GB2272947A - Gas turbine engine interstage seal - Google Patents

Abstract

A gas turbine engine sealing apparatus particularly for an industrial gas turbine engine comprises sealing segments 72, 74 located between adjacent rotor discs 38, 42 and 42, 46 of a turbine rotor. The sealing segments 72, 74 have feet 78 which are positioned between inner and outer lands 88, 90 and 94, 96. The outer lands 90, 96 are provided with loading slots 98 and the inner lands 88, 94 with a cut away portion A - B to allow the arcuate segments 72, 74 to be loaded into position. Use of this apparatus avoids the manufacturing and stress problems inherent in the use of seal wings cast into rotor blades. <IMAGE>

Description

GAS TURBINE ENGINE SEALING APPARATUS 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, 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 smaller engines, rotating sealing elements, against which the stator inner platforms run, can be achieved by casting axially extending projections or 'wings' 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 seal with 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 sealing apparatus comprising a plurality of sealing segments forming in combination a rotatable circumferential sealing surface arranged to cooperate with a static sealing surface, the sealing segments being located between at least one of an adjacent pair of turbine rotors, each segment having an axially extending projection on opposed sides engageable with corresponding projections on the respective turbine rotors, the turbine rotor projections having loading means enabling the segments to be secured between the turbine rotors.

The axially extending projections on the turbine rotors can comprise inner and outer circumferential lands formed on opposed faces of the turbine rotors.

The loading means can comprise a pair of diametrically opposed arcuate slots formed on each outer land and a cut away length on each inner land, the arcuate slots and cut away lengths being adjacent to one another.

The sealing segments can include segments of first and second arcuate lengths, there being a greater number of segments of the first arcuate length than the second arcuate length, the first arcuate length being greater than the second arcuate length.

Each sealing segment can comprise in section a bridge piece having legs, the legs terminating in feet, the feet being engageable with the loading means.

The bridge piece can be formed with sealing fins.

The legs can also be provided with openings in order to reduce weight.

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, showing part of a gas generator turbine incorporating a known type of gas flow path sealing construction, Fig. 3 shows a gas generator turbine incorporating one form of sealing apparatus, including a rotating annular sealing assembly, according to the present invention, Fig. 4 illustrates one sealing segment of the sealing assembly illustrated in Fig. 3, Fig. 5 shows a spacer sealing segment of the sealing assembly illustrated in Fig. 3, Fig. 6 is an end elevation of the sealing assembly illustrated in Fig. 3 and illustrates a loading means for the sealing segments illustrated in Figs. 3 to 5, Figs. 7A to 7H inclusive illustrate eight stages of assembling the sealing apparatus illustrated in Fig. 3, and Fig. 8 shows a modified form of sealing segment in a view similar to that of Fig.4.

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 mounted on a common shaft with the compressor.

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 rotor blades 40,44,48 all have inner platforms 40A,44A,48A, respectively. 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 abradeable 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 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 will be appreciated that as the engine size increases to produce increased power output, the spacing between turbine rotors will increase, and so will the diameter of the rotors. 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 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.

In Fig. 3, the three rotors 38, 42 and 46 are welded together at their abutting faces. Rotor blades 40, 44 and 48 are mounted on the rotors 38, 42 and 46 respectively by for example, the blades being formed with fir tree roots which engage in corresponding serrated slots in the rims of the rotors.

The ring formed by the circumferentially abutting platforms 30A of the stator blades co-operates with a rotating annular sealing assembly 64 located between and mounted on the rotors 38 and 42. The sealing assembly 64 has two sets of fins 66 which cooperate with the platforms 30A to aid in sealing the gas flow passage 60.

A similar ring formed by the circumferentially abutting platforms 32A at the inner ends of the stator blades 32 co-operates with a further rotating annular sealing assembly 68 located between and mounted upon the rotors 42 and 46. The sealing assembly 68 has two sets of fins 70 which cooperate with the platform 32A to further aid in sealing the gas flow passage 60. The two sealing assemblies 64 and 68 are very similar in construction as are the methods of mounting these sealing assemblies between the rotors 38 and 42, and between the rotors 42 and 46. The sealing assembly and construction of the rotors 42 and 46 will be described in detail though the description will apply also to the assembly 64 and the construction of the rotors 38 and 42.

The annular sealing assembly 68 comprises a plurality of arcuate sealing segments 72 (Fig. 4) and 74 (Fig. 5).

Each segment 72 extends around a substantial portion of the circumference of the annulus, but segments 74 are much shorter in circumferential length, being spacer segments.

In the present case there are six long segments 72 and two spacer segments 74.

The arcuate sealing segments 72 and 74 shown in Figs.

4 and 5 respectively comprise a pair of legs 76,84 which terminate in feet 78,85, the legs being connected by a bridge part 80,81. The outer surface of each bridge part is formed with the two sets of sealing fins 70. Each leg 76,84 is also formed with an arcuate projection 82,83 which in combination with the arcuate feet 78,85 defines a part annular recess 84,87.

