Note: Descriptions are shown in the official language in which they were submitted.
CA 02674175 2011-11-07
TURBINE ROTOR BLADE AND FIXATION STRUCTURE THEREOF
Field of the Invention
The present invention relates to a turbine rotor blade
for a turbine such as a steam turbine or a gas turbine. The
present invention also relates to a fixation structure of such
a turbine rotor blade.
Background
A blade base portion (blade implant portion) of a
turbine rotor blade for a steam turbine, gas turbine, or the
like is variously shaped. The turbine rotor blade is engaged
with a blade groove to be mounted on a turbine rotor, the
blade groove being complementarily shaped relative to the
blade base portion.
At a high- or intermediate-pressure stage in which the
turbine rotor blade is exposed to high-temperature steam or
gas, high centrifugal force is applied to the turbine rotor
blade for a long period of time in a high-temperature
atmosphere. Therefore, the blade base portion may suffer
creep damage. In view of such circumstances, a technology
concerning a steam turbine rotor blade is developed to bore a
platform through-hole from the bottom of the blade by an
electric spark forming method or the like for the purpose of
decreasing the weight of the blade and reducing the stress
caused by centrifugal force (refer, for instance, to JP-2005-
195021-A).
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However, as the electric spark forming method or the
like is selected for the above-described turbine rotor blade,
the forming of the turbine rotor blade takes a considerable
amount of time. Further, steam-induced oscillatory load is
imposed on the steam turbine rotor blade. Therefore, if there
is a hole in a platform, bending load on the blade may impose
increased stress on the platform.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a
turbine rotor blade that is highly manufacturable and capable
of reducing the stress caused by centrifugal force.
Certain exemplary embodiments can provide a turbine
rotor blade comprising: a vane portion having a blade leading
edge positioned upstream in the distribution direction of
working fluid and a blade trailing edge positioned downstream
of the blade leading edge; and a blade base portion which is
extended unidirectionally on a base side of the vane portion
and engaged with a blade groove formed in the outer
circumference of a turbine rotor; wherein an end of the blade
base portion at the side of the blade leading edge is
positioned to be different in the circumferential direction of
a turbine rotor from an end of the blade base portion at the
side of the blade trailing edge; wherein the position of the
blade leading edge in the circumferential direction of the
turbine rotor is displaced in the rotational direction of the
turbine rotor with respect to that of the blade trailing edge
in the circumferential direction of the turbine rotor; wherein
the position of the end of the blade base portion at the side
of the blade leading edge in the circumferential direction of
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= the turbine rotor is displaced in the rotational direction of
the turbine rotor with respect to that of the end of the blade
base portion at the side of the blade trailing edge in the
circumferential direction of the turbine rotor; and wherein
the blade base portion is provided along the direction of a
line joining the blade leading edge to the blade trailing
edge, and is a plurality of dovetails which are projected on
the inward side of the turbine rotor, wherein the projection
directions of the plurality of dovetails are parallel to each
other.
Certain exemplary embodiments can provide a turbine
rotor blade comprising: a vane portion having a blade leading
edge positioned upstream in the distribution direction of
working fluid and a blade trailing edge positioned downstream
of the blade leading edge; and a blade base portion which is
extended unidirectionally on a base side of the vane portion
and engaged with a blade groove formed in the outer
circumference of a turbine rotor; wherein the blade base
portion is a plurality of dovetails which are projected on the
inward side of the turbine rotor, with the plurality of
dovetails being projected in the direction parallel to each
other.
Certain exemplary embodiments can provide a turbine rotor
blade fixation structure comprising: a turbine rotor blade
having: a vane portion having a blade leading edge positioned
upstream in the distribution direction of working fluid and a
blade trailing edge positioned downstream of the blade leading
edge, and a blade base portion which is extended
unidirectionally on a base side of the vane portion and
projected on the inward side of the turbine rotor; and a blade
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groove that is engaged with the blade base portion and
provided in the outer circumference of a turbine rotor;
wherein the position of the end of the blade base portion at
the side of the blade leading edge in the circumferential
direction of the turbine rotor is displaced in the rotational
direction of the turbine rotor with respect to that of the end
of the blade base portion at the side of the blade trailing
edge in the circumferential direction of the turbine rotor,
and wherein the blade base portion is extended in a direction
inclined from the rotation axis of the turbine rotor, and is
and is a plurality of dovetails which are projected on the
inward side of the turbine rotor, wherein the projection
directions of the plurality of dovetails are parallel to each
other.
Various described embodiments enable the blade groove
to efficiently support the centrifugal load on the turbine
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rotor blade through the blade base portion, thereby making
it possible to reduce the stress on the blade groove with
ease.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view taken in an axial direction of
a turbine rotor to illustrate a turbine rotor blade
according to an embodiment of the present invention.
