U.S. patent application number 09/746255 was filed with the patent office on 2002-06-27 for reduced stress rotor blade and disk assembly.
Invention is credited to Wong, Charles K..
Application Number | 20020081205 09/746255 |
Document ID | / |
Family ID | 25000063 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081205 |
Kind Code |
A1 |
Wong, Charles K. |
June 27, 2002 |
Reduced stress rotor blade and disk assembly
Abstract
A bladed rotor disk assembly includes a plurality of
circumferentially spaced apart blade root slots extending through
the disk at an angle to the disk axial direction. Each slot has a
radially inwardly facing load reaction surface along each side
thereof extending continuously over less than the full the length
of the slot in contact with a corresponding radially outwardly
facing load reaction surface of a blade root disposed within the
slot. This eliminates highly concentrated reaction loads adjacent
the ends of the slot and results in a more uniform load
distribution over the remaining smaller reaction surface area,
reducing maximum stresses.
Inventors: |
Wong, Charles K.;
(Manchester, CT) |
Correspondence
Address: |
Stephen E. Revis
11 Brenthaven
Avon
CT
06001-3941
US
|
Family ID: |
25000063 |
Appl. No.: |
09/746255 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
416/219R ;
416/248 |
Current CPC
Class: |
Y02T 50/60 20130101;
Y02T 50/671 20130101; F01D 5/147 20130101; F01D 5/3007
20130101 |
Class at
Publication: |
416/219.00R ;
416/248 |
International
Class: |
F01D 005/30 |
Claims
What is claimed is:
1. A rotor assembly comprising: a disk having a rotational axis,
opposing front and rear surfaces, a rim, and a plurality of
circumferentially spaced apart blade retaining slots extending
through said rim from said front disk surface through said rear
disk surface in a direction D which forms an angle .theta. of at
least 10.degree. with said disk axis, each pair of adjacent slots
defining a disk lug therebetween, each of said slots having a first
radially inwardly facing slot load reaction surface extending from
said front disk surface in said direction D a distance M on a first
of said lugs, and a second radially inwardly facing slot load
reaction surface extending from said rear disk surface in said
direction D a distance N on a second of said lugs adjacent said
first lug, each of said slots having a length L from said disk
front surface to said disk rear surface in said direction D; and a
plurality of blades, each having an airfoil and a root integral
with said airfoil, said root disposed within a respective one of
said slots, said root having a radially outwardly facing first root
load reaction surface extending in said direction D a distance M
and a radially outwardly facing second root load reaction surface
extending in said direction D a distance N, said first root load
reaction surface adapted to contact said first slot load reaction
surface over said distance M, and said second root load reaction
surface adapted to contact said second slot load reaction surface
over said distance N, wherein said slot length L is greater than at
least one of said distances M and N.
2. The rotor assembly according to claim 1, wherein M equals N.
3. The rotor assembly according to claim 1, wherein the slot length
L is greater than both M and N.
4. The rotor assembly according to claim 1, wherein said blade root
has oppositely facing end surfaces perpendicular to said direction
D.
5. The rotor assembly according to claim 1, wherein said blade root
has oppositely facing end surfaces perpendicular to said axial
direction.
6. The rotor assembly according to claim 2, wherein each of said
blade root end surfaces includes a planar portion substantially
parallel to a radial line over at least the radial extent of said
root reaction surfaces, and the angle between each of said planar
portions and the direction D is between 90.degree. and .theta..
7. The rotor assembly according to claim 6, wherein said planar
portions are parallel to each other and spaced apart a distance P,
wherein the distance P is less than the length L of said blade
slot.
8. The rotor assembly according to claim 7, wherein P, M and N are
substantially equal.
9. The rotor assembly according to claim 1, wherein at least one of
said blade root end surfaces is substantially in the plane of one
of said opposing disk front and rear surfaces over the radial
extent of said root reaction surfaces, and wherein at least one of
said root load reaction surfaces includes an extension, in the
direction D, to said at least one of said root end surfaces, said
slot being spaced from said load reaction surface extension leaving
a gap therebetween.
