Abstract:
A method for assembling a combustor for use in a turbine engine is provided. The method includes providing at least one support leg, forming at least one opening in the support leg, wherein the at least one opening has a perimeter defined only by a plurality of non-linear segments, and coupling the support leg to the combustor.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to turbine engines, and more particularly, to a method and apparatus that facilitates reducing stress in combustor support legs used in turbine engines. 
   At least some known combustors are supported at an aft end of the combustor by support legs. Known support legs control the axial, radial and circumferential location of the combustor in a core gas turbine engine, and generally include a plurality of openings, called windows. Cooling fluid is channeled through such windows towards downstream components, such as turbine components. Generally, known windows are rectangular-shaped, square-shaped or elliptical-shaped. 
   Known rectangular-shaped and square-shaped windows include rounded corners that are each formed with the same radius, and that are connected together with straight line segments extending between adjacent corners. Known elliptical windows include two straight line segments that are substantially parallel to each other, and that are also connected at respective ends by arcuate segments having the same radii. Furthermore, known support legs also include bolt holes that are used to couple the support legs to a combustor casing at alternating window locations. 
   The rounded corners and/or sides of known window configurations may develop high concentrations of stress during turbine operations. Over time the stresses induced to the windows may cause cracking adjacent to the corners and may lead to failure of the support leg and/or reduce the on-wing service time of the support legs. As a result and based on the high failure frequency and potential, known support legs are generally replaced more frequently, thereby increasing engine downtime and increasing maintenance costs. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method for assembling a combustor for use in a turbine engine is provided. The method includes providing at least one support leg, forming at least one opening in the support leg, wherein the at least one opening has a perimeter defined only by a plurality of non-linear segments, and coupling the support leg to the combustor. 
   In another aspect, a support leg for use with a turbine engine combustor is provided. The support leg includes a window portion including at least one window including a perimeter defined only by a plurality of non-linear segments, and a coupling portion configured to couple to an aft end of the combustor such that the support leg supports the combustor within the turbine engine. 
   In yet another aspect, a support system for locating a combustor in a turbine engine is provided. The support system includes a support leg, the support leg includes a liner coupling portion, and a window portion including at least one window. The at least one window includes a perimeter only defined by a plurality of non-linear segments. The support system also includes a coupling portion configured to couple to an aft end of the combustor such that the support leg supports the combustor within the turbine engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of an exemplary turbofan gas turbine assembly; 
       FIG. 2  is a schematic cross-sectional view of an exemplary combustor that may be used with the turbofan gas turbine assembly shown in  FIG. 1 ; 
       FIG. 3  is an enlarged cross-sectional view of an exemplary support leg; 
       FIG. 4  is a perspective view of a segment of the support leg shown in  FIG. 3 ; 
       FIG. 5  is an enlarged view of a portion of the support leg shown in  FIG. 4 ; and 
       FIG. 6  is an enlarged cross-sectional view of the support leg shown in  FIG. 3  and including an exemplary diagram for locating the window shown in  FIGS. 4 and 5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a cross-sectional view of a portion of an exemplary turbofan engine assembly  10  having a longitudinal axis  11 . In the exemplary embodiment, turbofan engine assembly  10  includes a core gas turbine engine  12  that includes a high-pressure compressor  14 , a combustor  16 , and a high-pressure turbine  18 . Turbofan engine assembly  10  also includes a low-pressure turbine  20  that is disposed axially downstream from core gas turbine engine  12 , and a fan assembly  22  that is disposed axially upstream from core gas turbine engine  12 . 
     FIG. 2  is a schematic cross-sectional view of an exemplary combustor  16  that may be used with core gas turbine engine  12  (shown in  FIG. 1 ). Combustor  16  includes an outer liner  52  and an inner liner  54  disposed between an outer combustor casing  56  and an inner combustor casing  58 . Outer and inner liners  52  and  54  are spaced radially from each other such that a combustion chamber  60  is defined therebetween. Outer liner  52  and outer casing  56  form an outer passage  62  therebetween, and inner liner  54  and inner casing  58  form an inner passage  64  therebetween. A cowl assembly  66  is coupled to the upstream ends of outer and inner liners  52  and  54 , respectively. An annular opening  68  leading to an opening formed in cowl assembly  66  enables compressed fluid to enter combustor  16  in a direction generally indicated by arrow A. It should be appreciated that the term “fluid” as used herein includes any material or medium that flows, including but not limited to, gas and air. The compressed fluid flows through annular opening  68  to support combustion and to facilitate cooling liners  52  and  54 . 
   Combustor  16  includes a longitudinal axis  74  which extends from a forward end  70  to an aft end  72  of combustor  16 . In the exemplary embodiment, combustor  16  is a single annular combustor. Alternatively, combustor  16  may be any other combustor, including, but not limited to a double annular combustor. An aft end  53  of inner liner  54  is coupled to and held in position by an exemplary support leg  76 . Support leg  76  is also coupled to inner combustor casing  58 . 
