Note: Descriptions are shown in the official language in which they were submitted.
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CO~ STOR~LIN~R WIT~ DUAL FUNCTION
COOLING AIRFLOW
BACKGROUND OF THE- INVENTION
.. ..
Field of the Invention
This invention reIates to combustor liners for gas
turbine'engines an~ more particularly to ~hose combustor
liners that provide dilution airflow into the combustion
zone.
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Background of the~Related Art
Increased efficiency in gas turbine engines is
accomplished, in part, by an increase in the operating
temperatures wit~in the engine's combustor~ In order
to withstand these higher temperatures within an
acceptable operating life term, it is necessary not only
to use highIy sophisticated alloys and materials, but to
provide an e~ficient and reliable means for cooling liners
of the combustion chambers.
One oE the efficient techniques for cooling the
combustor liner is that of ~ilm convection cooling. A
, protective film boundary o cool air is direct~d to flow
along an inner surface of a combustor liner so as to
insulate the liner from the adjacent hot gases of com-
bustion. The cooling air film not only forms a pro-
tective barrier between the liner and the hot gases, but
it also provides convective cooling of the liner itself.
The air thàt is employed in this manner can be described
as combustor liner film cooling air.
In addition to film cooling the combustor liner,
compressed air discharged from ~he en~ine's compressor
is also directed through the combustor liner to the
interior of the combustor for the purpose of providing
oxygen for the combustion processes occurring inside the
combustor. Significant volumes o air must be directed
into the cQmbustor along the full length of the combustor
structure in order to support the process of combustion.
Air used in this manner is referred to as dilution flow
air.
One fairly common way of introducing this dilution
~low air has been the use of relatively large radius dilution
flow apertures. Th~se apertures are usually constructed in
the form of tube members that extend through the entire
length of the combustor liner.
One of the problems with current use of dilution
flow apertures is that large amounts of compressed air are
drawn into the combustor through a flowpath that does not
fully utilize the cooling potential of the compressor
2~ discharge air. Substantial work has been expended to
compress this air so it is very desirable to use this air
in the most efficient way possible.
Therefore, it is an object of the present invention
to provide a combustor liner structure that better utilizes
X5 the useul ~roperties of dilution flow air.
It is another object of the present invention to
utilize dilution flow air for additional purposes in the
~rocess o entexing the zone of combustion.
. . .
S~M~Y OF THE INVENTION
In accordance with one embodiment of the present
invention, compressed air drawn from a region surrounding
the`combustor is utilized for at least two separate
purposes. First, the air is drawn through an outer
combustor liner for impingement coolin~ of co~bustor
inner liner segments. Second, a portion of the air uti~lized
for impingement cooling the inner liner thereafter flows
through dilution holes for dilution flow into the combustor
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chamber. In addition, the remaining portion of the air
originally used for impingement cooling can also be
directed through film cooling holes for film cooling
the inner walls of the combustor inner liner segments.
The compressed air can be used in ~hese separate ways
because of a novel combustor liner construction wherein
the inner and outer liner are separated by a space where
the compressed air forms an impingement blanket between
the two liners. The blanket of air serves as a source
for dilution flow and can also be a source of film cooling
air.
DESCRIPTION OF THE DRAWINGS
While the specification concludes with a series
of claims that particularly point out and distinctly claim
the subject matter comprising the present invention, a
clear understanding of the invention is available from the
following description, in conjunction with the accompanying
drawings.
Fig. l is a schematic representation, partly in
cross section and partLy broken away, of a gas turbine
engine in which the present invention might be utilized.
Fig. 2 is a cross-sectional schematic illustra~ion
o a typical combustor from a gas turbine engine.
Fig. 3 is a cross-sectional schematic represent-
2$ ation of one embodiment of the present invention asincorporated in a gas turbine engine combustor.
