Note: Descriptions are shown in the official language in which they were submitted.
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CONTOURED STATOR SHROUDS
[00011 FIELD OF THE INVENTION
BACKGROUND
[0002] The disclosed embodiments generally pertain to gas turbine
engines. More
particularly, present embodiments relate to shrouds within gas turbine engines
which are
utilized with pivoting vanes.
[0003] In a gas turbine engine a typical gas turbine engine generally
possesses a
forward end and an aft end with its several components following inline
therebetween. An
air inlet or intake is at a forward end of the engine. Moving toward the aft
end, in order, the
intake is followed by a compressor, a combustion chamber, a turbine, and a
nozzle at the aft
end of the engine. It will be readily apparent from those skilled in the art
that additional
components may also be included in the engine, such as, for example, low-
pressure and
high-pressure compressors, high-pressure and low-pressure turbines, and an
external shaft.
This, however, is not an exhaustive list. An engine also typically has an
internal shaft
axially disposed through a center longitudinal axis of the engine. The
internal shaft is
connected to both the turbine and the air compressor, such that the turbine
provides a
rotational input to the air compressor to drive the compressor blades.
[0004] In operation, air is pressurized in a compressor and mixed with
fuel in a
combustor for generating hot combustion gases which flow downstream through
turbine
stages. These turbine stages extract energy from the combustion gases. A high
pressure
turbine first receives the hot combustion gases from the combustor and
includes a stator
nozzle assembly directing the combustion gases downstream through a row of
high pressure
turbine rotor blades extending radially outwardly from a supporting rotor
disk. In a two
stage turbine, a second stage stator nozzle assembly is positioned downstream
of the first
stage blades followed in turn by a row of second stage rotor blades extending
radially
outwardly from a second supporting rotor disk. The turbine converts the
combustion gas
energy to mechanical energy.
[0005] Vanes or airfoils are typically designed with a primary or
optimal position
for operation. However, depending on the desired operating condition of the
turbine engine,
the vanes may be actuated to alternate positions. Current stator shroud
designs utilize a
circular cross-section across which vanes are actuated. As the vanes move from
the open
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design position to off design closed positions, clearance between the vane and
shroud
increases due to the curvature of the shroud, the flow path geometry and the
lower edge
shape of the vane, all of which are required to meet the compressor operating
requirements.
[0006] When this clearance increases, flow disruptions can affect the
intended
purpose of the vane shape function and configuration. It would be desirable to
overcome
these and other deficiencies so that the clearance between the vane and shroud
is reduced,
for example in the off design closed angular positions of the vane.
SUMMARY
[0007] According to at least some embodiments, a contoured stator shroud
vane
assembly in a gas turbine engine having an inlet end, an outlet end and a
plurality of
propulsor components comprises a stator shroud having a generally circular
cross ¨ section,
the shroud having a forward end, an aft end and at least one surface extending
between said
first end and said second end, the shroud having a plurality of pivots
disposed
circumferentially about the shroud to support a trunnion of a vane, the at
least one surface of
varying elevation adjacent to said plurality of pivots and extending in a
circumferential
direction.
[0008] According to at least some embodiments, a contoured stator shroud,
comprises a forward end, an aft end and at least one surface extending between
the forward
end and the aft end, the at least one surface being tapered from the forward
end to the aft
end, a plurality of areas of varying elevation disposed about the at least one
surface, the
plurality of areas each having a peak and a valley, a plurality of pivot
apertures spaced
about a forward end of the at least one surface,
[0009] According to still other embodiments, a contoured stator shroud,
comprises a
forward end and an aft end, at least one surface extending between the forward
end and the
second end, the at least one surface having a scalloped chord overhang area,
the scalloped
area extending in a circumferential direction, a plurality of vane mounting
locations
disposed circumferentially between the forward end and the aft end.
BRIEF DESCRIPTION OF THE ILLUSTRATIONS
[0010] Embodiments of the invention are illustrated in the following
illustrations.
[0011] FIG. 1 is a side section view of a gas turbine engine;
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[0012] FIG. 2 is an exploded perspective view of a stator shroud vane
assembly;
[0013] FIG. 3 is a perspective view of the stator shroud vane assembly;
[0014] FIG. 4 is a side section view of an exemplary stator shroud vane
assembly;
[00151 FIG. 5 is a detail perspective view of stator shroud vane
assembly;
[0016] FIG. 6 is an aft view of the stator shroud vane assembly in a
first position;
[0017] FIG. 7 is an aft view of the stator shroud vane assembly in a
second position;
[0018] FIG. 8 is an all view of the stator shroud vane assembly in a
third position;
and,
[0019] FIG. 9 is a graph of vane position as related to clearance
between the shroud
and the vane.
