BACKGROUND OF THE INVENTION
This application relates generally to rotary machines and more particularly, to shape-memory alloy seals for sealing flow paths in a turbomachine.
At least some known rotary machines such as, but not limited to, steam turbines and gas turbines, include a plurality of seal assemblies in a steam-flow path, air path, or combustion gas path to facilitate increasing operating efficiency. Typically, the seal assemblies are positioned between adjacent stationary components (for example, between a high-pressure area and a low pressure area of a stationary nozzle assembly comprised of multiple arcuate segments), or between a stationary component, e.g., a nozzle assembly) and a rotary component (for example, a rotor wheel supporting an annular array of buckets) to prevent leakage into or out of the hot gas path.
Known seal assemblies include seals such as, but not limited to, brush seals, leaf seals, shingle seals, etc. In the context of a rotary machine, the seals are also typically provided in the form of arcuate segments arranged in an annular array about the machine rotor.
At least some known seal assemblies include a seal housing and an adjustable clearance control mechanism that is coupled to the stationary component. The seal housing includes at least a high-pressure-side front wall that is separated from a low-pressure-side back wall by a fixed gap that is set by the manufacturer. The clearance control mechanism actuates the seal housing including the seals to adjust a clearance between seal tips and the rotary component. Because current seal systems often involve springs that are biased in a given direction, typically opposite the actuation direction, seal assembly and/or installation is hindered by the fact that such springs must oftentimes be compressed to permit installation and in many cases removal of the seals. In addition, the mechanical, hydraulic or pneumatic mechanisms required to actuate such springs add complexity and expense.
It would therefore be desirable to provide a unique seal arrangement that simplifies operation and reduces assembly installation and/or replacement time, thereby providing an overall increase in the efficiency of, for example, a steam or gas turbine.
BRIEF DESCRIPTION OF THE INVENTION
In one exemplary but nonlimiting embodiment, there is provided a high-temperature seal for use in sealing gaps between adjacent turbine components comprising a seal body constructed of a shape-memory alloy having a first inoperative size and shape that, in use, expands to a predetermined operative size and shape where it is in sealing engagement with the adjacent turbine component upon reaching a predetermined transition temperature, and upon subsequent cooling to a temperature below the predetermined temperature, reverts to a second inoperative size and shape different than the first inoperative size and shape.
In another exemplary aspect, there is provided a high-temperature seal for use in sealing gaps between adjacent turbine components comprising a seal body including substantially planar center portion and a pair of profiled end portions, at least the profiled portions formed of a shape-memory alloy material designed to expand upon exposure to temperatures in a range of from about 600° F. to about 2400° F. to an operative shape, thereby causing the profiled portions to engage surfaces of the adjacent turbine components; and wherein the profiled end portions are designed to revert to an inoperative shape when the temperatures drop below the range.
In still another aspect, there is provided a high-temperature seal for use in sealing gaps between surfaces of adjacent turbine components comprising a seal body including substantially planar center portion and a pair of profiled end portions each profiled end portion comprising at least one curl; at least the pair of profiled end portions formed of a shape-memory alloy material designed to change shape upon heating to temperatures higher than a predetermined transition temperature from an inoperative shape to an operative shape, thereby causing the profiled end portions to expand and establish a seal between the surfaces of the adjacent turbine components; and wherein the center portion is rigidified by a separate seal component and covered with a cloth seal fabric.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, in conjunction with the drawings identified below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic, fragmentary and partially-sectioned view of a portion of a gas turbine;
FIG. 2 is a simplified, schematic side view of a shape-memory alloy seal extending between two gas turbine gas path components in accordance with a first exemplary embodiment, the seal being shown in an inoperative condition or state;
FIG. 3 shows the seal of FIG. 2 in an operative, expanded condition or state upon heating above a transition temperature of the shape-memory alloy;
FIG. 4 shows the seal of FIGS. 1 and 2 in a second inoperative condition or state upon cooling of the shape-memory alloy to a temperature below its transition temperature;
FIG. 5 is a side elevation of a shape-memory alloy seal in accordance with a second exemplary but nonlimiting embodiment of the invention;
FIG. 6 is a schematic side view of the shape-memory alloy seal shown in FIG. 5, in an operative, expanded condition or state;
FIG. 7 shows the shape-memory alloy seal of FIG. 6, but also showing in dotted lines, a partially retracted, second inoperative condition or state;