DESCRIPTION OF ~ PREFERRED E~BODIMENT
Referring now to Fig. l, a typical gas turbine
en~ine 10 is shown for the purpose of describi~g the
3Q functions of components within that engine. The engine
10 includes an outer housing ll having an inlet end 12
for receiving ambient air into a multi-stage axial flow
compressor 14. The compressor 14 includes rows of
rotating compressor blades 16 interspersed between rows
of non-rotating stator vanes 18. The rotating compressor
blades 16 serve to compress the inlet air which, after
undergoing compression, is discharged at a downstream end
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of the compressor 14 through a row of compressor outlet
guide vanes 20, followed by an annular diffuser indicated
generally at 22. The diffuser 22 discharges the pressur-
ized compressor discharge air into a region su~rounding
a combustor 30l indicated generally at 28.
Portions of this compressed air in the region
28 surrounding a combustor 30 are directed into the
combustor 30 where they are combinea with fuel and ignited
to form hig~-pressure, high-velocity combustion gases.
The combustion gases are directed at high ~elocity into
a turbine section 32. The turbine section extracts work
from the high-pressure combustion gases to drive the
rotating blades of the compressor 14 by means of a
connecting shaEt 34. In addition, -the turbine section 32
may extract additional work from the combustion gases for
the purpose of driving a shaft providing mechanical power
for whatever purpose the user of the engine desired. As
an example, the mechanical power shaft might power a
rotating helicopter blade (not shown~ or a propeller (also
not shown), or any of a variety of othex uses. ~fter
passing through the turbine section 32 the combustion gases
can be discharged into the atmosphere through an engine
nozzle 38 thereby providing forward thrust to the engine 10.
The basic principals of gas turbine engines,
-their yeneral structure, and operation are well known to
those skilled in the art. The engine shown in Figure 1
is a turbojet variety, however, it should be understood
that the present invention is applicable to any gas
~uxbine engine. The engine 10 is described to promote
the reader's understanding of the use~ulness of the
present invention in a gas turbine engine environment.
Referring now to Figure 2, a combustor 30 of a
variety that might be employed in a typical gas turbine
engine, such as the one shown in Figure 1, is shown for
the purpose of describing airflow from the region 28
surrounding t~e combustor into the combustor its~lf.
The air in the region 2~ surrounding the combustor 30 is
highly compressed because it has been discharged from
a compressor (not shown). It is also relatively cool in
respec-t to temperatures inside the combustor where the
combustic,n process occurs during engine operation.
The air discharged from the compressor 30, also
known as compressor discharge air, it utilized for both
supporting the combustion process and ~or cooling the
combustor structure itself.
Fuel is injected into the combustor 30 through a
fuel in~ector 40 as a fine stream of droplets that easily
mixes with compressed air to form a combustible mixture.
Compressor discharge air enters the combustor through a
variety of orifices in the combustor structure. At its
upstream end, the combustor 30 has a dome 42 provided with
inlet air holes 44 that provide impingement cooling of a
dome flange 46.
Moving in the downstream direction, film cooling
holes 48 direct compressed air into the combustor in the
2~ form o a thick film that flows along inner walls 50 of the
combustor structure. Further downstream, dilution air
is introduced through dilution apertures 52. The purpose
of this dilution air is to reed the combustion processes
occurring wikhin an inner chamber 54. The high-pressure
hi~h-velocity combustion gases flow downstrea~l throu~h a
combustor outlet 56 into a turbine section (not shown).
It can be readily appreciated by the reader that
the compressor discharge air introduced into the combustor
through the dilution apertures 52 is used solely Eor
the function of providing air to support the combustion
processes.
Referring now to Figure 3~ the present invention
i5 shown as it might be employed in a typical combustor
30. As in most combustors, a fuel injection 40 is provided
at an upstream end for injecting a fine spray of fuel into
an inner chamber 54 of the combustor 30~ Inside the
chamber 54 the fine spray of fuel mixes with air and is
ignited to form the high-pressure, high-temperature
combustion gases that flow downstream out o~ a
combustor outlet 56. At its upstream end, the combustor
takes the shape of a dome 42. The dome ~2 is provided
with inlet air holes 44 for impingement cooling of a dome
flange 460 Moving downstream~ a first row of film cooling
air holes 48 are used to direct a film of cooling air along
inner walls of the combustor for film cooling thereof. Up
to this point, the description of combustor 30 shown in
Figure 3 is similar to typical prior art combustors.
