Flow directing assembly for a gas turbine engine

A nonrotating flow directing assembly 14 for a gas turbine engine is disclosed. The flow directing assembly is formed of a circumferentially segmented inner case 24 supported by an annular sleeve 22. The inner case 24 is formed of a plurality of arcuate segments 26 extending axially continuously through the engine. A method of assembling the circumferentially continuous annular sleeve about an axially continuous rotor is also disclosed. In an alternate embodiment the inner case 124 is formed of several pluralities of arcuate segments 126.

DESCRIPTION 
1. Technical Field 
This invention relates to axial flow rotary machines, and more particularly 
to flow directing assemblies of the nonrotating type, such as the stator 
assemblies of gas turbine engines having arrays of stator vanes in the 
compression section or the turbine section of such an engine. 
2. Background Art 
In the compression section of a gas turbine engine, a rotor structure 
extends axially through the compression section. A stator structure is 
spaced radially from the rotor structure and circumscribes the rotor 
structure. Arrays of rotor blades extend outwardly from the rotor 
structure into proximity with the stator structure. Arrays of stator vanes 
extend inwardly from the stator structure into proximity with the rotor 
structure. A flow path for working medium gases extends axially through 
the compression section between the rotor structure and the stator 
structure. 
An example of such a construction is shown in U.S. Pat. No. 4,019,320 
entitled "External Gas Turbine Engine Cooling For Clearance Control" 
issued to Redinger, Jr. et. al. In this construction, the stator vanes and 
axially discrete outer air seals are supported from an outer case. The 
outer case has circumferentially extending flanges which are bolted 
together during assembly. The hoop strength of these circumferentially 
continuous flanges aids the outer case in maintaining a true, circular 
shape during operative conditions which subject the case to thermal growth 
and internal pressure. 
In some modern engines, the rotor assembly is comprised of a rotor drum and 
rotor blades. The rotor drum is axially continuous. To assemble the stator 
vanes about such a rotor drum, the outer case of the stator structure is 
axially split and provided with axially extending flanges which are bolted 
together during assembly. An example of such a construction is shown in 
U.S. Pat. No. 2,848,156 issued to Oppenheimer entitled "Fixed Stator Vane 
Assemblies". Drum rotors are used because of their light weight as 
compared with bolted up constructions, better fatigue life through the 
elimination of axially extending bolt holes, and the higher critical speed 
margin resulting from their axial stiffness. 
DISCLOSURE OF INVENTION 
According to the present invention, a longitudinally split inner case 
carrying arrays of stator vanes is supported by a circumferentially 
continuous outer sleeve circumscribing the longitudinally split inner 
case. 
In accordance with the present invention, vanes of a stator assembly are 
assembled in a plurality of arcuate segments disposed about the rotor 
assembly; an annular sleeve is slid over the arcuate segments to hold the 
segments in place. 
A primary feature of the invention is a longitudinally split inner case 
which is formed of a plurality of arcuate segments. Each segment of the 
inner case is axially continuous. Each segment of the inner case engages a 
portion of more than one array of stator vanes. Another feature is an 
annular sleeve which is circumferentially continuous. The annular sleeve 
holds the inner case in circumferential alignment. Another feature is the 
means for engagement between the inner case and the annular sleeve 
permitting the annular sleeve and the inner case to be slidably assembled 
with respect to each other. In one embodiment the inner case is made up of 
more than one plurality of axially continuous segments. 
A principal advantage of the present invention is the ease with which 
stator components can be assembled about a rotor. An increase in engine 
efficiency results from the true circularity of the circumferentially 
continuous annular sleeve which positions the inner case about the rotor 
structure. Another advantage is the increased efficiency which results 
from the aerodynamic smoothness of the axially continuous flow path as 
compared with constructions having a multiplicity of rings each of which 
extends at a slightly different diameter into the working medium flow 
path. The efficiency of the engine is increased by the close 
correspondence between the rotor structure and the stator structure 
enabled by the free acting radial inward and outward movement of the 
segmented inner case which is supported from the outer sleeve. 
