Abstract:
Disclosed are assemblies and articles for restricting leakage of a pressurized fluid from a cavity. In accordance with an embodiment of the invention, a vane support defines at least one land, and an interrupted rim region of a bladed rotor assembly defines at least one segmented ring. The at least one segmented ring protruding outward from the bladed rotor assembly in the interrupted rim region, spans across the cavity and cooperates with the at least one land to define a seal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application discloses subject matter related to copending US patent applications “HAMMERHEAD FLUID SEAL” (APPLICANT REFERENCE NUMBER EH-11279) and “BLADE NECK FLUID SEAL” (APPLICANT REFERENCE NUMBER EH-11507) filed concurrently herewith.  
       BACKGROUND OF THE INVENTION  
       [0002]     (1) Field of the Invention  
         [0003]     The invention relates to gas turbine engines, and more specifically to a seal for providing a fluid leakage restriction between components within such engines.  
         [0004]     (2) Description of the Related Art  
         [0005]     Gas turbine engines operate by burning a combustible fuel-air mixture in a combustor and converting the energy of combustion into a propulsive force. Combustion gases are directed axially rearward from the combustor through an annular duct, interacting with a plurality of turbine blade stages disposed within the duct. The blades transfer the combustion gas energy to one or more blades mounted on disks, rotationally disposed about a central, longitudinal axis of the engine. In a typical turbine rotor assembly, there are multiple, alternating stages of stationary vanes and rotating blades disposed in the annular duct.  
         [0006]     Since the combustion gas temperature may reach 2000 degrees Fahrenheit or more, some blade and vane stages are cooled with a lower temperature cooling air for improved durability. Air for cooling the first-stage blades bypasses the combustor and is directed to an inner diameter cavity located between a first-stage vane support and a first-stage rotor assembly. The rotational force of the rotor assembly pumps the cooling air radially outward and into a series of conduits within each blade, thus providing the required cooling.  
         [0007]     Since the outboard radius of the inner cavity is adjacent to the annular duct carrying the combustion gasses, it must be sealed to prevent leakage of the pressurized cooling air into the combustion gas stream. This area of the inner cavity is particularly challenging to seal due to the differences in thermal and centrifugal growth between the stationary, first-stage vane support and the rotating, first stage rotor assembly. In the past, designers have attempted to seal the outboard radius of inner cavities with varying degrees of success.  
         [0008]     An example of such an outboard radius seal is a labyrinth seal. In a typical configuration, a multi-step labyrinth seal separates the inner cavity into two regions of approximately equal size, an inner region and an outer region. Cooling air in the inner region is pumped between the rotating disk and labyrinth seal into the hollow conduits of the blades while the outer region communicates with the annular duct carrying the combustion gases. A labyrinth seal&#39;s lands must be pre-grooved to prevent interference between the knife-edge teeth and the lands during a maximum radial excursion of the rotor. By designing the labyrinth seal for the maximum radial excursion of the rotor assembly, the leakage restriction capability is reduced during low to intermediate radial excursions of the rotor assembly. Any cooling air that leaks by the labyrinth seal is pumped through the outer region and into the annular duct by the rotating disk. This centrifugal pumping action increases the temperature of the disk in the area of the blades and creates parasitic drag, which reduces overall turbine efficiency. The rotating knife-edges also add additional rotational mass to the gas turbine engine, which further reduces engine efficiency.  
         [0009]     Another example of such an outboard radius seal is a brush seal. As this example illustrates, a brush seal separates the inner cavity into two regions, an inner region and a smaller, outer region. A freestanding sideplate assembly defines a disk cavity, which is in fluid communication with the inner region. Cooling air in the inner region enters the disk cavity and is pumped between the rotating sideplate and disk to the hollow conduits of the blades. The seal&#39;s bristle to land contact pressure increases during the maximum radial excursions of the rotor and may cause the bristles to deflect and ‘set’ over time, reducing the leakage restriction capability during low to intermediate rotor excursions. Any cooling air that leaks by the brush seal is pumped into the outer region by the rotating disk. This centrifugal pumping action increases the temperature of the disk in the area of the blades and creates parasitic drag, which reduces overall turbine efficiency. The freestanding sideplate and minidisk also adds rotational mass to the gas turbine engine, which further reduces engine efficiency.  
