Note: Descriptions are shown in the official language in which they were submitted.
CA 02712952 2010-08-13
BLADE OUTER AIR SEAL SUPPORT
TECHNICAL FIELD
The described subject matter relates generally to gas turbine engines and
more particularly, to a blade outer air seal of gas turbine engines.
BACKGROUND
A typical gas turbine engine includes a fan, compressor, combustor and
turbine disposed along a common longitudinal axis. In most cases, the turbine
includes several stages, each having a rotor assembly and at least one
stationary vane
assembly located forward and/or aft of the rotor assembly to guide the hot gas
flow
entering and/or exiting the rotor assemblies. Each rotor assembly includes a
static
turbine shroud around the turbine rotor to form a blade outer air seal (BOAS)
in order
to guide the hot gas flow passing through the turbine rotor. The turbine
shroud is
supported by a support structure within a core case of the engine. The BOAS
works
in the hot section of the engine and is subject to elevated temperatures.
Therefore,
efforts have been made to improve the BOAS configuration in order to limit
and/or
properly transfer loads caused by dissimilar thermal expansion within the
engine,
thereby providing an axially straight tip clearance above the blades of the
turbine
rotor and maintaining appropriate tip clearance of the turbine blades, which
has a
significant affect on engine performance. The efforts for improving the BOAS
involve both a load transfer issue and a cooling issue of the BOAS.
Accordingly, there is a need to provide an improved BOAS.
SUMMARY
In one aspect, the described subject matter provides a gas turbine engine
having a main axis of rotation defining axial, radial and circumferential
directions, a
combustor, a static vane ring assembly and a turbine assembly supported within
an
outer case, the vane ring assembly being axially positioned between the
combustor
and the turbine assembly for directing combustion gases from the combustor to
pass
through the turbine assembly, the turbine assembly comprising an array of
circumferentially adjacent blade outer air seal segments forming a static
turbine
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shroud surrounding a turbine rotor; and an array of circumferentially adjacent
blade
outer air seal support segments forming a static support ring around the
turbine
shroud, each of the blade outer air seal support segments including at least
one
radially and outwardly extending front leg at a forward end of the blade outer
air seal
segment, the at least one front leg engaging with the outer case, the forward
end
including a radial surface adjacent to the vane ring assembly and thereby
receiving an
axial load from the static vane ring assembly, each of the blade outer air
seal support
segments further including a pair of circumferentially spaced and radially
elongated
rear prongs at a rearward end of the blade outer air seal support segment, the
rear
prongs only radially and outwardly abutting the outer case to transfer a
moment of
force created by said axial load from the vane ring assembly, to the outer
case.
In another aspect, the described subject matter provides a blade outer air
seal
support segment for supporting at least one of blade outer air seal segments
which in
combination form a static turbine shroud, within a gas turbine engine having a
main
axis of rotation defining axial, radial and circumferential directions, the
blade outer
air seal support segment being a circumferential part of a blade outer seal
support
ring surrounding the static turbine shroud and comprising a forward end, a
rearward
end, and opposed circumferential sides; a radial wall positioned at the
forward end
and circumferentially extending between the opposed circumferential sides, a
first
circumferential flange segment extending axially forwardly from a radially
outer end
of the circumferentially extending radial wall to thereby form a front leg
having an
inverted L-shaped cross section for engagement with an outer case of the
engine; a
pair of radially and outwardly extending elongated rear prongs, positioned
axially at
the rearward end of the support segment and circumferentially at the
respective
opposed circumferential sides of the support segment for radially abutting the
outer
case, the prongs in combination with the radial wall defining a space between
the
forward and rearward ends of the support segment, the space having a rearward
access between the rear prongs.
Further details of these and other aspects of the present invention will be
apparent from the detailed description and figures included below.