Other features and advantages will be apparent from the specification and 
claims and from the accompanying drawings which illustrate an embodiment 
of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION 
A gas turbine engine embodiment of the invention is illustrated in FIG. 1. 
A portion of a compression section 10 of such an engine is shown. The 
compression section includes a flow directing assembly which rotates about 
an axis A of the engine such as the rotor assembly 12 and a flow directing 
assembly which does not rotate such as the stator assembly 14 
circumscribing the rotor assembly. As will be appreciated, use of these 
flow directing assemblies is equally applicable to the turbine section of 
such an engine. A plurality of external tubes 15 for cooling air 
circumscribe the stator assembly. An annular flow path 16 for working 
medium gases extends axially through the engine between the stator 
assembly and the rotor assembly. The rotor assembly includes a rotor 18. A 
drum rotor type construction is shown. This invention has particular 
utility when used in conjunction with such rotor constructions, although 
the concepts are applicable to bolted-up rotors having individual rotor 
disks as well. The rotor assembly includes arrays of rotor blades 
extending outwardly from the rotor as represented by the single rotor 
blades 20. 
The stator assembly 14 is formed of an annular sleeve 22 and an inner case 
24. The inner case extends axially in the engine outwardly of the annular 
flow path 16 for working medium gases. The inner case is formed of a 
plurality of arcuate segments 26 circumferentially adjacent one to 
another. The arcuate segments are axially continuous. Each arcuate segment 
supports a portion of the vanes of two or more arrays of stator vanes as 
represented by the single vanes 28. The expression "axially continuous" 
denotes a structure unsplit in the circumferential direction. The annular 
sleeve is outwardly of the inner case and engages the segments of the 
inner case. The annular sleeve is formed of circumferentially continuous 
material. As used in this application "continuous material" is defined as 
material uninterrupted by a split. For example, axially continuous 
material is material uninterrupted by a circumferentially extending split. 
Circumferentially continuous material is material uninterrupted by an 
axially oriented split. Thus, even though the inner case 24 is interrupted 
by a bleed hole 30 and the annular sleeve is interrupted by a bleed hole 
32, the segments of the inner case are deemed to be formed of axially 
continuous material and the annular sleeve is formed of circumferentially 
continuous material as shown in FIG. 1. As will be realized, the annular 
sleeve 22 may be formed of axially continuous material or may have a 
plurality of circumferentially extending flanges 34 which are bolted 
together as shown in FIG. 7. 
The annular sleeve 22 has a large diameter end 36 and a small diameter end 
38. The sleeve has a plurality of flanges 40 extending circumferentially 
about the interior of the case. Each flange has a groove 42 facing the 
large diameter end. Each segment of the inner case includes a plurality of 
flanges 44, each flange extending circumferentially about the segment and 
extending outwardly to slidably engage in a circumferential direction a 
corresponding flange of the sleeve. Each flange on the inner case extends 
axially into one of the grooves towards the small diameter end of the 
annular sleeve. Each flange on the sleeve is radially outward of any 
flange on the inner case which is disposed entirely between the flange on 
the sleeve and the small diameter end of the sleeve. 
A means for preventing rotative movement between an inner structure, such 
as the inner case 24, and an outer sleeve, such as the annular sleeve 22, 
extends between the inner case and the outer sleeve at the large diameter 
end and the small diameter end of the annular sleeve. In this embodiment, 
the means is a splined ring 46 discussed infra and illustrated in FIG. 5. 
A plurality of shroud rings 48 extend circumferentially about the interior 
of the engine. The shroud rings are inward of the annular flow path 16 for 
working medium gases and spaced radially by a clearance gap C from the 
rotor 18. 
FIG. 2 is a partial perspective view of a portion of two of the arcuate 
segments 26 of the inner case and shows the arrays of stator vanes 28, the 
shroud rings 48 and the flanges 44. Each flange 44 of the inner case has 
gaps 50 interrupting the circumferential continuity of the flange. A thin, 
sheet metal shield 52 blocks the working medium gases from flowing through 
the gaps. 
Each shroud ring 48 engages a corresponding array of stator vanes. Each 
shroud ring is segmented and each segment of the shroud ring engages a 
plurality of vanes. As will be appreciated, "plurality" is intended to 
embrace any number in excess of one. In the embodiment shown, each segment 
of the shroud ring engages the inward ends of three vanes extending 
inwardly from a single arcuate segment 26 of the inner case 24. Each 
segment of the shroud ring is spaced cicumferentially from the adjacent 
segment leaving a gap D therebetween. The arcuate segments of the inner 
case are circumferentially adjacent and spaced one from another leaving a 
gap E therebetween. 
As shown in FIG. 3, means for sealing such as feather seal 54 extends 
circumferentially between the adjacent arcuate segments of the inner case. 
As will be appreciated the segments of the inner case might 
circumferentially overlap each other to provide sealing. Such a 
construction is shown in FIG. 4. 
FIG. 5 shows a portion of the splined ring 46, the inner case 24 and the 
annular sleeve 22. The ring engages the annular sleeve at a plurality of 
spline-type connections 56 and engages an arcuate segment 26 of the inner 
case at an inner spline-type connection 58. The circumferential portions 
of the arcuate segment on either side of the inner spline-type connection 
are free to move circumferentially with respect to the sleeve. As shown in 
FIG. 1 an upstream case 60 and a flange 44 on the inner case trap the ring 
in the axial direction. The ring may be circumferentially continuous or 
formed of a plurality of segments. As will be realized, other means for 
preventing rotative movement between an inner structure and an outer 
sleeve may be used such as a radial pin in flange 140 and a slot in flange 
144. 
FIG. 6 is a diagrammatic illustration of a portion of the compression 
section illustrating a fundamentally new method of constructing a stator 
assembly about a rotor. 
FIG. 6a illustrates the first step of forming the rotor assembly 12. The 
rotor assembly includes a rotor 18. The rotor may be of a drum rotor type 
or a bolted-up construction of individual disks and spacers. A drum rotor 
is illustrated. Arrays of rotor blades 20 are assembled to the rotor and 
extend outwardly from the rotor. Each array of rotor blades is spaced 
axially from the adjacent array of rotor blades leaving an axial space 
therebetween. 
FIG. 6a shows the step of forming an inner case 24 of at least two arcuate 
segments 26 extending longitudinally. In the diagrammatic illustration, 
two arcuate segments are shown. Two or more arrays of stator vanes 28 are 
assembled to each segment. The stator vanes of each segment extend 
inwardly from the arcuate segment. The vanes of the arrays of stator vanes 
are spaced axially one from another leaving an axial space therebetween. 
FIG. 6a illustrates the step of positioning each arcuate segment 26 of the 
inner case radially outwardly of the rotor assembly 12 such that the 
arcuate segments are circumferentially spaced one from another. The arrays 
of stator vanes are each aligned in opposing relationship to a 
corresponding axial space between the arrays of rotor blades and the 
arrays of rotor blades are each aligned in opposing relationship to a 
corresponding space between the arrays of stator vanes. 
FIG. 6b shows the completion of the step of assembling the inner case to 
the rotor assembly by moving the arcuate segments 26 of the inner case 
inwardly toward the longitudinal axis of the rotor assembly such that the 
arrays of rotor blades and the arrays of stator vanes are interdigitated. 
As will be appreciated, the segments of the inner case may be 
circumferentially spaced one from another by a predetermined distance E. 
Assembling a vertically oriented inner case 24 to a vertically oriented 
rotor assembly 12 obviates the need for ties to keep the inner case in the 
assembled position. Assembling a horizontally oriented inner case to a 
horizontally oriented rotor assembly might require circumferentially 
extending ties such as cotton string and shims to maintain the required 
clearance E. The string 60 is shown in phantom. 
FIG. 6c illustrates the step of forming an annular sleeve having a 
longitudinal axis of symmetry. 
FIG. 6d shows the step of assembling the annular sleeve 22 to the arcuate 
segments 26 of the inner case 24 and the rotor assembly 12. The step 
includes aligning the axis of symmetry of the rotor assembly with the axis 
of symmetry of the sleeve and causing relative movement between the sleeve 
and the inner case such that the sleeve slidably engages each segment of 
the inner case. 
