U.S. patent application number 09/733293 was filed with the patent office on 2002-06-13 for turbine bucket cover and brush seal.
This patent application is currently assigned to General Electric Company. Invention is credited to Turnquist, Norman Arnold, Willey, Lawrence D., Wolfe, Christopher Edward.
Application Number | 20020071764 09/733293 |
Document ID | / |
Family ID | 24947016 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020071764 |
Kind Code |
A1 |
Turnquist, Norman Arnold ;
et al. |
June 13, 2002 |
Turbine bucket cover and brush seal
Abstract
The adjoining edges of bucket covers are sealed one to the
other. A brush seal projecting from a stationary shroud overlies
the bucket covers. A joint at which the adjacent covers sealingly
engage each other precludes radial outflow of high pressure fluid
into bristles of the brush seal, preventing radial and axial
deflection of the bristles and consequent failure of the bristles.
The joints between the covers may comprise lap or tongue-and-groove
joints.
Inventors: |
Turnquist, Norman Arnold;
(Sloansville, NY) ; Willey, Lawrence D.; (Burnt
Hills, NY) ; Wolfe, Christopher Edward; (Schenectady,
NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
CRD PATENT DOCKET ROOM 4A59
P O BOX 8
BUILDING K 1 SALAMONE
SCHENECTADY
NY
12301
US
|
Assignee: |
General Electric Company
|
Family ID: |
24947016 |
Appl. No.: |
09/733293 |
Filed: |
December 11, 2000 |
Current U.S.
Class: |
415/173.3 ;
277/355; 415/173.5; 415/173.6; 416/191 |
Current CPC
Class: |
F05D 2240/56 20130101;
F16J 15/3288 20130101; F01D 5/225 20130101; F16J 15/442
20130101 |
Class at
Publication: |
415/173.3 ;
277/355; 415/173.5; 415/173.6; 416/191 |
International
Class: |
F01D 011/12 |
Claims
What is claimed is:
1. In a turbine having a plurality of rotatable buckets, a
stationary shroud surrounding the rotatable buckets, and a fluid
medium flow path through the turbine, a seal between said buckets
and said stationary shroud, comprising: a plurality of arcuate
covers carried by radial outer ends of said buckets for rotation
with said buckets about an axis of the turbine in a predetermined
circumferential direction, said covers having leading edges and
trailing edges in the direction of rotation of the buckets; a brush
seal projecting from the shroud and comprising a plurality of
bristles for sealingly engaging radially outer surfaces of said
covers; and a joint between circumferentially adjacent covers
wherein adjoining leading and trailing edges sealingly engage one
another substantially to preclude radial outflow of the fluid
medium onto said bristles as the buckets and covers rotate relative
to the brush seal.
2. A seal according to claim 1 wherein said joint comprises a lap
joint.
3. A seal according to claim 1 wherein said joint comprises a
tongue-and-groove joint.
4. A seal according to claim 1 wherein each of said buckets
includes a discrete cover, said bucket and said cover being
integrally cast.
5. A seal according to claim 4 wherein said joint comprise a lap
joint.
6. A seal according to claim 4 wherein said joint comprise a
tongue-and-groove joint.
7. A seal according to claim 1 wherein said covers form a discrete
band extending in a circumferential direction, said band being
connected to at least two adjacent buckets.
8. A seal according to claim 7 wherein said joint comprises a lap
joint.
9. A seal according to claim 7 wherein said joint comprises a
tongue-and-groove joint.
10. A seal according to claim 1 wherein said adjoining edges have
linear, generally axially extending, end margins axially and
circumferentially spaced from one another and angled margins
intermediate said end margins and interconnecting said end margins,
said brush seal bristles engaging said cover surfaces at an axial
location corresponding to axial locations of said intermediate
angled margins.
11. A seal according to claim 1 wherein said joint includes an
outer cover overlying said covers and spanning between said
adjacent covers, said outer cover sealing any gap between said
adjacent covers.
12. In a turbine having a plurality of rotatable buckets, a
stationary shroud surrounding the rotatable buckets, and a fluid
medium flow path through the turbine, a seal between said buckets
and said stationary shroud, comprising: a plurality of arcuate
covers carried by radial outer ends of said buckets for rotation
with said buckets about an axis of the turbine in a predetermined
circumferential direction, said covers having adjoining edges; a
brush seal projecting from the shroud and comprising a plurality of
bristles for sealingly engaging radially outer surfaces of said
covers; a joint between circumferentially adjacent covers wherein
at least portions of said adjoining edges overlap one another to
substantially seal said adjacent covers to one another at axial
locations corresponding to axial locations of said cover surfaces
engaged by said bristles to substantially preclude radial outflow
of the fluid medium past the overlapping portions of said adjoining
edges.
13. A seal according to claim 12 wherein said joint comprises a lap
joint.
14. A seal according to claim 12 wherein said joint comprises a
tongue-and-groove joint.
15. A seal according to claim 12 wherein each of said buckets
includes a discrete cover, each said bucket and said cover being
integrally cast.
16. A seal according to claim 15 wherein said joint comprises a lap
joint.
17. A seal according to claim 15 wherein said joint comprises a
tongue-and-groove joint.
18. A seal according to claim 12 wherein said covers form a
discrete band extending in a circumferential direction, said band
being connected to at least two adjacent buckets.
19. A seal according to claim 18 wherein said joint comprises a lap
joint.
20. A seal according to claim 18 wherein said joint comprises a
tongue-and-groove joint.
21. A seal according to claim 12 wherein said adjoining edges have
linear, generally axially extending, end margins axially and
circumferentially spaced from one another and angled margins
intermediate said end margins and interconnecting said end margins,
said brush seal bristles engaging said cover surfaces at an axial
location corresponding to axial locations of said intermediate
angled margins.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to covers carried by the tips of
turbine buckets and brush seals surrounding and engaging the bucket
covers, and more particularly relates to seals between the
adjoining edges of bucket covers for minimizing or eliminating
radial outflow of the fluid medium flowing through the turbine onto
the bristles of the surrounding brush seal.
[0002] As set forth in U.S. Pat. No. 6,036,437, of common assignee
herewith, turbine bucket covers and brush seals surrounding the
bucket covers for sealing between upstream and downstream portions
of a turbine stage are known. Turbine bucket covers are typically
provided in either of two forms. A bucket and a discrete bucket
cover are often integrally cast one with the other and applied to
the turbine wheel. Adjoining edges of the adjacent covers typically
form a generally Z-shaped joint as viewed in a radial direction.
Other bucket covers are provided in the form of a cover band which
spans two or more buckets. The bucket cover bands typically have
openings for receiving tenons formed on the tips of the buckets and
which tenons are peened to secure the cover bands to the bucket.
Like the integrally cast buckets and covers, the adjoining edges of
the cover bands engage one another, generally in a Z-shaped joint
when viewed radially.
[0003] As will be appreciated, the pressure of the fluid medium
within the flow path through the turbine, for example, steam
flowing in the steam path of a steam turbine, is at a significantly
higher pressure than the steam pressure radially outwardly of the
covers. This difference in pressure causes radial outflow of the
fluid medium through the gaps between the edges of adjoining
covers. These gaps permit both radial and axial outflow of the
fluid medium and turbine performance is thereby degraded. Labyrinth
seals and/or brush seals are typically employed in the shroud
surrounding the buckets and covers and those seals can limit the
performance losses attributable to axial flow through and around
the gaps. Brush seals also afford an added performance benefit over
the use of labyrinth seals. However, turbine bucket tip brush seals
are affected by radial flow in the region of the bristle pack. The
radial flow into the bristle pack through the radial gaps between
the bucket covers causes bristle fatigue and failure. That is, the
discrete flows of the fluid medium radially outwardly through the
gaps between adjacent bucket covers tend to deflect the bristles in
an outward direction, as well as to splay the bristles in an axial
direction. Thus, for every pass of a gap by a given bristle
location, the bristles are deflected both axially and radially by
the radial flow. Moreover, the bristles attempt to recover before
the next radial outward flow repeats those deflections. These
deflection cycles cause bristle fatigue and failure. It will be
appreciated that for a 60 Hz machine having eighty covers and gaps
in a stage, a 40,000 Hz stimulus is provided to the bristle pack at
the various circumferential locations of the bristles about the
turbine wheel.
BRIEF SUMMARY OF THE INVENTION
[0004] In accordance with a preferred embodiment of the invention,
the gaps between the adjoining edges of the covers are sealed to
the extent that the radial flow leakage is minimized or eliminated.
These portions of the edges of the adjoining covers interlock with
one another such that radial leakage, e.g., steam, from the flow
path is minimized or prevented, with the result that turbine
performance is enhanced. By sealingly engaging the cover portions
to one another along the area of contact between the tips of the
bristles and the outer cover surfaces, the potentially damaging
effect on the seal bristle pack by the radial outflow is
eliminated. Particularly, the adjoining edges of the covers are
overlapped with one another. For example, lap joints are formed
between the adjoining edges. In another form, tongue-and-groove
joints may be provided. In a still further form, additional cover
segments may overlie the covers in staggered circumferential
relation to the underlying covers such that the gaps between
adjoining underlying covers are sealed by the overlying covers.
[0005] In another preferred embodiment, in a turbine having a
plurality of rotatable buckets, a stationary shroud surrounding the
rotatable buckets, and a fluid medium flow path through the
turbine, sealing between the buckets and the stationary shroud is
accomplished by a plurality of arcuate covers carried by radial
outer ends of the buckets for rotation with the buckets about an
axis of the turbine in a predetermined circumferential direction,
the covers having leading and trailing edges in the direction of
rotation of the buckets, a brush seal comprising a plurality of
bristles projecting from the shroud for sealingly engaging outer
surfaces of the covers, and a joint between circumferentially
adjacent covers sealing adjoining leading and trailing edges
thereof to one another, thus substantially precluding radial
outflow of the fluid medium onto the bristles as the buckets and
covers rotate relative to the brush seal.
[0006] In a further preferred embodiment, in a turbine having a
plurality of rotatable buckets, a stationary shroud surrounding the
rotatable buckets, and a fluid medium flow path through the
turbine, sealing between the buckets and the stationary shroud is
accomplished by a plurality of arcuate covers carried by radial
outer ends of the buckets for rotation with the buckets about an
axis of the turbine in a predetermined circumferential direction,
the covers having adjoining edges, a brush seal comprising a
plurality of bristles projecting from the shroud for sealingly
engaging outer surfaces of the covers, and a joint between
circumferentially adjacent covers including at least portions of
the adjoining edges overlapping one another and sealingly engaging
the adjacent covers to one another at axial locations corresponding
to axial locations of the cover surfaces engaged by the bristles,
to substantially preclude radial outflow of the fluid medium past
the overlapping portions onto the bristles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a view partly in cross section and in elevation
taken in a radial plane along the axis of a turbine, illustrating
buckets, bucket covers and bristles forming an improved seal
according to a preferred embodiment of the invention;
[0008] FIG. 2 is a partial schematic view in an axial direction
illustrating buckets, bucket covers and a brush seal segment
according to the prior art;
[0009] FIGS. 3, 4, 5 and 6 are partial schematic views in an axial
direction illustrating various preferred embodiments of the
invention.
[0010] FIG. 7 illustrates a plurality of bucket covers and a brush
seal looking in a radially inward direction down to a plane normal
to the axis of rotation of the turbine bucket; and
[0011] FIG. 8 is a cross-sectional view illustrating the engagement
of the bristles and the bucket cover.
DETAILED DESCRIPTION OF THE INVENTION
[0012] FIG. 1 illustrates a plurality of buckets 10 forming part of
a rotating component of turbomachinery such as a turbine and
secured at their inner ends to turbine wheels 11 rotatable about an
axis 13. The radial outer ends of buckets 10 are provided with
bucket covers 12 which rotate with the buckets. A cover 12 may be
provided on the radial outer end of each bucket or on the outer
ends of two or more buckets in the form of a band so as to allow
adjacent buckets to be coupled to a common cover or band 12. The
joints between adjacent bucket covers or bands 12 are in a
generally Z-shaped configuration as viewed in a radial direction
(see for example FIG. 7).
[0013] As illustrated in FIG. 1, a sealing shroud 14 is fixed to a
stationary component 16 of the turbomachinery in radial opposition
to the buckets in the plane of rotation. Typically, the sealing
shroud includes a plurality of circumferentially spaced sealing
segments forming an annulus about bucket covers 12. The shroud or
shroud segments include axially spaced labyrinth teeth 17 to effect
a seal between the stationary component and the rotatable bucket
covers. In lieu of the labyrinth seal, or in combination with the
labyrinth seal as illustrated, a brush seal 18 is provided. Brush
seal 18, as shown in FIG. 8, may comprise a brush seal bracket 20
housing a plurality of bristles 22 which project from bracket 20
and engage their tips or distal ends against outer surfaces of
bucket covers 12. Bracket 20 may comprise a pair of parallel plates
21 and 23 joined to one another at their proximal ends by a weld 25
that also serves to secure the bristles to bracket 20. Bracket 20
is segmented circumferentially such that a plurality of such
brackets form an annular brush seal about bucket covers 12.
[0014] FIG. 2 illustrates bucket covers 26 of the prior art as
extending circumferentially between two or more buckets 27.
Adjoining edges 28 and 29 of circumferentially extending bucket
covers 26 form a gap 30 that permits flow of a high pressure fluid
medium, e.g., steam in a steam turbine, radially outwardly between
bucket covers 26 for radial impact on bristles 22 of a brush seal
23. The radial outward flow deflects bristles 22 both radially and
axially and at high frequency as gaps 30 between bucket covers 26
rotate past the stationary bristles, tending to degrade turbine
performance and also causing bristle fatigue and failure.
[0015] FIG. 3 illustrates a brush seal 18 having bristles 22 in
engagement with bucket covers 40. Instead of gaps between adjacent
bucket cover segments, the adjoining edges of the adjacent cover
segments form lap joints 41. For example, and as illustrated in
FIG. 3, the trailing edge portion 44 of each leading bucket cover
45 in the direction of rotation indicated by arrow 42 lies radially
outwardly of, and overlaps in sealing engagement with, a radially
inward leading edge portion 46 of the trailing bucket cover 48. The
overlapped edge portions 44 and 46 form a seal between bucket
covers 45 and 48. The lapped joint is provided at each of the
adjoining edges of circumferentially adjacent bucket covers or
cover bands.
[0016] The bucket cover bands or segments have an axial extent
greater than the axial extent of bristles 22 forming the bristle
pack of brush seal 18. Preferably, the tips of bristles 22 engage
the bucket cover outer surfaces at an axial location along a
downstream side of the cover, as distinguished from an upstream
side of the cover. In FIG. 7, the fluid medium flow is indicated by
arrow 50 and the direction of rotation of the bucket covers is
indicated by arrow 51. The brush seal bristles 22 engage the
downstream sides of the bucket covers. Additionally, as illustrated
in FIG. 7, the joint between the adjacent bucket covers such as
covers 45 and 48 is generally Z-shaped in configuration, and thus
the adjoining overlapped edge portions 44 and 46 of covers 45 and
48, respectively, have a similar generally Z-shaped configuration
as illustrated by the parallel solid and dashed Z-shaped lines in
FIG. 7. In this configuration, the brush seal bristles engage the
outer surfaces of covers 40 at an axial location corresponding to
the axial locations of intermediate axially angled margins 52 of
the Z-shaped joint. While the lapped joint may extend for the full
extent of the adjoining edges in an axial direction, it is
important that the bristle tips engage the bucket covers at an
axial location of the lapped joint. The linear extending margins 53
and 55 along upstream and downstream sides respectively of the
adjoining covers 40 need not be lapped, provided the angled margins
52 are lapped to form a seal and the bristle tips engage the outer
surfaces of the covers at the axial location of the seal thus
formed, i.e. the lapped joint, to preclude radial outflow of high
pressure fluid medium into the bristle pack.
[0017] FIG. 4 illustrates lapped joints between adjacent bucket
covers 60 of individual buckets. That is, instead of bucket cover
bands or segments spanning two or more buckets as illustrated in
FIG. 3, a discrete bucket cover 60 is provided for each bucket,
respectively. A lapped joint 64 is illustrated between each
respective pair of adjoining edges 66 and 68.
[0018] As shown in FIG. 5, each one of buckets 70 is provided with
an individual bucket cover 72, respectively. Adjoining edges of
bucket covers 72 are provided with tongue-and-groove connections
74. For example, the leading bucket cover has a generally axially
extending slot 76 for receiving a tongue 78 formed along the
leading edge of a trailing bucket cover. In this manner, the
tongue-and-groove forms an overlapping seal, preventing radial
outflow of the high pressure fluid medium in the axial flow stream
into the bristles of brush seal 18. As in the preceding
embodiments, the bristle pack is located at an axial position
radially overlying the seal between adjoining bucket covers. The
tongue-and-groove overlapping seal may also be used with bucket
cover segments spanning two or more buckets, in the manner
illustrated in FIG. 5 with respect to the discrete covers on
individual buckets.
[0019] FIG. 6 illustrates a plurality of bucket covers or bands 80
spanning in a circumferential direction a plurality of buckets 82.
In this embodiment, however, a second or outer cover 84 overlies
inner covers 80 at circumferentially staggered locations relative
to the inner covers. Thus, as illustrated, outer covers 84 are
provided in discrete lengths as bands or segments. These outer
covers 84 also span circumferential gaps 86 between adjacent inner
covers 80 and hence together with adjacent covers 80 form a sealed
joint 88 therebetween. The overlying covers 84 thus seal gaps 86
and also seal at axial locations corresponding to the axial
location of the engagement of the bristle tips along covers 84. As
a consequence, the bristles engage outer covers 84 along surfaces
which do not have any radial outflow of high pressure fluid medium
that would tend to deflect the bristles and cause fatigue.
[0020] While only certain preferred features of the invention have
been illustrated and described, many modifications and changes will
occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *