Abstract:
A brush seal assembly for use between two stationary turbine components includes a plurality of arcuate carrier segments, each having a front plate and a back plate having substantially equal radial length dimensions, and a bristle pack sandwiched therebetween. The front plate and the back plate define a hook portion adapted to be received in an annular slot in a first radially inner turbine component, the bristle pack extending substantially radially outwardly beyond the front and back plates and supported by the back plate along the entire radial length dimension and by the front plate along a minor portion of the radial length dimension, thereby leaving an axial gap between the bristle pack and the front plate along a major portion of the radial length dimension. The bristle pack is fixedly secured to the back plate and the front plate along the minor portion of the length dimension, and the bristle pack is slanted in a circumferential clockwise or counterclockwise direction and adapted to sealingly contact a second radially outward turbine component.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to gas turbine compressors and, in an exemplary but nonlimiting example, to seals between static components at exit stages of the compressor. 
         [0002]    Seals are oftentimes employed between static components of a turbine. For example, in a steam turbine, seals between the inlet and the inner web of the first stage nozzle have included a plurality of labyrinth seal teeth mounted on sealing ring segments which may be spring biased to engage and seal against the opposing stationary component surface. The packing ring seals carrying the labyrinth seal teeth can be preloaded and oriented in either radially outward or radially inward directions, depending on which component of the inlet region the seals are mounted. While labyrinth seals have been effective for minimizing leakage flows in these high pressure regions, the static annular or cylindrical seal components may become out-of-round or distorted, which can result in increased leakage flow from the high pressure region to the low pressure end seal packing ring region. Thermal distortion or creep of one or both of the components can cause an out-of-roundness and the creation of a gap between the tips of the labyrinth seal teeth and the surface that they are sealing against. Thus, as long as the labyrinth seal teeth and the component parts remain circular, the labyrinth teeth are effective to minimize leakage flows. However, if one or both of the sealing surfaces becomes out-of-round, a generally crescent-shaped gap is created between the tips of the teeth and the adjacent sealing surface, resulting in leakage across the seal through the gap and a performance loss. 
         [0003]    Another static seal arrangement is shown in commonly-owned U.S. Pat. No. 6,951,339. In that patent, a turbine construction includes a nozzle supporting a plurality of airfoils circumferentially spaced one from the other between inner and outer barrels, and carrying an inner web. In the inlet region of the turbine flowpath, a static brush seal is disposed between the inlet and a radially-opposed flange of the inner web. The brush seal includes a plurality of bristles disposed between a pair of side plates on opposite axial sides of the bristles. The brush seal is carried by either the inner web or the inlet, and the bristles are preloaded to engage the other of the inner web or inlet. 
         [0004]    In other situations, a leak passage exists between the last stage/exit vane tips/shrouds supported from outer casing structures and inner casing structures of a compressor that can affect compressor performance in two ways. The leakage air can either re-enter and mix with the main compressor flow and cause aero-performance losses or, the leakage air can pass through the high pressure packing region (both stator and rotor) and reduce compressor efficiency. 
         [0005]    There remains a need for improved static sealing efficiency with respect to gaps or leak passages that exist between stationary last stage/exit vanes/tip shrouds supported from outer case structures, and stationary, radially-adjacent inner casing structures e.g., between the inner barrel of the compressor discharge case (CDC) and a stator vane shroud ring at the compressor exit stage(s). 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In accordance with one exemplary but nonlimiting embodiment, the invention provides a brush seal assembly for use between two stationary turbine components comprising a plurality of arcuate carrier segments, each having a front plate and a back plate having substantially equal radial length dimensions, and a bristle pack sandwiched therebetween, the front plate and the back plate defining a hook portion adapted to be received in an annular slot in a first radially inner turbine component, the bristle pack extending radially outwardly beyond the front and back plates and supported by the back plate along the entire radial length dimension and by the front plate along a minor portion of the radial length dimension, thereby leaving an axial gap between the bristle pack and the front plate along a major portion of the radial length dimension; the bristle pack fixedly secured to the back plate and the front plate along the minor portion of the length dimension; and wherein the bristle pack is slanted in a circumferential clockwise or counterclockwise direction. 
         [0007]    In another exemplary but nonlimiting embodiment, the invention provides a brush seal assembly located between radially inner and radially outer turbine components, substantially concentrically arranged relative to each other, and each having upper and lower half-sections joined along a substantially horizontal split line, comprising at least three arcuate brush seal segments seated in an arcuate slot in the radially inner turbine component and which, when combined, form a half-annular seal terminating at the substantially horizontal split line; each of the at least three arcuate brush seal segments having a front plate and a back plate and a bristle pack sandwiched therebetween, the bristle pack extending radially outwardly beyond the front and back plates and engaged with the radially-outer turbine component in a cold condition and slanted in a circumferential clockwise or counterclockwise direction; and wherein two of the at least three arcuate brush seal segments adjacent the split line have bristle packs with radial length dimensions less than remaining ones of the at least three arcuate brush seal segments. 
