Patent Grant
9689268
The present invention relates generally to turbine engines, and more particularly, to an axial entry integrally shrouded turbine bucket closure assembly.
In at least some known turbine engines, such as gas turbines and steam turbines, axial entry buckets, i.e., rotor blades, are coupled to a rotor wheel by sliding the buckets generally parallel to the rotor axis and into mating dovetails formed on the rotor wheel. Some known buckets include radially-inwardly projecting dovetails that mate in dovetails on the rotor wheel. The rotor wheel dovetails are circumferentially spaced apart from each other about the periphery of the rotor wheel.
Some known turbines, however, use integral covers or shrouds along the bucket tips. Generally, the shrouds have overlapping protrusions that nest with the shrouds of adjacent buckets. Some known shrouds may have a Z-shaped configuration when viewed in a radially-inward direction. As the buckets are assembled around the rotor wheel using the axial entry dovetail system, the shrouds of the first and the next to the last assembled buckets may prevent assembly of the final axial entry bucket. The blocking portions of the shrouds cannot be removed because the shrouds are designed to fit tightly together and in contact with each other to maintain a continuous circumferential coupling of the buckets at their tips. As a result, the clearance between the shrouds on the buckets adjacent to the closure bucket location is insufficient to permit axial insertion of the closure bucket.
To facilitate insertion of the final axial entry bucket, at least some known turbines use a dovetail closure insert to secure the closure bucket. However, using a dovetail closure insert increases the cost of such known turbines and may also increase operating stresses induced in the bucket to the rotor wheel assembly. As such, known methods of securing the final or closure bucket with its shroud to the otherwise completed rotor wheel assembly by the axial entry assembly method may be difficult and time-consuming, and may increase operating stresses on the turbine.
In one aspect, a rotor wheel assembly is provided. The rotor wheel assembly includes a rotor wheel having a plurality of dovetail slots spaced circumferentially about a periphery of the rotor wheel. The rotor wheel assembly also has a bucket closure assembly. The bucket closure assembly includes a leading auxiliary bucket coupled to the rotor wheel. The leading auxiliary bucket has a dovetail configured to attach to a respective one of the plurality of dovetail slots. Furthermore, the leading auxiliary bucket has an integral cover including a first back side circumferential edge oriented at a first angle relative to an axis of rotation of the rotor wheel. In addition, the bucket closure assembly includes a closure bucket coupled to the rotor wheel. The closure bucket has a dovetail configured to attach to a respective one of the plurality of dovetail slots and an integral cover with a second back side circumferential edge and a first front side circumferential edge. The first front side circumferential edge is oriented substantially parallel to the first back side edge, and the second back side circumferential edge is oriented at a second angle relative to the axis of rotation. The second angle is inclined in the same direction as the first angle. Furthermore, the bucket closure assembly includes a trailing auxiliary bucket coupled to the rotor wheel. The trailing auxiliary bucket has a dovetail configured to attach to a respective one of the plurality of dovetail slot. The trailing auxiliary bucket also has an integral cover including a second front side circumferential edge oriented substantially parallel to the second back side circumferential edge. The first back side circumferential edge is coupled in mating engagement to the first front side circumferential edge, and the second back side circumferential edge is coupled in mating engagement to the second front side circumferential edge.
In another aspect, a turbine engine is provided. The turbine engine includes a rotatable shaft having an axis of rotation. The turbine engine also includes a casing extending circumferentially about the rotatable shaft. The casing defines at least one passage configured to channel a working fluid along a length of the rotatable shaft. The turbine engine also includes a rotor wheel assembly attached to a portion of the rotatable shaft for rotation therewith. The rotor wheel assembly is configured to expand the working fluid. The rotor wheel assembly includes a rotor wheel having a plurality of dovetail slots spaced circumferentially about a periphery of the rotor wheel. Furthermore, the rotor wheel assembly includes a plurality of buckets arranged in a circumferential array about the axis of rotation. Each of the buckets includes a dovetail configured to attach to a respective one of the plurality of dovetail slots, a platform portion, an airfoil portion, and an integral cover formed integrally with the bucket. The rotor wheel assembly includes a bucket closure assembly configured to close and secure the circumferential array of buckets. The bucket closure assembly has a trailing auxiliary bucket including a dovetail configured to attach to a respective one of the plurality of dovetail slots, a platform portion, an airfoil portion, and an integral cover formed integrally with the trailing auxiliary bucket. The integral cover includes a first circumferential width configured to generate an interference condition with an adjacent integral cover. The integral cover has a first front side circumferential edge and a first back side circumferential edge wherein the first back side circumferential edge is oriented at a first angle relative to the axis of rotation, and the first front side circumferential edge is oriented at a second angle relative to the axis of rotation. Furthermore, the closure bucket assembly includes a closure bucket having a dovetail configured to attach to a respective one of the plurality of dovetail slots, a platform portion comprising a keyway, an airfoil portion, and an integral cover formed integrally with the closure bucket. The integral cover includes a second circumferential width configured to generate an interference condition with an adjacent integral cover. The integral cover also has a second front side circumferential edge and a second back side circumferential edge where the second back side circumferential edge is oriented substantially parallel to the first back side circumferential edge, and the second back side circumferential edge is oriented substantially parallel to the first front side circumferential edge.