FIG. 8 is a perspective view of a shape-memory alloy seal in accordance with a third exemplary but nonlimiting embodiment;
FIG. 9 is a perspective view of a shape-memory alloy seal in accordance with a fourth exemplary but nonlimiting embodiment; and
FIG. 10 is a perspective view of a shape-memory alloy seal in accordance with a fifth exemplary but nonlimiting embodiment.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, there is illustrated a representative example of a turbine section of a gas turbine, generally designated at 10. Hot combustion gases from an annular array of combustors, not shown, are supplied to the turbine through a like number of transition pieces 12 that introduce the gases into an annular hot gas path 14 which extends axially through the various turbine stages. Each stage comprises a plurality of circumferentially-spaced buckets mounted on individual turbine wheels forming part of the turbine rotor assembly, and a plurality of stationary, circumferentially-spaced stator vanes. For example, the first turbine stage may include a plurality of circumferentially-spaced buckets 16 mounted on a first-stage rotor wheel 18 and a plurality of stationary, circumferentially-spaced stator vanes 20 (comprising the first stage nozzle assembly) located upstream of the buckets. Similarly, the second stage may include a plurality of buckets 22 mounted on a rotor wheel 24 and a plurality of stationary, circumferentially-spaced stator vanes 26 (comprising the second stage nozzle assembly). Additional stages may be provided, for example, a third stage comprised of a plurality of circumferentially-spaced buckets 28 mounted on a third-stage rotor wheel 30 and a plurality of stationary, circumferentially-spaced stator vanes 32 (comprising the third stage nozzle assembly). It will be appreciated that the stator vanes 20, 26 and 32 are mounted on and fixed to the turbine casing (or stator), while the buckets 16, 22 and 28 and wheels 18, 24 and 30 form part of the turbine rotor assembly. Between the rotor wheels 18, 24 and 30 are spacers 34 and 36, which also form part of the turbine rotor. It will be appreciated that compressor discharge air is present in a region 37 disposed radially inwardly of the buckets and is used to cool, for example, the root portions of the buckets, thus establishing an axially-directed cooling air flow radially inward of the hot gas path 14.
Referring to the first stage of the turbine, the stator vanes 20 forming the first-stage nozzle assembly are disposed between inner and outer bands 38 and 40, respectively, supported from the turbine casing. As noted above, the nozzle assembly of the first stage is formed of a plurality of arcuate vane segments, with stator vanes extending between the inner and outer bands 38, 40. A nozzle retaining ring 44 connected to the turbine casing is coupled to the outer band and secures the first-stage nozzle assembly. Shroud segments 46 arranged in an annular array, surround the rotatable buckets, e.g., the buckets 16 of the first stage. The shroud segments include an axial facing surface 50, which lies in sealing engagement with a confronting axial facing surface 48 of the nozzle-retaining ring 44. A seal 52 is shown at the interface to prevent leakage along a gap between these surfaces from the high pressure region to a lower pressure region. This is one of several locations where a seal as described herein may be employed.
FIG. 1 also illustrates other exemplary locations at 54 and 56 where seals may be applied to minimize radially-outward leakage in gaps between confronting stationary surfaces. Other locations where seals as described herein may be employed include confronting stationary and rotating components as indicated, for example at 58 where the rotating spacer 34 confronts the stationary inner nozzle ring 60. Similar locations are found in connection with all of the turbine stages along the gas path.
FIG. 2 illustrates diagrammatically an exemplary seal installation amenable to the utilization of a shape-memory alloy seal. Here, the shape-memory alloy seal (shown diagrammatically at 62) is seated within adjacent grooves 64, 66 of respective, adjacent stationary components 68, 70. The segments 68, 70 represent any confronting stationary surfaces along the gas path where leakage may occur along a gap 72 between the confronting surfaces of the components. The seal 62 in accordance with exemplary embodiments described below may be a constructed of a shape-memory alloy that is designed to change shape in response to, for example, temperatures experienced in use. The change in shape is due to a temperature related, solid state micro-structural phase change that enables the alloy to change from one physical shape to another physical shape. The shape change may be manifest as a change in size, i.e., expanded but similarly shaped, and/or a change in shape, i.e., expanded to a different shape (generally referred to herein as a shape change).
In the manufacture of an article intended to change shape during operation, the article (a seal in this case) is formed to have an operative shape at or above a transition temperature. This operative shape is developed by working and annealing an article preform of the alloy at or above a temperature at which the solid state micro-structural phase change occurs. The temperature at which such phase change occurs generally is called the critical or transition temperature of the alloy.
