Abstract:
A method facilitates assembling a gas turbine engine including a combustor assembly and a nozzle assembly. The method comprises providing a transition piece including a first end, a second end, and a body extending therebetween, where the body includes an inner surface, an opposite outer surface, coupling the first end of the transition piece to the combustor assembly, and coupling the second end of the transition piece to the nozzle assembly such that a turbulator extending helically over the outer surface of the transition piece extends from the transition piece first end to the transition piece second end to facilitate inducing turbulence to cooling air supplied to the combustor assembly.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines and more particularly, to transition pieces used with gas turbine engines. 
   At least some known gas turbine engines include a transition piece that is coupled between a combustor assembly and a turbine nozzle assembly. To facilitate controlling operating temperatures of the transition piece within known engines, cooling air is channeled from a compressor towards the transition piece. More specifically, in at least some known gas turbine engines, the cooling air is discharged from the compressor into a plenum that extends at least partially around the transition piece of the combustor assembly. A portion of the cooling air entering the plenum is supplied into a channel defined between an impingement sleeve extending around the transition piece and the transition piece. Cooling air entering the cooling channel is discharged towards a combustor. 
   To enhance the effectiveness of the cooling air in the channel, at least some known transition pieces include axially-spaced turbulence-promoting ribs or turbulators, that extend outward from an outer surface of the transition piece. Known transition piece turbulators are oriented substantially perpendicularly to the flow of the cooling air in the cooling channel. These known transition pieces create turbulence by attaching a plurality of turbulators on a surface over which the air travels which creates air turbulence. When air flow comes into contact with the axially adjacent circumferential turbulator rings, the air flow slows as the air is forced over the turbulators and the pressure drop across the transition piece increases. To facilitate reducing such pressure drops, at least some known transition pieces are fabricated with a limited number of turbulators. However, as the number of turbulators is decreased, the efficiency of cooling the transition piece may also be decreased. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method facilitates assembling a gas turbine engine including a combustor assembly and a nozzle assembly. The method comprises providing a transition piece including a first end, a second end, and a body extending therebetween, where the body includes an inner surface, an opposite outer surface, coupling the first end of the transition piece to the combustor assembly, and coupling the second end of the transition piece to the nozzle assembly such that a turbulator extending helically over the outer surface of the transition piece extends from the transition piece first end to the transition piece second end to facilitate inducing turbulence to cooling air supplied to the combustor assembly. 
   In another aspect, a transition piece for a gas turbine engine is provided. The transition piece includes a first end, a second end, and a body extending therebetween, the body comprises an inner surface, an opposite outer surface, and a turbulator extending helically over the outer surface, the turbulator configured to facilitate cooling the transition piece. 
   In a further aspect, a gas turbine engine is provided. The gas turbine engine system includes a combustion assembly and a transition piece coupled to the combustion assembly and extending downstream therefrom, the transition piece comprises a first end, a second end, and a body extending therefrom, the body comprises an inner surface, an outer surface, and a turbulator extending helically over the outer surface, from the first end to the second end. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view of an exemplary gas turbine engine; 
       FIG. 2  is an enlarged cross-sectional view of a portion of an exemplary combustor assembly that may be used with the gas turbine engine shown in  FIG. 1 ; 
       FIG. 3  is a perspective view of a transition piece that may be used with the combustor assembly shown in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic cross-sectional view of an exemplary gas turbine engine  100 . Engine  100  includes a compressor assembly  102 , a combustor assembly  104 , a turbine assembly  106  and a common compressor/turbine rotor shaft  108 . It should be noted that engine  100  is exemplary only, and that the present invention is not limited to engine  100  and may instead be implemented within any gas turbine engine that functions as described herein. 
   In operation, air flows through compressor assembly  102  and compressed air is discharged to combustor assembly  104 . Combustor assembly  104  injects fuel, for example, natural gas and/or fuel oil, into the air flow, ignites the fuel-air mixture to expand the fuel-air mixture through combustion and generates a high temperature combustion gas stream (not shown). Combustor assembly  104  is in flow communication with turbine assembly  106 , and discharges the high temperature expanded gas stream into turbine assembly  106 . The high temperature expanded gas stream imparts rotational energy to turbine assembly  106  and because turbine assembly  106  is rotatably coupled to rotor  108 , rotor  108  subsequently provides rotational power to compressor assembly  102 . 
     FIG. 2  is an enlarged cross-sectional view of a portion of combustor assembly  104 . Combustor assembly  104  is coupled in flow communication with turbine assembly  106  and with compressor assembly  102 . Compressor assembly  102  includes a diffuser  140  and a discharge plenum  142  that is coupled in flow communication to, and downstream from, plenum  142  to facilitate channeling air towards combustor assembly  104  as described in more detail below. 
   In the exemplary embodiment, combustor assembly  104  includes an annular dome plate  144  that at least partially supports a plurality of fuel nozzles  146  and that is coupled to a substantially cylindrical combustor flowsleeve  148  with retention hardware (not shown in  FIG. 2 ). A substantially cylindrical combustor liner  150  is positioned within flowsleeve  148  and is supported via flowsleeve  148 . A substantially cylindrical combustor chamber  152  is defined by liner  150 . More specifically, liner  150  is spaced radially inward from flowsleeve  148  such that an annular combustion liner cooling passage  154  is defined between combustor flowsleeve  148  and combustor liner  150 . Flowsleeve  148  includes a plurality of inlets  156  which provide a flow path into cooling passage  154 . 
   An impingement sleeve  158  is coupled substantially concentrically to combustor flowsleeve  148  at an upstream end  159  of impingement sleeve  158 , and a transition piece  160  is coupled to a downstream side  161  of impingement sleeve  158 . Transition piece  160  facilitates channeling combustion gases generated in chamber  152  downstream towards a turbine nozzle  174 . A cooling passage  164  is defined between impingement sleeve  158  and transition piece  160 . A plurality of openings  166  defined within impingement sleeve  158  enable a portion of air flow discharged from compressor discharge plenum  142  is channeled into transition piece cooling passage  164 . 
   During operation, compressor assembly  102  is driven by turbine assembly  106  via shaft  108  (shown in  FIG. 1 ). As compressor assembly  102  rotates, compressed air is discharged into diffuser  140  as indicated in  FIG. 2  with a plurality of arrows. In the exemplary embodiment, the majority of air discharged from compressor assembly  102  is channeled through compressor discharge plenum  142  towards combustor assembly  104 , and a smaller portion of air discharged from compressor assembly  102  is channeled downstream for use in cooling engine  100  components. More specifically, a first flow leg  168  of compressed air within plenum  142  is channeled into transition piece cooling passage  164  via impingement sleeve openings  166 . Air entering opening  166  is channeled upstream within transition piece cooling passage  164  and discharged into combustion liner cooling passage  154 . A second flow leg  170  of compressed air within plenum  142  is channeled around impingement sleeve  158  and enters combustion liner cooling passage  154  via inlets  156 . Air entering inlets  156  and air from transition piece cooling passage  164  is then mixed within passage  154  and is then discharged into fuel nozzles  146  wherein it is mixed with fuel and ignited within combustion chamber  152 . 
   Flowsleeve  148  substantially isolates combustion chamber  152  and its associated combustion processes from the outside environment, for example, surrounding turbine components. The resultant combustion gases are channeled from chamber  152  through transition piece  160  towards turbine nozzle  174 . 
     FIG. 3  is a perspective view of transition piece  160 . Transition piece  160  includes an outer surface  180 , an inner surface  182 , a first end  184 , and a second end  186 . A helical turbulator  188  extends from outer surface  180 . In the exemplary embodiment, turbulator  188  is a continuous structure that is formed integrally with transition piece  160  and extends helically about transition piece  160 . In the exemplary embodiment wounded helical turbulator  188  is coupled to transition piece  160  using a braising process. In other embodiments, turbulator  188  is coupled to transition piece  160  using any other suitable coupling means, including a welding process. In another embodiment, turbulator  188  is formed onto surface  180  via a machining process. The cross-sectional shape of turbulator  188  may include but is not limited to being substantially circular, semi-circular, rectangular, or any other shape. 
   Alternatively, in another embodiment, turbulator  188  consists of a plurality of arcuate segments extending in a helical pattern across outer surface  180 . The arcuate segments do not form a continuous helical turbulator, but rather adjacent segments are separated by a gap. Although the turbulator in such an embodiment is not continuous, the segments follow a single common path and induce a helical flow of compressed air around transition piece  160 . Alternatively, in such an embodiment, posts or other equivalent structures may be positioned between adjacent segments. 
   In another alternative embodiment, turbulator  188  includes a plurality of independent parallel structures that extend helically about transition piece  160  in a wound pattern. Although the helical segments are independent and each follows a separate path, the plurality of helical segments induce a helical flow of compressed air around transition piece  160 . 
   Referring to  FIGS. 2 and 3 , during operation, the majority of air discharged from compressor assembly  102  is channeled through compressor discharge plenum  142  towards combustor assembly  104 , and the remaining air discharged from compressor assembly  102  is channeled downstream for use in cooling engine  100  components. More specifically, a first flow leg  168  of pressurized compressed air within plenum  142  is channeled into transition piece cooling passage  164  via impingement sleeve openings  166 . Air entering openings  166  is channeled upstream through cooling passage  164  and discharged into combustion liner cooling passage  154 . Turbulators  188  induce turbulence into the air entering passage  164 . Moreover, turbulators  188  facilitate inducing a helical flow path of cooling air about transition piece  160 . More specifically, air flowing through passage  164  is generally channeled in a helical path about transition piece  160  via turbulators  188 , prior to being discharged into combustion liner cooling passage  154 . 
   Air flowing around outer surface  180  facilitates enhanced cooling of transition piece  160  as compared to air flowing past a non-turbulated transition piece. More specifically, because the air flows helically over outer surface  180 , the air remains against or “in contact” with transition piece  160  for a longer period of time as compared to a non-turbulated transition piece. As a result, transition piece  160  is more efficiently cooled by the helically-routed air due to its increase staying time. Moreover, unlike known transition piece turbulators, in the exemplary embodiment, turbulators  188  not only channel the air helically about transition piece  160 , but also induce turbulence to the air. 
   In the exemplary embodiment, helical turbulators  188  channel a portion of the air flow around transition piece  160  in a helical manner. When air flow comes into contact with helical turbulators  188 , a first portion of the air flow is channeled helically around transition piece and a second portion of air flow is forced over helical turbulator  188 . Pressure losses are facilitated to be reduced with helical turbulators because only a portion of the air flow is forced over turbulator  188 . The remaining portion of air flow flows around transition piece  160  in a helical path. The helical flow of air around transition piece  160  facilitates minimizing a pressure drop of air flow, while allowing air to cool transition piece  160 . Moreover, turbulator  188  enhances the cooling of transition piece  160  such that the component useful life is facilitated to be increased. 
   Exemplary embodiments of transition pieces for use with turbine engines are described above in detail. The turbulators are not limited to use with the specific transition pieces described herein, but rather, the turbulators can be utilized independently and separately from other transition pieces described herein. Moreover, the invention is not limited to the embodiments of the transition piece or the turbulators described above in detail. Rather, other variations of helical turbulator embodiments may be utilized within the spirit and scope of the claims. 
   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.