Patent Publication Number: US-7909300-B2

Title: Combustor bracket assembly

Description:
BACKGROUND OF THE INVENTION 
     The present invention pertains to the art of gas turbine engines and, more particularly, to an assembly for securing a transition segment to a combustion liner in a gas turbine engine. 
     A gas turbine combustor includes a combustion liner that defines a combustion chamber. A transition segment extends between the combustion liner and a turbine first stage. A conventional assembly for securing a transition segment to a combustion liner includes a bullhorn. The bullhorn includes a plurality of bullhorn fingers. The bullhorn fingers extend axially away from the bullhorn and engage corresponding H-shaped guide blocks secured to the transition segment. The bullhorn fingers are disposed within the H-shaped block both below and above a cross sectional bar. With this arrangement, the transition segment is secured to the combustion liner through an axially floating interface. The floating interface allows the transition segment to expand axially and contract as a result of exposure to high temperature thermal conditions that exist in an operating turbine. Unfortunately, the floating interface places stress on the bullhorn fingers. Over time, the bullhorn lingers fail, and the gas turbine engine must be taken offline for repair. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with one aspect of the invention, a bracket assembly for securing a transition segment to a combustion liner of a gas turbine engine is provided. The bracket assembly includes at least one flange mounted to the transition segment. The at least one flange includes a channel that extends radially from the transition segment. The bracket assembly further includes a bracket fixedly mounted relative to the gas turbine engine. The bracket includes an elongated section having at least one end section that is received by the channel to establish an axially floating interlace that secures the transition segment to the combustion liner. 
     In accordance with another aspect of the present invention, a bracket is provided. The bracket includes an elongated section having opposing ends. The bracket further includes first and second curved sections that extend from respective ones of the opposing ends of the elongated section. The bracket also includes first and second end sections that extend from end portions of respective ones of the first and second curved sections. Each of the first and second end sections is angled relative to the elongated section. The bracket is adapted to establish an axially floating interface that secures a transition segment or a gas turbine engine to a combustion liner. 
     At this point it should be appreciated that the present invention provides a robust attachment mechanism for securing a transition segment to a combustion liner it a gas turbine engine. The design of the bracket significantly improves High Cycle fatigue (HCF) life and reliability, as well as reduces maintenance costs associated with engine down time resulting from a bracket failure. Moreover, it has been found that a bracket constructed as described above is capable of withstanding loads approximately 35% higher than prior alt constructions. In any event, additional objects, features and advantages of various aspects of the present invention will become more readily apparent from the following detailed description when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view illustrating a conventional gas turbine engine combustor, in accordance with prior art; 
         FIG. 2  is a partial cross-sectional view of the gas turbine engine combustor of  FIG. 1  taken along the line  2 - 2 ; 
         FIG. 3  is an exploded view illustrating a guide block and cooperating guide fingers in accordance with the prior art; 
         FIG. 4  is a side elevational view illustrating a gas turbine engine combustor including a combustor bracket assembly in accordance with one aspect of the present invention; 
         FIG. 5  is a partial cross-sectional view of the gas turbine engine combustor of  FIG. 4  taken along the line  6 - 6 ; and 
         FIG. 6  is a perspective view of a bracket of the combustor bracket assembly of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With initial reference engine to  FIG. 1 , a combustor assembly  10  of a multiple combustor gas turbine engine (not shown) includes a fuel nozzle  12  (some gas turbines employ multiple nozzles in each combustor), a combustion chamber  14  and a transition segment  16  that extends between combustion chamber  14  and a turbine first stage  18 . Combustion chamber  14  is defined by a substantially cylindrical combustion liner  20  that, in turn, is surrounded by a substantially cylindrical flow sleeve  22 . A radial space between flow sleeve  22  and liner  20  provides all airflow passage (not separately labeled) that allows compressor discharge air to be reverse flowed to an upstream or nozzle end  25  of liner  20  and then introduced into combustion chamber  14  for mixing with fuel. 
