Abstract:
A brush seal is provided between a first stationary component and a second rotating component. A cooling medium is provided through a plurality of jet nozzles for flow along an upstream surface portion of the brush seal bristles and along the rotating component surface adjoining the tips of the bristles. The cooling medium cools the brush seal bristles to a temperature below the temperature of the working fluid passing through the turbine. The jet nozzles may be arranged in the shroud or in the upstream backing plate of the brush seal to direct the cooling medium toward the juncture of the brush seal and the sealing surface.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to brush seals for sealing between adjacent components and, more particularly, relates to brush seals for use in high temperature environments, such as between shrouds and bucket tips or covers in gas or steam turbines, and requiring cooling by a cooling medium. 
     Brush seals are increasingly being used in gas and steam turbine applications. In many instances, brush seals are being installed in lieu of, or in conjunction with, labyrinth-type seals, and at various locations in the apparatus. Brush seals are also being utilized at locations subjected to increasing temperatures and pressures. A typical brush seal comprises a plurality of elongated bristles formed of a ceramic or metal material disposed between one or more backing plates. The brush seal is conventionally fixed to one component, e.g., a fixed component, with the bristle tips projecting from the seal to engage another component, e.g., a rotatable shaft, to form a seal therewith. 
     Current brush seals however, cannot withstand operating environments in which the temperatures are above 1200° F. Application of brush seals to areas of the turbine having higher temperatures has thus been inhibited by this temperature limitation. For example, in hot gas path applications in gas turbines, such as bucket tip sealing, operating temperatures can be 1800° F. or higher. Consequently, there is a need for an improved brush seal for use in applications at high temperatures. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment of the invention, a film-cooled high temperature brush seal is cooled by jets of a cooling medium injected adjacent the upstream side of the brush seal; that is, in one preferred embodiment, a thin film of cooling medium serving as a thermal insulator flows along upstream surfaces of the bristles and past the bristle pack to maintain temperature of the bristles below a predetermined temperature, for example, 1200° F. The cooling flow protects the bristles from the high temperature working fluid medium. A typical application of this preferred embodiment includes provision of a brush seal formed in the shroud surrounding bucket tip covers of a gas turbine. The buckets lie in the hot gas path with the bristles projecting from the shrouds for engagement with the rotating components, e.g., bucket tip covers. Nozzles are circumferentially spaced one from the other about the shrouds for flowing jets of a cooling medium in a generally radial direction to provide a thermal insulating film of the cooling medium on upstream surfaces of the brush seal bristles and along the rotating component, i.e., the bucket tip covers. In conjunction with a typical brush seal arrangement, i.e., a brush seal having a pair of backing plates on opposite sides of the bristle pack and with the upstream backing plate spaced from the bristle pack, a spacer or a flange between the upstream backing plate and the bristle pack is provided. The spacer or flange includes a plurality of circumferentially spaced nozzles to flow the cooling medium between the upstream backing plate and the upstream face of the bristle pack to reduce the temperature of the bristles to well below the temperature of the hot gas stream; that is, the nozzles provide a thin, thermally insulating film of cooling medium between the bristles and the hot gas path. Additionally, the cooling medium flows along the bucket tip covers, cooling the covers and buckets. 
     In another preferred embodiment of the invention, the nozzles are arranged upstream of the brush seal and open through the stationary component. For example, the nozzles may be arranged upstream of the upstream backing plate and open through the shroud. The nozzles preferably lie in communication with a plenum containing the cooling medium, e.g., air. The jets of air thus flow along the forward surface of the backing plate into the gap between the upstream backing plate and the rotating component, and form a thin-film layer along the upstream faces of the bristles adjacent their tips. The thin film of air then flows through the juncture of the bristle tips and the bucket covers. In another form, the nozzles may be angled from the shrouds to direct the jets of cooling medium directly at the juncture of the bristle tips and the rotating component. The nozzles may also be formed through the upstream backing plate such that the jets of cooling medium are angled or directed onto the juncture of the bristle tips and the rotating component. 
