Abstract:
A method facilitates assembling a gas turbine engine with a flameholder. The method comprises coupling at least one turning vane between a radially outer casing and a radially inner casing to form a flameholder, forming at least two slots that extend substantially radially through the outer and inner casings, coupling at least one fuel injector to the flameholder, and coupling the flameholder within the augmenter.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to turbine engines, and more specifically, to flameholders used therein. 
   At least some know gas turbine engines used with aircraft include in serial flow communication a fan, compressor, combustor, high pressure turbine, and low pressure or booster turbine. High performance aircraft engines may also include an afterburner or augmenter at the engine&#39;s aft end for providing additional thrust when required. During engine operation, air compressed as it flows through the fan and compressor, is mixed with fuel in the combustor. The fuel/air mixture is ignited and the combustion gases are channeled downstream through the turbines which extract energy therefrom. The hot combustion gases are then discharged from the engine into an augmenter wherein a portion of the exhausted gas is mixed with fuel and reignited prior to being discharged from the engine through a variable area exhaust nozzle. 
   Known augmenters include an exhaust casing and liner which defines a combustion zone. Flameholders and fuel spraybars within the augmenters introduce additional fuel into the exhaust discharge from the turbine engine. Various types of flameholders are known and at least some augmenters include at least one circumferential flameholder. More specifically, such flameholders include V-shaped gutters which define regions of relatively low velocity in the otherwise high velocity core gases. The afterburner flame may be initiated within such low velocity regions. 
   At least one known augmenter includes an annular flameholder assembly that includes a row of swirl vanes mounted between radially outer and inner casings. Each of the swirl vanes has opposite pressure and suction sidewalls that each extend from a leading edge to a trailing edge. An aft end of each flameholder includes a generally planar aft panel that extends about the circumference of the flameholder to facilitate holding the flame during augmenter operation. An annular opening defined in an upstream side of the augmenter enables exhaust gases to flow into the flameholder. A flow restricting structure downstream from the annular opening meters an amount of air flow entering the flameholder. 
   However, in at least one known flameholder, the flow restricting structure creates a flow pattern that extends downstream to the fuel sprayers. The fuel and exhaust flow mixture in such flow patterns may migrate upstream and spontaneously combust within the flameholder. Over time, spontaneous combustions within the flameholder may reduce the useable life of the augmenter. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method facilitates assembling a gas turbine engine with a flameholder. The method comprises coupling at least one turning vane between a radially outer casing and a radially inner casing to form a flameholder, forming at least two slots that extend substantially radially through the outer and inner casings, coupling at least one fuel injector to the flameholder, and coupling the flameholder within the augmenter. 
   In another aspect, an augmenter for a gas turbine engine, including a flameholder is provided. The flameholder includes a radially outer casing, a radially inner casing, at least one turning vane extending radially between the outer and inner casings, and at least two slots that extend substantially radially through the outer and inner casings. 
   In a further aspect, a gas turbine engine is provided. The gas turbine engine system includes an augmenter, a flameholder including a radially outer casing, a radially inner casing, at least one turning vane extending between the outer and inner casings, and at least two slots extending substantially radially through the radially outer and inner casings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of an exemplary gas turbine engine that includes an augmenter. 
       FIG. 2  is a perspective view of a flameholder that may be used with the augmenter shown in  FIG. 1 . 
       FIG. 3  is a perspective view of the flameholder shown in  FIG. 2  and with an outer casing removed. 
       FIG. 4  is cross-sectional view of a portion of the flameholder shown in  FIG. 2 . 
       FIG. 5  is a cross-sectional view of another portion of the flameholder shown in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a cross-sectional view of a gas turbine engine  10  including a low pressure compressor  12 , a high pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high pressure turbine  18 , and a booster or low pressure turbine  17 . An augmenter  22  extends downstream from low pressure turbine  17  to a variable area exhaust nozzle  23 . Augmenter  22  includes a flameholder assembly  30  that in the exemplary embodiment, includes a radially outer flameholder  32  and radial inner flameholder  34 . A center axis  25  extends through the center of engine  10  and augmenter  22 . 
   In operation, air flows through low pressure compressor  12  and compressed air is supplied from low pressure compressor  12  to high pressure compressor  14 . Highly compressed air is then delivered to combustor  16  and combustion gases flow from combustor  16  through turbines  17  and  18 . Exhausted combustion gases enter augmenter  22  are mixed with fuel and bypass airflow  27  entering augmenter  22  from a bypass duct  20 . The fuel/air mixture is reignited and the resulting combustion gases are channeled aftward through exhaust nozzle  23 . 
