Note: Descriptions are shown in the official language in which they were submitted.
CA 02608479 2007-10-25
GAS TURBINE FLOATING COLLAR ARRANGEMENT
TECHNICAL FIELD
The invention relates generally to gas turbine
engine combustors and, more particularly, to a floating
collar arrangement therefor.
BACKGROUND OF THE ART
Gas turbine combustors are typically provided with
floating collars or seals to permit relative radial or
lateral motion between the combustor and the fuel nozzle
while minimizing leakage therebetween. The collar is
typically welded to the edge of a fuel nozzle hole
defined in the dome end portion of the combustor wall.
The collar is subject to wear and heat. Radial cracks
occur around the fuel nozzle hole, and floating collar
assemblies crack due to the metal being exposed to hot
air. One cause of the cracking is that the thermal
barrier coating, applied on the inner surface of the
combustor wall near the fuel nozzle hole, cannot be
brought to the edge of the fuel nozzle hole to protect
the metal due to weld contamination. A band of
unprotected metal must be left exposed in order to
perform the weld and, thus, secure the floating collar to
the combustor wall. In addition, the welds are exposed to
hot air, which inevitably results in cracking.
Accordingly, there is a need to provide a solution
which addresses these and other limitations of the prior
art, and in particular, there is a need to reduce the
occurrence of cracking on gas turbine combustors.
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SUMMARY OF THE INVENTION
In one aspect, the present invention provides a
floating collar and combustor arrangement for receiving a
fuel nozzle, comprising: a combustor having an opening
defined in a dome thereof for receiving the fuel nozzle,
the combustor having an inner surface and an outer
surface; a mounting
arrangement comprising a mounting
flange circumscribing the opening, the mounting flange
being fixedly bonded from outside of the combustor to the
outer surface thereof, and a cap spaced-apart in an axial
direction relative to the combustor from the mounting
flange, the cap fixed to the mounting flange; a floating
collar slidably trapped between the mounting flange and
the cap such that relative axial movement is
substantially restrained but relative radial movement is
permitted, the floating collar having a central aperture
substantially aligned with the opening in the dome and
adapted for receiving the fuel nozzle; and a thermal
barrier applied to the inner surface of the combustor all
the way to an edge of the opening in the dome.
In another aspect, the present invention provides a
method of mounting a float4.ng collar assembly to a
combustor of gas turbine engine, the method comprising:
fixedly bonding the floating collar assembly from outside
of the combustor to an outer surface of the combustor
such that a central opening of the floating collar
assembly be substantially aligned with an opening of the
combustor for receiving a fuel nozzle.
Further details of these and other aspects of the
present invention will be apparent from the detailed
description and Figures included below.
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DESCRIPTION OF THE DRAWINGS
Reference is now made to the accompanying Figures
depicting aspects of the present invention, in which:
Figure 1 is a schematic longitudinal sectional view
of a turbofan engine;
Figure 2 is a partial sectional view of a combustor
in accordance with an embodiment of the present
invention;
Figure 3 is an isometric view of a portion of Figure
2; and
Figure 4 is an exploded isometric view of Figure 3.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 illustrates a gas turbine engine 10 of a
type preferably provided for use in subsonic flight,
generally comprising in serial flow communication a fan
12 through which ambient air is propelled, a multistage
compressor 14 for pressurizing the air, a combustor 16 in
which the compressed air is mixed with fuel and ignited
for generating an annular stream of hot combustion gases,
and a turbine section 18 for extracting energy from the
combustion gases.
Figure 2 shows an enlarged axial sectional view of
an annular combustor 16 comprising a combustor wall or
liner 20 defining a dome 22 having inner and outer
surfaces 23 and 24 and a circumferential array of central
fuel nozzle openings (only one being shown at 26) for
receiving a plurality air swirler fuel nozzles (one being
depicted in stippled lines in Figure 2) of the type
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generally described in U.S. Patent Nos. 6,289,676 or
6,082,113, for example. Each fuel
nozzle is associated
with a floating collar arrangement 28.
The floating collar arrangement 28 generally
comprises an annular mounting flange 30, an annular cap
40 and a floating collar 50 mounted between the mounting
flange 30 and the cap 40.
The mounting flange 30 has a forwardly projecting
annular lip 30a, a radially disposed annular flange
portion 30b, both defining a central aperture 34 therein.
Central aperture 34 can be aligned with dome opening 26
when mounting flange 30 is mounted on the combustor 16.
Mounting flange 30 may also include a plurality of
rearwardly projecting legs 36 as will be described
further below.
As shown in Fig. 2, the mounting flange 30 is
mounted from the outside of the combustor 16. More
particularly, the mounting flange 30 is fixed along the
annular lip 30a thereof, preferably by braze 32, to the
outer surface 24 of dome 22. The soldering, done using a
hard solder with a high melting point, such as with an
alloy of zinc and copper, is done from the outside of the
flange 30, i.e. at the connection point 32 between the
outer surface 24 of the dome 22 and the radially outer
side of the forwardly projecting lip 30a opposite the
side facing the opening 26. The braze is on the outside
of the assembly outside of the combustor and therefore
not exposed to the hot combustor temperatures coming
through the central opening 26. The outside mounting of
flange 30 advantageously allows to apply a thermal
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barrier coating 25 to the inner surface 23 of the liner
22 all the way to the edge of the fuel nozzle opening 26,
protecting the entire surface of the dome from the hot
air. The thermal
barrier coating 25 is applied before
brazing but it does not melt and is thus unaffected by
braze, due to lower braze temperatures and remote
location. This allows the thermal barrier coating 25 to
come to the edge of the part, protecting the entire
metal.
The annular cap 40 has a central aperture 44 which
is aligned with dome opening 26 and the mounting flange
aperture 34 when mounted on combustor 16 for receiving
the fuel nozzle therein. The annular cap 40 is mounted at
42, such as by welding, to the rearwardly projecting legs
36 of mounting flange 30. Alternatively, cap 40 could be
brazed to the mounting flange 30, from the outer surface,
i.e. at the connection point of the outer surface of the
flange 30 and the outer surface of the cap 40.
The floating collar 50 is disposed axially between
the mounting flange 30 and the cap 40. The floating
collar 50 has an axially forwardly projecting nozzle
collar portion 50a, and a radially disposed annular
flange portion 50b, both surrounding a central aperture
54, and a smooth transition from axial to radial joins
portions 50a and 50b. Central
aperture 54 and collar
portion 50a are provided for axially slidingly engaging a
circumferential shoulder of the fuel nozzle swirler body
(stippled lines in Figure 2). Collar portion
50a
preferably extends to, or inside, dome 22 though opening
26. Flange portion 50b is trapped between opposed
surfaces of mounting flange 30 and cap 40, with mounting
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flange 30 and cap 40 being sufficiently spaced apart to
permit radial (relative to the engine axis of Figure 1)
sliding motion to occur between floating collar 50 and
the mounting flange and cap sub-assembly. An anti-
rotation tang 56 depends from flange portion 50b and is
likewise trapped between adjacent mounting flange legs
36, to thereby limit the amount by which floating collar
50 may rotate relative to mounting flange and cap sub-
assembly.
In use, the fuel nozzle air swirler is positioned
within central aperture 54 and delivers a fuel air
mixture to combustor 16. As forces acting upon the fuel
nozzle and the combustor 16 tend to cause relative
movement therebetween, floating collar 50 is able to
displace radially with the nozzle while maintaining
sealing with respect to combustor 16 through maintaining
sliding engagement with mounting flange 30 and cap 40.
Connection points 32 and 42 ensure that mounting flange
30 and cap 40 maintain their spaced-apart relation and
thereby keep floating collar 50 trapped therebetween. In
accordance with one embodiment of the invention, both
connection points 32 and 42 are brazed from the outside
of the assembly such that the braze is not exposed to the
hot combustor temperatures. As mentioned herein above,
the external mounting is advantageous in that a thermal
barrier coating 25 can be applied to the inner surface 23
of the dome 22 all the way to the edge of the opening 26,
protecting all metal, preventing radial cracks to appear
in rows of holes around the opening 26 and preventing
weld crack of the mounting arrangement 28.
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Referring to Figure 4, mounting arrangement 28 is
assembled through a process involving at least the
following steps: brazing mounting flange 30 to combustor
dome 22 at an outer surface 24 thereof so that the flange
central opening 34 is generally aligned with dome opening
26; inserting floating collar 50 into the mounting flange
30, so that the collar portion 50a extends through
central opening 34 and is generally aligned with dome
opening 26, and preferably also so that anti-rotation
tang 56 is trapped between two closely adjacent legs 36;
and fixing cap 40 to mounting flange 30, preferably at
legs 36, to slidingly trap the floating collar 50 between
cap 40 and the mounting flange 30. The step of fixing cap
40 to mounting flange 30 may also be a brazing step, by
applying the solder at an outer surface of both the cap
40 and the flange 30. The order of operations may be any
suitable, and need not be chronologically as described.
Floating collar arrangement 28 and floating collar
50 are preferably provided from sheet metal using a
suitable fabrication process. A simplified
example
process is to provide a sheet of metal, cut a blank, and
perform at least one bending operation to provide the
floating collar. Referring again to Figure 2, it is
illustrated that a sheet metal collar 50 has a continuous
transition provided as a result of a sheet metal forming
operation, such as bending, and helps strengthen the
collar 50. Unlike prior art collars made by investment
casting and/or machining processes (see US Patent Nos.
4,454,711, 4,322,945 and 6,497,105, for example), the use
of sheet metal advantageously permits a very light weight
and inexpensively-provided part, due to its simple
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geometry, and yet provides good performance and
reliability.
Unlike the prior art, the mounting assembly of the
present invention is more resistant to radial cracks
around the dome opening 26 and the floating collar
assembly 28 cracks at the points of fixation between the
flange 30 and the dome 22, and the flange 30 and the cap
40. Contrary to the prior art which teaches welding the
floating collar assembly to the edge of dome opening 26
or the inner surface 23 of the liner 22 and thereby
needing to provide for an unprotected band of metal on
the inner surface of the dome 22, the design and method
of the present invention instead allows the thermal
barrier coating 25 to extend all the way to the edge of
the opening 26, protecting the entire surface of the dome
from hot air. As well, the
mounting assembly is also
better protected by having the fixation points brazed
from the outside, thereby protecting them from the hot
air and potential cracking.
The above description is meant to be exemplary only,
and one skilled in the art will recognize that changes
may be made to the embodiments described without
departing from the scope of the invention disclosed. For
example, the present invention may be applied to any gas
turbine engine, and is particularly suitable for airborne
gas turbine applications. The means by which flange 30
is mounted to cap 40 may be different than that
described. For example legs 36 may be replaced or
supplemented with a continuous or discontinuous flange or
lip, and/or may extend from flange 30, cap 40 or both.
The mode of anti-rotation may be any desirable. Though
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brazing is preferably, other bonding methods which would
allow the pieces to be fixed from the outside of the
combustor may be used. Other modifications which fall
within the scope of the present invention will be
apparent to those skilled in the art, in light of a
review of this disclosure, and such modifications are
intended to fall within the equivalents accorded to the
appended claims.
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