Patent Publication Number: US-6655149-B2

Title: Preferential multihole combustor liner

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of application Ser. No. 09/934,182, filed Aug. 21, 2001, now U.S. Pat. No. 6,513,331. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to film cooled combustor liners for use in gas turbine engines and more particularly to such combustor liners having regions with closely spaced cooling holes. 
     A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. The fuel is injected into the combustor through fuel tubes located at uniformly spaced injection points around the combustor. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. Combustors used in aircraft engines typically include inner and outer combustor liners to protect the combustor and surrounding engine components from the intense heat generated by the combustion process. A variety of approaches have been proposed to cool combustor liners so as to allow the liners to withstand greater combustion temperatures. One such approach is multi-hole film cooling wherein a thin layer of cooling air is provided along the combustion side of the liners by an array of very small cooling holes formed through the liners. Multi-hole film cooling reduces the overall thermal load on the liners because the mass flow through the cooling holes dilutes the hot combustion gas next to the liner surfaces, and the flow through the holes provides convective cooling of the liner walls. 
     In the assembled combustor, certain portions of the combustor liners are aligned with the injection points defined by the circumferential location of the center of the fuel tubes. These locations are hereinafter referred to as “cup centers”. In operation, the flow of combustion gases past these circumferential locations create “hot streaks” of locally increased material temperatures. The portions of the combustor liners subject to hot streaks can exhibit oxidation, corrosion and low cycle fatigue (LCF) failures after return from field use. 
     Accordingly, there is a need for a combustor liner in which cooling film effectiveness is increased in the areas of the liner that are subject to unusually high temperatures and resulting material distress. 
     BRIEF SUMMARY OF THE INVENTION 
     The above-mentioned need is met by the present invention, which provides a gas turbine combustor liner made up of a shell having cooling holes formed therein, a group of which are disposed upstream of the dilution holes and divided into two sub-groups. The second sub-group of this group of cooling holes is located in circumferential alignment with a hot streak and are more closely spaced than the cooling holes of the first sub-group. The shell may also have additional cooling hole groups disposed between dilution holes in the liner. The additional groups are arranged so as to provide a converging flow in the circumferential direction to provide enhanced cooling to the area of the liner downstream of the dilution holes. 
    
    
     The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, however, may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
     FIG. 1 is a cutaway perspective view of a gas turbine combustor having combustor liners of the present invention. 
     FIG. 2 is a perspective view of a portion of a combustor liner depicting angled multi-hole cooling holes. 
     FIG. 3 is a top view of a portion of a combustor liner depicting the arrangement of the multi-hole cooling holes of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views, FIG. 1 shows a combustor  10  of the type suitable for use in a gas turbine engine. Combustor  10  includes an outer liner  12  and an inner liner  14  disposed between an outer combustor casing  16  and an inner combustor casing  18 . Outer and inner liners  12  and  14  are radially spaced from each other to define a combustion chamber  20 . Outer liner  12  and outer casing  16  form an outer passage  22  therebetween, and inner liner  14  and inner casing  18  form an inner passage  24  therebetween. A cowl assembly  26  is mounted to the upstream ends of. outer and inner liners  12  and  14 . An annular opening  28  is formed in. cowl assembly  26  for the introduction of compressed air into combustor  10 . The compressed air is supplied from a compressor (not shown) in a direction generally indicated by arrow A of FIG.  1 . The compressed air passes principally through annular opening  28  to support combustion and partially into outer and inner passages  22  and  24  where it is used to cool the liners  12  and  14 . 
     Disposed between and interconnecting the outer and inner liners  12  and  14  near their upstream ends is an annular dome plate  30 . A plurality of circumferentially spaced swirler assemblies  32  are mounted in dome plate  30 . Each swirler assembly  32  receives compressed air from annular opening  28  and fuel from a corresponding fuel tube  34 . The fuel and air are swirled and mixed by swirler assemblies  32 , and the resulting fuel/air mixture is discharged into combustion chamber  20 . The combustor has forward  60  and aft  62  ends and defines a longitudinal axis (not shown), which in the case of an annular combustor is coincident with the longitudinal axis of the engine. It is noted that although FIG. 1 illustrates one preferred embodiment of a single annular combustor, the present invention is equally applicable to any type of combustor, including double annular combustors, which uses multi-hole film cooling. 
     Outer and inner liners  12  and  14 .each comprise a single wall, metal shell having a generally annular and axially extending configuration. Outer liner  12  has a hot side  36  facing the hot combustion gases in combustion chamber  20  and a cold side  38  in contact with the relatively cool air in outer passage  22 . Similarly, inner liner  14  has a hot side  40  facing the hot combustion gases in combustion chamber  20  and a cold side  42  in contact with the relatively cool air in inner passage  24 . Both liners  12  and  14  include a large number of closely spaced cooling holes  44  formed therein. 