DETAILED DESCRIPTION'
[0020] Reference now will be made in detail to embodiments provided, one
or more
examples of which are illustrated in the drawings. Each example is provided by
way of
explanation, not limitation of the disclosed embodiments. In fact, it will be
apparent to
those skilled in the art that various modifications and variations can be made
in the present
embodiments without departing from the scope or spirit of the disclosure. For
instance,
features illustrated or described as part of one embodiment can be used with
another
embodiment to still yield further embodiments. Thus it is intended that the
present
invention covers such modifications and variations as come within the scope of
the
appended claims and their equivalents.
[0021] Referring to FIGS. 1-9, various embodiments of a contoured stator
shroud
capable of use with pivoting vanes. The stator shroud includes a stator shroud
overhang
surface over which vanes are pivoted during engine operation. The stator
shroud overhang
surface has varying elevations to eliminate leakage between the vane and the
shroud which
would normally occur when a vane pivots an outer surface of the shroud. This
reduces any
flow disruptions or flow disturbances along the vane or airfoil.
[0022] As used herein, the terms "axial" or "axially" refer to a
dimension along a
longitudinal axis of an engine. The term "forward" used in conjunction with
"axial" or
"axially" refers to moving in a direction toward the engine inlet, or a
component being
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relatively closer to the engine inlet as compared to another component. The
term "aft" used
in conjunction with "axial" or "axially" refers to moving in a direction
toward the engine
nozzle, or a component being relatively closer to the engine nozzle as
compared to another
component.
[0023] As used herein, the terms "radial" or "radially" refer to a
dimension
extending between a center longitudinal axis of the engine and an outer engine
circumference. The use of the terms "proximal" or "proximally," either by
themselves or in
conjunction with the terms "radial" or "radially," refers to moving in a
direction toward the
center longitudinal axis, or a component being relatively closer to the center
longitudinal
axis as compared to another component. The use of the terms "distal" or
"distally," either
by themselves or in conjunction with the terms "radial" or "radially," refers
to moving in a
direction toward the outer engine circumference, or a component being
relatively closer to
the outer engine circumference as compared to another component.
[0024] As used herein, the terms "lateral" or "laterally" refer to a
dimension that is
perpendicular to both the axial and radial dimensions.
[0025] Referring initially to FIG. 1, a schematic side section view of a
gas turbine
engine 10 is shown having an engine inlet end 12 wherein air enters the
propulsor 13 which
is defined generally by a compressor 14, a combustor 16 and a multi-stage high
pressure
turbine 20. Collectively, the propulsa.)r 13 provides thrust or power during
operation. The
gas turbine 10 may be used for aviation, power generation, industrial, marine
or the like.
Depending on the usage, the engine inlet end 12 may alternatively contain
multi-stage
compressors rather than a fan. The gas turbine 10 is axis-symmetrical about
engine axis 26
or shaft 24 so that various engine components rotate thereabout. In operation
air enters
through the air inlet end 12 of the engine 10 and moves through at least one
stage of
compression where the air pressure is increased and directed to the combustor
16. The
compressed air is mixed with fuel and burned providing the hot combustion gas
which exits
the combustor 16 toward the high pressure turbine 20. At the hid' pressure
turbine 20,
energy is extracted from the hot combustion gas causing rotation of turbine
blades which in
turn cause rotation of the shaft 24. The shaft 24 passes toward the front of
the engine to
continue rotation of the one or more compressor stages 14, a turbofan 18 or
inlet fan blades,
depending on the turbine design.
[0026] The axis-symmetrical shaft 24 extends through the through the
turbine
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engine 10, from the forward end 12 to an aft end. The shaft 24 is journaled
along its length.
The shaft 24 may be hollow to allow rotation of a low pressure turbine shaft
28 therein and
independent of the shaft 24 rotation. Both shafts 24, 28 may rotate about the
centerline axis
26 of the engine. During operation the shafts 24, 28 rotate along with other
structures
connected to the shafts such as the rotor assemblies of the turbine 20 and
compressor 14 in
order to create power or thrust depending on the area of use, for example
power, industrial
or aviation.
