U.S. patent application number 09/778042 was filed with the patent office on 2001-11-29 for axial thermal medium delivery tubes and retention plates for a gas turbine rotor.
Invention is credited to Mashey, Thomas Charles.
Application Number | 20010046441 09/778042 |
Document ID | / |
Family ID | 23306012 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046441 |
Kind Code |
A1 |
Mashey, Thomas Charles |
November 29, 2001 |
Axial thermal medium delivery tubes and retention plates for a gas
turbine rotor
Abstract
In a multi-stage turbine rotor, tubes are disposed in openings
adjacent the rotor rim for flowing a thermal medium to rotor
buckets and returning spent thermal medium. The tubes have axially
spaced lands of predetermined wall thickness with thin-walled tube
sections between the lands and of increasing thickness from the
forward to the aft ends of the tubes. A pair of retention plates
are carried on the aft end face of the aft wheel and straddle the
tube and engage against a shoulder on the tube to preclude
displacement of the tube in an aft direction.
Inventors: |
Mashey, Thomas Charles;
(Coxsackie, NY) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
1100 North Glebe Road, 8th Floor
Arlington
VA
22201-4714
US
|
Family ID: |
23306012 |
Appl. No.: |
09/778042 |
Filed: |
February 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09778042 |
Feb 7, 2001 |
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09334187 |
Jun 16, 1999 |
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Current U.S.
Class: |
416/96R ;
415/115; 415/116; 416/198A; 416/201R; 416/95 |
Current CPC
Class: |
F01D 5/081 20130101;
F01D 5/06 20130101 |
Class at
Publication: |
416/96.00R ;
415/115; 415/116; 416/95; 416/198.00A; 416/201.00R |
International
Class: |
F01D 005/14; F01D
005/08 |
Claims
What is claimed is:
1. A multi-stage rotor for a gas turbine, the rotor having an axis,
comprising: a plurality of turbine wheels and spacers disposed
alternately relative to one another along the rotor axis and
secured generally in axial alignment with one another; a plurality
of axially aligned, circumferentially spaced, openings through the
wheels and spacers at locations spaced radially from said axis; and
tubes disposed in said openings for flowing a thermal medium, said
tubes having raised lands at axially spaced locations therealong
for mounting the tubes in said openings, said lands having a
predetermined wall thickness, said tubes including thin-walled tube
sections between said lands of a thickness less than said
predetermined thickness and with exterior wall surfaces thereof at
radii less than radii of exterior wall surfaces of said lands.
2. A rotor according to claim 1 including arcuate transition areas
along said tubes between said raised lands and said thin-walled
sections.
3. A rotor according to claim 1 wherein said openings and said
thin-walled sections lie spaced one from another forming an annular
space therebetween.
4. A rotor according to claim 1 wherein the thickness of at least
certain of said thin-walled sections of each tube is different than
the thickness of other thin-walled sections of said tube.
5. A rotor according to claim 1 wherein the thickness of succeeding
thin-walled sections of each tube in a first axial direction along
said tube is less than the thickness of axially preceding
thin-walled sections.
6. A rotor according to claim 1 wherein the thickness of each next
adjacent thin-walled section of each tube in a first axial
direction along said tube is less than the thickness of each next
axially preceding thin-walled section.
7. A rotor according to claim 1 wherein the thickness of succeeding
thin-walled sections of each tube in a first axial direction along
said tube is less than the thickness of axially preceding
thin-walled sections, said tubes being fixed to said rotor adjacent
one end thereof, said tube being expandable in said first axial
direction responsive to flow of the thermal medium through said
tubes.
8. A rotor according to claim 1 wherein said wheels include
bushings in said openings, certain of said lands and certain of
said bushings having first clearances therebetween, another of said
lands and another of said bushings at corresponding axial locations
along said tubes having a second clearance therebetween less than
said first clearance to discourage flow of air between said another
land and said another bushing and along said tube.
9. A rotor according to claim 1 including retention plates carried
by said rotor for fixing said tubes to said rotor against axial
displacement in one axial direction, each tube including a shoulder
for engaging said plate to preclude displacement of said tube in
said one axial direction.
