GB2296295A

GB2296295A - Sealing arrangement for a gas turbine engine

Info

Publication number: GB2296295A
Application number: GB9426176A
Authority: GB
Inventors: John S L Gabbitas
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1994-12-23
Filing date: 1994-12-23
Publication date: 1996-06-26
Also published as: GB9426176D0

Abstract

A sealing arrangement for use between adjacent nozzle guide vane segments comprises a primary sealing member 40 positioned in a slot (26) (Figure 1) formed in an end face 22, 24 of at least one of the segments, and a secondary sealing member 56 positioned in a pocket which intersects an interior end wall of the slot. The secondary sealing member 56 is arranged within the pocket such that it cooperates with the primary sealing member 40 to obturate a leakage path between the primary sealing member and the endwall of the slot. Three secondary sealing members may be positioned along each slot, and the secondary sealing members may be resiliently mounted (to allow deflection by movement of the primary sealing member) and comprise a bundle of wires. <IMAGE>

Description

SEALING ARRANGEMENT FOR A GAS TURBINE ENGINE This invention relates to a sealing arrangement for use between spaced apart components. In particular the invention concerns a sealing arrangement for use between spaced components in a gas turbine engine.

It is often necessary to provide a gas tight seal between adjacent components in a gas turbine engine. In today's engines for example, the engines gas path components are usually exposed to a high pressure flow of cooling air on one side, and to the engine gas stream flow on the other.

Because a number of the gas stream components are segmented it is usually necessary to provide a seal between the components to prevent ingress of the higher pressure cooling air into the gas stream.

In a known sealing arrangement an elongate strip is positioned between the end faces of adjacent components.

The sealing strip is located along its side edges in slots formed in the end faces of the components. In use, the sealing strip is urged against the sidewalls of the slots by the radial pressure differential acting upon it.

Unfortunately significant leakages are often encountered with this type of seal. The slots formed in the adjacent end faces are always, to some extent, offset and skewed relative to one another as a result of manufacturing tolerances. In extreme cases this can cause the sealing strip to lift off the sidewalls at most points along its length, causing significant loss of cooling air to the gas stream. This is undesireable since more cooling air than is otherwise necessary is required to be bled from the engine's compressor to cool the gas path components.

It is an object of the present invention to provide a sealing arrangement for use between components which addresses the problem of the prior art.

According to the invention in its broadest sense there is provided a sealing arrangement for use between spaced apart components, comprising at least one primary sealing member positioned in, and extending from, a slot formed in an end face of a first of the components, and at least one secondary sealing member positioned in a pocket, which pocket intersects the slot, the primary sealing member having a pair of opposing side edges, a first of which extends externally of the slot for engagement with a second component spaced from the first, and a second of which extends internally of the slot for engagement with the secondary sealing member to obturate a leakage path between the primary sealing member and an interior endwall of the slot.

Preferably the secondary sealing member is disposed substantially orthogonal to the primary sealing member, and is resiliently mounted in relation to the pocket.

Preferably the pocket is dimensioned to permit deflection of the secondary sealing member and the secondary sealing member is adapted to be deflected within the pocket by movement of the primary sealing member in the slot.

Preferably the secondary sealing member comprises a proximal end and distal end, and the secondary sealing member is arranged within the pocket such that its distal end is disposed in the region of the pocket which intersects the slot. A gap may also be provided between the distal end of the secondary sealing member and an adjacent endwall of the pocket.

The secondary sealing member may be an elongate strip or alternatively comprise a plurality of elongate filaments secured at their proximal end to a housing which opens into the pocket.

Preferably a secondary sealing member is positioned midway along the slot. A secondary sealing member may also be positioned at each end of the slot.

Preferably the pocket is disposed substantially orthogonal to the slot and intersects the interior endwall of the slot.

Preferably the primary selaing member comprises an elongate strip.

Preferably the first and second components are adjacent circumferentially spaced segments in a gas turbine engine, and may be nozzle guide vane platforms.