     Dilution air is primarily introduced into, combustor chamber  20  through a plurality of circumferentially spaced dilution holes  48  (FIG. 1) disposed in each of outer and inner liners  12  and  14 . Dilution holes  48  are generally far smaller in. number than the cooling holes  44 , and each dilution hole  48  has a cross-sectional area that is substantially greater than the cross-sectional area of one of the cooling holes  44 . Dilution holes  48 , and to a smaller extent cooling holes  44 , serve to admit dilution air into combustor chamber  20 . The dilution holes are arranged in circumferentially extending bands around the periphery of the liners  12  and  14 . The forward-most band of dilution holes  48  are referred to as primary dilution holes. 
     In the assembled combustor, certain ones of the primary dilution holes  48  are aligned with the injection points defined by the circumferential location of the center of the fuel injectors  34  and swirlers  32 . In operation, the flow of combustion gases past these circumferential locations create “hot streaks” of locally increased material temperatures. These streaks are not strictly longitudinal; because of the swirl of the flow in the combustor caused by the swirlers  32 , the streaks are curved in the circumferential direction when viewed along the length of the combustor. Although the prior art cooling provisions provide adequate cooling for the other portions of the combustor liners  12  and  14 , the portions of the combustor liners  12  and  14  subject to hot streaks can exhibit oxidation, corrosion and low cycle fatigue (LCF) failures from field use. 
     Referring now to FIG. 2, cooling holes  44  disposed through a portion of outer liner  12  are shown in more detail. Although FIG. 2 depicts cooling holes in outer liner  12 , it should be understood that the configuration of cooling holes of inner liner  14  is substantially identical to that of outer liner  12 . As such, the following description will also apply to inner liner  14 . FIG. 2 includes a frame of reference having axes labeled X, Y and Z, wherein X is the downstream axial, direction of flow (indicated by arrow B) through combustor  10 , Y is the circumferential direction, and Z is a radial direction. Cooling holes  44  are axially slanted from cold side  38 , to hot side  36  at a downstream angle A, which is preferably in the range of about 15° to 20°. Cooling holes  44  are arranged in a series of circumferentially extending rows,  46 . Adjacent holes  44  in each row have a circumferential hole spacing S, between their respective centerlines, and adjacent rows  46  have an axial row spacing P. 
     Referring now to FIG. 3, the cooling holes  44  are arranged into three primary groups: a group  45  located in the area aft of the primary dilution holes  48 , another group  70  located in the area forward of the primary dilution holes  48 , and another group  88  disposed in the area circumferentially in-line with primary dilution holes  48  (i.e., neither forward nor aft of the primary dilution holes  48 ). The circumferential location of the nearest cup center is represented by line  82  in FIG.  3 . The particular primary dilution hole that is circumferentially aligned with the cup center  82  is identified by reference number  48   a.    
     The group  45  of cooling holes  44  is located aft of the primary dilution holes  48 . The cooling holes  44  of this group  45  square angled downstream in a Z direction at an angle A as discussed above. The cooling holes  44  of group  45  may be all of the same diameter and cross-sectional shape in order to ease manufacture. Alternatively, selected ones of the cooling holes  44  may have larger diameters for increased local cooling. The cooling holes  44  of group  45  are also circumferentially slanted or clocked at a clock angle B as shown in FIG.  2 . Clock angle B preferably corresponds to the swirl of flow through combustor chamber  20 , which is generally in the range of about 30° to 65°. In an exemplary embodiment, angle B may be about 45°. 
     A group  70  of cooling holes  44  is arranged around the periphery of the liner  12  upstream of the primary dilution holes  48 . The cooling holes  44  of this group  70  are angled downstream in a Z direction at an angle A as discussed above. The cooling holes  44  of group  70  may be all of the same diameter and cross-sectional shape in order to ease manufacture. The cooling holes  44  of group  70  may be aligned parallel to the combustor&#39;s longitudinal axis in the circumferential direction, or they may be disposed at an angle to the longitudinal axis to better direct the airflow as desired. For example, the cooling holes  44  of group  70  may be circumferentially slanted or clocked at a clock angle B, as shown in FIG.  2  and described above. Group  70  is divided into first and second sub-groups referenced as  71  and  72  respectively. The center-to-center spacing of the cooling holes in the first sub-group  71  is generally equal in the axial and circumferential directions, as described more fully below. The second sub-group  72  of the group  70  of cooling holes  44  is provided to address the hot streaks in the liner  12 . The cooling holes  44  of second sub-group  72  are, the same diameter as the cooling holes  44  of first sub-group  71 , but they are more closely spaced in order to provide more cooling holes  44  per unit area, as described below. This denser pattern of the second sub-group  72  provides increased cooling air flow which is used to reduce the temperature of the sections of the liner  12  subject to hot streaks. In an exemplary embodiment the sub-group  72  is arranged in the form of a rectangle when viewed in a radial direction. 
     Because of the swirl in the flow through the combustor, the hot streaks are not precisely aligned with the circumferential positions of the cup centers  82  at the forward end  60  of the liner  12 . Rather, there is some offset of the hot streaks with respect to the cup centers  82 . Therefore, the position of the sub-group  72  is selected to provide enhanced cooling in a particular circumferential location as needed. The center of sub-group  72  may-be offset circumferentially from the cup center  82  in the direction of the flow swirl. 
     Conventionally, cooling holes in typical combustor liners have very small diameters on the scale of about 0.02 inches (0.51 mm) and circumferential hole spacing of about 0.13 inches (3.30 mm), or about 6.5 hole diameters. The axial row spacing is generally equal to the circumferential hole spacing. Specifically, FIG. 3 shows a portion of combustor liner  12  having the sub-group  71  of cooling holes  44  having conventional spacing (i.e., circumferential hole spacing S and axial row spacing P are both about 6.5 hole diameters or 0.13 inches (3.30 mm)) and the sub-group  72  of cooling holes  44  (enclosed by dotted lines in FIG. 3) with a tighter circumferential hole spacing S′. Preferably, cooling holes  44  of sub-group  72  have a diameter of about 0.02 inches (0.51 mm) and a circumferential hole spacing S′ of about 4 hole diameters or 0.08 inches ( 2 . 03  mm). It is within the scope of the present invention to provide the sub-group  72  with a tighter axial row spacing; however, the axial row spacing P in sub-group  72  is preferably the same as that of sub-group  71 . By using the same hole diameter for both sub-group  71  and sub-group  72 , machining operations can be performed continually without requiring an additional setup operation. 
     The cooling holes  44  of group  88  are disposed circumferentially, i.e., same axial position, in line with primary dilution holes  48 . Within this group  88 , sub-groups of cooling holes  44  adjacent to the primary dilution holes  48   a  aligned with the cup centers  82  are disposed at alternating angles such that the holes on each side of a cup center position are angled towards the primary dilution hole  48   a  in the circumferential direction. In this way additional cooling flow is provided at the circumferential location of the primary dilution hole  48   a . In the exemplary embodiment shown, a first sub-group  74  of cooling holes  44  is located even with primary dilution hole  48   a  in the longitudinal direction, and is disposed to one side of the primary dilution hole  48   a  in the circumferential direction. The cooling holes  44  of sub-group  74  are angled in the circumferential direction so that they point towards primary dilution hole  48   a  in the downstream direction. The cooling holes  44  of sub-group  74  may be angled at about +45° with respect to the longitudinal axis. Another sub-group  76  of cooling holes  44  are located opposite sub-group  74  on the other side of primary dilution hole  48   a  in the circumferential direction. The cooling holes  44  in sub-group  76  are angled in the circumferential direction opposite to cooling holes  44  in sub-group  74 , so that this sub-group  76  also directs cooling air flow to a location directly downstream of primary dilution hole  48   a . The cooling holes  44  in sub-group  76  may be angled at about −45° with respect to the longitudinal axis. 
     Additional sub-groups  78  and  80  of cooling holes  44  may be added to further improve cooling at the cup center position. Again referring to FIG. 3, these additional sub-groups  78  and  80  of cooling holes  44  are the same shape and size as groups  74  and  76 , and may be disposed outside of sub-groups  74  and  76  in the circumferential direction, and may be interspersed with additional primary dilution holes  48 . In one embodiment, groups of cooling holes  44  may be interspersed with primary dilution holes  48  in alternating order in a circumferential band around the liner  12 . The cooling hole sub-groups may be arranged such that alternate pairs of hole sub-groups  74 ,  78  and  76 ,  80  are disposed at positive and negative angles with respect to the longitudinal axis, such that each cup center  82  is associated with two pairs of cooling hole sub-groups  74 ,  78  and  76 ,  80  arranged to converge downstream of the primary dilution holes  48   a . In effect, the pattern of cooling holes as shown in FIG. 3, with four converging sub-groups of cooling holes arranged around primary dilution hole  48   a , would be repeated at each cup center  82  around the circumference of the combustor liner  12 . 
     The foregoing has described a multi-hole film cooled combustor liner having an improved arrangement of cooling holes to reduce temperature gradients and hot streaks. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention as defined in the appended claims.