     Referring to  FIGS. 2 and 3 , transition segment  16  is secured to combustion liner  20  through an axially floating interface i.e. transition segment  16  is allowed to expand axially due to exposure to high temperature thermal conditions associated with an operating gas turbine. A forward support  24  of combustor  10  is defined by a pair of arms  26  and  28  that extend outwardly and upwardly to either side of transition segment  16 . Each arm  26 ,  28  of forward support  24  includes a corresponding axially extending guide finger element  30 ,  32 . As each guide finger element  30 ,  32 , is identical, a detailed description will follow with reference to guide finger element  30  with an understanding that guide finger element  32  is identically constructed. Guide finger element  30  is constructed of steel and, as shown in  FIG. 3 , includes a solid body portion  38  and a pair of axially extending, laterally spaced, fingers  40  and  42 . Fingers  40  and  42  extend axially outward away from solid body portion  38 . In use, as shown in  FIG. 1 , fingers  40  and  42  extend axially, in an upstream direction, i.e., towards and parallel to a longitudinal axis of and combustor  10 . Forward support  24 , together with arms  26  and  28  and guide finger elements  30  and  32  are collectively known as a bullhorn. Fingers  40 ,  42  are commonly referred to as bullhorn fingers. Bullhorn fingers  40  and  42  of guide finger element  30  slidably engage an H-shaped guide block  43 . As shown, H-shaped guide block  43  includes parallel elongated portions  44  and  46  interconnected by a cross portion  48 . Elongated portions  44  and  46  are welded within a flange  50  of transition segment  16 , as shown in  FIG. 2 , relatively closely adjacent the upstream or combustor end thereof. H-shaped guide block  43  is positioned such that elongated portions  44  and  46  are tangential to transition segment  16 , as shown in  FIG. 2 . At this point it should be understood that a plurality of bullhorns and cooperating H-shaped blocks provide an interface that secures transition segment  16  to combustion liner  20 , as discussed above. 
     Reference will now be made to  FIGS. 4-5  in describing an exemplary embodiment of the invention. A combustor assembly  52  of a multiple combustor gas turbine engine includes a fuel nozzle  54  (some gas turbines employ multiple nozzles in each combustor), a combustion chamber  56  and a transition segment  58 . In a manner similar to that described above, transition segment  58  extends between combustion chamber  56  and a turbine first stage  60 . Combustion chamber  56  is defined by a substantially cylindrical combustion liner  62  that, in turn, is surrounded by a substantially cylindrical flow sleeve  64 . A radial space  65  between flow sleeve  64  and liner  62  provides an airflow passage (not separately labeled) that allows compressor discharge air to be reverse flowed to an upstream or nozzle end  66  of liner  62  and introduced into combustion chamber  56  to mix with fuel. 
     As shown, transition segment  58  is secured to combustion liner  62  through an axially floating interface, i.e., transition segment  58  is allowed to expand and contract axially as a result of exposure to high temperature thermal conditions associated with an operating gas turbine engine. Combustor assembly  52  includes a flange  78  having mounted thereto a support  80  that extends toward transition segment  58 . Support  80  includes a pair of mounting holes (not shown) extending therethrough, for securing support  80  to flange  78 . An H-shaped guide block  84 , having a pair of generally parallel elongated portions  86  and  88  interconnected by a cross portion  90 , is welded within a flange  92  provided on transition segment  58 . Flange  92  is positioned relatively closely adjacent to an upstream or combustor end (not separately labeled) of transition segment  58 . H-shaped guide block  84  is positioned such that elongated portions  86  and  88  extend radially outward from transition segment  58 . In this manner, elongated portions  86  and  88 , define at least one channel  94 , the purpose of which will become more fully evident below. At this point it should be understood that while only two H-shaped guide blocks  84  and associated flanges  92  are illustrated in  FIG. 5 , transition segment  58  is provided with multiple H-shaped guide blocks  84  and corresponding flanges  92  not shown in the figures for sake of clarity. In any event, a bracket  66  secures transition segment  58  to support  80  and provides and axially floating interface as will be discussed more fully below. 
     As best shown in  FIG. 6 , bracket  66  is formed in a generally elongated U-shape, defined by a central elongated section  68  having opposing ends (not separately labeled). Bracket  66  further includes first and second curved sections  70  and  72  that extend from respective ones of the opposing ends of elongated section  68  and terminate at inwardly extending end sections  74  and  76  respectively. End sections  74  and  76  include a width and length sufficient for being securely positioned within channels  94  of corresponding H-shaped blocks  84 . Bracket  66 , in accordance with one aspect of the invention, is constructed from a single steel plate that is bent to form all previous discussed sections. In accordance with one aspect of the invention, bracket  66  is formed from 304 stainless steel, however, it should be understood that various other materials can also be employed. In any event, each curved section  70 ,  72  includes an upward curve having a gradual slope initiating at a respective one of the opposing ends of elongated section  68  and which continue to a steeper slope prior to terminating at end sections  74  and  76  respectively. As shown, end sections  74  and  76  are bent upwardly and inwardly relative to elongated section  68 . 
