TURBINE BUCKET SHROUD ARRANGEMENT AND METHOD OF CONTROLLING TURBINE BUCKET INTERACTION WITH AN ADJACENT TURBINE BUCKET

Abstract

A turbine bucket shroud arrangement for a turbine system includes a contact region of a tip shroud, wherein the contact region is in close proximity to an adjacent tip shroud. Also included is a negative thermal expansion material disposed proximate the contact region, the contact region comprising a first volume during a startup condition and a shutdown condition of the turbine system and a second volume during a steady state condition of the turbine system, wherein the second volume is less than the first volume.

Description

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to turbine systems, and more particularly to turbine bucket shroud arrangements, as well as a method of controlling turbine bucket interaction with an adjacent turbine bucket.

Turbine systems employ a number of rotating components or assemblies, such as compressor stages and turbine stages that rotate at high speed when the turbine is in operation, for example. In general, a stage includes a plurality of free-floating blades that extend radially outward from a central hub. Some blades include a shroud that limits vibration within a stage and provides sealing to increase efficiency of the overall system. The shroud is typically positioned at a tip portion of the blade, a mid-portion of the blade or at both the mid portion and the tip portion of the blade. The shrouds are designed such that the free-floating blades interlock to form an integral rotating member during operation.

Prior to rotation of the free-floating blades, a gap between contact surfaces of the shrouds is present. The distance of the gap determines how early an interlock of the shrouds occurs upon startup of the turbine system. Too large of a gap inefficiently delays the locking speed, which may result in resonance, for example. Too small of a gap results in undesirable effects at high speed operation of the turbine system. Such effects include lower damping effectiveness and flutter margin, as well as high stresses imposed on the turbine bucket due to increased transfer of forces between the contacting shrouds, for example. Therefore, current efforts to beneficially reduce the gap to provide an early interlock to address potential low speed aeromechanics issues are mitigated by the detrimental effects on tip shroud life that occur at steady state operating conditions.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a turbine bucket shroud arrangement for a turbine system includes a contact region of a tip shroud, wherein the contact region is in close proximity to an adjacent tip shroud. Also included is a negative thermal expansion material disposed proximate the contact region, the contact region comprising a first volume during a startup condition and a shutdown condition of the turbine system and a second volume during a steady state condition of the turbine system, wherein the second volume is less than the first volume.

According to another aspect of the invention, a method of controlling turbine bucket interaction with an adjacent turbine bucket is provided. The method includes reducing a gap disposed between a contact region of a tip shroud and an adjacent tip shroud by depositing a negative thermal expansion material proximate the contact region. Also included is engaging the contact region of the tip shroud with the adjacent tip shroud during a startup operating condition and a shutdown operating condition. Further included is decreasing a volume of the contact region during increased temperature operating conditions upon contraction of the negative thermal expansion material, wherein decreasing the volume reduces tip shroud contact forces and stresses during a steady state operating condition.

These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic view of a turbine system;

FIG. 2 is a partial perspective view of a turbine stage of the turbine system;

FIG. 3 is a top plan view of a turbine bucket shroud arrangement having a contact region;

FIG. 4 is an enlarged top plan view of the contact region of FIG. 3;

FIG. 5 is a schematic view of the contact region comprising a composition;

FIG. 6 is a schematic view of a plurality of layers of the composition; and

FIG. 7 is a flow diagram illustrating a method of controlling turbine bucket interaction with an adjacent turbine bucket.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a turbine system, shown in the form of a gas turbine engine, constructed in accordance with an exemplary embodiment of the present invention, is indicated generally at 10. The turbine system 10 includes a compressor 12 and a plurality of combustor assemblies arranged in a can annular array, one of which is indicated at 14. As shown, the combustor assembly 14 includes an endcover assembly 16 that seals, and at least partially defines, a combustion chamber 18. A plurality of nozzles 20-22 are supported by the endcover assembly 16 and extend into the combustion chamber 18. The nozzles 20-22 receive fuel through a common fuel inlet (not shown) and compressed air from the compressor 12. The fuel and compressed air are passed into the combustion chamber 18 and ignited to form a high temperature, high pressure combustion product or air stream that is used to drive a turbine 24. The turbine 24 includes a plurality of stages 26-28 that are operationally connected to the compressor 12 through a compressor/turbine shaft 30 (also referred to as a rotor).

