Abstract:
A method facilitates assembling a flap system for a gas turbine engine exhaust nozzle including at least one backbone assembly. The method comprises providing a basesheet including a pair of circumferentially-spaced sides coupled together by an upstream side and a downstream side, forming at least one relief cut in the basesheet that extends at least partially across the basesheet from at least one of the circumferentially-spaced sides, and coupling the basesheet to the backbone assembly.

Description:
GOVERNMENT RIGHTS STATEMENT  
       [0001]     The U.S. Government has rights in this invention present to Contract No. F336957-99-D-2050. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates generally to gas turbine engine exhaust nozzles and more particularly, to methods and apparatus for reducing turbine engine exhaust nozzle basesheet stresses.  
         [0003]     At least some known gas turbine engines include an exhaust nozzle including a variable geometry system. The variable geometry system adjusts an area of the exhaust nozzle through the use of flaps and seals. The flaps define discrete sectors of the flowpath, and the seals form the remaining flowpath between adjacent flaps. Because the exhaust nozzles are subjected to high temperatures and thermal gradients as a result of hot combustion gases exiting the engine, the variable geometry systems must maintain a coherent flowpath while shielding the structural components of the variable geometry system.  
         [0004]     At least some known flap systems consist of a backbone and a basesheet. The backbone secures the basesheet within the variable geometry system. To facilitate extending a useful life at high temperature operation, at least some known basesheets are fabricated from non-metallic materials, such as ceramic matrix composite (CMC) materials.  
         [0005]     At least some known basesheets are divergent and are attached to the backbone using mechanical fasteners, such as rivets or bolts. Over time, continued thermal expansion may create local stress concentrations within the divergent basesheets. Furthermore, continued thermal cycling may cause the divergent basesheet to deform or distort. Because such tensile strength may be a weakest load path through the basesheet, continued thermal cycling may cause premature failure of the basesheet.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     In one aspect, a method for assembling a flap system for a gas turbine engine exhaust nozzle including at least one backbone assembly is provided. The method comprises providing a basesheet including a pair of circumferentially-spaced sides coupled together by an upstream side and a downstream side, forming at least one relief cut in the basesheet that extends at least partially across the basesheet from at least one of the circumferentially-spaced sides, and coupling the basesheet to the backbone assembly.  
         [0007]     In another aspect, an assembly for a gas turbine engine exhaust nozzle is provided. The assembly includes a backbone and a basesheet that is configured to couple to the backbone. The basesheet includes at least one relief cut and a pair of circumferentially-spaced sides coupled together by an upstream side and a downstream side. The at least one relief cut extends from at least one of the circumferentially-spaced sides towards the other respective circumferentially-spaced side.  
         [0008]     In a further aspect, a gas turbine engine including a variable engine exhaust nozzle that includes a flap system coupled to the engine exhaust nozzle is provided. The flap system inlcudes a backbone and a basesheet that is configured to couple to the backbone. The basesheet includes at least one relief cut and a pair of circumferentially-spaced sides coupled together by an upstream side and a downstream side. The at least one relief cut extends from at least one of the circumferentially-spaced sides towards the other respective circumferentially-spaced side. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a schematic illustration of a gas turbine engine;  
         [0010]      FIG. 2  is a perspective view of a portion of a flap system that may be used with the engine shown in  FIG. 1 ; and  
         [0011]      FIG. 3  is a perspective view of an exemplary basesheet that may be used with the gas turbine engine shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  is a schematic illustration of a gas turbine engine  10  including a fan assembly  12 , a high pressure compressor  14 , and a combustor  16 . In one embodiment, engine  10  is a F414 engine available from General Electric Company, Cincinnati, Ohio. Engine  10  also includes a high pressure turbine  18  and a low pressure turbine  20 . Fan assembly  12  and turbine  20  are coupled by a first shaft  24 , and compressor  14  and turbine  18  are coupled by a second shaft  26 .  
         [0013]     In operation, air flows through fan assembly  12  and compressed air is supplied from fan assembly  12  to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Airflow from combustor  16  drives rotating turbines  18  and  20  and exits gas turbine engine  10  through an exhaust system  28 . Exhaust system  28  includes a variable geometry system  30 .  
         [0014]      FIG. 2  is a perspective view of an exemplary flap system  100  that may be used with engine  10  (shown in  FIG. 1 ).  FIG. 3  is a perspective view of an exemplary basesheet assembly  106  that may be used with gas turbine engine  10 . Flap system  100  is coupled to an exhaust nozzle, such as exhaust system  28  (shown in  FIG. 1 ) to facilitate shielding variable geometry system components from high temperature combustion gases exiting the engine. More specifically, flap system  100  is coupled to the exhaust nozzle such that a flowpath side  102  of flap system  100  is exposed to combustion gases exiting engine. Accordingly, flap system flowpath side  102  defines a portion of the flowpath through the nozzle.  
