Abstract:
A combustor liner assembly includes a liner and a first group of cooling holes formed in the liner and having an increasing density in a downstream direction. The first group of cooling holes include a generally circumferential first row of cooling holes, a generally circumferential second row of cooling holes immediately downstream from, consecutive to, and separated from the first row at a first distance, a generally circumferential third row of cooling holes immediately downstream from, consecutive to, and separated from the second row at a second distance, and a generally circumferential fourth row of cooling holes immediately downstream from, consecutive to, and separated from the third row at a third distance. The first distance is greater than the second distance and the third distance, and the second distance is greater than the third distance.

Description:
TECHNICAL FIELD 
     The present invention relates generally to combustor systems, and more particularly to combustor systems with liners having improved effusion cooling hole patterns. 
     BACKGROUND 
     Typically, a combustor system for a gas turbine engine includes outer and inner casings that house outer and inner liners. The liners and casings are radially spaced apart to form a passage for compressed air. The inner and outer liners form a combustion chamber within which compressed air mixes with fuel and is ignited. As such, each of the liners includes a hot side exposed to hot combustion gases and a cold side facing the passage formed between the liners and the casings. The liner may also be a dual wall construction, where the side of the liner which is exposed to the combustion gases is thermally decoupled from the side which is exposed to compressor discharge gases, thereby forming an intervening cavity. 
     In typical combustors, a plurality of effusion cooling holes supply a thin layer of cooling air that insulates the hot sides of the liners from extreme combustion temperatures. The liners also include major openings, much larger than the cooling holes, for the introduction of compressed air to feed the combustion process. The thin layer of cooling air can be disrupted by flow through the major openings, potentially resulting in elevated liner temperatures adjacent the major openings. Elevated or uneven temperature distributions within the liners can promote undesired oxidation of the liner material, coating-failure, or thermally induced stresses that degrade the effectiveness, integrity, and life of the liners. 
     It is known to arrange cooling holes in a dense grouping upstream of major openings, in the primary combustion zone where higher radiation loads and temperatures are located, to distribute ample cooling airflow in regions via film cooling and effective heat removal through the thickness of the liners by convection along the surfaces of the holes. Disadvantageously, the greater flow through the major openings can disrupt the flow of cooling air around the major openings. This situation can result in a deficiency of cooling air downstream of the major openings that may cause an undesirable increase in liner temperature. Further, the overall amount of cooling airflow is limited and it is therefore desirable to efficiently allocate available cooling airflow to provide even temperature distribution throughout the liner. 
     Accordingly, it is desirable to develop combustor systems with liners that improve cooling layer properties, particularly adjacent to major openings, to eliminate uneven temperature distributions or undesirable temperature levels. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
     BRIEF SUMMARY 
     In one exemplary embodiment, a combustor liner assembly includes a liner and a first group of cooling holes formed in the liner and having an increasing density in a downstream direction. 
     In another exemplary embodiment, a combustor system includes an inner liner; and an outer liner circumscribing the inner liner and forming a combustion chamber therebetween for the combustion of a fuel and air mixture. The outer liner includes a first group of cooling holes having an increasing density in a downstream direction. 
     In yet another exemplary embodiment, a combustor liner assembly includes an inner liner and an outer liner circumscribing the inner liner to form a combustion chamber therebetween. The inner liner includes a first group of cooling holes having an increasing density in a downstream direction, a second group of cooling holes downstream of the first group and having a constant density, and a third group of cooling holes downstream of the second group and having a varying density. The inner liner includes a fourth group of cooling holes having an increasing density in the downstream direction, a fifth group of cooling holes downstream of the fourth group and having a constant density, and a sixth group of cooling holes downstream of the fifth group and having a varying density. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a cross-sectional view of a combustor assembly in accordance with an exemplary embodiment; 
         FIG. 2  is an enlarged plan view of a section of an inner liner of the combustor assembly of  FIG. 1 ; and 
         FIG. 3  is an enlarged plan view of a section of an outer liner of the combustor assembly of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
       FIG. 1  is a cross-sectional view of a combustor assembly  100  in accordance with an exemplary embodiment. The combustor assembly  100  includes an outer casing  102  and an inner casing  104 . The outer and inner casings  102 ,  104  circumscribe an axially extending engine centerline  106  to define an annular pressure vessel  108 . Within the annular pressure vessel  108 , an outer liner  110  and inner liner  112  are respectively radially spaced apart from the outer casing  102  and the inner casing  104  to form outer and inner air plenums  114 ,  116 . The outer and inner liners  110 ,  112  can be single-wall or double-wall construction, single-piece construction or segmented construction in the form of discrete heat shields, panels or tiles. The outer and inner liners  110 ,  112  are radially spaced apart to define a combustion chamber  118 . 