     FIG. 3  is an enlarged cross-sectional view of support leg  76 . In the exemplary embodiment, support leg  76  includes a liner coupling portion  78 , a window portion  80 , a knuckle portion  82  and a casing coupling portion  84 . Liner coupling portion  78  is configured to couple to inner liner aft end  53  (shown in  FIG. 1 ) Window portion  80  is formed with an opening or window  86 , that is sized and shaped to facilitate channeling cooling fluid from inner passage  64  (shown in  FIG. 2 ) towards downstream turbine components  18  and  20  (shown in  FIG. 2 ). In the exemplary embodiment, knuckle portion  82  is S-shaped and includes a bend  90  that defines a forward-most point  91 . Casing coupling portion  84  includes at least one opening  88  that is sized and shaped to receive a fastener therethrough to couple leg  76  to inner combustor casing  58 . Specifically, a bolt (not shown) is inserted through opening  88  to secure support leg  76  to inner combustor casing  58 . In the exemplary embodiment, support leg  76  is fabricated from a material, such as HS188 that enables leg  76  to withstand operating stresses and that facilitates increasing on-wing service time of support leg  76 . However, it should be appreciated that other embodiments may use any material that enables support leg  76  to function as described herein. 
   Modifying the outer perimeter and/or geometry of known windows facilitates changing the interaction between the window border edges and stress fields  87  that may develop about the windows. Consequently, the exemplary embodiments described herein modify known window configurations to facilitate reducing stress field interruption about window perimeters. 
     FIG. 4  is a perspective view of a segment of support leg  76 . In the exemplary embodiment, windows  86  are each defined by a first arcuate segment  92 , a second arcuate segment  94 , a third arcuate segment  96 , a fourth arcuate segment  98 , a fifth arcuate segment  100  and a sixth arcuate  102 . Each arcuate segment  92 ,  94 ,  96 ,  98 ,  100  and  102  is defined by a radius. As such, window  86  is defined only by curved segments. More specifically, in the exemplary embodiment, windows  86  are defined only by non-linear segments. Because windows  86  are defined with only arcuate segments, windows  86  are shaped in a configuration that facilitates minimally interrupting a stress field  87  that may be induced to leg  76 . The curved window configuration also facilitates reducing stress development along the perimeter of window  86  as defined by arcs  92 ,  94 ,  96 ,  98 ,  100  and  102  and along the areas surrounding each window  86 . 
   Support leg  76  extends between a radially inner edge  97  and a radially outer edge  99 . In the exemplary embodiment, support leg  76  has an annular configuration and circumscribes aft end  72  of combustor  16 . More specifically, support leg  76  is coupled to inner liner aft end  53  such that aft end  53  circumscribes support leg  76 . It should be understood that support leg  76  includes twenty windows  86  circumferentially and uniformly spaced about the perimeter of support leg  76 . However, it should be appreciated that although the exemplary embodiment is described as including twenty windows  86  uniformly spaced about support leg  76 , other embodiments may include any number of windows  86  spaced in any manner, that enable support leg  76  to function as described herein. Moreover, it should be appreciated that the size, dimensions, and shape of windows  86  is variably selected depending on the area required to provide adequate cooling flow therethrough to downstream components. 
     FIG. 5  is an enlarged view of an exemplary window  86 . In the exemplary embodiment, arcuate segments  92  and  98  each have radii R 1  and R 2 , respectively. It should be understood that radii R 1  and R 2  are measured from the same center point  200  and that radius R 2  is longer than radius R 1 . In the exemplary embodiment, the difference between radii R 1  and R 2  defines a width  120  of each window  86 . Arcuate segments  94  and  102  are each defined by a radius R 3 , and arcuate segments  96  and  100  are each defined by a radius R 4 . Arcuate segments  94  and  102  are each defined with respect to a center point,  122  and  124 , respectively. Arcuate segments  96  and  100  are each defined with respect to a center point  126  and  128 , respectively. It should also be understood that in the exemplary embodiment, radii R 3  and R 4  are different and are selected to facilitate reducing stresses along the perimeter of window  86 . 
   In the exemplary embodiment, arcuate segment  92  extends from arcuate segment  102  to arcuate segment  94 . More specifically, arcs  92  and  94  have a common tangent, a compound curvature point  104  which forms a smooth transition between arcs  92  and  94 . Arc  94  extends from arcuate segment  92  to arc  96 . Specifically, arcuate segments  94  and  96  have a common tangent at a compound curvature point  106  which defines a smooth transition point between arcs  94  and  96 . Arcuate segment  96  extends from arcuate segment  94  to arc  98 . Arcuate segments  96  and  98  have a common tangent at a compound curvature point  108  which defines a smooth transition point between arcs  96  and  98 . Arc  98  extends from arcuate segment  96  to arcuate segment  100 . Arcuate segments  98  and  100  have a common tangent at a compound curvature point  110  which defines a smooth transition point between arcuate segments  98  and  100 . Arcuate segment  100  extends from arcuate segment  98  to arcuate segment  102 . Arcuate segments  100  and  102  have a common tangent at a compound curvature point  112  which defines a smooth transition point between arcs  100  and  102 . Arc  102  extends from arcuate segment  100  to arc  92 . Arcs  102  and  92  have a common tangent at a compound curvature point  114  which defines a smooth transition point between arcs  102  and  92 . The window configuration described herein defines a window  86  that is shaped to facilitate reducing stress induced to support leg  76  because the shape defined by the arcuate segments  92 ,  94 ,  96 ,  98 ,  100  and  102  minimally interrupts the stress fields  87  that may develop around window  86 . 