         [0015]     Flap system  100  includes a plurality of backbones  104  and basesheet assemblies  106  extending circumferentially within the engine exhaust nozzle. More specifically, backbone  104  is exemplary and is known in the art. Basesheet assembly  106  is coupled within the engine exhaust nozzle by backbone  104 , and includes has a leading edge  110  and a trailing edge  112 . Basesheet assembly leading and trailing edges  110  and  112 , respectively, are coupled together by a pair of side edges  114  and  116 . Basesheet assembly  106  also includes an opening  118  extending through basesheet assembly  106  between opposite sides  120  and  122  of basesheet assembly  106 . Opening  118  is sized to receive a fastener (not shown) therethrough for securely coupling basesheet assembly  106  to backbone  104 . In the exemplary embodiment, basesheet side  120  is a flowpath side of basesheet assembly  106  and side  122  is a radially outer side of basesheet assembly  106 .  
         [0016]     Leading edge  110  and trailing edge  112  each have a respective width W 1  and W 2  measured between side edges  114  and  116 . In the exemplary embodiment, basesheet assembly  106  is divergent such that trailing edge width W 2  is wider than leading edge width W 1 . A centerline axis  120  extends through basesheet assembly  106  between leading and trailing edges  110  and  112 , respectively. In the exemplary embodiment, leading and trailing edges  110  and  112 , respectively, are substantially perpendicular to centerline axis  120 . In an alternative embodiment, leading and trailing edges  110  and  112  are non-parallel.  
         [0017]     In the exemplary embodiment, basesheet assembly  106  includes a plurality of relief cuts  200  which extend through basesheet assembly  106  between basesheet sides  120  and  122 . In an alternative embodiment, basesheet assembly  106  only includes one relief cut  200 . Each relief cut  200  extends circumferentially inward from a respective side edge  114  and  116  towards basesheet centerline axis  120 . In an alternative embodiment, relief cuts  200  extend only from one of side edges  114  or  116 . More specifically, in the exemplary embodiment, each relief cut  200  is oriented substantially perpendicularly to centerline axis  120 . In another embodiment, each relief cut  200  is oriented obliquely with respect to centerline axis  120 .  
         [0018]     In the exemplary embodiment, basesheet assembly relief cuts  200  include long relief cuts  230  and short relief cuts  232 . Each relief cut  230  and  232  has a length L L  and L S  measured from a respective basesheet assembly side  114  or  116  to an end  234  and  236  of respective relief cuts  230  and  232 . In the exemplary embodiment, relief cuts  230  and  232  extending inwardly from each side  114  and  116  are axially aligned with respect to each other across basesheet assembly  106 , such that sides  114  and  116  are mirror images of each other. It should be noted that the size, length, width, number, orientation, and location of relief cuts  200  are variably selected, as described in more detail below, to facilitate each relief cut  200  reducing thermal stresses, deformation, and distortion of basesheet assembly  106 .  
         [0019]     During assembly of flap system  100 , initially relief cuts  200  are formed within basesheet assembly  106 . More specifically, the number, size, length, width, number, orientation, and location of relief cuts  200  with respect to basesheet assembly  106  is variably selected to facilitate relief cuts reducing thermal stresses induced to basesheet assembly  106 . More specifically, as basesheet assembly  106  is thermally cycled during engine operation, relief cuts  200  facilitate reducing thermal stresses induced to basesheet assembly  106  such that deformation, thermal yield, and/or distortion of basesheet assembly  106  is also reduced. More specifically, relief cuts  200  permit basesheet assembly  106  to thermally expand relative to backbone  104  while facilitating reducing thermal stresses induced to basesheet assembly  106  and backbone  104 .  
         [0020]     In the exemplary embodiments described herein, a divergent flap basesheet has been illustrated. However, the stress relief techniques described herein can be applied to a similarly constructed convergent flap basesheet.  
         [0021]     The above-described flap system is cost-effective and highly reliable. The flap system includes a basesheet assembly that is coupled to the backbone. The basesheet assembly includes a plurality of relief cuts that facilitate reducing thermal stresses induced to the basesheet assembly. Accordingly, deformation and/or distortion of the basesheet assembly is facilitated to be reduced in a cost-effective and reliable manner.  
         [0022]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.