COMBUSTOR CONSTRUCTION

CONSTITUTION DE CHAMBRE DE COMBUSTION

English Abstract

A reverse flow combustor for a gas turbine engine having an outer combustor liner and an inner combustor liner defining an annular combustion chamber,and a compound-angle frustoconical portion in the outer liner having a first and second conical slopes towards an engine centreline..

French Abstract

Chambre de combustion à flux inversé conçue pour un moteur à turbines à gaz doté dune chemise de chambre de combustion externe et dune chemise de chambre de combustion interne définissant une chambre de combustion annulaire et une partie tronconique à angle composé dans la chemise externe présentant une première et une deuxième pente conique orientée vers le centre du moteur.

Claims

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Claims

1. A reverse flow combustor for a gas turbine engine, the
combustor comprising:
a cylindrical head portion;
an outer liner and an inner liner cooperating to define
continuous outer and inner gas flow directing surfaces of an annular
reverse flow combustion chamber for directing a hot combustion gas
to change direction from a first direction adjacent the cylindrical
head portion to a second reverse flow direction, wherein the hot
combustion gas is directed to flow adjacent to the gas directing
surfaces of the outer liner and the inner liner;
the outer liner having a compound-angle frustoconical portion,
being defined as a frustum of a right circular cone, extending
downstream from the cylindrical head portion relative to hot gas
flow inside the combustor, the compound-angle frustoconical portion
including a first frustoconical portion merging continuously with
the cylindrical head portion and having a first conical non-zero
slope towards an engine centreline and a second frustoconical
portion merging continuously with the first frustoconical portion
wherein the first frustoconical portion and the second frustoconical
portion define at least part of the outer gas flow directing surface
for directing the hot combustion gas, the second frustoconical
portion having a second conical non-zero slope towards the engine
centreline, the first conical slope being greater than the second
conical slope and a ratio of the second conical slope to the first
conical slope is in the range of 0.7 to 1 and 0.3 to 1;
wherein the first and second frustoconical portions meet at a
circumferentially-extending hinge line having a bend radius of less
than 1 inch and a plurality of effusion cooling holes are provided
in the outer liner at the hinge line; and


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wherein the second frustoconical section comprises two portions
of substantially identical conical slope and a butt weld interposed
between and joining said two portions, the butt weld being adjacent
the hinge line and a plurality of effusion cooling holes being
provided through the butt weld.
2. A reverse flow combustor according to claim 1, wherein the
holes through the hinge line location are angled relative to a
surface of the liner in which the holes are provided.
3. A reverse flow combustor according to claim 1 wherein the first
and second frustoconical portions meet angularly at a line adjacent
an exit of at least one diffuser pipe of the engine.
4. A reverse flow combustor according to claim 3 wherein the
conical slopes of the first and second frustoconical portions are
selected to provide a desired clearance between the at least one
diffuser pipe exit.
5. A reverse flow combustor according to claim 1 wherein the first
frustoconical portion includes a plurality of dilution holes.
6. A gas turbine engine comprising:
a case housing a compressor stage, an annular reverse flow
combustor and a turbine stage in serial flow communication;
the compressor stage including a centrifugal impeller and a
diffuser stage having diffuser pipes;
the combustor comprising a cylindrical head portion, an outer
liner and an inner liner cooperating to define continuous outer and
inner gas flow directing surfaces of an annular reverse flow
combustion chamber for directing a hot combustion gas to change
direction from a first direction adjacent the cylindrical head
portion to a second reverse flow direction, wherein the hot
combustion gas is directed to flow adjacent to the gas directing
surfaces of the outer liner and the inner liner;


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the outer liner having a compound-angle frustoconical portion,
being defined as a frustum of a right circular cone, extending
downstream from the cylindrical head portion relative to hot gas
flow inside the combustor, a first frustoconical section of the
compound-angle frustoconical portion merging continuously with the
cylindrical head portion and having a first conical non-zero slope
towards an engine centreline, a second frustoconical section of the
compound-angle frustoconical portion merging continuously with the
first frustoconical section wherein the first frustoconical section
and the second frustoconical section define at least part of the
outer gas flow directing surface for directing the hot combustion
gas, the second frustoconical section having a second non-zero
conical slope towards the engine centreline, the first conical slope
being greater than the second conical slope and a ratio of the
second conical slope to the first conical slope is in the range of
0.7 to 1 and 0.3 to 1;
wherein the first and second frustoconical sections meet at a
hinge line having a bend radius of less than 1 inch and a plurality
of effusion cooling holes are provided in the outer liner at the
hinge line; and
wherein the second frustoconical section comprises two portions
of substantially identical conical slope and a butt weld interposed
between and joining said two portions, the butt weld being adjacent
the hinge line and a plurality of effusion cooling holes being
provided through the butt weld.
7. A gas turbine engine according to claim 6 wherein the first and
second frustoconical sections meet angularly at a line adjacent an
exit of at least one diffuser pipe of the engine.
8. A gas turbine engine according to claim 7 wherein the conical
slopes of the first and second frustoconical sections are selected
to provide a desired clearance between the at least one diffuser
pipe exit.


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9. A gas turbine engine according to claim 6 wherein the first
frustoconical section includes a plurality of dilution holes.
10. A gas turbine engine according to claim 6, wherein the holes
through the hinge line location are angled relative to a surface of
the liner in which the holes are provided.

Description

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COMBUSTOR CONSTRUCTION
TECHNICAL FIELD

[0001] The invention relates to a gas turbine combustor,
and more particularly, to the construction of such a

combustor.
BACKGROUND OF THE ART

[0002] A reverse flow combustor for a gas turbine engine
comprises an annular bulkhead or combustor dome in which is
mounted a number of fuel nozzles. From the dome, inside

and outside combustor liner walls extend to contain the
combustion gases which reverse direction and exit the
combustion zone via a large/outer exit duct and a
small/inner exit duct towards the high and low pressure
turbine zones. With all combustors, the space inside the

combustor, or combustion volume, is designed to provide the
desired combustion characteristics, while the space outside
the combustor, between the combustor and surrounding engine
case, is designed to permit the desired airflow around the
combustor. However, the constraints of the engine

configuration do not always permit both to be individually
optimized, and consequently trade-offs are some time
necessary. Nonetheless, there is a desire to improve the
overall efficiency and performance of combustors, while
ever reducing costs and weight.

SiJNIIMARY

[0003] In one aspect, provided is a reverse flow
combustor for a gas turbine engine comprising an outer
liner and an inner liner cooperating to define an annular


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reverse flow combustion chamber having a cylindrical head
portion, the outer liner having a compound-angle
frustoconical portion extending downstream from the
cylindrical head portion relative to airflow inside the

combustor, the compound-angle frustoconical portion
including a first frustoconical portion extending from the
cylindrical head portion and having a first conical slope
towards an engine centreline and a second frustoconical
portion extending from the first frustoconical portion and
having a second conical slope towards the engine
centreline, the first conical slope being greater than the
second conical slope.

[0004] In another aspect, provided is a gas turbine
engine comprising a case housing compressor, combustor and
turbine stages in serial flow communication, the compressor

stage including a centrifugal impeller with a diffuser
stage having diffuser pipes, the combustor stage have a
reverse flow combustion liner with an outer liner having a
compound-angle frustoconical portion extending downstream

from the cylindrical head portion relative to airflow
inside the combustor, a first frustoconical section of the
compound-angle frustoconical portion extending from the
cylindrical head portion and having a first conical slope
towards an engine centreline, a second frustoconical

section of the compound-angle frustoconical portion
extending from the first frustoconical section and having a
second conical slope towards the engine centreline, the
first conical slope being greater than the second conical
slope.


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DESCRIPTION OF THE DRAWINGS

[0005] The invention is illustrated by way of example in
the accompanying drawings, in which:

[0006] Figure 1 is an axial cross-sectional view through
a prior art gas turbine engine showing the various
components that are assembled to produce an engine.

[0007] Figure 2 is a detailed axial cross-section
through a prior art combustor.

[0008] Figure 3 is a detailed axial cross-section
through a combustor in accordance with the invention.
[0009] Figure 4 is an enlarged view of a portion of
Figure 3.

[00010] Further details will be apparent from the
detailed description included below.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[00011] Figure 1 shows an axial cross-section through a
turbofan gas turbine engine. It will be understood however
that the invention is applicable to any type of gas turbine
engine with an annular reverse flow combustor, such as a

turboshaft engine, a turboprop engine, or auxiliary power
unit. Air intake into the engine passes over fan blades 1
in a fan case 2 and is then split into an outer annular
flow through the bypass duct 3 and an inner flow through
the low-pressure axial compressor 4 and high-pressure

centrifugal compressor 5. Compressed air exits the
compressor 5 through a diffuser 6 and is contained within a
plenum 7 that surrounds the combustor 8. Fuel is supplied


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to the combustor 8 through fuel tubes 9 which is mixed with
air from the plenum 7 when sprayed through nozzles into the
combustor 8 as a fuel air mixture that is ignited. A
portion of the compressed air within the plenum 7 is
admitted into the combustor 8 through orifices in the side
walls to create a cooling air curtain along the combustor
walls or is used for cooling to eventually mix with the hot
gases from the combustor and pass over the nozzle guide
vane 10 and turbines 11 before exiting the tail of the

engine as exhaust.

[00012] Figure 2 shows a detailed axial cross-section
through a prior art combustor 8. The outer combustor liner
12 and the inner combustor liner 13 define the annular
combustion chamber into which fuel-air mixture is injected

and ignited. The outer combustor liner 12 is axially
restrained with a plurality of support pins 14. The ends
of the support pins 14 radially slidingly engage a boss 15
in the outer combustor liner 12 which permits radial

expansion and contraction while restraining the combustor 8
axially to an inside wall of the bypass duct 3.

[00013] The large exit duct 16 extends from the outer
liner 12 and the small exit duct 17 extends from the inner
liner 13 defining a reverse flow combustor duct that
directs hot gases from a forward direction to a rearward

direction passing the nozzle guide vanes 10.

[00014] Figure 3 illustrates a combustor in accordance
with the invention. The sheet metal combustor 8 has an
outer liner 12 comprising a compound-angle frustoconical
portion 20 extending the entire distance between an axially


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extending cylindrical head portion 22, in which the boss 15
is provided, and an entry portion 24 of the large exit duct
16. The cylindrical head portion 22 provides a desired
primary combustion zone, but is located in a position more

or less on the same radius as the exits of diffuser 6.
Consequently, compound-angle frustoconical portion 20 is
comprised of a first frustoconical portion 20a, having a
first conical slope or angle a, and a second frustoconical
portion 20b, having a second conical slope angle (3, where a

>(3, preferably such (3 is in the range of 0.7a and 0.3a.
Bends A, B, and C in the sheet metal of outer liner 12
define frustoconical portions 20, 20a and 20b. Bend B is
located axially generally in alignment with, but preferably
slightly downstream or, the diffuser outlet (relative to
flow exiting the diffuser outlet). Bend B provides a hinge
line between adjacent sections. The radius of bend B is
preferably relatively "sharp" - i.e. with a radius of less
than an inch. Bend C is provided between the LED 16 and
the frustoconical portion 20. Bend A is provided between

the cylindrical head section 22 and the frustoconical
portion 20. A plurality of dilution holes 26 are provided
in first frustoconical portion 20a, also downstream of the
diffuser outlet.

[00015] A butt weld 23 (provided in the region indicated
by the circle 23 in Figure 4) is preferably provided, in
any suitable manner, to join adjacent sections of the
second frustoconical portion 20b. Effusion cooling holes
21 are provided through the outer liner, in particular,
through the compound-angle frustoconical portion 20, and

more particularly though the hinge line provided at bend B,


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and through the butt weld 23. Preferably two rows of holes
are provided through the weld region.

[00016] By providing a compound-angle frustoconical
portion 20, clearance is maintained between the outer liner
12 and the fishtails of diffuser 6 as the cylindrical head
22 is joined to the LED 16, thereby optimizing airflow

around combustor 8 within plenum 7 while optimizing
combustion volume inside the combustor. As mentioned
above, this allows flow and combustor performance to be

optimized. Effusion cooling augments the design by
provided cooling where required to cool local hot spots in
the kinked design. The sheet metal liner provides a low-
cost, easy to manufacture and lightweight solution. The
butt weld between adjacent sections of the liner and LED

provide joining without unnecessary surface disruptions to
obstruct airflow. Providing cooling through the weld
region.

[00017] Although the above description relates to a
specific preferred embodiment as presently contemplated by
the inventors, it will be understood that the invention in
its broad aspect includes mechanical and functional
equivalents of the elements described herein.

Representative Drawing