Abstract:
A method for decreasing combustor acoustics in gas turbine engines is provided. The method includes fabricating a plurality of premixers, chamfering a trailing edge of a main swirler shroud of each premixer, coupling a respective one of the chamfered premixers to each of a plurality of combustor domes, and coupling the plurality of combustor domes to an inlet of a combustor in a circumferential arrangement such that, during operation, the chamfered edge facilitates reducing combustor acoustics.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to combustors and, more particularly to a method and apparatus for decreasing combustor acoustics.  
         [0002]     Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from industrial gas turbines are subject to Environmental Protection Agency (EPA) standards. These standards regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). With the continuing concerns for the environment, the trend toward more stringent emission standards can be expected to continue.  
         [0003]     In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures that do not allow the fuel-air reaction to proceed to completion (HC &amp; CO). In at least some engines, water is injected into the combustor to facilitate reducing flame temperature and thus (NOx) emissions. Alternatively, dry low emission (DLE) combustors are designed to facilitate reducing (CO) and (NOx) emissions without the use of water injection. However, to facilitate low emissions, the DLE combustor is run at lean fuel-air ratios which require uniform dispersion of fuel throughout the combustor. More specifically, such combustors include fuel delivery systems that circumferentially stage fuel flows through the premixers to facilitate evenly dispersing fuel throughout the combustor.  
         [0004]     However, one problem that may arise with the DLE combustor and its associated fuel delivery system is the potential for high acoustics in the combustor. Combustor acoustics can result from several mechanisms, such as may be associated with thermally induced pressure disturbances resulting from instabilities or unsteadiness in heat released from the lean premixed flame. Such thermal instabilities can combine with natural acoustics generated within the combustor to produce high energy acoustic vibrations which over time may damage the combustor and other components. As a result, high combustor acoustics may limit the operation of the combustor.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     In one aspect, a method for decreasing combustor acoustics in gas turbine engines is provided. The method includes fabricating a plurality of premixers, chamfering a trailing edge of a main swirler shroud of each premixer, coupling a respective one of the chamfered premixers to each of a plurality of combustor domes, and coupling the plurality of combustor domes to an inlet of a combustor in a circumferential arrangement such that, during operation, the chamfered edge facilitates reducing combustor acoustics.  
         [0006]     In another aspect, a fuel delivery apparatus for a dry low emission (DLE) combustor for a gas turbine engine is provided. The apparatus includes a plurality of combustor domes circumferentially arranged and coupled to the combustor inlet and a premixer coupled to a respective one of each of the plurality of domes. Each premixer includes a chamfered trailing edge configured to suppress coupling of a vortex shedding with acoustic vibrations in the combustor.  
         [0007]     In another aspect, a gas turbine engine is provided that includes a combustor and a fuel delivery system coupled to the combustor. The fuel delivery system includes a plurality of combustor domes circumferentially arranged and coupled to an inlet of the combustor and a premixer coupled to a respective one of each of the plurality of domes. Each premixer includes a chamfered trailing edge configured to suppress coupling of a vortex shedding with acoustic vibrations in the combustor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic illustration of an exemplary gas turbine engine;  
         [0009]      FIG. 2  is a cross-sectional view of an exemplary combustor that may be used with the gas turbine engine shown in  FIG. 1 ;  
         [0010]      
         [0011]      FIG. 3  is a cross sectional view of an exemplary combustor premixer that may be used with the combustor shown in  FIG. 2 ;  
         [0012]      FIG. 4  is a cross-sectional view of an exemplary main swirler shroud that may be used with the premixer shown in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIG. 1  is a schematic illustration of an exemplary 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 low pressure turbine  20  arranged in a serial, axial flow relationship. Compressor  12  and turbine  20  are coupled by a first shaft  24 , and compressor  14  and turbine  18  are coupled by a second shaft  26 . In one embodiment, gas turbine engine  10  is an LMS100 engine commercially available from General Electric Company, Cincinnati, Ohio.  
         [0014]     In operation, air flows through low pressure compressor  12  from an upstream side  28  of engine  10 . Compressed air is supplied from low pressure compressor  12  to high pressure compressor  14 . Highly compressed air is then delivered to combustor assembly  16  where it is mixed with fuel and ignited. Combustion gases are channeled from combustor  16  to drive turbines  18  and  20 .  
         [0015]      FIG. 2  is a cross-sectional view of an exemplary combustor  16  that may be used with a gas turbine engine, such as engine  10  (shown in  FIG. 1 ). In the exemplary embodiment, combustor  16  is a dry low emission (DLE) combustor that is designed to operate with reduced levels of (NOx). Combustor  16  operates with a lean fuel/air mixture. Specifically, combustor  16  is operable with a fuel/air mixture that contains more air than is required to fully combust all of the fuel in the mixture.  
         [0016]     Combustor  16  includes a domed end  30  an inner liner  32  an outer liner  33 . Inner liner  32  and outer liner  33  extend downstream from domed end  30  to define a combustion zone  34 . A plurality of combustor domes  36  are mounted at an upstream end of liners  32  and  33  and are spaced radially across combustor  16 . Each dome  36  includes a plurality of premixers  40  that facilitate mixing fuel and air to deliver a desired fuel/air mixture to combustion zone  34 .  
         [0017]      FIG. 3  is a cross sectional view of a combustor premixer  40 . In the exemplary embodiment, premixer  40  is a co-axially piloted premixer, and includes a pilot section  42  and a main section  43 . Pilot section  42  includes a pilot inlet  44 , a center body  46 , an inner swirler  48 , and an outer swirler  50 . An axis of symmetry  52  of premixer  40  extends through premixer  40  from a forward end  54  of premixer  40  to an aft end  56  of premixer  40 . Pilot inner swirler  48  includes inner swirler vanes  58  and pilot outer swirler  50  includes outer swirler vanes  60 . In one embodiment, inner swirler  48  and outer swirler  50  are integrally formed with each other. Alternatively, inner swirler  48  and outer swirler  50  may be fabricated separately.  
