Fluid reaction surfaces (i.e. – impellers) – Rotor having flow confining or deflecting web – shroud or... – Axially extending shroud ring or casing
Reexamination Certificate
2002-12-19
2004-09-07
Nguyen, Ninh H. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Rotor having flow confining or deflecting web, shroud or...
Axially extending shroud ring or casing
C416S19300A
Reexamination Certificate
active
06786698
ABSTRACT:
The present invention relates to steam turbine buckets, and in particular, to an improved steam turbine bucket flowpath design that eliminates flowpath steps between adjacent buckets.
BACKGROUND OF THE INVENTION
In a steam turbine (not shown), the turbine buckets are typically installed adjacent to one another circumferentially around a turbine wheel (also not shown).
FIG. 1
a
shows a stage
10
that includes a plurality of prior art buckets
12
as they would be mounted adjacent to one another around a portion of a turbine wheel. Each bucket
12
includes a dovetail
14
for mounting the buckets around the turbine wheel. To the outside of each dovetail
14
is a parallelogram-shaped platform
16
from which protrudes an airfoil
18
. Each airfoil
18
includes a pressure side
20
that is partially concave in shape and a suction side
22
that is convex in shape. To the outside of each airfoil
18
is a parallelogram-shaped shroud
24
.
Each bucket
12
's platform
16
includes a flat inner flowpath surface
26
at which one end
28
of the corresponding airfoil
18
intersects with platform
16
. Similarly, each bucket
12
's shroud
24
includes a second flat outer flowpath surface
30
(
FIG. 1
c
) at which the other end
32
of the corresponding airfoil
18
intersects with shroud
24
.
Adjacent buckets, such as buckets
12
a
and
12
b
shown in
FIG. 1
b
, form an inner flowpath
34
, which is established by adjacent inner flowpath surfaces
26
a
and
26
b
of adjacent platforms
16
a
and
16
b
, by way of example. Adjacent buckets also form an outer flowpath
36
, which is established by adjacent outer flowpath surfaces
30
a
and
30
b
of adjacent shrouds
24
a
and
24
b
of buckets
12
a
and
12
b
, again by way of example.
When buckets
12
are installed circumferentially around a turbine wheel, their airfoils
18
are each skewed with respect to the centerline (not shown) of the turbine. As they follow the circumference of the turbine wheel, airfoils
18
are staggered with respect to the centerline of the turbine. Each bucket
12
's platform
16
is then angled with respect to the centerline of the turbine to follow the stagger angle of the airfoils
18
around the turbine wheel. As such, as shown in
FIG. 1
b
, flowpath steps
38
in flowpath
34
are created between the platforms
16
of adjacent buckets, such as platforms
16
a
and
16
b
of buckets
12
a
and
12
b
, shown by way of example in
FIG. 1
b.
Similarly, each bucket
12
's shroud
24
is angled with respect to the centerline of the turbine to, again, follow the stagger angle of the airfoils
18
around the turbine wheel. Here again, as shown in
FIG. 1
c
, flowpath steps
40
are created in an outer flowpath
36
between the shrouds
24
of adjacent buckets, such as shrouds
24
a
and
24
b
of buckets
12
a
and
12
b
, again by way of example.
FIGS. 1
b
and
1
c
depict typical distinct steps in the flowpaths of prior art steam turbine buckets. These circumferential steps in a turbine's flowpath reduce the aerodynamic performance of the turbine. Advantageously, however, these prior art buckets can be manufactured using 3-axis milling machines that are not too expensive to buy or operate. In addition, manufacturing shops typically have 3-axis machines.
It should be noted that steam turbine buckets without flowpath steps can be made. Such buckets have inner and outer flowpath surfaces that are “surfaces of revolution” about the centerline of the turbine. However, these buckets can be made only with 5-axis milling machines that are much more expensive to buy and operate than 3-axis machines. Thus, it would be very desirable for a manufacturer of steam turbines to have the ability to make buckets with 3-axis milling machines and that do not form flowpath steps when mounted together around a turbine wheel.
BRIEF DESCRIPTION OF THE INVENTION
In an exemplary embodiment of the invention, a turbine bucket comprises a platform, a shroud, and an airfoil connected between the platform and the shroud, the platform including an inner flowpath surface at which the airfoil is connected to the platform, the inner flowpath surface being formed from a first inclined plane and a second inclined plane that meet at a first common boundary and form a first ridge or valley, the shroud including an outer flowpath surface at which the airfoil is connected to the shroud, the outer flowpath surface being formed from a third inclined plane and a inclined plane that meet at a second common boundary and form a second ridge or valley.
In another exemplary embodiment of the invention, a turbine bucket comprises a dovetail for mounting the bucket within the turbine, a platform connected to the dovetail, a shroud, and an airfoil connected between the platform and the shroud, the platform including an inner flowpath surface at which the airfoil is connected to the platform, the inner flowpath surface being formed from a first inclined plane and a second inclined plane that meet at a first common boundary and form a first ridge or valley, the shroud including an outer flowpath surface at which the airfoil is connected to the shroud, the outer flowpath surface being formed from a third inclined plane and a inclined plane that meet at a second common boundary and form a second ridge or valley, an inner flowpath being formed without steps by inner flowpath surface when it is positioned adjacent to a second inner flowpath surface of a second platform of a second bucket positioned adjacent to the bucket, and an outer flowpath being formed without steps by outer flowpath surface when it is positioned adjacent to a second outer flowpath surface adjacent of a second shroud of the second bucket positioned adjacent to the bucket.
In yet another exemplary embodiment of the invention, a turbine bucket comprises a dovetail for mounting the bucket within the turbine, a parallelogram-shaped platform connected to the dovetail, a parallelogram-shaped shroud, and an airfoil connected at a first end to the platform and at a second end to the shroud, the platform including an inner flowpath surface at which the first end of the airfoil intersects the platform, the inner flowpath surface being parallelogram-shaped and formed from a first triangular-shaped inclined plane and a second triangular-shaped inclined plane that meet at a first common boundary and form a first ridge or valley, the first common boundary bisecting the inner flowpath surface, the shroud including an outer flowpath surface at which the second end of the airfoil intersects the shroud, the outer flowpath surface being parallelogram-shaped and formed from a third triangular-shaped inclined plane and a fourth triangular-shaped inclined plane that meet at a second common boundary and form a second ridge or valley, the second common boundary bisecting the outer flowpath surface.
In a further exemplary embodiment of the invention, a stage of turbine buckets includes at least two buckets, each bucket comprises a dovetail for mounting the bucket within the turbine, a parallelogram-shaped platform connected to the dovetail, a parallelogram-shaped shroud, and an airfoil connected at a first end to the platform and at a second end to the shroud, the platform including an inner flowpath surface at which the first end of the airfoil intersects the platform, the inner flowpath surface being parallelogram-shaped and formed from a first triangular-shaped inclined plane and a second triangular-shaped inclined plane that meet at a first common boundary and form a first ridge or valley, the first common boundary bisecting the inner flowpath surface, the shroud including an outer flowpath surface at which the second end of the airfoil intersects the shroud, the outer flowpath surface being parallelogram-shaped and formed from a third triangular-shaped inclined plane and a fourth triangular-shaped inclined plane that meet at a second common boundary and form a second ridge or valley, the second common boundary bisecting the outer flowpath surface, an inner flowpath bein
Couture, Jr. Bernard Arthur
Korzun Ronald Wayne
Lavash John Cleland
Warner Craig M.
General Electric Company
Nguyen Ninh H.
Nixon & Vanderhye P.C.
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