U.S. patent application number 09/742284 was filed with the patent office on 2002-06-27 for low windage loss, light weight closure bucket design and related method.
Invention is credited to Caruso, David Alan, Colwell, Douglas Carl, Maughan, James Rollins, Reluzco, George Ernest.
Application Number | 20020081196 09/742284 |
Document ID | / |
Family ID | 24984199 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081196 |
Kind Code |
A1 |
Reluzco, George Ernest ; et
al. |
June 27, 2002 |
Low windage loss, light weight closure bucket design and related
method
Abstract
A turbine closure bucket adapted to complete assembly of a row
of tangential entry buckets on a rotor wheel includes an airfoil
portion and a mounting portion for mounting the bucket to a turbine
wheel. The mounting portion has front and back faces, with weight
reduction cavities formed internally in the front and back faces.
Externally, the front and back faces of the closure bucket are
substantially identical to front and back faces of adjacent buckets
in the row.
Inventors: |
Reluzco, George Ernest;
(Schenectady, NY) ; Caruso, David Alan; (Ballston
Lake, NY) ; Colwell, Douglas Carl; (Schenectady,
NY) ; Maughan, James Rollins; (Scotia, NY) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
8th Floor
1100 North Glebe Road
Arlington
VA
22201
US
|
Family ID: |
24984199 |
Appl. No.: |
09/742284 |
Filed: |
December 22, 2000 |
Current U.S.
Class: |
415/173.7 |
Current CPC
Class: |
F01D 5/3046
20130101 |
Class at
Publication: |
415/173.7 |
International
Class: |
F01D 005/00 |
Claims
What is claimed is:
1. A turbine closure bucket adapted to complete assembly of a row
of tangential entry buckets on a rotor wheel comprising an airfoil
portion and a mounting portion for mounting the bucket to a turbine
wheel, said mounting portion having front and back faces, and
wherein weight reduction cavities are formed internally in the
front and back faces of the mounting portion, but wherein said
front and back faces of the closure bucket are substantially
identical to front and back faces of adjacent buckets in the
row.
2. The turbine closure bucket of claim 1 wherein a pair of said
cavities are provided internally of said front and back faces.
3. The turbine closure bucket of claim 2 wherein each pair of
cavities is separated by a radially oriented rib.
4. The turbine closure bucket of claim 1 including a sealing
platform adapted for engagement with an adjacent diaphragm
seal.
5. The turbine closure bucket of claim 1 wherein, internally, said
mounting portion is devoid of any dovetail hook elements.
6. A turbine closure bucket for completing assembly of a row of
tangential entry buckets on a rotor wheel, said bucket having a
pair of sides and front and rear faces, said front and rear faces
each having a pair of internal cavities separated by a
substantially radially extending rib.
7. A turbine rotor wheel having a dovetail formed about its
periphery, with an axial opening therein, said rotor wheel having a
plurality of turbine buckets received on said dovetail, each bucket
having front and back faces; and a closure bucket that is received
in said opening, said closure bucket having external front and back
faces substantially identical to corresponding front and back faces
of said plurality of buckets.
8. The turbine rotor wheel of claim 7 wherein said plurality of
buckets and said closure bucket have substantially identical
sealing platforms.
9. The turbine rotor wheel of claim 7 wherein, in said closure
bucket, a pair of said cavities are provided internally of both
said front and back faces.
10. The turbine rotor wheel of claim 9 wherein each pair of
cavities is separated by a radially oriented rib.
Description
[0001] This invention relates to turbine rotors and specifically to
a new bucket design for the last or "closure" bucket assembled in a
row of tangential entry type buckets on a turbine rotor wheel.
BACKGROUND OF THE INVENTION
[0002] Typically, turbine buckets, or blades, are assembled onto a
rotor wheel either individually in axial directions, or
tangentially through an opening to a circumferential dovetail. More
specifically, tangential entry buckets each have dovetail hooks
formed at its base. The buckets are assembled by inserting them,
one at a time, axially into an opening at a tangent to the wheel
surface so that the bucket dovetail hooks are aligned with the
dovetail on the wheel, and then sliding the buckets
circumferentially about the wheel along the dovetail, until all but
one bucket has been assembled. The final or closure bucket is then
inserted axially into the opening and secured to adjacent already
in-place buckets.
[0003] In general, the purpose of the closure bucket is to complete
the assembly of a row of tangential entry buckets on the rotor
wheel, and, thus, it is the last bucket mounted on the wheel. Since
the closure bucket cannot be attached directly to the rotor wheel
dovetail like the remaining buckets, there is no need for the
dovetail hooks found on all of the other buckets in the row.
[0004] Centrifugal stresses in the bucket/wheel dovetail are
greatest near the closure bucket, and therefore, it is desirable to
minimize the weight of the closure bucket. Current steam turbine
closure buckets are designed such that the unnecessary interior
hook elements are substantially removed, but material is added for
strength. On the other hand, the overall weight is reduced by: 1)
externally, removing material from the sides of the dovetail hooks;
2) removing material from the closure bucket sealing platform; and
3) removing material by forming cutouts on the front and back faces
of the dovetail hooks. Material removal from these areas, however,
increases performance losses. Specifically, this approach results
in a discontinuity in the otherwise circumferentially continuous
external dovetail hook surfaces when the entire row of buckets is
assembled on the rotor wheel. This surface discontinuity
contributes to performance losses first by windage heating of the
steam flowing near the bucket dovetail, and second by allowing
increased leakage flow through the stationary seal.
