Abstract:
A gas turbine engine is provided with turbine sealing structures including knife edge seals which extend at an angle relative to an axial center line of the engine. Each knife edge seal is associated with a concave pocket defined between a radially inner surface and a spaced radially outer surface. The concave pockets and their associated knife edge seals create a pair of vortices which prevent leakage into radially inner portions of the turbine section.

Description:
BACKGROUND OF THE INVENTION 
   This application relates to knife edge seals which rotate with a gas turbine rotor, and are associated with concave pockets in a stationary sealing surface. The combination of the knife edge seals and the concave pockets create vortices, which limit leakage past the knife edge seals. 
   Gas turbine engines are known, and typically include a series of sections. Generally, a fan delivers air to a compressor section. Air is compressed in the compressor section, and delivered downstream to a combustor section. In the combustor section, air and fuel are combusted. The products of combustion then pass downstream over turbine rotors. The turbine rotors rotate to create power, and also to drive the fan and compressors. 
   The turbine rotors typically are provided with a plurality of removable blades. The blades are interspersed with stationary surfaces, and stationary vanes. It is desirable to limit leakage of the products of combustion radially inwardly of the turbine blades. Thus, the turbine blades are provided with knife edge seals which are spaced closely from sealing surfaces on the static members. 
   In the prior art, labyrinth seal structures are known. Generally, the sealing surfaces have been formed as cylindrical surfaces at a plurality of different radial distances. The combination of these different radial distances, and a plurality of associated knife edge blades create a labyrinth path for leakage fluid to limit it reaching radially inner locations in the gas turbine engine. Even so, some leakage does occur, and it would be desirable to further reduce the leakage. 
   SUMMARY OF THE INVENTION 
   In a disclosed embodiment of this invention, the generally cylindrical sealing surfaces of the prior art are replaced by concave pockets. The pockets generally are defined between a radially inner surface spaced from a radially outer surface. As the products of combustion flow, they are forced into the pockets in a swirling movement. Vortices form in the pockets, and block or limit leakage. 
   At the same time, in a disclosed embodiment, knife edge seals are associated with the pockets. The knife edge seals preferably extend at an angle of at least 30° and less than 90° relative to an axial center line of the gas turbine engine. By angling the knife edge seals further vortices are provided that also limit leakage. The combination of the angled knife edge seals and the concave pockets provide vortices at each of several radially spaced sealing locations. 
   These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically shows a gas turbine engine. 
       FIG. 2  shows a sample sealing location with a gas turbine engine of the present invention. 
       FIG. 3A  shows a prior art seal. 
       FIG. 3B  shows a first sealing arrangement. 
       FIG. 3C  shows a second sealing arrangement. 
       FIG. 4  shows one embodiment of the present invention. 
       FIG. 5  shows another embodiment of the present invention. 
       FIG. 6  shows another embodiment of the present invention. 
       FIG. 7  shows yet another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A gas turbine engine  10 , such as a turbofan gas turbine engine, circumferentially disposed about an engine centerline, or axial centerline axis  12  is shown in  FIG. 1 . The engine  10  includes a fan  14 , a compressor  16 , a combustion section  18  and a turbine  20 . As is well known in the art, air compressed in the compressor  16  is mixed with fuel and burned in the combustion section  18  and expanded in turbine  20 . The turbine  20  includes rotors  22  which rotate in response to the expansion, driving the compressor  16  and fan  14 . The turbine  20  comprises alternating rows of rotary airfoils or blades  24  and static airfoils or vanes  26 . In fact, this view is quite schematic, and blades  24  and vanes  26  are actually removable. It should be understood that this view is included simply to provide a basic understanding of the sections in a gas turbine engine, and not to limit the invention. This invention extends to all types of turbine engines for all types of applications. 
     FIG. 2  is an enlarged view of turbine blades  24 , and intermediate stationary vanes  26 . As known, sealing surfaces  34  are associated with knife edge seals  36 . As can be seen in this figure, in the present invention, these knife edge seals extend at an angle relative to the axial centerline  12  of the jet engine. Also, the knife edge seals are associated with concave pockets  38 , as will be explained in more detail below. As can be appreciated in at least some of the locations, there are a plurality of radially spaced sealing pockets and associated knife edge blades. 
