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Title:
FILM-RIDING SEALING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2019/106024
Kind Code:
A1
Abstract:
A seal segment (128) for a machine (100) includes a circumferentially extending stationary seal body (200) configured to be coupled to a casing (110) of the machine, and a support member (204) extending radially inward from the stationary seal body to a radially inner end (210). The seal segment also includes a pair of flexible arms (208) extending in circumferentially opposite directions from the radially inner end of the support member to a respective circumferentially outer end (214), and a circumferentially extending seal pad (202) disposed radially inward from the pair of flexible arms and defining a first gap (262) therebetween. The seal pad is coupled to the pair of flexible arms proximate the respective circumferentially outer ends.

Inventors:
TIBOS, Stacie (Willans Works 2NH, Newbold RdRugby, Warwickshire CV21 2NH, CV21 2NH, GB)
GEORGAKIS, Christos (Willans Works 2NH, Newbold RdRugby, Warwickshire CV21 2NH, CV21 2NH, GB)
Application Number:
EP2018/082868
Publication Date:
June 06, 2019
Filing Date:
November 28, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
GENERAL ELECTRIC TECHNOLOGY GMBH (Brown Boveri Strasse 7, Baden, CH-5400, CH)
International Classes:
F01D11/02; F16J15/44
Domestic Patent References:
WO2004053365A12004-06-24
Foreign References:
US20160130963A12016-05-12
US20110133410A12011-06-09
US20160069269A12016-03-10
US20140119912A12014-05-01
US20080265513A12008-10-30
US20170248236A12017-08-31
US20140062024A12014-03-06
US7216871B12007-05-15
EP3018298A12016-05-11
Other References:
None
Attorney, Agent or Firm:
CORIC, Dragan (General Electric Technology GmbH, Global Patent Operation - EuropeBrown Boveri Strasse 7, Baden, CH-5400, CH)
Download PDF:
Claims:
WHAT IS CLAIMED IS:

1. A seal segment for a machine, said seal segment comprising: a circumferentially extending stationary seal body configured to be coupled to a casing of the machine; a support member extending radially inward from said stationary seal body to a radially inner end; a pair of flexible arms extending in circumferentially opposite directions from said radially inner end of said support member to a respective circumferentially outer end; and a circumferentially extending seal pad disposed radially inward from said pair of flexible arms and defining a first gap therebetween, said seal pad coupled to said pair of flexible arms proximate said respective circumferentially outer ends.

2. The seal segment according to Claim 1, wherein said seal pad comprises a primary sealing extension extending radially outward from said seal pad axially downstream from a leading face of said seal pad.

3. The seal segment according to Claim 2, wherein said stationary seal body comprises a secondary seal retention member axially adjacent to said primary sealing extension and extending radially inward, said secondary seal retention member cooperates with said primary sealing extension to define a retention cavity.

4. The seal segment according to Claim 3, wherein said stationary seal body, said support member, said pair of flexible arms, said seal pad, said primary sealing extension, and said secondary seal retention member are integrally formed.

5. The seal segment according to Claim 3, wherein said retention cavity is configured to receive a secondary seal therein.

6. The seal segment according to Claim 5, wherein said primary sealing extension is configured to receive an axial force from the secondary seal when the secondary seal is received in said retention cavity, such that radial movement of said seal pad relative to said stationary seal body is damped.

7. The seal segment according to Claim 1, wherein said seal pad comprises a divergent section extending axially downstream to a trailing edge of said seal pad at an angle relative to a longitudinal axis of said seal pad.

8. The seal segment according to Claim 7, wherein said angle is in a range between about zero degrees and about fifteen degrees.

9. The seal segment according to Claim 7, wherein said angle is in a range between about three degrees and about eight degrees.

10. The seal segment according to Claim 1, wherein said seal pad further comprises a groove defined therein and extending radially outward from a radially inner face of said seal pad, said groove configured to facilitate retaining fluid between said seal pad and a rotor of the machine.

11. The seal segment according to Claim 10, wherein said seal pad further comprises a feed channel defined therein and extending axially downstream from a leading face of said seal pad, said feed channel configured to direct fluid into said groove.

12. The seal segment according to Claim 1, wherein said stationary seal body extends circumferentially from a first end to a second end, and said seal pad extends circumferentially between a first end and a second end of said stationary seal body.

13. A machine comprising: a rotor; a casing extending circumferentially around said rotor; and a sealing system disposed radially inwardly of said casing and circumferentially around said rotor, said sealing system comprising a plurality of film riding seal segments, at least one of said film-riding seal segments comprising: a circumferentially extending stationary seal body coupled to said casing; a support member extending radially inward from said stationary seal body to a radially inner end; a pair of flexible arms extending in circumferentially opposite directions from said radially inner end of said support member to a respective circumferentially outer end; and a circumferentially extending seal pad disposed radially inward from said pair of flexible arms and defining a first gap therebetween, said seal pad coupled to said pair of flexible arms proximate said respective circumferentially outer ends.

14. The machine according to Claim 13, wherein said seal pad comprises a primary sealing extension extending radially outward from said seal pad axially downstream from a leading face of said seal pad.

15. The machine according to Claim 14, wherein said sealing system further comprises a secondary seal retention member axially adjacent to said primary sealing extension and extending radially inward from said stationary seal body, said secondary seal retention member cooperates with said primary sealing extension to define a retention cavity.

16. The machine according to Claim 15, wherein said stationary seal body, said support member, said pair of flexible arms, said seal pad, said primary sealing extension, and said secondary seal retention member are integrally formed.

17. The machine according to Claim 15, wherein said sealing system further comprises a secondary seal received in said retention cavity.

18. The machine according to Claim 17, wherein said secondary seal exerts an axial force on said primary sealing extension, such that radial movement of said seal pad relative to said stationary seal body is damped.

19. The machine according to Claim 13, wherein said seal pad comprises a divergent section extending axially downstream to a trailing edge of said seal pad at an angle relative to an axis of rotation of said rotor.

20. The machine according to Claim 13, wherein said seal pad further comprises: a groove defined therein and extending radially outward from a radially inner face of said seal pad, said groove configured to facilitate retaining fluid between said seal pad and said rotor; and a feed channel defined therein and extending axially downstream from a leading face of said seal pad, said feed channel configured to direct fluid into said groove.

Description:
FILM-RIDING SEALING SYSTEM

BACKGROUND

[0001] The field of the disclosure relates generally to sealing systems for machines, and more particularly to film-riding seals for a machine.

[0002] At least some known rotary machines include at least one rotor assembly coupled to a rotor shaft. The rotor assembly includes a plurality of circumferentially-spaced blades that extend radially outward to define a stage of the rotary machine. For example, but not by way of limitation, the rotor assembly is part of a steam turbine, or part of a compressor or turbine section of a gas turbine engine. A casing surrounds at least a portion of the rotor assembly. Some known casings include at least some type of sealing system surrounding the rotor shaft to facilitate sealing against leakage of a working fluid between the rotor shaft and the casing. At least some known sealing systems include circumferentially disposed film-riding seal segments coupled to the casing and configured to reduce a clearance gap between the film-riding seal segment and the rotor shaft to facilitate sealing the rotor shaft.

[0003] In some known rotary machines, a pre-set clearance gap is defined between the film-riding seal segments and the outer surface of the rotor shaft to enable assembly of the rotary machine and to account for dimensional changes of the rotor shaft, casing, and film-riding seal segments during operation of the turbine. However, leakage resulting from the pre-set clearance gap may limit an efficiency of at least some rotary machines. As such, at least some known film-riding seal segments include at least a portion of the seal that may flex to move radially inward and outward relative to the surface of the rotor shaft to facilitate maintaining a relatively small clearance gap. However, at least some film-riding seal segments incorporating flexible features may exhibit dynamic instability and yawing of the sealing element relative to the rotor shaft surface during operation and/or may have limited effectiveness in reducing flow path leakage. BRIEF DESCRIPTION

[0004] In one aspect, a seal segment for a machine is provided. The seal segment includes a circumferentially extending stationary seal body configured to be coupled to a casing of the machine, and a support member extending radially inward from the stationary seal body to a radially inner end. The seal segment also includes a pair of flexible arms extending in circumferentially opposite directions from the radially inner end of the support member to a respective circumferentially outer end, and a circumferentially extending seal pad disposed radially inward from the pair of flexible arms and defining a first gap therebetween. The seal pad is coupled to the pair of flexible arms proximate the respective circumferentially outer ends.