BRIEF SUMMARY OF THE INVENTION
[0005] This invention provides a steam turbine closure bucket that
maintains the external shape of the neighboring buckets, thereby
minimizing windage losses, while maintaining sealing surfaces on
the bucket dovetail. In accordance with an exemplary embodiment of
the invention, the weight of the closure bucket is reduced by
removing pockets of material internally, from the front and back
faces of the dovetail hooks. This removal of material creates
internal cavities that do not alter the external shape of the
bucket. The cavity geometry has been designed to remove the maximum
amount of material while maintaining sufficient strength for
assembly and operation.
[0006] In its broader aspects, therefore, the invention provides a
turbine closure bucket adapted to complete assembly of a row of
tangential entry buckets on a rotor wheel comprising an airfoil
portion and a mounting portion for mounting the bucket to a turbine
wheel, the mounting portion having front and back faces, and
wherein weight reduction cavities are formed internally in the
front and back faces of the mounting portion, but wherein the front
and back faces of the closure bucket are substantially identical to
front and back faces of adjacent buckets in the row.
[0007] In another aspect, the invention relates to a turbine
closure bucket adapted to complete assembly of a row of tangential
entry buckets on a rotor wheel comprising a blade portion and a
dovetail portion for mounting the bucket to a turbine wheel, the
dovetail portion having front and back faces and a sealing
platform, and wherein weight reduction cavities are formed
internally in the front and back faces of the dovetail portion, but
wherein the front and back faces of the closure bucket are
substantially identical to front and back faces of adjacent buckets
in the row.
[0008] In still another aspect, the invention relates to a turbine
rotor wheel having a dovetail formed about its periphery, with an
axial opening therein, the rotor wheel having a plurality of
turbine buckets received on the dovetail, each bucket having front
and back faces; and a closure bucket that is received in the
opening, the closure bucket having external front and back faces
substantially identical to corresponding front and back faces of
the plurality of buckets.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a partial elevation, partly sectioned, of a
conventional turbine rotor, illustrating a bucket mounted on a
rotor wheel and an adjacent diaphragm;
[0010] FIG. 2 is a partial elevation of a conventional closure
bucket;
[0011] FIG. 3 is an end view of the closure bucket shown in FIG.
2;
[0012] FIG. 4 is a partial elevation of a closure bucket dovetail
hook region in accordance with this invention;
[0013] FIG. 5 is a section taken along the line 5-5 of FIG. 4;
and
[0014] FIG. 6 is a perspective view of the dovetail hook region of
the closure bucket in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Referring now to FIGS. 1-3, particularly to FIG. 1, a
portion of a rotor 10 is shown, including a rotor wheel 12 provided
with a male dovetail 14 that extends circumferentially about
substantially the entirety of the periphery of the wheel, save a
single axial opening or break in the dovetail that permits assembly
of the plurality of buckets, one of which is shown at 16.
[0016] Each bucket includes a blade or airfoil portion 18 and a
pair of mating dovetail hooks 20, 22 including internal pairs of
hook elements 24, 26, 28 that enable the bucket 16 to be assembled
onto the wheel 12 at the single opening about the circumference of
the dovetail 14.
[0017] Outside surfaces of the dovetail hooks 20, 22 have front and
rear faces 30, 32 that are upstream and downstream, respectively,
in the direction of flow. A fixed diaphragm 34, including a row of
fixed vanes 36, is located immediately adjacent the row of buckets
16, with conventional platform and labyrinth seals 38, 40,
respectively, between the rotor and the diaphragm. During assembly,
the buckets 16 are inserted, axially, into the circumferential
opening in the dovetail 14, and then slid along and around the
dovetail 14, this assembly procedure being followed for all of the
buckets 16, until the only space remaining is that at the opening,
where the closure bucket is inserted.
[0018] FIGS. 2 and 3 illustrate a conventional closure bucket,
evidencing the prior methodology for reducing the weight of the
closure bucket. Note initially that internal hook elements have
been removed but material added, for example, in areas 42, 44 for
strength. Weight reduction is achieved, however, by removal of
material in three areas. First, material has been removed
externally from the front and rear faces 46, 48. Second, notches or
cut-outs 50, 52 have been formed in the sides of the dovetail hook
region as best seen in FIG. 3. Third, the seal platform 54 has been
axially shortened as compared to platform 29 in FIG. 1.
[0019] Turning now to FIGS. 4-6, the present invention provides a
closure bucket 56 that includes an airfoil portion 58 and a
mounting portion 60, and with no internal dovetail hook elements.
At the same time, however, the external shape of the closure bucket
is substantially identical to the adjacent buckets in the row. In
other words, the front and back faces 62, 64, and the sealing
platform 66 are substantially identical to the front and rear faces
30, 32 and sealing platform shown in the typical tangential entry
bucket 16 shown in FIG. 1. This uniformity of the external surfaces
provides uniform flow of steam near the bucket dovetail without the
windage loss experienced with prior designs. Here, material is
removed internally, behind the front and back faces 62, 64. The
material removed from behind one face forms cavities 68, 70 that
lie on either side of a radially oriented rib 72, and similar
cavities (one shown at 74) on either side of an opposed radial rib
76 from the opposite face. This arrangement removes the maximum
amount of material while maintaining sufficient strength to drive
the closure bucket at assembly and during operation.
[0020] This new configuration also reduces the size of the leakage
path for flow through the stationary seal at the closure bucket, by
retaining the full sealing platform 66.
[0021] This approach can be employed with many dovetail
configurations, and it will be appreciated that the cavity geometry
may be changed for each application, depending upon such variables
as internal and external dovetail shapes, the number of buckets in
a row, etc. It has also been determined that the weight reduction
technique in accordance with this invention produces closure
buckets that weigh within 5% of the existing closure buckets.
[0022] 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.
* * * * *