     Bracket  66  is provided with a pair of mounting holes  102  and  104  arranged equidistant from a center portion (not separately labeled) of elongated section  68 . More specifically, mounting holes  102  and  104  on bracket  66  are aligned with corresponding openings (not shown) provided on support  80 . In this manner, mechanical fasteners (not shown) are passed through mounting holes  102  and  104  and engage with the openings (not shown) provided on support  80 . Various types of mechanical fasteners such as bolts, threaded rods and the like can be employed to secure bracket  66  to support  80 . In any event, bracket  66  is secured to support  80  with end sections  74  and  76  being received by corresponding channels  94  in respective H-Shaped blocks  84 . With this arrangement, bracket  66  serves to limit movement of transition segment  58  in a direction toward turbine first stage  60  while still allowing transition segment  58  to expand and/or contract axially as a result of exposure to high temperature thermal conditions of an operating gas turbine engine. 
     Improved wear characteristics are provided at an interface between bracket  66  and a cooperating H-shaped block  84  by utilizing a harder, more wear resistant Cobalt-based alloy. That is, in accordance with one aspect of the invention, H-shaped block  84  is formed from an alloy containing between approximately 28.5 and 30.5% Chromium and about 52% Cobalt. More preferably, H-Shaped block  84  is formed from an alloy having a composition of 10.5% wt Nickel, 2.0% wt Iron, 29.5% wt Chromium, 7% wt Tungsten, 1% wt Silicone, 1% wt Manganese, 0.25% wt Carbon with the balance being Cobalt such as FSX-414. 
     In accordance with another aspect of the invention, wear characteristics are further improved through the use of a wear cover  96  provided on each end section  74  and  76  of bracket  66 . As shown in  FIG. 6 , wear cover  96  is formed from sheet material configured in a generally rectangular shape and provided with an opening  98 . In this manner, opening  98  receives, for example, end section  74 . Wear cover  96  is preferably constructed of a high temperature wear resistant Cobalt-based alloy. Preferably, wear cover  96  is formed from an alloy containing approximately 0.05/0.15% wt. Carbon, 1.00/2.00% wt Manganese, 0.040% wt Silicone, 0.030% wt Phosphorus, 0.3% wt Sulfur, 19.00/21.00% wt Chromium, 9.00/11.00% wt Nickel, 14.00/16.00% wt Tungsten and 3.00% wt Iron with the balance being Cobalt such as, for example, L-605. The use of an alloy having a high percentage by weight of Cobalt provides increased wear resistance for otherwise relatively soft end sections  74  and  76 . The combination of FSX-414 and L-605 has advantageously been found to establish a resilient interface between H-shaped block  84  and bracket  66 . Moreover, with the above described materials for the bracket  66  and H-shaped block  84 , wear patterns have been found to develop on the softer, e.g., L-605 material that is more easily replaceable/repairable and less costly as compared to transition segment  58  and associated H-shaped blocks  84 . 
     In accordance with another aspect of the invention, wear characteristics are improved through the use of a first wear cover, in the form of a wear resistant coating  105  applied to respective ones of end sections  74  and  76  of bracket  66 , and a second wear cover in the form of a wear resistant coating  106  applied to channel  94  of H-shaped block  84  such as illustrated in  FIG. 5 . Wear resistant coatings  105  and  106  are formed from a cobalt-based alloy containing approximately 1.1% wt Carbon, 66.9% wt Cobalt, 28% wt Chromium, and 4% wt tungsten such as, for example, Stellite-6. Stellite-6 can be readily applied to both end sections  74 ,  76 , and channel  94  to provide an easily repairable and maintainable wear resistant interface. 
     In an alternative arrangement, bracket  66  may be formed entirely of a high temperature, wear resistant alloy such as, for example, the L-605 alloy described above. It will also be appreciated that other wear resistant alloys having similar characteristics may also be used in accordance with the invention. In any event, bracket  66  significantly improves High Cycle fatigue (HCF) life and reliability, as well as reduces maintenance costs associated with engine down time resulting from a bracket failure. Moreover, it has been found that a bracket constructed as described above is capable of withstanding loads approximately 35% higher than prior art constructions. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the scope and scope of the invention. For example, the particular material used to form the bracket can vary without departing from the scope of the present invention. In addition, it should be understood that the H-shaped blocks can be formed from various materials having similar characteristics to FSX-414, including cobalt and non-cobalt based alloys, the wear covers can also be formed from various materials having wear characteristics similar to L-605 including both cobalt and non-cobalt based alloys, and a variety of materials, having attributes similar to Stellite-6, can be used to form the wear coatings. It should be readily appreciated that the above described materials should not be considered to represent an exhaustive list of acceptable materials for the various components and component portions of the present invention. In general, the invention is only intended to be limited by the scope of the following claims.