U.S. patent number RE33,954 [Application Number 07/656,337] was granted by the patent office on 1992-06-09 for rotor blade assembly.
This patent grant is currently assigned to United Technologies Corporation. Invention is credited to Keith T. Honda, Stephen L. Smith, Peter E. Voyer.
United States Patent |
RE33,954 |
Honda , et al. |
June 9, 1992 |
Rotor blade assembly
Abstract
Rotor blade and disk structures enabling the disassembly and
reassembly of a single rotor blade are disclosed. The concepts are
particularly suited to configurations employing interlocking
mid-span shrouds which inhibit the withdrawal of a single blade
from a disk. In one specific geometry the rotor blade root section
(20) and the disk attachment slot (24) are contoured to provide
increasing clearance between the bottom of the blade root section
and the attachment slot as the blade is withdrawn axially from the
slot. Rocking of the blade within the provided clearance enables
withdrawal of the blade around the shroud segments (30,32) and
airfoil sections (16) of the adjacent blades (12).
Inventors: |
Honda; Keith T. (Manchester,
CT), Smith; Stephen L. (South Windsor, CT), Voyer; Peter
E. (Tolland, CT) |
Assignee: |
United Technologies Corporation
(Hartford, CT)
|
Family
ID: |
26996916 |
Appl.
No.: |
07/656,337 |
Filed: |
December 24, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
351061 |
Feb 22, 1982 |
04451205 |
May 29, 1984 |
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Current U.S.
Class: |
416/219R;
416/196R; 416/220R |
Current CPC
Class: |
F01D
5/3007 (20130101); F01D 5/22 (20130101) |
Current International
Class: |
F01D
5/22 (20060101); F01D 5/00 (20060101); F01D
5/12 (20060101); F01D 5/30 (20060101); F01D
005/30 () |
Field of
Search: |
;416/219R,219A,190,191,193,196,22R,22A |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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632001 |
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Jul 1936 |
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DE2 |
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1025421 |
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Mar 1958 |
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DE |
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S108277 |
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Dec 1967 |
|
DE |
|
1083734 |
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Jan 1955 |
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FR |
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312864 |
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Nov 1933 |
|
IT |
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46-29565 |
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Aug 1971 |
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JP |
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49-75904 |
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Jul 1974 |
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JP |
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1332935 |
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Oct 1973 |
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GB |
|
Primary Examiner: Kwon; John T.
Claims
We claim: .[.
1. For an axial flow gas turbine engine having a rotor assembly of
a type including an array of rotor blades extending outwardly from
the periphery of a rotor disk and wherein the airfoil section of
each of said rotor blades has shroud segments extending laterally
from the suction and pressure sides thereof into opposing
relationship with corresponding shroud segments of the adjacent
rotor blades, the improvement comprising:
means for attaching each rotor blade to a corresponding attachment
slot at the periphery of the rotor disk wherein the root section of
the blade and the attachment slot of the disk are contoured to
provide increasing clearance between the bottom of the blade root
section and the attachment slot as the blade is withdrawn axially
from the slot..].
2. .[.The invention according to claim 1.]. .Iadd.For an axial flow
gas turbine engine having a rotor assembly of a type including an
array of rotor blades extending outwardly from the periphery of a
rotor disk and wherein the airfoil section of each of said rotor
blades has shroud segments extending laterally from the suction and
pressure sides thereof into opposing relationship with
corresponding shroud segments of the adjacent rotor blades, the
improvement comprising:
means for attaching each rotor blade to a corresponding attachment
slot at the periphery of the rotor disk wherein the root section of
the blade is a dovetail-shaped root section, and wherein said root
section and the attachment slot of the disk are contoured to
provide increasing clearance between the bottom of the blade root
section and the attachment slot as the blade is withdrawn axially
from the slot and are contoured such that the blade root section is
able to rock within such clearance, .Iaddend.wherein the disk
attachment slot has a wedge-shaped protrusion extending from the
center portion of the bottom of the attachment slot and tapered to
increasing cross section from the front to the rear sides of the
disk, and wherein the rotor blade root section has a bottom surface
of taper corresponding to that of the wedge-shaped protrusion of
the attachment slot.
Description
DESCRIPTION
TECHNICAL FIELD
This invention relates to axial flow rotary machines, and more
particularly to the rotor blades of such machines.
The concepts were developed in the aircraft gas turbine engine
industry to enable the disassembly of single fan blades from the
fan sections of turbofan engines, but have wider applicability both
within that industry and others as well.
BACKGROUND ART
Modern aircraft gas turbines are of the turbofan type having large
rotor blades usually at the forward end of the engine. The blades
are termed "fan blades" and are utilized to accelerate air directed
thereover in a manner much the same as a propeller.
Being located at the forward end of the engine, the blades are
susceptible to foreign object damage as a result of debris picked
up along the airport runway and ingested into the engine. Large
birds are not an infrequent cause of fan damage. Damaged blades
must be replaced to restore aerodynamic efficiency to the fan and
to prevent destructive rotor imbalance.
Fan blade roots are conventionally formed to a dovetail
cross-section geometry and extend from fore to aft across the rim
of a supporting disk. The root attachments are usually canted
circumferentially with respect to the centerline or axis of the
engine. Blades of long span have one or more shrouds at an
intermediate position along the span of the blades or at the blade
tips. Such a shroud is formed of elements extending laterally from
the pressure and suction sides of the blades into opposing
relationship with the shroud elements of adjacent blades. In
combination, the shroud elements form an annular ring when viewed
in a direction along the axis of the engine. The plane of opposing
relationship between adjacent shroud elements is nonparallel to the
axis of the blade attachment, thereby locking each individual blade
into the assembly.
To avoid the expense and necessity of removing all blades of a
rotor stage in order to replace a single blade, scientists and
engineers in the industry are searching for new blade concepts and
techniques of this assembly.
DISCLOSURE OF INVENTION
According to the present invention, the disassembly of a single
shrouded blade from an axial flow rotary machine is enabled by
providing a wedge-shaped protrusion at the base of the disk
attachment slot such that the blade can be rocked about the
wedge-shaped protrusion upon partial withdrawal of the blade from
the slot to effect disengagement of the blade from the shrouds of
adjacent blades.
Primary features of the present invention are the wedge-shaped
protrusions extending outwardly from the base of each disk
attachment slot and the tapered surfaces at the bottoms of the root
sections of the corresponding blades. Partial withdrawal of the
root section of a blade from the corresponding attachment slot
increases the radial clearance therebetween and enables rocking of
the blade about the wedge-shaped protrusion.
A principal advantage of the present invention is the enabled
disassembly of a single blade from the rotor assembly. In an
aircraft installation, removal of a fan blade can be accomplished
in situ without removing the engine from the aircraft. Such
disassembly is accomplished without recourse to increased part
clearances in the installed condition. Rocking the blade in a first
direction about the wedge-shaped protrusion enables partial
withdrawal notwithstanding the nonparallel relationship of the axis
of the attachment slot and the planes along which adjacent shrouds
abut. Rocking of the blade in a second direction permits
circumferential displacement of the blade shroud about the trailing
edge of the adjacent blade, such that the blade may be completely
withdrawn from the attachment slot.
The forgoing, and other features and advantages of the present
invention, will become more apparent from the following description
and the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a simplified front elevation view of a portion of the fan
assembly of a turbofan gas turbine engine;
FIG. 2 is an exploded perspective view illustrating the wedge
against which the blade root seats;
FIG. 3 is a view taken in the direction 3--3 as shown in FIG.
1;
FIG. 4 is a sectional view taken along the line 4--4 as shown in
FIG. 1;
FIG. 5 is an enlarged view of the fan blade root illustrating the
ability of a partially removed blade to tilt about the wedge at the
base of the attachment slot;
FIG. 6 is a perspective view illustrating partial withdrawal of a
single rotor blade from the assembly;
FIG. 7 is a perspective view illustrating the sequential partial
withdrawal of two adjacent rotor blades with the shroud of the most
forwardly withdrawn blade free of interference with the shroud of
the adjacent blade; and
FIG. 8 is a perspective view illustrating circumferential
displacement of the most forwardly withdrawn blade to a position at
which the shroud of the blade is free of interference with the
airfoil section of the adjacent blade.
BEST MODE FOR CARRYING OUT THE INVENTION
The best mode for carrying out the invention is described with
respect to the fan section of a turbofan gas turbine engine. A
portion of a fan rotor assembly is illustrated in the FIG. 2 front
elevation view. A plurality of rotor blades 12 extend outwardly
from the periphery of a rotor disk 14. Each rotor blade has an
airfoil section 16, a platform section 18 and a root section 20.
Each platform section defines a portion of the inner wall of the
flowpath 22 for working medium gases. Each root section engages a
corresponding attachment slot 24 at the periphery of the disk. The
airfoil section of each blade has a suction side 26 and a pressure
side 28. Shroud segments 30 and 32 extend laterally from the
suction and pressure sides of the blade respectively into opposing
relationship with the shroud segments of adjacent blades. In
composite the shroud segments of adjacent blades form an annular
ring extending circumferentially around the engine. The shroud
illustrated is positioned at a midpoint along the span of the blade
and is termed a "mid-span" shroud. The spanwise location of the
shroud varies with engine design. Multiple shrouds are employed in
some embodiments and in others a shroud is positioned at the tips
of the blades.
