Note: Descriptions are shown in the official language in which they were submitted.
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TURBINE DISC WITH REDUCED NECK STRESS CONCENTRATION
BACKGROUND
The present invention relates to discs, and, more particularly, to a disc for
a gas turbine engine.
Discs are included in many types of rotary machines, and in many
applications, discs must rotate at high speeds during operation. This rotation
requires the
disc to have enough structural integrity to generate the necessary centripetal
force to keep
the disc intact. Otherwise the reaction to the centripetal force, known as
centrifugal force
(an imaginary force created by the inertia of the disc itself) will cause
stress within the
disc to exceed the material strength of the disc, breaking the disc apart. In
addition to the
mass of the disc itself, other components may be attached to the outer
periphery of the
disc. This increases the amount of rotating mass, requiring that the disc have
greater
strength. This can be solved by adding material to the disc, but doing so also
adds cost
and weight. Adding cost to a design is always undesirable, and, in the case of
a vehicle
application such as a gas turbine engine, adding weight may not be an option.
SUMMARY
According to one embodiment of the present invention, a disc with two
sides includes a hub having a bore and a bore radius, a neck, and a rim. The
neck is
connected to and radially outward of the hub and has an inner wedge with a
curved
section on one side of the disc, an outer wedge with a curved section on that
same side of
the disc, and a center section between the wedges with a flat side on that
same side of the
disc. The rim is connected to and radially outward of the neck, the rim having
a radius
that is no more than seven times greater than the bore radius.
In another embodiment, a gas turbine engine includes a compressor
section, combustor section downstream of the compressor section with an inner
radius,
and a turbine section downstream of the combustor section with a rotor with an
outer
radius. The outer radius is no more than 0.83 times as large as the inner
radius of the
combustor. The turbine section also includes a disc with a neck that has an
inner wedge
with a curved section on one side of the disc, an outer wedge with a curved
section on
that same side of the disc, and a center section between the wedges with a
flat side on that
same side of the disc.
In another embodiment, a gas turbine engine includes a compressor
section, combustor section downstream of the compressor section, and a turbine
section
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downstream of and substantially surrounded by the combustor section. The
turbine
section includes a disc with a neck that has an inner wedge with a curved
section on one
side of the disc, an outer wedge with a curved section on that same side of
the disc, and a
center section between the wedges with a flat side on that same side of the
disc.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross-section view of a gas turbine engine of an
auxiliary power unit.
FIG. 2 is a perspective view of a section of a rotor of the gas turbine
engine section, including a disc and a blade.
FIG. 3 is a cross-section view of a neck of the disc.
DETAILED DESCRIPTION
In FIG. 1, a partial cross-section view of gas turbine engine 10 of an
auxiliary power unit (APU) is shown. In the illustrated embodiment, the APU is
designed
for use on an aircraft. The APU includes gas turbine engine 10 that provides
rotational
force that can drive auxiliary equipment (not shown), such as an electrical
generator or a
pump.
Gas turbine engine 10 extends along engine axis 12 and includes
compressor section 14, combustor section 16 downstream of compressor section
14, and
turbine section 18 downstream of combustor section 16. Compressor section 14
includes
impeller 19, and turbine section 18 includes first rotor 20 and second rotor
22. Impeller
19, first rotor 20, and second rotor 22 are all connected to shaft 23, which
is rotatably
positioned in gas turbine engine 10. More specifically, impeller 19, first
rotor 20, second
rotor 22 are connected to shaft 23 with a plurality of joints 25A-25D,
respectively. In
addition, first rotor 20 and second rotor 22 are connected to each other at
joint 25C. Each
joint 25 is a mechanical joint that prevents relative rotation between the
connecting
components, such as a spigot fit, a spline, a curvic coupling, or an axially
toothed Hirth
joint.
In one embodiment, gas turbine engine 10 is a compact gas turbine engine.
In general, a compact gas turbine engine has a proportionally shorter axial
length when
compared to a more traditional gas turbine engine. In a traditional gas
turbine engine, the
whole combustor section is axially aft of the compressor section and the whole
turbine
section is axially aft of the combustor section, with the three sections
having similar outer
diameters. As shown in FIG. 1, compact gas turbine engine 10 has combustor
section 16
inside of turbine section 18. More specifically, turbine section 18 is
substantially
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surrounded by combustor section 16. This reduces the axial length of gas
turbine engine
because turbine section 18 is not wholly axially aft of combustor section 16.
