Note: Descriptions are shown in the official language in which they were submitted.
CA 02709933 2010-06-17
Docket 1WO 2009/085620 PCT/US2008/086310
TURBINE NOZZLE SEGMENT AND ASSEMBLY
BACKGROUND OF THE INVENTION
[0001] The exemplary embodiments relate generally to gas turbine
engine components and more specifically to leaf seal assemblies for turbine
nozzle
assemblies.
[0002] Gas turbine engines typically include a compressor, a
combustor, and at least one turbine. The compressor may compress air, which
may be
mixed with fuel and channeled to the combustor. The mixture may then be
ignited for
generating hot combustion gases, and the combustion gases may be channeled to
the
turbine. The turbine may extract energy from the combustion gases for powering
the
compressor, as well as producing useful work to propel an aircraft in flight
or to
power a load, such as an electrical generator.
[0003] The turbine may include a stator assembly and a rotor
assembly. The stator assembly may include a stationary nozzle assembly having
a
plurality of circumferentially spaced apart airfoils extending radially
between inner
and outer bands, which define a flow path for channeling combustion gases
therethrough. Typically the airfoils and bands are formed into a plurality of
segments,
which may include one (typically called a singlet) or two spaced apart
airfoils radially
extending between an inner and an outer band. The segments are joined together
to
form the nozzle assembly.
[0004] The rotor assembly may be downstream of the stator
assembly and may include a plurality of blades extending radially outward from
a
disk. Each rotor blade may include an airfoil, which may extend between a
platform
and a tip. Each rotor blade may also include a root that may extend below the
platform and be received in a corresponding slot in the disk. Alternatively,
the disk
may be a blisk or bladed disk, which may alleviate the need for a root and the
airfoil
may extend directly from the disk. The rotor assembly may be bounded radially
at the
tip by a stationary annular shroud. The shrouds and platforms (or disk, in the
case of
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a blisk) define a flow path for channeling the combustion gases therethrough.
The
nozzles and shrouds are separately manufactured and assembled into the engine.
Accordingly, gaps are necessarily provided therebetween for both assembly
purposes
as well as for accommodating differential thermal expansion and contraction
during
operation of the engine.
[0005] The gaps between the stationary components are suitably
sealed for preventing leakage therethrough. In a typical turbine nozzle, a
portion of
air is bled from the compressor and channeled through the nozzles for cooling
thereof.
The use of bleed air reduces the overall efficiency of the engine and,
therefore, is
minimized whenever possible. The bleed air is at a relatively high pressure,
which is
greater than the pressure of the combustion gases flowing through the turbine
nozzle.
As such, the bleed air would leak into the flow path if suitable seals were
not provided
between the stationary components.
[0006] A typical seal used to seal these gaps is a leaf seal. A typical
leaf seal is arcuate and disposed end to end around the circumference of the
stator
components. For example, the radially outer band of the nozzle includes
axially
spaced apart forward and aft rails. The rails extend radially outwardly and
abut a
complementary surface of an adjoining structural component, such as, but not
limited
to, a shroud, a shroud hanger, and/or a combustor liner, for providing a
primary
friction seal therewith. The leaf seal provides a seal at this junction and
bridges a
portion of the rail and the adjoining structural component. Leaf seals are
typically
relatively thin, compliant sections, which are adapted to slide along a pin
fixed to one
of the adjoining structural components.
[0007] Regardless of the particular shape of the structural
components to be sealed, leaf seals are movable to a closed, sealing position
in which
they engage each structural component and seal the space therebetween, and an
open
position in which at least one portion of the leaf seals disengage a
structural
component and allow the passage of gases in between such components. In most
applications, movement of the leaf seals along the pins to a closed position
is affected
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by applying a pressure differential across seal, i.e., relatively high
pressure on one
side of the seal and comparatively low pressure on the opposite side thereof
forces the
seal to a closed, sealed position against surfaces of the adjoining structural
components to prevent the passage of gases therebetween.
[0008] While leaf seals have found widespread use in turbine
engines, their effectiveness in creating a fluid tight seal is dependent on
the presence
of a sufficient pressure differential between one side of the seal and the
other. During
certain operating stages of a turbine engine, the difference in fluid pressure
on
opposite sides of the leaf seals is relatively low. Under these conditions, it
is possible
for the leaf seals to unseat from their engagement with the abutting
structural
components of the turbo machine and allow leakage therebetween. A relatively
small
pressure differential across the leaf seals also permits movement or vibration
of the
leaf seals with respect to the structural components that they contact. This
vibration
of the leaf seals, which is caused by operation of the turbine engine and
other sources,
creates undesirable wear both of the leaf seals and the surfaces of the
structural
components against which the leaf seals rest. Such wear not only results in
leakage of
gases between the leaf seals and structural components of the turbine engine,
but can
cause premature failure thereof.