     The combustor assembly  100  further includes a front end assembly  120  at a forwardmost end of the combustion chamber  118 . The front end assembly  120  comprises an annularly extending shroud  122 , fuel injectors  124 , and fuel injector guides  126 . One fuel injector  124  and one fuel injector guide  126  are shown in the cross-sectional view of  FIG. 1 . In one embodiment, the combustor assembly  100  includes a total of sixteen circumferentially distributed fuel injectors  124 , but it will be appreciated that the combustor assembly  100  could be implemented with more or less than this number of fuel injectors  124 . 
     The shroud  122  extends between and is secured to the forwardmost ends of the outer and inner liners  110 ,  112 . The shroud  122  includes a plurality of circumferentially distributed shroud ports  128  that accommodate the fuel injectors  124  and introduce air into the forward end of the combustion chamber  118 . Each fuel injector  124  is secured to the outer casing  102  and projects through one of the shroud ports  128 . Each fuel injector  124  introduces a swirling, intimately blended fuel-air mixture  130  that supports combustion in the combustion chamber  118 . 
     During operation, fuel and air within the combustion chamber  118  are ignited to generate hot combustion gases  132 . Compressed air  134  is fed into the plenums  114 ,  116  and further into the combustion chamber  118  to feed the combustion process. The hot combustion gases  132  exit the combustion chamber  118  at speeds and elevated temperatures required to provide energy that drives a turbine (not shown), as is known. 
     The outer liner  110  includes a hot side  138  that is exposed to the hot combustion gases  132  and a cool side  136  facing the plenum  114 . Similarly, the inner liner  112  includes a hot side  140  that is exposed to the hot combustion gases  132  and a cool side  142  facing the plenum  116 . The hot sides  138 ,  140  of the outer and inner liners  110 ,  112  are respectively insulated from the extreme heat and radiation generated by the hot combustion gases  132  by layers of cooling airflow  144 ,  146 . The layer of cooling airflow  144  is supplied by a plurality of effusion cooling holes  148  arranged throughout the outer liner  110 , and the layer of cooling airflow  146  is supplied by a plurality of effusion cooling holes  150  arranged throughout the inner liner  112 . The cooling holes  148 ,  150  also provide a mechanism for additional cooling via convection along the surface areas of the cooling holes  148 ,  150 . The cooling holes  148  of the outer liner  110  and the cooling holes  150  of the inner liner  112  can have the same or different patterns. The cooling holes  148 ,  150  are better illustrated in the more detailed views of  FIGS. 2 and 3  and described in greater detail below. 
     In addition to the cooling holes  148 ,  150 , the outer and inner liners  110 ,  112  also respectively include major openings  152 ,  154  that are relatively larger than the cooling holes  148 ,  150 . The major openings  152 ,  154  can be dilution, quench or trim holes supplying air for combustion and to tailor the combustor exit temperature distribution. Further, the major openings  152 ,  154  can be borescope holes or igniter portholes. Each of the major openings  152 ,  154  can disrupt the layers of cooling airflow  144 ,  146 , thereby reducing the effective cooling around the corresponding major opening  152 ,  154 . An igniter port hole  153  may also be provided in the outer liner  110 . Other major openings, in the form of access ports, and other geometric obstructions or protrusions may also be significant enough to impact cooling flow similarly. 
     The cooling airflow  144 ,  146  may be generated by the angular orientation of the cooling holes  148 ,  150  throughout the outer and inner liners  110 ,  112 . The cooling holes  148 ,  150  are angled from the cool sides  136 ,  142  to the hot sides  138 ,  140 . Each cooling hole  148 ,  150  is disposed at a simple or compound angle relative to the hot side  138 ,  140  of the outer and inner liners  110 ,  112 . The cooling airflow  144 ,  146  through the cooling holes  148 ,  150  may generate directional flow axially, circumferentially or both axially and circumferentially along the hot sides  138 ,  140  of the outer and inner liners  110 ,  112  that create the thin air film of radial thickness that insulates the outer and inner liners  110 ,  112  from the hot combustion gases  132 . 
     The cooling holes  148 ,  150  may also be axially slanted from the cool sides  136 ,  142  to the hot side  138 ,  140  at axial angle. Preferably, the axial angle is between 10 and 45 degrees. In another example, the axial angle is between 20 to 30 degrees relative to the hot side  138 ,  140  of each of the outer and inner liners  110 ,  112 . The cooling holes  148 ,  150  are also disposed at a transverse angle oriented circumferentially to provide a preferential cooling air flow orientation along the entire surface of the outer and inner liners  110 ,  112 . The transverse angle can be as much as 90 degrees relative to an axial coordinate of the combustion chamber  118 . It can be appreciated that other angles of the cooling holes  148 ,  150  can be provided to produce a desired cooling airflow  144 ,  146 . 