[0005] In another aspect, a machine is provided. The machine includes a rotor, a casing extending circumferentially around the rotor, and a sealing system disposed radially inwardly of the casing and circumferentially around the rotor. The sealing system includes a plurality of film-riding seal segments. At least one of the film-riding seal segments includes a circumferentially extending base coupled to the casing, and a support member extending radially inward from the stationary seal body to a radially inner end. The at least one of the film-riding seal segments also includes a pair of flexible arms extending in circumferentially opposite directions from the radially inner end of the support member to a respective circumferentially outer end, and a circumferentially extending seal pad disposed radially inward from the pair of flexible arms and defining a first gap therebetween. The seal pad is coupled to the pair of flexible arms proximate the respective circumferentially outer ends.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a schematic view of an exemplary rotary machine;

[0007] FIG. 2 is a perspective view of an exemplary film-riding seal segment that may be used with a sealing system of the rotary machine shown in FIG. i; [0008] FIG. 3 is a perspective view of the film-riding seal segment shown in FIG. 2 illustrating an exemplary groove and an exemplary feed channel;

[0009] FIG. 4 is a front view of the film-riding seal segment shown in

FIG. 2;

[0010] FIG. 5 is a cross-section of a downstream portion of the film riding seal segment shown in FIG. 2 taken along lines 5-5 shown in FIG. 4;

[0011] FIG. 6 is a cross-section of an exemplary secondary seal that may be used with the film-riding seal segment shown in FIG. 2;

[0012] FIG. 7 is a side view of the secondary seal shown in FIG. 6;

[0013] FIG. 8 is a plan view of the secondary seal shown in FIG. 6; and

[0014] FIG. 9 is a perspective view of an alternative embodiment of the film-riding seal segment shown in FIG. 3 illustrating exemplary angled grooves.

DETAILED DESCRIPTION

[0015] The embodiments described herein overcome at least some of the disadvantages of known film-riding seals. The embodiments include a seal segment including a stationary body and a seal pad coupled to the stationary body via flexible arms. The flexible arms enable the seal pad to be radially compliant to radial movements of the rotor. In some embodiments, a secondary seal is arranged to create a damping force on radial movement of the seal pad relative to the stationary body, further improving a dynamic performance of the seal. Additionally or alternatively, in certain embodiments, the seal pad has a divergent section adjacent to the trailing edge. The divergent section facilitates cooperating with a non-divergent portion of the seal pad to allow the seal pad to set at a clearance at which hydrostatic film-riding forces and hydrodynamic film-riding forces between the seal pad and rotor complement each other to facilitate improving performance of the seal segment. In at least some embodiments, working fluid leakage reduction between the rotor and a casing is achieved without modifying the existing rotor and/or casing. [0016] Unless otherwise indicated, approximating language, such as “generally,”“substantially,” and“about,” as used herein indicates that the term so modified may apply to only an approximate degree, as would be recognized by one of ordinary skill in the art, rather than to an absolute or perfect degree. Accordingly, a value modified by a term or terms such as “about,” “approximately,” and “substantially” is not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Additionally, unless otherwise indicated, the terms“first,”“second,” etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to, for example, a“second” item does not require or preclude the existence of, for example, a“first” or lower-numbered item or a“third” or higher-numbered item.

[0017] FIG. 1 is a schematic view of an exemplary rotary machine 100. In the exemplary embodiment, rotary machine 100 is a single-flow steam turbine. In alternative embodiments, rotary machine 100 is an opposed-flow steam turbine. Moreover, the present embodiments are not limited to only being used in steam turbines, but rather can be used in other rotary machine systems, such as gas turbines. Alternatively, rotary machine 100 is any other turbine engine and/or rotary machine, including, without limitation, a gas turbofan aircraft engine, other aircraft engine, a wind turbine, a compressor, a pump, and/or any other machine.

