Abstract:
Disclosed is a compliant seal arrangement  50  for restricting leakage through a gap between a first  54  and second  56  component. A seal assembly  58  is formed by stacking leaf strips  70  flat and sandwiching the stacked leaf strips  70  between a back plate  76  and a side plate  78 . The leaf strips  70  are secured to the plates at a joint  84  along an edge  86  of the strips  70  that are in contact with the plates  76, 78 . The seal assembly  58  is installed across the gap  52  to form the seal arrangement  50 . The strips  70  extend from the first component  54 , bridge the gap  52  and contact the second component  56 , thereby restricting the leakage of fluid through the gap. Because the strips  70  are compliant, relative motion between the components  54, 56  deflects the strips  70 , not causing permanent deformation.

Description:
[0001]    This invention was made with Government support under F33657-89-2014 awarded by the United States Air Force. The Government has certain rights in this invention. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    (1) Field of the Invention 
         [0003]    The invention relates to gas turbine engine components in general, and more specifically to a sealing arrangement for restricting leakage of a pressurized fluid through a gap formed between such components. 
         [0004]    (2) Description of the Related Art 
         [0005]    Gas turbine engines operate according to a continuous-flow, Brayton cycle. Ambient air is pressurized in a forward compressor section, fuel is added to the air and the mixture is burned in a central combustor section, and the combustion gases are expanded through a rearward turbine section before being expelled from a rearmost nozzle. Bladed rotors in the turbine section convert thermodynamic energy from the expanding gases into mechanical energy to rotate centrally mounted, longitudinal shafts. The rotating shafts drive the forward compressor section, thus completing the cycle. Gas turbine engines are compact and efficient power plants that are typically used to power aircraft, heavy equipment, waterborne vehicles and electrical generators. 
         [0006]    The fuel burn of a gas turbine engine may be negatively impacted if pressurized compressor air leaks through gaps or if the expanding gas leaks around the bladed turbine rotors. Fluid leakage can occur at stationary component interfaces where gaps exist, but leakage is most prevalent at the interfaces between rotating and stationary components. Engineered clearance gaps between components allow for thermal and centripetal growth of the components and require abradable or compliant sealing systems for restricting fluid leakage. In the past, designers have attempted to seal the gaps between stationary and rotating components with varying degrees of success. 
         [0007]    What is needed is a compliant interface seal that provides a greater restriction to fluid leakage between gas turbine engine components. A seal providing a reduction in weight over prior art seals would also be beneficial. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    In accordance with the present invention, there is provided a compliant seal assembly for restricting leakage between components. Leaf strips made of a compliant material are stacked flat and sandwiched between a back plate and a side plate. The leaf strips are secured to the plates along an edge of the strips in contact with the plates. Since the strips are secured to the back and side plates only where they contact the plates, an overall weight reduction of the seal results. 
         [0009]    The seal assembly is installed across gaps between stationary and rotating components to form a seal arrangement. The strips extend from the first component, bridge the gap and contact the second component, thereby restricting the leakage of fluid through the gap. Because the strips are compliant, relative motion between the components deflects the strips, not causing permanent deformation. 
         [0010]    An advantage of the present seal arrangement is its ability to deflect during relative motion between components. By deflecting as the gap closes, the strips and components don&#39;t suffer permanent damage from interference so the useful life is extended. Compliant contact between the strips and the components also provides an improved restriction to fluid leakage over all operating conditions for reduced fuel burn. Another advantage is the reduction of weight over prior art seals, since the strips are secured to the back and side plates only where they contact the plates. 
         [0011]    These and other objects, features and advantages of the present invention will become apparent in view of the following detailed description and accompanying illustrations of multiple embodiments, where corresponding identifiers represent like features between the various drawings. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0012]      FIG. 1  is a simplified cross sectional view of an axial flow gas turbine engine with an upper half illustrating a geared fan and variable area fan nozzle and a lower half illustrating a conventional fan with constant area fan nozzle; 
           [0013]      FIG. 2  is a partial front view of a seal arrangement of the type used in the gas turbine engine of  FIG. 1 , according to an embodiment of the present invention; 
           [0014]      FIG. 3  is an enlarged view of area  3  the seal arrangement of  FIG. 2 ; 
           [0015]      FIG. 4  is a partial sectional side view of the seal arrangement of  FIG. 2 ; 
           [0016]      FIG. 5  is a partial top view of another seal arrangement of the type used in the gas turbine engine of  FIG. 1 , according to another embodiment of the present invention; 
           [0017]      FIG. 6  is a partial sectional side view of the seal arrangement of  FIG. 5 ; 
           [0018]      FIG. 7  is a partial top view of yet another seal arrangement of the type used in the gas turbine engine of  FIG. 1 , according to yet another embodiment of the present invention; and 
           [0019]      FIG. 8  is a partial perspective view of the seal arrangement of  FIG. 7  with a second component removed for clarity. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    A gas turbine engine  10  of  FIG. 1  includes in series from front to rear, rotating low-pressure  12  and high-pressure  14  compressors, a stationary combustor  16  and rotating high-pressure  18  and low-pressure  20  turbines. Each section is disposed about a central, longitudinal axis  22  of the engine  10  and enclosed within cylindrical casing structures  24 . The turbines  18 ,  20  are coupled to the compressors  14 ,  12  via one or more centrally mounted, concentric shafts  26 . A forward most fan  28  may be driven directly by a shaft  26  along with the low-pressure compressor  12  or driven independently by a gearbox  30  attached to a shaft  26 . 
