U.S. patent application number 14/867424 was filed with the patent office on 2017-03-30 for single skin combustor heat transfer augmenters.
The applicant listed for this patent is Pratt & Whitney Canada Corp.. Invention is credited to SI-MAN AMY LAO, MICHAEL PAPPLE, SRI SREEKANTH.
Application Number | 20170089581 14/867424 |
Document ID | / |
Family ID | 57042683 |
Filed Date | 2017-03-30 |
United States Patent
Application |
20170089581 |
Kind Code |
A1 |
LAO; SI-MAN AMY ; et
al. |
March 30, 2017 |
SINGLE SKIN COMBUSTOR HEAT TRANSFER AUGMENTERS
Abstract
A combustor for a gas turbine engine comprises a single skin
liner defining a combustion chamber. The single skin liner has an
inner surface facing the combustion chamber and an outer surface
exposed to a coolant flow discharged in a plenum extending from the
outer surface of the single skin liner to the engine casing.
Cooling holes extend through the single skin liner. Open flow
guiding channels are provided on the outer surface of the single
skin liner, the open flow guiding channels being uncovered and
aligned with the flow of air over the outer surface of the single
skin liner.
Inventors: |
LAO; SI-MAN AMY; (TORONTO,
CA) ; SREEKANTH; SRI; (MISSISSAUGA, CA) ;
PAPPLE; MICHAEL; (VERDUN, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pratt & Whitney Canada Corp. |
Longueuil |
|
CA |
|
|
Family ID: |
57042683 |
Appl. No.: |
14/867424 |
Filed: |
September 28, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F23R 3/10 20130101; F23R
3/002 20130101; F23R 2900/03045 20130101; Y02T 50/60 20130101; F23R
3/06 20130101 |
International
Class: |
F23R 3/10 20060101
F23R003/10; F23R 3/00 20060101 F23R003/00 |
Claims
1. A single skin combustor for a gas turbine engine, the single
skin combustor comprising: a single skin liner defining a
combustion chamber, the single skin liner having an inner surface
exposed to the combustion chamber and an outer surface exposed to
an open-channel flow of air in a plenum circumscribed by a gas
generator case of the gas turbine engine, the outer surface of the
single skin liner being an outermost surface of the combustor,
cooling holes extending through the single skin liner, and open
flow guiding channels provided on the outer surface of the single
skin liner, the open flow guiding channels being uncovered and
aligned with the flow of air over the outer surface of the single
skin liner.
2. The single skin combustor defined in claim 1, wherein at least
some of the open flow guiding channels define a curve to in use
redirect a portion of the flow of air to a predetermined hot spot
region.
3. The single skin combustor defined in claim 2, wherein heat
transfer augmenters are provided in the hot spot region, the heat
transfer augmenters projecting from the outer surface of the single
skin liner.
4. The single skin combustor defined in claim 3, wherein the heat
transfer augmenters are selected from the group consisting of: pin
fins, fins, trip strips, dimples and knurled surfaces.
5. The single skin combustor defined in claim 1, wherein the open
flow guiding channels are defined between pairs of adjacent ribs
projecting from the outer surface of the single skin liner.
6. The single skin combustor defined in claim 5, wherein at least
some of the ribs are curved.
7. The single skin combustor defined in claim 5, wherein the ribs
are non-uniformly distributed on the outer surface of the single
skin liner to in use direct more air towards predetermined hot spot
regions of the single skin liner.
8. The single skin combustor defined in claim 5, wherein pin fins
project from the outer surface of the single skin liner downstream
from the ribs relative to the flow of air over the outer
surface.
9. The single skin combustor defined in claim 8, wherein a
circumferential row of fins extends from the outer surface of the
single skin liner downstream from the pin fins.
10. The single skin combustor defined in claim 9, wherein a
circumferential row of dilution holes is provided downstream of the
circumferential row of fins.
11. The single skin combustor defined in claim 3, wherein the heat
transfer augmenters are an extension of a base metal of the single
skin liner.
12. The single skin combustor defined in claim 11, wherein each
heat transfer augmenter comprises successive layers of sequentially
deposit material on a sheet metal base.
13. The single skin combustor defined in claim 3, wherein the
density of heat transfer augmenters varies over the outer surface
of the single skin liner.
14. A gas turbine engine comprising a gas generator case, a
combustor disposed within the gas generator case, the combustor
having a single skin liner circumscribing a combustion chamber, the
single skin liner and the gas generator case defining therebetween
a plenum, the single skin liner having an outer surface exposed to
a flow of air discharged in the plenum and an inner surface exposed
to combustion gases in the combustion chamber, cooling holes
defined in the single skin liner, the cooling holes fluidly liking
the plenum to the combustion chamber, and heat transfer augmenters
provided on the outer surface of the single skin liner, the heat
transfer augmenters including ribs configured to redirect the flow
of air from a first direction to a second direction.