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DESCRIPTION OF THE DRAWINGS
Reference is now made to the accompanying drawings depicting aspects of
described subject matter, in which:
FIG. 1 is a schematic cross-sectional view of a turbofan gas turbine engine
as an example of the application of the described subject matter,
schematically
illustrating a blade outer air seal (BOAS) assembly around a turbine of the
engine;
FIG. 2 is a partial cross-sectional view of the gas turbine engine of FIG. 1,
showing the structural configuration of the BOAS assembly according to one
embodiment;
FIG. 3 is a partial perspective view of the BOAS assembly of FIG. 2,
showing a pair of BOAS segments supported by a BOAS support segment;
FIG. 4 is a partial perspective view of the BOAS support segment of FIG. 3,
showing an impingement baffle plate attached to the radially inner side of the
BOAS
support segment;
FIG. 5 is a partial perspective view of the BOAS support segment of FIG. 3,
with the impingement buffer plate removed to show a dump plenum within the
BOAS support segment;
FIG. 6 is a perspective view of the BOAS support segment of FIG. 3,
showing a circumferentially extending radial wall at a forward end and a pair
of
circumferentially spaced and radially elongated rear prongs at a rearward end
of the
BOAS support segment;
FIG. 7 is a partial perspective view of the BOAS assembly of FIG. 2,
showing one of inlet cavities of a cooling air distribution system in a
segmented
support ring of the BOAS assembly;
FIG. 8 is a perspective view of the BOAS segment in the BOAS assembly
of FIG. 3, showing a pair of cast anti-rotation tabs integrated with the BOAS
segment;
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FIG. 9 is a partial perspective view of the BOAS assembly of FIG. 2 with the
paired BOAS segments circumferentially slid away from each other, to show a
pair of
stoppers attached to the BOAS support segment;
FIG. 10 is a perspective view of the BOAS segment in the BOAS assembly
of FIG. 3 according to another embodiment, showing a plurality of cavities
defined in
the platform of the BOAS segment to form bucket inlets of cooling passages in
the
BOAS segment;
FIG. 11 is a partial perspective view of the BOAS segment of FIG. 10 with
half of the segment cut away along line 11-11 in FIG. 10, to shown a cross-
section
thereof having the cooling passage defined therein;
FIG. 12 is a top plan view of the BOAS segment of FIG. 10, showing the
layout of the plurality of cooling passages extending through the platform of
the
segment; and
FIG. 13 is a perspective view of the BOAS support segment similar to that
of FIG. 6, optionally having an additional middle rear prong, according to
another
embodiment.
DETAILED DESCRIPTION
FIG. 1 schematically illustrates a turbofan gas turbine engine which includes
a nacelle configuration 10, a core casing 13, a low pressure spool assembly
seen
generally at 12 which includes a fan assembly 14, a low pressure compressor
assembly 16 and a low pressure turbine assembly 18, and a high pressure spool
assembly seen generally at 20 which includes a high pressure compressor
assembly 22 and a high pressure turbine assembly 24. The core casing 13
surrounds
the low and high pressure spool assemblies 12 and 20 in order to define a main
fluid
path (not indicated) therethrough. In the main fluid path there is provided a
combustion chamber 26 in which a combustion process takes place, producing
combustion gases for powering the high and low pressure turbine assemblies 24
and 18. The engine has a main axis 28 of rotation and therefore, axial, radial
and
circumferential/tangential directions mentioned in this description and
appended
claims are defined with respect to this axis 28.
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Referring to FIGS. 1 and 2, the engine further includes a static vane ring
assembly 30 axially positioned between the combustion chamber 26 and a turbine
assembly, for example the high pressure turbine assembly 24 for directing
combustion gases from the combustion chamber 26 to pass through the high
pressure
turbine assembly 24. The vane ring assembly 30 and the high pressure turbine
assembly 24 are both supported within an outer case 32 which may be part of
the core
casing 13. The turbine assembly 24 includes a blade outer air seal (BOAS)
assembly 34 having an array of circumferentially adjacent BOAS segments 36
(only
one shown) forming a static turbine shroud (not indicated) surrounding a
turbine
rotor 38. The BOAS assembly 34 further includes an array of circumferentially
adjacent BOAS support segments 40 (only one shown) forming a static support
ring
(not indicated) around the array of BOAS segments 36.
Referring to FIGS. 2-6, each of the BOAS support segments 40 has a
forward end 42 (upstream end) and a rearward end 44 (downstream end) with
respect
to the gas flow passing through the turbines, opposed circumferential sides
46, 48, a
radially inner side 50 and radially outer side 52. The one or more BOAS
segments 36
are connected to the radially inner side 50 of the BOAS support segment 40. A
pair
of BOAS segments 36 is connected to one BOAS support segment 40, according to
this embodiment as shown in FIG. 3. The radially outer side 52 provides a
radially
outwardly abutting surface (not indicated) to support the support ring formed
by the
BOAS support segments 40, within the outer case 32.