In operation, air flows into the compressor 12 and is compressed into a high pressure gas. The high pressure gas is supplied to the combustor assembly 14 and mixed with fuel, for example process gas and/or synthetic gas (syngas), in the combustion chamber 18. The fuel/air or combustible mixture ignites to form a high pressure, high temperature combustion gas stream. Alternatively, the combustor assembly 14 can combust fuels that include, but are not limited to, natural gas and/or fuel oil. In any event, the combustor assembly 14 channels the combustion gas stream to the turbine 24 which converts thermal energy to mechanical, rotational energy.

At this point, it should be understood that each of the plurality of stages 26-28 is similarly formed, thus reference will be made to FIG. 2 in describing stage 26 constructed in accordance with an exemplary embodiment of the present invention with an understanding that the remaining stages, i.e., stages 27 and 28, have corresponding structure. Also, it should be understood that the present invention could be employed in stages in the compressor 12 or other rotating assemblies that require wear and/or impact resistant surfaces. In any event, the stage 26 is shown to include a plurality of rotating members, such as an airfoil 32, which each extend radially outward from a central hub 34 having an axial centerline 35. The airfoil 32 is rotatable about the axial centerline 35 of the central hub 34 and includes a base portion 36 and a tip portion 38.

A tip shroud 50 covers the tip portion 38 of the airfoil 32. The tip shroud 50 is designed to receive, or nest with, tip shrouds on adjacent rotating members in order to form a continuous ring that extends circumferentially about the stage 26. The continuous ring creates an outer flow path boundary that reduces gas path air leakage over top portions (not separately labeled) of the stage 26, so as to increase stage efficiency and overall turbine performance. In the exemplary embodiment shown, during high or operational speeds, adjacent airfoils interlock through the tip shroud 50 of each respective airfoil by virtue of centrifugal forces and thermal loads created by the operation of the turbine 24.

Referring now to FIGS. 3 and 4, the tip shroud 50 is illustrated in greater detail and is in close proximity with an adjacent tip shroud 52. The tip shroud 50 includes a contact region 54 configured to engage the adjacent tip shroud 52 during operation of the turbine system 10. Specifically, the contact region 54 engages an adjacent contact region 56 of the adjacent tip shroud 52. A gap 58 is present between the tip shroud 50 and the adjacent tip shroud 52, and more particularly between the contact region 54 and the adjacent contact region 56. The gap 58 is present prior to startup of the turbine system 10. The gap 58 is dimensionally selected based on a desirable early interlock of the tip shroud 50 and the adjacent tip shroud 52 upon operation of the turbine system 10 and rotation of the airfoil 32. Subsequent to interlock of the tip shroud 50 and the adjacent tip shroud 52, the operating environment increases in temperature, thereby resulting in thermal expansion of most components within the turbine 24.

To alleviate the stresses imposed by potential expansion of already contacted components, at least one of the contact region 54 and the adjacent contact region 56, but typically both the contact region 54 and the adjacent contact region 56, include a negative thermal expansion material 60. The negative thermal expansion material 60 is defined by having a negative coefficient of thermal expansion, such that the material contracts in response to increased temperature exposure, rather than expanding. It is to be appreciated that any material having a negative coefficient of thermal expansion may be suitable for inclusion with the contact region 54 and the adjacent contact region 56. Examples of such materials include zircon, zirconium tungstate and A₂(MO₄)₃ compounds. Forming at least a portion of the contact region 54 and the adjacent contact region 56 with the negative thermal expansion material 60 advantageously allows for the gap 58 to be dimensionally reduced to facilitate an early interlock between the tip shroud 50 and the adjacent tip shroud 52, while also reducing the contact forces associated with interaction between the tip shroud 50 and the adjacent tip shroud 52, thereby reducing stresses imposed on various portions of the tip shroud 50, the adjacent tip shroud 52 and the airfoil 32 attached thereto. The stress reduction is achieved by maintaining an interlock, but contracting the negative thermal expansion material 60. In other words, the contact region 54 comprises a first volume during a startup condition of the turbine system 10 and a smaller, second volume during a steady state operating condition of the turbine system 10.

Referring now to FIGS. 5 and 6, the contact region 54 is schematically illustrated in greater detail. The tip shroud 50 includes a base metal region 62 that is coated or integrally formed with the contact region 54. The contact region 54 is formed of one or more composition layers that typically include a fraction of the negative thermal expansion material 60 and a fraction of a wear resistant material. As noted above, the contact region 54 may include a single composition layer (FIG. 5) or a plurality of composition layers (FIG. 6). In an embodiment having a plurality of composition layers 72, it is to be appreciated that distinct volume and/or weight fractions of the negative thermal expansion material 60 may be present in the plurality of composition layers 72, such as a first layer 64, a second layer 68 and a third layer 70, as shown. In one embodiment, the fraction of the negative thermal expansion material 60 progressively increases in each layer, relative to moving away from the base metal region 62. Specifically, the first layer 64 may include a lower fraction of the negative thermal expansion material 60 than the second layer 68, with the second layer 68 having a lower fraction than the third layer 70. Gradually transitioning the inclusion of the negative thermal expansion material 60 from the base metal region 62 reduces thermal fight at the interface between the contact region 54 and the base metal region 62 of the tip shroud 50. It is to be appreciated that each of the plurality of composition layers 72 may vary in thickness from one another and may comprise the negative thermal expansion material 60 in a fraction ranging from about 0% to about 100%.