   As shown in  FIG. 3A , in the prior art, a labyrinth seal was created by cylindrical sealing surfaces  49  and  51  spaced at different radial positions, and knife edge seals  50  spaced from the associated static sealing surfaces  51  and  49 . As known, and as shown for example in  FIG. 2 , an abradable sealing material may actually be positioned to allow the knife edge seal to wear the material and provide a close fit. With the radially distinct sealing surfaces  49  and  51 , a labyrinth leakage path  54  is presented to any fluid which may leak radially inwardly of the rotor. The labyrinth seal path does provide a good restriction to linkage fluid. However, it would be desirable to even further improve the resistance of this path. 
   Thus, as shown in  FIGS. 2 and 3B , fluid can be forced into vortices  40  and  42  by angling the knife edge seals  36  relative to a central line of the gas turbine engine, and creating pockets  38  from radially inner walls  39  and a radially outer wall  34 . A vortex  42  is created in the pocket  38 , and the angled knife edge seal  36  creates yet another vortex  40 . The combination of the vortices  40  and  42  present a great resistance to fluid leakage. This is particularly true when there are additional knife edge seals at different radial positions, and positioned along a path of the fluid flow, as shown in  FIG. 3B . In  FIG. 3B , the knife edge seals  36  are angled into the pockets  38 . 
   As shown in  FIG. 3C , a similar vortex pair can be created if the knife edge seals  36  are angled away from the pockets  38 . Again, vortices  42  and  40  are created and function as mentioned above. 
   The present invention thus provides a great resistance to leakage flow by utilizing angled knife edge seals and associated concave pockets. Several possible arrangements of these two concepts are shown in  FIG. 4-7 . In  FIGS. 4-7  it can be understood that fluid is flowing from the right to the left. 
   As shown in  FIG. 4 , in embodiment  60 , knife edge seals  62  are angled into the flow, and the pockets  64  face the flow of fluid. This arrangement will create vortices as mentioned above. 
     FIG. 5  shows an embodiment  70  where the knife edge seal  72  are angled into the path of the fluid, however, the pockets  74  face away from the path of the fluid. This configuration is preferred when the rotating structure that is the rotor and carries the knife edge seals, are already in place, and the static structure is being assembled from an aft to forward position. 
     FIG. 6  shows an embodiment  80  wherein the knife edge seals  82  are angled along the path of the flow, and the pockets  84  face the path of the flow. This embodiment is particularly well suited when the static structure is in place and the rotating structure is moved from an aft location to a forward location for assembly. 
   An embodiment  90  is illustrated in  FIG. 7 . In embodiment  90  the knife edge seals  92  are angled along the path of flow, and the pockets  94  face away from the path of flow. This configuration is well-suited for when the rotating structure is in place and a static structure is moved from an aft location to a forward location. 
   In  FIGS. 4-7 , the flow direction could be stated with regard to the location of the components such as shown in  FIG. 1 . As an example, the combustor would be upstream in the  FIGS. 4-7  embodiments. Thus, a component “facing into” the flow could alternatively be said to be “facing the combustion section.” Also, a component which “faces away” from the flow could be said to “face away” from the combustion section. 
   As can be appreciated, in the  FIG. 6  embodiment, the greater outer diameter knife edge seals are positioned upstream, and lesser outer diameter knife edge seals are positioned downstream. Also, the knife edge seals extend along an angle such that they extend toward the pockets. The angle is non-parallel, and non-perpendicular, to a central axis. 
   As known in the art, a “knife-edge seal” includes a sealing member at an outermost point which narrows to a tip, such that the tip is smaller than portions spaced more radially inwardly. 
   The present invention thus provides concave pockets formed of a radially inner surface spaced from a radially outer surface. The concave pockets create a vortex in the fluid flow which prevents leakage past the associated knife edge seal. Further, when the knife edge seals are angled, they create a second vortex further limiting leakage flow. The angle of the seals may range between 30 and 90° in example embodiments. 
   Although preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.