing seals also perform a valuable function as rotating heat shields to prevent penetration of hot gases and radiative heat from the turbine gas passage 60 to the rotor discs 38,42,46.

It will be appreciated that as the engine size increases to produce increased power output, the spacing between turbine rotor discs will increase, and so will the diameter of the rotor discs. Thus the wings 61,62 will tend to increase in length and be located at larger radii, while their support webs must increase in number and thickness to cope with the increased centrifugal working loads. Of course, not only do the centrifugal loads increase as the product of mass and radius, but also as the square of angular velocity. Hence, increasing engine power by increasing rotational speed instead of size will also increase centrifugal loading on the wing seals.

Eventually, having regard to the working loads experienced by the wing seals and imposed by the wing seals on the blade roots 40C,44C,48C and on the rotor discs 38,42,46, the strength of available materials and the manufacturing methods available will limit the length of the wings and their diameters to those which will maintain adequate sealing and/or impose acceptable stresses on the blade roots and discs.

A further problem arises even for small size engines, in that while blades cast by directional solidification techniques are to be preferred for use because of their superior strength and temperature resistance, such casting techniques cannot be used for blades with integral wing seals because the extent of the wing seal lies in the a different direction from the desired radial metallurgical orientation in the body of the blade.

These problems, as presented in an engine of larger size than in Fig. 2, can be addressed as illustrated in Fig. 3, in which similar components described with reference to Fig. 2 have been allotted the same references for convenience.

In Fig. 3, the rings formed by the circumferentially abutting platforms 30A,32A of the stator blades co-operate with rotating annular sealing assemblies 63,64, which also act as rotating heat shields, as did the wing seals 61A, etc., in Fig. 2. Further, each sealing assembly 63,64 has two sets of sealing fins 56,58 which co-operate with abradable linings on the radially inner sides of the platforms 30A,32A to aid in sealing the gas flow passage 60. However, in distinction from the arrangement of Fig.

2, the sealing assemblies 63,64 in Fig. 3 are located between and mounted on the rotor discs 38,42 and 42,46.

In the present embodiment, the root portions 40C,44C,48C of the rotor blades 40, 44 and 48 are mounted on the rotor discs 38, 42 and 46 respectively by means of so-called "fir trees" or serrated roots which engage in correspondingly serrated slots in the rims of the rotor discs. The sealing assemblies 63, 64 comprises the same number of sealing segments 66, 68 as there are serrated slots in the rims of the rotor discs 38 and 42, the sealing segments having the same circumferential extent as the blade platforms 40A,44A and being secured in the same disc rim slots as the blade root portions. Consequently, the axial widths of the rotor discs 38, 42 are dimensioned accordingly.

It should be understood that because of the size of the machine, and the relatively small stagger angle required by the aerofoils of the blades 40 and 44, it is convenient for the serrated slots in the rims of rotor discs 38, 42 to extend axially, with no stagger angle. The serrations in both discs can therefore be cut using an end mill cutter which passes in a straight cut through both disc rims on a common diameter D.

However, blades 48 have a larger aerofoil stagger angle, requiring the serrated slots in the rim of rotor disc 46 to follow the stagger angle of the platforms.

One of the sealing segments 66 is shown in more detail in Fig. 4. Each sealing segment 66 comprises a bridge piece 66A and two legs 66B and 66C. The bridge piece 66A is arcuate when seen in radial section and its outer surface is part of a frustum, as are the outer surfaces of all of the sealing segments 66, which in combination form a complete frustum. Each bridge piece 66A is also provided with a slot 66D which extends around the edge of the bridge piece. This is for receiving the edges of sealing strips which seal with similar slots in adjacent ones of the sealing segments 66 and adjacent blade platforms.

Both of the legs 66B and 66C are formed with serrated roots which are engagable with the slots formed in the rotor discs 38 and 42 for the root portions of the blades 40 and 44.

The sealing segment assembly 64 similarly comprises a number of sealing segments 68, one of which is shown in more detail in Fig. 5.

Each sealing segment 68 comprises legs 68B and 68C.

Leg 68B is similar to the corresponding legs 66B in the segment 66, being formed with serrations for engagement with the slots formed in rotor disc 42 for the root portions 44C of the blades 44.

The bridge piece 68A of each seal segment 68 is also of similar shape and configuration to the bridge piece 66A, and in combination with each other provide a similar frusto-conical outer surface for seal assembly 64. Again, each bridge piece 68A is provided with a slot 68D for sealing strips.

