U.S. patent application number 13/917051 was filed with the patent office on 2014-12-18 for combustor exit duct for gas turbine engines.
The applicant listed for this patent is Pratt & Whitney Canada Corp.. Invention is credited to Ion Dinu, Jason Herborth, Si-Man Lao, Douglas MACCAUL, Robert Sze.
Application Number | 20140366544 13/917051 |
Document ID | / |
Family ID | 52016980 |
Filed Date | 2014-12-18 |
United States Patent
Application |
20140366544 |
Kind Code |
A1 |
MACCAUL; Douglas ; et
al. |
December 18, 2014 |
COMBUSTOR EXIT DUCT FOR GAS TURBINE ENGINES
Abstract
A gas turbine engine combustor includes an exit duct having
annular first and second exit duct walls radially spaced apart to
define therebetween the combustor exit opening. The first and/or
second exit duct walls has a double-skin wall section which
includes an inner hot wall facing the combustor exit opening and an
outer cold wall fastened to the inner hot wall and radially spaced
away therefrom to define a radial gap therebetween. The outer cold
wall has a coefficient of thermal expansion greater than that of
the inner hot wall. This helps reduce thermal growth mismatch
between the outer cold wall and the inner hot wall during operation
of the combustor, and reduces thermal stress at the joint between
the hot and cold walls.
Inventors: |
MACCAUL; Douglas; (Varennes,
CA) ; Lao; Si-Man; (Toronto, CA) ; Herborth;
Jason; (Acton, CA) ; Dinu; Ion; (Candiac,
CA) ; Sze; Robert; (Mississauga, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pratt & Whitney Canada Corp. |
Longueuil |
|
CA |
|
|
Family ID: |
52016980 |
Appl. No.: |
13/917051 |
Filed: |
June 13, 2013 |
Current U.S.
Class: |
60/752 ;
29/888 |
Current CPC
Class: |
F23R 2900/00005
20130101; Y02T 50/671 20130101; Y02T 50/60 20130101; Y02T 50/676
20130101; F23R 3/06 20130101; F05D 2230/642 20130101; Y10T 29/49229
20150115; F23R 2900/03044 20130101; F05D 2300/50212 20130101; F23R
3/002 20130101; F23R 2900/03042 20130101; F05D 2260/201 20130101;
F01D 9/023 20130101; F23R 3/54 20130101 |
Class at
Publication: |
60/752 ;
29/888 |
International
Class: |
F23R 3/00 20060101
F23R003/00 |
Claims
1. A gas turbine engine combustor comprising outer and inner
annular liners and an exit duct at a downstream end, the exit duct
circumscribing an annular combustor exit opening defining a
combustion gas path therethrough, the exit duct including annular
first and second exit duct walls radially spaced apart to define
therebetween the combustor exit opening, at least one of the first
and second exit duct walls having a double-skin wall section at a
most downstream end thereof, the double-skin wall section including
an inner hot wall facing said combustor exit opening and an outer
cold wall radially spaced away from the hot wall to define a radial
gap therebetween, the outer cold wall being disposed outside of
said combustion gas path, the inner hot wall and the outer cold
wall being fastened together by at least one joint therebetween,
the outer cold wall having a coefficient of thermal expansion
greater than that of the inner hot wall to reducing thermal growth
mismatch between the outer cold wall and the inner hot wall during
operation of the combustor and reduce thermal stress at the
joint.
2. The gas turbine engine combustor as defined in claim 1, wherein
the combustor is a reverse flow combustor, the first and second
exit duct walls respectively comprising a large exit duct portion
and a small exit duct portion.
3. The gas turbine engine combustor as defined in claim 2, wherein
both the large exit duct portion and the small exit duct portion
comprise said double-skin wall section at the most downstream ends
thereof.
4. The gas turbine engine combustor as defined in claim 3, wherein
the inner hot wall and the outer cold wall of the short exit duct
comprise spaced apart curved wall portions, a radius of curvature
of the inner hot wall being different from that of the outer cold
wall.
5. The gas turbine engine combustor as defined in claim 1, wherein
the joint between the inner hot wall and the outer cold wall
includes a welded joint disposed upstream of an exit end of the
double-skin wall section.
