U.S. patent application number 13/427427 was filed with the patent office on 2012-10-18 for annulus filler system.
This patent application is currently assigned to ROLLS-ROYCE PLC. Invention is credited to Ian C.D. CARE, Dale E. EVANS.
Application Number | 20120263596 13/427427 |
Document ID | / |
Family ID | 44123053 |
Filed Date | 2012-10-18 |
United States Patent
Application |
20120263596 |
Kind Code |
A1 |
EVANS; Dale E. ; et
al. |
October 18, 2012 |
ANNULUS FILLER SYSTEM
Abstract
An annulus filler system bridges the gap between two adjacent
blades attached to a rim of the rotor disc of a gas turbine engine.
The system includes an annulus filler having a lid which extends
between the adjacent blades and defines an airflow surface for air
being drawn through the engine. The filler also has a support body
extending beneath the lid and terminating in an elongate foot
which, in use, extends along a groove provided in the rim of the
disc. The groove has a neck which prevents withdrawal of the foot
through the neck in a radially outward direction of the disc. The
system further includes a sleeve which, after installation of the
filler, is slidably locatable into a gap between the foot and sides
of the groove.
Inventors: |
EVANS; Dale E.; (Derby,
GB) ; CARE; Ian C.D.; (Derby, GB) |
Assignee: |
ROLLS-ROYCE PLC
London
GB
|
Family ID: |
44123053 |
Appl. No.: |
13/427427 |
Filed: |
March 22, 2012 |
Current U.S.
Class: |
416/193A |
Current CPC
Class: |
F05D 2300/603 20130101;
F01D 5/30 20130101; F01D 5/3092 20130101; F01D 5/28 20130101; F01D
11/008 20130101 |
Class at
Publication: |
416/193.A |
International
Class: |
F01D 11/00 20060101
F01D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2011 |
GB |
1106276.7 |
Claims
1. An annulus filler system bridging the gap between two adjacent
blades attached to a rim of the rotor disc of a gas turbine engine,
the system including: an annulus filler having a lid which extends
between the adjacent blades and defines an airflow surface for air
being drawn through the engine, and a support body extending
beneath the lid and terminating in an elongate foot which, in use,
extends along a groove provided in the rim of the disc, the groove
having a neck which prevents withdrawal of the foot through the
neck in a radially outward direction of the disc, and a sleeve
which, after installation of the filler, is slidably locatable into
a gap between the foot and sides of the groove; wherein the foot is
formed of composite material and the sleeve provides a galvanic
isolation layer preventing galvanic corrosion between the foot and
the disc.
2. An annulus filler system according to claim 1, wherein the
composite material comprises carbon fibres.
3. An annulus filler system according to claim 1, wherein the
galvanic isolation layer is selected from the group consisting of:
a layer of glass fibre in a non-conductive matrix; a glass layer
formed or fused onto the surface of the sleeve; and a paint layer
or coating.
4. An annulus filler system according to claim 1, wherein the
sleeve has a layer of ballotinis within the galvanic isolation
layer.
5. An annulus filler according to claim 3, wherein the sleeve has a
layer of ballotinis within the galvanic isolation layer.
6. An annulus filler system according to claim 4, wherein the layer
of ballotinis are at the inner surface of the sleeve and contact,
in use, the foot.
7. An annulus filler system according to claim 4, wherein the
ballotinis are embedded in an adhesive or resin.
8. An annulus filler system according to claim 1, wherein the
sleeve has an anti-frettage coating at its outer surface, the
anti-frettage coating contacting, in use, the disc.
9. An annulus filler system according to claim 1, wherein the
sleeve has a metallic main body with the galvanic isolation layer
on the inner surface of the sleeve.
10. An annulus filler system according to claim 1, wherein the lid
is formed from fibre-reinforced plastic.