         [0008]    In still another exemplary but nonlimiting embodiment, the invention provides a brush seal assembly located radially between an annular inner barrel of a compressor and an annular stator vane shroud ring for preventing leakage flow in a direction opposite to a direction of main flow through the compressor, the shroud ring comprised of plural arcuate shroud ring segments, and wherein the annular inner barrel and the stator vane shroud ring each have upper and lower half-sections joined along a substantially horizontal split line, the brush seal assembly comprising a plurality of arcuate brush seal segments seated in an annular slot formed in the inner barrel, each of the plurality of arcuate brush seal segments having a front plate and a back plate and a bristle pack sandwiched therebetween, the bristle pack extending radially outwardly beyond the front and back plates and engaged with the stator vane shroud ring in a cold condition, the bristle pack slanted in a circumferential clockwise or counterclockwise direction and in an axial forward or aft direction; and wherein the arcuate shroud ring segments are, in number, equal to or greater than the brush seal segments. 
         [0009]    The invention will now be described in detail in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a section view of an arcuate segment incorporating a brush seal in accordance with a first exemplary but nonlimiting embodiment; 
           [0011]      FIG. 2  is a partial section view of the arcuate segment shown in  FIG. 1  expanded to show more of the CDC inner barrel and a compressor exit stage stator vane shroud ring, with the brush seal assembly located at a forward end of the CDC inner barrel; 
           [0012]      FIG. 3  is a perspective view, partially sectioned, of the brush seal assembly of  FIG. 1  seated in the CDC inner barrel; 
           [0013]      FIG. 4  is and end view of an annular, segmented brush seal assembly in accordance with an exemplary but nonlimiting embodiment; 
           [0014]      FIG. 5  is an enlarged detail  5  taken from  FIG. 4 ; 
           [0015]      FIG. 6  is an enlarged detail  6  taken from  FIG. 4 ; 
           [0016]      FIG. 7  is an enlarged detail for a brush seal segment located in radial opposition to an interface between a pair of adjacent vane shroud ring segments; 
           [0017]      FIG. 8  is a partial perspective of a brush seal segment and an anti-rotation locking key in accordance with another feature of the invention; 
           [0018]      FIG. 9  is a partial section view similar to  FIG. 2  but illustrating an alternative brush seal assembly; 
           [0019]      FIG. 10  is a simplified schematic similar to  FIG. 9  but illustrating a brush seal relocated to an aft end of the CDC inner barrel in light of a differently configured compressor exit stage stator vane shroud ring; 
           [0020]      FIG. 11  is a schematic generally similar to  FIG. 2  but illustrating an alternative brush seal assembly at the forward end of the CDC inner barrel; 
           [0021]      FIG. 12  is a schematic showing how the bristle pack in a forward-located brush seal assembly may be slanted or inclined in one axial direction; and 
           [0022]      FIG. 13  is a schematic similar to  FIG. 13  but showing how the bristle pack in an aft-located brush seal assembly may be slanted or inclined in an opposite axial direction. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    With reference initially to  FIGS. 1-3 , a static brush seal assembly  10  in accordance with a first exemplary but nonlimiting embodiment is located radially between an annular, stationary, inner barrel portion (or, simply, inner barrel)  38  of the compressor discharge casing (CDC)  40  and a stationary stator vane shroud ring  48 . The brush seal assembly  10  includes a plurality of arcuate segments which, when assembled, form an annular brush seal ring (see  FIG. 4 ) as discussed further herein. Each arcuate segment of the brush seal assembly  10  is composed of a front plate  12  and a back plate  14  located on opposite sides of a brush or bristle pack  26 . The front and back plates together form a radially-inner hook  16 . Specifically, the hook  16  is defined by the relatively wide inner hook portion  18  of the back plate  14  and a similar relatively wide inner hook portion  20  of the front plate  12 . 