Alternatively the second component may comprise an abutment face axially spaced from the side face of the first component, and engaged by the first side edge of the primary sealing member.

The invention will now be described in greater detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of two adjacent nozzle guide vane segments constructed in accordance with the present invention, Figure 2 is a sectional view of the nozzle guide vane segments taken along line 1-1 of Figure 1 showing a first preferred embodiment of the sealing arrangement of the invention, Figure 2a is a sectional view of the nozzle guide vane segments taken along line 1-1 of Figure 1 showing an alternative construction of the first preferred embodiment of the sealing arrangement, Figure 3 is a sectional view of the sealing arrangement of Figure 2 taken along line 2-2, Figure 4 is a schematic side view of the sealing arrangement of Figure 2 along line 3-3, Figure 5 shows the same sectional view as Figure 2 but with the sealing arrangement in a deflected configuration, Figure 6 shows the same sectional view as Figure 3 but with the sealing arrangement in the deflected configuration of Figure 5, Figure 7 is a perspective view of the sealing arrangement of the present invention, Figure 8 is a schematic side view similar to that of Figure 4, but of an intersegment sealing arrangement of the prior art, Figure 9 is a schematic side view of an intersegment sealing arrangement employing the present invention, Figure 10 is an end view of a nozzle guide vane pair of the type shown in Figure 1, but constructed in accordance with a second preferred embodiment of the invention, and Figure 11 is a sectional view of a first of the nozzle guide vanes of Figure 10 taken along line 4-4 showing the second preferred embodiment of the invention.

Referring to Figure 1, there is shown a pair of circumferentially spaced nozzle guide vane segments 10 and 12. A plurality of such vane segments are arranged in sequence in a gas turbine engine (not shown) for directing engine gases onto a corresponding array of turbine rotor blades. In Figure 1 the two vane segments 10 and 12 are shown in isolation, the remainder having being omitted for clarity.

The nozzle guide vane segments 10 and 12 are of identical construction. Each of the vanes includes a pair of radially extending aerofoils 14, an inner platform section 16 and an outer platform section 18. The inner platforms 16 and outer platforms 18 are of generally arcuate shape and extend circumferentially to form part of a segmented annular flow boundary. The vane segments are each provided with a plurality of circumferentially extending rails 20a, 20b, 20c and 20d for attachment to surrounding engine structure (not shown). The inner and outer platform sections 16 and 18 are each provided with a pair of opposed end faces 22 and 24 which abut, or are arranged to abut, an end face 22 or 24 of an adjacent platform section. The end faces 22 and 24 are disposed perpendicular to the circumferential direction of the platform segments, and are each formed with an axially extending elongate slot 26 which forms part of an interplatform sealing arrangement.

For the purposes of the present discussion the platform sealing arrangement will be described in relation to the outer platform sections 18 of the neighbouring vanes 10 and 12, it being understood that the sealing arrangement at the inner platform location is of identical construction.

With reference to Figure 2, an interplatform sealing arrangement according to a first embodiment of the invention is shown generally at 27. Figure 2 illustrates the sealing arrangement in the cold build condition. In this condition an oversize gap or clearance 28 exists between the two components.

As shown each slot 26 is formed substantially midway between a radially inner platform surface 30 and a radially outer platform surface 32. The slots 26 are of identical U-shaped configuration, each having a pair of opposing internal sidewalls 34 and 36 and an interior endwall 38 between the sidewalls 34 and 36. The endwalls 38 lie substantially parallel to the platform end faces 22 and 24. The platform extremities of the adjacent segments are aligned such that the slots 26 formed in the opposing end faces co-operate to form an elongate cavity at the platform interface.

