GB2523139A

GB2523139A - A leaf seal

Info

Publication number: GB2523139A
Application number: GB1402575.3A
Authority: GB
Inventors: Gervas Franceschini; Adele Nasti
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2014-02-14
Filing date: 2014-02-14
Publication date: 2015-08-19
Also published as: GB201402575D0

Abstract

A leaf seal 131 between first 134 and second 51 coaxial components which rotate about a common axis 52, the seal having an annular pack 50 of stacked leaves 132 between a pair of axially spaced cover plates. The cover plates are characterised by a rubbing material 139 which makes contact with the second component during rotation. Preferably the rubbing material is an abradable, wearable or deformable layer. The cover plates 135a, 135b and the leaves 132 are mountable to the first component, extending radially towards the second component. In use, a pressure drop is maintained axially across the leaf stack 50. The free edge of either one or both of the cover plates may be defined by the rubbing material. The cover plates may either be flexible to deflect is use when in contact with the second component, or they may be rigid. In one embodiment one cover plate is flexible and the other cover plate is rigid to resist deflection in use. Preferably the cover plate presents a sharp, pointed or rounded rubbing edge to the second component. In the embodiment the seal is used in a gas turbine and the second component is a rotor.

Description

A LEAF SEAL

The present invention relates to a leaf seal, and more particularly relates to a leaf seal for effecting a seal between first and second coaxial components arranged for relative rotation about a common axis.

Leaf seals may be used to form a seal between two relatively rotating components in order to maintain a relatively high pressure on one side of the seal and a relatively low pressure on the other. A leaf seal is arranged with a large number of typically rectangular leaves which are held ata defined angle (the lay angle") to the radial all the way round the seal circumference. The leaves give the seal a low stiffness, and the leaves are packed together such that the total leakage through the seal is reduced. Nonetheless, interleaf gaps do provide the seal with a porous aerodynamic working section. Such seals may be used, for example, in gas turbine engines.

Figure 1 shows schematically a cut-away perspective view of a portion of a conventional leaf seal 31 comprising a pack of leaves 32. Figure 2 shows (a) a view along the axial direction of an arc segment of the pack to better show some of the leaves 32 edge-on, and (b) a plan view of a single leaf 32.

The leaves 32 each have a root portion 40 and a working portion 41, and have a width win the axial direction and a thickness t. The leaves alternate with spacer elements 33 at their root portions 40, and are secured thereat to a backing ring 34 of a housing, which typically also comprises front 35a (high pressure side) and rear (low pressure side) 35b rigid cover plates. The working portions 41 of the leaves 32 present end edges 36 towards a surface 37 of a rotating component (shaft) generally rotating in the direction depicted by arrowhead 38.

The leaves 32, and in particular the end edges 36 of the leaves 32, act against the surface 37 in order to create a seal across the assembly 31. Each leaf 32 is sufficiently compliant in order to adjust with rotation of the surface 37, so that a good sealing effect is created. The spacers 33 ensure that flexibility is available to appropriately present the leaves 32 towards the surface 37 which, as illustrated, is generally with an inclined angle between them. The spacers 33 also help to form interleaf gaps 39 between adjacent working portions 41 of the leaves 32. A leakage flow through these gaps 39 is induced by the pressure differential across the seal.

As illustrated most clearly in figure 1, in a conventional leaf seal 31, the cover plates 35a, 35b are radially spaced from the rotor. This spacing between the cover plates and the rotor is considered essential in conventional leaf seals in order to avoid the cover plates making contact with, and rubbing against the rotor. Furthermore, because individual gas turbine engines often vary in terms of their cold and running tolerances, leaf seals for use in such engines are generally designed to have significant clearance between the radially innermost edges of their cover plates and the rotor (for example a shaft) of the engine, in order to ensure that contact between the cover plates and the rotor will not occur in any engine installation in which the seals might be used. This can result in an unnecessarily large clearance space between the cover plates and the rotor.

A large gap between the radially innermost edge of the cover plates and the rotor reduces the overall sealing efficiency of a leaf seal, because it permits the leakage of flow through the gap.