         [0024]    Extending radially outwardly from the inner hook portion  18  of the back plate  14 , there is relatively narrow neck  22  extending to a radially outer and relatively wide outer hook portion or flange  24 . As noted above, the brush or bristle pack  26  is sandwiched between the front plate  12  and the back plate  14 , and extends substantially radially outwardly beyond the outermost surfaces of both the front and back plates  12 ,  14 , respectively. The brush or bristle pack  26  is substantially fully engaged along a surface  28  of the back plate  14  which faces the front plate  12 . The bristle pack  26  is also engaged by a surface  30  of the front plate  12  that faces the back plate  14 . The surface  30 , however, extends only a small or minor portion of the radial length of the front plate  12  and connects to an offset radial surface  32  of the front plate  12 , leaving a radially-extending, axial gap  34  between a major portion of the length of the bristle pack  26  and the surface  30  of the front plate  12 . The front and back plates  12  and  14 , taken together, have a generally I-beam shape, with one side of the radially-outer I-beam “flange” omitted (axially-opposed to the outer hook flange  24 ), and with the partial radial gap  34  added in a direction perpendicular to the inner and outer “flanges” or hooks. 
         [0025]    The arcuate segments of the brush seal assembly  10  are located within an inverted T-shaped slot  36  formed in the annular, stationary, inner barrel  38  of the CDC  40 . Thus, the inner hook  16  of each of the brush seal assembly segments  10  is received within the wider cross portion  42  of the T-shaped slot, while the narrow neck portion  22  is received within a stem portion  44  of the T-shaped slot. The outer hook portion  24  is supported on an axial surface  46  of the inner barrel  38 . The gap  34 , which may be on the order of 0.10 in. in width, accommodates changes in bristle pack width due to radial excursion loading with the mating part. i.e. with inner barrel  38 . Differential axial length dimensions for the inner hook portions  18  and  20  relative to the width of the stem portion  44  of the T-shaped slot  36  insure against improper reverse installation of the segments within the T-shaped slot. 
         [0026]    The bristle pack  26  may be formed of metal bristles, or non-metal bristles made from materials such as ceramics, carbon fiber or silica. The bristle pack  26  is secured between the facing surfaces  30  and  28  of the front and back plates  12 ,  14 , respectively, by welding, crimping, high temperature adhesives or other suitable attachment techniques. 
         [0027]    It may be seen that the bristle pack  26  is engaged with the stationary stator vane shroud ring  48  that surrounds the inner barrel  38  in order to seal leakage flow axially along the inner barrel, between the inner barrel and the stator vane shroud ring. As shown in  FIGS. 1 and 2 , the leakage flow direction is indicated by the flow arrow F, which is opposite the main flow of air exiting the compressor indicated in  FIG. 2 . However, the invention also contemplates employing the brush seal assembly in situations where the main flow and leakage are in the same direction. 
         [0028]    As noted above, the brush seal assembly may be composed of plural arcuate segments which, together, make up a 360° annular brush seal ring (see  FIG. 4 ) received in the annular T-shaped slot  36 . As will be discussed further herein, the arcuate segments may be arranged to have abutting edges at the horizontal interfaces between the upper and the lower half-sections of the inner barrel  38  and shroud ring  48 , sometimes referred to as the horizontal “split line”. For purposes of discussion herein, it will be assumed that there are at least three brush seal segments above and below the split line, although the invention is not so limited. It is also noted here that the stator vane shroud ring is also composed of plural arcuate segments and in the preferred arrangement, the number of shroud segments is equal to or unequal to the number of brush seal segments. 
         [0029]    Thus, the bristle pack  26  extends substantially radially outwardly between two stationary turbine components  38 ,  48 , with an interference fit between the free ends of the bristles of the bristle pack and the stator vane shroud ring  48 . In this regard, the cold interference in the exemplary embodiment is about 0.05 in. and the cold gap  34  is between about 0.10 to 0.14 in. The cold interference is shown at  33  in  FIG. 1  by indicating that portion of the length of the bristle pack which extends beyond the surface of the vane shroud ring  48  with which it is engaged. In reality, the bristle pack will be compressed and thus slanted to one side to accommodate the interference fit. In the exemplary embodiment, the bristles  50  ( FIGS. 5-7 ) of the bristle pack  26  may be slanted in a clockwise circumferential direction, viewing the brush assembly from a downstream position (relative to the compressor main flow). In  FIGS. 5-7 , the bristles  50  in substantially diametrically opposed segments  52  and  60  are slanted or inclined in a clockwise direction. In the exemplary embodiment, the angle may be, for example 45°±5°, and may be substantially identical to angled segment end cuts. It will be appreciated however, that the bristles  50  may be slanted in either a clockwise or counterclockwise circumferential direction. The specified cold build radial interference with the vane shroud ring  48  maximizes the seal effectiveness at operating conditions, countering the effects of 3D distortions (out of roundness effects), hot opening due to thermal loading of the parts, and manufacturing tolerance stack-up variations that can lead to gap opening between the bristle pack and the vane shroud ring  48 . 
         [0030]      FIG. 7  shows another feature of the invention where the number of shroud segments is greater than the number of brush seal segments, and specifically at the interface of adjacent vane shroud ring segments  70 ,  72 . Because the interfaces of adjacent brush seal segments are circumferentially offset from adjacent shroud ring segments, the bristles  50  of the brush seal segment  74  will extend into and substantially fill the gap between the shroud ring segments. 