[0027] Referring still to FIG, 1, the inlet 12 includes a turbofan 18
which has a
plurality of blades, The turbofan 18 is connected by the shaft 28 to the low
pressure turbine
19 and creates thrust for the turbine engine 10. The low pressure air may be
used to aid in
cooling components of the engine as well.
[0028] Referring now to FIG. 2 an exploded perspective view of a stator
shroud
vane assembly 30 is depicted. A plurality of vanes 40 are spaced about the
shroud 32, most
of which are not shown. Three vanes 40 are shown exploded from the outer
surface of the
shroud. For clarity sake, however, it should be understood that a plurality of
vanes 40 are
disposed about the shroud 32. The shroud 32 of the exemplary embodiment is
circular in
cross section and frusto-conical in shape having a forward end 34, an aft end
36. Within the
hollow central portion of the shroud the propulsor components 13 of the gas
turbine engine
may pass through. The exemplary shroud 32 is located in the compressor 14 area
of the
engine. For example, a multi-stage compressor typically includes several rows
of rotating
blades mounted on a rotor and several rows of stator vanes 40 mounted between
a stator
casing and the shroud 32. The shroud is axisymmetric to the shaft 24 (FIG. I)
of engine 10.
[0029] Near the forward end 34 are a plurality of pivots 38, which are
represented
in the exemplary embodiment as a number of circular pockets wherein the vanes
40 are
seated for rotation relative to the shroud 32. The shroud 32 also tapers from
a smaller
diameter near the forward end 34 to a larger diameter near the aft end 36. As
will be better
understood upon further reading of this disclosure, a clearance is created
between a lower
edge of the vanes 40 and the outer surface of the shroud 32 when the vanes 40
are seated
within the pivots 38. In a normal shroud, the circular cross-section results
in increased
clearance between the vane and the shroud when the vane is rotated to off
design positions.
However, present embodiments provide for a wavy or variable surface height to
reduce
clearance in the off-design positions of the vane 40,
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[0030] The vane 40 includes an outer spindle 44 and an inner spindle 45.
The
spindles 44, 45 may be formed as a vertical line or at an angle to the
vertical. For example,
the depicted spindles are at an angle of between 10 and 15 degrees from the
vertical. At the
inner spindle 45 is a button 42 which along with the spindle 45 is seated
within the pivot 38.
An upper button 56 also controls rotation within the casing of the engine,
through which the
outer spindle passes.
[0031] Referring now to FIG. 3, a perspective view of a stator shroud
vane
assembly 30 is depicted. As previously described, the instant shroud assembly
30 is located
within the compressor 14 of the turbine engine. However the principles
embodied in the
contoured stator shroud 32 may be utilized in alternate locations of the
engine wherein
shrouds and vanes or air foils are utilized, such as the stator vanes of a
turbine, for example.
The stator shroud 32 depicted is at an inner diameter of the vanes 40. An
engine casing (not
shown) may be used to provide the outer diameter pivot location ibr the vanes
40. The
stator vane shroud assembly 30 utilizes a shroud 32 having a forward end 34
and aft end 36.
The shroud 32 is generally circular in cross section as partially shown in the
view depicted.
The diameter at the forward end 34 may be larger than the diameter at the aft
end 36. The
forward end includes a plurality of pivots 38 wherein vanes 40 may be
positioned. The
pivots 38 are recessed areas wherein the vane or air foils 40 are positioned
for pivoting
utilizing buttons or guides 42. At a radially outward position of the vane 40
is a spindle 44
which may be utilized to mount the second end of the vanes 40 to provide
guided pivoting
or rotation. The spindle 44 may pass through an aperture in an engine casing
to stabilize the
spindle and allow for pivoting motion. A lever arm (not shown) guides the
rotation through
the desired angular displacement providing the different positions for
improved efficiency
and performance of the engine at multiple operating conditions. The plurality
of vanes 40
extend about the circumference of the shroud 32 near the forward end 34 of the
shroud,
although some are not shown for clarity.
[0032] Extending rearwardly from the pivots 38 is at least one shroud
surface 46,
for example a stator chord overhang surface 46. The stator chord overhang
surface 46
tapers from a smaller diameter near the pivots 38 to a larger diameter near
the aft end 36.
This axial direction taper or change in elevation may be curved or may be
linear.
