The present invention generally relates to combustion technology and, more specifically, sealing configurations between rotating and stationary components within the hot gas path of the combustion turbine.
Typically, a near-flow-path seal is located between adjacent stages of buckets just below the neighboring nozzle. More specifically, the near-flow-path seal is loaded into a spacer wheel or disk located axially between adjacent wheels or disks that support peripheral rows of turbine buckets. The near-flow-path seal has arms that extend axially in opposite directions from the spacer wheel dovetail to form a flow path below the nozzle and to keep hot combustion gases out of the radially inner wheel space. The axial arms of the near-flow-path seal are not self-supported, however, and each requires a loading surface when the turbine is under normal operation and exposed to centrifugal forces exerted as the turbine rotor rotates. In a typical configuration, the near-flow-path seal is loaded at three points: on the spacer wheel located between the neighboring wheels through a dovetail; and on loading surfaces of the two adjacent buckets, typically surfaces of the integral cover plates on the respective buckets.
There remains a need, therefore, for a near-flow- path seal design that ameliorates the loading (e.g., centrifugal and/or axial) into the adjacent buckets.
In accordance with an exemplary but nonlimiting embodiment, there is provided a turbine bucket comprising an airfoil portion; a platform radially-inward of the airfoil portion; a shank portion radially-inward of the platform; a mounting portion radially-inward of the shank portion; and wherein the shank portion has at least one axially-extending near-flow-path seal-engaging surface, the near-flow-path seal-engaging surface and part of the mounting portion forming an isolation element separable from the turbine bucket.
In another aspect, there is provided a turbine rotor assembly comprising at least two rotor disks with a spacer disk axially therebetween, each rotor disk provided with an annular row of buckets each bucket comprising an airfoil portion; a platform radially-inward of the airfoil portion; a shank portion radially-inward of the platform; a mounting portion radially-inward of the shank portion; and wherein the shank portion has at least one near-flow-path seal-engaging surface, the near-flow-path seal-engaging surface and part of the mounting portion forming an isolation element separable from the turbine bucket.
In still another aspect, there is provided a method for reducing centrifugal or axial loading on a turbine bucket caused by a near-flow-path seal-engaging with an adjacent surface portion formed on the bucket, comprising removing material from the bucket including the adjacent surface portion to form a cut-out; and replacing the material with an isolation element fitted in the cut-out and engageable with the near-flow-path seal during operation of the turbine.
The invention will now be described in detail in connection with the drawings identified below.
The near-flow-path seal-engaging surfaces 20, 22 may be provided on bucket cover plates or other surfaces that are independent of radially adjacent angel wing seals.
In this known arrangement, it will be appreciated that loads exerted by the arms 16, 18 on the bucket cover plate or other seals 20, 22 are transferred directly to the buckets 24, 26, thus generating undesirable stresses on the buckets or stiffness in the rotor system.
Turning now to
It will be appreciated that the isolation element 56 may be comprised of the very portion removed from the bucket 36, or it may be a newly-manufactured element formed to match the removed material. It will also be appreciated that the isolation feature described herein may be retrofit to existing buckets or incorporated into newly-manufactured buckets.
By substantially eliminating the centrifugal forces resulting from engagement of the near-flow-path seal arms with the bucket seal structure, extended bucket life may be realized.
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.