Legs 68C, however, differ from legs 66C in Fig. 4, in that they are not of "fir tree" serrated form, but comprise a lip engagable with a shoulder formed on the face of rotor disc 46 in the rim region of the disc. Specifically, the legs 68C are formed with a part-annular foot having a spigot 68E which engages in an annular groove or slot 70 in the upstream face of the rotor disc 46. This eliminates the need for the rim of rotor disc 46 to have the same number of serrated slots as rotor disc 42, and avoids any problem of machining serrations with a stagger angle in the leg 68C to match the stagger angle of the slots in rotor disc 46.

Figs. 6 and 7 show modified forms of the sealing segments illustrated respectively in Figs. 4 and 5. One major difference is that each sealing segment 166, 168 is provided with a stiffening panel 166E, 168F extending between the legs 166B, 166C and 168B, 168C, respectively, in order to strengthen each segment. The radially inner edge of each panel is formed as a rib 166F, 168G for additional strength.

With respect to Fig.6, a further difference from Fig.

4 should be noted, in that the radially outer parts 166G, 166H of the legs 166B, 166C are inclined towards each other, whereby the front and rear edges of the bridge piece 166A are "overhung" with respect to the legs, i.e., the bridge piece projects forwardly and rearwardly beyond the points where the legs join it.

The bridge piece 168A in Fig. 7 is similarly overhung with respect to the legs 168B, 168C, which also have mutually inclined radially outer parts.

Fig. 8 is a further view similar to Fig. 3, showing a turbine rotor assembly including segments 166, 168 like those shown in Figs. 6 and 7.

The sealing segment assemblies 63 and 64 (Fig. 3) are assembled onto the rotor discs 38, 42 and 46 in the following manner.

After assembly of blades 48 onto rotor disc 46, the sealing segment assembly 64 is assembled onto the rotor discs 42 and 46, followed by assembly of blades 44 onto the rotor disc 42. Sealing segment assembly 63 is then assembled onto the rotor discs 38 and 42 followed by assembly of the rotor blades 40 onto the rotor disc 38. It will be appreciated that the stators 30 and 32 are assembled to form the complete turbine subsequent to the assembly of the rotors.

With reference to Figs. 9A to 9C, each sealing segment 68 is dimensioned so that the distance between the legs 68B and 68C is greater than the width of the rotor disc 42. Each segment 68 is located over the rim of the rotor disc 42 as illustrated in Fig. 9A so that the serrated leg 68B is aligned with one of the correspondingly serrated blade root slots in the rim of the rotor disc 42. The serrated leg 68B can then slide axially through the respective blade root slot so that leg 68C abuts root portion 48C of blade 48 and the spigot 68E engages in the annular recess 70 in the front face of the rotor disc 46.

In this position the serrated leg 68B is located in the rear end of the serrated root slot in the rotor disc.

Successive segments 68 are assembled onto the rotor discs 42 and 46 in a similar manner in order to complete the assembly 64.

After assembly of blades 44 onto the rotor disc 42, sealing segment assembly 63 is attached to the rotor discs 38 and 42. It will be recalled that both ends of the segments are provided with serrated legs 66B, 66C. Because the blade root slots in rotor discs 38 and 42 extend axially, have the same angular spacing around their disc rims and are formed at the same diameter D thereon, the serrated legs 66B, 66C slide into their required positions in the rear and front ends respectively of the serrated root slots in the rotor discs 38, 42.

The segments 66, 68 are trapped securely in position in the blade root slots of the rotor discs 38, 42, 46 when rotor blades 40 are assembled into their slots in the rotor disc 38.

A similar scheme of assembly can be adopted for the segments 166, 168 shown in Figs. 6 and 7.

Fig. 10 shows a modified form of sealing segment 268 for assembly between the second stage turbine rotor disc 42 and a modified form of the third stage turbine rotor disc 246. To simplify manufacture of the segments 268, and aid assembly into the rotor if required, each sealing segment 268 is formed with two identical serrated legs 268B, 268B'. Each leg 268B fits into a serrated slot in the rim of disc 42, as for Fig.8. However, legs 268B' fit into corresponding serrated slots provided in a separate ring 271. Ring 271 is formed to mate with an annular flange 272 on the front face of the rotor disc 246 and is secured to the flange 272 by dowels or studs 274 angularly spaced around the ring.The modified form of sealing segment 268 illustrated in Fig. 10 can be assembled into the position shown in Fig. 10 in the same manner as described above for Fig. 9, or can be slid axially into position without radial inward movement, if desired.

In the type of turbine illustrated in Figs. 3, 8 and 10, cooling air is required to flow into the chambers between the turbine rotor discs through passages (not shown) to help cool the undersides of the inter-stage seal segments, the turbine discs, the blade root portions, the undersides of the blade platforms, and internal passages (not shown) in the blades themselves. Because the turbine gases are hotter and at higher pressure at the upstream (front) end of the turbine, the cooling air supplied to the space between the first and second stage turbine rotor discs 38 and 42 respectively must be at a higher pressure than the cooling air supplied to the space between the second and third stage turbine rotor discs 42 and 46 or 246.