         [0018]     Premixer  40  also includes a pilot fuel inlet  62  that channels fuel into a pilot fuel manifold  64 . Fuel and air are mixed in inner and outer swirlers  48  and  50 , respectively, and the resulting mixture is channeled through pilot inner and outer swirler vanes  58  and  60 , respectively, to an inner chamber  68  surrounding center body  46  prior to entering combustion zone  34 . Center body  46  includes a cooling air passage  70  that routes cooling air through an outlet tip  72  of center body  46 . Premixer  40  may be provided with an auxiliary fuel circuit that includes an auxiliary fuel passage  76  that is coupled in fluid communication with pilot fuel manifold  64 . A cooling air manifold  80  surrounds fuel passageway  76 , and a deflector plate  82  extends circumferentially around a downstream end  84  of cooling air manifold  80 . Cooling air is discharged from cooling air manifold  80  through an orifice plate  86  to facilitate cooling deflector plate  82 . A cooling air passage  90  delivers cooling air to a cooling air chamber  92  that supplies cooling air to cooling air manifold  80 .  
         [0019]     Premixer main section  43  is substantially concentrically aligned with respect to pilot section  42  and extends circumferentially around pilot section  42 . An annular main fuel manifold  96  channels fuel from a fuel reservoir  98  to a main swirler  99  that mixes fuel and air to provide a desired lean fuel/air mixture to a outer chamber  100  within premixer  40  prior to entering combustion zone  34 . A plurality of main swirler vanes  102  extend circumferentially around premixer  40  and are coupled to, and extend around, a trailing end  104  of main fuel manifold  96  and an edge  106  of cooling air manifold  80 . Each main swirler vane  102  is hollow and includes an outer wall  110  and an inner wall  112  that define a cavity  114  therebetween. Cavity  114  extends along a longitudinal length of main swirler vanes  102 . Main fuel manifold reservoir  98  extends into cavities  114  defined within main swirler vanes  102 . In one embodiment, main swirler vanes  102  include a plurality of injection ports  116  that enable the adjustment the mixing of fuel and air to facilitate achieving low (NOx) emissions and combustion stability within combustor  16 .  
         [0020]     A main swirler shroud  120  is coupled to, and extends aftward from, an aft end  122  of main swirler vanes  102 . Main swirler shroud  120  is annular and extends circumferentially around aft end  56  of premixer  40 . An inner surface  124  of shroud  120  extends longitudinally toward aft end  56  and is substantially parallel to axis of symmetry  52 .  
         [0021]      FIG. 4  is a cross-sectional view of main swirler shroud  120 . Main swirler shroud  120  includes a U-shaped outer surface  126  that is opposite inner surface  124 , a forward end  128 , and an aft or trailing end  130 . Forward end  128  includes an L-shaped notch  132  that receives main swirler vane end  122 . Inner surface  124  includes a forward edge  134  that is arcuate and is formed with a radius of curvature. Shroud  120  includes a chamfered trailing edge  136  that is formed at an angle α relative to inner surface  124 . A rounded transition corner  138  extends between inner surface  124  and trailing edge  136 . A cooling air passage  140  is provided to direct cooling air towards main swirler shroud trailing end  130 .  
         [0022]     During operation of engine  10 , premixer  40  provides a lean, well-dispersed fuel/air mixture to combustor  16  to facilitate reducing (NOx) emissions from engine  10 . Combustor  16  has naturally occurring acoustic frequencies that may be experienced during operation of engine  10 . When operated under such lean conditions, high thermal acoustics can be produced in combustor  16 . One potential source of high acoustics in DLE combustors, such as combustor  16 , is associated with an interaction of flame acoustics in combustor  16  and a vortex shedding at trailing end  130  of main swirler shroud  120 . This interaction is pronounced when trailing edge  136  is perpendicular with inner surface  124  forming a right angled corner. The vortex shedding has been empirically determined to cause oscillations in the fuel/air mixture and in the heat release from the lean premixed flame that can couple with the thermal acoustics in combustor  16 . When such coupling occurs, high acoustics can result that can produce dangerous levels of acoustic vibrations.  
         [0023]     Trailing edge  136  and transition corner  138  are oriented to alter the vortex shedding to facilitate suppressing excitation from vortex shedding at trailing edge  136  and transition corner  138  from a flow of fuel and air through premixer  40 . The alteration in the vortex shedding produces changes in the vortex frequency and changes in local pressure distribution within and at an exit of main swirler shroud  120  that facilitate suppressing acoustic vibrations that may be generated in combustor  16 . In the exemplary embodiment, angle a is approximately forty-five degrees measured relative to inner surface  124  of main swirler shroud  120 .  
         [0024]     The above-described fuel delivery system for a gas turbine engine is cost-effective and reliable. The fuel delivery system includes a dry low emission (DLE) premixer that facilitates minimizing (NOx) emissions while reducing the generation of potentially damaging acoustic vibrations. The premixer includes a main swirler shroud having a chamfered trailing edge that inhibits the coupling of pressure disturbances resulting from vortex shedding at the shroud trailing end with other combustor acoustics. The avoidance of such pressure disturbances facilitates the avoidance of damaging vibrations in the combustor and surrounding hardware.  
         [0025]     Exemplary embodiments of a fuel delivery system for a gas turbine engine are described above in detail. The systems and assembly components are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each system and assembly component can also be used in combination with other systems and assemblies.  
         [0026]     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.