10. A rotor according to claim 9 wherein one of said wheels and
said spacers includes an annular face about said axis, said
openings opening through said face, radially opposite stops
engaging said retention plates along radially opposite margins of
said plates to preclude displacement of said plate in radial
directions and a stop spaced circumferentially from said tube and
engaging said retention plate to preclude movement of said plate in
at least one circumferential direction about said face.
11. A rotor according to claim 9 wherein one of said wheels and
said spacers includes an annular face about said axis, said
openings opening through said face, radially opposite stops
engaging said retention plates along radially opposite margins of
said plates to preclude displacement of said plates in radial
directions, said radially opposite stops comprising flanges
projecting axially from an axial face of said one wheel and spacer,
a radially outermost flange of said opposite stops being
interrupted to define a plurality of slots, each said retention
plate being movable in a circumferential direction along said
flanges for registration with a respective slot thereby enabling
said retention plate for removal from said one wheel and spacer in
a radial outward direction through said slot.
12. A rotor according to claim 1 including pairs of retention
plates carried by said rotor, each pair of retention plates
disposed at a predetermined axial position along a tube for fixing
said tube against axial displacement in one axial direction, each
said pair of plates straddling said tube along opposite sides
thereof, each tube including a shoulder for engaging said pair of
plates to preclude displacement of said tubes in said one axial
direction.
13. A rotor according to claim 12 wherein one of said wheels and
said spacers includes an annular recess about said axis defined in
part by radially spaced, circumferentially extending flanges, said
openings opening into said recess with said tubes passing through
said recess in an axial direction, said retention plates lying in
said recess with said flanges engaging radially opposite margins of
said plates to preclude displacement of said plates in radial
directions, the radially outermost flange of said radially spaced
flanges being interrupted to define circumferentially spaced slots,
said retention plates being movable in circumferential directions
along said recess for radial registration with said slots thereby
enabling said retention plates for removal from said one wheel and
spacer in radial outward directions through said slots.
14. A multi-stage rotor for a turbine, the rotor having an axis,
comprising: a plurality of turbine wheels and spacers disposed
alternately relative to one another along the rotor axis and
secured generally in axial alignment with one another; a plurality
of axially aligned, circumferentially spaced, openings through the
wheels and spacers at locations spaced radially from said axis;
tubes disposed in said openings for flowing a thermal medium; and a
retention plate carried by said rotor for fixing each tube to said
rotor against axial displacement in one axial direction and located
at a predetermined axial position along said tube, each tube
including a shoulder for engaging said plate to preclude
displacement of said tube in said one axial direction.
15. A rotor according to claim 14 wherein one of said wheels and
said spacers includes an annular face about said axis, said
openings opening through said face, radially opposite stops
engaging said retention plates along radially opposite margins of
said plates to preclude displacement of said plates in radial
directions and stops spaced circumferentially from said tubes and
engaging said retention plates to preclude movement of said plates
in at least one circumferential direction about said face.
16. A rotor according to claim 14 wherein one of said wheels and
said spacers includes an annular face about said axis, said
openings opening through said face, radially opposite stops
engaging said retention plates along radially opposite margins of
said plates to preclude displacement of said plates in radial
directions, said radially opposite stops comprising flanges
projecting axially from an axial face of said one wheel and spacer,
a radially outermost flange of said opposite stops being
interrupted to define circumferentially spaced slots, said
retention plates being movable in circumferential directions along
said flanges for registration with said slots thereby enabling said
retention plates for removal from said one wheel and spacer in
radial outward directions through said slots.
17. A rotor according to claim 14 including pairs of retention
plates carried by said rotor, each pair of retention plates
disposed at a predetermined axial position along a tube for fixing
said tube against axial displacement in one axial direction, each
said pair of plates straddling said tube along opposite sides
thereof, each tube including a shoulder for engaging said pair of
plates to preclude displacement of said tubes in said one axial
direction.
18. A rotor according to claim 17 wherein one of said wheels and
said spacers includes an annular recess about said axis defined in
part by radially spaced circumferentially extending flanges, said
openings opening into said recess with said tubes passing through
said recess in an axial direction, said retention plates lying in
said recess with said flanges engaging radially opposite margins of
said plates to preclude displacement of said plates in radial
directions, the radially outermost flange of said radially spaced
flanges being interrupted to define circumferentially spaced slots
therebetween, said retention plates being movable in
circumferential directions along said recess for radial
registration with said slots thereby enabling said retention plates
for removal from said one wheel and spacer in radial outward
directions through said slots.