     Compressed air  134  flowing through the major openings  152 ,  154  generates three-dimensional airflows along the hot side surfaces  138 ,  140  of the outer and inner liners  110 ,  112 . As discussed above, the three-dimensional flows disrupt the cooling airflow  144 ,  146  adjacent the surface of the outer and inner liners  110 ,  112 . As cooling airflow  144 ,  146  approaches the major openings  152 ,  154  and the airflow  134  therethrough, the cooling airflow  144 ,  146  can stagnate at a leading edge  156  of the major opening  152  and generate three-dimensional or recirculating flows. The local stagnation pressures, associated pressure gradients and flow patterns drive the cooling airflow  144 ,  146 , if inadequate, away from the surface areas in the vicinity of the major opening  152  and locally depress or siphon flow locally from cooling holes  148 ,  150 . These factors may reduce cooling effectiveness. Further, if airflow  134  from the major openings  152 ,  154  is of significant momentum or pressure gradients of ample strength, cooling airflow  144 ,  146  may lift off the hot sides  138 ,  140 , which can result in uneven temperatures at localized areas of the outer and inner liners  110 ,  112 . 
       FIG. 2  is an enlarged plan view of a section of an inner liner  112  of the combustor assembly  100  of  FIG. 1 . The combustor assembly  100  includes the cooling holes  148  disposed in specific patterns and densities relative to the major openings  152 ,  154  to effect local cooling. The patterns of the cooling holes  150  provide for the build up and dense placement of cooling airflow  146  ( FIG. 1 ) upstream of the major openings  152  and immediately adjacent the opening  154  to overcome local combustor aerodynamics and undesired heat transfer patterns. 
     The cooling holes  150  may have a diameter of about 0.01-0.05 inches. The cooling holes  150  may have circular or non-circular shapes, such as oval, egg-shaped, diverging or tapered. 
     The cooling holes  150  are spaced in patterns that need not be symmetric or geometrically repeating. Generally, the cooling holes  150  are disposed in patterns such that the greatest amount of cooling air is provided in areas that require the greatest cooling, i.e., “hot spots,” such as adjacent the major openings  152 ,  154  and in areas adjacent the end of the combustion chamber  118 . As discussed above, the hot spots may be a result of disruptive airflows, generally increased temperature of the combustion gases  132  in certain areas, or the geometries of the combustion chamber  118 . 
     In one exemplary embodiment, a first group  208  of cooling holes  150  is disposed adjacent an upstream end  214  of the inner liner  112 . The first group  208  of cooling holes  150  may range in densities from about 5-20 holes per square inch to about 30-80 holes per square inch. Generally, the density of the cooling holes  150  in the first group  208  increases in a downstream direction  202 . This provides a smooth transition for the build up of the cooling airflow  146  ( FIG. 1 ), as well as a smooth transition between the first group  208  of cooling holes  150  and downstream groups. The smooth transition also provides a more efficient use of cooling air. In one embodiment, the density of the cooling holes  150  is about 10 holes per square inch immediately adjacent the upstream end  214  of the inner liner  112 , and the density of the cooling holes  150  increases to about 40 holes per square inch adjacent the termination of the first group  208 . The density of cooling holes  150  of the first group  208  can increase at a constant rate or a varying rate. In another embodiment, the first group  208  of cooling holes  150  can be arranged in a plurality of rows, and the distances between each of the plurality of rows decreasing in the downstream direction  202 . As an example, the distances between consecutive rows can decrease at a rate of 10-15% per row. 
     A second group  210  of cooling holes  150  is disposed adjacent the first group  208  of cooling holes  150  in the downstream direction  202  and extends to the downstream edge  220  of the major openings  154 . The second group  210  of cooling holes  150  may range in density from about 30-80 holes per square inch. In one embodiment, the second group  210  of cooling holes  150  has the same density as the last rows of first group  208  of cooling holes  150 , such as, for example, 40 holes per square inch. Generally, the density of the cooling holes  150  in the second group  210  is constant. 
     A third group  212  of cooling holes  150  is disposed adjacent the second group  210  of cooling holes  150  in the downstream direction  202 . The third group  212  of cooling holes  150  generally extends to the downstream edge  216  of the inner liner  112 , which is typically the exit of the combustion chamber  118  ( FIG. 1 ) that mates with a turbine (not shown). The third group  212  of cooling holes  150  may range in density from about 5-80 holes per square inch. In one embodiment, the density of the cooling holes  150  of the third group  212  varies. The density of the third group  212  can particularly vary to provide the most effective cooling pattern. As an example, the third group  212  of cooling holes  150  can initially have a relatively high density adjacent the downstream side  220  of major openings  154 . The third group  212  of cooling holes  150  may then have a relatively lower density, and finally gradually increase in density to the downstream edge  216  of the inner liner  112 , in order to overcome the increased convective heating of the hot gases accelerating towards the turbine. 