6. The gas turbine engine combustor as defined in claim 5, wherein
said welded joint is disposed at an upstream end of the combustor
exit duct in a transition area of the combustor disposed between
the outer and inner annular liners and the exit duct.
7. The gas turbine engine combustor as defined in claim 1, wherein
the outer cold wall of the double-skin wall section includes an
annular flange wall being formed from a formable metal sheet of a
type compatible for welding to the inner hot wall.
8. The gas turbine engine combustor as defined in claim 1, wherein
both the inner hot wall and the outer cold wall are made of sheet
metal.
9. The gas turbine engine combustor as defined in claim 1, wherein
outer cold wall is formed of Hastalloy X.TM..
10. The gas turbine engine combustor as defined in claim 1, wherein
the inner hot wall is formed of one of IN625, Haynes 188 and Haynes
230.
11. The gas turbine engine combustor as defined in claim 1, wherein
at least the outer cold wall of said double-skin wall section
includes one or more impingement cooling holes therein.
12. A combustor exit duct for a gas turbine engine, the combustor
exit duct comprising annular first and second exit duct walls
radially spaced apart to define therebetween a combustor exit
opening, at least one of the first and second exit duct walls
having a double-skin wall section at a most downstream end thereof,
the double-skin wall section including an inner hot wall facing
said combustor exit opening and an outer cold wall radially spaced
away from the hot wall to define a radial gap therebetween, the
outer cold wall being disposed outside of said combustion gas path,
the inner hot wall and the outer cold wall being fastened together
by at least one joint therebetween, the outer cold wall having a
coefficient of thermal expansion greater than that of the inner hot
wall to reducing thermal growth mismatch between the outer cold
wall and the inner hot wall during operation of the combustor and
reduce thermal stress at the joint.
13. The combustor exit duct as defined in claim 12, wherein both
the first and second exit duct walls comprise said double-skin wall
section at the most downstream ends thereof.
14. The combustor exit duct as defined in claim 12, wherein the
joint between the inner hot wall and the outer cold wall includes a
welded joint disposed upstream of an exit end of the double-skin
wall section.
15. The combustor exit duct as defined in claim 12, wherein the
outer cold wall of the double-skin wall section includes an annular
flange formed from a formable metal sheet of a type compatible for
welding to the inner hot wall.
16. The combustor exit duct as defined in claim 12, wherein both
the inner hot wall and the outer cold wall are made of sheet
metal.
17. The combustor exit duct as defined in claim 12, wherein outer
cold wall is formed of Hastalloy X.TM., and the inner hot wall is
formed from one of IN625, Haynes 188 and Haynes 230.
18. The combustor exit duct as defined in claim 12, wherein at
least the outer cold wall of said double-skin wall section includes
one or more impingement cooling holes therein.
19. A method of forming a gas turbine engine combustor, the
combustor having outer and inner annular liners and an exit duct at
a downstream end, the method comprising: providing a first and a
second annular wall of the exit duct which circumscribe an annular
combustor exit opening defining a combustion gas path therethrough;
forming a double-skin wall section on at least one of the first and
second annular walls of the exit duct, by welding an annular outer
cold wall flange to an inner hot wall portion facing said combustor
exit opening to form an annular welded joint therebetween, the
annular outer cold wall flange being spaced apart from the inner
hot wall downstream of said welded joint to define a radial gap
therebetween at a downstream end of the double-skin wall section;
and reducing thermal stress at the welded joint between the outer
cold wall flange and the inner hot wall of the double-skin wall
section by forming the outer cold wall flange from a material
having a coefficient of thermal expansion that is greater than that
of the inner hot wall to thereby reducing thermal growth mismatch
between the outer cold wall flange and the inner hot wall.
20. The method as claimed in claim 19, further comprising forming
both the inner hot wall and the outer cold wall flange with a
curved portion, the curved portion of the annular outer cold wall
flange having a different radius of curvature than that of the
inner hot wall.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to gas turbine
engines, and more particularly to combustors for such engines.
BACKGROUND
[0002] Combustor performance directly impacts the overall pollutant
emission and performance of a gas turbine engine. While cooling air
is typically required to cool hot surfaces of combustor liners, the
introduction of such cooling air into the main gas path dilutes the
hot combustion gas flowing to the turbine and thus reduces the
combustor performance. Combustor to turbine transition ducts,
particularly in reverse flow combustor configurations, allow the
combustion products to have a longer distance to mix with the cool
dilution air before striking the turbine blades. This extra mixing
length reduces the combustion maximum gas exit temperature. With
the help of such longer combustor to turbine transition ducts,
lower peak combustor gas exit temperature can be achieved with less
dilution flow, so that more can be used for cooling, carbon
formation and emission control. The fuel nozzle count may also be
able to be reduced, which reduces weight and costs of the
combustion system. Also, such reverse flow transitions ducts which
feed the combustion gases into the turbine shorten the overall
length of the combustor and thus the engine, which greatly reduces
weight, cost and simplifies shaft/bearing design. However, these
transition ducts are extra areas that need to be cooled and
therefore an effective combustor wall construction and/or cooling
system thereof is required.
SUMMARY OF THE INVENTION
[0003] There is provided a gas turbine engine combustor comprising
outer and inner annular liners and an exit duct at a downstream
end, the exit duct circumscribing an annular combustor exit opening
defining a combustion gas path therethrough, the exit duct
including annular first and second exit duct walls radially spaced
apart to define therebetween the combustor exit opening, at least
one of the first and second exit duct walls having a double-skin
wall section at a most downstream end thereof, the double-skin wall
section including an inner hot wall facing said combustor exit
opening and an outer cold wall radially spaced away from the hot
wall to define a radial gap therebetween, the outer cold wall being
disposed outside of said combustion gas path, the inner hot wall
and the outer cold wall being fastened together by at least one
joint therebetween, the outer cold wall having a coefficient of
thermal expansion greater than that of the inner hot wall to
reducing thermal growth mismatch between the outer cold wall and
the inner hot wall during operation of the combustor and reduce
thermal stress at the joint.
[0004] There is also provided a combustor exit duct for a gas
turbine engine, the combustor exit duct comprising annular first
and second exit duct walls radially spaced apart to define
therebetween a combustor exit opening, at least one of the first
and second exit duct walls having a double-skin wall section at a
most downstream end thereof, the double-skin wall section including
an inner hot wall facing said combustor exit opening and an outer
cold wall radially spaced away from the hot wall to define a radial
gap therebetween, the outer cold wall being disposed outside of
said combustion gas path, the inner hot wall and the outer cold
wall being fastened together by at least one joint therebetween,
the outer cold wall having a coefficient of thermal expansion
greater than that of the inner hot wall to reducing thermal growth
mismatch between the outer cold wall and the inner hot wall during
operation of the combustor and reduce thermal stress at the
joint.
[0005] There is further provided a method of forming a gas turbine
engine combustor, the combustor having outer and inner annular
liners and an exit duct at a downstream end, the method comprising:
providing a first and a second annular wall of the exit duct which
circumscribe an annular combustor exit opening defining a
combustion gas path therethrough; forming a double-skin wall
section on at least one of the first and second annular walls of
the exit duct, by welding an annular outer cold wall flange to an
inner hot wall portion facing said combustor exit opening to form
an annular welded joint therebetween, the annular outer cold wall
flange being spaced apart from the inner hot wall downstream of
said welded joint to define a radial gap therebetween at a
downstream end of the double-skin wall section; and reducing
thermal stress at the welded joint between the outer cold wall
flange and the inner hot wall of the double-skin wall section by
forming the outer cold wall flange from a material having a
coefficient of thermal expansion that is greater than that of the
inner hot wall to thereby reducing thermal growth mismatch between
the outer cold wall flange and the inner hot wall.
[0006] Further details of these and other aspects of the present
invention will be apparent from the detailed description and
figures included below.
