High pressure turbine rotor two-piece blade retainer

A blade retainer for holding a turbine blade on a turbine rotor disc and sealing a cooling cavity formed between the disc and blade has a two-piece construction. The first piece performs the blade loading function, while the second piece performs the cavity sealing function. The two pieces are attached to the disc by a common set of fasteners, such as bolts.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention broadly relates to gas turbine rotors and, more 
particularly, is concerned with a retainer construction for locking 
turbine rotor blades in the periphery of a turbine rotor disc and for 
sealing coolant passageways within the disc. 
2. Description of the Prior Art 
In a gas turbine engine, turbine blades are typically attached to a rotor 
disc by inserting them in axially-directed slots formed in the rim of the 
disc. The blades are usually held in place by a thin circular plate called 
a blade retainer which is attached to either or both sides of the disc by 
suitable fastening means such as conventional bolts. Examples of such a 
blade retainer are represented by the one-piece prior art designs 
illustrated in FIGS. 1 and 2. 
In addition to holding the blades in stationary positions on the rotor 
disc, the retainer commonly serves two additional functions. First, it 
seals a cavity between the blades and the rotor disc to allow cooling air 
to flow to the blades with minimal leakage to the external environment. 
Second, it dampens vibration of the blades as a result of an axial load 
imparted into the blades at an area below the airfoil of each blade. 
In certain high pressure turbines, these blade retainer designs have proven 
unacceptable for applications where long cyclic lives are required, in 
that, they are low cycle fatigue limited in the bolt hole region. In 
addition, they typically impart large loads into the rotating discs and 
create cyclic life problems in the disc itself. Consequently, a need 
exists for a blade retainer design which effectively reduces the high 
stresses encountered in both the disc and the retainer itself, and thereby 
greatly improves component cyclic life. 
SUMMARY OF THE INVENTION 
The present invention provides a unique two-piece construction for a blade 
retainer which is designed to satisfy the aforementioned needs. Underlying 
the present invention is the recognition that the incorporation by the 
prior art designs of incompatible or conflicting funtions within a 
one-piece blade retainer construction was the problem. These conflicting 
functions involved using the blade retainer for sealing the cooling cavity 
formed between the blades and the rotor disc, while at the same time using 
the blade retainer to dampen any vibration of the blades by imparting an 
axial load into the blades. This recognition of the problem paved the way 
to the solution proposed by the present invention whose elegance is 
augmented rather than diminished by its simplicity, low cost and 
reliability. The solution proposed by the present invention is to provide 
a two-piece design which separates these conflicting functions from one 
another in such a way that the functions can be carried out side-by-side 
without interfering with one another. 
Accordingly, the present invention provides a unique two-piece construction 
of a blade retainer for combination with a turbine rotor disc and at least 
one turbine blade mounted in a peripheral rim of the disc such that a 
cavity is formed between the blade and the disc and open at least at one 
side of the disc. The blade retainer is comprised by: (a) a first blade 
loading piece; and (b) a second cavity sealing piece. The blade loading 
piece includes in serially interconnected relationship the following: (i) 
a first element for engaging the blade; (ii) a second element for abutting 
a first shoulder on the disc rim and anchoring the blade loading piece 
against centrifugal forces generated during rotor disc rotation; and (iii) 
a third element for attachment of the blade loading piece to the disc rim 
so as to impose a vibration-damping loading force on the blade via the 
first element. The second cavity sealing piece is separate from the first 
blade loading piece and includes the following: (i) a first member for 
closing the cavity at least at the one side thereof and for attachment of 
the cavity sealing piece to the disc rim; and (ii) a second member for 
anchoring the cavity sealing piece against centrifugal forces generated 
during rotor disc rotation. Further, the third element of the blade 
loading piece has defined therein spaced apart holes through which the 
blade loading piece may be attached to the disc rim by suitable fasteners 
such as bolts. Stress concentration reducing means are incorporated in the 
third element for relieving stress concentration in the region of the bolt 
holes in the blade loading piece. Such stress concentration reducing means 
may take the form of an intermediate set of holes defined between the bolt 
holes or, alternately, scallops instead of the intermediate holes.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, and more particularly to FIGS. 1 and 2, 
there are shown fragmentary portions of prior art gas turbine engines 
which include respective annular rotor discs 10, 12 of slightly different 
configurations and respective turbine blades 14, 16 mounted to each of the 
discs and stationarily held in place by respective prior art blade 
retainers 18, 20 of slightly different one-piece constructions. 
The rotor discs 10, 12 have enlarged peripheral rims 22, 24 with a 
plurality of individual blade receiving slots or grooves 26 (see FIG. 4) 
extending through the peripheral rim in a generally axial direction 
relative to the rotor disc. The rotor blades 14, 16 are respectively made 
up of root portions 28, 30, platform portions 32, 34, and airfoil portions 
36, 38. As seen in FIG. 4, the root portion 28 of the blade 14 is 
configured to be received in intermeshing fashion in one of the 
complementarily configured grooves 26 in the peripheral rim 22 of rotor 
disc 10. The blade 14 has interior passageways (not shown) which 
communicate with passageways (not shown) in the rotor disc 22 via a cavity 
40 defined by the space between the bottom 42 of the root portion 28 and 
the lower wall portion 44 of the channel 26. Suitable cooling fluid is 
flowed to the blade interior through these passageways and cavity 40 for 
maintaining the blades below a desired temperature. Similar interior 
passageways and cavities are present in disc 12 and blade 16 but not shown 
in the drawings. 
The blades 14, 16 are held in place on the corresponding rotor discs 10, 12 
by respective blade retainers 18, 20 which take the form of thin circular 
or annular-shaped plates. The retainers 18, 20 include sealing portions 
46, 48 and loading portions 50, 52. The sealing and loading portions are 
integrally connected together and formed by any suitable method, such as 
by machining from a common forging to provide a rigid one-piece 
construction. Both retainers 18, 20 are attached to enlarged rims 22, 24 
on respective discs 10, 12 at either or both sides thereof by a plurality 
of bolts 54, 56 (only one of which is shown for each respective retainer 
in FIGS. 1 and 2). Holes 58 defined in rim 22 of disc 10 for receiving 
bolts 54 are shown in FIG. 4. 
Sealing portions 46, 48 of respective retainers 18, 20 seal either or both 
ends of the cavity 40 formed between the blades 14, 16 and the discs 10, 
12 so as to facilitate the flow of cooling fluid, such as air, through the 
discs to the blades with minimal leakage to the external environment. 
Loading portions 50, 52 of respective retainers 18, 20 impart an axial 
load into the blades at their root portions 28, 30 for dampening any 
vibration which may be induced into the blades during operation of the 
turbine engines. 
Both retainers 18, 20 employ a wire seal cavity 58, 60 at the junctures 62, 
64 between the respective sealing and loading portions thereof. The 
purpose of the wire seal cavities 58, 60 is to provide a cavity for 
circumferential wire 65 to assist in sealing the cavity formed by the 
rounded edges on the root portions of the blades 28, 30 and the grooves 26 
in the disc posts 72. The wire seal 65 also provides sealing to the gap 
established by slight axial thickness variations between the disc post 72 
and the root portions of the blades 28, 30. Also, recessed shoulders 66, 
68 are defined at the respective junctures 62, 64. 
It will also be noted that the prior art retainers 18, 20 of FIGS. 1 and 2, 
respectively, have slightly different designs. This adapts them to be 
applied to rotor discs 10, 12 which have slightly different designs. The 
recessed shoulder 66 of retainer 18 is utilized for anchoring it on the 
disc 10, while the recessed shoulder 68 of retainer 20 is not so utilized. 
The rotor disc 10 has a protruding ledge 70 on its outer post portions 72 
(see FIG. 4) under which recessed shoulder 66 of retainer 18 is disposed. 
The rotor disc 12 has no such ledge. Instead, the sealing portion 52 of 
retainer 20 has an integrally attached hook 74 which is disposed under a 
lower edge 76 of the rim 24 of rotor disc 12 for anchoring the retainer 20 
to the disc 12. No comparable hook feature is present on sealing portion 
46 of retainer 18. 
The prior art retainers 18, 20 have proven unacceptable for applications 
where long cyclic stress lives are required. Due to their one-piece 
constructions, which combines the sealing and loading functions into a 
single integrally formed part, severe cyclic stress problems occur in the 
regions of discs where the respective retainers are anchored and in the 
regions of the retainer bolt holes 78, 80 through the sealing portions 46, 
48 of the retainers. In the case of retainer 18, the cyclic life problem 
due to loading occurs in the region of the shoulder 70 on the disc post 74 
since the entire load of the retainer 18 is carried at that region. In the 
case of retainer 20, the cyclic life problem due to loading occurs in the 
region of the lower edge 76 of rim 24 of disc 12 and in the retainer hook 
74 itself. Loading forces in these regions of the discs and retainers are 
created by radially-directed centrifugal forces which arise upon rotation 
of the rotor discs during operation of the turbine engines. 
The unique two-piece construction for the blade retainer of the present 
invention is shown in FIGS. 3, 5 and 6, and is generally designated 82. 
This retainer design effectively reduces the high stresses encountered in 
both the rotor disc 84 and the retainer itself, and consequently greatly 
improves component cyclic life. 
The blade retainer 82, as seen in FIG. 3, is comprised by a separate first 
blade loading piece 86 and a separate second cavity sealing piece 88. The 
blade loading piece 86 now holds and dampens the blade 90, while the 
separate cavity sealing piece 88 seals or closes the cavity (same as seen 
in FIG. 4) between the disc 84 and blade 90. 
The first blade loading piece 86 includes, in interconnected serial 
relationship, a first element 92 for engaging the blade 90 in order to 
impart an axial load required for vibration dampening, a second element 96 
for abutting a protruding shoulder or ledge 98 on the disc rim 94 and 
thereby anchoring the first piece 89 against centrifugal forces generated 
during rotation of the rotor disc 84, and a third element 100 for 
attachment of the first piece 86 to the disc rim 94 so as to impose a 
vibration-dampening loading force on the blade 90 through the first 
element 92. 
The second cavity sealing piece 88 which is separate from the first blade 
loading piece 86 includes, in interconnected serial relationship, a first 
member 102 for closing the cavity at the side of the disc 84 and for 
attachment of the second piece 88 to the disc rim 94, and a second member 
104 anchoring the second piece 88 against centrifugal forces generated 
during rotation of rotor disc 84. The second member 104 may take the form 
of a hook 106, as seen in FIG. 3, for extending under and abutting a lower 
edge or shoulder 108 of the disc rim 94. Alternatively, the second member 
may take the form of an end shoulder 110 which abuts a shoulder 112 on the 
first piece 86, such as seen in FIG. 7. 
Since the first blade loading piece 86 of the retainer 82 is now relieved 
of the cavity sealing function, the area between a first set of bolt holes 
114 (FIG. 5) may be stress relieved by a second intermediate set of holes 
116, or, alternatively, by scallops 118, which are shown in combination 
with the second set of holes 116 in FIG. 5. This allows a reduction in 
bolt hole stress concentration and consequently greatly improves component 
life. Such stress relieving is not possible in the prior art retainer 
designs of FIGS. 1 and 2 since such would permit large amounts of blade 
cooling air leakage. 
As seen in FIG. 3, the first member 102 of the cavity sealing piece 88 is 
overlapped by the third element 100 of the blade loading piece 86. Also, 
the first member 102 of second piece 88 includes a set of bolt holes 120 
which align with those holes 114 of the third element 100 of first piece 
86 when the two pieces are positioned for attachment to the disc rim 94 by 
bolts 122. 
It will now be realized that the preferred two-piece design of retainer 82 
in FIG. 3 allows the radial load of the retainer to be carried in two 
separate areas on the rotor disc. The retainer itself is now lighter due 
to the reduction in weight of the retainer 82 over the previous designs in 
the bolt hole region by the removal of material due to the introduction of 
the intermediate stress-reducing holes. This reduction of weight reduces 
the load imparted into the disc and consequently the cyclic life of the 
disc posts are improved over the prior designs. Further, the radial load 
of piece 88 imparted to the disc 84 is small due to the light weight of 
piece 88. Consequently, a cyclic life problem in the rim area due to the 
seal function is eliminated in the retainer 82. 
The second cavity sealing piece 88 is entrapped by the disc ledge 98 at the 
top and by the first piece 86 and bolts 122 on the outer side. 
Furthermore, the hook 106 on the second piece 88 is designed to have a 
long cyclic life. The rigid entrapment of the second piece 88 reduces the 
consequence of any failure. It can then be classified as non-critical 
since any failure is expected to be adequately contained. 
In summary, this improved two-piece design of the retainer 82 "divides" the 
functions performed by previous blade retainers and allows them to be 
performed side-by-side without interference with one another by separate 
components. However, this unexpectedly alleviates cyclic life problems in 
both the disc and retainer. The sealing piece 88 may have the potential 
for a low cyclic life but is a non-critical part as a result of the 
retainer construction. 
It is thought that the two-piece blade retainer of the present invention 
and many of its attendant advantages will be understood from the foregoing 
description and it will be apparent that various changes may be made in 
the form, construction and arrangement of the parts thereof without 
departing from the spirit and scope of the invention or sacrificing all of 
its material advantages, the form hereinbefore described being merely a 
preferred or exemplary embodiment thereof.