       FIG. 3  is an enlarged plan view of a section of an outer liner  110  of the combustor assembly  100  of  FIG. 1 . The combustor assembly  100  includes the cooling holes  148  disposed in specific patterns and densities relative to the major openings  152 ,  154  to effect local cooling. The patterns of the cooling holes  148  provide for the build up and dense placement of cooling airflow  144  ( FIG. 1 ) upstream of the major openings  152  and immediately adjacent the opening  154  to overcome local combustor aerodynamics and undesired heat transfer patterns. The cooling holes  148  can have a geometric configuration similar to the cooling holes  150 . 
     The cooling holes  148  are spaced in patterns that need not be symmetric or geometrically repeating. Generally, the cooling holes  148  are disposed in patterns such that the greatest amount of cooling air is provided in areas that require the greatest cooling, i.e., “hot spots,” such as adjacent the major openings  152 ,  154  and in areas adjacent the end of the combustion chamber  118 . As discussed above, the hot spots may be a result of disruptive airflows, generally increased temperature of the combustion gases  132  in certain areas, or the geometries of the combustion chamber  118 . 
     In one exemplary embodiment, a first group  308  of cooling holes  148  is disposed adjacent an upstream end  314  of the outer liner  110 . The first group  308  of cooling holes  148  may range in densities from about 5-20 holes per square inch to about 30-80 holes per square inch. Generally, the density of the cooling holes  148  in the first group  308  increases in a downstream direction  302 . This provides a smooth transition for the build up of the cooling airflow  144  ( FIG. 1 ), as well as a smooth transition between the first group  308  of cooling holes  148  and downstream groups. The smooth transition also provides a more efficient use of cooling air. In one embodiment, the density of the cooling holes  148  is about 10 holes per square inch immediately adjacent the upstream end  314  of the outer liner  110 , and the density of the cooling holes  148  increases to about 40 holes per square inch adjacent the termination of the first group  308 . The density of cooling holes  148  of the first group  308  can increase at a constant rate or a varying rate. In another embodiment, the first group  308  of cooling holes  148  can be arranged in a plurality of rows, and the distances between each of the plurality of rows decreasing in the downstream direction  302 . As an example, the distances between consecutive rows can decrease at a rate of 10-15% per row. 
     A second group  310  of cooling holes  148  is disposed adjacent the first group  308  of cooling holes  148  in the downstream direction  302  and extends to the downstream edge  320  of the major openings  154 . The second group  310  of cooling holes  148  may range in density from about 30-80 holes per square inch. In one embodiment, the second group  310  of cooling holes  148  has the same density as the last rows of first group  308  of cooling holes  148 , such as, for example, 40 holes per square inch. Generally, the density of the cooling holes  148  in the second group  310  is constant. 
     A third group  312  of cooling holes  148  is disposed adjacent the second group  310  of cooling holes  148  in the downstream direction  302 . The third group  312  of cooling holes  148  generally extends to the downstream edge  316  of the outer liner  110 , which is typically the exit of the combustion chamber  118  ( FIG. 1 ) that mates with a turbine (not shown). The third group  312  of cooling holes  148  may range in density from about 5-80 holes per square inch. In one embodiment, the density of the cooling holes  148  of the third group  312  varies. The density of the third group  312  can particularly vary to provide the most effective cooling pattern. As an example, the third group  312  of cooling holes  148  can initially have a relatively high density adjacent the downstream side  320  of major openings  154 . The third group  312  of cooling holes  148  may then have a relatively lower density, and finally gradually increase in density to the downstream edge  316  of the outer liner  110 , in order to overcome the increased convective heating of the hot gases accelerating towards the turbine. 
     Although several patterns and of hole density patterns have been illustrated by way of the example, it will be recognized that different hole patterns and densities can be provided. Further, although three different spacing of cooling holes  148  are shown in the example embodiments, the number of and relative difference between different hole spacings and groups may be adjusted. 
     The combustor assembly  100  includes the cooling holes  148 ,  150  disposed in specific patterns and densities relative to the major openings  152 ,  154  to effect local cooling. The denser cooling hole patterns provide for increased cooling flow in areas where cooling airflow  144 ,  146  effectiveness is degraded, and is an efficient method of utilizing the limited volume of available cooling air. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.