DESCRIPTION OF THE DRAWINGS
[0007] Reference is now made to the accompanying figures depicting
aspects of the present invention, in which:
[0008] FIG. 1 is a schematic cross-sectional view of a gas turbine
engine, partly fragmented, to show the location of the combustor
and its exit duct;
[0009] FIG. 2 is a fragmented cross-section view showing a portion
of the annular exit duct;
[0010] FIG. 3 is an enlarged view showing the construction of the
double-skin inner annular curved wall of the exit duct; and
[0011] FIG. 4 is a cross-section view of the outer annular curved
wall of the exit duct.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] Referring to the drawings and more particularly to FIG. 1,
there is schematically illustrated a gas turbine engine 10, which
is a turbofan in the depicted embodiment but may also be other
types of gas turbine engines, preferably adapted for use in an
aircraft and subsonic flight. The gas turbine engine 10 generally
comprises, in serial flow communication, a fan 12 through which
ambient air is propelled, a multi-stage compressor 14 which
pressurizes the air from the fan 12 and feeds it towards a
combustor 16 in which the compressed air is mixed with fuel and
ignited for generating an annular pressurized stream of combustion
gases which exits from a combustor exit duct 16' into a turbine
section 18 having turbine rotors 17 and 17' for extracting energy
from the combustion gases.
[0013] The combustor 16, and more particularly the combustor exit
duct 16' thereof, will now be described in further detail. As
described above, it is desirable to keep cool the
combustor-to-turbine transition duct portions but preferably
without introducing undue amounts of diluting cooling air flow into
the main combustion gas stream.
[0014] Accordingly, the combustor exit duct 16' of the presently
described combustor 16 includes a double-skin exit duct wall
configuration, which uses the coolant air flow twice, firstly by
impingement cooling and secondly by film cooling of the downstream
turbine section. As best seen in FIGS. 3 and 4, at least the cold
outer walls 24 and 37 of the short exit duct 29 and the long exit
duct 20 respectively therefore have impingement cooling holes 40
therein, which direct impingement cooling air flow through the cold
outer walls 24, 37 and onto the outer surface of the hotter inner
walls 23, 19. Once this cooling airflow has impinged on the outer
surfaces of the hotter inner walls 23, 19, it then flows downstream
and joins the main combustion flow gas path at the outlet of the
combustor exit duct 16' as film cooling airflow 42. Thus, this same
airflow acts to film cool the downstream surfaces, such as the
turbine vane platforms. In an alternate embodiment, one or both of
the walls or skins which make up the double-skin duct as described
herein may therefore have a plurality of cooling air holes therein,
such as film cooling holes, impingement cooling holes, effusion
cooling holes, etc.
[0015] This impingement/film cooling combination using a
double-skin duct configuration, however, requires the cooler outer
skin to be attached, such as by welding, to the hotter inner skin
adjacent the exit end of the combustor exit duct. If left
unchecked, this can lead to a thermal fight between the two skins
due to the different temperatures to which they are exposed,
thereby producing high thermal stresses at the joint (weld, braze,
fastening point, etc) interconnecting the two skins. This can cause
a reduced fatigue life. Accordingly, the present combustor duct
configuration, as will be described in further detail below,
provides a design which reduces the high thermal stress at the weld
junction between the two skins of the double-skin configuration. By
reducing the thermal fight between the double-skins, the fatigue
life of the weld junction can be greatly increased.
[0016] The combustor exit duct 16' as described herein includes at
least one double-skin wall section which is formed of two formable
metal sheets having different coefficients of expansion, thereby
greatly reduce the thermal fight between the two skins of the
double-skin wall section and thus reducing the thermal stress at
the weld joint between these two skins. This combination of welded
skins having respective low and high coefficients of expansion
allows the designer to have the options of (a) higher fatigue life
due to lower stress resulting from the lower thermal fight or for
the same fatigue life, (b) higher metal temperature gradient
between the two skins for the same fatigue life which results in
lower cooling flow and higher combustion performance, (c) thinner
skin for less weight and cost or (d) less expensive material.