A primary sealing member 40 having a pair of opposed side surfaces 42 and 44 and opposed side edges 46 and 48 extends within the cavity to provide a primary seal between the platform extremities. The sealing member 40 is arranged such that its side edge 46 lies within the one of the slots 26 and its side edge 48 within the other. The primary sealing member is dimensioned such that the distance between its side edges 46 and 48 is slightly less than the combined depth of the slots, that dimension being the distance between the interior endwall 38 and end face 22,24 of one of the slots. In this respect a gap 50 is maintained between each of the side edges 46 and 48 and the endwalls 38 irrespective of platform clearance 28. The sealing member 40 is similarly undersized with respect to the distance between the slot sidewalls 34 and 36.In this respect the sealing member is dimensioned so that a gap 52 is defined between its radially outer surface 44 and the radially outer sidewall 36 of each slot 26.

In accordance with the invention each platform extremity is of identical construction and comprises a secondary sealing arrangement 53 at a point midway, or substantially midway along its length. For the purposes of the present discussion the secondary sealing arrangement will be described with reference to one side of the sealing interface.

With reference to Figure 2 the sealing arrangement 53 comprises a radially extending pocket 54 formed in the radially outward facing surface of the platform, and a radially extending secondary sealing member 56 positioned within the pocket 54. The pocket 54 extends towards the radially inner surface of the platform in a direction substantially perpendicular to the direction of the slot 26. The pocket 54 intersects the side and end walls 34,36 and 38 of the slot in the region of the gap 50 adjacent the endwall 38, and extends past the slot to define a region 58 between the slot and the internal end face 60 of the pocket 54.

At its end opposite the pocket end face 60 the pocket 54 opens into a region 64 enclosed by a hollow cylindrical housing 66. The housing 66 extends generally in the same direction as the pocket 54 and is joined by welding or otherwise to the radially outer surface 32 of the platform 18. At its end furthest from the platform the housing 66 includes an end cap 68 which carries the secondary sealing member 56. At its opposite end the housing is positioned in a spigot recess 70 formed in the platform 18 around the pocket periphery.

In the embodiment shown the secondary sealing member 56 comprises an elongate resilient strip secured at its proximal end 72 to the end cap 68 of the housing 66. The secondary sealing member 56 extends longitudinally within the pocket 54 towards the pocket extremity 60 in a direction substantially perpendicular to that of the slot 26 and primary sealing member 40. The secondary sealing member is disposed such that it extends in the region of the pocket 54 which intersects the slot 26. In this region the secondary sealing member 56 bridges the gap 50 between the primary sealing member 40 and the slot, and engages the primary sealing member along its side edge 46 to form an air tight seal. The sealing member 56 terminates at a point between the slot and the pocket extremity 60 to create a clearance between the pocket and its distal end 74.

An alternative arrangement to that of Figure 2 is shown in Figure 2a wherein the elongate secondary sealing strips 56 are replaced by a plurality of elongate elements 56a. In the arrangement shown the elements 56a are wires arranged collectively in a bundle. Having a greater aspect ratio the wires 56a tend to be more flexible than the one piece secondary sealing member construction of Figure 2. The advantages of this will become apparent from the description to follow.

With reference now to Figure 3 it will be seen that the pocket 54 intersects a relatively small portion of the slot endwall 38. As shown the secondary sealing member 56 has a dimension in the longitudinal direction of the primary sealing member 40 substantially equal to that of the pocket 56, and a dimension in the lateral direction of the primary sealing member substantially less than the pocket 56. It will be seen also from Figure 3 that the secondary sealing member 56 divides the pocket creating a forward region 80 and a rearward region 82.

With reference now to Figure 4 each slot 26 includes an endwall 84 at one end of the platform and an opposing endwall 86 at the other. The endwalls 84 and 86 provide for axial retention of the primary sealing member 40.

Clearance gaps 88 and 90 are defined between the endwalls 84 and 86 and the respective forward and rearwards edges 92 and 94 of the primary sealing member. The gaps 88 and 90 are provided for thermal expansion of the sealing member during engine operation and also to aid assembly during manufacture.

In accordance with the preferred embodiment, three secondary sealing arrangements 53 are positioned along the slot. A first of the secondary sealing arrangements is positioned at the mid point position described, a second in the region of the forward endwall 84, and a third in the region of the rearward endwall 86. The additional sealing arrangements at the endwall positions are positioned such that they cooperate with the primary sealing member 40 irrespective of its position within the slot.

