Patent Publication Number: US-7217089-B2

Title: Gas turbine engine shroud sealing arrangement

Description:
TECHNICAL FIELD 
   The invention relates generally to gas turbine engine and, more particularly, to a new gas turbine engine shroud sealing arrangement. 
   BACKGROUND OF THE ART 
   Over the years various sealing arrangements have been designed to seal the annular shrouds surrounding the tips of turbine blades. Feather seals are typically installed in the aft and forward rails of the shroud support structures to minimize cooling air leakage through the shroud segments. 
   A main disadvantage of such feather seals is that it provides for a multi-part sealing arrangement (e.g. 12–24 feather seals) which renders the assembly procedure more complex, thereby resulting in extra costs. Furthermore, feather slots must be machined in each shroud segments for allowing the feather seals to be positioned in the aft and forward rails of the outer shroud support, which further increases the manufacturing cost of the engine. Finally, such a multi-part sealing arrangement contributes to increase the overall weight of the gas turbine engine. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of this invention to provide a new sealing arrangement which addresses the above mentioned concerns. 
   In one aspect, the present invention provides a turbine blade tip shroud assembly comprising an annular shroud support having at least one radially inner annular flange defining a groove, a shroud supportively engaged in said groove, said shroud having a platform, the platform having a hot gas path side and a back side, an annular gap being defined radially inwardly of said groove between said back side of said platform and a radially inwardly facing side of said at least one annular flange, and a ring seal having a spring-loaded annular sealing portion and a radial flange extending from one end of said spring-loaded annular sealing portion, the spring-loaded annular sealing portion extending axially in said annular gap in sealing engagement with said back side and said radially inwardly facing surface of said at least one annular flange, and wherein the radial flange is in axial abutment relationship with an axially facing surface of one of said shroud and said at least one annular flange of said shroud support. 
   In another aspect, the present invention provides a ring seal in combination with a turbine shroud adapted to surround a stage of turbine blades, the turbine shroud comprising a support ring and a shroud mounted within said support ring, the shroud comprising a platform having an aft overhanging portion, said aft overhanging portion having a gas path side and a back side opposite said gas path side, said back side defining with an opposed facing radially inner surface of said support ring an annular gap, said ring seal being mounted in said annular gap and maintained in sealing engagement with said radially inner surface of said support ring and said back side of said aft overhanging portion of said platform. 
   In another aspect, the present invention provides a method for sealing a turbine shroud comprising a platform overhanging portion having a gas path side and an opposed back side, the back side being spaced-radially inwardly from a radially inner surface of a surrounding support ring, the method comprising the step of mounting an annular seal in sealing engagement with said the back side of the platform overhanging portion and the radially inner surface of the surrounding support ring. 
   Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below. 

   
     DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the accompanying figures depicting aspects of the present invention, in which: 
       FIG. 1  is an axial cross-sectional view of a gas turbine engine; 
       FIG. 2  is an enlarged fragmentary cross-sectional view of the turbine section showing details of a turbine shroud sealing arrangement in accordance with an embodiment of the present invention; and 
       FIG. 3  is a perspective view of a one-piece ring seal in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan  12  through which ambient air is propelled, a multistage compressor  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  18  for extracting energy from the combustion gases. 
   The turbine section  18  comprises, among others, a turbine rotor mounted for rotation about a centerline axis of the engine  10 . The turbine rotor comprises a plurality of circumferentially spaced-apart blades  22  (only one shown in  FIG. 2 ) extending radially outwardly from a rotor disk. An annular turbine shroud  26  surrounds the tip of the blades  22 . The turbine shroud  26  typically comprises a plurality of circumferentially adjoining segments  28  (only one shown in  FIG. 2 ) forming a continuous 360 ° concentric annular band about the turbine blades  22 . 
   Each shroud segment  28  comprises a platform  30  and a pair of retention hooks  32  and  34  extending radially outwardly from a back side  36  (i.e. the radially outwardly facing side) of the platform  30  opposite to a gas path side  38  thereof (i.e. the radially inwardly facing side). The platform  30  has an aft overhanging portion  40  extending axially rearward of the aft retention hook  34 . The forward and aft retention hooks  32  and  34  are respectively provided with axially aft extending terminal components  32   a  and  34   a  conventionally axially engaged in respective forwardly facing annular grooves  42  and  44  defined by a pair of forward and aft annular flanges  46  and  48  extending integrally radially inwardly from a radially inner surface  50  of a surrounding annular shroud support  52 . 
   Holes  54  are defined in the shroud support  52  to allow cooling air to flow into the annular cavity  56  formed between the shroud  26  and the support structure  52 . As shown in  FIG. 2 , a one-piece ring seal  58  extends in the annular gap  59  between the overhanging portion  40  of the platform  30  and the aft annular flange  48  to seal the cavity  56 . The ring seal  58  has an axially extending annular wave-shaped component  60  and an annular axial retaining flange  62  extending radially outwardly from a forward end or upstream end of the axially wave-shaped component  60   
   The wave-shaped component  60  has first, second and third peaks  64 ,  66  and  68 . The configuration of wave-shaped component  60  is such that the radial extent between top peak  66  and bottom peaks  64  and  68  is slightly greater than the radial dimension between the radially inwardly facing surface  70  of the aft flange  48  of the shroud support  52  and the back side  36  of the overhanging portion  40  of the shroud platform  30 . The seal  58  is made up of a heat resistant material having an inherent resiliency suitable to maintain spring fitted continual contact with the opposed facing surfaces  36  and  70  of the gap  59 . Thus, the wave-shaped component  60  is spring loaded between the aft overhanging portion  40  of the shroud platform  30  and the aft flange  48  of the shroud support  52  so that peaks  64 ,  66  and  68  are in continual contact with the opposed facing surfaces  36  and  70  of the annular gap  59 . In addition to prevent cooling air leakage through the annular gap  59 , the wave-shaped component  60  spring loads the shroud segments  28  radially inwardly. During engine operation, the wave-shaped component  60  will accommodate different thermal growth between the platform  30  and the aft flange  48 . 
   As shown in  FIG. 2 , the axial retaining flange  62  axially abuts against a forward facing end surface  72  of the shroud support aft flange  48  for retaining the ring seal  58  against axially aft movement during engine operation. The use of such an axial retaining feature is advantageous in that it allows the ring seal  58  to be positioned about the overhanging portion  40  in a single step without having to machine any spring placement slot in the shroud segments  28 , thereby contributing to reduce the overall engine manufacturing costs. 
   As shown in  FIG. 3 , the ring seal  58  may be constructed as a one-piece endless ring to be first installed in the annular shroud support  52  with the radially outwardly extending flange  62  thereof in axial abutment relationship with the forward facing end surface  72  of the annular aft flange  48 . Then, the shroud segments  28  can be successively mounted to the shroud support  52 . The use of a single piece seal is advantageous as compared to compared to conventional multi-pieces feather seals in that it greatly simplify the assembly procedures. Also, the spring seal  58  can be conveniently cold formed or rolled from a lightweight sheet metal blank, thereby providing a sealing arrangement which is cheaper and lighter than a typical feather seal arrangement. 
   The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without department from the scope of the invention disclosed. For example, it will be appreciated that ring seal  58  is not limited to being installed to a high pressure shroud, but rather, it can be installed in other engine stages which exhibit similar problems and needs. Also, it is understood that the wave-shaped portion  60  could have more or less than three peaks. In fact, could have any configuration adapted to accommodate different thermal gradient between the engine parts to be sealed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.