11. An annulus filler system bridging the gap between two adjacent
blades attached to a rim of the rotor disc of a gas turbine engine,
the system including: an annulus filler having a lid which extends
between the adjacent blades and defines an airflow surface for air
being drawn through the engine, and a support body extending
beneath the lid and terminating in an elongate foot which, in use,
extends along a groove provided in the rim of the disc, the groove
having a neck which prevents withdrawal of the foot through the
neck in a radially outward direction of the disc, and a sleeve
which, after installation of the filler, is slidably locatable into
a gap between the foot and sides of the groove; wherein the foot is
formed of composite material and the sleeve provides a galvanic
isolation layer preventing galvanic corrosion between the foot and
the disc, wherein the composite material comprises carbon fibres;
wherein the galvanic isolation layer is selected from the group
comprising: a layer of glass fibre in a non-conductive matrix; a
glass layer formed or fused onto the surface of the sleeve; or a
paint layer or coating.
12. An annulus filler system according to claim 11, wherein the
sleeve has a layer of ballotinis within the galvanic isolation
layer.
13. An annulus filler system according to claim 12, wherein the
layer of ballotinis are at the inner surface of the sleeve and
contact, in use, the foot.
14. An annulus filler system according to claim 12, wherein the
ballotinis are embedded in an adhesive or resin.
15. An annulus filler system according to claim 11, wherein the
sleeve has an anti-frettage coating at its outer surface, the
anti-frettage coating contacting, in use, the disc.
16. An annulus filler system according to claim 11, wherein the
sleeve has a metallic main body with the galvanic isolation layer
on the inner surface of the sleeve.
17. A rotor assembly for a gas turbine engine including: a rotor
disc, a plurality of blades attached to a rim of the disc of a gas
turbine engine, and annulus filler systems according to claim 1
bridging the gaps between adjacent blades; wherein respective
grooves are provided in the rim, the feet of the annulus fillers
extending along the grooves, and the sleeves being located in the
gaps between the feet and the sides of the grooves.
18. A rotor assembly for a gas turbine engine including: a rotor
disc, a plurality of blades attached to a rim of the disc of a gas
turbine engine, and annulus filler systems according to claim 11
bridging the gaps between adjacent blades; wherein respective
grooves are provided in the rim, the feet of the annulus fillers
extending along the grooves, and the sleeves being located in the
gaps between the feet and the sides of the grooves.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an annulus filler system
for bridging the gap between adjacent blades of a gas turbine
engine stage.
BACKGROUND OF THE INVENTION
[0002] With reference to FIG. 1, a ducted fan gas turbine engine
generally indicated at 10 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.
[0003] The gas turbine engine 10 works in a conventional manner so
that 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.
[0004] 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.
[0005] Conventionally, a compressor rotor stage comprises a
plurality of radially extending blades mounted on a disc. The
blades are mounted on the disc by inserting a root portion of the
blade in a complementary retention groove in the outer face of the
disc periphery. To ensure a radially smooth inner surface for air
to flow over as it passes through the stage, annulus fillers can be
used to bridge the spaces between adjacent blades. Typically, a
seal between the annulus fillers and the adjacent fan blades is
also provided by resilient strips bonded to the annulus fillers
adjacent the fan blades.
[0006] Annulus fillers of this type are commonly used in the fan
stage. The fillers may be manufactured from relatively lightweight
materials and, in the event of damage, may be replaced
independently of the blades
[0007] It is known to provide annulus fillers with features for
removably attaching them to the rotor disc. An annulus filler may
be provided with a hook member at its axially rear end, the hook
member sliding into engagement with part of the rotor disc and/or a
component located axially behind the rotor assembly, for example a
rear fan air seal. Typically, such an annulus filler is slid
axially backwards over the rotor disc following an arc which
matches the chord-wise curvatures of the aerofoil surfaces of the
adjacent blades until the hook member engages, and is then retained
in place by a front attachment disc which is fastened over the
fronts of all the annulus fillers located around the rotor
disc.
[0008] U.S. Pat. No. 4,655,687 proposes an annulus filler that can
be fitted to the rotor disc in a radial direction of the disc. The
annulus filler that has a salient foot that is shaped similarly to
re-entrant grooves formed in the disc rim between pairs of adjacent
blades. The foot is proportioned so as to pass radially of the disc
through the neck of a respective groove. Wedges positioned between
opposing walls of the grooves and respective feet then prevent
withdrawal of the feet in a direction radially outwardly of the
disc.
