Abstract:
A method of making a gas turbine engine combustor using the steps of: providing a combustor; providing a circumferentially extending louver member for ducting a flow of compressed air through at least one inlet opening in a combustor wall from a source of compressed air outside the combustor; and mounting the louver member in a non-destructive manner for releasable connection and disconnection to an interior surface of the combustor wall and at least partially covering the at least one inlet opening, the louver having a number of outlet openings in flow communication with an inlet opening.

Description:
RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of U.S. Ser. No. 10/357,363, now U.S. Pat. No. ______. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The invention relates to a combustor liner v-band louver, which may be manufactured of cast segments and removably fastened to the combustor liner.  
         BACKGROUND OF THE ART  
         [0003]    Gas turbine engine combustors are relatively thin sheet metal shells surrounded by a plenum containing compressed air from the compressor. Air flows into the combustor through the fuel nozzles to mix with the fuel and through several small openings or louvers in the combustor liner wall which create an air curtain along the inside surface of the combustor liner, provide further air for combusting the fuel and create circulation currents of gas and air flowing within the combustor.  
           [0004]    Conventional combustors may include circumferential V-shaped bands machined into inner wall surfaces that protrude into the combustor from the liner surface or sheet metal double band louver, to generate single or double toroidial fluid flow in the primary combustion zone. In an annular combustor the toroidial flow increases gas residence time in the combustor and thereby improves the fuel/air mixing, engine efficiency and reduces emission levels.  
           [0005]    Conventional so-called machined V-band louvers as well double band sheet metal louvers protrude into the hot gas path and are exposed to a harsh environment of rapidly flowing hot gases which tend to oxidize the metal liner material.  
           [0006]    A particular disadvantage of conventional machined V-band or standard double band sheet metal louvers circumferential louvers is the development of axial cracks due to the high hoop stresses resulting from temperature differentials. Thermal expansion and contraction stresses exerted on the louver together with the high temperatures expose these protruding components of the combustor wall to durability problems including cracking and oxidation.  
           [0007]    Further, V-band lovers or other similar machined louvers are very expensive to manufacture and often require repair during engine overhauls. Conventional combustor liner designs however incorporate the V-band louvers in the unitary machined structure of the combustor liner, and so repair is required to the liner itself.  
           [0008]    It is an object of the present invention to provide a more cost effective means of generating the single or double toroidal flow in the primary zone of the combustor liner.  
           [0009]    It is a further object of the invention to reduce or eliminate the high hoop stresses in the combustor liner which promote the development of axial cracks in the prior art.  
           [0010]    It is a further object of the invention to reduce the cost of manufacture and repair of a combustor liner.  
           [0011]    Further objects of the invention will be apparent from review of the disclosure, drawings and description of the invention below.  
         DISCLOSURE OF THE INVENTION  
         [0012]    The invention provides a method of making a gas turbine engine combustor using the steps of: providing a combustor; providing a circumferentially extending louver member for ducting a flow of compressed air through at least one inlet opening in a combustor wall from a source of compressed air outside the combustor; and mounting the louver member in a non-destructive manner for releasable connection and disconnection to an interior surface of the combustor wall and at least partially covering the at least one inlet opening, the louver having a number of outlet openings in flow communication with an inlet opening.  
           [0013]    As in the prior art, the primary function of the machined V-band/sheet metal double band louver is to generate single or double toroidal flow pattern in the combustor liner to promote fuel combustion efficiency, increase residence time and reduce emissions. However the invention permits reduction in machining required to create the toroidial flow inducing feature in the combustor liner, easing the assembly due to bolted construction and permitting repair or replacement of only the damaged sections through use of separate segments to assemble a circumferential band member about the combustor liner wall.  
           [0014]    A benefit of the segmental construction is the reduction of hoop stresses and increasing of the fatigue life of the V-band. Prior art designs induce significant hoop stresses due to the unitary annular structure when exposed to temperature differentials or fluctuations. By creating separate, preferably cast, segments which are assembled together to form the circumferential louver assembly, with a circumferential expansion and contraction joint between adjacent pairs of segments, hoop stresses and axial cracking due to thermal expansion and contraction can be reduced.  
           [0015]    In addition, the segmental construction permits a higher degree of assembly and manufacturing tolerance and permits the segments to be manufactured of metals or other materials which have different oxidation or other characteristics and different fatigue strength than the combustor liner to which they are releasably fastened in a non-destructive manner. The interior channels and outlets of the louver can be easily inspected for corrosion or damage by removing modular segments from the combustor wall. A segmented cast metal construction is more cost effective to manufacture than conventional designs due to reduced machining, and assembly is simplified by the bolted connection. These features result in lower cost operation since oxidation damaged sections can be replaced individually in a simple bolted connection.  
           [0016]    A further advantage of the invention is the diversion of any leakage between the cast V-band segment and the section of the combustor liner wall to which it is releasable attached. Leakage of air through any gap between the cast V-band segment and the combustor liner forms a beneficial film or curtain cooling layer adjacent the liner in the immediate local area. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0017]    In order that the invention may be readily understood, embodiments of the invention are illustrated by way of example in the accompanying drawings.  