FIG. 2 is a perspective view of the turbine rotor
blade according to an embodiment of the present invention.
FIG. 3 is a view that is taken in the direction of
arrow B in FIG. 1 to illustrate the turbine rotor blade
according to an embodiment of the present invention.
FIG. 4 is a view that is taken in the same direction
as in FIG. 3 to present a comparative example of the turbine
rotor blade according to an embodiment of the present
invention.
FIGS. 5A and 5B are schematic diagrams illustrating
blade base portions of the turbine rotor blade according to
an embodiment of the present invention and of a conventional
turbine rotor blade.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will now be
described with reference to the accompanying drawings.
FIG. 1 is a front view taken in an axial direction of
a turbine rotor to illustrate a turbine rotor blade
according to an embodiment of the present invention. FIG. 2
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is a perspective view of the turbine rotor blade. A radial
direction of a turbine rotor, a circumferential direction of
a turbine rotor, and an axial direction of a turbine rotor
are defined as indicated in these figures.
Turbine rotor blades 40a and 40b shown in FIGS. 1 and
2 are used with a steam turbine. The turbine rotor blades
40a and 40b each include: a vane portion 3; a shroud 1 which
is provided on the leading end of the vane portion 3 (the
outer end portion in the radial direction of the turbine
rotor); a seal (fin seal) la which is provided on the outer
circumference of the shroud 1; blade base portion 5 (5a, 5b,
and 5c, 5d) which engages with blade groove 6 (6a, 6b, and
6c, 6d) provided on the outer circumference of a turbine
rotor 8; and a platform 4 which is provided between the vane
portion 3 and the blade base portion 5.
The blade base portion 5 is extended unidirectionally
on a base side of the vane portion 3 (on the inner end of
the vane portion 3 in the radial direction of the turbine
rotor), and inserted into the blade groove 6 along the
extension direction of the blade base portion 5. The
extension direction of the blade base portion 5 will now be
described with reference to FIG. 3.
FIG. 3 is a view taken in the direction of arrow B in
FIG. 1. Like elements in FIGS. 1 to 3 are designated by the
same reference numerals and will not be redundantly
described (the same is also true for the subsequent
drawings).
Referring to FIG. 3, the vane portion 3 includes a
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_
blade leading edge 21 which is positioned upstream in the
distribution direction of working fluid, and a blade trailing
edge 22 which is positioned downstream of the blade leading
edge 21. When the working fluid flows in a direction
indicated by arrow C in the figure (an axial direction of a
turbine rotor) and toward the turbine rotor blade 40a, the
turbine rotor 8 rotates upward in FIG. 3.
At a blade base portion 5a (5b) shown in FIG. 3, an end
(leading edge side end) 51a (51b) of the blade base portion 5a
(5h) at the side of the blade leading edge 21 is positioned to
be different in the circumferential direction of the turbine
rotor from an end (trailing edge side end) 52a (52b) of the
blade base portion 5a (5b) at the side of the blade trailing
edge 22. In other words, the blade base portions 5a and 5b
are not extended in parallel with the rotation axis of the
turbine rotor 8 (the axial direction C of the turbine rotor),
but extended in a direction that is inclined at an angle of D
(see FIG. 3) from the axial direction C of the turbine rotor.
Further, the blade grooves 6a and 6b are provided in the outer
circumference of the turbine rotor 8 and arranged in a
direction (an axial direction of a groove) that is inclined at
an angle of D from the axial direction of the turbine rotor,
as is the case with the blade base portions 5a and 5b. When
the blade base portion 5 and blade groove 6 are positioned as
described above, they are longer than those when they are
positioned in parallel with the axial direction C of the
turbine rotor. Therefore, the contact area between the blade
base portion 5 and blade groove 6 can be increased.
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Meanwhile, the vane portion 3 according to the present
embodiment is configured so that the position of the blade
trailing edge 22 in the circumferential direction of the
turbine rotor is displaced in the rotational direction of the
turbine rotor with respect to that of the blade leading edge
21 in the circumferential direction of the turbine rotor, and
the degree of reaction of the vane portion 3 is several tens
of percent. When the vane portion 3 has such a high degree of
reaction, the blade base portion 5 should preferably be
configured in accordance with the shape of the vane portion 3
so that the position of the leading edge side end portion 51
(51a, 51b) in the circumferential direction of the turbine
rotor is displaced in the rotational direction of the turbine
rotor (upward in FIG. 3) with respect to that of the trailing
edge side end portion 52 (52a, 52b) in the circumferential
direction of the turbine rotor. The reason is that when the
blade base portion 5 is configured as described above, the
overlap between the vane portion 3 and the blade base portion
can be increased. This makes it possible to effectively
support the vane portion 3 even when centrifugal force is
applied to a turbine rotor blade 40a, 40b during an operation.