The spacer sealing segments 74 are identical in section to the segments 72 and differ from the segments 72 only in arcuate length.

The alternative sealing segments 72 shown in Fig. 8 differ from those shown in Fig. 4 in that there are fewer sealing fins 70' and holes 100 are cast into the legs 76 to reduce the weight of the segments.

Referring again to Fig. 3, the downstream face of the rotor 42 is formed with an annular groove 86 between an inner circular land 88 and an outer circular land 90. The upstream face of the rotor 46 is formed in a similar way with an annular slot 92 formed between an inner circular land 94 and an outer circular land 96.

Referring also to Fig. 6, there is shown an assembly of segments 72 and 74 located between the two rotor discs 42 and 46. Each outer land 90 and 96 is formed with an arcuate loading slot 98 having a radius R1 offset from the centre of the rotor discs. The radially inner lands 88 and 94 are cut away over an arc length A-B to enable the segments 72 to be loaded into position between the rotor discs 42 and 46. The loading slots 98 and the cut away lengths A-B on the inner lands on each rotor discs are located diametrically opposite one another for balancing purposes.

The loading of the segments 72 and 74 between the rotors 42 and 46 will now be described with particular reference to Figs. 7A to 7H, which for the sake of clarity only show the outer land 90 on the rotor disc 42, and only one loading slot 98.

A first long segment 72 is initially located between the discs 42 and 46 by inserting the feet 78 on the legs 76 of the segment into the loading slots 98 in the outer lands 90 and 96. The cut away length A-B (Fig.6) on the inner lands 88 and 94 allows the feet at the leading end 102 of the first segment 72 to pass inwardly of the radius of the inner lands 88,94 so that the feet at the trailing end 104 can be located in the grooves 86,92 just inwardly of the outer lands 90,96. The leading end 102 can then be pushed radially outwardly so that over their whole circumferential extent, the feet of the segment are located in the grooves 86,92 between the inner and outer lands 88, 90 and 94, 96, on the rotor discs 42 and 46.

The first segment 72 can then be pushed to the position shown in Fig. 7B and a second segment 72 can be similarly loaded between the inner and outer lands of the rotor discs. The first and second segments 72 are moved to the position shown in Fig. 7C and a third segment 72 is loaded into position.

The first three segments 72 are moved to the positions shown in Fig. 7D and a first spacer segment 74 is loaded into position in a similar manner to the loading of the segments 72. The first spacer segment 74 is moved to the position shown in Fig. 7E and three further segments 72 are loaded into position as shown in Figs. 7E, 7F and 7G. A second spacer segment 74 is loaded as shown in Fig.

7H and all of the segments 72 and the two spacer segments 74 are moved between the lands 88, 90 and 94, 96 to the final position shown in Fig. 6. In the final position a segment 72 spans each of the loading slots 98 and the spacer segments are positioned diametrically opposite one another for balancing purposes between the loading slots 98.

It will be appreciated that the arcuate length of the spacer segments 74, the form of the loading slots 98 and the cut away length A-B are chosen so that the spacer segment 74 can be accurately located between two adjacent segments 72.

Claims (9)

CLAIMS:

1. A gas turbine engine sealing apparatus comprising a plurality of sealing segments forming in combination a rotatable annular seal having a circumferential sealing surface arranged to cooperate with a static sealing surface, the sealing segments extending between at least one adjacent pair of turbine rotors, each segment having radial location features on axially opposed sides thereof for radially locating the segment, the radial location features being engageable with corresponding features on the respective turbine rotors, the turbine rotor features having segment loading means for enabling the annular seal to be assembled between the turbine rotors.

2. An apparatus as claimed in Claim 1 in which the radial location features on the turbine rotors comprise inner and outer circumferential lands formed on opposed faces of the turbine rotors.

3. An apparatus as claimed in Claim 2 in which the loading means comprises a pair of diametrically opposed arcuate slots in each outer land, and a cut away length in each inner land, the arcuate slots and cut away lengths being adjacent to one another.

4. An apparatus as claimed in any one of the preceding claims in which the sealing segments include segments of first and second arcuate lengths, there being a greater number of segments of the first arcuate length than segments of the second arcuate length, the first arcuate length being greater than the second arcuate length.

5. An apparatus as claimed in any one of the preceding claims in which each sealing segment comprises in radial section a bridge piece having legs, the legs terminating in feet, the feet being engageable with the loading means.

6. An apparatus as claimed in Claim 5 in which the bridge piece is formed with sealing fins which are on the circumferential sealing surface and are arranged to cooperate with the static sealing surface.

7. An apparatus as claimed in Claim 5 or Claim 6 in which the legs are formed with openings therein for reduced weight.

8. A gas turbine engine sealing apparatus substantially as herein described and with reference to Figs. 3 to 8 inclusive of the accompanying drawings.

9. A gas turbine engine including a sealing apparatus as claimed in any one of the preceding claims.