[0018] In the exemplary embodiment, rotary machine 100 includes a plurality of stages 102. Each stage 102 includes a plurality of rotor blades 104 coupled to a rotor 106. It should be noted that, as used herein, the term“couple” is not limited to a direct mechanical, electrical, and/or communication connection between components, but may also include an indirect mechanical, electrical, and/or communication connection between multiple components. Rotor blades 104 of each stage 102 are disposed circumferentially around, and extend radially outward from, rotor 106. Each stage 102 includes any suitable number of rotor blades 104 that enables rotary machine 100 to operate as described herein. Rotor 106 is supported at opposing end portions 108 of rotor 106 by bearings (not shown). [0019] A casing 110 surrounds plurality of stages 102. In the exemplary embodiment, a plurality of diaphragms 112 is coupled to casing 110, such that a respective diaphragm 112 is positioned upstream of each stage 102. Each diaphragm 112 includes a row of partitions 114. Partitions 114 are generally airfoil shaped and are disposed circumferentially around, and extend radially inward from, casing 110. Alternatively, any stationary vane or nozzle assembly, or no stationary vane or nozzle assembly, is disposed upstream of each stage 102.

[0020] Rotary machine 100 also includes a sealing system 127 disposed between casing 110 and rotor 106. Sealing system 127 includes a plurality of film riding seal segments 128 coupled to casing 110. More specifically, the plurality of film-riding seal segments 128 extend radially inward from casing 110 and are disposed circumferentially around rotor 106. In the exemplary embodiment, when rotary machine is not in operation, film-riding seal segments 128 extend to a predetermined clearance distance from an outer surface of rotor 106.

[0021] Rotary machine 100 includes a high pressure steam inlet 116 and a low pressure steam exhaust 118. Rotor 106 is rotatable about a centerline axis 120. During operation, high-pressure and high-temperature steam 122 is channeled from a steam source, such as a boiler or the like (not shown), through high pressure steam inlet 116 into a working fluid path 124, in a downstream direction 126 through casing 110, where it encounters rotor blades 104. As the steam impacts rotor blades 104, it induces rotation of rotor 106 about centerline axis 120. Thus, thermal energy of steam 122 is converted to mechanical rotational energy by stages 102. Mechanical rotational energy of rotor 106 may be used to drive a load such as, but not limited to, an electrical generator and/or a mechanical drive application. Steam 122 exits casing 110 at low pressure steam exhaust 118. Steam 122 is then channeled to the boiler (not shown), where it is reheated, and/or to other components of the system, for example, a low pressure turbine section or a condenser (not shown). Alternatively, rotor blades 104 are included in a turbine section or compressor section of a gas turbine (not shown), or in any suitable rotary machine, as discussed above. For example, but not by way of limitation, the working fluid delivered to the turbine section may be combustion gases. [0022] FIG. 2 is a perspective view of film-riding seal segment 128 that may be used with sealing system 127 for rotary machine 100 (shown in FIG. 1). FIG. 3 is a perspective view of film-riding seal segment 128 (shown in FIG. 2) illustrating an exemplary groove 234 and an exemplary feed channel 236. FIG. 4 is a front view of film-riding seal segment 128 (shown in FIG. 2). FIG. 5 is a cross-section of a downstream portion of film-riding seal segment 128 (shown in FIG. 2) taken along lines 5-5 shown in FIG. 4. With reference to FIGs. 2-5, in the exemplary embodiment, film-riding seal segment 128 includes a stationary seal body 200 and a seal pad 202 configured to extend radially between casing 110 and rotor 106. Moreover, sealing system 127 includes a secondary seal 203 coupled between stationary seal body 200 and seal pad 202 of each film-riding seal segment 128. Sealing system 127 is configured to facilitate inhibiting leakage of working fluid from working fluid path 124 past seal pad 202 and secondary seal 203, and between seal pad 202 and rotor 106. In alternative embodiments, film-riding seal segment 128 may be coupled to any component of rotary machine 100 that facilitates operation of rotary machine 100.