15. The gas turbine engine defined in claim 14, wherein the ribs
are oriented towards a predetermined hot spot region of the single
skin liner.
16. The gas turbine engine defined in claim 15, wherein the heat
transfer augmenters further comprise turbulators in the
predetermined hot spot region, the turbulators projecting from the
outer surface of the single skin liner.
17. The gas turbine engine defined in claim 16, wherein the
turbulators are selected from the group consisting of: pin fins,
trip strips, dimples and knurled surfaces.
18. The gas turbine engine defined in claim 15, wherein the ribs
are curved.
19. The gas turbine engine defined in claim 14, wherein the heat
transfer augmenters further comprise a plurality of pin fins
downstream from the ribs relative to the flow of air over the outer
surface of the single skin liner, and a set of fins downstream from
the pin fins, the pin fins and the fins projecting into the
plenum.
20. The gas turbine engine defined in claim 14, wherein the single
skin liner is provided in the form of a metal sheet, and wherein
the heat transfer augmenters include free standing ribs projecting
from the outer surface of the metal sheet.
Description
TECHNICAL FIELD
[0001] The application relates generally to gas turbine engines
and, more particularly, to single skin combustor liner cooling.
BACKGROUND OF THE ART
[0002] Compared to double or multi-skinned combustors, a single
skin design has the potential to be lighter in weight and hence
lower in cost. However, current effusion cooled liner designs are
limited in efficiency due to manufacturing constraints such as hole
size and angle. Therefore, without increasing cooling air
consumption, additional heat removal is a challenge. In aviation
gas turbine engines, it is desirable that the amount of air
supplied for cooling combustor walls be minimized in order not to
negatively affect the overall performances of the engine. This
poses challenges to meeting the durability requirements of single
skin combustor walls, because the reduction in combustion wall
cooling air may lead to unwanted material oxidation, thermal
mechanical fatigue and/or thermal wall buckling due to thermal
gradients. Particularly in small aero gas turbine engines, the
total amount of air available for combustor wall cooling within the
gas turbine thermodynamic cycle can be limited, especially where
rich-burn combustion is sought. Therefore, it is a challenge to
optimize the combustor wall cooling while still meeting the
durability requirements of single skin combustors.
SUMMARY
[0003] In one aspect, there is provided a single skin combustor for
a gas turbine engine, the single skin combustor comprising: a
single skin liner defining a combustion chamber, the single skin
liner having an inner surface exposed to the combustion chamber and
an outer surface exposed to a flow of air, the outer surface of the
single skin liner being an outermost surface of the combustor,
cooling holes extending through the single skin liner, and open
flow guiding channels provided on the outer surface of the single
skin liner, the open flow guiding channels being uncovered and
aligned with the flow of air over the outer surface of the single
skin liner.
[0004] In another aspect, there is provided a gas turbine engine
comprising a gas generator case, a combustor disposed within the
gas generator case, the combustor having a single skin liner
circumscribing a combustion chamber, the single skin liner and the
gas generator case defining therebetween a plenum, the single skin
liner having an outer surface exposed to a flow of air discharged
in the plenum and an inner surface exposed to combustion gases in
the combustion chamber, cooling holes defined in the single skin
liner, the cooling holes fluidly liking the plenum to the
combustion chamber, and heat transfer augmenters provided on the
outer surface of the single skin liner, the heat transfer
augmenters including ribs configured to redirect the flow of air
from a first direction to a second direction.
DESCRIPTION OF THE DRAWINGS
[0005] Reference is now made to the accompanying figures in
which:
[0006] FIG. 1 is a schematic cross-section of a gas turbine
engine;
[0007] FIG. 2 is an enlarged cross-section view of a portion of the
combustor of the engine shown in FIG. 1 and illustrating a single
skin liner with a combination of different heat transfer augmenters
for guiding the incoming flow of cooling air and locally increasing
heat exchange surfaces on the cold outer side of the liner;
[0008] FIG. 3 is an enlarged cold side view illustrating the heat
transfer augmenters projecting from the outer surface of the single
skin combustor liner; and
[0009] FIG. 4 is a schematic conceptual isometric view illustrating
a flow field as modulated by a set of fins/ridges provided
immediately downstream from a jet impact site on the cold outer
surface of the single skin combustor liner; the impinging jet
nozzle is fictitious and provided to illustrate the concept not an
actual engine design .
DETAILED DESCRIPTION
[0010] FIG. 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 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.
[0011] The combustor 16 is a single skin combustor. That is the
combustor 16 has a single skin liner. According to one embodiment,
the single skin liner comprises a radially inner liner 20a and a
radially outer liner 20b concentrically disposed relative to a
central axis of the engine and defining therebetween an annular
combustion chamber 22. The radially inner and radially outer liners
20a, 20b may each be made from a single sheet of metal with through
holes defined therein for cooling purposes. In contrast, double or
multi-sheet liners have gaps of cooling air made by sandwiching two
or more sheets of metal or mounting heat shields on the inner
surface of a liner to maintain some form of air gap through which
cooling air may be guided to cool the innermost skin of the
liner.
[0012] A plurality of circumferentially spaced-apart nozzles (only
two being shown at 28) are provided at the dome end of the
combustor 16 to inject a fuel/air mixture into the combustion
chamber 22. Igniters (not shown) are provided along the upstream
end portion of the combustion chamber 22 downstream of the tip of
the nozzles 28 in order to initiate combustion of the fuel/air
mixture delivered into the combustion chamber 22. The inner and
outer liners 20a, 20b define a primary zone of the combustion
chamber 22 at the upstream end thereof, where the fuel/air mixture
provided by the fuel nozzles is ignited. The primary zone is
generally understood as the region in which the fuel is burned and
has the highest flame temperature within the combustor 16. The
combustor 16 also has a secondary zone, which is the region
characterized by first additional air jets to quench the hot
product generated by the primary zone; and a dilution zone
corresponding to the region where second additional jets quench the
hot product and profile the hot product prior to discharge to the
turbine section 18.
[0013] The combustor 16 is mounted in a plenum 17 circumscribed by
an engine casing 26 (e.g. a gas generator case). The plenum 17
extends from the single skin liner of the combustor 16 to the
engine casing 26. In other words, the single skin liner is an
outermost surface of the combustor 16. The single skin liner is
free of coverage in the plenum 17 (it is not surrounded/covered by
any flow guiding sleeve to form an air gap like in a double skin
design). The plenum 17 is supplied with compressor bleed air from
the compressor 14. Compressor exit tubes such as the one shown at
21 in FIG. 4, can be used to direct high momentum air cooling jets
onto the outer surface 36 of the combustor liner.
[0014] As illustrated in FIG. 2 in relation with the inner single
skin liner 20a, a plurality of cooling holes 30 are defined in the
inner and outer single skin liners 20a, 20b for allowing air in the
plenum 17 to flow through the liners 20a, 20b, thereby picking up
heat therefrom, and to then form a protective film of cooling air
over the inner or combustion facing surface 32 of the liners 20a,
20b. The amount of cooling that is required is typically higher in
the primary zone than in the secondary zone in the combustor.
Dilution holes 33 also extend through the inner and outer liners
20a, 20b in the secondary zone of the combustor 16. The dilution
holes 33 are not to be confused with the cooling holes 30. The
dilution holes 33 are used to introduce dilution air into the
combustion zone of the combustor 16. The dilution air quenches the
flames so as to control the gas temperature to which the turbine
hardware downstream of the combustor will be exposed. The quenching
also reduces the level of NOx emissions in the engine exhaust. The
dilution holes 33 are generally far smaller in number than the
cooling holes 30, and each dilution hole 33 has a cross-sectional
area that is substantially greater than the cross-sectional area of
one of the cooling holes 30. The dilution holes 26 are typically
arranged in a circumferentially extending row.
[0015] The compressor bleed flow discharged in the plenum 17
typically produces an uneven profile which causes some regions to
exhibit flow stagnation or recirculation and others to experience
flow separation. Specifically, for combustor cold side cooling, the
heat removal occurs mainly at the surface by means of forced
convection. Stagnation zones have a detrimental effect on this form
of heat transfer. Such detrimental effects can be minimized and
cooling efficiency thus improved by augmenting cold side surface
flow characteristics and enhancing heat transfer. This can be
accomplished by providing positive and/or negative material
features on the outer or cold side surface 36 of the single skin
liners 20a, 20b to channel and guide cooling flows into hotter
regions for enhanced cooling. For instance, heat transfer
augmenters, including various types of flow guiding structures and
flow heat transfer enhancement features, may be strategically
positioned on the cold outer surface or back side 36 of the inner
and outer liners 20a, 20b to guide the coolant flow in open
channels 37 (FIG. 4) to most thermally solicited regions of the
inner and outer liners 20a, 20b and provide additional cooling
thereat by increasing the surface area available for convection
cooling. As will be seen hereinafter, the open channel concept of
cold side heat transfer augmenters allow incident flow to approach
the combustor as it normally does but once it nears the outer
surface 36, diverts it towards much needed areas. Once it reaches
the desired areas, heat transfer promoting features such as
turbulators (e.g. pin fins) can be used to create a larger heat
transfer benefit. Open-channel flow may be defined as a type of
flow where the fluid is partially contained by a hard surface but
also has a free surface exposed (example: a river). Closed-channel
flow is where the fluid does not have any free surface and is fully
contained by the solid walls (example: a pipe). In this case, the
heat transfer augmenters are formed by a series of small ribs that
channel surface flow similar to a moat or a river. Since the
surfaces features (or channels) are so small compared to the casing
around the combustor, it is similar to open-channel flow. If one
were to take a cross-sectional tracing of the wall boundaries
containing the flow, 90 degrees to the streamline, an open-channel
would have an open profile (a line) whereas a closed-channel would
have a closed profile (a circuit).
[0016] Referring more particularly to the embodiment shown in FIGS.
2 and 3, it can be seen that the heat transfer augmenters may
comprise an upstream row of circumferentially distributed ribs 34
oriented to guide the upcoming flow of cooling air to an
intermediate band of circumferentially distributed pin fins 39
positioned upstream of a downstream circumferential row of ridges
or fins 38, which is in turn disposed upstream of the dilution
holes 33. It is understood that the illustrated combination of heat
transfer augmenters constitute only one possible combination and
arrangement of back side heat transfer augmenters that could be
used to guide the coolant flow and enhance heat transfer on the
cold outer side surface 36 of the single skin inner and outer
liners 20a, 20b. In the illustrated embodiment, the ribs 34, the
pin fins 39 and the fins 38 are all disposed in the primary zone of
the combustor 16. However, it is understood that similar cold side
heat transfer augmenters could be provided in the secondary zone of
the combustor as well.
[0017] The ribs 34 are aligned with the flow of air on the outer
surface 36 of the combustion liners 20a, 20b. The ribs may be
curved so that as the flow of air changes direction, the ribs
remain aligned. As best shown in FIG. 4, the adjacent ribs 34 form
open flow guiding channels 37 on the outer surface of the liners to
guide the flow to a desired location thereon. Depending on the flow
direction of the incoming air and on the location of the hotter
regions requiring additional cooling, the ribs 34 may be angled to
the axial direction or curved. Also, adjacent ribs 34 may be
non-uniformly spaced to vary the amount of cooling air being
channeled to differently thermally solicited regions of the
liner.
[0018] The pin fins 39 are typically provided on the hotter regions
of the liners 20a, 20b where additional cooling is required. The
pin fins 39 are disposed to receive the flow of air guided by the
upstream set of ribs 34. Other turbulators, such as trip strips,
could be used in place or in combination with the pin fins 39. The
downstream fins 38 can performed a flow guiding function as well as
heat exchange promoting function. As the ribs 34 they can be curved
or angled to direct the flow of cooling air coming from the pin
fins 39 in any desired direction over the outer surface 36 of the
liners 20a, 20b.
[0019] The ribs 34, the pin fins 39 and the fins 38 may each be
provided in the form of free-standing protrusions integrally
projecting from the outer surface 36 of the radially inner and
outer single skin liners 20a, 20b. Each of these features may be
integrally formed on the outer surface 36 of the liner by means of
additive manufacturing or other suitable manufacturing processes.
According to one embodiment, the cold side ribs 34, the pin fins 39
and the fins 38 are obtained as an extension of a base metal of the
single skin liner by laying down successive layers of the base
metal onto the outer surface of a sheet metal substrate.
[0020] It is understood that the ribs 34, the pin fins 39 and the
fins 38 could each have various configurations and geometries. For
instance, as shown in FIG. 4, the ribs 34 could include a
combination of straight and curved ribs 34a, 34b to provide for a
better distribution of the cooling air over the outer surface 36 of
the single skin liners 20a, 20b. Such ribs could be positioned to
receive and guide the flow of cooling air discharged by compressor
exit tubes 21 onto the outer surface 36 of the single skin liners
20a, 20b. The straight ribs 34a are centrally disposed relative to
the jet impact site, whereas the curved ribs 38b curve away from
the straight ribs 34a on opposed lateral sides thereof. As can be
appreciated from FIG. 4, the flow of incoming jet is captured and
the edges (lateral portions of the jet) are redirected sideways by
the curved lateral ribs 34b. The flow speed is maintained for a
longer distance from the jet impact site, which increases heat
transfer.
