Patent Publication Number: US-6334298-B1

Title: Gas turbine combustor having dome-to-liner joint

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH &amp; DEVELOPMENT 
     The U.S. Government may have certain rights in this invention pursuant to contract number F33615-97-C-2778 awarded by the Department of the Air Force. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to combustors for gas turbine engines and more particularly to joints that connect a combustor dome plate to the combustor liners. 
     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. 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 surrounding engine structure from the intense heat generated by the combustion process. The combustor liners are cooled to meet life expectancy requirements by diverting a portion of the compressed air and causing it to flow over the surfaces of the liners. 
     Advanced aircraft gas turbine engine technology is driving combustors to be shorter in length, have higher performance levels over wider operating ranges, and produce lower emission levels. To achieve these goals, the so-called trapped vortex combustor has been proposed. A trapped vortex combustor has a non-linear cavity section located immediately downstream of an inlet dome. Fuel and air injected into the cavity, which is substantially rectangular in cross-section, form a trapped vortex for igniting and stabilizing a flame in the combustor. This arrangement has shown robust operability including stable burning over a range of fuel/air ratios, high performance, low emissions and high efficiency at very high fuel/air ratios. 
     A trapped vortex combustor generally includes a flat dome plate that is joined to the outer and inner liners. This typically results in some dome-to-liner joint structure being located forward of the dome plate. A number of radial fuel injectors are located upstream of the dome plate. The radial fuel injectors are preferably located parallel to and in close proximity with the dome plate so as to avoid auto-ignition of the fuel prior to reaching the combustion zone. This leaves little room for dome-to-liner joints, particularly at the outer liner. In addition, a lack of streamlining at the external comer of the dome-to-liner joint can cause an undesirable pressure loss in the air diverted from the combustor for cooling purposes. This can decrease the cooling efficiency to the combustor liners as well as turbine components. 
     One approach to alleviating interference between the dome-to-liner joints and the fuel injectors would be to scallop the liners to fit around the fuel injectors. However, because of the large number of radial fuel injectors usually employed, the mechanical integrity of the liners would be at risk. Sealing between the liners and the dome plate would also be very difficult. Another possible approach would be to form each fuel injector with a bend so that the fuel injectors would fit around the joints. A drawback to this approach is that assembly of the combustor would become more complicated. Each fuel injector would be first slid radially inward forward of the dome plate and then slid axially aft to engage the dome plate. This installation method would require longer holes in the case enclosing the combustor liners. Longer holes would weaken the case and create more opportunity to undesirably leak air. Furthermore, the overall length of the engine would be increased to accommodate the sliding installation of the fuel injectors. 
     Accordingly, there is a need for a streamlined dome-to-liner joint that has no structure forward of the dome plate. 
     BRIEF SUMMARY OF THE INVENTION 
     The above-mentioned need is met by the present invention, which provides a joint for joining a dome plate to a combustor liner. The joint includes a first flange formed on the dome plate and a second flange formed on the liner. A mounting ring having a groove formed therein is provided such that the first flange is disposed in the groove and the second flange engages the mounting ring. A retainer is secured to the mounting ring and engages the second flange. 
     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 which 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 longitudinal cross-sectional view of a trapped vortex combustor having dome-to-liner joints. 
     FIG. 2 is an enlarged view of the combustor of FIG. 1 showing an igniter. 
     FIG. 3 is an enlarged view of a dome-to-liner joint from FIG.  1 . 
     FIG. 4 is an aft-looking-forward schematic end view of the combustor of FIG.  1 . 
     FIG. 5 is a partial sectional view of the combustor of FIG. 3 taken along line  5 — 5 . 
     FIG. 6 is a partial sectional view of the combustor of FIG. 3 taken along line  6 — 6 . 
    
    
     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 trapped vortex combustor  10  for use in a gas turbine engine. The combustor  10  includes a hollow body  12  defining a combustion chamber  14  therein. The hollow body  12  is generally annular in form about the engine centerline axis and includes an outer liner  16  and an inner liner  18  disposed between an outer combustor casing  20  and an inner combustor casing  22 . The outer liner  16  and the outer casing  20  form an outer passage  24  therebetween, and the inner liner  18  and the inner casing  22  form an inner passage  26  therebetween. The outer and inner liners  16  and  18  can be made of metal, ceramic matrix composite or any other suitable material. 
     The upstream end of the hollow body  12  is substantially closed off by a generally flat, annular dome plate  28  attached to the outer liner  16  by an outer dome-to-liner joint  30  and to the inner liner  18  by an inner dome-to-liner joint  32 . The dome plate  28 , which is preferably but not necessarily segmented to alleviate thermal stress, lies in a plane that is substantially perpendicular to the core flow streamline through the combustor  10 . A number of openings  34  is formed in the dome plate  28  to provide ingress for fuel and compressed air into the combustion chamber  14 . Forward extending baffles  36  are formed on the forward surface of the dome plate  28 , adjacent to the openings  34 . The baffles  36  define inlet passages  38  that are aligned with the openings  34 . 