For purposes of this invention, near-equiatomic Nb—Ru and Ta—Ru alloys have been found to be particularly well-suited, with transition temperatures of between 600° F. and 2400° F. specified in the elevated temperature environment of turbomachinery.
Depending on specific applications, the shape-memory alloy seal 62 may have one-way or two-way shape characteristics. For example, the shape-memory alloy seal 62 may transition change to an operative shape upon reaching its predetermined temperature, and remain in that operative shape after the seal cools below the transition temperature. A two-way seal on the other hand, reverts to an inoperative shape, which may be its original first, inoperative shape (FIG. 2) or another intermediate (or second) but still inoperative shape (FIG. 4) when the temperature drops below the critical or transition temperature. The two-way seal has the added benefit of facilitating removal of the seal upon cooling below the transition temperature.
In FIG. 5, a shape-memory alloy seal 74 in accordance a second exemplary but nonlimiting embodiment is shown in its normal (room temperature) or inoperative shape or state. The seal 74 is formed to include a pair of flexible, profiled portions, or curls 76, 78 at opposite ends of a flat middle portion 80. It is the end curls 76, 78 that provide the sealing function. When heated above the predetermined critical or transition temperature of the shape-memory alloy, the seal 74 will deform to an operative shape, where the end curls expand to engage surfaces of the respective adjacent components, for example, surfaces within the grooves 64, 66 of the segments 68, 70 in FIG. 2, to thereby prevent radial leakage through the gap 72 between the segments. The expansion of the end curls 76, 78 is shown diagrammatically in FIG. 6. It will be appreciated that if the seal alloy changes shape in the middle section 80, and if that aspect of the shape change is not needed to achieve the desired sealing, the middle section may be physically confined to minimize or even prevent shape change in that section of the seal by confining the middle section within any substantially-rigid structure, as exemplified at 82. As explained above, the seal curls 76, 78 could revert to the shape shown in FIG. 5 upon cooling below the transition temperature; or revert to an intermediate or second inoperative shape as shown dotted lines in FIG. 7. Thus, it is possible to control the shape of the seal as a function of temperature, as dictated by the properties of the materials used.
In another exemplary but nonlimiting example illustrated in FIG. 8, a shape-memory alloy seal 84 is comprised of an elongated center portion 86 and a pair of end curls 88, 90 at opposite ends of the center portion. In this exemplary embodiment, the center portion 86 is formed integrally with a rigid reinforcement plate 92 bonded thereto by welding, brazing, adhesive or other suitable means. The center portion 86 thus facilitates assembly and placement of the seal but does not in and of itself contribute to the sealing function. It is the flexible end curls 76, 78 that provide the sealing function, exhibiting one-way or two-way shape-change characteristics as described above.
The end curls 86, 88 may have a normal (room-temperature) inoperative shape as shown in FIG. 8. When heated above its transition or critical temperature in use, the end curls 86, 88 will expand in a manner similar to the expanded end curls 76, 78 described in connection with FIGS. 5-7. In a two-way version of the seal, the curls 86, 88 will return to their original shape or to some intermediate but still inoperative inoperative shape as determined by material properties and temperatures.
FIG. 9 illustrates a variation of the seal shown in FIG. 8. Here, the opposite ends of the seal 94 are formed with double end curls 96, 98, i.e., each end is formed with a pair of curls or convolutions 100, 102 and 104, 106, respectively. The center section 108 is again rigidified by a reinforcement plate 110, otherwise similar to the plate 92 in the embodiment shown in FIG. 8. This arrangement provides for extended sealing range and increased sealing bias, useful in specific applications. Here again, one or two-way shape-change characteristics as described above are contemplated.
FIG. 10 illustrates another exemplary embodiment where the shape-memory seal 112 is formed as a cloth seal with shape-memory alloy features substantially as described above. Specifically, the seal is formed with a center section 114 and opposite end curls 116, 118. The center section 114 is sandwiched between rigid plates 120, 122 one or both of which may be covered with conventional cloth seal fabric. The end curls 116, 118 are formed to exhibit one-way or two-way shape-change characteristics as described above.
For all of the above-described embodiments, it will be appreciated that whether the sealing surfaces engage or simply establish predetermined clearances under operating conditions will depend on specific applications, for example, whether both surface are stationary, or if one of the adjacent surfaces is rotating, etc.
While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Patent Application
20140361499