     In still another preferred embodiment of the invention, sealing apparatus comprises first and second components movable relative to one another and defining a gap therebetween for flowing a fluid medium at a high temperature, and a brush seal carried by the first component for disposition between the first component and the second component and sealing the gap between high and low pressure regions on respective opposite sides of the seal. The brush seal includes a plurality of projecting bristles having free ends terminating in bristle tips in engagement with the second component so as to form a seal between the components to minimize fluid flow from the high pressure region through the gap to the low pressure region, and means for forming a thin layer of cooling medium along a surface portion of the bristles to thermally insulate the bristles from the high temperature fluid medium. 
     In a further preferred embodiment of the invention, a rotary machine comprises a rotatable component and a component that is fixed against rotation, or stationary. The components are disposed about an axis, with a brush seal carried by one of the components including a plurality of bristles projecting from the one component and having free ends terminating in bristle tips in engagement with another of the components to minimize flow of a high temperature fluid from a high pressure region on one side of the brush seal to a low pressure region on an opposite side of the seal. A plurality of nozzles are carried by one component for directing a cooling medium toward a juncture of the bristle tips and the other component to form a layer of cooling medium adjacent a surface of the bristles on an upstream side thereof to thermally insulate the bristles from the fluid. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary cross-sectional view of a prior art brush seal in a shroud of a turbine in sealing relation with a bucket tip cover; 
     FIG. 2 is an enlarged fragmentary cross-sectional view of a film-cooled high temperature brush seal according to a preferred embodiment of the invention; and 
     FIGS. 3-6 are views similar to FIG. 2 illustrating further embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an annular brush seal, generally designated  10 , constructed in accordance with the prior art. This prior brush seal  10  includes a pair of backing plates  12  and  14  on opposite sides of elongated bristles  16 . Backing plates  12  and  14  and the proximal ends of bristles  16  are typically welded together, for example, by a weld  18 . Brush seal  10 , as illustrated, is mounted to a shroud  20 , and bristle tips  22  bear against the covers of buckets  24 , effecting a seal therewith. The buckets and brush seal lie in an annular gas flowpath which, at increasingly higher temperatures, may inhibit or prevent use of a brush seal in such high temperature applications. 
     FIG. 2, illustrates an annular brush seal, generally designated  30 , constructed in accordance with a preferred embodiment of the invention. Brush seal  30  may be mounted in a groove  31  formed in an annular shroud  32  constituting a first stationary component surrounding, and about the axis of, a second rotary component, for example, a bucket  34 . The brush seal is provided in a plurality of arcuate segments, e.g., six segments, each extending about 60°. The brush seal also seals between a high pressure region on an upstream side thereof and a lower pressure region on a downstream side thereof. As illustrated, brush seal  30  includes an upstream backing plate  36 , a downstream backing plate  38 , a plurality of bristles  40  disposed between the backing plates, and a spacer or flange  42  disposed between upstream backing plate  36  and the proximal ends of bristles  40 . The bristles are elongated, formed of metal or ceramic materials and disposed in a bristle pack  43 . Bristles  40  generally extend at a cant angle relative to the radii of the axis of rotation of buckets  34 , for example, a cant angle of about 30-40° in the direction of rotation. Spacer  42  may comprise a flange integral with upstream backing plate  36 . As illustrated, a weld  44  maintains the backing plates, spacer and bristles connected one to the other along the radially outermost margin of brush seal  30 . 
     In the apparatus of FIG. 2, a thin film of cooling medium, for example, air, is supplied for flow along the forward surface portion, or face, of the bristle pack  43 . The flow is provided by a plurality of circumferentially spaced nozzles  46  formed through spacer  42  or through openings between the spacer and either upstream plate  36  or bristles  40 . Nozzles  46  are in communication with a supply or plenum  48  containing the cooling medium. The cooling medium is under pressure and therefore flows through nozzles  46  and along the forward face of bristle pack  43  between the bristle pack and the downstream face of upstream backing plate  36 . The cooling medium exits adjacent the juncture of bristle tips  50  and sealing surface  52  of rotating component  34 . The flow of cooling medium produces a thin layer of cooling medium that acts as a thermal insulator between the hot gases in the hot gas flowpath, generally indicated by arrows  54 , and the bristle pack. The bristles are thus cooled to a temperature well below the temperature of the hot gas stream and below the high temperature limitations of the bristle material. Also, portions of bucket sealing surface  52  are thermally insulated from the hot gas and therefore cooled. 