The BOAS support segment 40 has a hollow configuration and may include
a circumferential wall 54 (see FIGS. 5 and 6) extending between the forward
and
rearward ends 42, 44 and between the opposed circumferential sides 46, 48 to
define
an inner space 56 (see FIG. 6) at a radial and outward portion of the BOAS
support
segment 40. The inner space 56 is substantially open at both the radially
outer
side 52 and at the rearward end 44 of the BOAS support segment 40. The
circumferential wall 54 also defines a cavity 58 (see FIGS. 2 and 5) at a
radial and
inner portion of the BOAS support segment 40. The cavity 58 defines an opening
(not indicated) at the radially inner side 50 of the BOAS support segment 40.
A
radial wall 60 is positioned at the forward end 42 and extends
circumferentially
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between the opposed circumferential sides 46, 48. A circumferential flange
segment 62 extends axially forwardly from a radially outer end of the
circumferentially extending radial wall 60 to thereby in combination with the
radial
wall 60, form a front leg 64 (only indicated in FIG. 2) having an inverted L-
shaped
cross-section, for engagement with the outer case 32.
A pair of radially and outwardly extending elongated rear prongs 66 are
positioned axially at the rearward end 44 and circumferentially at the
respective
opposed circumferential sides 46, 48, of the BOAS support segment 40. Each of
the
rear prongs 66 provides a surface at its radially outer end to radially and
outwardly
abut the outer case 32. The two rear prongs 66 are circumferentially spaced
apart,
therefore the space 56 within the support segment 40 is conveniently
accessible from
an open area (not indicated) between the two rear prongs 66, even when the
BOAS
support segment 40 is assembled in the BOAS assembly 34 and installed in the
outer
case 32, as shown in FIG. 2.
The BOAS support segment 40 further includes a circumferential flange
segment 67 extending axially forwardly from the forward end 42 at a location
near
the radially inner side 50 of the BOAS support segment 40, to provide a radial
surface (not indicated) which may be in contact with the static vane ring
assembly 30,
for receiving an axial load from an adjacent component of the static vane ring
assembly 30. This axial load, acting on a location of the support segment 40
near the
radially inner side 50 creates a moment of force in an anti-clockwise
direction about
the radially outer end of the front leg 64 (see FIG. 2). This moment of force
could
cause a rocking motion of the BOAS support segment 40 in the same direction,
if not
properly transferred to the outer case 32. The rear prongs 66 provide an
adequate
load transfer link such that the moment of force created by vane loads acting
axially
on the circumferential flange segment 67 is properly transferred by the rear
prongs 66
in a radially outward direction, to the outer case 32, thereby preventing the
rocking
motion of the BOAS support segment 40 from being transferred to the BOAS
segment 36, and thereby contributing to maintaining an axially straight tip
clearance
around the turbine rotor 38.
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The rear prongs 66 also properly transfer other loads, such as radial thermal
expansion loads of the turbine shroud formed with the BOAS segment 36.
However,
the rear prongs 66 do not axially and circumferentially engage with the outer
case 32.
The BOAS support segments 40 are allowed for axial and/or circumferential
thermal
expansion within a limited tolerance
The radial wall 60 is provided with one or more apertures 68 for receiving
fasteners (not indicated) extending axially through the radial wall 60 and
into the
inner space 56, as shown in FIG. 2. The fasteners are used to secure the front
leg 64
to a radial wall (not indicated) of the outer case 32 in order to secure the
entire BOAS
assembly 34 to the outer case 32. In this embodiment, two apertures 68 are
circumferentially spaced apart. The fasteners received in the apertures 68 are
conveniently accessible from the rearward end 44 through the open area between
the
pair of rear prongs 66. A radial central wall 55 may be provided (see FIG. 6)
extending axially from the radial wall 60 across the inner space 56 to divide
the same
into two circumferential portions, each accommodating one of the fasteners.
As shown in FIG. 13, the BOAS support segment 40 according another
embodiment may optionally include additional rear prongs, for example such as
an
additional middle prong 65 at the rearward end 44 of the BOAS support segment
40,
circumferentially located between the pair of rear prongs 66 at the opposed
circumferential sides 46, 48. Other structures and features are similar to
those shown
in FIG. 6, and are indicated by the same numerals. It is understood that the
fasteners
received in the respective apertures 68 are still accessible from the rearward
end 44 of
the BOAS support segment 40 because the apertures 68 are circumferentially
aligned
with the open areas between the middle rear prong 65 and the respective rear
prongs 66 at the opposed circumferential sides 46, 48 of the BOAS support
segment 40.