Description
TECHNICAL FIELD
[0001] The present invention relates to gas turbines having
rotational components cooled by a thermal medium flowing within the
rotor and particularly relates to thermal medium supply and return
tubes extending parallel to the rotor axis adjacent the rim of the
rotor for supplying a thermal medium to buckets carried by the
turbine wheels and returning spent cooling thermal medium.
BACKGROUND OF THE INVENTION
[0002] In assignee's prior U.S. Pat. No. 5,593,274, there is
disclosed a gas turbine having a closed cooling circuit for
supplying a thermal medium, e.g., cooling steam, generally in an
axial direction along the rotor to turbine buckets to cool the
buckets and returning the spent thermal medium in an opposite,
generally axial direction for flow from the rotor, for example, to
the steam turbines of a combined-cycle system. In the turbine
disclosed in that patent, cooling steam is supplied via an axial
bore tube assembly, radially outwardly extending tubes and a
plurality of axially extending tubes along the rims of the wheels
and spacers for supplying steam to the buckets. Spent cooling steam
returns from the buckets through passages in substantially
concentric relationship with the cooling steam supply tubes for
return via the bore assembly. While such arrangement has proven
satisfactory, a new and improved cooling circuit has been designed
in connection with a new and further advanced gas turbine.
BRIEF SUMMARY OF THE INVENTION
[0003] In accordance with a preferred embodiment of the present
invention, the thermal medium, for example, steam, is supplied in
an axially forward direction through an aft bore tube assembly,
through a plurality of radial tubes in an aft disk, and for flow in
supply tubes disposed in aligned openings through the stacked
wheels and spacers comprising the rotor and adjacent the rims of
the wheels and spacers. The supply tubes lie in communication with
the buckets of one or more turbine wheels, preferably the first and
second stage buckets, whereby bucket cooling is effected. Spent
cooling steam is returned from the buckets via another set of tubes
passing in an axial direction through aligned openings adjacent the
rims of the wheels and spacers for flow through radially inwardly
directed tubes provided in the aft disk for return along the
centerline of the bore tube. It has been found highly desirable to
minimize the heat lost from the thermal medium flowing through the
supply and return tubes into the rotor structure. To accomplish
that, the cooling steam is insulated from the rotor structure to
minimize the thermal effect on the rotor resulting from the flow of
cooling steam through the rotor. Particularly, the tubes are spaced
from the walls of the openings to provide insulation between the
tubes and the rotor wheels and spacers.
[0004] The supply and return tubes also accommodate mechanical and
thermal stresses during operation. For example, when the rotor
wheels and spacers are assembled, the openings through the wheels
and spacers are aligned with one another co-linearly, enabling the
tubes to be inserted into the passages defined by the aligned
openings after rotor assembly. However, at steady-state turbine
operation, the passages do not remain co-linear. Rather, the
passages shift out of position relative to one another as a result
of mechanical and thermal stresses. Because the masses of the
wheels and spacers are different from one another and hence have
different mechanical and thermal responses at steady-state, the
passages at steady-state turbine operation tend to misalign with
one another. Further, the thermal stresses induced by passing
cooling steam through the tubes and returning even hotter spent
cooling steam causes the tubes to thermally respond, tending to
expand the tubes. Additionally, during steady-state operation, the
rotor rotates at 3600 rpm. Because the tubes are located about the
periphery of the rotor at substantial distances from the rotor
axis, substantial centrifugal forces act on the tubes, causing
significant stresses in the tubes. With the wheel and spacer
passages somewhat misaligned because of the mechanical and thermal
stresses on the rotor, the tubes must be designed to minimize any
tendency to rupture, crack or become fatigued as a result of lying
in a high centrifugal field. Moreover, because the tubes carry
cooling steam and are oftentimes during different operational modes
at different temperatures than the temperature of the rotor,
thermal strain differentials will appear between the tube and rotor
which, combined with the centrifugal loading and friction, cause
substantial loads on the tubes. If unrestricted, such loads could
result in an unpredictable shift in the axial position of the
tubes. The axial location of the tubes within the rotor must be
constrained within limits to facilitate the flow of steam in
different directions relative to the tubes.