In a conventional leaf seal, such as that shown in Figures 1 and 2, circumstances can arise in which the pressure drop across the seal can contribute to leaf "blow-down", whereby the end edges 36 of the leaves bear down strongly on the surface 37 of the rotor. Although a limited amount of blow-down is desirable to create a good seal between the end edges 36 and the rotating surface 37, excessive blow-down deflection causes high end edge contact loading and wear. Excessive blow-down deflection can also lead to increased wear of the rotor. The wear of the end edges of the leaves and/or the rotor can limit the useful life of the seal. In this legard, it has also been found that a large gap between the cover plates of a leaf seal and the rotor increases the "blow-down" tendency of the seal's leaves, thereby causing the early onset of the aforementioned disadvantages of blow-down.

There thus exists a conflict in the conventional design of leaf seals. In order to reduce the blow-down effect, a small radial gap is required between the cover plates 35a, 35b and the rotor surface 37. However, a small radial gap must generally be avoided in order to prevent the cover plates from rubbing against the rotor.

It is a preferred object of the present invention to provide an improved leaf seal.

According to the present invention, there is provided a leaf seal for effecting a seal between first and second coaxial components arranged for relative rotation about a common axis, the seal having: a pair of axially spaced apart cover plates, each cover plate being mountable to said first component and extending radially towards said second component so as to define a free edge proximate the second component; an annular pack of stacked leaves mountable to a said first component at root portions of the leaves between said cover plates, said leaves extending between said cover plates towards the second component such that end edges of the leaves are presented for interaction with the second component during relative rotation between the components and, in use, a pressure drop is maintained axially across the pack; the seal being characterised in that the free edge of at least one of said cover plates is defined by a rubbing material configured to make rubbing contact with the second component during relative rotation between the two components.

ic The rubbing material may be abradable and configured to abrade upon said rubbing contact with the second component. Alternatively, the rubbing material may be wearable and thus configured to wear upon said rubbing contact with the second component. In other embodiments it is envisaged that the rubbing material may be deformable and thus configured to deform during said rubbing contact with the second component.

Preferably, said first component is provided around said second component, and the cover plates extend radially inwardly towards said second component such that said free edges of the cover plates define the radially innermost extent of the respective cover plates.

The free edge of the or each cover plate may comprise a rubbing layer applied to the cover plate in the region of said free edge.

In some embodiments, the free edges of both cover plates are defined by said rubbing material. Alternatively, the free edge of only one of said cover plates may be defined by said rubbing material.

The pack is preferably arranged so as to have an axially upstream high pressure side and an axially downstream low pressure side across which said pressure drop is maintained in use, and in such an arrangement the cover plate having a rubbing free edge may be located on the upstream high pressure side of the pack. In alternative embodiments, however, the cover plate having a rubbing free edge may be located on the downstream low pressure side of the pack.

Optionally, the or each cover plate having a rubbing free edge is flexible so as to be configured to deflect in use during relative rotation between said components. In alternative arrangements, however, the or each cover plate having a rubbing free edge may be sufficiently rigid to resist deflection in use during relative rotation between said components.

It is possible, in some embodiments, for one of said cover plates to be flexible so as to be configured to deflect in use during relative rotation between said components, and for the other cover plate to be sufficiently rigid to resist deflection in use during relative rotation between said components.

Embodiments are proposed in which at least one cover plate having a rubbing free edge is configured such that its free edge presents a sharp edge for interaction with the second component. Alternatively, at least one cover plate having a rubbing free edge may be configured such that its free edge presents a surface for interaction with the second component which is convex in radial cross-section. In other possible arrangements, at least one cover plate having a rubbing free edge may be configured such that its free edge presents a surface for interaction with the second component which is linear in radial cross-section.

According to another aspect of the present invention, there is provided a gas turbine engine having a leaf seal of the type described above.