This is
possible because turbine section 18 is radially smaller than combustor section
16. Second
rotor 22 has outer radius 24 that is no more than 0.83 times as large as inner
radius 26 of
5 combustor
section 16. In equation form, (rotor outer radius 24) < 0.83 * (combustor
inner
radius 26).
During operation of gas turbine engine 10, gas G enters compressor
section 14 and is compressed. Then gas G enters combustor section 16 and is
mixed with
fuel (not shown) and ignited, turning gas G into high pressure exhaust. Gas G
is then
10 expanded
through turbine section 18 where energy is extracted and utilized to drive
compressor section 24 and the auxiliary equipment (not shown). More
specifically, as
gas G expands through turbine section 18, first rotor 20 and second rotor 22
are rotated at
high speed.
The components and configuration of gas turbine engine 10 allow for gas
G and fuel to drive the auxiliary equipment by rotating first rotor 20 and
second rotor 22.
In addition, gas turbine engine 10 can have a compact size by positioning
turbine section
18 at least partially inside of combustor section 16.
Depicted in FIG. 1 is one embodiment of the present invention, to which
there are alternative embodiments. For example, gas turbine engine 10 can be
used for
propulsion. In such an embodiment, shaft 23 can be connected to a fan.
In FIG. 2, a perspective view of a section of second rotor 22 of gas turbine
engine 10 is shown, including disc 28 and blade 30. While first rotor 20 and
second rotor
22 are not identical, for the purposes of this discussion it will be
understood that the
below embodiments are applicable to both first rotor 20 and second rotor 22.
Second rotor 22 includes disc 28, which is a body of revolution about
engine axis 12. Disc 28 has hub 32 with bore 33 and bore radius 34, rim 38
with rim
radius 40, and neck 36 extending between hub 32 and rim 38. More specifically,
neck 36
is connected to and radially outward of hub 32, and rim 38 is connected to and
radially
outward of neck 36.
Hub 32 includes front ring 44 to interface with first rotor 20 (shown in
FIG. 1) and rear ring 46 to interface with shaft 23 (shown in FIG. 1). First
rotor 20 may
have a similar front and rear rings, although the front ring on first rotor 20
interfaces with
shaft 23 and the rear ring interfaces with second rotor 22 (at front ring 44).
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Extending radially outward from hub 32 is neck 36. The portion of neck
36 that is adjacent to hub 32 is inner wedge 48. Inner wedge 48 has a concave
side and
serves as a transition from hub 32 to center section 50, which is radially
outward from
inner wedge 48. Center section 50 is a thin, flat ring that extends between
inner wedge 48
and outer wedge 52, which is radially outward from center section 50. Outer
wedge 52
has a concave side and serves as a transition between center section 50 and
rim 38.
Rim 38 includes root cut 42 into which blade 30 is positioned and serves to
attach blade 30 to disc 28. (While only one blade 30 and one root cut 42 is
shown in FIG.
2 for clarity, it will be understood that there are a plurality of blades 30
around the
circumference of rim 38 and a plurality of circumferentially spaced root cuts
42, with
each blade 30 being connected at a root cut 42.) The assembled second rotor 22
has outer
radius 24, with outer radius 24 being the distance from engine axis 12 to the
radially outer
tip of blade 30.
As stated previously, in one embodiment, gas turbine engine 10 (shown in
FIG. 1) is a compact engine. Thereby, in that embodiment, outer radius 24 is
no more
than ten times greater than bore radius 34. In equation form, (outer radius
24) < 10 *
(bore radius 34). In the illustrated embodiment, the ratio of outer radius 24
to bore radius
34 is 7.9. In addition, in this embodiment, rim radius 40 is no more than
seven times
greater than bore radius 34. In equation form, (outer radius 24) < 7 * (bore
radius 34). In
the illustrated embodiment, the ratio of rim radius 40 to bore radius 34 is
4.9.
When gas turbine engine 10 (shown in FIG. 1) is operating, second rotor
22 rotates about engine axis 12. During rotation, there is stress on disc 28
caused by
items attached to disc 28 (for example, blade 30) as well the body force of
disc 28 itself.
In other words, all of the rotating mass in second rotor 22 desires to move
away from
engine axis 12, but the structural integrity of disc 28 must prevent this from
happening to
avoid a catastrophic event. While this stress is spread throughout disc 28,
different
regions of disc 28 have different magnitudes of stress. For example, the
stress is at a
maximum magnitude at neck 36 (more specifically, at center section 50) because
this
region has the smallest cross-sectional area of any portion of disc 28.