         [0031]    It is also a feature of this invention that the radial height of the bristle pack may be decreased in those brush seal segments at the horizontal interface or split line of the upper and lower inner barrel half sections (as shown, e.g., in  FIGS. 5 and 6 ). Specifically, in one exemplary embodiment shown in  FIG. 8 , the radial height of the bristle pack  76  may be reduced from the split line end of the segment  78  extending less than 1/10 of the segment circumferential length. The reduced height can be the form of a uniform reduction as shown at  80  or a tapered reduction (shorter to longer in a direction away from the split line). This arrangement facilitates assembly and disassembly of the compressor vane assembly without damaging the bristles of the split line segments of the brush seal assembly  10 . The specific differential radial height dimensions may vary depending on turbine model, etc. 
         [0032]    It is still another feature to apply wax to the ends of the bristle pack  26  (or  76 ) during shipping and assembly. Applying a thin layer of wax to the outer ends of the bristles, after canting the bristles to one side as when installed, holds the bristles in the slanted position, thereby protecting the bristles from damage during shipping and handling, as well as during installation. In the exemplary embodiment, if the bristles have a free unsupported radial length, measured from the radially outer surface of the outer hook  24  to the tip of bristle pack  26  in a radial direction of, for example, 0.1 to 0.2 inch, after waxing the radial height of the bristle pack may be reduced to permit a nominal gap at cold build between the bristle pack  26  and the inner diameter of the vane shroud ring  48  of about 0.02 to 0.1 inch The wax will be melted away during operation of the compressor/turbine when the operating temperature reaches about 135-200° F. (57-93° C.). Carnauba wax has been found to meet the requirements of sustaining integrity of reduced height bristles until assembly, and the melting away completely at turbine operating temperature. Other suitable waxes meeting the specified requirements may be utilized as well. 
         [0033]      FIG. 8  also illustrates one or more “keys”  82  may be added in notches or recesses  84  formed in the inner barrel and located to engage the end or ends of one or more segments of the brush seal assembly  10  to prevent rotational movement of the segments within the annular slot  36 . To accommodate the key  82 , it may be desirable to provide a cut-out  86  in the front plate  12  so that the key  82  does not otherwise interfere with the assembly and positioning of the brush seal carrier segments and to provide a reaction surface against the key. The key  82  may have any desired circumferential length, and, advantageously, will be located at least where the carrier segments interface with the horizontal split line. 
         [0034]    In an alternative exemplary embodiment shown in  FIG. 9 , a brush seal assembly segment  88  such that the front plate  90  is also provided with an outer hook portion  92  to complement the outer hook portion  94  on the back plate  96  supported on surface  98  of the inner barrel  38 . The exact configuration is dependent on the specific compressor/turbine model and an amount of space available to accommodate the structural features of the brush seal carrier segment. 
         [0035]      FIG. 10  illustrates yet a further exemplary but nonlimiting embodiment where the brush seal carrier segment  100  is located at an aft portion  104  of the inner barrel  106 . The brush seal carrier segment  100  is otherwise substantially similar to the brush seal segment shown in  FIG. 1  except that a circumferential groove  108  is formed in the radially inner surface of the inner hook  110 . 
         [0036]    In  FIG. 11  another exemplary but nonlimiting embodiment is shown where a brush seal segment  112  is located in a forward portion of the inner barrel  114 , similar to  FIG. 2 , but here, the inner barrel  114  is formed with a reverse L-shaped slot  116  such that the inner hook  118  is provided with a single inner hook portion  120  on the back plate  122 . The front plate  124  includes an upper hook portion  126  complementing the upper hook portion  128  of the back plate  122 . The brush seal carrier segment  112  is otherwise substantially similar to the brush seal segment shown in  FIG. 9 , but with an inner annular groove  130  similar to the groove  108  in the carrier segment shown in  FIG. 10 . 
         [0037]    With reference now to  FIGS. 12 and 13  it is also within the scope of the invention to slant or incline the bristles axially in either an upstream or downstream direction. In  FIG. 12 , a brush seal carrier segment  132  is located in a forward portion of an inner barrel  134 , and the bristle pack  136  is slanted in a forward axial direction. In  FIG. 13 , the brush seal carrier segment  138  is located in an aft portion of an inner barrel  140  with the bristle pack  142  slanted in an aft axial direction. 
         [0038]    It will be understood that the bristle packs as described herein may be slanted circumferentially and slanted axially in clockwise, counterclockwise, and fore or aft directions, respectively. 
         [0039]    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.