As used herein, the terms “axial” and “axially” refer to directions and orientations extending substantially parallel to a longitudinal axis of a turbine engine. Moreover, the terms “radial” and “radially” refer to directions and orientations extending substantially perpendicular to the longitudinal axis of the turbine engine. In addition, as used herein, the terms “circumferential” and “circumferentially” refer to directions and orientations extending arcuately about the longitudinal axis of the turbine engine.
In the exemplary embodiment, steam turbine engine 10 is a single-flow steam turbine engine. Alternatively, steam turbine engine 10 may be any type of steam turbine, such as, without limitation, a low-pressure turbine, an opposed-flow, high-pressure and intermediate-pressure steam turbine combination, a double-flow steam turbine engine, and/or other steam turbine types. Moreover, as discussed above, the present invention is not limited to only being used in steam turbine engines and can be used in other turbine systems, such as gas turbine engines.
In the exemplary embodiment shown in
In the exemplary embodiment, steam turbine engine 10 also includes a stator component 42 coupled to an inner shell 44 of casing 16. The plurality of sealing members 34 are coupled to stator component 42. Casing 16, inner shell 44, and stator component 42 each extend circumferentially about shaft 14 and sealing members 34. In the exemplary embodiment, sealing members 34 form a tortuous sealing path between stator component 42 and shaft 14. Shaft 14 includes a plurality of turbine stages 12 through which high-pressure high-temperature steam 40 is passed via one or more steam channel 46. The turbine stages 12 include a plurality of inlet nozzles 48. Steam turbine engine 10 may include any number of inlet nozzles 48 that enables steam turbine engine 10 to operate as described herein. For example, steam turbine engine 10 may include more or fewer inlet nozzles 48 than shown in
During operation, high pressure and high temperature steam 40 is channeled to turbine stages 12 from a steam source, such as a boiler (not shown), wherein thermal energy is converted to mechanical rotational energy by turbine stages 12. More specifically, steam 40 is channeled through casing 16 from HP steam inlet 20 where it impacts a plurality of turbine blades or buckets, generally indicated at 38, coupled to shaft 14 to induce rotation of shaft 14 about centerline axis 24. Steam 40 exits casing 16 at LP steam outlet 22. Steam 40 may then be channeled to the boiler (not shown) where it may be reheated or channeled to other components of the system, e.g., a condenser (not shown).
Centerline axis 24 is substantially parallel to the Z-axis of the coordinate system as shown in
In the exemplary embodiment, each bucket 38 includes a root portion or dovetail 60, a platform 62, an airfoil 64, and an integral cover 66. With reference to the coordinate system, the most forward circumferential side of each bucket 38 with respect to the direction of rotation of rotor wheel assembly 50 is referred to as a front side 65. The opposite circumferential side of each bucket 38, or the most rearward side with respect to the direction of rotation of rotor wheel assembly 50 (i.e., the positive direction of the Y-axis) is referred to as a back side 63.
In the exemplary embodiment, dovetail 60 is formed with a shape that is substantially complementary to a respective dovetail slot 54 and each includes tapered sidewalls that include a series of axially-extending projections 68 and grooves 70 that are configured to interlock with a respective dovetail slot 54. As described, dovetail slot 54 and dovetail 60 are aligned substantially parallel to centerline axis 24 of steam turbine engine 10, such that buckets 38 can be installed on rotor wheel 52 as dovetail 60 of a respective bucket 38 is inserted axially into a respective dovetail slot 54. When assembled, buckets 38 form an array of buckets that extend about the periphery of rotor wheel 52.
In the exemplary embodiment, bucket closure assembly portion 94 includes a leading auxiliary bucket 73. Leading auxiliary bucket 73 is similar to regular bucket 72. Bucket closure assembly portion 94 also includes a trailing auxiliary bucket 78. Integral cover 66 of trailing auxiliary bucket 78 is generally formed in the shape of a trapezoid and includes edges 80 and 82 that are substantially parallel to each other and are oriented substantially perpendicular to centerline axis 24 of rotor wheel 52 when rotor wheel assembly 50 is fully assembled. Trailing auxiliary bucket 78 includes a back side circumferential edge 32 that is oriented substantially parallel to a respective edge 32 of regular bucket 72 when rotor wheel assembly 50 is fully assembled. In addition, integral cover 66 of trailing auxiliary bucket 78 includes a front side circumferential edge 84 that is oriented at an angle B with respect to centerline axis 24. In the exemplary embodiment, angle B is an acute angle less than or equal to about 10° and greater than about 0°. In addition, angle B is smaller than angle A such that the expression 0°<|B|<|A| is met. Alternatively, angle B may be any angle that enables trailing auxiliary bucket 78 to operate as described herein.