[0017] Referring now to FIGS. 2 to 4, the combustor exit duct 16'
includes generally annular first and second exit duct walls which
are radially spaced apart to circumscribe and thus define
therebetween the annular exit opening 33 of the combustor 16. In
the depicted embodiment, wherein the combustor 16 is a reverse flow
combustor, the first and second exit duct walls of the combustor
exit duct 16' respectively comprise a Large Exit Duct (LED) portion
20 and a Small Exit Duct (SED) portion 23. The combustion gases
leave the combustor 16 via the annular exit end 33 and are fed into
the turbine section 18 disposed downstream therefrom. The LED 20
includes a curved annular wall 19 which is integrally formed at an
upstream end thereof with an outer wall 21 of the outer combustor
liner 22. Similarly, the SED 29 includes an annular curved wall 23
which is integrally formed at an upstream end thereof with an inner
wall 25 of the inner combustor liner 15.
[0018] At least one of the first and second exit duct walls, in
this embodiment the LED portion 20 and the SED portion 23, have a
double-skin wall section at a most downstream end thereof. As will
be seen, the double-skin wall section includes inner hot walls 19,
23 facing the combustor exit opening 33 and outer cold walls 37, 24
radially spaced away from the hot wall to define a radial gap 36,
32 therebetween. The outer cold walls 37, 24 are disposed outside
of the combustion gas path flowing through the combustor exit
opening 33, and are thus exposed to lower temperatures during
operation of the engine. The inner hot walls and the outer cold
walls are fastened together by at least one joint therebetween,
which may include an annular welded joint for example.
[0019] As can be see in FIGS. 2 and 3, the SED 29 includes a
double-skin wall section comprising an annular inner hot wall 23
facing the combustion chamber 28 and a spaced apart annular outer
cold wall 24, in the form of an annular flange wall, at least a
portion of which is radially spaced apart from the inner hot wall
23 at the downstream end thereof proximate the exit end opening 33
of the combustor exit duct 16'. An air gap or air plenum 32 is
defined between the inner hot wall 23 and the annular flange
forming the outer cold wall 24. The annular flange of the outer
cold wall 24 is fastened to the inner hot wall 23 of the SED 29 by
at least one joint 27. This joint between the inner hot wall 23 and
the outer cold wall 24 may be a welded or brazed joint, however
other fastening joints may also be possible. In at least the
depicted embodiment of FIG. 2, the joint 27 is disposed upstream of
the exit end 33 of the combustor exit duct 16' in a transition area
28.
[0020] Similarly, as best seen in FIGS. 2 and 4, the LED 20
includes an outer cold wall 37 at least a portion of which is
radially spaced apart from the inner hot wall 19 of the LED 20 at
the downstream end thereof proximate the exit 33 of the combustor
exit duct 16', such as to such as to define a radial air gap or air
plenum 36 between the hot inner wall 19 and the outer cold wall 37
of the LED 20. While in the embodiment described herein both the
LED 20 and the SED 29 are formed having such a double-wall or
double-skin construction, it is to be understood that in an
alternate embodiment, only one of these portions of the combustor
exit duct 16' may have such a construction (i.e. the other may be
simply formed of single liner wall).
[0021] Referring back to FIGS. 2 and 3, the annular flange of the
cold outer wall 24 of the SED 29 is, in at least one possible
embodiment, composed of a formable sheet metal of a type compatible
for joining with the sheet metal of the inner hot wall 23, such
that a high strength weld joint 27 can be formed therebetween near
the upstream transition area 28 as shown.
[0022] As the inner hot wall 23 is directed exposed to the hot
combustion gases within the combustor 16, it is subjected to higher
temperatures than the outer cold wall 24 which is both spaced apart
from the hotter inner hot wall 23 of the SED 29 and also exposed to
more cooling air disposed around the combustor. Accordingly, in
order to compensate for this temperature difference, the outer cold
wall 24 has a coefficient of thermal expansion that is higher than
the coefficient of thermal expansion of the inner hot wall 23 of
the SED 29. This acts to reduce the thermal imbalance in the double
skin wall which forms the SED 29 at the exit end 33 of the
combustor exit duct 16'. In other words, as the inner hot wall 23
heats up during operation of the combustor 16, the difference in
the coefficients of thermal expansion between the inner hot wall 23
and the outer cold wall 24 will result in both walls, or skins,
expanding at approximately the same rate and approximately the same
amount. Thus, the thermal growth of the two "skins" of the
double-skin SED 29 are more closely matched, as a result of this
mismatch in the coefficients of thermal expansion of the two walls
23 and 24.