         [0010]     Although each of the above mentioned seal configurations restrict leakage of cooling air under certain engine operating conditions, a consistent leakage restriction is not maintained throughout all the radial excursions of the rotor. The seals may also increase the temperature of the disk and cooling air due to centrifugal pumping, reduce engine efficiency due to parasitic drag and add additional engine weight. What is needed is a seal that maintains a more consistent leakage restriction throughout all the radial excursions of the rotor, without negatively affecting disk and cooling air temperature, engine efficiency or engine weight.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     In accordance with an embodiment of the present invention, there is provided a seal for restricting leakage of pressurized cooling air from an inner cavity flanked by a vane support and a bladed rotor assembly. The seal comprises a segmented ring defined by the bladed rotor assembly and a land defined by the vane support. The bladed rotor assembly includes a disk rotationally disposed about a central axis of the engine. The disk includes a radially outermost rim and a plurality of slots circumferentially spaced about the rim for accepting an equal plurality of blades. An interrupted rim region extends radially outward from a radius circumscribing a radially innermost floor of each slot to the outermost rim. The segmented ring extends from the interrupted rim region to define a segregated inner and outer cavity. The circumferential land is located radially above the inner cavity, proximate to the segmented ring. The segmented ring spans across the inner cavity, interacting with the land to define the seal.  
         [0012]     By locating the seal radially outboard and in the interrupted rim region of the disk, temperature rise and parasitic drag due to duct placement and centrifugal pumping are minimized. Also, engine rotating mass is reduced with the elimination of freestanding sideplates and complex, multi-step labyrinth seal hardware as well.  
         [0013]     Other features and advantages will be apparent from the following more detailed descriptions, taken in conjunction with the accompanying drawings, which illustrate by way of an example a seal in accordance with specific embodiments of the invention.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0014]      FIG. 1  illustrates a simplified schematic sectional view of a gas turbine engine along a central, longitudinal axis.  
         [0015]      FIG. 2  illustrates a partial sectional view of a turbine rotor assembly of the type used in the engine of  FIG. 1 , showing a seal in accordance with an embodiment of the present invention.  
         [0016]      FIG. 3  illustrates a partial sectional view of a turbine rotor assembly of the type used in the engine of  FIG. 1 , showing a multiple step seal in accordance with an embodiment of the present invention.  
         [0017]      FIG. 4  illustrates a partial isometric view of the turbine rotor assembly of the present invention of  FIG. 2 .  
         [0018]      FIG. 5  illustrates a partial front view of the turbine rotor assembly of the present invention of  FIG. 2 .  
         [0019]      FIGS. 6   a - 6   h  illustrate a series of enlarged schematics illustrating various seals of  FIGS. 2 and 3  in accordance with several embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     The major sections of a typical gas turbine engine  10  of  FIG. 1  include in series, from front to rear and disposed about a central longitudinal axis  11 , a low-pressure compressor  12 , a high-pressure compressor  14 , a combustor  16 , a high-pressure turbine  18  and a low-pressure turbine  20 . A working fluid  22  is directed rearward through the compressors  12 ,  14  and into the combustor  16 , where fuel is injected and the mixture is burned. Hot combustion gases  24  exit the combustor  16  and expand within an annular duct  30  through the turbines  18 ,  20  and exit the engine  10  as a propulsive thrust. A portion of the working fluid  22  exiting the high-pressure compressor  14 , bypasses the combustor  16  and is directed to the high-pressure turbine  18  for use as cooling air  40 .  
         [0021]     Referring now to  FIGS. 2 and 3 , an inner cavity  50  is located radially inward of the annular duct  30  and axially between a first-stage vane support  52  and a first-stage rotor assembly  54 . The rotor assembly comprises a disk  56  and a plurality of outwardly extending blades  58 , rotationally disposed about the central axis  11 . As best shown in  FIGS. 4 and 5 , the disk  56  includes a radially outermost rim  60 , a plurality of fir tree profiled slots  62  and a plurality of lugs  64  alternating with the slots  62  about the circumference of the rim  60 . Each slot  62  accepts a radially inner most attachment  66  of a blade  58  in a sliding arrangement. One or more teeth  67  extend between a forward, axial face  68  and a rearward, axial face  69  of the attachment  66 , engaging adjacent lugs  64  to prevent loss of the blade  58  as the disk  56  rotates. The one or more teeth  67 , project a complementary fir tree profile about the periphery of each face  68 ,  69 .  
         [0022]     During the operation of the engine  10 , pressurized cooling air  40  is pumped into the inner cavity  50  by a duct  70 , where a major portion of the cooling air  40  is dedicated to internally cooling the blades  58 . The cooling air  40  enters the blades  58  via a series of radially extending conduits  72  communicating with a plenum  74  flanked by the blade attachment  66  and the disk  56 . The cooling air  40  exits the blade  58  via a series of film holes  76 . To ensure a continuous flow of cooling air  40  through the blades  58 , the pressure of the cooling air  40  must remain greater than the pressure of the combustion gases  24  or the combustion gases  24  may backflow into the film holes  76 , potentially affecting the durability of the blades  58 .  