Referring to FIGS. 2 and 8, each of the BOAS segments 36 includes a
platform 70 extending axially from a leading edge 72 to a trailing edge 74
(with
respect to the gas flow direction in the engine) and circumferentially
extending
between opposed circumferential sides 75, and further includes front and rear
hooks 76 and 78 integrated with the platform 70 to support the platform 70,
radially
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and inwardly spaced apart from the support ring formed by the BOAS support
segments 40. The front hook 76 includes a radial wall 80 circumferentially
extending
between the opposed circumferential sides 75 and a circumferential flange
segment 82 extending radially rearwardly from a radially outer end of the
radial
wall 80, thereby forming the front hook 76 in an inverted L-shape. The rear
hook 78
includes a radial wall 84 circumferentially extending between the opposed
circumferential sides 75 and axially spaced apart from the radial wall 80, and
a
circumferential flange segment 86 extending axially forwardly from the radial
wall 84, thereby forming the rear hook 78 in an inverted L-shape. The front
and rear
hooks 76 and 78 in combination form an engaging device for connection with the
BOAS support segment 40.
Referring to FIGS. 2-4 and 8-9, the BOAS support segment 40 according to
this embodiment may be provided with a complementary engaging device for
radial
and axial engagement with the front and rear hooks 76, 78 of the BOAS segments
36.
The complementary engaging device of the BOAS support segment 40 according to
this embodiment, may include at least one circumferentially extending front
engaging
element 88 projecting axially and forwardly from the BOAS support segment 40
near
the radially inner side 50, and a circumferentially extending rear engaging
element 90
projecting axially and rearwardly from the BOAS support segment 40 near the
radially inner side 50. The front and rear engaging elements 88, 90 radially
and
axially engage the respective front and rear hooks 76, 78 of the BOAS segment
36
and allow a circumferential movement of the BOAS segment 36 relative to the
BOAS support segment 40 such that the BOAS segment 36 can be circumferentially
slid from one of the opposed circumferential sides 46, 48 of the BOAS support
segment 40 into a predetermined circumferential position, while maintaining
connection with the BOAS support segment 40.
An anti-rotation apparatus is provided for restricting relative
circumferential
movement between the turbine shroud formed by the BOAS segments 36 and the
support ring formed by the BOAS support segments 40. The anti-rotation
apparatus
may include a stopper 92 (see FIG. 9) provided at least in one of the BOAS
support
segments 40 and at least one cast anti-rotation tab 94 integrated with one of
the
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BOAS segments 36 supported on the at least one BOAS support segments 40. The
stopper 92 and the cast anti-rotation tab 94 circumferentially abut each
other. Those
BOAS support segments having no stoppers will be circumferentially restricted
by
those having stoppers. Those BOAS segments having no cast anti-rotation tabs
will
be circumferentially restricted by those having the cast anti-rotation tabs.
In this embodiment, each of the BOAS support segments 40 supports a pair
of the BOAS segments 36, and the anti-rotation apparatus may include at least
one
stopper 92 provided on each of the BOAS support segments 36 and at least one
cast
anti-rotation tab 94 integrated with each of the BOAS segments 36. The stopper
92
of each of the BOAS support segments 40, defines circumferentially opposed
side
surfaces for abutting the at least one cast anti-rotation tab 94 of the
respective BOAS
segments 36 supported on the BOAS support segment 40. Therefore, every BOAS
segment 36 and every BOAS support segment 40 is circumferentially restricted
with
their own cast anti-rotation tab 94 and the stoppers 92. The anti-rotation
tolerance
between the BOAS support segment 40 and the pair of BOAS segments 36 supported
thereon is therefore more controllable.
As shown in FIGS. 4 and 8-9, two stoppers 92 and two cast anti-rotation
tabs 94 may be provided to the respective BOAS support segment 40 and the BOAS
segment 36 and casting process of the BOAS segment 36. The cast anti-rotation
tab 94 may be positioned in an inner corner of each BOAS segment 36 and
integrated
with both the front hook 76 and the platform 70 of the BOAS segments 36. The
stoppers 92 may be attached to a forward end 42 near the radially inner side
50 of the
BOAS support segment 40. The two stoppers 92 may be a machined component
which is attached for example to a circumferentially middle area of the BOAS
segment 40 between two front engaging elements 88, by fasteners (not shown).
The
machined stoppers 92 may be circumferentially spaced apart from each other and
the
space therebetween may be slightly adjustable. The respective stoppers 92
define
abutting surfaces circumferentially facing away from each other to abut one
cast anti-
rotation tab 94 of the respective BOAS segments 36 which are circumferentially
slid
into position from the opposed circumferential sides 48 of the BOAS support
segment 40.