Downstream of a first xow 49 of film cooling
holes, the combustor has a liner structure 58 that is
unique and utilizes dilution air in a new and useful
manner. The liner 58 includes an outer liner wall 60
that is generally configured in a cylindrical shape
around the enginels center line so as to define the basic
confines o~ the combustor 30. A plurality of outer liner
cooling air holes 62 are distributed in the outer liner
wall 60 thereby providing access for compressor discharge
air from the region 2B surrounding the combustor to flow
through the outer liner wall 60. This compressed air
flowing through the outer liner cooling air holes 62
provides impingement cooling ~or one or more inner liner
wall segments 64. The inner liner wall segments 64 are
spaced radially in respect to the outer liner wall 60
thereby forming a space wherein an impingement blanket 66
Eorms of cooling air. The impingement blanket 66 serves
~o continuously cool the inner liner segments 6~. The
spacin~ is structurally ~ormed by circumferential ridges
7~ that are part of the inner wall segments 64. The
ridges 7~ abut the outer liner wall 60.
The air that forms the impingement blanket 66
thereafter can be utilized in two different ways. A
portion of the impingement blanket air can be directed
through dilution flow holes 6B to provide a substantial
source o~ air to support combustion processes occurring
inside the combution chamber 54. The remaining portion
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of the air in the impingement blan~et 66 can be directed
through secondary film cooling holes 70 to form a film of
cooling air along inside walls of the inner liner wall
segments 64.
Wi~h this unique combustor liner structure,
compressed air in the region 28 surrounding the
combustor 30 can be utili~ed to perform either two or
three separate and distinct functions. First, the
compressed air is utilized for impingement cooling of
the combustor inner liner wall segements 64. Secondly,
this same air utilized for impingement cooling can be
utilized for dilution flow into the combustor chamber
54 and/or thirdly, for film cooling inner liner wall
3egmentR 64. Therefore, the air forming the impingement
blanket accomplishes at least two functions and can
potentially accomplish three functions.
An alternate arrangement is shown at a
downstream section of the combustor 30 where impingement
air is utilized for impingement cooling and dilution
10w only. This alternate embodiment of the present
invention is useful in segments of combustors where
film cooling of inner walls is no longer as desirable.
One of the highly useful features of the
present invention is that the potential coolin~ propexties
o:~ dilution flow air are utilized for the purpose of
i~pingement cooling of: inner liner wall segments 64 of
t~e combustor 30. This function is desirable in present-
da~ combustors where combustion temperatures ca~ exceed
3000 degrees Fahxenheit (1649 degreescelsius) and can
be very harmful to combustor materials.
In one embodiment of the present invention
shown in Figure 3, a general flow distribution of cooling
air can be described in the following manner. Of the
total quantity (I00 percent) of air flowing into the
combustor inner chamber 54, approximately 30 percent of
-this quantity of air flows through the fueI injector 40
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and the dome inlet holes 44 in the dome 42 and approximately
another lO percent of this air flows through the first row
~9 of film cooling holes. The remaining 60 percent of this
quantity of air is utilized for impingement cooling to form
the impingement blanket 66.
From the impingement blanket 66, approximately
2/3 (or about 40 percent of the total quantity of inner
chamber air) is utilized for dilution flow through the
dilution holes 68 and the remaining 1~3 (or about 20
percent of the total quantity of inner chamber air) is
utilized as film cooling air directed through the
secondary film cooling holes 70.
It is to be understood that all of these
percentages are only approximate and can be varied
substantially while still performing the functions
of the present invention.
As an example, in an embodiment of the present
invention, a combustor liner might be utilized wherein
none of the impingement blanket air is utilized for film
cooling and all of it is directed through dilution air
holes as dilution flow air.
While a preferred and an alternate embodiment
of -the present invention have been described for purpose~
o~ descrip~ion, it shall be understood that modifica-tions
and variations will occur to those skilled in the art
which do not depart from the scope of the invention as
set orth in the appended claims.