[0021] The heat transfer augmenters (ribs 34, the pin fins 39 and
the fins/ridges 38) could be distributed on a partial surface of
the single skin liner or over a full surface thereof. The heat
transfer augmenters are distributed so as to provide for a uniform
temperature distribution all around the combustor liners 20a, 20b.
For instance, the density of pin fins 39 (or other suitable
turbulators) could be greater in hot spot regions and less in
cooler regions of the combustor 16. Also, a greater concentration
of heat transfer augmenters can be provided in certain regions of
the combustor 16 where it is desirable to limit the quantity of
cooling air flowing into the combustor because the cooling air may
have a detrimental effect on the overall combustion process. For
instance, in some applications, it might be desirable to cut down
on the amount of cooling air directed into the primary zone of the
combustor 16 in order to maintain a rich fuel/air mixture ratio.
This may be achieved by reducing the density of cooling holes 30 in
the primary zone and correspondingly increasing the density of heat
transfer augmenters in this same primary zone so as to compensate
for the reduced number of cooling holes.
[0022] The heat transfer augmenters can be of uniform or
non-uniform height. Also, it is understood that a combination of
different shapes and kind of heat transfer augmenters could be
provided on the cold outer surface 36 of a same single skin liner
20a, 20b. In fact, various combinations of sizes, distributions and
dimensions are possible.
[0023] In use, the compressor bleed air is discharged into the
plenum 17 with significant momentum. A significant portion of this
momentum is converted to static pressure upon encountering the
combustor liner, prior to entering the combustion chamber 22. The
heat transfer augmenters (the ribs 34, the pin fins 39 and the fins
38) are passive features that utilize some of the air momentum
before it gets converted. The air is captured in the open channels
37 formed between the ribs 34 and is guided and redistributed over
the outer surface 36 of the liners 20a, 20b to promote a more
uniform temperature thereover. It allows to augmenting the local
flow such that the heat transfer coefficient is higher where it is
needed. The air flowing through the guiding channels 37 between the
ribs 34 is directed at least in part to the pin fins 39, which are
provided in the hot spot regions to enable higher heat transfer
efficiency in the most thermally solicited regions of the combustor
liner. In this way, the risk of having over-cooled and under-cooled
regions may be reduced. It provides for a more uniform temperature
distribution around the combustor liner. The cooling air leaving
the pin fins 39 is then received and guided by the fins 38. As the
air flows in the open channels defined between adjacent fins 38, it
picks up heat from the fins . As mentioned hereinbefore, the fins
may be curved and/or appropriately oriented relative to the flow of
cooling air to guide the air to a desired location before it
reaches the row of dilution holes 33.
[0024] From the foregoing, it can be appreciated that the cold side
heat augmenters allow the designer to reduce hot spots, improving
both the thermal mechanical and oxidation life of the part. This is
all done without the need to increase cooling air consumption;
thereby minimizing the impact on combustor and overall engine
efficiency.
[0025] The air guided on the outer surface 36 of the liners 20a,
20b has a second opportunity to cool the liners 20a, 20b by flowing
through the cooling holes 30. Indeed, as the air flows through the
cooling holes 30, it cools the liners 20a, 20b by in-hole heat
transfer. At its exits from the cooling holes 30, the air flows
over the inner or hot combustion facing surface 32 of the liners
20a, 20b, thereby providing for the formation of a protective
cooling film thereover. Accordingly, with the addition of the heat
transfer augmenters on the cold side of the liner, the air has
several opportunities to cool down the liner. Multiple usage of the
same cooling air provides for improved cooling efficiency. In this
way, single skin combustors may be used in high temperature
applications where double skin combustor designs would have
typically been retained. Also, since the heat transfer augmenters
are located on the cold side of the combustor liner, they are not
exposed to the hot combustion gasses and are, thus, less subject to
erosion over time. This provides for a more robust design.
[0026] While cold side heat transfer augmenters have been mainly
described in connection with positive material features (e.g.
ridge, ribs, fins and pin fins), it is understood that they could
also take the form of negative material features. For instance,
dimples could be formed in the outer surface 36 of the liner to act
as turbulators. The open channels between the ribs could take the
form of closed bottom grooves or slots machined or otherwise
suitably formed in the outer surface 36 of the liners 20a, 20b.
Surface knurling could also be used to form heat transfer augmenter
patterns of various configuration (e.g. star pattern, fan pattern)
in the outer surface 36 of the liners 20a, 20b.
[0027] 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 instance, the same principle could be
applied to a combustor can. Any 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.
* * * * *