BACKGROUND
The subject matter disclosed herein relates generally to bleed air systems for gas
turbine engines, and, more specifically, to bleed air systems capable of providing
pressure drops, acoustic improvements, and desirable flow properties.
In a gas turbine engine, air is pressurized in a compression module. The air
channeled through the compression module is mixed with fuel in a combustor and
ignited, generating hot combustion gases, which flow through turbine stages that extract
energy therefrom for powering the fan and compressor rotors and generate engine thrust
to propel an aircraft in flight or to power a load, such as an electrical generator.
In some gas turbine engines, a portion of the high-pressure air, such as, for
example, bleed air from a compressor, may be extracted or bled from the compressor for
various needs. These needs include, for example, compressor flow bleeding which may
be used to improve operability as well as to provide turbine cooling, bearing sump
pressurization, purge air, or aircraft environment control. The air may be bled off from
the compressor using bleed slots located over specific portions or stages of the
compressor.
In at least some gas turbine engines, during engine operation occurring in some
operating conditions, the compressor may pump more air than is required for needs
including the combustion process. In order to manage operability of the engine and
combustion performance, a portion of the excess bleed air from the compressor may be
routed through bleed conduits and exhausted into the bypass flow stream, engine exhaust,
or to ambient. The pressure and temperature of the air stream bled from the compressor
may be very high. For example, bleed air pressure may be greater than about 1375 kPa
and the bleed air temperature may be greater than about 538 degrees C. A transient bleed
valve system (TBV) system andlor a variable bleed valve (VBV) system is sometimes
used for bleeding and exhausting the air removed from the compressor. For example, the
exhaust area of some conventional bleed systems may be oversized to lower the flow
velocity at the exhaust location to assure that the acoustic requirements are met for the
application. The exhaust area, as well as the expansions between the source pressure and
exhaust, may contribute to the large size andor weight of these systems.
I In addition, some exhaust designs on aircraft may require extensive thermal
shielding on other components near the exhaust location,. Due to the nature of the high
temperature and high pressure air, once it is discharged into the flow path, it may
overwhelm the flowpath stream, causing the bleed air to impinge on the surrounding
structure around the engine. In some aircraft, the surrounding structure may be made of
lightweight composite material or of other metallic material with lesser temperature
capability.
The problem: In some applications (e.g., aircraft), it may be necessary to direct
bleed air flow into the bypass stream to avoid thermal damage to bypass duct
components.
BRIEF DESCRIPTION
At least one solution for the above-mentioned problem(s) is provided by the
present disclosure to include example embodiments, provided for illustrative teaching
and not meant to be limiting.
An example louver system for a gas turbine engine bleed system according to at
least some aspects of the present disclosure may include a bleed system discharge
opening arranged to vent bleed air from a bleed flow conduit andor a plurality of
pivotable louvers disposed proximate the discharge opening, the pivotable louvers being
pivotable between a shut position and an open position. In the shut position, individual
louvers may at least partially obstruct the discharge opening. In the open position,
individual louvers may at least partially control a direction of flow of the bleed air exiting
the discharge opening.
An example gas turbine engine according to at least some aspects of the present
disclosure may include a compressor; a combustor arranged to combust fuel in
compressed air received from the compressor; a turbine configured to receive hot,
pressurized gas from the combustor and to drive the compressor; a bleed conduit
arranged to receive bleed air from the compressor; andlor a louver system operatively
coupled to the bleed conduit. The louver system may include a plurality of louvers
disposed in a discharge opening, the plurality of louvers being pivotable between a shut
position and an open position.
An example method of operating a bleed system associated with a gas turbine
engine according to at least some aspects of the present disclosure may include receiving
a flow of bleed air from a compressor of a gas turbine engine at a discharge opening;
pivoting a plurality of louvers disposed in the discharge opening from a shut position to
an open position; discharging the flow of bleed air through the discharge opening; and
directing the flow of bleed air through the discharge opening using the plurality of
louvers.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter for which patent claim coverage is sought is particularly
pointed out and claimed herein. The subject matter and embodiments thereof, however,
may be best understood by reference to the following description taken in conjunction
with the accompanying drawing figures in which:
FIG. 1 is a schematic cross-sectional view of a gas turbine engine
including an example louver system;
FIG. 2 is a cross-sectional view of an example louver system in an open
position;
FIG. 3 is a cross-sectional view of an example louver system in a shut
position;
FIG. 4 is a plan view of an example louver system;
FIG. 5 is a cross-sectional view of an example louver system including a
first connecting rod and a second connecting rod;
FIG. 6 is a plan view of an example louver system including louvers with
scalloped or chevron trailing edges;
FIG. 7 is a perspective view of an example louver including a grooved
trailing edge; and
FIG. 8 is flow chart of an example method of operating a bleed system
associated with a gas turbine engine, all in accordance with at least some aspects
of the present disclosure.