[0005] To alleviate or minimize mechanical and thermal stresses on
the tubes, the tubes are specifically constructed to have raised
lands at axially spaced positions along the tubes separated by
thin-walled tube sections. The raised lands thus have exterior
surfaces at radial locations larger than the radial locations of
the exterior surfaces of the thin-walled sections between the
lands. The raised lands engage bushings in the passages through the
rotor and, hence, the exterior surfaces of the thin-walled sections
are separated by annular spaces from the interior surfaces of the
passages. These annular spaces form insulation blankets minimizing
the thermal effect of the cooling medium on the rotor.
[0006] Transition areas between the lands and the thin-walled
sections are also provided to minimize transmission of stresses
between the lands and the thin-walled sections. The transition
portions include arcuate annular surfaces transitioning from the
exterior surface of the lands to the radially reduced exterior
surfaces of the thin-walled sections.
[0007] Additionally, because the tubes lie in a high centrifugal
field during rotor rotation, the heavier the tube, the higher the
load applied to tube support bushings. This increased loading on
the tube supports increases friction loading as the tubes respond
thermally. As the tube responds to the thermal load, the tube grows
axially, increasing frictional loading at each support location.
The friction load decreases, however, in a direction away from a
support which fixes the axial location of the tube in the rotor. By
varying the thickness along the tube in accordance with a preferred
embodiment of the present invention, and in a direction away from a
fixed support for the tube, the load accumulation decreases.
Consequently, the thin-walled sections, which are dead weight, can
be made progressively thinner in a direction away from the fixed
support. That is, the thinner the thin-walled section, the less
weight a given support carries and, accordingly, the friction load
carried by the tubes decreases as the tube thermally grows. In a
preferred form of the invention, the tube is axially fixed adjacent
an aft end thereof so that axial tube growth occurs in an axial
forward direction. Consequently, the thin-walled sections are
increasingly thinner in a direction away from the fixed support,
e.g., thinner in an axially forward direction from an aft fixed
tube support.
[0008] In accordance with another preferred aspect of the present
invention, axial retention assemblies are provided on the rotor,
preferably on the aft rotor wheel to fix the supply and return
tubes at that location, enabling axial thermal growth in an axially
forward direction. Each retention assembly, in accordance with a
preferred embodiment hereof, includes, for each tube, a pair of
retention plates disposed in an annular recess along an annular
face of the last wheel of the rotor, e.g., the aft face of the
fourth stage wheel in a four-stage turbine. The retention plates
are preferably disposed between opposed radial flanges and have
arcuate sections straddling the tube extending through the passages
and into the annular recess. The tube includes a shoulder against
which the retention plate bears to restrain the tube from movement
under thermal loading in an axially aft direction. The tube also
includes a shoulder for bearing against a portion of the wheel to
preclude movement of the tube in an axially forward direction.
Slots are preferably formed adjacent the retention plates in the
outer flange to facilitate assembly and removal of the retention
plates. The retention plates are held in position straddling the
tubes by pins engaging in the wheel. Upon removal of the pins, the
retention plates can be displaced in a circumferential direction to
register radially with slots in the outer flange, enabling the
retention plates to be removed from the rotor.
[0009] In a preferred embodiment according to the present
invention, there is provided multi-stage rotor for a gas turbine,
the rotor having an axis, comprising a plurality of turbine wheels
and spacers disposed alternately relative to one another along the
rotor axis and secured generally in axial alignment with one
another, a plurality of axially aligned, circumferentially spaced,
openings through the wheels and spacers at locations spaced
radially from the axis and tubes disposed in the openings for
flowing a thermal medium, the tubes having raised lands at axially
spaced locations therealong for mounting the tubes in the passages,
the lands having a predetermined wall thickness, the tubes
including thin-walled tube sections between the lands of a
thickness less than the predetermined thickness and with exterior
wall surfaces thereof at radii less than radii of exterior wall
surfaces of the lands.