[0009] U.S. Pat. No. 6,132,175 proposes a compliant sleeve for
ceramic turbine blades that addresses irregularities between the
ceramic blade dovetail and the disc. The sleeve also acts as a
compliant member to reduce frettage.
SUMMARY OF THE INVENTION
[0010] An aim of the present invention is to provide annulus
fillers that are suitable for use with composite blades, and in
particular carbon fibre reinforced plastic (CFRP) blades. As such
blades are lighter than metal blades and as the casing containment
system for the blades in the event of a blade off event also tends
to be lighter, it is desirable that the filler is lightweight to
increase engine efficiency and to reduce the energy of impact on
the containment system and blades if parts of the annulus filler
should be released.
[0011] Accordingly, a first aspect of the present invention
provides an annulus filler system for bridging the gap between two
adjacent blades attached to a rim of the rotor disc of a gas
turbine engine, the system including: [0012] an annulus filler
having a lid which extends between the adjacent blades and defines
an airflow surface for air being drawn through the engine, and a
support body extending beneath the lid and terminating in an
elongate foot which, in use, extends along a groove provided in the
rim of the disc, the groove having a neck which prevents withdrawal
of the foot through the neck in a radially outward direction of the
disc, and [0013] a sleeve which, after installation of the filler,
is slidably locatable into a gap between the foot and sides of the
groove; [0014] wherein the foot is formed of composite material and
the sleeve provides a galvanic isolation layer preventing galvanic
corrosion between the foot and the disc.
[0015] Thus the composite material foot (and typically other
composite material parts) of the filler can reduce the filler mass.
However, as galvanic corrosion can be a problem between composite
materials, particularly those containing carbon fibres, and metals,
the sleeve enables a filler having at least a composite material
foot to be used with, for example, a metal disc by preventing
galvanic corrosion between the foot and the disc. The sleeve can
also provide a suitable interface between a relatively soft filler
foot and a relatively hard disc.
[0016] The annulus filler system may have any one or, to the extent
that they are compatible, any combination of the following optional
features.
[0017] Typically, the disc is a metal disc.
[0018] Typically, the foot is formed of fibre-reinforced plastic,
e.g. carbon-fibre reinforced plastic. Galvanic corrosion can be a
particular problem between carbon fibres and metals.
[0019] Conveniently, the foot may be proportioned to pass through
the neck of the groove in a radial direction on installation of the
filler. The sleeve can then be proportioned to prevent withdrawal
of the foot through the neck, after installation of the filler, in
a radially outward direction of the disc.
[0020] Typically, the groove extends in substantially an axial
direction of the engine, i.e. substantially aligned with retention
slots in the disc rim for retaining the blades. The groove may
follow a straight or a curved path from the front to the rear of
the disc. The walls of the groove may be parallel, or the groove
may taper from one end to another.
[0021] The sleeve may have a stop which engages with the rim to
prevent the sleeve from sliding beyond its intended location
position.
[0022] Typically, the sleeve wraps around the foot to extend from
one side of the neck to the other. Indeed, the sleeve may be
configured to protrude past the neck of the groove and to flare
outwardly away from the support body. In this way, free edges of
the sleeve outside the groove can be kept away from the support
body of the annulus filler, avoiding damage to the support body
from those edges.
[0023] The annulus filler may further have sealing strips along the
edges of the lid to seal to the adjacent blades.
[0024] The sleeve may have a layer of ballotinis within the
galvanic isolation layer. The ballotinis can ensure a minimum
thickness for the galvanic isolation layer. For example, the layer
of ballotinis may be at the inner surface of the sleeve and
contact, in use, the foot. The ballotinis, which can be formed e.g.
of glass or resin, are generally effective galvanic isolators and
can reliably space the foot from other parts of the sleeve which
offer less galvanic corrosion protection. The ballotinis may be
completely or partially embedded in a matrix such as a layer of
resin or an adhesive. For example, with partial embedding, a
portion of each ballotini may be proud of the matrix such that only
the ballotinis and not the matrix contact the foot. This can help
to improve the galvanic isolation of the foot by reducing the foot
surface area in contact with the sleeve.
[0025] Alternatively a galvanic isolation layer can be provided by:
a layer of glass fibre in a non-conductive matrix; a glass layer
formed or fused onto the surface of the sleeve; or a paint layer or
coating. Whichever type of layer is adopted, it should be resilient
to direct loading, for example from forced rocking of the annulus
filler by the blades, or from foreign objects impacting the airflow
surface of the lid of the filler.
[0026] The sleeve may be bonded to the foot after the sleeve is
located in the gap, e.g. by a resin or adhesive. For example, a
cyno-acrylic adhesive may be applied to the inner surface of the
sleeve before location of the sleeve. The adhesive then cures after
location of the sleeve in the presence of water to bond the sleeve
to the foot. Such adhesives are relatively strong in tension,
helping the sleeve to remain in location in use, but relatively
weak in shear, allowing the sleeve to be removed for servicing,
inspection or maintenance. Conveniently, the ballotinis may be
embedded in the resin or adhesive, such as a paste adhesive. A
paste adhesive (e.g. a nitrile phenolic adhesive, or a two part
catalytic set epoxy adhesive such as 3M Scotch-Weld 2216.TM. or a
thermoset epoxy adhesive such as 3M Scotch-Weld AF500.TM.), whether
used with or without ballotinis, can advantageously act as a damper
between the foot and the sleeve. It can also act as a filler to
accommodate manufacturing tolerances between the foot and the
sleeve, and can help to exclude moisture from the interface between
the foot and the sleeve.
[0027] The foot may have an outer layer of glass fibre, e.g. woven
or braided glass fibre. Such a layer can also improve the galvanic
isolation of the foot.
[0028] The sleeve may have an anti-frettage coating at its outer
surface, the anti-frettage coating contacting, in use, the disc.
For example, the anti-frettage coating may be formed of molybdenum
disulphide, tungsten disulphide or polytetrafluoroethylene. The
anti-frettage coating may be selectively located at positions on
the outer surface most susceptible to fretting. The anti-frettage
coating may be applied e.g. by thermal spraying, PVD or ebPVD, as
appropriate.
[0029] The sleeve may have a main body, for example with the
galvanic isolation layer on an inner surface of the body and/or an
anti-frettage coating on its outer surface. The main body can be
metallic. For example, it can be formed from a conventional
titanium alloy, or a high damping alloy such as a titanium-niobium
alloy or a titanium-hafnium alloy of the type known as gum metal. A
damping alloy can help to resist shear motion at the sleeve-disc
interface and hence to reduce fretting. Other metallic or
non-metallic materials can be used to form the main body of the
sleeve depending on, loading, and filler foot interaction
required.
[0030] Typically, the foot has a dovetail-shaped cross-section. The
groove can be correspondingly dovetail-shaped in cross-section.
Alternatively, however, the foot may have a circular cross-section,
e.g. on a stalk extending from the support body.
[0031] Preferably, the lid is formed from fibre-reinforced plastic,
e.g. CFRP.
[0032] The support body may have a pair of side walls, each side
wall joining a respective edge of the lid to the foot to give the
support body a V-shaped cross-section. As the V-shaped
cross-section supports the lid at its edges, the edges of the lid
are less likely to disintegrate during an extreme event.
Preferably, the side walls are formed from fibre-reinforced
plastic, e.g. CFRP. Preferably a cavity formed by the lid and the
two side walls contains a foam core, e.g. formed from a plastic
material such as a foamed resin or syntactic foam. The foam core
can provide a stiffer filler structure, more able to retain its
shape. Alternatively, however, the cavity may contain a chopped
fibre composite, e.g. a chopped carbon fibre in a resin such as
epoxy.
[0033] An annulus filler in which the lid, support body and foot
are all formed of composite or plastic material can be made very
lightweight, helping to increase the efficiency of the engine.
[0034] A second aspect of the present invention provides a sleeve
of the annulus filler system according to the first aspect.
[0035] A third aspect of the present invention provides a rotor
assembly according to the first aspect.
[0036] A fourth aspect of the present invention provides a rotor
assembly for a gas turbine engine including: [0037] a rotor disc,
[0038] a plurality of blades attached to a rim of the disc of a gas
turbine engine, and annulus filler systems according to the first
aspect bridging the gaps between adjacent blades; [0039] wherein
respective grooves are provided in the rim, the feet of the annulus
fillers extending along the grooves, and the sleeves being located
in the gaps between the feet and the sides of the grooves.
[0040] Preferably, the rotor disc is a fan disc. The blades may be
formed of composite material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] Embodiments of the invention will now be described by way of
example with reference to the accompanying drawings in which:
[0042] FIG. 1 shows a longitudinal section through a ducted fan gas
turbine engine;
[0043] FIG. 2 shows schematically a perspective view of an annulus
filler of an embodiment of the present invention;
[0044] FIG. 3 shows schematically a perspective view of a retention
sleeve of the embodiment;
[0045] FIG. 4 shows schematically an end on view of the annulus
filler and the retention sleeve of the embodiment when fitted to a
groove of a rotor disc;
[0046] FIG. 5 shows schematically a side view of the fitted annulus
filler and retention sleeve;
[0047] FIG. 6 shows schematically a transverse cross-section
through the retention sleeve of FIGS. 3 to 5; and
[0048] FIG. 7 shows schematically a transverse cross-section
through another embodiment of a retention sleeve.
DETAILED DESCRIPTION
[0049] FIGS. 2 and 3 show schematically perspective views of
respectively an annulus filler 30 and a retention sleeve 35 of an
annulus filler system according to an embodiment of the present
invention. The filler has a lid 31 which, in use, extends between
two adjacent composite fan blades, and a support body 32 extending
beneath the lid and terminating in an elongate foot 33. The support
body is formed by two side walls 34 which join to the lid along
respective edges of the lid and meet at the foot to give the body a
V-shaped cross-section. The foot has a dovetail cross-section, e.g.
with about 55.degree. flank angles. The retention sleeve 35 is
shaped to wrap around the foot 33.
[0050] FIG. 4 shows schematically an end on view of the annulus
filler 30 and the retention sleeve 35 when fitted to a groove 36 of
a metal rotor disc, and FIG. 5 shows schematically a side view on
the engine axial line of the fitted filler and sleeve. The groove
is dovetail-shaped in cross-section, like the foot 33, and is
located on the disc rim in the outside face of post 38 formed
between slots 39 which hold the fan blades 40 to the disc. An
alternative arrangement has a circular foot cross-section and a
correspondingly circular groove cross-section. The groove may
follow a straight or a curved path from the front to the rear of
the disc, and the sleeve is correspondingly straight or curved. To
install the annulus filler system into the groove, the annulus
filler is positioned outwardly of the groove and then moved
radially inwardly. The widest part of the foot is proportioned to
pass through the neck 41 of the groove so that the foot can be
located completely in the groove. This enables fitting annulus
fillers between blades that are shaped such that the fillers cannot
be slid into position along the groove in a generally rearward
direction of the engine. To prevent withdrawal of the annulus
filler in a radially outward direction, the retention sleeve 35 is
slidingly located into the gap formed between the groove and the
foot. The sleeve wraps around the foot and protrudes past the neck
of the groove to flare outwardly away from the support body so that
the free edges 42 of the sleeve are kept away from the support body
32. This helps to prevent the free edges from damaging the support
body or posts 38 if there is relative movement between the sleeve
and the body.
[0051] A stop 43 at the end of the sleeve 35 prevents the sleeve
from sliding in one direction out of the groove 36. Sliding of the
sleeve in the other direction can be prevented by a support ring 44
fitted to the face of the disc 37 after location of the sleeve.
Thus together the stop and support ring can ensure repeatable axial
positioning and retention of the sleeve.
[0052] When fitted, the lid 31 of the annulus filler 30 forms a
continuous airflow surface along with a nose cone 45 at the front
of the lid and a seal ring 46 at the rear of the lid. Sealing
strips 47 extending along the edges of the lid seal the lid to the
sides of the adjacent blades 40.
[0053] Advantageously, the foot 33 and groove 36 retention system
can distribute loads over the entire axial length of the filler 30.