[0009] To overcome this problem, other designs have included a
biasing structure, such as a spring, to bias the leaf seal toward a certain
position. For
example, a band may have two circumferentially spaced apart, radially
extending tabs
spaced axially from a rail. A recess may be formed between the tabs and the
rail
where the leaf seal and spring are disposed. The tabs, leaf seals and springs
may
include holes for receiving a pin for mounting to the band. At least one of
the tabs is
typically spaced apart from the circumferential edges of the band. The tab,
leaf seal
and spring are arranged so that the spring forces the leaf seal against an
adjoining
structural component so as to maintain the leaf seal in a closed, sealed
position at all
times.
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[0010] In some instances, such as, but not limited to, low emissions
combustors, this configuration is not sufficient. For example, low emissions
combustors are susceptible to flame instability, which may lead to acoustic
resonance
and high dynamic pressure variation. The high frequency pressure fluctuations
can
damage the leaf seals, particularly the leaf seals between the aft edge of the
combustor
liner and the leading edge of the nozzle bands, by repeatedly loading and
unloading
the seals against the adjoining structural component. The seals are
particularly
susceptible to damage where they are unsupported by the springs and/or tabs.
The
seals may not be fully supported at their circumferential edges and/or between
the
tabs on the bands.
BRIEF DESCRIPTION OF THE INVENTION
[0011] In one exemplary embodiment, a turbine nozzle segment
includes a band having a plurality of circumferentially spaced apart tabs and
a single
airfoil extending from the band. In another exemplary embodiment, a turbine
nozzle
segment includes a band having three or more circumferentially spaced apart
tabs and
a plurality of airfoils extending from the band.
[0012] In yet another exemplary embodiment, a turbine nozzle
assembly includes a plurality of turbine nozzle segments assembled together to
form
an annular ring, each of the segments having an outer band having three or
more
circumferentially spaced apart tabs and a rail axially spaced from the tabs
defining a
recess therebetween. The segments also have a leaf seal disposed in the
recess, a pin
extending through each of the tabs and the leaf seal and a biasing structure
associated
with each of the pins, biasing the leaf seal in abutting contact with an
adjoining
component. The segments further include an inner band and a plurality of
airfoils
extending between the outer and inner bands.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 is a cross-sectional schematic view of an exemplary
gas turbine engine.
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[0014] Figure 2 is a cross-sectional schematic view of an exemplary
turbine nozzle assembly.
[0015] Figure 3 is a perspective view of an exemplary turbine nozzle
segment.
[0016] Figure 4 is a close-up cross-sectional view of an exemplary
turbine nozzle leaf seal assembly.
[0017] Figure 5 is a top view of an exemplary turbine nozzle
segment.
[0018] Figure 6 is a bottom view of an exemplary turbine nozzle
segment.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Figure 1 illustrates a cross-sectional schematic view of an
exemplary gas turbine engine 100. The gas turbine engine 100 may include a low-
pressure compressor 102, a high-pressure compressor 104, a combustor 106, a
high-
pressure turbine 108, and a low-pressure turbine 110. The low-pressure
compressor
may be coupled to the low-pressure turbine through a shaft 112. The high-
pressure
compressor 104 may be coupled to the high-pressure turbine 108 through a shaft
114.
In operation, air flows through the low-pressure compressor 102 and high-
pressure
compressor 104. The highly compressed air is delivered to the combustor 106,
where
it is mixed with a fuel and ignited to generate combustion gases. The
combustion
gases are channeled from the combustor 106 to drive the turbines 108 and 110.
The
turbine 110 drives the low-pressure compressor 102 by way of shaft 112. The
turbine
108 drives the high-pressure compressor 104 by way of shaft 114.
[0020] As shown in Figure 2, the high-pressure turbine 108 may
include a turbine nozzle assembly 116. The turbine nozzle assembly 116 may be
downstream of the combustor 106 or a row of turbine blades. The turbine nozzle
assembly 116 includes an annular array of turbine nozzle segments 118. A
plurality
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of arcuate turbine nozzle segments 118 may be joined together to form an
annular
turbine nozzle assembly 116. As shown in Figures 2-6, the nozzle segments 118
may
include one or more airfoils 120 extending between an inner band 122 and an
outer
band 124. The nozzle segments 118 may be formed in a singlet or doublet
configuration. The singlet configuration may include a single airfoil 120
extending
between an inner band 122 and an outer band 124. The doublet configuration may
include two airfoils 120 extending between an inner band 122 and an outer band
124.
It should be understood by one of ordinary skill in the art that any
configuration could
be used, including having more than two airfoils 120. The airfoils 120 may be
hollow
and have internal cooling passages or may receive one or more cooling inserts.
The
inner and outer bands 122 and 124 may have one or more axially spaced apart
rails for
connecting the nozzle segment 118 to upstream and downstream adjoining
components.
[0021] The inner band 122 may include a forward rail 126 and an aft
rail 128. The inner band 122 may also have a plurality of circumferentially
spaced
apart tabs 130. The tabs 130 may be axially spaced from the forward rail 126
defining a recess 132 between the tabs 130 and the forward rail 126. A leaf
seal 134
may be disposed within the recess 132 and positioned to abut an adjoining
component. In one exemplary embodiment, the adjoining component may be a
combustor liner, such as combustor liner 136. In another exemplary embodiment,
the
adjoining component may be a turbine shroud. The leaf seal 134 may be retained
in
the recess 132 with a pin 138. The pin 138 may be positioned through a hole
140 in
the tab 130 and a corresponding hole 142 in the leaf seal 134. A biasing
structure 144
may be retained by the pin 138 and bias the leaf seal 134 into abutting
contact with
the adjoining component. As shown in Figure 3, the tab 130, pin 138 and
biasing
structure 144, may be adjacent a circumferential edge 146 and/or a
circumferential
edge 147 of the nozzle segment 118.
[0022] The outer band 124 may include a forward rail 148 and an aft
rail 150. The outer band 124 may also have a plurality of circumferentially
spaced
apart tabs 152. The tabs 152 may be axially spaced from the forward rail 148
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defining a recess 154 between the tabs 152 and the forward rail 148. A leaf
seal 156
may be disposed within the recess 154 and positioned to abut an adjoining
component. In one exemplary embodiment, the adjoining component may be a
combustor liner, such as combustor liner 158. In another exemplary embodiment,
the
adjoining component may be a turbine shroud. The leaf seal 156 may be retained
in
the recess 154 with a pin 160. The pin 160 may be positioned through a hole
162 in
the tab 152 and a corresponding hole 164 in the leaf seal 156. A biasing
structure 166
may be retained by the pin 160 and bias the leaf seal 156 into abutting
contact with
the adjoining component. The tab 152, pin 160 and biasing structure 166, may
be
adjacent a circumferential edge 168 and/or a circumferential edge 170 of the
nozzle
segment 118.
[0023] Figures 3, 5 and 6 illustrate a nozzle segment 118 having a
doublet configuration 174, where two nozzle segments 118 having a singlet
configuration 172 are joined together or the nozzle segment 118 having a
doublet
configuration 174 is cast as one piece. Furthermore, the airfoils 120, inner
band 122
and/or outer band 124 may be formed as an integrally cast piece or may be
formed
separately and joined together by brazing. For example, an airfoil 120 may be
integrally cast with an outer band 124 and an inner band 122 may be brazed to
the
airfoil. The tabs 130 and 152 may be cast integrally with the inner and outer
bands,
respectively.
[0024] In one exemplary embodiment, having a singlet configuration
172, the outer band 124 may have a plurality of circumferentially spaced apart
tabs
152, at least one of which is adjacent to a circumferential edge 168, 170 of
the outer
band. In another exemplary embodiment, having a doublet configuration 174, the
inner band 122 may have three or more tabs 130, one adjacent to a
circumferential
edge 146 of the inner band 122, one adjacent to another circumferential edge
147 of
the inner band 122, and one or more therebetween. In yet another exemplary
embodiment, having a doublet configuration 174, the outer band 124 may have
three
or more tabs 152, one adjacent to a circumferential edge 168 of the outer band
124,
one adjacent to another circumferential edge 170 of the outer band 124, and
one or
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more therebetween. In still yet another exemplary embodiment, having a doublet
configuration 174, the inner band 122 may have three or more tabs 130, one
adjacent
to a circumferential edge 146 of the inner band 122, one adjacent to another
circumferential edge 147 of the inner band 122, and one or more therebetween.
The
outer band 124 may also have three or more tabs 152, one adjacent to a
circumferential edge 168 of the outer band 124, one adjacent to another
circumferential edge 170 of the outer band 124, and one or more therebetween.
[0025] During operation, the leaf seals are biased into abutting
contact with adjoining components to provide sealing between the turbine
nozzle
segment and the adjoining components. The exemplary embodiments described
provide additional support to the leaf seals in areas susceptible to damage,
such as, but
not limited to, areas adjacent to the circumferential edges of the inner
and/or outer
bands and the central areas therebetween. The exemplary embodiments may also
increase the mechanical sealing load and reduce the unsupported length of the
leaf
seals.
[0026] This written description discloses exemplary embodiments,
including the best mode, to enable any person skilled in the art to make and
use the
exemplary embodiments. The patentable scope 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.
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