The components and configuration of second rotor 22 allow for second
rotor 22 to spin without fracturing. In addition, because center section 50 is
narrower
than rim 38 and hub 32, the thickness of neck 36 is minimized which reduces
the volume
of material and the weight of disc 28.
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In FIG. 3, a cross-section view of neck 36 of disc 28 is shown. In this
view, both front side 54 and rear side 56 of disc 28 are visible. Between
front side 54 and
rear side 56 is radial line 58, which is perpendicular to engine axis 12
(shown in FIG. 1).
With respect to front side 54, inner wedge 48 has a concave curved section
60 with radius R1, center section 50 has flat side 61, and outer wedge 52 has
a concave
curved section 62 radius R2. Extending between curved sections 60, 62 is flat
side 61,
and, more specifically, flat side 61 abuts curved section 60 at P1 at one end
and flat side
61 abuts curved section 62 at P2 at the opposite end. Flat side 61 is straight
(which is an
infinite radius of curvature) and has length L1. In the illustrated
embodiment, length L1 is
at least 0.1 times greater than the smaller of either radii of curvature R1,
R2. In equation
form, L1 > 0.1 * R(smaller of 1 and 2)= In addition, flat side 61 is
substantially radial (as it is
parallel to radial line 58), and flat side 61 is continuous with and tangent
to both curved
sections 60, 62.
With respect to rear side 56, in the illustrated embodiment, rear side 56 is
substantially the same as front side 54, although rear side 56 has the
opposite orientation
from front side 56. More specifically, inner wedge 48 has a concave curved
section 64
with radius R3, center section 50 has flat side 65, and outer wedge 52 has a
concave
curved section 66 radius R1. Extending between curved sections 64, 66 is flat
side 65,
and, more specifically, flat side 65 abuts curved section 64 at P3 at one end
and flat side
65 abuts curved section 66 at P4 at the opposite end. Flat side 65 is straight
(which is an
infinite radius of curvature) and has length L2. In the illustrated
embodiment, length L2 is
at least 0.1 times greater than the smaller of either radii of curvature R3,
R4. In equation
form, L2 > 0.1 * R(smaller of 3 and 4)= In addition, flat side 65 is
substantially radial (as it is
parallel to radial line 58), and flat side 65 is continuous with and tangent
to both curved
sections 64, 66.
During operation (i.e. rotation) of second rotor 22 (shown in FIG. 2), the
inertia of rim 38 would separate rim 38 from hub 32 (both shown in FIG. 2) but
for neck
36 providing a reactionary force that prevents disc 28 (shown in FIG. 2) from
structurally
failing. This reactionary force generates stress that, according to the fluid
flow theory of
stress, can be said to flow through neck 36. Also according to the fluid flow
theory of
stress, a radiused feature such as one of curved sections 60, 62, 64, 66
redirects the flow
of stress, creating a stress concentration. In addition, if neck 36 were
configured such that
curved sections 60, 64 were adjacent to curved sections 62, 66, respectively,
(i.e. with no
center section 50 or flat sides 61, 65) then there would be a single radial
location at which
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neck 36 would have the smallest cross-sectional area. Unfortunately, the
result would be
a sharply increasing flow of stress intensity through neck 36 due to the
meeting of two
curved sections 60, 62 and 64, 66 and the small cross-sectional area thereat.
The stress
flow through this location would be choked, resulting in one large compound
stress
concentration at the junction of curved sections 60, 62 and another large
compound stress
concentration at the junction of curved sections 64, 66, wherein the former is
on front side
54 and the latter is on rear side 56. Although, the remainder of neck 36 would
have a
much lower magnitude of stress than at these compound stress concentrations.
In accordance with the present invention, during rotation, disc 28 (shown
in FIG. 2) lacks the aforementioned large compound stress concentrations. This
is
because flat sides 61, 65 have infinite radii of curvature and geometrically
separate
curved sections 60, 62 and 64, 66, respectively. Therefore, flat sides 61, 65
also separate
the stress concentrations resulting from curved sections 60, 62, 64, 66,
preventing the
large compound stress concentration that would be present if curved sections
60, 62 and
64, 66 were adjacent, respectively. Instead, the embodiment illustrated in
FIG. 3
smoothes the flow of stress through neck 36. More specifically, there is a
stress
concentration proximate to each of Pi, P2, P3, and P4. The exact magnitudes of
these
stress concentrations depends on the specific geometry and loading of neck 36,
including
radii of curvature 60, 62, 64, and 66. But because curved sections 60, 62 are
separated by
flat side 61, the magnitudes of the stress concentrations proximate to Pi and
P2 are less
than the compound stress that would result if flat side 61 did not separate Pi
and P2.