In use circumferential thermal expansion of the platform sections occurs and the platform end faces 22 and 24 move from the position shown in Figure 2 to that of Figure 5.

The clearance between the end faces 22,24 reduces in accordance with the expansion. The expansion is accommodated by movement of the primary sealing member 40 within the slots 26. This movement causes the secondary sealing members 56 to deflect. As shown in Figures 5 and 6 the secondary sealing members are deflected at their distal ends by the primary sealing member. The primary sealing member is maintained in a substantially central position with respect to the gap 28 by the opposing sealing members 56.

During operation the platform sections 18 are subject to a radial pressure differential which causes the primary sealing member 40 to be urged into sealing engagement with the sidewalls 34 of the respective end face slot 26.

The pressure differential arises as a result of the sealing member 40 being exposed to the direct effects of the gas stream on its side 44, and to high pressure cooling air on its side 42. The cooling air is directed to the radially outer surfaces 32 of the platforms 18 at a pressure greater than that of the gas stream. The sealing member 40 prevents leakage of the higher pressure cooling air by obturating a leakage path between the platform sections.

As indicated the effectiveness of the primary sealing member 40 depends on engagement with the slot sidewalls 34. In practice this is rarely achieved along the full length of the seal. When assembled the platform end faces 22 and 24 of adjacent segments are usually offset and or skewed with respect to one another. This creates a number of leakage paths past the primary sealing member 40. The problem is best illustrated with reference to Figure 7 wherein the nozzle guide vane platforms 18 are positioned in a relatively skewed and offset manner. As shown the primary sealing member 40 is disposed diagonally within the slot 26. In use high pressure cooling air flows into the slot on one side of the sealing member 40 and out into the engine gas stream on the other.Because the inlet and exit sections are less restricted at the axial extremities of the slot the majority of leakage flow passes behind the sealing member 40 along the gap 50. With reference to Figure 8 it will be seen that without the secondary sealing arrangements 53 of the present invention the leakage flow is able to pass from one axial extremity of the slot to the other.

Without the secondary sealing arrangements 53 the effective inlet flow area of the gap 50 is governed by the triangular area 99 between the primary sealing member 40 and sidewall 36, and likewise the exit flow area by the triangular area 101 between the primary sealing member and the opposing sidewall 34.

This compares with the situation in Figure 9 where secondary sealing arrangements 53 are positioned along the length of the slot as described. In this arrangement the mid point sealing arrangement effectively obturates the axial leakage path due to clearance 50. This divides the leakage region into two distinct parts. On a first side of the central sealing arrangement 53 leakage is governed by the effective area of the triangular inlet section 102, whereas on the other side leakage is governed by the effective area of the triangular outlet section 104. Because the combined area of the triangular sections 102 and 104 is half that of the arrangement shown in Figure 8, leakage flow past the primary selaing member is halved.

From the foregoing it will be appreciated that leakage is also prevented at the axial extremities of the slot 84 and 86 by the additional secondary sealing arrangements.

In accordance with a second embodiment of the invention a sealing arrangement of the type described is provided along each of the guide vane rails 20b. With reference to Figure 10 the rear face 106 of each rail 20b includes a circumferential arcuate slot 26a. The slots 26a of neighbouring rails align and form an annular recess around the gas flow periphery. The slots 26a form part of an axial sealing arrangement between the rails and axially spaced engine structure. For this purpose the slots are provided with a plurality of circumferentially spaced secondary sealing arrangements 53 positioned along their length.

As shown in Figure 11 the rails 20b are spaced from neighbouring structure 110, which may be an annular engine casing flange, by a predetermined clearance 112.

A primary sealing member 40a, which may be a ring or a plurality of circumferential segments, is positioned in the slot 26a to bridge the axial gap created by the clearance. Along one edge the primary selaing member cooperates with the secondary sealing members 56 in the manner described, and along its opposing edge with the adjacent structure 110. The primary sealing member is urged into contact with the structure 110 by the resilience of the primary sealing members 56. The arrangement is such that the seal permits expansion of the components, whilst at the same time prevents secondary type leakages of the type described in the region of the primary sealing member clearance 50a.