Unfortunately, as indicated in Figs. 10 and 11, there is are gaps 76 between the rim 42R of the disc 42 and the undersides of the blade platforms 44A and sealing segments 166. Unless prevented, high pressure cooling air H can escape through the gaps 76 into the chamber between turbine rotor discs 42 and 246. Each gap 76 is defined by the adjacent bridging pieces and the serrated legs of the sealing segments 166 and the parts of the disc rim 42R lying between circumferentially adjacent serrated slots 42S.

To close these gaps an annular array of sealing plates 78 is provided as shown in Figs. 10 and 12. Each plate 78 is formed with the female replica of the shape of the projecting portion 42P of the disc rim 42R between each adjacent pair of serrated blade root slots 42S, and is equivalent in circumferential angular width measurement W to the pitch of the serrated blade root slots 42S around the turbine rotor disc. The total radial height H of each plate 78 is equal to the distance from the bottom of the serrated slots 42S to the underside of the blade platforms 44A.

This arrangement results in the edges 78E of the plates 78 meeting along the centre lines of the blade root portions 44C. Consequently, leakage of cooling air through the small gaps between the edges 78E will be minimised.

To build the sealing plates 78 into the rotor assembly requires that the rotor blades 44 are first fitted onto the disc 42, the sealing panels 78 are slid over the disc projections 42P into contact with the blade root portions 44C, and the inter-stage seal segments or heat shields 166 are then slid into position, so trapping the sealing plates 78 as indicated in Fig. 10.

The resulting structure is approximately equivalent to an airtight ring being placed between the sealing segment assembly and the blade root portions. Fretting of the three components against each other should not be a significant problem because the thin sealing plates 78 are close fitting to the disc rim projections 42P and are clamped between the blade root portions 44C and the serrated legs 166B of the sealing segments 156.

Claims (14)

1. A gas turbine engine sealing assembly comprising a plurality of sealing segments spanning a gap between a pair of adjacent turbine rotor discs, the rotor discs having rim regions comprising a plurality of turbine blade attachment locations, the sealing segments forming in combination a circumferential sealing surface, each sealing segment having attachment means attaching it to attachment locations on both of the turbine rotor discs, the attachment means on at least one side of the gap between the rotor discs being attached to a turbine blade attachment location.

2. An assembly as claimed in claim 1, in which each sealing segment comprises a bridge piece and a leg located at each end of the bridge piece, the leg carrying the attachment means.

3. An assembly as claimed in claim 1 or claim 2, in which the attachment locations in the rotor disc rim regions comprise slots and the attachment means on the seal segments are shaped to engage with the slots.

4. An assembly as claimed in Claim 3 in which the slots have re-entrant geometric profiles.

5. An assembly as claimed in Claim 1 in which the attachment means at one side of the gap between the rotor discs comprises a lip engagable with a shoulder formed on a face of one of the rotor discs in the rim region of the disc.

6. An assembly as claimed in Claim 1 in which the attachment means comprises a spigot engagable with a recess of the rotor disc face.

7. An assembly as claimed in Claim 1 in which the attachment means at one side of the gap between the rotor discs engage attachment locations provided on a ring member extending from the rim region of a rotor disc.

8. An assembly as claimed in Claim 7 in which the ring member is attached to a projection on the rotor disc by stud means.

9. An assembly as claimed in claim 2 in which each sealing segment includes strengthening rib means extending between the legs.

10. An assembly as claimed in any one of the preceding claims in which the blade attachment locations comprise slots equi-angularly spaced around a rim region of a rotor disc, the slots being defined between outward projections of the rim region, blades being secured in the slots by root portions of the blades, wherein sealing plate means is trapped between the root portions of the blades and attachment means of the sealing segments to obturate a gap defined between radially inner platforms of the blades and the rim region of the rotor disc, the sealing plate means being formed with female replicas of the shape of the outward projections of the disc rim region, whereby the sealing plate means fits closely over the projections, the sealing plate means further being configured to fit closely against the blade platforms.

11. An assembly as claimed in claim 10, in which the sealing plate means comprises an annular array of sealing plates, a sealing plate having a circumferential angular width measurement equivalent to the angular spacing of the slots.

12. An assembly as claimed in claim 11, in which edges of adjacent sealing plates confront each other centrally of the blade root portions.

13. A gas turbine engine sealing assembly substantially as described herein with reference to, or as illustrated by, Figs. 3 to 5, or Figs. 6 to 8, or Figs. 10 to 12, of the accompanying drawings.

14. A gas turbine engine including a sealing assembly substantially as described in any of the preceding claims.