         [0023]     An exemplary seal  80  in accordance with an embodiment of the invention separates the inner cavity  50  from the annular duct  30 , thus ensuring adequate cooling air  40  pressure throughout all engine-operating conditions. The seal  80  is located radially inward of the annular duct  30 , defining an outer cavity  82  therebetween. Since the outer cavity  82  is relatively small, any leakage of cooling air  40  through the seal  80  is subject to relatively minimal centrifugal pumping by the rotor assembly  54 , prior to mixing with the combustion gases  24 . This level of centrifugal pumping has limited negative impact on disk  56  temperature and aerodynamic drag, thus improving engine efficiency.  
         [0024]     The exemplary seal  80  of  FIGS. 2 and 3 , comprises a circumferentially disposed land  84  defined by the vane support  52  and a segmented ring  86  defined by the rotor assembly  54 . In the examples shown, the lands  84  have a linear cross sectional profile; however, other profiles such as those shown in the examples of  FIGS. 6   a - 6   h  may also be used. Lands  84  at differing radial locations provide an increased restriction over a single land  84 . A land  84  may be integrally defined by the vane support  52  or may be defined by a separate arm  92  and affixed to the vane support  52  by welding, bolting, riveting or other suitable means. A land  84  is generally affixed to a face  94  of the vane support  52  or arm  92  by brazing and is comprised of honeycomb, or any other abradable structure known in the sealing art. The number of rings  86  and lands  84  depends on the leakage restriction requirements and installation area available.  
         [0025]     The segmented ring  86  is radially located in an interrupted rim region  110  of the disk  58 . The interrupted rim region  110  extends radially outward from a radius  112  circumscribing a floor  114  of each slot  62  to the outer rim  60 . As best shown in  FIGS. 4 and 5 , a first number  164  of the ring segments are defined by the disk lugs  64  and a second number  166  of the ring segments are defined by the blade attachments  66 . The first number of segments  164  are preferably formed with the disk  56  prior to milling or broaching the slots  62 . The second number of segments  166  are preferably cast or forged integrally with the blades  58  and machined with the attachment  66 . With the blades  58  interposed with the lugs  64 , the first  164  and second  166  ring segments substantially align, defining a complete segmented ring  86 .  
         [0026]     A runner  170 , also known as a knife-edge, extends outward from a segmented ring  86  as shown in  FIGS. 2 and 3 . The addition of multiple runners  170  provides for a greater cooling air  40  leakage restriction, but the actual number may be limited by the available area and weight restrictions. The width of a runner  170  should be as thin as possible adjacent to a land  84  to reduce the velocity of any cooling air  40  flowing therebetween. Since intermittent contact between a runner  170  and a land  84  may occur, a coating, hardface or other wear-resistant treatment is typically applied to the runner  200 . A runner  170  may also be canted in the direction opposing the cooling air  40  flow, as shown in  FIGS. 2 and 3 , from between about 22.5 degrees to about 68 degrees, preferably 55 degrees, relative to the engine axis  11 . By canting a runner  170  in the direction opposing the cooling air  40  flow, a damming effect is created, providing for an increased leakage restriction. Canting a runner  170  also reduces the length of the thicker, segmented ring  86 , reducing weight even further. Several examples of a runner  170  are shown in  FIGS. 6   a - 6   h.    
         [0027]     Referring now to  FIG. 5 , tangential sealing between adjacent ring segments  164 ,  166  occurs as centrifugal forces draw the blade  58  radially outward against the lugs  64  during the engine  10  operation. To achieve this sealing, the segmented ring  86  is radially positioned to include a contact surface  168  located at the interface of the lug  64  and the attachments  66 . Although a innermost contact surface  168  is included in the example for reduced weight, any one or more of the contact surfaces  168  may be included.  
         [0028]     With the rotor assembly  54  installed in the high pressure turbine  18  as shown in  FIGS. 2 and 3 , a segmented ring  86  extends outward from the interrupted rim region of the rotor assembly  54 , spans across the inner cavity  50 , aligning a runner  170  with a land  84 . Sufficient radial clearance between a runner  170  and a land  84  prevents interference during assembly and during engine  10  operation.  
         [0029]     Although an exemplary seal  80  is shown positioned between a stationary member and a rotating member, it is to be understood that an exemplary seal  80  may also be located between two rotating members or two stationary members as well.  
         [0030]     While the present invention has been described in the context of specific embodiments thereof, other alternatives, modifications and variations will become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications and variations as fall within the broad scope of the appended claims.