[0023] In the exemplary embodiment, stationary seal body 200 includes a radially outer base 201, an axially extending support member 204, a pair of flexible arms 208, and a secondary seal retention member 220. Seal pad 202 includes a primary sealing extension 216. In alternative embodiments, each film-riding seal segment 128 contains any feature(s) that enables rotary machine 100 to function as described herein.

[0024] In the exemplary embodiment, base 201 of stationary seal body 200 is configured to be coupled to casing 110 and extends circumferentially between a stationary body first end 205 and a stationary body second end 207. Support member 204 extends radially inward from a generally mid-portion of base 201 to a radially inner end 210 over a support height 240, and extends axially along base 201 over a support length 238. A pair of flexible arms 208 extend in circumferentially opposite directions from radially inner end 210 of support member 204 to a respective circumferentially outer end 214. In the exemplary embodiment, pair of flexible arms 208 are substantially symmetric about support member 204, such that each arm 208 extends over a substantially identical length 242. In alternative embodiments, pair of flexible arms 208 are other than substantially symmetric about support member 204.

[0025] In the exemplary embodiment, seal pad 202 is disposed radially inward from pair of flexible arms 208 and extends circumferentially between a seal pad first end 209 and a seal pad second end 217. Seal pad 202 is coupled to each of flexible arms 208 proximate the respective circumferentially outer end 214 of each of flexible arms 208. For example, in the exemplary embodiment, seal pad 202 is coupled directly to the respective circumferentially outer end 214 of each of flexible arms 208 via radially extending connecting portions 213. In alternative embodiments, connecting portions 213 are offset slightly circumferentially inward from the respective circumferentially outer end 214 of each of flexible arms 208. In other alternative embodiments, seal pad 202 is coupled to each of flexible arms 208 proximate the respective circumferentially outer ends 214 of flexible arms 208 in any suitable fashion that enables film-riding seal segment 128 to function as described herein. In the exemplary embodiment, seal pad first end 209 is radially aligned with stationary body first end 205, and seal pad second end 217 is radially aligned with stationary body second end 207. In an alternative embodiment, seal pad first end 209 and/or stationary body first end 205 are configured to sealingly interface with seal pad second end 217 and/or seal body second end 207, respectively, of a laterally adjacent film-riding seal segment 128 to facilitate inhibiting inter-segment leakage. In alternative embodiments, seal pad first end 209 is other than radially aligned with stationary body first end 205, and/or seal pad second end 217 is other than radially aligned with stationary body second end 207.

[0026] A first flow path 261 is defined between a radially inner face 244 of seal pad 202 and an outer surface of rotor 106. A first gap 262 is defined between a radially outer surface of seal pad 202 and a radially inward surface of pair of flexible arms 208. A pair of third flow paths 264 are defined between a respective radially outward surface of each flexible arm 208 and a radially inward surface of stationary seal body 200, and separated by support member 204. In alternative embodiments, film-riding seal segment 128 may be configured in any suitable manner that enables film-riding seal segment 128 to function as described herein. [0027] In the exemplary embodiment, seal pad 202 has a circumferential width 211 and has a longitudinal axis 215 parallel to centerline axis 120 of rotary machine 100 (shown in FIG. 1). In the exemplary embodiment, flexible arms 208 are configured to flex to allow radial movement of seal pad 202 relative to base 201 and rotor 106. More specifically, each flexible arm 208 is configured to be substantially rigid in the axial direction and substantially compliant in the radial direction. Moreover, the respective circumferentially outer end 214 of each flexible arm 208 is configured for radial movement independently of the other flexible arm 208. Flexible arms 208 thus are configured to cooperate with seal pad 202 to facilitate aligning seal pad 202 with rotor 106, and to inhibit seal pad 202 from tilting axially relative to centerline axis 120 throughout a radial range of motion of seal pad 202, facilitating reducing the operational clearance between seal pad 202 and rotor 106. In alternative embodiments, each flexible arm 208 may be configured in any suitable manner that enables film-riding seal segment 128 to function as described herein..

[0028] In the exemplary embodiment, seal pad 202 includes groove 234 defined in radially inner face 244 of seal pad 202. More specifically, groove 234 extends radially outward from radially inner face 244 and is configured to facilitate retaining fluid between seal pad 202 and rotor 106. Groove 234 extends circumferentially over a groove width 246, axially over a groove length 248, and radially outward into seal pad 202 by a groove depth 250. A feed channel 236 also is defined in radially inner face 244 of seal pad 202 in flow communication with groove 234. More specifically, feed channel 236 extends through, and axially downstream from, leading face 212 of seal pad 202 and is configured to direct fluid from upstream of seal pad 202 into groove 234. In alternative embodiments, groove 234 and feed channel 236 are configured in any suitable manner that enables film -riding seal segment 128 to function as described herein.

[0029] In the exemplary embodiment, feed channel 236 extends circumferentially over a feed channel width 252, axially over a feed channel length 254, and radially outward into seal pad 202 by a feed channel depth 256. In the exemplary embodiment, feed channel depth 256 is greater than groove depth 250. In alternative embodiments, feed channel depth 256 is less than or equal to groove depth 250. In the exemplary embodiment, groove width 246 is at least eighty percent of a width of seal pad 202, and feed channel width 252 is less than twenty percent of the width of seal pad 202. In alternative embodiments, groove width 246 and feed channel width 252 have any suitable values that enable film-riding seal segment 128 to function as described herein.

[0030] In the exemplary embodiment, seal pad 202 also includes a divergent section 226 extending axially downstream from a generally axially mid- portion of seal pad 202 to a trailing edge 228 of seal pad 202. More specifically, divergent section 226 is angled outward relative to longitudinal axis 215 of seal pad 202 at an angle 230. In the exemplary embodiment, angle 230 is selected to cooperate with the non-divergent portion of seal pad 202 to facilitate generating a hydrostatic film-riding force and a hydrodynamic film-riding force between seal pad 202 and rotor 106. More specifically, divergent section 226 facilitates enhancing hydrostatic forces between seal pad 202 and rotor 106 by causing a pressure drop in a volume of fluid between seal pad 202 and rotor 106 during operation of rotary machine 100. For example, hydrostatic film-riding forces may be created when a clearance between rotor 106 and seal pad 202 is greater than 100 micrometers, and hydrodynamic film riding forces become effective when the clearance between rotor 106 and seal pad 202 is less than 100 micrometers. Divergent section 226 facilitates allowing seal pad 202 to set at a clearance of greater than 100 micrometers, thus using hydrostatic film riding forces to control a bulk opening and closing of each film-riding seal segment 128 relative to rotor 106. Moreover, for example, if the clearance is dynamically reduced to less than 100 micrometers for any reason during operation, film-riding seal segment 128 facilitates creation of a buffer from hydrodynamic forces to avoid contact between film-riding seal segment 128 and rotor 106.

[0031] In some embodiments, angle 230 is selected to be in a range of between about zero degrees and about fifteen degrees, for example facilitating generating a hydrostatic film-riding force between seal pad 202 and rotor 106. In some such embodiments, angle 230 is selected to be in a range of between about three degrees and about eight degrees, for example further facilitating generating a hydrostatic film-riding force between seal pad 202 and rotor 106. In alternative embodiments, angle 230 is selected to have any suitable value that enables sealing system 127 to function as described herein. In other alternative embodiments, film riding seal segment 128 does not include divergent section 226.

[0032] In the exemplary embodiment, a primary sealing extension 216 extends radially outward and circumferentially from another generally axial mid- portion 218 of seal pad 202, axially downstream from flexible arms 208. Primary sealing extension 216 extends circumferentially along width 211 of seal pad 202, axially by a thickness 258, and radially outward from seal pad 202 by a height 260. A primary extension gap 266 is defined between a radially outer face 276 of primary sealing extension 216 and a radially inward face 274 of base 201. Primary extension gap 266 represents the distance that seal pad 202 may travel in a radially outward direction away from rotor 106 during operation of rotary machine 100 before contacting stationary seal body 200. Primary sealing extension 216 is configured to facilitate inhibiting a portion of the working fluid from leaking past film-riding seal segment 128 by passing through first gap 262 and/or third flow paths 264, by directing the portion of the working fluid to secondary seal 203. In alternative embodiments, primary sealing extension 216 is configured in any suitable manner that enables film-riding seal segment 128 to function as described herein..