     FIG. 2  is a perspective view of annular flameholder assembly  30 .  FIG. 3  is a perspective view of a portion of flameholder assembly  30 .  FIG. 4  is a cross sectional view of flameholder assembly  30  including a turning vane  42 .  FIG. 5  is a cross sectional view of flameholder assembly  30  including a flow restrictor  52 . In the exemplary embodiment, annular flameholder assembly  30  includes an outer flameholder  32  and an inner flameholder  34 . Outer flameholder  32  includes a radially outer casing  36  and a radially inner casing  38 . Radially outer casing  36  and radially inner casing  38  include a leading edge  72  and a trailing edge  74 . A plurality of generally axially aligned slots  39  extend through outer and inner casings  36  and  38 , respectively. More specifically in the exemplary embodiment, slots  39  are spaced circumferentially about flameholder assembly  30 . In the exemplary embodiment, inner flameholder  34  includes an annular V-shaped gutter  35  which faces downstream. 
   A plurality of circumferentially-spaced turning vanes  42  and a plurality of circumferentially-spaced flow restrictors  52  extend between outer and inner casings  36  and  38 , respectively. For example, in one embodiment, turning vanes  42  and flow restrictors  52  are coupled between outer and inner casings  36  and  38 , respectively, via a braising process. More specifically, in the exemplary embodiment each pair of circumferentially-adjacent axial slots  39  generally divides the plurality of turning vanes  42  into groups  60  of turning vanes  42 . In the exemplary embodiment, groups  60  are circumferentially-spaced about flameholder assembly  30 . Moreover, each pair of circumferentially-adjacent axial slots  39  also generally divides the plurality of flow restrictors  52  into groups  62  of flow restrictors  52 . In the exemplary embodiment, groups  62  are circumferentially-spaced about flameholder assembly  30 . More specifically, in the exemplary embodiment, each group  62  of flow restrictors  52  is positioned between a circumferentially-adjacent pair of groups  60  of turning vanes  42 . 
   In the exemplary embodiment, each turning vane  42  includes a leading edge  44 , a trailing edge  46 , a concave sidewall  48 , and a convex sidewall  50  connected to leading edge  44  and trailing edge  46 . In the exemplary embodiment, turning vane  42  leading edge  44  is downstream of inlet portion  64  leading edge  72 . Moreover, each turning vane  42  is substantially equi-spaced circumferentially between outer and inner casings  36  and  38  respectively. In the exemplary an upstream embodiment, each flow restrictor  52  is generally cylindrical in shape and include upstream side  54  and a downstream side  56 . Moreover, each flow restrictor  52  is substantially equi-spaced circumferentially between outer and inner casings  36  and  38  respectively. Other embodiments of flow restrictors  52  may include but are not limited to, semi-circular or rectangular structures. 
   Groups  60  of turning vanes  42 , in the exemplary embodiment, are coupled within portions of flameholder  32  that define a turning vane flow passage  76  that includes an inlet portion  64  upstream from turning vanes  42 , a discharge portion  66  downstream from turning vanes  42 , and an intermediate portion  65  extending therebetween. Passage  76  has a height H tv  measured from a radially outer surface  80  of inner casing  38  to a radially inner surface  82  of outer casing  36 . In the exemplary embodiment, passage height H tv  is substantially constant from inlet portion  64  through intermediate portion  65 , and increases gradually from intermediate portion  65  through discharge portion  66 . As such, outer casing  36  is formed with a substantially constant radius of curvature  94  from a leading edge  72  of inlet portion  64  to a trailing edge  74  of discharge portion  66 . The radius of curvature is the radial distance measured from center axis  25  to either radially outer or radially inner casing  36  or  38 . Moreover, in the exemplary embodiment, inner casing  38  is formed with a substantially constant radius of curvature  96  from leading edge  72  to turning vane trailing edge  46  and a gradually decreasing radius of curvature  96  within discharge portion  66 , from turning vane trailing edge  46  to discharge portion  66  trailing edge  74 . 
   Similarly, in the exemplary embodiment, groups  62  of flow restrictors  52  are positioned within portions of flameholder  32  that define a flow restrictor flow passage  78  that includes an inlet portion  68  upstream from flow restrictors  52 , a discharge portion  70  downstream from flow restrictors  52 , and an intermediate portion  69  extending therebetween. Flow restrictor flow passage  78  has a height H fr  that is measured from inner casing outer surface  80  to outer casing inner surface  82 . Moreover, in the exemplary embodiment, outer casing leading edge  90  is bent inward with respect to flow restrictor flow passage  78 . Similarly, inner casing leading edge  92  is bent inward with respect to flow restrictor flow passage  78 . As such, outer casing  36  is formed with a substantially constant radius of curvature  98  from flow restrictor upstream side  54  to disclosure portion trailing edge  74 . Moreover, in the exemplary embodiment, inner casing  38  is formed with a radius of curvature  99  that gradually decreases from inlet portion leading edge  72  to discharge portion trailing edge  74 . As such, height H fr  increases gradually from inlet portion  68  through to discharge portion  70 . 