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The two cast anti-rotation tabs 94 of each BOAS segment 36 are
circumferentially spaced apart one from another and are circumferentially
symmetric
about a central axis 96 (see FIG. 8) of the BOAS segment 36. It is noted that
only
one of the cast anti-rotation tabs 94 of each BOAS segment 36 is in contact
with a
stopper 92 of the BOAS support segment 40, in order to provide the anti-
rotation
function. However, the symmetrically positioned two cast anti-rotation tabs 94
allow
each of the BOAS segments 36 to be connected to the BOAS support segment 40 by
sliding into position from either one of the opposed circumferential sides 46,
48 of
the BOAS support segments 40 because the two stoppers 92 (or the at least one
stopper 92 if only one stopper 92 is provided) are also circumferentially
symmetrical
about an axially central axis 98 (see FIG. 6) of the BOAS support segment 40.
In
other words, the circumferential position of the paired BOAS segments 36
supported
by one BOAS support segment 40 as shown in FIG. 3, can be interchangeable with
each other.
The anti-rotation apparatus formed by the stoppers 92 in each BOAS support
segment 40 and the cast anti-rotation tabs 94 in each BOAS segment 36,
prevents the
paired BOAS segments 36 from rotating relative to the BOAS support segment 40
within an acceptable tolerance, after the BOAS assembly 24 is mounted into the
outer
case 32. The acceptable tolerance may be adjusted during or prior to the
assembly
procedure by the adjustment of the space between the two stoppers 92.
The BOAS assembly 34 defines a cooling system, particularly a cooling air
distribution system within the support ring formed by the BOAS support
segments 40, for intake of compressor bleed air, which distributes cooling air
radially
inwardly to and along the entire circumference of the static turbine shroud
formed by
the BOAS segments 36, to cool the same. As shown in FIGS. 2-7, the cooling air
distribution system includes a plurality of inlet cavities 100 (one shown in
FIG. 7)
axially and inwardly extending from a forward end of the support ring formed
by the
BOAS support segments 40. The forward end of the support ring is defined by
the
forward end 42 of the BOAS support segments 40 and the inlet cavities 100 are
circumferentially located at a respective adjacent area between two adjacent
BOAS
support segments 40.
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Still referring to FIGS. 2-7, each of the inlet cavities 100 is formed with
two
recesses 102 defined in the respective adjacent two BOAS support segments 40.
Each of the BOAS support segments 40 defines one of the two recesses 102 on
the
respective opposed circumferential sides 48 which for example may be formed by
a
cut-away portion of a comer of the BOAS support segment 40 between the forward
end 42 and the opposed circumferential sides 48 thereof. Therefore, each
recess 102
has openings at both the forward end 42 and the circumferential side 46 or 48
of the
BOAS support segment 40. Each of the BOAS support segments 40 further includes
a plurality of substantially circumferential or tangential passages 104
extending from
the respective recesses 102 inwardly to the inner space 56 (see FIG. 6). The
inner
space 56 is in fluid communication with a damp plenum formed by the cavity 58,
through a plurality of holes 106 radially extending through the
circumferential
wall 54 (see FIG. 5). A buffer plate 108 with a plurality of impingement holes
110
extending therethrough may be provided, to be attached to the radially inner
side 50
of the BOAS support segment 40 (see FIG. 4), covering the opening of the
cavity 58.
Therefore, the above-described configuration of the BOAS support
segment 40 defines the cooling air distribution system for intake of
compressor bleed
air from the forward end of the support ring formed by the BOAS support
segments 40, through the inlet cavities 100. The cooling compressor bleed air
is then
directed from the inlet cavities 100 through the substantially circumferential
passages 104 into the inner space 56 of the respective BOAS support segments
40. In
each of the BOAS support segments 40, the cooling air in the inner space 56
enters
the dump plenum formed by the cavity 58 radially and inwardly through the
holes 106 and then further passes through the impingement holes 110 of the
buffer
plate 108, to radially and inwardly impinge upon the BOAS segments 36
connected
to the BOAS support segment 40.