     As is known in the art, compressed air is supplied from a compressor (not shown) via a diffuser  40  located upstream of the combustor  10 . The compressed air passes principally into the combustion chamber  14  via the inlet passages  38  and the openings  34  to support combustion and partially into the outer and inner passages  24  and  26  where it is used to cool the liners  16  and  18  and turbomachinery further downstream. A plurality of radial fuel injectors  42  (only one shown in FIG. 1) is provided upstream or forward of the dome plate  28 . The fuel injectors  42  are attached at one end to the outer casing  20  and extend radially inward parallel to and in close proximity with the forward surface of the dome plate  28 . Each fuel injector  42  has an atomizer  44  aligned with each of the inlet passages  38 . Thus, fuel from a fuel manifold (not shown) flows through the radial fuel injectors  42  and is discharged into the inlet passages  38  via the atomizers  44 . The fuel mixes with the compressed air flowing through the inlet passages  38  so that a fuel/air mixture flows into the combustion chamber  14 . By locating the fuel injectors  42  (and thus the atomizers  44 ) immediately forward of the dome plate  28 , the residence time of the fuel in the inlet passages  38  is extremely short, thereby minimizing the opportunity for the fuel to auto-ignite. 
     The combustor  10  further includes a trapped vortex cavity  46  incorporated into the hollow body  12  immediately downstream of the dome plate  28 . The trapped vortex cavity  46  is preferably substantially rectangular in cross-section and is open to the combustion chamber  14 . Fuel and air are injected directly into the trapped vortex cavity  46  through secondary openings  48  that are formed in the dome plate  28  and are in fluid communication with the fuel injectors  42 . The trapped vortex cavity  46  is sized and shaped such that a trapped vortex of fuel and air is produced therein from the fuel and air injected through the secondary openings  48 . This trapped vortex of fuel and air is ignited as necessary by an igniter  50  mounted in the outer casing  20  and the outer liner  16  (see FIG.  2 ), and the combustion gases generated by the trapped vortex within the cavity  46  provide a continuous ignition and stabilization source for the primary fuel/air mixture entering the combustion chamber  14  via the dome plate openings  34 . It should be noted that a trapped vortex combustor is used here for purposes of illustration, but the present invention is not necessarily limited to trapped vortex combustors. 
     Referring now to FIG. 3, the outer dome-to-liner joint  30  is shown in more detail. Although FIG. 3 depicts the outer dome-to-liner joint  30 , it should be understood that the inner dome-to-liner joint  32  is substantially identical structurally to the outer dome-to-liner joint  30 , except that it is disposed radially inward of the inner liner  18  while the outer joint  30  is disposed radially outward of the outer liner  16 . The two joints are thus oriented in opposite radial directions, but are otherwise identical to one another. As such, the following description will also apply to the inner dome-to-liner joint  32 . 
     The dome-to-liner joint  30  comprises first and second complimentary radially extending flanges  52  and  54 . The first or dome flange  52  is formed on the periphery of the dome plate  28  and extends radially outwardly therefrom. The dome flange  52  is slightly offset in the aft direction with respect to the forward surface of the dome plate  28 . The second or liner flange  54  formed on the forward end of the outer liner  16  and extends radially outwardly therefrom. When the combustor  10  is properly assembled, the two flanges  52  and  54  are substantially parallel to one another. 
     The joint  30  further includes a mounting ring  56  that engages the dome flange  52  and the liner flange  54 . As will be described in more detail below, the mounting ring  56  can be either a continuous 360 degree ring or a segmented ring comprising two, three or even more arcuate segments. The segments would form a 360 degree ring; thus, a two-segment configuration would comprise 180 degree segments, a three-segment configuration would comprise 120 degree segments, and so on. In either case, the mounting ring  56  includes a forward radial flange  58  and an aft radial flange  60  extending radially inwardly therefrom. The two flanges  58  and  60  are spaced apart axially so as to define a radial groove  62  therebetween. The dome flange  52  is disposed in the groove  62  so as to axially retain the mounting ring  56  with respect to the dome plate  28 . Because of the offset of the dome flange  52 , the forward radial flange  58  is nearly flush with the forward surface of the dome plate  28  when the dome flange  52  is disposed in the groove  62 . 
     The mounting ring  56  further includes an axial flange  64  extending in an axially aft direction, and thus perpendicular to the radial flanges  58  and  60 . An annular recess  66  is formed in the radially inner surface of the axial flange  64  so as to define an aft-facing abutment  68 . The portion of the mounting ring  56  that joins the forward radial flange  58  and the axial flange  64  defines a convex curved surface. The mounting ring  56  thus has a rounded comer  70  on its forward, upstream-facing side. Accordingly, the joint  30  presents a streamlined external surface that minimizes pressure losses in the cooling air passing around the combustor body  12 . 
