Abstract:
Shroud assembly for use in a turbine, having an outer shroud having a side proximate to flow of operative fluid of the turbine, the side having a boss and an outer shroud aperture extending through the boss. An inner shroud is located between the side of the outer shroud proximate to the flow of operative fluid and the operative fluid flow of the turbine, the inner shroud having an inner shroud aperture which is dimensioned to fit over the boss.

Description:
[0001]    The present invention relates to a method for attaching a ceramic matrix composite (CMC) shroud and discourager to a metal outer shroud in such as way as to allow for adjustment of the CMC shroud and/or the discourager, for example during installation or due to expansion and/or contraction, while preventing hot gas in the turbine from reaching the outer metal shroud. The method involves utilizing a key slot arrangement for connecting the CMC shroud and discourager to the outer metal shroud. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is well known that industrial gas turbine and aircraft engine shrouds operate in a high temperature environment and require cooling methods to obtain a useful design life cycle. An alternative to using a metal shroud with cooling air is to use a CMC material for the shroud, thus eliminating the required cooling of the shroud due to the CMC&#39;s superior temperature capability over metal. 
         [0003]    Prior attempts to solve this problem have been made using conventional metal seals or complex assemblies. For example, one approach has been to use multiple pins to hold the CMC or to use hooks formed in the CMC component. Other prior art uses a CMC bonded to a ceramic core with pins going through the core. 
         [0004]    These arrangements utilizing pins have two distinct disadvantages, namely (1) additional cooling air is required to maintain design life of the seal, and (2) higher cost due to the use of expensive high temperature custom made metal pins. Metal pins at the flow-path also require cooling air to meet the required design life, thus reducing the benefit of the CMC. 
         [0005]    A more effective way of mounting the CMC shroud to the outer metal shroud and preventing hot gases from contacting the metal outer shroud is desirable. The present invention seeks to satisfy that desire. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In one aspect, the invention provides a shroud assembly for use in a turbine. The shroud assembly has an outer shroud with a side proximate to a flow of an operative fluid of the turbine, the side being provided with a boss and an aperture extending through the boss. An inner shroud is positioned between the side of the outer shroud proximate to the flow of operative fluid and the operative fluid flow of the turbine. The inner shroud is provided with an aperture which is dimensioned to fit over the boss. 
         [0007]    In another aspect, a discourager assembly is enclosed within the inner shroud and is positioned offset from the inner shroud so as to extend past the inner shroud and into an inner shroud of a neighboring shroud assembly. The discourager assembly has a discourager with an aperture and a plate member with an aperture mounted on a surface of the discourager. The discourager aperture and the plate member aperture are aligned with the inner shroud aperture and the boss to facilitate insertion of a bolt to fasten the assembly together. 
         [0008]    In another embodiment, the boss in the outer shroud is upstanding above the plane of the surface of the outer shroud in which the boss is present. The boss generally has a square profile when viewed in plan, and typically has rounded corners. 
         [0009]    In a further embodiment, the apertures in the inner shroud and the discourager are rectangular shaped in which the longer opposite sides of the rectangle are separated by a distance which is slightly larger than the distance between the opposite sides of the square boss in the outer shroud. In this way, the rectangular slot of the shroud or the discourager can be placed over the square boss such that the upstanding surfaces of the boss can be in contact with, and slide relative to, the longer sides of the rectangular aperture, thereby allowing for adjustment of the position of the discourager within the inner shroud. 
         [0010]    In yet another embodiment, the plate member has at least one aperture which aligns with the boss of the outer shroud and the rectangular aperture of the inner shroud. In a typical embodiment, the plate member is provided with two apertures which align with two bosses and two rectangular apertures in the inner shroud. 
         [0011]    In a further embodiment, the plate member is accommodated in a recess in a surface of the discourager. In an alternative embodiment, the plate member is housed in an internal space within the discourager. 
         [0012]    The apertures in the plate member are typically threaded to accommodate a fastening means such as a bolt. In this way, the inner shroud/discourager assembly can be mounted to the outer shroud by way of a bolt threadedly engaged with the plate member without the bolt force being applied directly to the inner shroud. Adjustment of the discourager within the inner shroud can be achieved by sliding relative movement of the discourager or the inner shroud by virtue of the rectangular apertures, prior to tightening with the bolt. 
         [0013]    The size and stiffness of the plate member is used to tune the amount of radial spring force that is applied to the inner shroud and discourager. The bolt is contained in the outer shroud block where cooling is not necessary. Typically, the inner shroud is fabricated from a ceramic matrix composite (CMC) which allows for greatly reduced cooling air requirements. 