         [0021]    Ambient air  32  is drawn into the engine  10  by the fan  28  and immediately directed into two fluid streams: a bypass fluid  34  and a working fluid  36 . The bypass fluid  34  is directed radially outboard of the casing structure  24 . The working fluid  36  is pressurized in the compressors  12 ,  14  and directed into the combustor  16 , where fuel is injected and the mixture is burned. Hot combustion gases exit the combustor  16  and expand within the turbines  18 ,  20 . The combustion gases exit the engine  10  as a propulsive thrust  38 . A portion of the working fluid  36  is bled from the compressors  14 ,  16  as a cooling fluid  40  and is directed radially around the combustor  16  for use in cooling the turbines  18 ,  20 . 
         [0022]    When installed on an aircraft, the engine  10  is aerodynamically streamlined with inner  42  and outer  44  cowlings. The outer cowling  44  includes an aft portion, which may be fixed  46  or variable  48 . A variable aft portion  48  meters the bypass air  34  to reduce fuel burn over all engine  10  operating conditions. 
         [0023]    Referring now to  FIGS. 2-4 , one skilled in the art will recognize an embodiment of a seal arrangement  50  for restricting leakage of a fluid  36  or  40  through a gap  52  disposed between a first component  54  and a second component  56 . In the embodiment shown, the first component  54  is stationary and circumscribes the second component  56 , which rotates about axis  22  to form the gap  52 . A seal assembly  58  restricts leakage of fluid  36  or  40  in a direction parallel to the axis  22 . In other configurations of the present seal arrangement  50 , both components  54  and  56  are stationary, only one of the components  54  or  56  is rotating, or both of the components  54  and  56  are rotating at identical or varying speeds and directions. 
         [0024]    An annular seal assembly  58  fits within a bore  60  and against a seat  62  formed in the first component  54 . The seal assembly  58  is secured to the first component  54  by fastening means  64  such as tabs, bolts, rivets, welding, or by any other means known in the art. The seal assembly  58  comprises a back plate  66 , a side plate  68  and a plurality of leaf strips  70  sandwiched by and secured to the plates  66 ,  68 . 
         [0025]    The plates  66  and  68  are ring shaped members, each with an outer diameter  72  slightly less than an inner diameter  74  of the bore  60 , but a line on line or interference fit may also be used. It is preferable to have an inner diameter  76  of the back plate  66  less than an inner diameter  78  of the side plate  68  to provide downstream support for the leaf strips  70  while subjected to the fluid pressure load. The back xx and side xx plates are made of any suitable high temperature and corrosion resistant material such as a Nickel based alloy for gas turbine engine applications. 
         [0026]    The leaf strips  70  are also preferably made of any high temperature and corrosion resistant material such as a Nickel based alloy. The strips  70  should be less than 0.010 inch (0.254 mm) thick and preferably less than or equal 0.005 inch (0.127 mm) thick to provide optimal flexural strength and resiliency. A surface finish of 32 micro inches or less on each leaf strip face  80  allows the leaf strips  70  to stack together without gaps, providing for increased restriction to fluid  36  or  40  leakage. 
         [0027]    The leaf strips  70  are sandwiched widthwise at a lay angle α to a radius line  82  extending from the axis  22 . The angle α is greater than 0 degrees but less than 90 degrees and preferably about 45 degrees. Once the stacked leaf strips  70  are sandwiched between the plates  66 ,  68 , the leaf strips  70  are secured to the plates along a joint  84  extending at least over a portion of an edge  86  in contact with the plates  66 ,  68 . The leaf strips  70  may be secured to the plates  66 ,  68  by Metal Inert Gas (MIG) welding, Tungsten Inert Gas (TIG) welding or Laser welding, but are preferably secured by brazing. To simplify assembly, braze paste may be applied directly to the plates  66 ,  68  and the seal assembly  58  may be heated in a furnace to melt the braze paste, thus creating the joint  84 . Since the leaf strips  70  are only secured over a portion of an edge  86  in contact with the plates  66 ,  68 , the overall weight of the seal assembly  58  is reduced. A free end  88  comprises an inner edge profile  90  that is shaped to match the second component  56 . The profile  90  may be linear or nonlinear shaped. The profile  90  may be formed during manufacture by grinding, electrodischarge machining (EDM) or other suitable method. 