     The mounting ring  56  is axially retained with respect to the outer liner  16  by means of a retainer  72 . The retainer  72  is a segmented, 360 degree ring, which can comprise two, three or more arcuate segments. The retainer  72  is generally L-shaped in cross-section and has a radially inward extending retaining flange  74  and an axially aft extending mounting flange  76 . The mounting flange  76  is received in the recess  66  of the axial flange  64  and engages the abutment  68  so as to be properly positioned with respect to the mounting ring  56 . The mounting flange  76  is secured to the axial flange  64  by a plurality of bolts  78  and nuts  80  (only one of each shown in FIG. 3) or any equivalent fastening means. With the retainer  72  thus attached to the mounting ring  56 , the liner flange  54  is captured between the aft side of the aft radial flange  60  and the forward side of the retaining flange  74 , which extend substantially parallel to the two flanges  52  and  54 . The outer liner  16  is thereby axially retained with respect to the mounting ring  56  (and thus with respect to the dome plate  28 ) so that the dome plate  28  and the outer liner  16  are joined together. The joint  30  is located primarily aft of the plane defined by the forward surface of the dome plate  28 . Alternatively, the dome plate  28  and the dome flange  52  could be configured such that the joint  30  is located entirely aft of the plane defined by the forward surface of the dome plate  28 . 
     As mentioned above, the mounting ring  56  can be either a continuous or segmented 360 degree ring. In either case, the retainer  72  is segmented to permit assembly. With a segmented mounting ring  56 , the arcuate segments of the mounting ring  56  are circumferentially staggered with respect to the arcuate segments of the retainer  72  so that when the mounting ring  56  and the retainer  72  are fastened together, a rigid 360 degree structure results. This is illustrated in FIG. 4 which schematically shows an aft-looking-forward view of the combustor  10  in which the mounting ring  56  comprises two 180 degree segments  56   a  and  56   b  and the retainer  72  comprises two 180 degree segments  72   a  and  72   b.  These elements are circumferentially staggered so that the first mounting ring segment  56   a  overlaps one half of each retainer segment  72   a  and  72   b,  and the second mounting ring segment  56   b  overlaps the other half of each retainer segment  72   a  and  72   b.  After being located on the dome flange  52  and the liner flange  54 , the first and second mounting ring segments  56   a  are each bolted to both retainer segments  72   a  and  72   b  so as to form a rigid 360 degree structure. In this embodiment, the various flanges that comprise the joint  30  can be, but are not necessarily, coextensive with their corresponding parent structure. 
     With a continuous mounting ring  56 , the dome flange  52  comprises a plurality of tabs  82  circumferentially spaced so that adjacent ones form a gap therebetween, as shown in FIG.  5 . Similarly, the aft radial flange  60  of the mounting ring  56  comprises a plurality of tabs  84  circumferentially spaced so that adjacent ones form a gap therebetween, as shown in FIG.  6 . Preferably, but not necessarily, each of the two flanges  52  and  60  has an equal number of tabs. The dome flange gaps are wide enough so that the aft radial flange tabs  84  can pass through, and the aft radial flange gaps are wide enough so that the dome flange tabs  82  can pass through. Thus, to assemble the joint  30 , the aft radial flange tabs  84  are aligned with, and axially slid through, the dome flange gaps. Then, the mounting ring  56  is rotated so that the aft radial flange tabs  84  are circumferentially aligned with the dome flange tabs  82 . This provides a breech-lock engagement that produces axial retention between the dome plate  28  and the outer liner  16 . Alternatively, the forward radial flange  58  could be provided with intermittent tabs instead of the aft radial flange  60 . 
     As seen in FIG. 2, the mounting ring  56  and the retainer  72  are scalloped to accommodate the igniter  50 . This does not significantly affect the mechanical integrity of either the mounting ring  56  or the retainer  72  because of the small number of igniters that are disposed around the circumference of the combustor  10 . Most combustors typically have two igniters. 
     Referring again to FIG. 3, it is seen that an annular, axial-extending lip  86  is formed on the aft side of the dome plate  28 , adjacent to the outer liner  16 . The lip  86  and the outer liner  16  form an annular cooling slot  88  therebetween. A plurality of cooling holes  90  (only one shown in FIG. 3) is provided in the dome plate  28 . The cooling holes  90  are arranged in a circle about the dome plate  28  and extend axially therethrough. The cooling holes  90  are radially located so as to supply cooling air to the cooling slot  88 . The cooling slot  88  is oriented in a substantially axial direction so that cooling air is directed downstream and forms a thin cooling film on the inner surface of the outer liner  16 . 
     The foregoing has described a dome-to-liner joint that has little or no structure forward of the dome plate and is relatively easy to assemble. The joint accommodates segmented dome plates by providing dimensional control of the segmented dome panels (i.e., maintaining the panels in a single plane). The joint has a streamlined external surface to enhance cooling air flow passage around the corner without using a cowl. This avoids the additional spatial requirements and weight penalty associated with a cowl. 
     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.