While the invention has been described with reference to gas turbine engine nozzle guide vanes it will be appreciated that the invention could be used in other areas. In particular it is envisaged that the invention could be used between other segmented turbine components.

However, the invention is not restricted to the field of gas turbine engines, and in general could be applied to any situation where a high efficiency seal is required between two or more components.

Claims

1A sealing arrangement for use between spaced apart components, comprising at least one primary sealing member positioned in, and extending from, a slot formed in an end face of a first of the components, and at least one secondary sealing member positioned in a pocket, which pocket intersects the slot, the primary sealing member having a pair of opposing side edges, a first of which extends externally of the slot for engagement with a second component spaced from the first, and a second of which extends internally of the slot for engagement with the secondary sealing member to obturate a leakage path between the primary sealing member and an interior endwall of the slot.

2 A sealing arrangement as claimed in claim 1 wherein the secondary sealing member is disposed substantially orthogonal to the primary sealing member.

3 A sealing arrangement as claimed in claims 1 or 2 wherein the secondary sealing member is resiliently mounted in relation to the pocket.

4 A sealing arrangement as claimed in claim 3 wherein the pocket is dimensioned to permit deflection of the secondary sealing member.

5 A sealing arrangement as claimed in claim 4 wherein the secondary sealing member is adapted to be deflected within the pocket by movement of the primary sealing member in the slot.

6 A sealing arrangement as claimed in claims 1 to 5 wherein the secondary sealing member comprises a proximal end and a distal end, and the secondary sealing member is arranged within the pocket such that it's distal end is disposed in the region of the pocket which intersects the slot.

7 A sealing arrangement as claimed in claim 6 wherein a gap is provided between the distal end of the secondary sealing member and an adjacent endwall of the pocket.

8 A sealing arrangement as claimed in any preceding claim wherein the secondary sealing member is an elongate strip.

9 A sealing arrangement as claimed in claims 1 to 7 wherein the secondary sealing member comprises a plurality of elongate filaments.

10 A sealing arrangement as claimed in claim 9 wherein the filaments are secured at their proximal end to a housing which opens into the pocket.

11 A sealing arrangement as claimed in claim 1 wherein a secondary sealing member is positioned midway along the slot.

12 A sealing arrangement as claimed in claim 1 wherein a secondary sealing member is positioned at each end of the slot.

13 A sealing arrangement as claimed in claim 1 wherein the pocket is disposed substantially orthogonal to the slot.

14 A sealing arrangement as claimed in claims 1 and 13 wherein the pocket intersects the interior endwall of the slot.

15 A sealing arrangement as claimed in any preceding claim wherein the primary sealing member comprises an elongate strip.

16 A sealing arrangement as claimed in claim 15 wherein the first and second components are of identical configuration in the region of the seal, and the primary sealing member cooperates with each in an identical manner.

17 A sealing arrangement as claimed in claim 16 wherein the first and second components are adjacent circumferentially spaced segments in a gas turbine engine.

18 A sealing arrangement as claimed in claim 17 wherein the circumferentially spaced segments are nozzle guide vane platforms.

19 A sealing arrangement as claimed in claims 1 to 14 wherein the primary sealing member comprises an arcuate strip.

20 A sealing arrangement as claimed in claims 1 to 14 wherein the primary sealing member comprises a ring seal.

21 A sealing arrangement as claimed in claim 19 or 20 wherein the second component comprises an abutment face axially spaced from the side face of the first component, and engaged by the first side edge of the primary sealing member.

22 A sealing arrangement as claimed in claim 21 wherein the first and second components are axially spaced gas turbine engine components.

23 A sealing arrangement as claimed in claim 22 wherein the first component is a nozzle guide vane and the second component and annular casing flange.

24 A sealing arrangement substantially as hereinbefore described with reference to the accompanying drawings.