[0033] Secondary seal retention member 220 extends radially inward from stationary seal body 200 axially adjacent to, and axially downstream of, primary sealing extension 216, such that secondary seal retention member 220 and primary sealing extension 216 cooperate to define a secondary seal retention cavity 224. In an alternative embodiment, secondary seal retention member 220 may extend radially inward from stationary seal body 200 axially adjacent to, and axially upstream of, primary sealing extension 216, such that secondary seal retention member 220 and primary sealing extension 216 cooperate to define a secondary seal retention cavity 224. Retention cavity 224 is configured to facilitate retaining secondary seal 203. Retention cavity 224 has a radially extending retention cavity height 270 and an axially extending retention cavity length 269. In the exemplary embodiment, retention cavity height 270 and a first portion 272 of axially extending retention cavity length 269 are defined within secondary seal retention member 220, and a remaining portion of axially extending retention cavity length 269 is defined by primary sealing extension 216. In alternative embodiments, secondary seal retention member 220 and primary sealing extension 216 cooperate to define retention cavity 224 in any suitable fashion that enables sealing system 127 to function as described herein.

[0034] In the exemplary embodiment, stationary seal body 200, support member 204, flexible arms 208, seal pad 202, primary sealing extension 216, and secondary seal retention member 220 are integrally formed together as a monolithic structure. In an alternative embodiment, stationary seal body 200, pair of flexible arms 208, seal pad 202, primary sealing extension 216, and secondary seal retention member 220 are other than integrally formed together as a monolithic structure.

[0035] FIG. 6 is a cross-section of secondary seal 203 that may be used with film-riding seal segment 128 (shown in FIG. 2). FIG. 7 is a side view of secondary seal 203 (shown in FIG. 6). FIG. 8 is a plan view of secondary seal 203 (shown in FIG. 6). With reference to FIGs. 2 and 6-8, in the exemplary embodiment, secondary seal 203 is sized and shaped to be retained by, and to extend between, secondary seal retention member 220 and primary sealing extension 216. In the exemplary embodiment, secondary seal 203 includes a first leg 308, a second leg 310, and a u-shaped portion 306 extending therebetween. U-shaped portion 306 is located generally centrally between first leg 308 and second leg 310. In the exemplary embodiment, each of first leg 308, second leg 310, and u-shaped portion 306 has an approximately uniform thickness 320. In an alternative embodiment, each of first leg 308, second leg 310, and u-shaped portion 306 may have a non-uniform thickness 320. In other alternative embodiments, secondary seal 203 is one of a c-seal and an o- ring-type seal. In alternative embodiments, secondary seal 203 has any suitable shape, size, and/or configuration that enables sealing system 127 to function as described herein.

[0036] In the exemplary embodiment, secondary seal 203 extends axially from a first end 326 to a second end 328 and, in an absence of external constraint, defines a resting width 312 therebetween. In the exemplary embodiment, resting width 312 is greater than retention cavity length 269. In addition, secondary seal 203 extends from a radially inner side 324 to a radially outer side 322 and defines a seal height 314 therebetween. In the exemplary embodiment, seal height 314 is approximately equal to retention cavity height 270 of retention cavity 224 to facilitate retaining secondary seal 203 within retention cavity 224. Secondary seal 203 also extends circumferentially between a first side 330 and a second side 332 and defines a circumferential length 316 therebetween. In the exemplary embodiment, circumferential length 316 is greater than circumferential width 211, such that secondary seal 203 extends circumferentially through retention cavity 224 of more than one film-riding seal segment 128. In alternative embodiments, secondary seal 203 is configured in any suitable manner that enables sealing system 127 to function as described herein.