[0023] This difference in thermal expansion may be achieved, for
example, by forming the inner and outer walls, or skins, 23 and 24
of the SED 29 out of different materials, such as two different
sheet metals for example, each having a different coefficient of
thermal expansion (i.e. the outer wall 24 expanding more at a given
temperature than the inner wall 23). Alternately, this difference
in thermal expansion between the two walls 23, 24 may be achieved
by other means, rather than by having different coefficients of
thermal expansion, for example by making the two walls of different
thickness or different material properties such as to achieve a
similar thermal growth match during operation of the engine, when
the inner wall 23 of the SED 29 is exposed to higher temperatures
than the outer wall 24 thereof.
[0024] In at least the depicted embodiment, the outer cold wall 24
is formed as an annular flange having a ring shape skin with an
outer flat portion 30 positioned against a planar section of the
combustor inner annular wall, where the weld joint 27 is formed.
The outer wall 24 also has a curved portion 31 which has a radius
of curvature different from the radius of curvature of the inner
wall 23 to form the annular gap or plenum 32 therebetween.
[0025] It at least one embodiment, the LED 20 is similarly
constructed with a double-skin wall section, as per the SED 29
described above. Referring now to FIGS. 2 and 4, as described above
the LED 20 includes an outer cold wall 37 at least a portion of
which is spaced apart from the curved annular inner hot wall 19 of
the LED 20 at the downstream end thereof proximate the exit 33 of
the combustor exit duct 16', such as to such as to define an air
gap or air plenum 36 between the annular wall 19 and the annular
flange wall 37 on a cold side of the wall 19 of the LED 20. The
outer cold wall 37 is joined to the main combustor wall which forms
the inner hot wall 19, such as by a welded joint for example, at
joint 38. The welded joint 38 may be disposed about the outer
surface 20' of the outer annular liner 21 and spaced from the exit
end 33. Much as per the SED described above, the outer cold wall 37
of the LED 20 has a coefficient of expansion which is higher than
the coefficient of expansion of the inner hot wall 19, such as to
reduce thermal growth mismatch in the double-skin wall arrangement
during operation of the combustor, and thus reducing the thermal
stress to which the welded joint between the hot and cold walls is
exposed.
[0026] The outer cold wall 37 is also formed from a formable metal
sheet of a type compatible for fastening, such as by a weld or
brace, to the inner hot wall 19. The outer cold wall 37 has an
outer portion 26 for connection to the outer liner 21 and an
outwardly offset wall section 37'. The radially extending annular
gap 36 is formed between an end section of said outer liner 21 and
the outwardly offset wall section 37'.
[0027] In one particular embodiment, the outer cold walls 24 and 37
may be formed from a Hastalloy X (registered trademark) sheet
metal, and the hot inner walls 19 and 23 are formed from one of
1N625, Haynes 188 and Haynes 230 sheet metals.
[0028] In an exemplary operating environment of the combustor 16,
the hot annular walls 19 and 23, of the LED 20 and the SED 29
respectively, which are directly exposed to the hot combustion
gases, are subjected to temperatures of at least 1650.degree. F.
The outer cold walls 37 and 24, of the LED 20 and the SED 29
respectively, are disposed in relatively cooler areas surrounding
the combustor, outside the main gas path, and are thus subjected to
lower temperatures of at least 800-1500.degree. F. This difference
in temperature would typically cause, in a double-wall construction
wherein the two skins are the same material, the hotter inner walls
to expand more than the cooler outer walls. In the combustor exit
duct 16' of the present combustor 16, the aforementioned
differential in the coefficients of thermal expansion between the
hot and the cold walls of the double skin liner construction
results in the two walls expanding approximately a similar amount,
thereby substantially compensating for the differential in
temperature during operation of the combustor. Accordingly, this
reduction of the thermal growth between the two walls results in
less stress being placed on the welded joints 27 and 38 between the
hot and cold walls of the double-wall construction.
[0029] 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 department from the scope of the
invention disclosed. Still 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 appended
claims.
* * * * *