         [0028]    With the seal assembly  58  installed in the bore  60 , the leaf strips  70  extend across the gap  52  with the free ends  88  contacting the second component  56 . The strips  70  may extend radially inward, radially outward or axially. The second component  56  preferably contains a hardface coating  92  or other surface treatment to reduce wear under extended operation. As is best illustrated in  FIGS. 2 and 3 , the lay angle α allows the leaf strips  70  to flex outward as the gap  52  closes and allows the second component  56  to move in relation to the first component  54  without the seal assembly  58  binding, permanently deforming or generating excessive heat. 
         [0029]    Referring now to  FIGS. 5-6 , one skilled in the art will recognize another embodiment of a seal arrangement  50  for restricting leakage of a fluid  36  or  40  through a gap  52  disposed between a first component  54  and the second component  56 . In the present embodiment, the first component  54  is stationary and is spaced from the second component  56  that rotates about axis  22  forming the gap  52 . A seal assembly  58  restricts leakage of fluid  36  or  40  in a direction perpendicular to the axis  22 . In other configurations of the present seal arrangement  50 , both of the components  54  and  56  are stationary, only one of the components  54  or  56  is rotating, or both of the components  54  and  56  are rotating at identical or varying speeds and directions. 
         [0030]    An annular seal assembly  58  fits over a shoulder  94  and against a seat  62  formed in the first component  54 . The seal assembly  58  is secured to the first component  54  by fastening means  64  such as tabs, bolts, rivets, welding, or by any other means known in the art. The seal assembly  58  comprises a back plate  66 , a side plate  68  and a plurality of leaf strips  70  sandwiched by and secured to the plates  66 ,  68 . 
         [0031]    The back plate  66  and side plate  68  are concentric, ring shaped members. A back plate width  96  is greater than a side plate width  98  to provide downstream support for the leaf strips  70  while subjected to the illustrated fluid  36  or  40  flow direction. As illustrated, back plate  66  is radially outboard of side plate  68 , while the placement is reversed if the fluid flow  36  or  40  direction is reversed. The plates  66 ,  68  are made of any suitable high temperature and corrosion resistant material such as a Nickel based alloy for gas turbine engine applications. 
         [0032]    The assembly and operation of the present embodiment are similar to the initially described embodiment and will not be replicated here for brevity. 
         [0033]    Referring lastly to  FIGS. 7-8 , one skilled in the art will recognize yet another embodiment of a seal arrangement  50  for restricting leakage of a fluid  36  or  40  through a gap  52  disposed between a first component  54  and a second component  56 . In the present embodiment, each component  54 ,  56  is stationary and spaced apart to form the gap  52 . A seal assembly  58  restricts leakage of the fluid  36  or  40  through the gap  52 . In other configurations of the present seal arrangement  50 , one of the components  54  or  56  is rotating, or both of the components  54  and  56  are rotating at identical or varying speeds and directions. 
         [0034]    A linear seal assembly  58  fits over a shoulder  94  and against a seat  62  formed in the first component  54 . The seal assembly  58  is secured to the first component  54  by fastening means  64  such as tabs, bolts, rivets, welding, or by any other means known in the art. The seal assembly  58  is comprised of a back plate  66 , a side plate  68  and a plurality of leaf strips  70  sandwiched by and secured to the plates  66 ,  68 . 
         [0035]    The back plate  66  and side plate  68  are rectangular shaped members. A back plate width  96  is greater than a side plate width  98  to provide downstream support for the leaf strips  70  while subjected to the illustrated fluid  36  or  40  flow direction. The plates  66 ,  68  are made of any suitable high temperature and corrosion resistant material such as a Nickel based alloy for gas turbine engine applications. 
         [0036]    The assembly and operation of the present embodiment are similar to the initially described embodiment and will not be replicated here for brevity. 
         [0037]    While the present invention has been described in the context of specific embodiments for use in the gas turbine engine industry, it is recognized that other industries would similarly benefit from the inventive seal arrangements. 
         [0038]    Other alternatives, modifications and variations will become apparent to those skilled in the art having read the foregoing description. Accordingly, the invention is intended to embrace those alternatives, modifications and variations as fall within the broad scope of the appended claims.