So that the invention may be more readily understood, and so that further features thereof may be appreciated, embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 (discussed above) shows schematically a cut-away perspective view of a portion of a generally conventional leaf seal; Figure 2 (discussed above) shows (a) a view along the axial direction of an arc segment of the pack of leaves of the seal of Figure 1, and (b) a plan view of a single leaf of the seal of Figure 1; Figure 3 shows schematically a longitudinal section through a gas turbine engine; Figure 4 is a schematic radial cross-sectional view through a leaf seal in accordance with an embodiment of the present invention; Figure 5 is a view similar to that of figure 4, but which shows a leaf seal in accordance with a second embodiment of the invention; Figure 6 is another similar view, showing a leaf seal in accordance with a third embodiment of the present invention; Figure 7 shows a leaf seal in accordance with a fourth embodiment of the present invention: Figure 8 shows a leaf seal in accordance with a fifth embodiment of the present invention; Figure 9 shows a leaf seal in accordance with a sixth embodiment of the present invention; Figure 10 shows a leaf seal in accordance with a seventh embodiment of the present invention; and Figure 9 shows a leaf seal in accordance with an eighth embodiment of the present invention.

With reference to Figure 3, a ducted fan gas turbine engine incorporating the invention is generally indicated at 10 and has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, and intermediate pressure turbine 17, a low-pressure turbine 18 and a core engine exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines the intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.

During operation, air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow A into the intermediate pressure compressor 13 and a second air flow B which passes through the bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 13 compresses the air flow A directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.

The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.

The engine has one or more leaf seals installed, for example, between an interconnecting shaft and a casing for the shaft.

Figure 4 shows, schematically, a radial cross-sectional view through a leaf seal 131 in accordance with the present invention. The leaf seal 131 is similar in several respects to a conventional leaf seal such as the seal 31 shown in Figures 1 and 2. Accordingly, the leaf seal 131 comprises an annular pack 50 of individual leaves 132. The pack of leaves 132 is preferably arranged and mounted relative to the surface 137 of a rotor 51 in a generally conventional manner.

The root portions 140 of the leaves 132 are held in a housing 134 which includes an upstream (high pressure) cover plate 135a and a downstream (low pressure) cover plate 1 35b, which are axially spaced apart relative to the direction of the rotational axis 52 of the rotor 51. The leaves 132 extend from their root portions 140, between the spaced apart cover plates 135a, 135b towards the rotor 51, and terminate with respective end edges 136 which are presented for interaction with the surface 137 of the rotor 51 in a generally conventional manner. For example, the end edges 136 may be arranged in closely spaced, intimate relation to the rotor surface 137 as illustrated. It is also envisaged that, when the rotor 51 is stationary and thus not moving relative to the pack 50, or when the rotor 51 is moving only at low speed relative to the pack 50, the end edges 136 of the leaves 132 may lightly touch the surface 137 of the rotor for wiping contact therewith during low speed operation of the seal.

As will thus be appreciated, during relative rotation between the rotor 51 and the housing 134, and hence relative rotation between the rotor 51 and the leaves 132, the end edges 136 of the leaves run in close proximity to the surface 137 of the rotor 51, or even in wiping contact therewith. The end edges 136 of the annular pack 50 of leaves thus cooperate to provide a seal at the surface 137 of the rotor such that a pressure drop is maintained axially across the pack 50.

Turning now to consider the configuration of the cover plates 135a, 135b in more detail, it is to be noted that each cover plate 135a, 135b extends radially inwardly from the region of the housing 134 which holds the root portions 140 of the leaves, towards the rotor 51. At their radially innermost extent, the cover plates 135a, 135b present free edges 138 which are proximate the surface 137 of the rotor 51. The free edges 138 are each defined by a rubbing material 139 which is configured to make rubbing contact with the surface 137 of the rotor during rotation.