[0037] In the exemplary embodiment, secondary seal 203 is resiliently deformable inwardly from resting width 312, such that first leg 308 and second leg 310 move toward each other and are receivable within retention cavity 224 during installation. Moreover, after insertion into retention cavity 224, secondary seal 203 is released such that first leg 308 and second leg 310 are biased back towards resting width 312, such that secondary seal 203 is compressed within retention cavity 224 to facilitate first leg 308 sealingly interfacing with an axially adjacent face of primary sealing extension 216 and second leg 310 sealingly interfacing with an axially adjacent face of secondary seal retention member 220.

[0038] Thus, in the exemplary embodiment, secondary seal 203 retained in retention cavity 224 is configured to exert a force on primary sealing extension 216 in the axially upstream direction. The axial force exerted by secondary seal 203 on primary sealing extension 216 inhibits, via friction, radial motion of primary sealing extension 216, and thus of seal pad 202, relative to stationary seal body 200, thus providing a damping effect for radial motion of seal pad 202. Moreover, a magnitude of the damping effect of secondary seal 203 on seal pad 202 is selectable based on design parameters of secondary seal 203, such as resting width 312 and a spring constant of secondary seal 203, for example. Thus, secondary seal 203 is selectable to provide substantially critically damping of an expected radial movement of seal pad 202 relative to stationary seal body 200 during operation of rotary machine 100, thereby facilitating improved dynamic performance of film-riding seal segment 128. In alternative embodiments, secondary seal 203 provides other than substantially critical damping of radial motion of seal pad 202.

[0039] FIG. 9 is a perspective view of an alternative embodiment of film-riding seal segment 128 (shown in FIG. 3) illustrating exemplary angled grooves 400. The embodiment shown in FIG. 9 is substantially identical to the embodiment shown in FIG. 3, except seal pad 202 includes a plurality of angled grooves 400. In the exemplary embodiment, seal pad 202 includes six angled grooves 400 defined in radially inner face 244 of seal pad 202. Angled grooves 400 extend radially outward from radially inner face 244 to a groove depth 408. Each angled groove 400 extends through leading face 212 of seal pad 202 over a groove width 404, such that fluid from upstream of seal pad 202 is directed into angled grooves 400. Moreover, angled grooves 400 extend axially downstream from leading face 212 of seal pad 202 at an angle 402 relative to longitudinal axis 215 of seal pad 202. In the exemplary embodiment, angled grooves 400 facilitate retaining fluid between seal pad 202 and rotor 106. In alternative embodiments, angled grooves 400 are configured in any suitable manner and/or in any suitable number that enables film-riding seal segment 128 to function as described herein.

[0040] The above-described embodiments of sealing systems overcome at least some disadvantages of known film-riding seals. Specifically, the embodiments include a seal segment including a stationary body and a seal pad coupled to the stationary body via flexible arms. The flexible arms enable the seal pad to be radially compliant to radial movements of the rotor. In some embodiments, a secondary seal is arranged to create a damping force on radial movement of the seal pad relative to the stationary body, further improving a dynamic performance of the seal. Additionally or alternatively, in certain embodiments, the seal pad has a divergent section adjacent to the trailing edge. The divergent section facilitates cooperating with a non-divergent portion of the seal pad to allow the seal pad to set at a clearance at which hydrostatic film-riding forces and hydrodynamic film-riding forces between the seal pad and rotor complement each other to facilitate improving performance of the seal segment. In at least some embodiments, working fluid leakage reduction between the rotor and a casing is achieved without modifying the existing rotor and/or casing.

[0041] Exemplary embodiments of a film-riding seal segment and sealing system are described above in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of methods may be utilized independently and separately from other components and/or steps described herein. For example, the system may also be used in combination with other machines and methods, and is not limited to practice with only a steam turbine assembly as described herein. Rather, the embodiments can be implemented and utilized in connection with many other machine applications.

[0042] Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. Moreover, references to“one embodiment” in the above description are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

[0043] This written description uses examples, including the best mode, to illustrate the disclosure and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.