10. The rotor assembly according to claim 1, wherein one of said
blade root end surfaces is substantially in the plane of said disk
front surface over the radial extent of said root load reaction
surfaces, and the other one of said blade root end surfaces is
substantially in the plane of said disk rear surface over the
radial extent of said root load reaction surfaces, and wherein each
of said root load reaction surfaces includes an extension, in the
direction D, to a respective one of said root end surfaces, said
slot being spaced from each of said load reaction surface
extensions leaving gaps therebetween.
11. The rotor assembly according to claim 10, wherein M and N are
equal.
12. The rotor assembly according to claim 10, wherein said root is
a dovetail root.
13. The rotor assembly according to claim 1, wherein said root is a
dovetail root.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] This invention relates to bladed rotor assemblies, and
especially to bladed rotor assemblies for gas turbine engines.
[0003] 2. Background Information
[0004] Bladed rotor assemblies are well known in the art, such as
for compressors and turbines of gas turbine engines. In such
assemblies, each blade is often attached to the rotor disk by means
of a root, integral with the radially innermost end of the blade.
The root fits closely within a corresponding blade root slot
extending generally axially through the disk rim, but at an angle
to the true direction of the disk axis. The disk material disposed
circumferentially between a pair of adjacent slots is often
referred to as a disk lug. The blade root includes radially
outwardly facing reaction surfaces that engage corresponding
radially inwardly facing reaction surfaces of a blade root slot.
During operation of the rotor, the blade loads are transferred into
the disk and disk lugs through these engaged surfaces. Typically, a
blade root extends from the front face to the rear face of the
disk; and the engaged load reaction surfaces also extend from the
front to the rear face of the disk (i.e. the full length of the
slot). This is true of bladed disks having conventionally designed
dovetail shaped roots and slots, as well as fir tree shaped roots
and slots.
[0005] It is generally desired to keep stresses within the disk and
within the blades as low as possible to extend part life. In gas
turbine engines designed for flight, it is also desired to minimize
the weight of parts, such as disks and blades, consistent with
efficient operation, long life and safety. Lighter weight blades
also generate lower centrifugal forces and thus may reduce stresses
within the disk.
BRIEF SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, a bladed rotor
disk assembly includes a plurality of circumferentially spaced
apart blade root slots extending through the disk at an angle to
the disk axial direction and having radially inwardly facing load
reaction surfaces extending continuously over less than the full
the length of the slot in contact with a corresponding radially
outwardly facing load reaction surface of a blade root disposed
within the slot.
[0007] By "load reaction surface", it is meant the surfaces of the
blade root and blade root slot that, during operation of the rotor,
contact or engage each other to transfer the loads from the blade
into the disk. When in contact these surfaces form a "load transfer
interface".
[0008] More specifically, the present invention eliminates what in
the prior art would be portions of the load transfer interface
adjacent the ends of the blade root slot, such that the loads over
the remaining load transfer interface result in one or more of the
following: a more symmetrical load distribution resulting in
reduced torque loads on the disk lugs; reduced total loads on the
disk lugs and blade roots; and, reduced maximum stress levels in
the disk lugs and blade roots.
[0009] One reason these benefits may occur is because, with
conventional root and slot designs, when the blade root load
reaction surface along a side of a blade root extends the full
length of the slot, the highest and most concentrated reaction
loads on that side of the slot occur adjacent one end of the slot,
while relatively lower and less concentrated (i.e. more uniform)
reaction loads on that same side of the slot occur adjacent the
other end of the slot. Therefore, at the low, more uniform reaction
load end of the slot, the disk lug material is carrying a
relatively small portion of the blade load per square inch of load
transfer interface, while at the high reaction load end the disk
lug material is carrying a much larger portion of the blade load
per square inch of load transfer interface. By eliminating load
transfer interface area at the low load end of each side of a slot,
the reaction loads over the remaining load transfer interface on
each side of the slot becomes more balanced, and results in lower
maximum stress.
[0010] In one embodiment of the present invention a small area of
each side of a slot adjacent an end of the slot and which faces
what would normally be the low load portion of the root reaction
surface is instead spaced from that low load portion such that
there is a gap between the blade root and slot over that area. In
all other respects, the blade and disk assembly may be considered
conventional. The reaction loads over the now smaller load transfer
interfaces on each side of the blade root are more balanced than
without the gaps, and the maximum stress in the disk lugs is
reduced.
[0011] In another embodiment of the present invention, end portions
of the conventional blade root that normally transfer relatively
low loads into the disk lugs are removed, providing the benefit of
reduced blade weight in addition to more balanced reaction loads
over the remaining length of a smaller load transfer interface on
each side of the blade root. Total reaction loads, stresses and/or
torque on the disk lugs may thereby be reduced. Reduced torque
loads means less twisting of the blade lugs, with correspondingly
less twisting of the blades.
[0012] The foregoing features and advantages of the present
invention will become more apparent in light of the following
detailed description of exemplary embodiments thereof as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an isometric rear view of a portion of a rotor
assembly according to one embodiment of the present invention, with
some of the blades removed to better show the blade root slots
through the rim of the rotor disk.
[0014] FIG. 2 is a sectional view taken along the line 2-2 of FIG.
1 through one of the rotor disk lugs, with the rotor disk axis
being in the plane of the figure.
[0015] FIG. 3 is a diagrammatic sectional view, taken along the
line 3-3 of FIG. 2, illustrating the differences in reaction loads
along the length of the slot as between a disk assembly of the
prior art and a disk assembly according to one embodiment of the
present invention.
[0016] FIG. 4 is a view in the direction D of FIG. 3, parallel to
the blade root slot length.
[0017] FIGS. 5 and 6 are schematic views in the directions 5-5 and
6-6, respectively, of FIG. 4 showing, for the embodiment of FIG. 1,
the disk/blade load transfer interfaces along opposite sides of a
blade root slot.
[0018] FIG. 7 is a schematic view, taken in the direction 7-7 of
FIG. 2, showing, for the embodiment of FIG. 1, the cross-sectional
shape of the blade root and its general orientation relative to the
front and rear disk surfaces and the blade platform.
[0019] FIG. 8 is a sectional view of a rotor assembly, like the
sectional view of FIG. 2, but showing a rotor assembly
incorporating an alternate embodiment of the present invention.
[0020] FIG. 9 is a simplified sectional view taken along the line
9-9 of FIG. 8.
[0021] FIG. 10 is an isometric view in the direction S of FIG. 9
perpendicular to the rear face of the disk, with the blade
removed.
[0022] FIGS. 11 and 12 are schematic views in the directions 11-11
and 12-12, respectively, of FIG. 4 showing, for the embodiment of
FIG. 8, the disk/blade load transfer interfaces along opposite
sides of a blade root slot.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Referring to FIGS. 1 and 2, a gas turbine engine rotor
assembly 100 incorporating an exemplary embodiment of the present
invention includes a rotor disk 102 and a plurality of rotor blades
104, only one of which is shown. Each blade comprises a root 106,
platform 108, and airfoil 110. The disk 102 has a rotational axis
111, a rear face 112, a front face 114, and a rim 116. A plurality
of blade root slots 118 extends through the rim from the rear face
to the front face in a direction D (FIG. 3). Each pair of adjacent
slots defines a disk lug 120 therebetween. The root 106 of each
blade is disposed within a respective one of the slots.
[0024] Referring to FIG. 3, each slot 118 extends in the direction
D at an acute angle .theta. to the direction of the disk axis 111.
Generally, this angle is between about 10.degree. and 30.degree..
In this example .theta. is 24.degree. and, as best shown in FIG. 4,
the blade roots 106 are of the well known "dovetail" shape,
although the invention is not limited to use with blades having
dovetail roots. The root of each blade has a pair of flat, radially
outwardly facing load reaction surfaces 122A, 122B, one extending
along each side of the root. The surfaces 122A, 122B abut
corresponding flat, radially inwardly facing slot load reaction
surfaces 124A, 124B, respectively. The interfaces formed by each of
these pairs of contacting surfaces are hereinafter referred to as
load transfer interfaces since, during operation of the rotor, the
blade loads are transferred into the disk lugs across these
interfaces.
[0025] In the prior art, blade roots and disk slots, as well as the
load transfer interfaces, are the same length, which is generally
the full length, L (FIG. 3), of the slot, as measured in the
direction D of the slot. In accordance with the present invention,
at least one of the blade root load reaction surfaces 122A, 122B,
and preferably both, is less than the slot length. This is best
seen in FIG. 3, wherein the blade root 106, although fully within
the slot 118, has oppositely facing end surfaces 126, 128 which are
perpendicular to the slot direction D. Thus, as best shown in FIGS.
5 and 6, the cross-hatched load transfer interfaces 130A, 130B,
have respective lengths M and N, corresponding to the respective
lengths of the blade root load reaction surfaces 122A, 122B. FIG. 7
provides a radially outwardly looking view of the blade 104,
showing the orientation and position of the blade root 106 relative
to the blade platform 108 and the disk front and rear faces 114,
112, respectively.
[0026] Reference is also made to FIGS. 3, 5 and 6 for an
understanding of certain of the benefits of the present invention
as compared to the prior art. In the present invention, the root
load reaction surfaces 122A, 122B contact the slot load reaction
surfaces 124A, 124B between the points Y and Z.sub.1, and W and
X.sub.1, respectively. Assume, for purposes of discussion, that the
blade root load reaction surfaces and slot load reaction surfaces
extend the full length of the slot, such that over the radial
extent (i.e. from R.sub.1 to R.sub.2 in FIG. 4) of the root load
reaction surfaces the root end surfaces 126, 128 are substantially
in the planes of the disk rear and front faces 112, 114,
respectively, as is generally the case with prior art rotor
assemblies (i. e. the angle .alpha. is 0.degree., rather than being
equal to .theta., as shown in FIG. 3). In that case, blade loads
would be transferred into the disk lugs over the full length L of
the slot from X.sub.2 to W on one side of the slot and from Z.sub.2
to Y on the other side. The magnitude of the reaction loads for
such a prior art configuration along the lengths L of the
respective blade root slot reaction surfaces are represented by the
curves 132, 134, which were generated by a computer model of such a
configuration. The curves 136, 138 of FIG. 3 are generated by a
computer model of the same rotor assembly modified according to the
present invention (i.e. generally as shown in FIG. 1), and
represent the magnitude of the reaction loads along the full
lengths M (from X.sub.1 to W) and N (from Z.sub.1 to Y) of the
blade root load reaction surfaces 122A, 122B, respectively. The
perpendicular distance from the curves 132, 136 to the line
X.sub.2-W, and the perpendicular distance from the curves 134, 138
to the line Z.sub.2-Y represent the magnitude of the reaction
load.
[0027] Compare the "prior art" curves 132, 134 to the curves 136,
138 for the present invention. Note that, in the prior art rotor
assembly configuration, the magnitude of the load along the length
of each side of the slot is high at one end of the slot and tapers
off to relatively low at the other end. On the other hand, the
curves show that, in the rotor assembly configuration of present
invention, the loads are more balanced over the blade root length,
with high loads near each blade root end, and relatively low loads
between the ends. Additionally, the maximum reaction load on each
side of the slot is lower in the rotor assembly of the present
invention. Computer modeling also indicates that the maximum stress
concentration in the disk lugs is lower for the rotor assembly of
the present invention, as compared to the prior art.
[0028] In the foregoing embodiment, the benefits are primarily the
result of lowering the weight of the blade by reducing the length
of the blade root. That reduces the total load on the disk lugs and
corresponding stress levels; and, by having a more balanced load
over the length of the root, the stress concentrations are even
further reduced. At first glance, it may appear that the reduced
reaction load surface areas might negate these benefits; however,
the loss of load reaction surface area is not particularly
detrimental because the eliminated portions of the prior art
reaction surfaces near the ends of the slots (the non-cross-hatched
portions of FIGS. 5 and 6) were carrying only a relatively small
portion of the total load per unit surface area, as compared to the
average load per unit surface area over the full length of the
slot.
[0029] Although in the foregoing embodiment the blade root end
surfaces 126, 128 are perpendicular to the blade root load reaction
surfaces 122A, 122B, this is not a requirement. It is preferred,
however, that the blade root end surfaces be parallel to each other
to maintain symmetry. Thus, a parallelogram cross-sectional shape
(in the view of FIG. 3) with the blade root of any length less than
the slot length L (in the direction D) may provide a benefit over
the prior art by reducing blade weight. Preferably, the angle
.alpha. is between 0.degree. and .theta.. Although the blade root
end surfaces 126, 128 are preferably parallel, they need not be;
and, thus, M does not need to equal N, although at least one of
them must be less than L.
[0030] In accordance with another embodiment of the present
invention, reference is made to FIGS. 8, 9 and 10. The rotor
assembly 200 includes a disk 202 and blades 204, only one of which
is shown. The disk axis is designated by the reference numeral 211.
The disk has front and rear parallel opposed faces 214, 212
adjacent its rim 216. The disk also has a plurality of
circumferentially spaced apart blade root slots 218 defined by and
between disk lugs 220, and extending through the disk rim from the
front face 212 to the rear face 214. As in the previous embodiment,
the slots 218 are cut at an angle to the disk axis 211. Each blade
204 comprises a dovetail-shaped root 206, platform 208, and airfoil
210. In this embodiment, as is also the case in rotor assemblies of
the prior art, the blade roots extend the full length of their
respective slots, whereby the root end surfaces 226, 228 are
substantially flush with respective end faces 212, 214 of the disk,
at least over the radial extent of the root load reaction
surfaces.
[0031] In accordance with this embodiment of the invention, the
lugs 220 on each side of a blade root 206 each have pockets 300,
302 cut into opposite end faces 212, 214 of the disk at the rim to
cut back or remove material that would otherwise form a portion of
a slot load reaction surface that engages a blade root load
reaction surface. Thus, as shown in FIG. 9, wherein the
cross-section through the blade root is shown crosshatched, the
root load reaction surface 222A and the slot load reaction surface
224A both extend from E1 to F. Similarly, the corresponding
reaction surfaces 222B and 224B on the other side of the slot
extend from G1 to H. Essentially, the pockets 300, 302 create gaps
304, 306 between each lug 220 and what are hereinafter referred to
as extensions 308 (having a length from E.sub.1 to E.sub.2) and 310
(having a length from G.sub.1 to G.sub.2) of the blade root load
reaction surfaces 222A, 222B, respectively.
[0032] FIGS. 11 and 12 are analogous to FIGS. 5 and 6 of the
previously described embodiment, and show the load transfer
interfaces 230A, 230B, on each side of a slot in the embodiment of
FIG. 8. L, M, and N represent the same lengths as in FIGS. 5 and 6.
It is readily seen that both embodiments can result in the very
same load transfer interfaces. The FIG. 1 embodiment accomplishes
this by effectively shortening the length of the blade root; and
the FIG. 8 embodiment does this by removing material from the slot
surface to create a gap between a portion of the lug and the blade
root. In each case the "removed" portion of the prior art load
transfer interface was previously located where the prior art
reaction loads were relatively low. Moreover, in both embodiments
the loads transferred along the length of the load transfer
interface are more balanced than those of the prior art, resulting
in lower maximum stresses in the lugs. Thus, the general shape of
the curves 136, 138 in FIG. 3 would be the same for the embodiment
of FIG. 8; however, the embodiment of FIG. 1 has the additional
advantage of reduced blade weight and correspondingly lower total
blade loads to be transferred into the lugs.
[0033] Although the invention has been described and illustrated
with respect to exemplary embodiments thereof, it should be
understood by those skilled in the art that the foregoing and
various other changes, omissions and additions may be made without
departing from the spirit and scope of the invention. For example,
gaps similar to the gaps 304, 306 between the blade root and slot
may be formed by removing a small amount of material from the blade
root load reaction surfaces rather than from the disk lugs.
* * * * *