Similarly, because curved sections 64, 66 are separated by flat side 65, the
magnitudes of
the stress concentrations proximate to P3 and P4 are less than the compound
stress that
would result if flat side 61 did not separate P3 and P4.
In the illustrated embodiment, having curved sections 60, 62 separated by
flat side 61 creates an region proximate to the center of flat side 61 that
has a magnitude
of stress that is less than the magnitude of stress in the stress
concentrations that are
proximate to Pi and P2. Similarly, having curved sections 64, 66 separated by
flat side 65
creates a region proximate to the center of flat side 65 that has a magnitude
of stress that
is less than the magnitude of stress in the stress concentrations that are
proximate to P3
and P4.
The configuration of disc 28 allows for a more homogenous stress
distribution in neck 36. This reduces the maximum magnitudes of stress
concentrations,
which lowers the amount of material necessary to withstand the forces within
neck 36
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during operation of gas turbine engine 10 (shown in FIG. 1). In the
illustrated
embodiment, the reduction in the maximum magnitude of stress in neck 36 is at
least
fifteen percent when compared to a conventional disc neck that lacks any flat
sides
separating the curved sections. Although, in other embodiments, other stress
reduction
levels are possible.
Depicted in FIG. 3 is one embodiment of the present invention, to which
there are alternative embodiments. For example, radius R1 of curved section 60
can be
substantially the same as radius R2 of curved section 62, and radius R3 of
curved section
64 can be substantially the same as radius R4 of curved section 66. For
another example,
radius R1 of curved section 60 can be substantially different from radius R3
of curved
section 64, and radius R2 of curved section 62 can be substantially different
from radius
R4 of curved section 66. For a further example, length L1 can be substantially
different
from length L2. For yet another example, flat sides 61, side 65 can be
oriented such that
one or both of them extend in a generally radial direction that is not
substantially radial.
It will be recognized that the present invention provides numerous benefits
and advantages. For example, the maximum stress concentration in neck 36 is
reduced,
which allows neck 36 to be thinner. This reduces the weight and cost of disc
28.
While the invention has been described with reference to an exemplary
embodiment(s), it will be understood by those skilled in the art that various
changes may
be made and equivalents may be substituted for elements thereof without
departing from
the scope of the invention. In addition, many modifications may be made to
adapt a
particular situation or material to the teachings of the invention without
departing from
the essential scope thereof. Therefore, it is intended that the invention not
be limited to
the particular embodiment(s) disclosed, but that the invention will include
all
embodiments falling within the scope of the appended claims.
Discussion of Various Embodiments
A disc according to an exemplary embodiment of this disclosure, among
other possible things includes: a first side and a second side, the disc
comprising: a hub
including a bore with a bore radius; a neck connected to and radially outward
of the hub,
the neck comprising: an inner wedge with a first concave curved section on the
first side
of the disc including a first radius of curvature; an outer wedge with a
second concave
curved section on the first side of the disc including a second radius of
curvature; and a
center section extending between the inner wedge and the outer wedge, the
center section
including a first flat side on the first side of the disc; and a rim connected
to and radially
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outward of the neck, the rim including a rim radius that is no more than seven
times
greater than the bore radius.
A further embodiment of the foregoing disc, wherein the first flat side can
include a length that is at least 0.1 times greater than the smaller of the
first radius of
curvature and the second radius of curvature.
A further embodiment of any of the foregoing discs, wherein the first flat
side can be tangent to the first concave curved section and tangent to the
second concave
curved section.
A further embodiment of any of the foregoing discs, wherein the first flat
side can extend substantially radially.
A further embodiment of any of the foregoing discs, wherein the disc can
further comprise: a third concave curved section on the inner wedge on the
second side of
the disc that includes a third radius of curvature that is substantially the
same as the first
radius of curvature; a fourth concave curved section on the outer wedge on the
second
side of the disc that includes a fourth radius of curvature that is
substantially the same as
the second radius of curvature; and a generally radial second flat side on the
center
section on the second side of the disc extending between the inner wedge and
the outer
wedge.