   In the exemplary embodiment, a plurality of circumferentially-spaced swirl vanes  100  are defined between outer and inner casings  36  and  38 . More specifically, in the exemplary embodiment, swirl vanes  100  are each defined downstream from each group  60  of turning vanes  42 . Each swirl vane  100  includes a leading edge  102 , a trailing edge  103 , a suction side wall  104 , a pressure side wall  106 , and an aft panel  108  that includes a plurality of vents  110 . Combustion gases  28  are channeled into each swirl vane  100  via a plurality of circumferentially-spaced scoops  112 . More specifically, each scoop  112  defines a channel  114  which extends in flow communication a plurality of inlet apertures (not shown) defined within inner casing  38 , and move specifically with an interior of swirl vane  100 . Pressure wall  106  is generally concave from leading edge  102  to aft panel  108  and suction wall  104  is generally convex from leading edge  102  to aft panel  108 . Swirl vanes  100  define a bluff body that facilitates enhancing flameholder capability. 
   Inserted radially through outer casing  36  is a pilot fuel injector  116  and an igniter  118 . In the exemplary embodiment, pilot fuel injector  116  is downstream from turning vanes  42 . More specifically, pilot fuel injector  116  is positioned within an aperture  41  defined within outer casing  36  and igniter  118  is downstream from pilot fuel injector  116 . A plurality of main fuel spraybars  120  extend through axial slots  39 . 
   During augmenter operation, exhausted combustion gases  28  enter augmenter  22  and flameholder  32  through inlet portions  64  and  68 . Specifically, each inlet portion  68  meters an amount of flow channeled into groups  62  of flow restrictors  52 , and each inlet portion  64  meters an amount of flow channeled into groups  60  of turning vanes  42 . Generally more combustion gases  28  are channeled through inlet portion  64  than through inlet portions  68 . 
   Combustion gases  28  entering inlet portion  64  are channeled turning vanes  42  downstream towards pilot fuel injector  116 , wherein gases  28  are mixed with injected fuel. The gas/fuel mixture flows around each swirl vane  100  towards igniter  118  wherein the gas/fuel mixture is ignited to initiate an augmenter flame. Additional fuel is injected into flameholder  32  via main fuel spraybars  120 . The augmenter flame is held by outer flameholders  32  and  34 . 
   The ignition of the combustion gas/fuel mixture generates additional combustion gases  122  and additional thrust. To facilitate cooling flameholder  32  during augmenter operation, bypass flow from engine  10  channeled to flameholders  32  and  34 . Specifically, bypass flow enters swirl vanes  100  via scoop channel  114  to facilitate cooling flameholder  32 . Sport cooling flow is discharged from swirl vane  100  via discharge vents  110 . The discharge of bypass combustion gases through discharge vents  110  facilitates thermally insulating flameholder  32  from exposure to hot combustion gases generated downstream from augmenter  22  during operation. 
   Turning vanes  42  facilitate producing a laminar flow of combustion gases  28  that facilitates preventing backflow and areas of low velocity. Combustion gases  28  mix with the injected fuel to form a combustion gas/fuel mixture in laminar flow. The laminar flow of the combustion gas/fuel mixture reduces areas of low velocity and the risk of the mixture backflowing upstream and spontaneously combusting. 
   Moreover, vanes  42  also facilitate reducing the possibility of turbulence, including wakes and eddies, being generated in the flow of the combustion gas/fuel mixture. Rather, turning vanes  42  facilitate creating a laminar flow of the combustion gas/fuel mixture which is less likely to migrate upstream and spontaneously combust. 
   In each embodiment, the above-described flameholder includes at least one turning vane that facilitates creating a laminar flow of a combustion gas/fuel mixture through the flameholder assembly. More specifically, in each embodiment, each turning vane facilitates reducing areas of low velocity of the combustion gas/fuel mixture within the flameholder. Moreover, during augmenter operation, the turning vanes facilitate preventing the combustion gas/fuel mixture from backflowing upstream and spontaneously combusting in the flameholder. Accordingly, augmenter performance and flameholder useful life are each facilitated to be enhanced in a cost effective and reliable means. 
   Exemplary embodiments of augmenters with flameholders are described above in detail. The turning vanes are not limited to use with the specific flameholder embodiments described herein, but rather, the turning vanes can be utilized independently and separately from other flameholder components described herein. Moreover, the invention is not limited to the embodiments of the turning vanes described above in detail. Rather, other variations of turning vane 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.