     In FIG. 3, wherein like reference numerals advanced by 100 represent like parts, a brush seal  130  is shown mounted in a groove  131  in a shroud  132 . Upstream backing plate  136  is spaced from the forward face of bristle pack  143  containing bristles  140 , while downstream backing plate  138  serves to prevent deflection of bristles  140  in an axially downstream direction. In this embodiment, nozzles  146  are provided in shroud  132  and are in communication with a plenum  148  for supplying cooling medium to the nozzles. In this form, jets of cooling medium from the nozzles flow along the upstream surface of upstream backing plate  136  and along and through tips  150  of brush seal  130  in engagement with surface  152  of buckets  134 . Thus a thin film of cooling medium is provided along bristle portions  153  adjacent tips  150 , thereby effectively thermally insulating such bristle portions from the hot gases of the hot gas path. Surface  152  of rotating component  134  is also cooled by the flow of the cooling medium. 
     In FIG. 4, wherein like reference numerals advanced by  100  relative to the preceding embodiment are applied to like parts, brush seal  230  is similarly disposed in a groove  231  of a shroud  232 . In this form, however, a plurality of circumferentially spaced nozzles  246  are formed in shroud  232  and open at an angle relative to the axis of rotation and into the gas path such that the jets of cooling medium flowing from a supply or plenum  248  are directed to the juncture of bristle tips  250  and sealing surface  252 . As illustrated, nozzles  246  are located axially upstream of brush seal  230 . A thin film of cooling medium thus flows along portions  253  adjacent tips  250 , thereby thermally insulating bristle portions  253  from the hot gases in the flowpath. The cooling medium also flows along surface  252 , cooling the bucket portions adjacent the cooling flow. 
     In FIG. 5, wherein like reference numerals advanced by 100 are applied to like parts, brush seal  330  includes an upstream backing plate  336 , a downstream backing plate  338 , and a plurality of bristles  340  forming a bristle pack  343  disposed between the plates, the upstream plate  336  being spaced from the forward surface of bristle pack  343 . In this form, circumferentially spaced nozzles  346  are angled through the upstream backing plate  336  such that jets of cooling medium flow from the cooling medium supply or plenum  348  through the nozzles  346  directly onto the juncture of bristle tips  350  and sealing surface  352 . As in the embodiments discussed above, a thin film of thermally insulating cooling medium is provided along bristle portions  353  adjacent bristle tips  350  and sealing surface  352  of the rotating component. 
     In FIG. 6, wherein like reference numerals advanced by  100  are applied to like parts as in the preceding embodiment, a brush seal  430  includes an upstream backing plate  436 , a downstream backing plate  438 , and a plurality of bristles  440  forming a bristle pack  443  between the plates. In this form, shroud  432  mounts a plurality of circumferentially spaced nozzles  446  in communication with a plenum  448  for supplying cooling medium through the nozzles. Brush seal  430  of FIG. 6 is similar to the brush seal illustrated in FIG. 3 except that brush seal  430  is situated adjacent an upstream portion of the buckets. In this embodiment, the brush seal reduces the bucket temperature along substantially the entirety of the bucket tip or cover surface  452 , thereby increasing bucket life. 
     It will be appreciated that the brush seal hereof may be employed in other and diverse applications and not necessarily only between a fixed component and a rotating component as specifically described herein. Thus, the brush seal hereof may be used where brush seals have not been previously used, e.g., sealing between irregularly-shaped components in high temperature environments such as between a combustion transition piece and a first-stage inlet nozzle of a turbine. 
     While only certain preferred features of the invention have been illustrated and described, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.