[0033] In addition to this taper, the stator chord overhang surface 46 is
contoured so
that the elevation changes in the circumferential direction. As shown with the
broken lines
48 extending in the circumferential direction, the curvature 48 of the broken
lines depicts
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the contour of the stator chord overhang surface 46 which varies between a
lower elevation
and an upper elevation in a circumferential direction. Thus rather than having
a circular
surface, the broken line depicts the contour 48 along wavy or sinuous surface
46. According
to one embodiment of the present disclosure, the stator chord overhang surface
46 has a
wavy contour 48 to reduce clearance between the vane 40 and the shroud 32
during
movement of the vane 40. According to alternate embodiments, the variation in
elevation in
the circumferential direction may be linear. In either embodiment, the surface
48 includes a
plurality of peaks and valleys. The axis of the peaks or valleys are generally
parallel to the
axis of the engine 26 (FIG. 1) or at an angle to engine axis 26 is the shroud
tapers from
forward to aft end. As will be described further herein, the contour 48
significantly reduces
the flow field disruptions created by the clearance between the vanes 40 and
shroud 32.
These clearances would normally adversely affect the intended purpose of the
vane airfoil
shape, function and configuration when the vane moves between open and closed
angular
positions.
[0034] The exemplary vane or air foil 40 includes a leading edge 50, and
a trailing
edge 52 and opposed surfaces extending between. The opposed surfaces define a
suction
side and a pressure side which will be understood by one skilled in the art.
At a radially
outward end of the vane 40 an outer enlarged portion or button 56. The spindle
or trunion
44 may be connected to a lever arm or other feature to actuate the vane 40 to
a desired
position. The rotation of the vane 40 provides more than one optimal condition
for the vane
or air foil to provide improved efficiency and performance at differing
operating conditions
of the gas turbine engine 10.
[0035] Near a lower end of the vane 40, a fillet 54 connects the vane 40
to the
button 42 at the radially inner end, The lower edge 58 of the vane 40, or vane
overhang, is
curved and during movement of the vane 40, the lower edge 58 moves away from
the
typical shroud surface (FIG. 6) which is purely circular in cross section and
represented by
line 70. This creates clearance between the lower vane edge 58 and the chord
overhang
surface 46 due to the divergent geometries of the two parts. The increased
clearance which
occurs with prior art to systems reduces performance, air flow turn and
increases loss in this
region which is undesirable and inhibits improvements in engine performance.
The contour
represented by the wavy or curved broken line 48 decreases clearance between
the shroud
32 and the vane 40 improving the air turning performance and reducing loss in
this region.
[0036] Referring now to FIG. 4, a side section view of the assembly 30 of
Fig. 3 is
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depicted. The shroud 32 is shown sectioned vertically between the forward end
34 and the
aft end 36 so as to depict the button 42 which is seated within the pivot 38.
The vane 40
further includes a lower spindle or trunnion 45 which extends downwardly into
the pivot so
that the vane 42 is pivotally secured in the shroud 32 and, as previously
described, the upper
spindle 44 is pivotally retained through an engine casing. As also shown in
the figure, the
stator chord overhang 46 is curved in the axial direction between the forward
end 34 and the
aft end 36, and more specifically aft of the pivots 38. According to
alternative
embodiments, the surface 46 is tapered linearly in the axial direction between
forward end
34 and the aft end 36.
[0037] Referring now to FIG. 5, a detailed perspective view of the shroud
32 and
vanes 40 are depicted. The detailed view shows a pivot 38 in both an empty
condition and a
filled by a vane 40. A button 42 is seated within the generally circularly
shaped pivot 38
and the vane 40 is connected to the button 42 by fillet 54. Between a lower
edge 58 of the
vane and the stator chord overhang 46 a clearance 60 is shown. The clearance
is reduced
relative to prior art stators due to the curvature in the axial direction,
between the forward
end 34 and the aft end 36. Similarly, the clearance is decreased through the
arcuate
movement of the vane 40 within the pivot 38 due to the contour 48 along the
circumferential direction of the overhang surface 46.
[0038} In the view of FIG. 5, the contour 48 is more clearly shown due to
the
curvature of the broken line 48 which represents the contour of the stator
shroud 32. A
plurality of axially extending contour lines 49 also are shown on the stator
chord overhang
surface 46 which depict another curvature of the stator 32. In combination
with the lower
edge 58 of the vane 40 decrease clearance between the vane 40 and stator 32
which
improves engine performance through multiple positions of the pivoting vane
40. Relative
to operation of the engine 10, the vanes 40 are closed when the engine speed
is at or very
near zero. In this closed position, the vanes 40 are near the uppermost
elevation of the
contour surface 48. Alternatively, as engine speed increases and approaches a
maximum,
the vane 40 approaches the lowermost elevation of the contour surface 48.
[0039] Referring now to FIGs. 6-8, the shroud 32 is shown in an aft view
looking
forward with a vane 40 shown move in multiple positions. The contour of the
stator chord
overhang surface 46 is best described in reference to this view. The wavy or
sinuous
surface 48 is formed by a plurality of scallop-like humps which change between
first and
second elevations. Although the term sinuous is used, it should not be limited
to
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mathematically exact sin curve. The term is instead used in a general sense to
indicate a
repeating change in elevation. A broken line 70 is shown in the view to
represent a circular
reference shape of a prior art shroud. The line 70 may also represent a base
or first
elevation of the stator chord overhang surface 46. Alternatively, the line 70
of the instant
embodiment may be above or below the valley or lower elevation of the stator
chord
overhang surface since, as shown, the surface 46 also changes elevation in the
axial
direction. The contour 48 elevation changes are shown by referencing the
difference
between first elevation 70 and the second upper elevation 72 of the contour.
Thus the
overhang surface 46 changes elevation between a first elevation and a second
elevation and
with such changing elevation, the clearance between the vane 40 is reduced
throughout the
positions depicted in FIGs. 6-8.
[00401 Additionally shown in the figure is an axial flow line 70 which
indicates the
direction of air flow across the stator shroud 32 between the vanes 40 and in
the axial
direction parallel to the engine axis 26 (Fig. I),
[0041] The vane 40 may rotate from, for example, minus 3 degrees and
about 25
degrees. Thus the exemplary vane 40 may move about 14 degrees from the center
position
in either of two rotational directions. However this is exemplary and
alternate angular
ranges may be designed into the vane movement.
[0042] Referring now to FIG. 7, the vane is shown in a central position
which more
clearly depicts the lower edge 58 of the vane. The vane 40 is in the II degree
position,
according to the exemplary range as previously described. This is generally a
central
position, A pair of clearance arrows are shown in Fig. 7. Clearance 60 depicts
the
clearance provided by the contoured 48 in cooperation with the lower edge 58
of vane 40.
Meanwhile the clearance P is shown which depicts the larger clearance between
the lower
edge 58 and the prior art circular shroud reference previously described as
line 70. From this
embodiment, one skilled in the art can clearly see the reduced differential
that the contour
48 provides.
[0043]
Referring now to FIG. 8, a second extreme position of the vane 40 is depicted,
for example at the 25 degree position. Again the clearance 60 is much smaller
than the
prior art clearance P as related to the circular shroud reference 70,
[0044] it should be understood by one skilled in the art that vanes may
take various
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shapes and forms depending upon the design characteristics of the engine.
Accordingly, the
shape of the contours may be formed to correspond to the shape of the vane
lower edge
through a preselected arcuate motion. The shroud surface, spindle angle,
amount of vane
chord overhang and travel are all designed/optimized with reduced clearance
for reduced
loss and improved performance in mind when optimizing the variable vane
system,
[0045] Referring now to FIG. 9, a chart is shown depicting a relationship
between
the vane's angle measured in degrees and the clearance between the vane lower
edge 58 and
the shroud chord overhang 46. As shown by the line 80, having diamond-shaped
data
points, the clearance between an angle of minus 10 degrees and 25 increases
rather
constantly. The stator shroud 32 of this prior art embodiment is circular in
shape and is
lacking the contour shape of the instant embodiments. To the contrary, line 82
represented
by square-shaped data points begins at the previously defined range of minus 3
degrees and
moves to a position of 25 degrees. The clearance represented by line 82 is
generally
constant from about 0 degrees to about 12 degrees, before increasing up to the
25 degree
position. Thus, by comparing the data points along the lines 80, 82 one
skilled in the art
will recognize the clearance is much less in the contoured stator shroud than
that of the prior
art.
[0046] The foregoing description of structures and methods has been
presented for
purposes of illustration. It is not intended to be exhaustive or to limit the
invention to the
precise steps and/or forms disclosed, and obviously many modifications and
variations are
possible in light of the above teaching. Features described herein may be
combined in any
combination. Steps of a method described herein may be performed in any
sequence that is
physically possible. It is understood that while certain forms of a contoured
stator shroud
have been illustrated and described, it is not limited thereto and instead
will only be limited
by the claims, appended hereto.