A further embodiment of any of the foregoing discs, wherein the first
radius of curvature can be substantially the same as the second radius of
curvature.
A further embodiment of any of the foregoing discs, wherein can be
configured to react to a stress in the neck by distributing the stress to a
first stress
concentration of a first magnitude in the neck and a second stress
concentration of a
second magnitude in the neck, the first stress concentration and the second
stress
concentration separated by a region in the center section, the region having
stress of a
third magnitude that is lower than both the first magnitude and the second
magnitude.
A gas turbine engine according to an exemplary embodiment of this
disclosure, among other possible things includes: a compressor section; a
combustor
section downstream of the compressor section, the combustor section including
an inner
radius; and a turbine section downstream of the combustor section, the turbine
section
including a rotor with an outer radius that is no more than 0.83 times as
large as the inner
radius of the combustor, the rotor including a disc with a first side, a
second side and a
neck comprising: an inner wedge with a first concave curved section on the
first side of
the disc; an outer wedge with a second concave curved section on the first
side of the
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disc; and a center section extending between the inner wedge and the outer
wedge, the
center section including a first flat side on the first side of the disc.
A further embodiment of the foregoing gas turbine engine, wherein the
first flat side can include a length that is at least 0.1 times greater than
the smaller of the
first radius of curvature and the second radius of curvature.
A further embodiment of any of the foregoing gas turbine engines, wherein
the disc can be configured to react to a stress in the neck by distributing
the stress to a
first stress concentration of a first magnitude in the neck and a second
stress concentration
of a second magnitude in the neck, the first stress concentration and the
second stress
concentration separated by a region in the center section, the region having
stress of a
third magnitude that is lower than both the first magnitude and the second
magnitude.
A further embodiment of any of the foregoing gas turbine engines, wherein
the first flat side can be tangent to the first concave curved section and
tangent to the
second concave curved section.
A further embodiment of any of the foregoing gas turbine engines, wherein
the first flat side can extend substantially radially.
A further embodiment of any of the foregoing gas turbine engines, wherein
the gas turbine engine can further comprise: a third concave curved section on
the inner
wedge on the second side of the disc that includes a third radius of curvature
that is
substantially the same as the first radius of curvature; a fourth concave
curved section on
the outer wedge on the second side of the disc that includes a fourth radius
of curvature
that is substantially the same as the second radius of curvature; and a
generally radial
second flat side on the center section on the second side of the disc
extending between the
inner wedge and the outer wedge.
A further embodiment of any of the foregoing gas turbine engines, wherein
the first radius of curvature can be substantially the same as the second
radius of
curvature.
A further embodiment of any of the foregoing gas turbine engines, wherein
the gas turbine engine can further comprise: a hub with a bore radius
connected to and
radially inward of the neck; and a rim connected to and radially outward of
the neck, the
rim including a rim radius that is no more than seven times greater than the
bore radius.
A further embodiment of any of the foregoing gas turbine engines, wherein
the turbine section can be substantially surrounded by the combustor section.
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A gas turbine engine according to an exemplary embodiment of this
disclosure, among other possible things includes: a compressor section; a
combustor
section downstream of the compressor section; and a turbine section downstream
of and
substantially surrounded by the combustor section, the turbine section
including a disc
with a first side, a second side and a neck comprising: an inner wedge with a
first concave
curved section on the first side of the disc; an outer wedge with a second
concave curved
section on the first side of the disc; and a center section extending between
the inner
wedge and the outer wedge, the center section including a first flat side on
the first side of
the disc.
A further embodiment of the foregoing gas turbine engines, wherein the
first flat side can include a length that is at least 0.1 times greater than
the smaller of the
first radius of curvature and the second radius of curvature.
A further embodiment of any of the foregoing gas turbine engines, wherein
the combustor section includes an inner radius, and the turbine section
includes a rotor
that includes the disc, the rotor including an outer radius that can be no
more than 0.83
times as large as the inner radius of the combustor.
A further embodiment of any of the foregoing gas turbine engines, wherein
the disc can be configured to react to a stress in the neck by distributing
the stress to a
first stress concentration of a first magnitude in the neck and a second
stress concentration
of a second magnitude in the neck, the first stress concentration and the
second stress
concentration separated by a region in the center section, the region having
stress of a
third magnitude that is lower than both the first magnitude and the second
magnitude.