   In the exemplary embodiment, each window  86  has an arcuate centerline  132  extending from point  106  to point  112 . Fastener openings  88  are defined along center line  134  such that each opening  88  is substantially concentrically aligned with a midpoint  116  of each window centerline  132 . More specifically, in the exemplary embodiment, each opening  88  is a distance D 2  from each window centerline  132  such that openings  88  are circumferentially aligned with each other. Openings  88  facilitate reducing stresses about the perimeter of window  86 . It should be appreciated that although the exemplary embodiment is described using substantially circular openings  88 , in other embodiments openings  88  may have any size and/or shape that enables support leg  76  to function as described herein. 
     FIG. 6  is an enlarged cross-sectional view of support leg  76  and illustrates an exemplary diagram for locating each window  86 . In the exemplary embodiment, each window  86  is initially defined by using the slope of each support leg window portion  80  to generate a conical shape  136 . More specifically, initially the slope of window portion  80  is extended to define a line  138 . A horizontal line  146  is then generated to extend through a center of the conical shape  136  generated. Line  146  intersects line  138  at a point  144  such that an angle θ is defined between lines  138  and  146 . At forward-most point  91  of bend  90 , a substantially vertical line  150  is defined tangentially to point  91  such that line  150  is substantially perpendicular to line  146 . Then, a location  140  is determined on window portion  80  at a distance L 4  from line  150 . The location  140  is based on adjacent geometry, part specific conditions and empirical data. A line D 4  is extended through location  140  such that line D 4  is substantially perpendicular to line  146 . 
   A vertical line D 3  is then extended through a location  142 . Location  142  is a distance L 3  from line  150 . Specifically, line D 3  is extended through location  142  such that line D 3  is substantially perpendicular to line  146 . A line  139  is then constructed along the opposite slope of the conical shape  136  generated. Accordingly, lines  138 ,  139 , and D 4  define conical shape  136 . Next, the angle θ measured between lines  146  and  138  is determined using the formula θ=tan −1 (((D 4 /2)−(D 3 /2))/(L 4 −L 3 )). After determining angle θ, radius R 2  is computed using the formula R 2 =D 4 /2 cos θ, and radius R 1  is computed using the formula R 1 =D 3 /2 cos θ. Thus, the lengths of radii R 1  and R 2  depend on cone diameters D 3  and D 4 , and angle θ. In the exemplary embodiment, angle θ is approximately 26.246 degrees. However, it should be appreciated that in other embodiments, any angle θ may be selected that enables support leg  76  to function as described herein. 
   In the exemplary embodiment, radii R 1 , R 2 , R 3  and R 4  are each a different length. Specifically, in the exemplary embodiment, radius R 1  is approximately 24.55 inches, radius R 2  is approximately 25.21 inches, radius R 3  is approximately 0.25 inches, and radius R 4  is approximately 0.45 inches. It should be appreciated that other embodiments, radii R 1 , R 2 , R 3  and R 4  may be any length that enables support leg  76  to function as described herein. Moreover, it should be appreciated that although the exemplary embodiment includes four curves, other embodiments may use any number of non-linear segments to define the perimeter of window  86  that enable support leg  76  to function as described herein. It should also be understood that the dimensions described herein have a tolerance of ±0.010 inches. 
   In each embodiment the above-described support leg windows facilitate reducing stresses induced to the support leg about each window&#39;s perimeter and thus facilitate improving the durability and useful life of each support leg. More specifically, in each embodiment, the support leg windows facilitate reducing stresses induced to each support leg by shaping each window to avoid stress fields  87  that may be generated. As a result, the windows facilitate performing less support leg  76  maintenance within a corresponding turbine engine. Accordingly, core gas turbine engine performance and component useful life are each facilitated to be enhanced in a cost effective and reliable means. 
   Although the apparatus and methods described herein are described in the context of positioning windows in a combustor liner support leg of a core gas turbine engine, it should be understood that the apparatus and methods are not limited to core gas turbine engines, combustor liners, or windows. Likewise, the core gas turbine engine and support leg illustrated are not limited to the specific embodiments described herein, but rather, components of both the core gas turbine engine and the support leg can be utilized independently and separately from other components described herein. 
   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.