It is also preferred that the blade base portion 5 be provided
along the direction G of the blade chord length, that is, the
direction of a line joining the blade leading edge 21 to
the blade trailing edge 22, as shown in FIG. 3. In other
words, the blade base portion 5 should preferably be
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configured so that the angle D formed between the blade base
portion 5 and the axial direction C of the turbine rotor is
equal to the angle formed between the direction G of the
blade chord length and the axial direction C of the turbine
rotor. The reason is that such a configuration makes it
possible to further increase the overlap and efficiently
position the blade base portion 5 relative to the vane
portion 3.
Referring again to FIGS. 1 and 2, the turbine rotor
blade 40a of this embodiment includes the two blade base
portions 5a and 5b. The two blade base portions 5a and 5b
are dovetail-shaped type, and are molded integral with the
vane portion 3, the platform 4, and the shroud 1. When the
number of blade base portions 5 is larger than that of vane
portions 3 for one turbine rotor blade 40a, 40b as described
above, it is possible to reduce the stress that arises due
to steam force acting on the turbine rotor blades 40a, 40b
during a steam turbine operation.
The blade base portions 5a, 5b are projected inward
in the radial direction of the turbine rotor from the
platform 4. The directions of their projections are
parallel to each other. In other words, the centerline 41a
(41c) of the blade base portion 5a (Sc) is parallel to the
centerline 41b (41d) of the blade base portion 5b (5d).
Further, a blade hook portion 7 is projected toward each
side in the circumferential direction of the turbine rotor
from the leading ends of the blade base portion 5. The
blade hook portion 7 is engaged with a groove hook portion
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13 which is projected in the circumferential direction of
the turbine rotor from the blade groove 6. Such an
engagement structure fastens the turbine rotor blades 40a
and 40b to the turbine rotor 8.
A contact area between the blade hook portion 7 and
groove hook portion 13 is provided with a pinhole 9a which
is extended in the axial direction of the turbine rotor
through the blade hook portion 7 and groove hook portion 13.
A fixing pin 9b is inserted in the axial direction of the
turbine rotor into the pinhole 9a. The fixing pin 9b is
inserted into the pinhole 9a after the blade base portion 5
is implanted in the blade groove 6 to accurately fasten the
turbine rotor blades 40a and 40b in the circumferential
direction of the turbine rotor and in the radial direction
of the turbine rotor. When the turbine rotor blades 40a and
40b are fastened with the fixing pin 9b as described above,
they are fastened more securely than when they are fastened
merely by an engagement method. This makes it possible to
reduce the stress applied to the blade base portion 5 and
blade groove 6.
Operations and advantages of the present embodiment
will now be described with reference to a comparative
example.
FIG. 4 is a view that is taken in the same direction
as in FIG. 3 to present a comparative example of the turbine
rotor blade according to the present embodiment.
The turbine rotor blade 90 shown in FIG. 4 includes
blade base portions 91a and 91b which are extended in the
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,
same direction as the axial direction C of the turbine rotor.
Further, the turbine rotor has blade grooves 92a and 92b
which are provided in the same direction as the blade base
portions 91a and 91b. When the turbine rotor blade 90 is
formed as described above, the lengths of the blade base
portions 91a and 91b are decreased to reduce the area that
supports the load on the turbine rotor blade 90. Therefore,
when the turbine rotor blade 90 described above is used,
increased stress is imposed on the blade base portions 91a,
91b and blade grooves 92a, 92b.
Particularly when the employed turbine rotor blade 90
includes a vane portion 93 having a high degree of reaction,
its platform 94 may not stay quadrilateral, as shown in FIG.
4, while providing adequate clearance to an adjacent turbine
rotor blade. Therefore, the blade base portion 91b has to
terminate at a point (91e) before the end of the platform 94
on the side of the blade trailing edge 22. As a result, the
blade base portion 91b is shorter than the platform 94.
Decreasing the length of the blade base portion 91b in this
manner not only increases the stress imposed on the blade
base portion 91b but also produces a gap 92e in the blade
groove 92b. This further increases the imposed stress.
On the other hand, the turbine rotor blade according
to the present embodiment includes the blade base portion 5
which is formed so that the position of the leading edge
side end portion 51 is different from that of the trailing
edge side end portion 52 in the circumferential direction.
When the blade base portion 5 is formed as described above,
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the portion can be made longer than when it is formed in
parallel with the axial direction C of the turbine rotor.
Therefore, the contact area between the blade groove 6 and
blade base portion 5 can be increased. As this increases an
area that supports the load on the turbine rotor blade
portion 40, the stress imposed on the blade base portion 5 and
blade groove 6 decreases, making it easy to enhance the
structural reliability of the blade base portion 5 and blade
groove 6.
Further, when the vane portion 3 is configured as
described in connection with the present embodiment so
that the position of the blade leading edge 21 in the
circumferential direction of the turbine rotor is displaced
in the rotational direction of the turbine rotor with
respect to that of the blade trailing edge 22 in the
circumferential direction of the turbine rotor, the blade
base portion 5 should preferably be configured in accordance
with the shape of the vane portion 3 so that the position
of the leading edge side end portion 51 in the circumferential
direction of the turbine rotor is displaced in the rotational
direction of the turbine rotor with respect to that of
the trailing edge side end portion 52 in the circumferential
direction of the turbine rotor. Configuring the blade base
portion 5 as described above makes it possible to increase
the overlap between the vane portion 3 and blade base
portion 5. Consequently, the centrifugal force applied
to the turbine rotor blade portion 40 can be effectively
shared by the blade base portion 5 and blade
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groove 6. As a result, the structural reliability of the
blade base portion 5 and blade groove 6 can be further
enhanced.
Furthermore, the blade base portion 5 should
preferably be configured so that the angle D formed between
the blade base portion 5 and the axial direction C of the
turbine rotor is equal to the angle formed between the
direction G of the blade chord length and the axial
direction C of the turbine rotor. Configuring the blade
base portion 5 as described above makes it possible to not
only further increase the overlap between the vane portion 3
and blade base portion 5, but also dispose the blade base
portion 5 efficiently in relation to the vane portion 3.
Consequently, the structural reliability can be further
enhanced. The present invention produces a striking effect
particularly when the vane portion has a high degree of
reaction (e.g., several tens of percent) and its blade chord
length direction G is oblique to the axial direction of the
turbine rotor.
The present embodiment has been described on the
assumption that the blade base portion 5 is dovetail-shaped.
However, the present invention can be applied to a turbine
rotor blade as far as an engagement structure is employed to
couple the blade base portion to the blade groove. A
typical turbine rotor blade of this type includes blade base
portion that is shaped like an inverted Christmas tree.
More specifically, the width of this blade base portion
increases outward in the radial direction of the turbine
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rotor with a plurality of convexes projected toward both
sides in the width direction. When the inverted-Christmas-
tree-shaped blade base portion is extended in the above-
described direction, the area of contact with the blade
groove can be unprecedentedly large as implied earlier.
This makes it possible to reduce the stress resulting from
centrifugal load.
Meanwhile, the blade base portion 5 according to the
present embodiment has the following features which
contribute toward stress reduction. Such stress reduction
features will be described below with reference to FIGS. 5A
and 5B.
FIGS. 5A and 5B schematically illustrate the blade
base portions of the turbine rotor blade according to the
present embodiment and of a conventional turbine rotor blade.
FIG. 5A is a schematic diagram illustrating the blade base
portion 5 according to the present embodiment and their
vicinity. FIG. 5B is a schematic diagram illustrating the
blade base portion of a conventional turbine rotor blade and
their vicinity.
Referring to FIG. 5A, the centerline 41a of the
dovetail 5a is parallel to the centerline 41b of the
dovetail 5b. Further, the distance E between the dovetail
5a and dovetail 5b is maintained constant. On the other
hand, the dovetails 50a and 50b of the conventional example
are disposed so that their centerlines 42a and 42b
respectively radiate from the center 43 of the turbine rotor
8. In other words, the distance between the dovetail 50a
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and dovetail 50b decreases with closing to the center 43,
and equals F (F < E) at their leading ends.
Meanwhile, the stress imposed on the dovetails and
blade grooves in the area between the dovetails generally
increases with a decrease in the distance between the
dovetails. According to the present embodiment, the
distance E between the dovetails can be longer than the
conventional distance F. Therefore, the stress imposed on
the dovetails 5a, 5b and blade groove 6 can be reduced.
This makes it possible to further reduce the stress in
addition to the stress reduction effect based on the
direction in which the blade base portion 5 is extended.
The present invention has been described with
reference to the turbine rotor blade having the vane portion
3 which is configured so that the positions of the blade
leading edge 21 and blade trailing edge 22 in the
circumferential direction are different from each other.
However, the stress resulting from centrifugal load can also
be reduced even when the present invention is applied to a
turbine rotor blade having a vane portion which is
configured so that the positions of the blade leading edge
and blade trailing edge in the circumferential direction are
equal to each other. In addition, while the present
invention has been described with reference to a case where
the present invention is applied to a steam turbine, the
present invention is also applicable to a gas turbine.
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