In the exemplary embodiment, buckets 38 also include a closure bucket 86. Closure bucket integral cover 66 is generally formed in the shape of a trapezoid and includes edges 88 and 90 that are substantially parallel to each other and are oriented substantially perpendicular to centerline axis 24 of rotor wheel 52 when rotor wheel assembly 50 is fully assembled. Closure bucket 86 includes a front side circumferential edge 32 that is substantially parallel to a respective edge 32 of leading auxiliary bucket 73 when rotor wheel assembly 50 is fully assembled. In addition, closure bucket integral cover 66 includes a back side circumferential edge 92 that extends at an angle B with respect to the Z-axis and that is substantially parallel to front side circumferential edge 84 of trailing auxiliary bucket 78. As described above, angle B is a positive angle with respect to centerline axis 24 and is an acute angle that is smaller than angle A and that is greater than about 0° such that the expression 0°<|B|<|A| is satisfied.
In the exemplary embodiment, dovetail slot 54 and dovetail 60 are each aligned substantially parallel to centerline axis 24. Alternatively, dovetail slot 54 and dovetail 60 may be oriented at an angle C. In the exemplary embodiment, angle C is 0°. However, angle C may be any acute angle that satisfies the expression |C|<|B|<|A|. In alternative embodiments, angle C may be any angle that enables bucket closure assembly portion 94 to operate as described herein.
In the exemplary embodiment, a retaining key 114 is positioned within keyway 110 and notch 118 to secure the axial location of closure bucket 86. Key 114 is substantially rectangular in shape and has a predetermined thickness 108 that is smaller than distance 98 of keyway 110 to enable closure bucket 86 to be inserted as the last bucket onto rotor wheel assembly 50 without key 114 interfering with trailing auxiliary bucket 78. Alternatively, key 114 may be any shape that enables key 114 to operate as described herein. Key 114 has a width 109 and a height 107 that enable key 114 to substantially align with the dimensions of keyway 110 and notch 118 while enabling key 114 to move vertically within keyway 110 and notch 118.
In the exemplary embodiment, platform 62 includes an opening 112 extending therethrough. Opening 112 extends generally axially through platform 62 and is substantially parallel to centerline 24 of steam turbine engine 10 (Shown in
In operation, trailing auxiliary bucket 78 is inserted into dovetail slot 54 of rotor wheel 52 and secured in place with a retaining key (not shown). Alternatively, auxiliary bucket 78 may be secured in place by any conventional means used for securing rotor buckets, for example, without limitation, by use of a twist-lock retainer. Regular bucket 72 is inserted into an adjacent dovetail slot 54 of rotor wheel 52 and, likewise, is secured in place. An additional regular bucket 72 is subsequently inserted into an adjacent dovetail slot 54 of rotor wheel 52 and secured in place, working around rotor wheel 52 until two dovetail slots 54 remain. Leading auxiliary bucket 73 is inserted in the second to last dovetail slot 54 and secured in place. Trailing auxiliary bucket 78 and leading auxiliary bucket 73 are spread apart to form an opening for closure bucket 86. Closure bucket 86 is inserted into the last dovetail slot 54. To spread trailing auxiliary bucket 78 and leading auxiliary bucket 73 apart, a first substantially tangential force is applied to trailing auxiliary bucket 78 in a direction away from leading auxiliary bucket 73, and a second substantially tangential force is applied to leading auxiliary bucket 73 in the opposite direction. Spreading trailing auxiliary bucket 78 and leading auxiliary bucket 73 apart is necessary because the relationship between angles A, B, and C is such that it meets the expression |C|<|B|<|A|. This relationship, along with circumferential width 100 of integral covers 66, assures that closure bucket 86 cannot be inserted into rotor wheel 52 without first spreading the opening defined between trailing auxiliary bucket 78 and leading auxiliary bucket 73, thus locking each of the buckets in place after final assembly of closure bucket 86.
In the exemplary embodiment, closure bucket 86 is assembled with key 114 in the radial outward position, captured entirely within keyway 110. After closure bucket 86 is inserted into dovetail slot 54 of rotor wheel 52, rod 116 is used to move key 114 to a radially inward position. Key 114 is positioned to engage both keyway 110 and notch 118 simultaneously. Rod 116 is removed from opening 122, and retaining pin 124 is inserted into opening 112 to secure key 114 in the engaged position.
The systems and methods described herein facilitate improving turbine engine performance by providing an axial entry bucket system that substantially reduces operating stresses induced to the turbine. Specifically, a closure bucket and trailing auxiliary bucket with a unique integral cover interface is described. The closure bucket may be assembled on or disassembled from a rotor wheel in an axial manner without the use of a dovetail insert or other similar retaining mechanism. Therefore, in contrast to known turbines that use axial entry buckets, the apparatus, systems, and methods described herein facilitate reducing the time and difficulty in assembling axial entry buckets with integral covers, and facilitate reducing operating stresses and cost associated with dovetail closure inserts.
The methods and systems described herein are not limited to the specific embodiments described herein. For example, components of each system and/or steps of each method may be used and/or practiced independently and separately from other components and/or steps described herein. In addition, each component and/or step may also be used and/or practiced with other assemblies and methods.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
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| Number | Date | Country | |
|---|---|---|---|
| 20150167469 A1 | Jun 2015 | US |