This allows the use of a lightweight filler which can improve
engine efficiency. The weight of the filler can be reduced, for
example, by forming the lid 31, the side walls 34 and the foot 33
from carbon fibre reinforced plastic.
[0054] The lid may be secured to the side walls by stitching
through laminate layers, which can help to stiffen the edges of the
lid, thereby providing a secure base for the sealing strips 47. The
cavity formed by the lid and side walls can be filled with a foam
core 48 or have an internal lattice structure, which can provide a
lightweight resilient support to the lid and side walls. Such
support can absorb impact energy and help the lid and side walls to
retain their shape after impact deformation. The filler may be
produced by foaming the material of the core within a pre-preg
envelope of the lid, side walls and foot, and then completing the
lid, side walls and foot by resin transfer moulding.
[0055] More specifically, the basic filler structure can be formed
as a pre-preg tube by 3D Braiding or 3D weaving carbon fibres. An
outer layer of glass fibre, e.g. woven or braided glass fibre can
be applied to the foot to improve the galvanic isolation of the
foot. A former can be placed inside the preform, which is then
resin transfer moulded. The foam core is foamed in situ in the
cavity and the surfaces sealed. The lid may have a coating, such as
an elastomer (e.g. polyurethane), applied to resist sand, debris,
and tool drops. Typically the coating would be applied as a sheet
or sprayed on. A more sophisticated 3D braided or woven structure
can be made to provide internal struts or lattice within the
cavity, in which case more than one former may be required during
moulding.
[0056] FIG. 6 shows schematically a transverse cross-section
through the sleeve 35. The inner surface of the sleeve is covered
with a layer of ballotinis 48. The ballontinis are partially or
fully embedded in a layer of resin or adhesive 49 such that the
ballotinis ensure a minimum thickness for the galvanic isolation
layer formed by the ballotinis and the resin. The galvanic
isolation layer isolates the carbon fibres in the foot from the
rest of the sleeve and the metal disc 37. If the ballotinis are
partially embedded in the resin, only the proud portions of the
ballotinis may make contact, in use, with the foot 33. This can
reduce the contact area of the foot with the sleeve. However, a
paste adhesive may be used to fill the gaps between the ballotinis
and provide a loose bond to the filler foot. Such a paste adhesive
is preferably chosen to provide damping to the filler foot.
[0057] Two sizes of ballotinis may be used: the larger size being
only partially embedded and having proud portions penetrating to an
extent into the surface of the foot and thereby improving the
locking between the foot and the sleeve, and the smaller size being
fully embedded with the resin or paste adhesive to ensure a minimum
thickness for the galvanic isolation layer.
[0058] The sleeve has a main body 50 which carries the layer of
ballotinis 48 on its inner surface. The main body can be formed,
for example, of a conventional titanium alloy, or a high damping
alloy such as a titanium-niobium-oxygen alloy or a
titanium-hafnium-oxygen alloy. Advantageously, a damping alloy can
help to resist shear motion at the sleeve-disc interface and hence
to reduce fretting.
[0059] The outer surface of the main body 50 may be treated with an
anti-frettage coating 51, such as molybdenum disulphide, tungsten
disulphide or polytetrafluoroethylene. The coating may be applied
only where needed rather than over the entire outer surface. The
coating may be a sprayed on or applied by PVD/ebPVD.
[0060] FIG. 7 shows schematically a transverse cross-section
through another embodiment of the sleeve 35. The sleeve is formed
with various layers. The main body 52 is preferably metallic and
may, for example, be an alloy of titanium, or a high damping
titanium alloy such as Ti.sub.3(Ta, Nb, V)+(Zr, Hf, O) (known as
gum metal). The outer surface of the main body carries an
anti-fretting coating 53. The inner surface of the main body
carries a galvanic isolation layer 54 formed, for example, by a
layer of glass fibre in a non-conductive matrix.
[0061] 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. For example, the filler may be
slid into position along the groove in a generally rearward
direction of the engine, i.e. the sleeve may not need to prevent
withdrawal of the annulus filler in a radially outward direction.
Accordingly, the exemplary embodiments of the invention set forth
above are considered to be illustrative and not limiting.
[0062] All references referred to above are hereby incorporated by
reference.
* * * * *