The contact region 54, whether a single layer or the plurality of composition layers 72, may be deposited or integrated with the tip shroud 50 in a number of application processes. Examples of such processes include brazing, welding, laser cladding, cold spraying and a plasma transferred arc (PTA) process. The preceding list is merely illustrative and is not intended to be limiting of numerous other suitable application procedures.

As illustrated in the flow diagram of FIG. 7, and with reference to FIGS. 1-6, a method of controlling turbine bucket interaction with an adjacent turbine bucket 100 is also provided. The turbine system 10, as well as the tip shroud 50 and the contact region 54, have been previously described and specific structural components need not be described in further detail. The method of controlling turbine bucket interaction with an adjacent turbine bucket 100 includes reducing a gap between a contact region of a tip shroud and an adjacent tip shroud by depositing a negative thermal expansion material proximate the contact region 102. The contact region is engaged with the adjacent tip shroud during a startup operating condition 104. A volume of the contact region is decreased during increased temperature operating conditions upon contraction of the negative thermal expansion material 106.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

1. A turbine bucket shroud arrangement for a turbine system comprising:

a contact region of a tip shroud, wherein the contact region is in close proximity to an adjacent tip shroud; and

a negative thermal expansion material disposed proximate the contact region, the contact region comprising a first volume during a startup condition and a shutdown condition of the turbine system and a second volume during a steady state condition of the turbine system, wherein the second volume is less than the first volume.

2. The turbine bucket shroud arrangement of claim 1, wherein the negative thermal expansion material comprises at least one of zircon, zirconium tungstate and an A2(MO4)3 compound.

3. The turbine bucket shroud arrangement of claim 1, further comprising an adjacent contact region of the adjacent tip shroud.

4. The turbine bucket shroud arrangement of claim 3, wherein the adjacent contact region comprises a negative thermal expansion material.

5. The turbine bucket shroud arrangement of claim 1, wherein the contact region comprises a composition of the negative thermal expansion material and a wear resistant material.

6. The turbine bucket shroud arrangement of claim 5, wherein the composition comprises a layer disposed on a base metal of the tip shroud.

7. The turbine bucket shroud arrangement of claim 5, wherein the composition comprises a plurality of layers disposed on a base metal of the tip shroud.

8. The turbine bucket shroud arrangement of claim 7, wherein each of the plurality of layers comprise a distinct volume fraction of the negative thermal expansion material.

9. The turbine bucket shroud arrangement of claim 5, wherein the composition is brazed to the tip shroud.

10. The turbine bucket shroud arrangement of claim 5, wherein the composition is welded to the tip shroud.

11. A method of controlling turbine bucket interaction with an adjacent turbine bucket comprising:

reducing a gap disposed between a contact region of a tip shroud and an adjacent tip shroud by depositing a negative thermal expansion material proximate the contact region;

engaging the contact region of the tip shroud with the adjacent tip shroud during a startup operating condition and a shutdown operating condition; and

decreasing a volume of the contact region during increased temperature operating conditions upon contraction of the negative thermal expansion material, wherein decreasing the volume reduces turbine bucket tip shroud contact forces and stresses during a steady state operating condition.

12. The method of claim 11, further comprising depositing the negative thermal expansion material proximate an adjacent contact region of the adjacent tip shroud.

13. The method of claim 11, further comprising forming a composition proximate the contact region, wherein the composition comprises the negative thermal expansion material and a wear resistant material.

14. The method of claim 13, further comprising forming a plurality of layers of the composition proximate the contact region.

15. The method of claim 14, wherein each of the plurality of layers comprises a distinct volume fraction of the negative thermal expansion material.

16. The method of claim 13, wherein the composition is brazed to the tip shroud.

17. The method of claim 13, wherein the composition is welded to the tip shroud.

18. The method of claim 13, wherein the composition is laser cladded to the tip shroud.

19. The method of claim 13, wherein the composition is cold sprayed onto the tip shroud.

20. The method of claim 13, wherein the composition is deposited during a plasma transferred arc process.