FIG. 6e shows the assembled rotor assembly 12, the inner case 24 and the 
annular sleeve 22. 
FIG. 7 is an alternate embodiment of FIG. 1 showing an inner case 124 
formed of at least two pluralities of arcuate segments which are axially 
continuous. The inner case includes a first plurality of arcuate segments 
126 circumferentially adjacent one to another. Each arcuate segment is 
axially continuous. Each arcuate segment supports a portion of at least 
two arrays of stator vanes 128. And, the inner case includes a second 
plurality of arcuate segments 127 circumferentially adjacent one to 
another. Each arcuate segment 127 abuts a corresponding arcuate segment 
126 of the first plurality of arcuate segments. Each arcuate segment 127 
supports a portion of not less than two arrays of stator vanes. An annular 
sleeve 122 of circumferentially continuous material outwardly of the inner 
case engages the arcuate segments 126, 127 of the inner case to hold the 
segments in circumferential alignment. 
Each of the first plurality of arcuate segments 126 is integrally attached 
to a corresponding segment 127 of the second plurality of arcuate 
segments. The segments may be attached, for example, by rivets 160 or by 
other suitable fastening means such as a plurality of bolt and nut 
assemblies. The annular sleeve 122 which circumscribes the arcuate 
segments has a plurality of flanges 140 spaced axially one from another. 
The flanges extend circumferentially about the interior of the annular 
sleeve. Each arcuate segment 126, 127 of the inner case includes at least 
one flange 144, each flange extending circumferentially about the arcuate 
segment and extending outwardly to slidably engage in the circumferential 
direction a corresponding flange of the sleeve. In the embodiment shown, 
each of the first plurality of arcuate segments 126 is integrally attached 
to a corresponding segment at a flange 144 of an arcuate segment. A means 
for axial retention such as the snap ring 166 engages a groove 168 in the 
outer case. The snap ring abuttingly engages an upstream flange on each 
segment of the inner case such as flange 144. 
Each arcuate segment of the inner case 126, 127 has a plurality of 
rubstrips as represented by the single rubstrip 170 and the single 
rubstrip 172. Each segment has a plurality of flanges 174 for 
reinforcement. Each flange extends outwardly from a corresponding segment 
and is outward of the rubstrip. 
The inner case 124 has at least one bleed opening 130 for working medium 
gases. The annular sleeve 122 has a corresponding bleed opening 132 for 
working medium gases in gas communication with the bleed opening in the 
inner case. At least one seal member 176 extends circumferentially about 
the inner case and is disposed between the bleed openings and a flange 144 
of the inner case. The seal member is formed of a plurality of arcuate 
seal segments 178, each seal segment engaging an arcuate segment of the 
inner case, such as arcuate segment 126 or arcuate segment 127, and 
extending outwardly into proximity with the annular sleeve 122. 
During operation of a gas turbine engine, as shown in FIG. 1 working medium 
gases are flowed along the flow path 12 for working medium gases. The 
gases pass through the arrays of stator vanes 28 and rotor blades 20. The 
rotor assembly 12 and the stator assembly 14 confine the working medium 
gases to the flow path. In particular, the clearance gap C between the 
rotor assembly and the stator assembly is small enough to block the 
leakage of working medium gases past the inward ends of the stator vanes 
and the outward ends of the rotor blades. 
The operative temperatures of these assemblies and the rotational forces 
acting on the rotor assembly 12 cause relative movement between the stator 
assembly 14 and the rotor assembly. In some cases this relative movement 
increases the clearance gap C between the rotor assembly and the stator 
assembly. Cooling air is flowed through the external tubes 15 to impinge 
on the annular sleeve 22 of the stator assembly. The cooling air removes 
heat from the annular sleeve causing the sleeve to contract and move 
inwardly. The ends of the arcuate segments 26 on either side of the inner 
spline-type connection 56 are free to slide circumferentially with respect 
to the annular sleeve. As the annular sleeve moves inwardly, the annular 
sleeve forces the inner case to a smaller diameter decreasing the 
clearance gap C between the rotating assembly and the stator assembly. 