DETAILED DESCRIPTION
In the following detailed description, reference is made to the accompanying
drawings, which form a part hereof. In the drawings, similar symbols typically identify
similar components, unless context dictates otherwise. The illustrative embodiments
described in the detailed description, drawings, and claims are not meant to be limiting.
Other embodiments may be utilized, and other changes may be made, without departing
from the spirit or scope of the subject matter presented here. It will be readily understood
that the aspects of the present disclosure, as generally described herein, and illustrated in
the figures, can be arranged, substituted, combined, and designed in a wide variety of
different configurations, all of which are explicitly contemplated and make part of this
disclosure.
The present disclosure includes, inter alia, gas turbine engines, bleed air systems,
and methods of operating bleed air systems.
FIG. 1 is a schematic cross-sectional view of a gas turbine engine (GTE) 10
including an example louver system 100, according to at least some aspects of the present
disclosure. GTE 10 may include a bleed system 40, which may incorporate louver
system 100. GTE 10 may include a core gas turbine engine 12 that includes a highpressure
compressor 14, a combustor 16, and/or a high-pressure turbine 1 8. GTE 10 may
also include a low-pressure compressor 19, a low-pressure turbine 20, andlor a fan
assembly 22.
In operation, air may flow through fan assembly 22. A portion of the air
discharged from fan assembly 22 may be channeled to high-pressure compressor 14,
where it may be further compressed and channeled to combustor 16. Products of
combustion from combustor 16 may be utilized to drive high-pressure turbine 18 and/or
low-pressure turbine 20. Another portion of the air discharged from fan assembly 22
may bypass core gas turbine engine 10 andlor may be referred to as a bypass flow stream
4.
At some operating conditions, a portion of the compressed air produced by highpressure
compressor 14 may be routed through bleed system 40, thereby becoming bleed
air 2. Bleed air 2 from high-pressure compressor 14 may enter a bleed flow conduit 44.
Bleed air 2 may pass through bleed flow conduit 44, a muffling device 46, andlor louver
system 100, which may direct bleed air 2 into a flow path, such as the bypass flow stream
4. Bypass flow stream 4 may flow through a duct at partially defined by bypass duct
walls 148, 149. Flow of bleed air 2 through bleed flow conduit 44 may be controlled by
a transient bleed valve 45.
In some example embodiments, transient bleed valve 45 may fluidicly interpose
compressor 14 and bleed conduit 44. Muffling device 46 may fluidicly interpose bleed
conduit 44 and discharge opening 48. An example muffling device 46 that may be used
in connection with louver systems of the present disclosure is described in co-pending
U. S. Patent Application No. , filed on even date herewith, which is
titled "HIGH BLEED FLOW MUFFLING SYSTEM," and which is incorporated herein
by reference.
Louver system 100, described in more detail below, may be in flow
communication with bleed flow conduit 44 such that bleed air 2 is discharged as exit flow
stream 5 into bypass flow stream 4. Louver system 100 may direct exit flow stream 5
andlor may facilitate mixing of exit flow stream 5 and bypass flow stream 4. Some
example embodiments may include one or more structures configured to assist in
controlling exit flow stream 5, such as an aero chimney, as described in U.S. Patent
Application Publication No. 201 110265490, which is incorporated herein by reference.
FIG. 2 is a cross-sectional view of an example louver system 100 in an open
position, according to at least some aspects of the present disclosure. FIG. 3 is a crosssectional
view of an example louver system 100 in a shut position, according to at least
some aspects of the present disclosure. Louver system 100 may be disposed proximate a
bleed system discharge opening 48, which may be arranged to vent bleed air from a bleed
conduit 44. Louver system 100 may include a plurality of louvers 102, 104, 106, 108,
1 10, 1 12, which may pivotably disposed, such as by pivot pins 1 14, 1 16, 1 18, 120, 122,
124, respectively.