It is envisaged that the rubbing material 139 may be an abradable material which is configured to abrade in the event that it makes rubbing contact with the surface 137 of the rotor during rotation. Alternatively, the rubbing material may be a wearable material which is configured to wear in the event that it makes rubbing contact with the surface 137 of the rotor during rotation. In other embodiments of the present invention, the rubbing material can be ic provided in the form of a resiliently deformable material (such as a material having a honeycomb structure) which is configured to deform and thus yield against the surface 137 of the rotor in the event that it makes rubbing contact with the surface 137 of the rotor during rotation. Accordingly, it is to be appreciated that whilst reference is made to the use of rubbing material hereinafter, the rubbing material could be either abradable, wearable, or deformable.

The rubbing material 139 at the free edges 138 of the cover plates can be applied to the underlying structure of the cover plate 135a, 135b in the form of a relatively thin layer, or can be formed as a somewhat larger rubbing insert which is affixed or otherwise mounted to the radially innermost region of the cover plate so as to define the free edge 138. Alternatively, it is envisaged that in some embodiments, the entire cover plate might be formed from rubbing material, although it is envisaged that such an arrangement is unlikely to be optimal for most installations.

Because the free edges 138 of the cover plates 135a, 135b are formed from rubbing material 139, the radial gap g between the cover plates and the rotor surface 137 can be reduced significantly in comparison to prior art seals such as that illustrated in figure 1. This is because the risk of wearing damage to either the cover plates or the rotor arising from contact therebetween is eliminated by the provision of the rubbing material 139.

By reducing the radial gap g in this way, leakage through the gap is significantly reduced when compared to conventional leaf seals, which thus improves the overall sealing effect of the seal 131 as a whole. Additionally, the smaller gap g also reduces the blow-down effect on the leaves 132 at high pressure (i.e. corresponding to high power conditions in the case of a gas turbine engine), with a resulting reduction in wear at the end edges 136 of the leaves through excessive force being applied against the rotor. This reduction in blow-down at high pressure conditions means that there is less variation in the blow-down effect over a typical operating cycle involving transitions between low and high pressure conditions.

It is to be noted that whilst Figure 4 shows a leaf seal arrangement 131 in which both cover plates 135a, 135b are provided with rubbing free edges 139, it is possible instead to provide only one of the cover plates (either the upstream one or the downstream one) with the rubbing edge material 139.

Figure 4 actually illustrates a seal arrangement having relatively narrow cover plates 135a, 135b (in the axial direction), such that the cover plates are flexible and thus susceptible to a degree of deflection during rotation of the rotor 51. In the particular arrangement illustrated in which the cover plates have constant axial thickness across their radial extent, it is to be noted that the minimum axial thickness of the cover plates 135a, 135b suitable for an effective seal 131 in accordance with the present invention is likely to be determined by the need to have sufficient thickness on which to apply a layer of rubbing material 139.

Figure 5 illustrates a seal arrangement which is very similar to the one shown in figure 4 and described above. However, in the arrangement of figure 5, the two cover plates 135a, 135b are both configured to have sufficient axial thickness so as to be substantially rigid and non-flexible. As will be noted, therefore, in this arrangement the regions of rubbing material 139 provided at the free edges 138 of the cover plates are also thicker in the axial direction.

Having regard to figures 4 and 5, it is also to be noted that variants of the seal arrangements may include one flexible cover plate of the type shown in figure 4, and one rigid cover plate of the type shown in figure 5.

The embodiments shown in figures 4 and 5 both have cover plates 135a, 135b which are configured such that their rubbing free edges 138 present respective annular surfaces for interaction with the rotor 51 which are linear in radial cross-section, and also parallel to the surface 137 of the rotor 51 when viewed in radial cross-section as illustrated. However, other free edge profiles are also possible, as explained below with reference to figures 6 and 7.

Figure 6 shows an arrangement in which the rubbing material 139 defining the free edges 138 of the cover plates 1 35a, 1 35b, is provided in the form of a sharp point, as viewed in radial cross section, the point thus defining a sharp edge 143 around the rotor 51.

Figure 7 shows an arrangement in which the rubbing material 139 defining the free edges 138 of the cover plates 1 35a, 1 35b, is provided in the form of a more gently rounded point, as viewed in radial cross section, the tip of which thus defines a convex surface 144 in radial cross-section.