Decreasing the clearance gap decreases the penalty to aerodynamic 
efficiency caused by leakage of the working medium gases through the 
clearance gap. 
The inner case 24 being formed of circumferentially adjacent arcuate 
segments 26 has reduced hoop strength as compared with circumferentially 
continuous cases. The gaps 50 in the flanges 44 extending between the 
inner case and the annular sleeve further reduce the hoop strength of the 
inner case. Similarly, the shroud ring 48 is segmented to reduce the hoop 
strength of the shroud ring. The reduction in hoop strength of the shroud 
ring and the arcuate segments reduces the retardant effect of the inner 
case on the thermal response of the annular sleeve. 
As the working medium gases pass through the arrays of stator vanes 28, the 
gases exert a circumferential force on the stator vanes. The shroud ring 
48 engages the inward ends of a plurality of the vanes and together with 
an arcuate segment 26, supports the vanes against this force in guided 
cantilevered fashion. This circumferential force is transmitted outwardly 
through the vanes, the arcuate segments 26 of the inner case, and the 
splined ring 46 to the annular sleeve 22. Because the splined ring is free 
to move in the radial direction, bending forces on the arcuate segment of 
the inner case are not increased by the radial moment arm of the ring 
acting cicumferentially on the inner case. Thus, the spline ring avoids 
the moment arm and the associated forces which would exist if the ring 
were integrally attached to the inner case. Accordingly, the splined ring 
avoids inducing the circumferential distortion in the arcuate segments 
which is associated with such bending forces. 
The axial continuity of the inner case 24 and the circumferential 
continuity of the annular sleeve 22 have advantages which are not found 
together in the prior art. The axially continuous arcuate segments 26 of 
the inner case bound the annular flow path 16 with an aerodynamically 
smooth surface in the axial direction. This decreases flow losses caused 
by small projections into the flow path associated with structures built 
up of a multiplicity of circumferential rings extending into the flow path 
from the stator structure. Because the annular sleeve is circumferentially 
continuous, the annular sleeve is not split and avoids the need for 
axially oriented flanges. These axial flanges are required for split case 
constructions and are particularly helpful for drum rotor constructions. 
However, the flanges cause the outer case to be structurally stiff in the 
vicinity of the flange. Structural stiffness affects the radial growth of 
the outer sleeve and results in ovalization of the sleeve. Because the 
outer sleeve is circumferentially continuous and does not have these 
flanges, the case is not subject to ovalization as a result of those 
flanges and avoids variations in the clearance gap C between the rotor 
assembly and the stator assembly. 
In a similar fashion, the inner case 124 shown in FIG. 7 is segmented to 
permit inward and outward movement of the inner case in response to 
changes in diameter of the annular sleeve 122. As will be realized, the 
annular sleeve may be axially continuous as well as circumferentially 
continuous. In the embodiment shown the annular sleeve is 
circumferentially continuous and has a first annular sleeve and a second 
annular sleeve which are integrally secured to each other. Such a 
circumferentially extending flange does not introduce an axial extending 
discontinuity as does the axially extending flange of split cases. The 
seal members 176 block the working medium gases from contacting the 
flanges 144 as the gases proceed from the bleed opening 130 in the inner 
case to the bleed opening 142 in the annular sleeve. 
One flange 144 on each first arcuate segment engages a corresponding flange 
140 on the annular sleeve. Each first arcuate segment 126 is also 
integrally attached to a flange 144 of a corresponding adjacent second 
arcuate segment 127. The flange 144 on the second arcuate segment 127 
supports the arcuate segment 126 from the annular sleeve. By joining the 
segment from the first plurality of arcuate segments to the adjacent 
segment of the second plurality of arcuate segments at the flange, the 
chance for a flow path discontinuity is minimized because both segments 
are positioned by the same flange 140 on the annular sleeve 122. 
Although this invention has been shown and described with respect to a 
preferred embodiment thereof, it should be understood by those skilled in 
the art that various changes and omissions in the form and detail thereof 
may be made therein without departing from the spirit and scope of the 
invention.