Each of the BOAS support segments 40 according to one embodiment, may
further include seal slots defined in the opposed circumferential sides 46,
48, to
receive seals (shown in FIG. 7 but not indicated) to prevent cooling air
leakage from
a circumferential gap (not indicated) between the two recesses 102 on the
respective
adjacent BOAS support segments 40, which forms one inlet cavity 100. For
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example, each of the opposed circumferential sides 46, 48 of the BOAS support
segment 40, may define a seal slot 112 extending axially from the forward end
42 to
the rearward end 44 and a seal slot 113 extending radially and inwardly from
the
forward end 42 to the rearward end 44 and adjacent the seal slot 112 near the
rearward end 44. Therefore, the recess 102 is positioned between the seal
slots 112
and 113.
Referring to FIGS. 2 and 10-12, the axially spaced apart front and rear
hooks 76 and 78 of the respective BOAS segments 36, support the platform 70 to
be
radially and inwardly spaced apart from the support ring formed by the BOAS
support segments 40, thereby defining an annular cavity 114 between the front
and
rear hooks 76, 78. According to another embodiment, each of the BOAS
segments 36 may define a plurality of cooling passages 116 extending axially
through
the platform 70 from individual inlet cavities 118 which are defined in a
radially
outer surface of the platform 70, to an exit hole 120 defined on the leading
edge 72 of
the platform 70. Each inlet cavity 118 may be cylindrical and may have a
diameter
larger than the connected cooling passage 116, and may be referred to as a
"bucket"
inlet for the cooling passage 116. The inlet cavity 118 is in fluid
communication
with the annular cavity 114 for intake of cooling air discharged from the
cooling air
distribution system of the support ring formed by the BOAS support segments
40,
through the impingement holes 110 of the impingement buffer plate 108 into the
annular cavity 114 (see FIG. 2). At least one of the cooling passages 116
which is
particularly indicated as 116a and is positioned close to respective opposed
circumferential sides 75 of each BOAS segment 36 (see FIG. 12) according to
one
embodiment, extends linearly from an inlet cavity 118a and is skewed away from
the
axial direction in order to direct cooling air to cool a corner area between
the leading
edge 72 and the respective opposed circumferential sides 75 of the platform
70. It
may not be convenient or possible to position the inlet cavity 11 8a in a
proximity of
the respective opposed circumferential sides 75 of the platform 70 due to the
existence of a seal slot 122 defined in the respective opposed circumferential
sides 75
of the platform 70 and extending between the leading edge 72 and trailing edge
74 of
the platform 70. The skewed orientation of the cooling passage 116a provides a
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solution in this circumstance to cool the corner areas of the leading edges 72
of the
platform 70.
The inlet cavities 118 (including 118a) extend radially and inwardly from the
radially outer surface of the platform 70 to a depth at which inlet cavity 118
(or 118a)
can communicate with the respective cooling passages 116 (or 116a) such that
the
cooling passages 116 (or 116a) are closer to a radially inner surface (not
indicated) of
the platform 70 and are radially spaced apart from the seal slots 122. The
inlet
cavity 118a is circumferentially spaced apart from the seal slot 122. An exit
hole 120a of the cooling passage 116a may be circumferentially aligned with
the seal
slot 122 defined in the opposed circumferential sides 75 of the platform 70
(see
FIG. 12).
The platform 70 of the BOAS segment 36 is configured such that each of the
seal slots 122 is in a curved shape and may have an opening 124 in the
radially outer
surface of the platform 70. The opening 124 has a size in the circumferential
direction equal to the circumferential depth of the seal slot 122. Therefore,
the inlet
cavity 118a is circumferentially spaced apart from the opening 124 of the
respective
seal slots 122. It may be convenient for the cooling passage 116a and an
adjacent
cooling passage 116 to share the inlet cavity 118a due to the skewed
orientation of
the cooling passage 118a. In contrast to cylindrical inlet cavities 118 which
communicate individually with the cooling passage 116, the shared inlet cavity
11 8a
may have a larger size in the circumferential direction such as in an oblong
shape.
The leading edge 72 of the platform 70 may further define an axially
outward projection configuration 126 to prevent the exit holes 120 on the
leading
edge 72 from being blocked by adjacent engine components when the BOAS
assembly 34 is installed in the outer casing case 32 of the engine. Therefore,
the
cooling air passing through the cooling passages 116 and 116a cools the
platform 70
of the respective BOAS segments 36 and is discharged through the exit holes
120,
into the hot gas path defined by the turbine shroud.
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
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departure from the scope of the described subject matter. For example, a
turbofan
gas turbine engine is used as an exemplary application of the described
subject
matter, however, other types of gas turbine engines are applicable for the
described
subject matter. Still other modifications which fall within the scope of the
described
subject matter 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.
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