[0010] In a further preferred embodiment according to the present
invention, there is provided a multi-stage rotor for a turbine, the
rotor having an axis, comprising a plurality of turbine wheels and
spacers disposed alternately relative to one another along the
rotor axis and secured generally in axial alignment with one
another, a plurality of axially aligned, circumferentially spaced,
openings through the wheels and spacers at locations spaced
radially from the axis, tubes disposed in the openings for flowing
a thermal medium and a retention plate carried by the rotor for
fixing each tube to the rotor against axial displacement in one
axial direction and located at a predetermined axial position along
the tube, each tube including a shoulder for engaging the plate to
preclude displacement of the tube in the one axial direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a cross-sectional view of a portion of a gas
turbine illustrating a turbine section;
[0012] FIG. 2 is a fragmentary perspective view of portions of a
turbine rotor with parts broken out and in cross-section for ease
of illustration;
[0013] FIG. 3A is a fragmentary enlarged cross-sectional view
illustrating, in cross-section, a rim of the rotor with the thermal
medium return tube being illustrated;
[0014] FIG. 3B is an enlarged cross-sectional view of an aft
portion of the rotor adjacent its rim illustrating the location of
retention plates for a thermal medium return tube according to the
present invention;
[0015] FIGS. 4 and 5 are fragmentary cross-sectional views of the
thermal medium supply and return tubes, respectively, with portions
broken out for ease of illustration;
[0016] FIG. 6 is an enlarged fragmentary cross-sectional view
illustrating a retention plate for one of the tubes in position on
the aft face of the aft wheel;
[0017] FIG. 7 is an enlarged fragmentary elevational view of the
aft face of the aft wheel illustrating the retention plates in
position about a tube and a single retention plate in position for
removal;
[0018] FIG. 8 is a fragmentary perspective view with parts in
cross-section illustrating the aft face of the aft wheel; and
[0019] FIGS. 9 and 10 are side and end elevational views of a
preferred retention plate.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Referring to FIG. 1, there is illustrated a turbine section,
generally designated 10, incorporating the present invention. The
turbine section 10 includes a turbine housing 12 surrounding a
turbine rotor R. Rotor R includes in the present example four
successive stages comprising wheels 14, 16, 18 and 20, carrying a
plurality of circumferentially spaced buckets or blades 22, 24, 26
and 28, respectively. The wheels are arranged alternately between
spacers 30, 32 and 34. The outer rims of spacers 30, 32 and 34 lie
in radial registration with a plurality of stator blades or nozzles
36, 38 and 40, with the first set of nozzles 42 lying forwardly of
the first buckets 22. Consequently, it will be appreciated that a
four-stage turbine is illustrated wherein the first stage comprises
nozzles 42 and buckets 22; the second stage, nozzles 36 and buckets
24; the third stage, nozzles 38 and buckets 26 and, finally, the
fourth stage, nozzles 40 and buckets 28. The rotor wheels and
spacers are secured one to the other by a plurality of
circumferentially spaced bolts 44 passing through aligned openings
in the wheels and spacers. A plurality of combustors, one being
illustrated at 45, are arranged about the turbine section to
provide hot gases of combustion through the hot gas path of the
turbine section in which the nozzles and buckets for rotating the
rotor are disposed. The rotor also includes an aft disk 46 formed
integrally with a bore tube assembly, generally designated 48.
[0021] At least one and preferably both sets of buckets 22 and 24
of the first two stages are provided with a thermal medium for
cooling, the thermal medium preferably being cooling steam. Cooling
steam is provided and returned through the bore tube assembly 48.
With reference to FIGS. 1 and 2 and in a preferred embodiment, the
bore tube assembly includes an annular passage 50 supplied with
cooling steam, from a steam plenum 52 for flow to a plurality of
radially extending tubes 54 provided in the aft disk 46. Tubes 54
communicate with circumferentially spaced, axially extending
thermal medium supply tubes 56 in communication with cooling
passages in the first and second-stage buckets. Spent or returned
cooling steam at an elevated temperature flows from the first and
second-stage buckets through a plurality of circumferentially
spaced, axially extending return tubes 58. Return tubes 58
communicate at their aft ends with radially inwardly extending
return tubes 60 in aft disk 46. From tubes 60, the spent steam
flows into the central bore of the bore tube assembly 48 for return
to a supply or for flow to steam turbines for use in a
combined-cycle system.