It is envisaged that the actual shape profile of the rubbing free edges 138 of the cover plates 135a, 135b will be selected and optimised to suit the intended functionality of any particular seal arrangement and to minimise the effect of wiping contact with the rotor. The shape profile of the rubbing free edges can have an effect on the amount of deflection which occurs in the case of flexible cover plates upon contact with the rotor, and so the shape profile can be selected to minimise degradation of the rubbing material 139 through rubbing contact against the rotor surface 137.

The rubbing free edges 138 of the cover plates according to the present invention provide a reduction in leakage across the leaf seal and a reduced variation of leaf blow-down as a function of the pressure differential across the seal. The reduced variation of blow-down can minimise the amount of leaf wear due to leaf-to -rotor contact and therefore improves the seal life. The effect of the degradation of the cover plate inner bore on the seal performance due to contact of the cover plate rubbing layer 139 with the rotor 51 should be taken into account to estimate the performance of a deteriorated seal 131.

Cover plates 135a, 135b of the type described above and embodied in the present invention are particularly useful for leaf seals having a very small cold build clearance to the rotor 51, or in the case of a leaf seal which is operated with the end edges 136 of its leaves 132 in contact with the rotor surface 137, orfora seal run in interference with the rotor 51. An example of such a seal arrangement 131 is illustrated in figure 8, where it can be seen that the end edges 136 of the leaves 132 are arranged in contact with the rotor surface 137 along their entire axial length. The reduction in the blow-down effect arising from the smaller gap g between the free edges 138 of the cover plates 135a, 135b is particularly beneficial in such an arrangement because of the importance of reducing leaf edge wear in order to maximize seal life.

Figure 9 illustrates another embodiment of leaf seal 131 in accordance with the present invention, which in some respects can be considered to represent a modification of the arrangement described above and shown in figure 4. In particular, it is to be noted that the leaf seal arrangement 131 shown in figure 9 has relatively narrow cover plates 135a, 135b (in the axial direction), such that the cover plates are flexible in a similar manner to that described above in connection with the arrangement of figure 4. However, in order to provide a larger surface area to accept a layer of rubbing material 139, the cover plates 135a, 135b each have a lip 145 which extends axially outwardly, away from the stack 50 of leaves 132, at the radially innermost region of the cover plate. The lips 145 each define a respective annular surface 146 which has an axial dimension significantly greater than the axial thickness of the main regions of the cover plates 1 35a, 1 35b. This configuration of the cover plates 135a, 135b allows the provision of a larger region of rubbing material 139 than in the previously described arrangement of figure 4, whilst still permitting the cover plates 135a, 135b to be flexible.

is Figures 10 and 11 show further embodiments which represent variations of the arrangement shown in figure 9. In each of these arrangements, the cover plates 135a, 135b are each provided with a plurality of through-holes 147 which are spaced apart around the cover plates. In figure 10, the holes 147 are shown extending through the respective cover plates 135a, 135b at positions immediately above the outwardly directed lips 145. In figure 11, the holes 147 extend radially through the lips 145, and extend through the rubbing material 139 applied to the lips. In each case the holes 147 are effective to reduce the pressure drop across the lipped radially innermost regions of the cover plates 135a, 135b which helps to reduce deflection of the lips relative to the cover plates 1 35a, 1 35b during operation of the leaf seal 131 against the rotor 51. Other orientations of bores 147 are also possible to achieve a similar technical effect.

It is to be noted that for embodiments of the present invention in which the rubbing material 139 is provided in the form of abradable material, it is preferable for the abradable material 139 at the free edges 138 of the cover plates 135a, 135b to be configured so as to be significantly more abradable in the direction of relative rotation between the cover plates and the rotor 51 (i.e. the circumferential direction) than in the axial direction of flow across the seal 131. This is because the presence of the abradable material 139 at the cover plates 135a, 135b should not limit the pressure capability of the seal. It is therefore preferable that the abradable material 139 is configured such that it can withstand shear in the axial direction of flow, but to abrade in the circumferential direction such that it wears away in layers during relative rotation between the cover plates and rotor.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or integers.

The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

Claims

CLAIMS1. A leaf seal (131) for effecting a seal between first (134) and second (51) coaxial components arranged for relative rotation about a common axis (52), the seal having: a pair of axially spaced apart cover plates (135a, 135b), each cover plate being mountable to said first component (134) and extending radially towards said second component (51) so as to define a free edge (138) proximate the second component (51); an annular pack (50) of stacked leaves (132) mountable to a said first component (134) at root portions (140) of the leaves between said cover plates (135a, 135b), said leaves (132) extending between said cover plates (135a, 135b) towards the second component (51) such that end edges (136) of ic the leaves (132) are presented for interaction with the second component (51) during relative rotation between the components and, in use, a pressure drop is maintained axially across the pack (50); the seal being characterised in that the free edge (138) of at least one of said cover plates (135a, 135b) is defined by a rubbing material (139) configured to make rubbing contact with the second component (51) during relative rotation between the two components.
2. A leaf seal according to claim 1, wherein said rubbing material (139) is abradable and configured to abrade upon said rubbing contact with the second component (51).
3. A leaf seal according to claim 1 or claim 2, wherein said first component (134) is provided around said second component (51), and the cover plates (135a, 135b) extend radially inwardly towards said second component (51) such that said free edges (138) of the cover plates define the radially innermost extent of the respective cover plates.
4. A leaf seal according to any preceding claim, wherein said free edge (138) of the or each cover plate (135a, 135b) comprises a rubbing layer (139) applied to the cover plate in the region of said free edge (138).
5. A leaf seal according to claim any preceding claim, wherein the free edges (138) of both cover plates are defined by said rubbing material (139).
6. A leaf seal according to any one of claims ito 4, wherein the free edge (138) of only one of said cover plates is defined by said rubbing material (139).
7. A leaf seal according to claim 6, wherein said pack (50) has an axially upstream high pressure side and an axially downstream low pressure side across which said pressure drop is maintained in use, the cover plate (135a) having a rubbing free edge (138) being located on the upstream high pressure side of the pack (50).
8. A leaf seal according to claim 6, wherein said pack (50) has an axially upstream high pressure side and an axially downstream low pressure side across which said pressure drop is maintained in use, the cover plate (135b) having a rubbing free edge (138) being located on the downstream low pressure side of the pack (50).
9. A leaf seal according to any preceding claim, wherein the or each cover plate (135a, 135b) having a rubbing free edge (138) is flexible so as to be configured to deflect in use during relative rotation between said components (134, 51).
10. A leaf seal according to any one of claims 1 to 8, wherein the or each cover plate (135a, 135b) having a rubbing free edge (138) is sufficiently rigid to resist deflection in use during relative rotation between said components (134, 51).
11. A leaf seal according to claim 5, wherein one of said cover plates (1 35a, 1 35b) is flexible so as to be configured to deflect in use during relative rotation between said components (134, 51), and the other cover plate (135b, a35a) is sufficiently rigid to resist deflection in use during relative rotation between said components (134, 51).
12. A leaf seal according to any preceding claim, wherein at least one cover plate (135a, 135b) having a rubbing free edge (138) is configured such that its free edge presents a sharp edge (143) for interaction with the second component (51).
13. A leaf seal according to any one of claims 1 toll, wherein at least one cover plate (135a, 135b) having a rubbing free edge (138) is configured such that its free edge presents a surface (144) for interaction with the second component (51) which is convex in radial cross-section.
14. A leaf seal according to any one of claims 1 toll, wherein at least one cover plate (135a, 135b) having a rubbing free edge (138) is configured such that its free edge presents a surface (142) for interaction with the second component (51) which is linear in radial cross-section.
15. A gas turbine engine (10) having a leaf seal (131) according to any preceding claim.
16. A leaf seal substantially as hereinbefore described, with reference to and as shown in figures 4 to 8.