         [0014]    Use of a CMC inner shroud with no cooling air additionally affords the advantage of an engine performance benefit in efficiency and output. The invention enables the use of CMC inner shrouds at a much lower cost structure than has previously been possible. The attachment method of the invention does not require the use of custom pins made from exotic materials, and thus reduces the overall cost of the associated hardware. In addition, the attachment is shielded from the hot gas environment, thereby significantly reducing the cooling and purge air requirements of the attachment compared to what has been done previously. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of an outer metal shroud assembly including a hollow CMC inner shroud and discourager seal located internally of the CMC inner shroud; 
           [0016]      FIG. 2  is a cross-sectional end view of the outer metal shroud assembly of  FIG. 1  showing attachment of the CMC inner shroud and discourager seal assembly via a plate member/bolt arrangement to a boss on a surface of the outer metal shroud; 
           [0017]      FIG. 3  is a view of the outer metal shroud assembly of  FIG. 1  from the underside showing the plate member with two threaded apertures mounted on a surface of the discourager and aligned with two bosses in the outer metal shroud; 
           [0018]      FIG. 4  is a view of the underside of the outer metal shroud showing upstanding generally square bosses on the right hand side and a discourager on the left hand side with a recess but without the plate member mounted in the recess; 
           [0019]      FIG. 5  is a perspective view of the discourager shown in  FIG. 4  but with the plate member positioned in the discourager recess and having two threaded boss members in the plate member which align with the bosses in the outer metal shroud; 
           [0020]      FIG. 6  is a perspective view of the CMC inner shroud showing a pair of rectangular key slots which align with the bosses on the outer metal shroud and the boss members on the plate member; 
           [0021]      FIG. 7  shows an alternative embodiment of the outer shroud assembly of  FIG. 1  from the underside showing an internal space or pocket in the discourager for housing the plate member and showing two apertures which communicate with the internal space and which align with the apertures in the plate member; 
           [0022]      FIG. 8  is an end view of the discourager shown in  FIG. 7  showing the internal space with the plate member in position; 
           [0023]      FIG. 9  is a perspective view of the discourager of  FIG. 8 ; 
           [0024]      FIG. 10  is cross-section showing the discourager of  FIG. 8  without the plate showing the internal space and two apertures communicating with the internal space; 
           [0025]      FIG. 11  is an alternative cross-section of the outer shroud assembly of  FIG. 7  showing the discourager with the internal space and the plate member within the internal space, and a bolt extending through the boss of the outer metal shroud into the threaded apertures of the plate member to tighten the CMC shroud and discourager up against the outer metal shroud; 
           [0026]      FIG. 12  is a perspective view of an alternative embodiment of a discourager having a male configured shiplap feature for permitting connection to a corresponding female configured discourager; 
           [0027]      FIG. 13  shows discouragers of different units connected to each other via the shiplap arrangement; 
           [0028]      FIG. 14  is an enlarged view of Box B in  FIG. 13 ; 
           [0029]      FIGS. 15 and 16  are cross-sectional views of discouragers connected to each other via the shiplap arrangement illustrated in  FIG. 12 , one with the plate member present ( FIG. 15 ) and one with the plate member absent ( FIG. 16 ). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Referring to the drawings,  FIG. 1  is a perspective view of an outer shroud assembly of the invention. The assembly includes an outer metal shroud  10  having an aperture  9  extending therethrough, a hollow CMC shroud  6  having apertures  14  therein (shown in more detail in  FIG. 6 ) and a discourager seal  2  having apertures  11  therein (shown in more detail in  FIG. 9 ) located internally of the CMC shroud  6 . 
         [0031]      FIG. 2  is a cross-sectional end view of the outer shroud assembly of  FIG. 1 , and shows attachment of the CMC shroud  6  and discourager seal  2  via a plate member/bolt arrangement to a boss  16  on a surface of the outer shroud  10 . The apertures  11  of discourager  2  are dimensioned such that bosses  16  on the outer metal shroud  10  fit into the apertures  11 . A metal plate member  4  having threaded apertures  5  is provided in recess  7  in the discourager  2 . 
         [0032]    The assembly of the CMC shroud  6 , the discourager  2  and the plate member  4  is mounted to the outer metal shroud  10  by aligning apertures  14  in the CMC shroud, apertures  11  in the discourager and threaded apertures  5  in the plate member  4  over the bosses  16  in the outer metal shroud, passing a fastening means such as a bolt  8  through aperture  9  in the outer metal shroud  10 , through the boss  16  and threadedly engaging with the threaded apertures  5  of the plate member  4 . Tightening the bolt  8  pulls the CMC shroud/discourager/plate member assembly into tight contact with surface  12  of the outer metal shroud, as shown in  FIG. 2 . 
         [0033]    The discourager and its function are disclosed in copending application Ser. No. 12/576,386, the disclosure of which is incorporated herein by reference. 
         [0034]      FIG. 3  is a view of the outer shroud assembly  10  from the underside showing (for ease of understanding, this is shown as if the CMC shroud  6  was transparent) the plate member  4  with two threaded apertures  5 , mounted in a recess  7  of the discourager  2 . In the embodiment shown, the threaded apertures  5  are formed as raised boss members  5  to provide extra thread length for the bolt  8 . 
         [0035]      FIG. 3  illustrates the situation where there are two CMC shrouds  6  mounted to the outer metal shroud with a small gap  13  therebetween. In this arrangement, the corresponding discouragers disposed internally of the CMC shrouds are adjusted relative to the CMC shrouds to create an overlap region  18  such that the gap  13  is essentially blocked by the discourager. In this way, each discourager prevents hot gas from having a direct line of sight to the metal outer shroud  10  and establishes a tortuous path through the gap  13  to the outer metal shroud  10 . This in turn allows for the use of conventional metallic seals in the outer shroud  10  to provide for effective sealing of the secondary flow leakages around the outer shroud  10 . 
         [0036]      FIG. 4  is a view of the underside of the outer metal shroud  10  showing upstanding generally square bosses  16  on the right hand side, and a discourager  2  on the left hand side with a recess  7  but without the plate member  4  mounted in the recess  7 .  FIG. 5  is a perspective view of the discourager  2  shown in  FIG. 4  but with the plate member  4  positioned in the discourager recess  7  and having two threaded raised boss members  5  in the plate member  4  which align with the bosses  16  in the outer metal shroud  10 . 
         [0037]      FIG. 6  is a perspective view of the CMC shroud  6  showing a pair of rectangular key slots  14  which are positioned to align with the bosses  16  on the outer metal shroud  10  and the boss members  5  on the plate member  4 . Each rectangular key slot  14  is dimensioned such that the distance separating the longer opposite sides of the rectangle is slightly greater than the length of the sides of the square bosses  16  in order to allow the key slots to fit over and slide relative to the square bosses  16  on the outer metal shroud  10 , thereby allowing for positional adjustment of the CMC shroud  6  with respect to the outer metal shroud  10  because of differences in thermal expansion of the components due to them being made from different materials, i.e. CMC expands differently than metal. 
         [0038]    In the embodiment shown in  FIG. 6 , the rectangular key slots  14  are arranged in the CMC shroud  6  such that the longitudinal axis of one rectangle (i.e., the axis parallel to the longer sides of the rectangle) is perpendicular to the axis of the other. This allows for additional positional adjustment of the CMC shroud  6  relative to the outer metal shroud  10  for the same reasons as discussed above. 
         [0039]      FIG. 7  shows an alternative embodiment of the outer shroud assembly from the underside showing an internal space or pocket  20  in the discourager  2  for housing the plate member  4 . The discourager  2  is provided with two apertures  11  which communicate with the internal space  20  and which align with the apertures  5  in the plate member  4 . 
         [0040]      FIG. 8  is an end view of the discourager  2  shown in  FIG. 7 . In this view, the plate member  4  is in position within the internal space  20 . 
         [0041]      FIG. 9  is a perspective view of the discourager of  FIG. 8 . The rectangular apertures  11  are positioned to align with the bosses  16  on the outer metal shroud  10  and the boss members  5  on the plate member  4 . Each rectangular aperture  11  is dimensioned such that the distance separating the longer opposite sides of the rectangle is slightly greater than the length of the sides of the square bosses  16  in order to allow the apertures to fit over and slide relative to the square bosses  16  on the outer metal shroud  10 . This allows for positional adjustment of the discourager  2  in the axial and tangential directions to the outer shroud  10  with respect to the CMC shroud  6  and the outer metal shroud  10 , as discussed above. 
         [0042]      FIG. 10  is a cross-section showing the discourager  2  of  FIG. 8  without the plate  4 . The internal space  20  is shown with two apertures  11  communicating with the internal space  20 . 
         [0043]      FIG. 11  is an alternative cross-section of the outer shroud assembly of  FIG. 7 . In this arrangement, the discourager  2  is provided with internal space  20  and plate member  4  within the internal space, and a bolt  8  extends through aperture  9  in the boss  16  of the outer metal shroud  10  into the threaded apertures  5  of the plate member  4  to tighten the CMC shroud  6  and discourager  2  up against surface  12  of the outer metal shroud  10 . 
         [0044]      FIG. 12  is a perspective view of an alternative embodiment of a discourager  2  having a male configured shiplap  24 . This permits connection to a discourager provided with a corresponding female portion  26 , such as shown in  FIGS. 13 and 14 .  FIG. 14  is an enlarged view of Box  7   c  in  FIG. 13 . 
         [0045]      FIGS. 15 and 16  are cross-sectional views of discouragers connected to each other via a shiplap arrangement  24 , 26 . In  FIG. 15 , the plate member  4  is present and in  FIG. 16 , the plate member  4  is absent. 
         [0046]    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.