[0022] It will be appreciated from the foregoing description that
the axially extending supply and return tubes 56 and 58,
respectively, lie adjacent the rim of the rotor, with each supply
and return tube extending through axially aligned openings through
the axially stacked wheels and spacers. For example, the aligned
openings 62 and 64 of wheels 20 and spacers 34, respectively, are
illustrated in FIG. 3A. Similar aligned openings are provided in
the wheels and spacers of the first, second and third stages.
[0023] As illustrated in FIG. 3A, bushings are provided at various
locations within the openings of the wheels and spacers for
supporting the cooling medium supply and return tubes 56 and 58,
respectively. For example, bushings 66 and 68 are disposed adjacent
opposite ends of the opening 64 through spacer 34. Similar bushings
are disposed at opposite ends of the third-stage spacer 32.
Bushings 73 and 75 are provided at the forward opening of wheel 16
and the aft opening of spacer 30. Similar bushings are provided in
the aligned openings for the supply tube.
[0024] Referring to FIGS. 4 and 5, the respective supply and return
tubes 56 and 58 are illustrated. The tubes are similar in aspects
relevant to this invention and a description of one will suffice as
a description of the other, except as otherwise noted. Each tube
comprises a thin-walled structure having a plurality of raised
lands 70 at axially spaced locations along the length of the tube.
The axial locations of the lands 70 coincide with the locations of
the bushings in the openings through the wheels and spacers.
Between the lands 70 are thin-walled tube sections 72 (FIG. 3A).
From a review of FIGS. 4 and 5, it will be appreciated that the
outer exterior surfaces of the lands 70 are radially outwardly of
the exterior surface of the thin-walled sections 72. Transition
sections 74 are provided between each land 70 and adjacent
thin-walled sections 72. The transition sections 74 have arcuate
outer surfaces transitioning radially inwardly from the outer
surface of the lands to the outer surfaces of the thin-walled
sections 72. These transition areas 74 smooth the stresses from the
raised lands to the thin sections. An enlarged land or flange 76 is
provided adjacent an aft portion of each tube, for reasons
explained below. As illustrated in FIG. 4, the interior end
portions of the supply tubes 56 have concave surfaces 78 for mating
engagement with convex surfaces of spoolies for flowing the thermal
medium into and out of the return tubes.
[0025] It will be appreciated that the thin-walled sections are not
supported between the lands and that, in the high centrifugal field
during rotor rotation, the heavier the tube, the greater will be
the friction forces carried by the tubes at the support points
between the lands and the bushings. As the tubes are subjected to
thermal or mechanical stresses, the higher the loading at the
supports, the higher the friction load as the tube thermally grows
in an axial direction from its fixed aft end. As a result of fixing
the aft end of the tubes, the friction load developed at each
support point creates a loading which is cumulative from forward to
aft. That is, actual tube loading from thermal growth increases in
the aft direction. By varying the thicknesses along the tube and
particularly increasing the thicknesses of the tube in the aft
direction, the higher frictional loads forwardly of each support
can be accommodated. Stated differently, the thinner each
thin-walled section becomes in the forward axial direction, the
less weight a given support carries and, consequently, a smaller
friction load is generated under thermal growth conditions. Because
the tubes are fixed at their aft ends, the thermal growth moves
axially forwardly. At each support location, the accumulating
frictional loading is the loading at that location with the added
loading of locations axially forwardly of the given location.
[0026] Particularly, the thicknesses t1-t5 of the thin-walled
sections 72 between the lands 70 decrease in thickness from the aft
end of the tubes 56 and 58 to their forward ends. That is, the wall
thickness t1 of the thin-walled section 72 between axially spaced
flange 76 and land 70a is thicker than the wall thickness t2
between axially adjacent lands 70a and 70b. Similarly, the wall
thickness t2 is greater than the wall thickness t3 of the
thin-walled section 72 between axially adjacent lands 70b and 70c.
The wall thickness t3 is greater than the wall thickness t4 between
lands 70c and 70d. The wall thickness t4 is greater than the wall
thickness t5 between axially adjacent lands 70d and the forward end
of the tube. Thus, the wall thicknesses of the thin-walled sections
72 decrease from the aft ends of the tubes toward the forward ends
of the tubes.