, Louvers 102, 104, 106, 108, 1 10, 1 12 may comprise respective trailing edges 150,
152, 154, 156, 158, 160. In some example embodiments, trailing edges 150, 152, 154,
156, 158, 160 may be located generally opposite pivot pins 1 14, 1 16, 1 18, 120, 122, 124,
respectively. Pivot pins 114, 116, 118, 120, 122, 124 may be generally upstream and
trailing edges 150, 152, 154, 156, 158, 160 may be generally downstream with respect to
bleed air 2 andfor exit flow stream 5.
Louvers 102, 104, 106, 108, 110, 112 may be pivotable between an open position
(e.g., FIG. 2) and a shut position (e.g., FIG. 3). In an example open position, individual
louvers 102, 104, 106, 108, 1 10, 1 12 may at least partially control a direction of exit flow
stream 5 of bleed air 2 exiting discharge opening 48. For example, when open, louvers
102, 104, 106, 108, 1 10, 1 12 may direct exit flow stream 5 generally upward and to the
right in FIG. 2. An example louver system 100 installed in a turbofan aircraft engine
may be configured to use louvers 102, 104, 106, 108, 1 10, 1 12 to direct exit flow 5
generally away from bypass duct walls 148, 149 (FIG. 1).
In an example shut position, individual louvers 102, 104, 106, 108, 1 10, 1 12 may
at least partially obstruct discharge opening 48. In the shut position, the plurality of
louvers 102, 104, 106, 108, 1 10, 1 12 may substantially obstruct discharge opening 48. In
some example embodiments, such as in aircraft turbofan engines, substantially
obstructing discharge opening 48 when shut may enable louvers 102, 104, 106, 108, 110,
112 to prevent acoustic effects (e.g., whistling) andlor undesirable flow effects that may
be caused by a substantially open discharge opening 48 with substantially no exit flow
stream 5.
In some example embodiments, louver system 48 may include a connecting rod
126 operatively coupled to two or more individual louvers 102, 104, 106, 108, 1 10, 1 12.
Some example embodiments may include more than one connecting rod (see, e.g., FIG.
5). Returning to FIGS. 2 and 3, connecting rod 126 may be pivotably connected to
louvers 102, 104, 106, 108, 110, 112 by pivot pins 128, 130, 132, 134, 136, 138.
Connecting rod 126 may provide substantially coordinated pivoting of louvers 102, 104,
106, 108, 1 10, 1 12. For example, louvers 102, 104, 106, 108, 1 10, 112 may pivot
between open and shut positions in a substantially coordinated manner.
In some example embodiments, louver system 100 may include an open position
stopper 140, which may be arranged to limit pivoting of one or more of louvers 102, 104,
106, 108, 110, 112 in an opening direction 142 (e.g., FIG. 3). For example, open position
stopper 140 may directly limit pivoting of louver 102 in opening direction 142 by
impeding rotation of louver 102 beyond a predetermined amount. Louvers 104, 106, 108,
1 10, 112 may also be limited in pivoting in opening direction 142 by louver 102
contacting open position stopper 140 because louvers 102, 104, 106, 108, 1 10, 1 12 may
be linked together by connecting rod 126.
In some example embodiments, louver system 100 may include a shut position
stopper 144, which may be arranged to limit pivoting of one or more of louvers 102, 104,
106, 108, 110, 112 in a shutting direction 146 (e.g., FIG. 3). For example, shut position
stopper 144 may directly limit pivoting of louver 112 in shutting direction 146 by
impeding rotation of louver 1 12 beyond a predetermined amount. Louvers 102, 104, 106,
108, 1 10 may also be limited in pivoting in shutting direction 146 by louver 112
contacting shut position stopper 144 because louvers 102, 104, 106, 108, 1 10, 1 12 may
be linked together by connecting rod 126 and/or because louvers 102, 104, 106, 108, 1 10
may lie against louvers 104, 106, 108, 1 10, 1 12, respectively, in the shut position.
Some example embodiments according to at least some aspects of the present
disclosure may include more than one open position stopper 140 and/or more than one
shut position stopper 144 (e.g., FIG. 3). An example embodiment may include open
position stoppers 140 and/or shut position stoppers144 associated with individual louvers
102, 104, 106, 108, 110, 112 andlor with groups of louvers 102, 104, 106, 108, 110, 112.
In some example embodiments, louvers 102, 104, 106, 108, 1 10, 1 12 may pivot
from the shut position to the open position upon receiving bleed air 2 flow from
compressor 14. For example, a pressure differential across shut louvers 102, 104, 106,
108,110,112 may cause louvers 102,104,106,108,110,112 to open. Upon
substantially stopping the flow of bleed air 2 from compressor 14, louvers 102, 104, 106,
108, 1 10, 1 12 may pivot from the open position to the shut position. Louvers 102, 104,
106, 108, 1 10, 1 12 may remain in the shut position during conditions when there is
substantially no bleed air 2 flow.
FIG. 4 is a plan view of an example louver system 100, according to at least some
aspects of the present disclosure. In some example embodiments, trailing edges 150,
152, 154, 156, 158, 160 may be generally straight andlor may include rounded peripheral
corners.
FIG. 5 is a cross-sectional view of an example louver system 200 including a first
connecting rod 226 and a second connecting rod 227, according to at least some aspects
of the present disclosure. Louver system 200 may be mounted in bleed system discharge
opening 48. Louver system 200 may include a plurality of louvers 202,204,206,208,
2 10,2 12, which may pivotably disposed, such as by pivot pins 2 14,2 16,2 18,220,222,
224, respectively.
Louvers 202,204,206,208,210,212 may comprise respective trailing edges 250,
252,254,256,258,260 (e.g., FIG. 5). In some example embodiments, trailing edges
250,252,254, 256,258,260 may be located generally opposite pivot pins 214,216,218,
220,222,224, respectively. Pivot pins 214,216,218,220,222,224 may be generally
upstream and trailing edges 250,252,254,256,258,260 may be generally downstream
with respect to exit flow stream 5.
Generally similar to louver system 100, louvers 202,204,206, 208, 210, 212 of
louver system 200 may be pivotable between an open position (e.g., louvers 202,204,
206) and a shut position (e.g., louvers 208,210,212) (e.g., FIG. 5). In an example open
position, individual louvers 202,204,206,208,210,212 may at least partially control a
direction of exit flow stream 5 of bleed air 2 exiting discharge opening 48. For example,
when open, one or more louvers 202,204,206,208,210,212 may direct exit flow stream
5 generally upward and to the right in FIG. 5. An example louver system 200 installed in
a turbofan aircraft engine may be configured to use one or more louvers 202,204,206,
208, 210,212 to direct exit flow 5 generally away from bypass duct walls 148, 149.
In an example shut position, individual louvers 202, 204, 206, 208,210,212 may
at least partially obstruct discharge opening 48. In the shut position, the plurality of
louvers 202, 204,206,208,210,212 may substantially obstruct discharge opening 48.
In some example embodiments, first connecting rod 226 may be operatively
coupled to two or more individual louvers 202,204,206 comprising a first group 262 of
louvers andlor second connecting rod 227 may be operatively coupled to two or more
individual louvers 208, 2 10,2 12 comprising a second group 264 of louvers (e.g., FIG. 5).
First connecting rod 226 may be pivotably connected to louvers 202,204,206 by pivot
pins 228,230,232. First connecting rod 226 may provide substantially coordinated
pivoting of first group 262 of louvers. For example, louvers 202,204,206 may pivot
between open and shut positions in a substantially coordinated manner. Second
connecting rod 227 may be pivotably connected to louvers 208,2 10,2 12 by pivot pins
234,236,238. Second connecting rod 227 may provide substantially coordinated
pivoting of first group 264 of louvers. For example, louvers 208,210,212 may pivot
between open and shut positions in a substantially coordinated manner.
In some example embodiments, louver system 200 may include an open position
stopper 240, which may be arranged to limit pivoting of one or more of louvers 202,204,
206,208,210,212 in an opening direction 242. For example, open position stopper 240
may directly limit pivoting of louver 202 in opening direction 242 by impeding rotation
of louver 202 beyond a predetermined amount. Louvers 204,206 may also be limited in
pivoting in opening direction 242 by louver 202 contacting open position stopper 240
because louvers 202,204,206 may be linked together by first connecting rod 226.
In some example embodiments, louver system 200 may include a shut position
stopper 244, which may be arranged to limit pivoting of one or more of louvers 202,204,
206,208,210,212 in a shutting direction 246. For example, shut position stopper 244
may directly limit pivoting of louver 212 in shutting direction 246 by impeding rotation
of louver 212 beyond a predetermined amount. Louvers 202,204,206,208,210 may
also be limited in pivoting in shutting direction 246 by louver 2 12 contacting shut
position stopper 244 because louvers 202, 204,206,208,210,212 may be linked together
by first connecting rod 226 and/or second connecting rod 227 and/or because louvers
202,204,206, 208,210 may lie against louvers 204,206,208,210,212, respectively, in
the shut position.
In some example embodiments, first connecting rod 226 and second connecting
rod 227 may be independently operable such that first group 262 of louvers and second
group 264 of louvers may be at least partially independently pivotable (e.g., FIG. 5). For
example, louver system 200 may be configured such that first group 262 of louvers may
be open at low and high bleed air 2 flow rates andlor second group 264 of louvers may be
open at relatively high bleed air 2 flow rates and may be shut at relatively low flow rates.
In an example embodiment, bleed air 2 flow may initially cause first group 262 of
louvers to open, thereby discharging bleed air 2 as exit flow stream 5. Second group 264
of louvers may be maintained in the shut position. In response to an increase in bleed air
2 flow, second group 264 of louvers may pivot to the open position. If the flow rate of
bleed air 2 decreases, second group 264 of louvers may pivot to the shut position. Upon
substantially stopping the flow of bleed air 2 from compressor 14, first group 262 of
louvers may pivot from the open position to the shut position.
Some example embodiments according to at least some aspects of the present
disclosure may include louvers comprising trailing edges with mixing features. For
example, FIG. 6 is a plan view of an example louver system 300 including louvers 302,
304,306, 308,3 10,3 12 with scalloped trailing edges 350,352,354 andlor chevronshaped
trailing edges 356, 358,360, respectively, according to at least some aspects of
the present disclosure. An example scalloped trailing edge 350 may include a plurality of
alternating, generally curved projections 370,372,374 andlor recesses 376,378. Some
example embodiments may include a plurality of louvers having substantially the same
shape of trailing edge, and some example embodiments may include a plurality of
louvers having a plurality of different trailing edge shapes.
Another example mixing feature may comprise a grooved edge. FIG. 7 is a
perspective view of an example louver 400 including a grooved trailing edge 404,
according to at least some aspects of the present disclosure. Louver 400 may be
pivotably mounted in a louver system generally as described in connection with other
embodiments herein. For example, louver 400 may receive a pivot pin through hole 402.
Trailing edge 404 may be grooved, including a plurality of recesses 406,408,4 10,4 12
interposed between a plurality of projections 414,416,418,420,422. In some example
embodiments, recesses 406,408,410,412 may be located on an area of trailing edge 404
that is generally opposite bypass flow stream 4.
In some example embodiments, trailing edges with mixing features (e.g.,
scalloped edges and/or grooved edges) may improve mixing of exit flow stream 5 with
bypass flow stream 4, for example. The sizes, proportions, and/or locations of
projections 370,372,374, recesses 376,378, projections 414,416,418,420,422, andlor
recesses 406,408,410,412 may be adjusted to achieve desired flow mixing
characteristics.
Some example embodiments may include one or more dampers operatively
connected to one or more louvers. Such dampers may prevent and or limit flutter of the
louvers. An example damper 161 may comprise a torsion spring operatively coupled
between louver 102 and pivot pin 114, which may be staitionary. Damper 161 may
initially resist opening movement of louver 102 until the differential pressure across
louver 102 is sufficient to overcome the spring force. Alternative example damping
systems may include one or more dampers operatively coupled to connecting rod 126
and/or one or more dampers operatively coupled between a rotating pivot pin 1 14 and a
stationary part, such as open position stopper 140.
FIG. 8 is flow chart of an example method 800 of operating a bleed system
associated with a gas turbine engine, according to at least some aspects of the present
disclosure. Method 800 may include an operation 802, which may include receiving a
flow of bleed air from a compressor of a gas turbine engine at a discharge opening.
Operation 802 may be followed by an operation 804, which may include pivoting a
plurality of louvers disposed in the discharge opening from a shut position to an open
position. Operation 804 may be followed by operation 806, which may include,
discharging the flow of bleed air through the discharge opening. Operation 806 may be
followed by operation 808, which may include directing the flow of bleed air through the
discharge opening using the plurality of louvers.
This written description uses examples to disclose the invention, including the
best mode, and also to enable any person skilled in the art to practice the invention,
including making and using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the claims, and may
include other examples that occur to those skilled in the art. Such other examples are
intended to be within the scope of the claims if they have structural elements that do not
differ from the literal language of the claims, or if they include equivalent structural
elements with insubstantial differences from the literal languages of the claims.

We Claim :
1. A louver system for a gas turbine engine bleed system, the louver system comprising:
a bleed system discharge opening arranged to vent bleed air from a bleed flow
conduit; and
a plurality of pivotable louvers disposed proximate the discharge opening, the
pivotable louvers being pivotable between a shut position and an open position;
wherein, in the shut position, individual louvers at least partially obstruct the
discharge opening; and
wherein, in the open position, individual louvers at least partially control a
direction of flow of the bleed air exiting the discharge opening.
2. The louver system of claim 1, further comprising a first coimecting rod operatively
coupled to a first louver of the plurality of louvers and to a second louver of the plurality
of louvers, the first connecting rod providing substantially coordinated pivoting of the
first louver and the second louver.
3. The louver system of claim 2, ftirther comprising a second connecting rod operatively
coupled to a third louver of the plurality of louvers and to a fourth louver of the plurality
of louvers, the second connecting rod providing substantially coordinated pivoting of the
third louver and the fourth louver.
4. The louver system of claim 3, wherein the first coimecting rod and the second
connecting rod are independently operable.
5. The louver system of claim 1, wherein the plurality of pivotable louvers comprises at
least two groups of louvers, each group of louvers being associated with a coimecting rod
providing substantially coordinated pivoting of the respective group of louvers.
6. The louver system of claim 1, further comprising an open position stopper arranged to
limit pivoting of at least one louver of the plurality of louvers in an opening direction.
7. The louver system of claim 1, further comprising a shut position stopper arranged to
limit pivoting of at least one louver of the plurality of louvers in a shutting direction.
8. The louver system of claim 1, wherein an individual louver comprises a trailing edge;
wherein the trailing edge comprises a mixing feature; and wherein the mixing feature
comprises at least one of a grooved edge, a scalloped edge, and a chevron-shaped edge.
9. A gas turbine engine, comprising:
a compressor;
a combustor arranged to combust fuel in compressed air received from the
compressor;
a turbine configured to receive hot, pressurized gas from the combustor and to
drive the compressor;
a bleed conduit arranged to receive bleed air from the compressor; and
a louver system operatively coupled to the bleed conduit, the louver system
comprising
a plurality of louvers disposed in a discharge opening, the plurality of louvers
being pivotable between a shut position and an open position.
10. The gas turbine engine of claim 9, wherein, in the shut position, the plurality of
louvers substantially obstructs the discharge opening.
11. The gas turbine engine of claim 9, wherein, in the open position, the plurality of
louvers are arranged to direct a flow of bleed air exiting the discharge opening.
12. The gas turbine engine of claim 9, fiuther comprising
a transient bleed valve fluidicly interposing the compressor and the bleed conduit; and
a muffling device fluidicly interposing the bleed conduit and the discharge opening.
13. The gas turbine engine of claim 9, wherein the discharge opening is arranged to vent
the bleed air into a bypass flow stream.
14. The gas turbine engine of claim 13, wherein, in the open position, the plurality of
louvers is arranged to prevent bleed air impingement on a bypass duct wall.
15. A method of operating a bleed system associated with a gas turbine engine, the
method comprising:
receiving a flow of bleed air from a compressor of a gas turbine engine at a
discharge opening;
pivoting a plurality of louvers disposed in the discharge opening from a shut
position to an open position;
discharging the flow of bleed air through the discharge opening; and
directing the flow of bleed air through the discharge opening using the plurality of
louvers.
16. The method of claim 15, further comprising
substantially stopping the flow of bleed air from the compressor; and
pivoting the plurality of louvers from the open position to the shut position, the
louvers substantially obstructing the discharge opening in the shut position.
17. The method of claim 15, wherein pivoting a plurality of louvers disposed in the
discharge opening from the shut position to the open position comprises
pivoting a first group of pivotable louvers from the shut position to the open
position, and
maintaining a second group of pivotable louvers in the shut position.
18. The method of claim 17, fiirther comprising pivoting the second group of louvers
from the shut position to the open position in response to an increase in a flow rate of
bleed air from the compressor.
19. The method of claim 15, wherein receiving the flow of bleed air from the compressor
of the gas tiirbine engine at the discharge opening comprises flowing the flow of bleed air
through a muffling device fluidicly coupled upstream of the discharge opening.