The shape of each blade root section and the geometry of the
corresponding attachment slot are shown in the FIG. 2 exploded,
perspective view. The attachment geometry is of the generic type
known as a "dovetail root". The geometry is modified, however, from
the conventional form in that the bottom surface 34 of the blade
root is tapered from the leading edge 36 to the trailing edge 38,
forming a root of decreasing cross section. The attachment slot 24
has a wedge-shaped protrusion 40 extending from the center portion
of the bottom of the attachment slot from the front side 42 to the
rear side 44 of the disk. The top surface 46 of the wedge-shaped
protrusion and the bottom surface of the blade root section are
matched to an angle .phi. measured with respect to a plane parallel
to the engine's centerline. The root section of the rotor blade and
the attachment slot of the disk are contoured to provide increasing
clearance between the bottom of the blade root section and the
attachment slot as the blade is axially withdrawn from the slot.
The blades 12 are trapped axially on the disk 14 in the assembled
mode by conventional means not specifically illustrated.
Concepts integrated into the described apparatus enable the in situ
disassembly and reassembly of a single rotor blade, such as might
be required after operation in an engine on account of foreign
object damage to the blades. In conventional construction such in
situ disassembly and reassembly of a single blade is inhibited by
circumferential interference between adjacent shroud segments and
axial interference of the shroud segments with forwardly extending
portions of the adjacent airfoil sections. As is viewable in FIG.
3, the axis A of the blade root attachment may not be parallel to
the plane of intersection B with the result that the blades held in
axial position on the disk are interlocked. Even without direct
restrain each blade is incapable of axial displacement greater than
the distance Y between the suction side shroud segment 30 of that
blade and the airfoil section 16 of the adjacent blade.
The revised root section and attachment slot geometry of the
present invention enables combined axial and circumferential blade
displacement freeing the shroud segments of the blade to be
withdrawn from both the adjacent shroud segments and the airfoid
section of the adjacent blade. The FIG. 4 illustrates increased
clearance between the bottom surface 34 of the blade root section
and the top surface 46 of the wedge-shaped protrusion 40 at the
base of the attachment slot. In the installed condition the
clearance is of a magnitude C.sub.1 ; in the partial withdrawn
condition as represented by the dotted configuration, the clearance
is of a magnitude C.sub.2.
The increased clearance upon partial axis withdrawal enables the
blade to initially rock about the wedge-shaped protrusion 40 in
accommodation of the differential alignment of the blade root axis
A and the plane of intersection B of the adjacent shroud segments
and to subsequently rock about the wedge-shaped protrusion 40 to
rotate the suction side shroud segment circumferentially free of
the adjacent airfoil section. The ability of the blade to rock
about the wedge-shaped protrusion in a partially withdrawn
condition is viewable in FIG. 5.
The sequential steps for withdrawing a single rotor blade from a
rotor disk in one embodiment are shown in FIGS. 6-8. Although not
shown in the installed condition on a gas turbine engine, the
principles of disassembly and reassembly of the blades 12 from the
rotor disk 14 are identical. Direct axial restraint trapping the
blades on the disk in the fully assembled mode has been
removed.
In FIG. 6 one of the blades 12A is adjusted forwardly on the disk
14 until the suction side shroud segment 30A abuts the airfoil
section 16 of the adjacent blade. The blade rocks slightly in the
attachment slot in a clockwise direction to accommodate the angular
mismatch of the root axis and the shroud segment plane of the
intersection. In FIG. 7 a second rotor blade 12B is adjusted
forwardly in the disk until the suction side shroud segment 30B of
the second blade abuts the airfoil section 16A of the adjacent
blade. In the embodiment illustrated the pressure side shroud
segment 32B is free of circumferential interference with the
suction side shroud segment 30C of the adjacent blade 12C. The
number of blades 12 which must be forwardly adjusted depends upon
the particular embodiment including such factors as the width of
the shroud segments and the geometry of the adjacent airfoil
section in the vicinity of the shroud.
In FIG. 8 the blade 12B is rotated in the attachment slot in a
counterclockwise direction to a position at which the suction side
segment 30B of the blade is free to move axially past the airfoil
section 16A of the adjacent blade. In this position full withdrawal
of a single blade from the disk can be made. Reassembly of the
single blade is made by a procedure reverse to that by which
disassembly is made.
Although the invention has been shown and described with respect to
detailed embodiments thereof, it should be understood by those
skilled in the art that various changes in form and detail thereof
may be made without departing from the spirit and the scope of the
claimed invention.
* * * * *