[0027] Because the interior wall surfaces of the tubes have smooth
bores, the progressive decrease in wall thickness of the
thin-walled sections toward the forward end of the rotor results in
decreasing outside diameters of the thin-walled sections. This, in
turn, results in an increase in the thickness of thermal insulation
cavities 77 between the tubes and the openings through the wheels
and spacers receiving the tubes and enhanced thermal insulation
between the tubes and the rotor.
[0028] The insulation cavities 77 between the tubes and aligned
openings of the wheels and spacers form essentially dead air spaces
for thermally insulating the cooling medium carried by the tubes
from the rotor. While the clearances between the bushings and the
tubes are relatively small, e.g., about 17 mils, the clearance
between the bushings 73 and the lands of the supply and return
tubes at that axial location are tighter, e.g., 10 mil clearances.
By reducing the clearance between the bushings at the forward face
of wheel 16 and the tube lands at that axial location, air flow
from the cavity 79 along the tubes in an aft direction is
discouraged thereby maintaining essentially stagnant air in the
cavities 77 between the tubes and the aligned openings of the
wheels and spacers.
[0029] Referring now to FIGS. 6-10, retention assemblies are
illustrated in accordance with a preferred embodiment of the
present invention for fixing the aft ends of the supply and return
tubes 56 and 58 to the rotor. In FIG. 6, a tube, for example, a
return tube 58, is illustrated with the radially enlarged land 76.
Also illustrated is the bushing 90 disposed in a counterbored
recess 92 in the aft face of the fourth wheel 20. The forward edge
of the raised land 76 of tube 58 bears against an interior flange
of the bushing 90 to prevent forward axial movement of the tube.
The rear shoulder 97 of each land 76 bears against a pair of
retention places 106, precluding movement in a rearward direction.
The retention plates 106 in turn bear against a forward face of the
aft disk 46.
[0030] Referring to FIG. 8, the aft wheel face includes an annular
recess 100 through which pass the openings 62 for receiving the
tubes. The recess 100 is bounded radially by flanges 102 and 104
which form radial inner and outer stops, respectively, for
retention plates 106. The radial outer flange 104 includes a
plurality of circumferentially spaced indents or slots 107 which
afford access openings for removal of the retention plates 106 as
described below. A reduced access slot 108 is formed in the flange
104 at circumferentially spaced positions about the aft face of the
wheel at each tube opening location, affording an access slot to
the retention plate whereby the plate can be shifted to a position
for removal in a manner which will now be described.
[0031] Referring to FIGS. 9 and 10, there is illustrated a
retention plate 106 which forms one-half of a retention assembly
for each tube, i.e., two retention plates are employed to retain
each axial tube fixed at an aft end portion of the tube. Each
retention plate 106 includes curved outer and inner edges 109 and
110, respectively, corresponding to the curvature of respective
flanges 104 and 102 so that the plates can be received between the
flanges. An ear 112 projects outwardly from the radially outer edge
109 of the retention plate and projects into one end of the access
slot 107 of the outer flange 104. The retention plates of each
retention assembly are mirror images of one another. The inside
edge of each plate 106 has a semi-circular edge 114 corresponding
in radius to the radius of the tube. Consequently, as seen in FIG.
7, the retention plates 106 are located between flanges 104 and 102
and straddle circumferentially opposite sides of the tube 58. In
order to lock the retention plates 106 in position behind the
raised land 76, a pair of pins, i.e., stops 118 are inserted into
openings in the face of the aft wheel and engage the
circumferential outer edges of the retention plates 106 to prevent
circumferential separating movement of the plates 106 from their
position straddling the tube. Access to the pins 118 for their
removal and removal of the retention plates is obtained after
removal of overlying windage plates. The pins 118 are then
withdrawn rearwardly from the aft shaft 46. Upon removal of the
pins 118 by inserting a suitable tool through slot 107, each
retention plate can slide in a circumferential direction away from
its retained tube for radial alignment with the slot 107 through
the radially outermost flange 104. A wedging tool may be disposed
through the slot 108 to engage the chamfered surfaces 120 of the
retention plates to initially separate the plates, if necessary.
Otherwise, the ears 112 can be engaged by a suitable tool for
displace the plates 106 into registration with slots 107 for
removal.
[0032] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *