Patent Publication Number: US-8118548-B2

Title: Shroud for a turbomachine

Description:
BACKGROUND 
     Exemplary embodiments of the present invention relate to the art of turbomachines and, more particularly, to a shroud for a turbomachine. 
     Gas turbine engines include a casing that houses a turbine rotor having a plurality of buckets. Hot gases passing from a combustor through a turbine nozzle and along a hot gas path, impinge upon the turbine buckets to spin the turbine rotor. The turbine includes shroud segments that are fixed in an annular array to form a shroud adjacent to tip portions of the buckets. The shroud segments provide protection for the casing. In addition, the shroud segments substantially limit airflow from leaking past the tip portions of the buckets. 
     BRIEF DESCRIPTION 
     In accordance with an exemplary embodiment of the invention, a turbomachine includes a casing defining a hot gas path, and a shroud member attached to the casing. The shroud member is spaced from the casing to define a gap. The shroud member includes a first end having a first hook member provided with a first sealing surface and a second end including a second hook member provided with a second sealing surface. At least one of the first and second sealing surfaces includes a plurality of labyrinth seal elements that reduce air leakage through the gap into the hot gas path. 
     In accordance with another exemplary embodiment of the invention, a shroud member for a turbomachine includes a first end having a first hook member provided with a first sealing surface and a second end including a second hook member provided with a second sealing surface. At least one of the first and second sealing surfaces includes a plurality of labyrinth seal elements that reduce air leakage through the gap into the hot gas path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional view of a turbine portion of a turbomachine including an inner shroud member in accordance with an exemplary embodiment of the invention; 
         FIG. 2  is a side elevational view of the inner shroud member of  FIG. 1 ; 
         FIG. 3  is a perspective view of the inner shroud member of  FIG. 1 ; and 
         FIG. 4  is a detail view of a labyrinth seal portion of the inner shroud of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a turbomachine constructed in accordance with the present invention is indicated generally at  2 . Turbomachine  2  includes a turbine casing  4  that houses a combustion chamber  6  and a turbine stage  8 . In the exemplary embodiment shown, turbine stage  8  is a first stage. Combustion gases from combustion chamber  6  pass through a first stage nozzle  10  along a hot gas path (HGP)  12  to a second stage nozzle  14 . The combustion gases drive a rotor disk  20  that, in turn drives a turbine shaft (not shown). More specifically, turbine stage  8  includes a plurality of turbine buckets, one of which is indicated at  24 , mounted to rotor disk  20 . Each turbine bucket  24  includes a base portion  30 , and an airfoil portion  32  having a first end section  34  and a second end section  35 . The combustion gases passing along hot gas path  12  impinge upon airfoil portion  32  causing rotor disk  20  to rotate. 
     Turbomachine  2  further includes a shroud assembly  45  having an inner shroud segment or member  48  and an outer shroud segment or member  50 . As best shown in  FIG. 2 , outer shroud member  50  includes a main body section  53  including a first mounting element  55  and a second mounting element  60 . First and second mounting elements  55  and  60  secure outer shroud member  50  to turbine casing  4 . Outer shroud member  50  is also shown to include first and second hook elements  63  and  64  that serve as an interface with inner shroud member  48 . When mounted, inner shroud member  48  is spaced from outer shroud member  50  defining a gap (not separately labeled) through which cooling air may pass into the HGP. 
     Reference will now be made to  FIGS. 3 and 4  in describing inner shroud member  48  constructed in accordance with exemplary embodiments of the invention. As shown, inner shroud member  48  is formed from a nickel-based super alloy and includes a main body portion  73  having a first end  76  that extends to a second end  77  through a wall member  79 . Wall member  79  includes a first or inner surface  82 , and a second or outer surface  83 . Inner shroud member  48  is also shown to include a first hook member  90  having a first sealing surface  92  and a second hook member  95  having a second sealing surface  97 . First hook member  90  extends from first end  76  and second hook member  95  extends from second end  77 . First and second hook members  76  and  77  engage with hook elements  63  and  64  on outer shroud member  50  to retain inner shroud  48 . Inner shroud member  48  further includes a flange  99  having a seal seat  100  that receives a leaf seal assembly  101 . Leaf seal assembly  101  provides a first seal between inner shroud member  48  and outer shroud member  50  that prevents cooling air from, for example, a compressor, from entering hot gas path  12 . During operation, a tight radial gap exists between first hook member  90  and casing  4  resulting from an axial load created by cooling air pressure. Thus, additional sealing between first hook member  90  and casing  4  is not typically necessary. 
     In further accordance with the exemplary embodiment shown, inner shroud member  48  includes a labyrinth seal  106  provided on second sealing surface  97 . Labyrinth seal  106  includes a plurality of trenches or labyrinth seal elements  110 - 116 . Labyrinth seal elements  110 - 112  are arranged in a first row  117  that extends longitudinally along second sealing surface  97 . Labyrinth seal elements  110 - 112  extend in a direction tangential to a flow of air passing through a pre-impingement cavity (not separately labeled) that extends between outer shroud member  50  and inner shroud member  48 . In this manner, the cooling airflow passes through an impingement plate (not separately labeled) and flows over inner surface  82  to cool inner shroud member  48 . In any event, labyrinth seal elements  110 - 112  are not contiguous, i.e., are spaced one from the other along second sealing surface  97  forming a plurality of gaps  120  and  121 . Similarly, labyrinth seal elements  113 - 116  are arranged in a second row  124  that extends longitudinally along second sealing surface  97 , parallel to first row  117 . With this arrangement, labyrinth seal elements  113 - 116  also extend in a direction tangential to a flow of air passing across outer shroud member  50 . Labyrinth seal elements  113 - 116  are spaced one from the other along second sealing surface  97  forming a plurality of gaps  130  and  132 . Actually, labyrinth seal elements  110 - 112  and  113 - 116  are shifted relative to one another such that gaps  120  and  121  do not align with gaps  130 - 132 . The discontinuity of labyrinth seal element  110 - 112  and  113 - 116  creates turbulences that substantially limit the cooling air from entering hot gas path  12 . That is, labyrinth seal reduces leakage from the pre-impingement cavity by as much as 10-18%. 
     At this point it should be understood that the number of seal elements can vary in accordance with the exemplary embodiment. Also, the number of rows can vary without departing from the scope of the invention. It should further be understood that while only shown on second sealing surface, the labyrinth seal can also be provided on the first sealing surface. Finally, the inner shroud member can be formed from a variety of techniques including molding and machining. 
     In general, this written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention 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 exemplary embodiments of the present invention 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 language of the claims.