Segmented stator vane seal

A "dog bone" in cross section shaped seal mounted in adjacent grooves of segmented stator vanes span the axial extent covering a single casted three rows of vanes. The outer diameter shroud of the stator vane defines a portion of an enclosed cavity subjected to leakage flow in and out of the gas path where the flow reverses at some axial extent of the seal such that the forces acting at different locations on the seal reverses. In a preferred embodiment, the bulbous ends of the "dog bone" are solid coated metallic material.

DESCRIPTION 
CROSS REFERENCE 
The subject matter of this application is related to the subject matter of 
the following commonly assigned patent applications: U.S. application Ser. 
No. 581,223 entitled "Fastener For Multi-State Compressor"; U.S. 
application Ser. No. 581,224 entitled "Fastener Mounting For Multi-Stage 
Compressor"; U.S. application Ser. No. 581,231 entitled "Case Typing Means 
For A Gas Turbine Engine"; U.S. application Ser. No. 581,230 entitled 
"Compressor Bleed"; U.S. application Ser. No. 581,228 entitled "Backbone 
Support Structure For Compressor"; U.S. application Ser. No. 581,227 
entitled "Compressor Case Construction With Backbone"; U.S. application 
Ser. No. 581,219 entitled "Compressor Case Construction"; U.S. application 
Ser. No. 581,240 entitled "Compressor Case Attachment Means"; U.S. 
application Ser. No. 581,220 entitled "Compressor Case With Controlled 
Thermal Environment"; all of the above filed on even date herewith. 
TECHNICAL FIELD 
This invention relates to the compressor section of a gas turbine engine 
and particularly to the seal between segments of a multiple stator vane 
configuration. 
BACKGROUND ART 
As is well known, the compressor case of a gas turbine engine powering 
aircraft is subjected to severe pressure and temperature loadings 
throughout the engine operating envelope and care must be taken to assure 
that the components remain concentric maintaining relatively close running 
clearances so as to avoid inadvertent rubs. Inasmuch as the engine case is 
thin relative to the rotor and stator components in the compressor 
section, it responds more rapidly to temperature changes than do other 
components. This is particularly true during periods of transient engine 
performance. Typical of these transients are throttle chops, throttle 
bursts, and the like. Obviously it is customary to provide sufficient 
clearances during these transients to assure that the rotating parts do 
not interfere with the stationary parts. 
The problem becomes even more aggravated when the engine case is fabricated 
in two halves (split case) which is necessitated for certain maintenance 
and construction reasons. Typically, the halves are joined at flanges by a 
series of bolts and the flanges compared to the remaining portion of the 
circumference of the case is relatively thick and hence does not respond 
to thermal and pressure changes as quickly as the thinner portion of the 
case. The consequence of this type of construction is that the case has a 
tendency to grow eccentrically or out of round. 
In certain instances in order to attain adequate roundness and 
concentricity to achieve desired clearance between the rotating and 
nonrotating parts, it was necessary to utilize a full hoop case for the 
highest stages of a multiple stage compressor. Since the stator 
components, i.e., stator vanes and outer air seals, are segmented the 
problem was to assure that the compressor maintained its surge margin 
notwithstanding the fact that the outer case would undergo large 
deflection at acceleration and deceleration modes of operation. The cavity 
that exists between the outer case and the inner case formed by the 
segmented stator components, being subjected to pressures occasioned by 
the flow of engine air through the various leakage paths, presented a 
unique problem. In the event of a surge, the pressure in the gas path 
would be reduced significantly. Because the air in the cavity is captured 
and cannot be immediately relieved, it would create an enormous pressure 
difference across the stator components, cause them to distort, with a 
consequential rubbing of the compressor blades, and a possible breakage. 
In addition and in the interest of weight reduction, fewer component parts, 
improved maintainability, certain stages of the compressor section were 
treated as integral components, such that three rows of stator vanes are 
included in a single casting of segmented components. Hence, the segmented 
arcuate castings are assembled end-to-end to define a ring containing the 
three rows of vanes. Because the axial extent of the three rows of vanes 
are included within the full hoop casing the pressure acting over the 
axial distance varies from a pressure differential that is opposite in 
direction at one end from that on the other end. This created a problem in 
preventing the leakage of flow from the gas path to the surrounding cavity 
and vice versa, thus imposing engineering problems in sealing between 
segments 
The invention teaches sealing means to solve the problem alluded to in the 
aforementioned paragraph by utilizing a dog-bone shaped seal that is 
capable of solving these engineering problems while exhibiting the 
structural integrity to satisfy the maintainability requirements of the 
overall engine. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide an improved seal for multiple 
rows of unitary segments comprising the stator vanes for multiple 
compression stages in the compressor section of a gas turbine engine. 
A feature of this invention is utilizing a "dog-bone" shaped seal extending 
axially between segments where the forces acting from one end of the seal 
to the other end of the seal reverses. 
The foregoing and other features and advantages of the present invention 
will become more apparent from the following description and accompanying 
drawings.

STATEMENT OF THE INVENTION 
The foregoing and other features and advantages of the present invention 
will become more apparent from the following description and accompanying 
drawings. 
BEST MODE FOR CARRYING OUT THE INVENTION 
To best understand this invention reference is made to FIGS. 1 and 2 
showing part of a multi-stage compressor for a gas turbine engine of the 
type for powering aircraft. For more details of a gas turbine engine the 
F100 family of engines manufactured by Pratt & Whitney, a division of 
United Technologies Corporation, the assignee of this patent application, 
is incorporated herein by reference. Suffice it to say that in the 
preferred embodiment the engine on which this invention is being utilized 
is a fan-jet axial flow compressor multi-spool type. As noted in FIG. 1 
the compressor section generally indicated by reference numeral 10 is 
comprised of a plurality of compressor rotors 12 retained in drum rotor 
14, where each rotor includes a disk 16 supporting a plurality of 
circumferentially spaced compressor blades 18. The rotors 12 are suitably 
supported in an outer engine case 20 and an inner case 22. 
In this configuration a portion of the outer case 20 is fabricated in two 
axial circumferential halves and the other portion is fabricated in a full 
hoop generally cylindrically shaped case. In FIG. 1 the first four lower 
pressure stages as viewed from the left hand side are housed in the split 
case and the last three stages are housed in the full case. 
Inasmuch as this invention pertains to the aft section (full case) of the 
compressor, for the sake of simplicity and convenience only the portion of 
the compressor dealing with the full case will be discussed hereinbelow. 
The inner case 22 which comprises the stator vanes 30 and outer air seal 
32 are supported in the full case 34 via the dog-jaw hook connection 36 
and the bulkhead 38 which carries suitable attaching flanges 40 and 42. 
As was mentioned above the problem associated with this construction is 
that the cavity 44 between the inner case 22 and outer case 34 is 
ultimately pressurized by the fluid leaking therein from the engine flow 
path. The engine flow path is defined by the annular passageway bounded by 
the inner surface of the inner case 22 and outer surface of drum rotor 14. 
This pressure can reach levels of 5-600 pounds per square inch (PSI). 
Should a surge situation occur the pressure level in the gas path can 
reduce instantaneously to a value much lower than the 5-600 PSI and since 
the pressure in cavity 44 is trapped and can only be reduced gradually, an 
enormous pressure differential exists across inner case 22. 
As can best be seen in FIGS. 3 and 4, the spool/bolt arrangement generally 
illustrated by reference numeral 50 ties the inner case 22 to outer case 
34 in such a manner as to enhance fatigue life and provide sufficient 
strength to withstand the compressor surge problems. Spool/bolt 50 
comprises a spool member 52 having a reduced diameter threaded portion 54 
at its lower extremity adapted to be threaded onto the complementary 
internal threads 56 formed in boss 58 extending radially from the outer 
surface 60 or inner case 22. 
The bolt 62 comprises a relatively long shank 64 carrying threads 65 at the 
lower extremity and a significantly large head 66. Head 66 may be 
hexagonally shaped and is thicker and has a larger diameter than otherwise 
would be designed for this particular sized shank. These unusual 
dimensions of the head allow for a larger fillet radius which serves to 
reduce the stress concentration and increase fatigue life of the head to 
shank fillet adjacent the head. 
The bolt 62 fits into bore 70 centrally formed in spool 52 that terminates 
just short of the remote end of the entrance to the bore. The inner 
diameter of bore 70 is threaded to accommodate the threaded portion of 
bolt 62. The spool 52 carries a tool receiving portion 72 for threadably 
securing the spool to inner case 22. 
In the assembled condition, the spool 52 is threaded to inner case 22 and 
the bolt 62 passing through opening 74 in the outer case 34 is threaded to 
the inner threads of the spool 52, until the head bears against the outer 
surface of outer case 34 or a suitable washer. Tab washer 76 may be 
employed to prevent the bolt from inadvertently retracting. 
After the spool 52 is torqued sufficiently to urge flange portion 78 to 
bear against inner case 22, the bolt 62 is sufficiently torqued so that 
the flange-like portion 80 bears against the surface of outer case 34. The 
amount of torque will depend on the particular application but it should 
be sufficient to keep spool 52 in compression throughout the operating 
range of the engine. 
As is apparent from the foregoing, the spool serves as a compressed 
flange-like member thus reducing both bolt fatigue and surge stresses. 
This configuration resists fatigue loads occasioned by thermal axial 
deflection differences between outer case 34 and the segmented inner case 
22. 
Also apparent from the foregoing and mentioned above is this arrangement 
resists the radial loads occasioned by a surge when there is an 
instantaneous and nearly complete loss in compressor flow path pressure. 
The spool 52 also makes the threads 54 that mates with the inner case 22 to 
be insensitive to fatigue loading because it is preloaded by the spool 
washer face 84 that bears against the inner case. 
The thread sizes of threads 65 of bolt 62 and threads 54 of spool 52 are 
different (the threads 54 are specifically designed to be larger). Because 
the diameter of the spool threads 54 are larger it has a higher 
disassembly breakaway torque than bolt 2. Consequently, the bolt 62 will, 
by design, loosen first. 
The bulkhead 38 is a load carry member and is generally annularly shaped 
forming a relatively straight piece but having a radially extending lower 
portion 40, an angularly extending middle portion 92 and another radially 
extending upper portion 42. As mentioned earlier the extremities, i.e. the 
lower and upper portion 40 and 42 serve basically as flanges and are 
adapted to be bolted to the inner and upper cases 22 and 34, respectively. 
The forward face of the lower portion 40 is recessed 101 to accept the 
radially extending flange 94 integrally formed on the rear end of the 
inner segmented case 22, forming a somewhat tongue-in-groove arrangement. 
The inner diameter 96 of bulkhead 38 is dimensioned so that it snugly fits 
onto the upper surface of the next adjacent stator vane assembly 98 which 
serves to reduce scrubbing of the case tied assembly, just described. 
Of course, it is desirable to minimize the leakage from the gas path into 
cavity 44 and vice-versa which would otherwise penalize the overall 
performance of the engine. As described above, the stator vane 30 cast 
into unitary segments that when mounted end-to-end in the circumferential 
direction forms three (3) rows of vanes. The stator vane comprises 
circumferentially spaced airfoil sections 100 and an inner shroud 102 and 
an outer shroud 104, the outer shroud defining the inner case. As viewed 
from the perspective drawing of FIG. 2, the three rows of vanes are 
unitary with the outer shroud 104 and each segment abuts the adjacent 
segment. 
In accordance with this invention a groove 106 adapted to receive 
"dog-bone" shaped seal 108, i.e., looking at a cross sectional view, 
extends from the most forward end to the most aft end at the edges of 
adjacent segments. 
The bulbous end 110 and 112 fit into respective adjacent grooves. The 
bulbous ends 110 and 112 in the preferred embodiment are solid and are 
fabricated from a suitable metal material capable of withstanding 
relatively hot temperatures. To prevent wear of the mating surfaces, the 
bulbous ends 110 and 112 may be coated with aluminum bronze by a well 
known vapor deposition technique. The width of the seal 108 is determined 
by the displacement and thermal growth of the stator vanes 30. As depicted 
in FIGS. 4A, 4B and 4C the dimension is selected to assure that the ends 
of the bulbous ends 110 and 112 do not press against the inner side walls 
118 and 120 when the adjacent edges abut (FIG. 4B) and that the ends do 
not fall out of the grooves 106 when the adjacent edges are spaced at the 
maximum axial and distorted distance. 
As is exemplified in the sectional end view depicted in FIG. 5, the 
"dog-bone" shaped scale may also be fabricated so that the central portion 
of the bulbous end is hollow and in the side view the end is "C" shaped. 
The "C" portion is compressed when inserted into groove 106 to provide a 
relatively tight fit. 
Although the invention has been shown and described with respect to 
detailed embodiments thereof, it will 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 scope of the claimed invention.