         [0018]    [0018]FIG. 1 is an axial cross-sectional view through a turbofan gas turbine engine showing a general arrangement of components including the location of combustor.  
         [0019]    [0019]FIG. 2 a  is an axial cross-sectional view through a combustor liner showing an inner and an outer V-band of conventional prior art design. FIG. 2 b  shows a cross section view of a sheet metal double band louver also of conventional prior art design.  
         [0020]    FIGS.  3 - 8  show a first embodiment of the invention, where FIG. 3 shows the separate cast metal combustor wall louver band mounted with threaded studs to the interior surface of the combustor wall.  
         [0021]    [0021]FIG. 4 is a detailed view of the louver shown in FIG. 3.  
         [0022]    [0022]FIG. 5 is a partial isometric view of the outer combustor with inlet openings and louver bands with threaded studs for mounting purposes.  
         [0023]    [0023]FIG. 6 is an interior isometric view of the combustor wall louver.  
         [0024]    [0024]FIG. 7 is an outer view of a combustor wall louver segment showing three threaded studs and the interior channel with outlet openings.  
         [0025]    [0025]FIG. 8 is an interior isometric view of the combustor wall louver segment shown in FIG. 7.  
         [0026]    [0026]FIG. 9 is an axial cross sectional view through a prior art reverse flow combustor liner.  
         [0027]    [0027]FIG. 10 is a like axial sectional view through a reverse flow combustor liner with segmented louver (according to a second embodiment) mounted to the combustor liner with threaded studs.  
         [0028]    [0028]FIG. 11 is an interior isometric view of the combustor wall louver segment mounted to the combustor liner wall with threaded studs.  
         [0029]    [0029]FIG. 12 is a side isometric view of a combustor wall louver segment showing internal channel with outlet openings and threaded studs for mounting to the combustor wall. 
     
    
       [0030]    Further details of the invention and its advantages will be apparent from the detailed description included below.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0031]    [0031]FIG. 1 shows an axial cross-section through a typical turbofan gas turbine engine. It will be understood however that the invention is equally applicable to any type of engine with a combustor such as a turbo-shaft, a turboprop, auxiliary power unit, gas turbine engine or industrial gas turbine engine. Air intake into the engine passes over fan blades  1  in a fan case  2  and is then split into an outer annular flow through the bypass duct  3  and an inner flow through the low-pressure axial compressor  4  and high-pressure centrifugal compressor  5 . Compressed air exits the compressor  5  through a diffuser  6  and is contained within a plenum  7  that surrounds the combustor  8 . Fuel is supplied to the combustor  8  through fuel tubes  9  which is mixed with air from the plenum  7  when sprayed through nozzles into the combustor  8  as a fuel air mixture that is ignited. A portion of the compressed air within the plenum  7  is admitted into the combustor  8  through orifices in the side walls to create a cooling air curtain along the combustor walls or is used for cooling to eventually mix with the hot gases from the combustor and pass over the nozzle guide vane  10  and turbines  11  before exiting the tail of the engine as exhaust. It will be understood that the foregoing description is intended to be exemplary of only one of many possible configurations of engine suitable for incorporation of the present invention.  
         [0032]    [0032]FIGS. 2 a  and  2 B show a detailed axial cross sectional view through a combustor  8  with a prior art integral machined V-band or sheet metal double band louver  15 . The fuel supply tube  9  is shown, however the fuel nozzle arrangement has not been shown, for simplicity. The inner combustor wall  12  and outer combustor wall  13  are joined with a bolted connection  14 . Of interest to the present invention, the outer combustor wall  13  includes a conventional prior art integral V-band louver  15  that admits air from the plenum  7  into the interior of the combustor  8  to create a toroidal flow of fuel/air mixture within the combustor dome  16 , as indicated with arrows in FIG. 2.  
         [0033]    [0033]FIG. 3 shows a detailed view of the outer combustor wall  13  with flanged connection  14 . In accordance with the invention, a combustor wall louver  15  comprising a circumferentially extending band member  17  is releasably mounted to the interior surface of the combustor wall  13  and covers a series of inlet openings  18  (which are best seen in FIG. 5). Compressed air flows through the inlet openings  18  in the combustor wall  13  from the surrounding plenum  7 .  
         [0034]    The band  17  includes a large number of laterally extending outlet openings  19  (best seen in FIG. 6). The circumferentially extending band  17  is mounted to the interior surface of the combustor wall  13  with threaded studs  20  through openings. The generally V-shaped band  17  preferably includes a central channel  21  in flow communication with each outlet opening  19  and with the inlet openings  18 .  
         [0035]    In the first embodiment shown in FIGS.  3 - 8 , the band  17  includes an inner circumferential surface  22  which protrudes into the interior of the combustor  8  and is exposed to hot gas flow. In order to provide cooling, the inner circumferential surface  22  preferably includes thumb nail cooling air openings  23  communicating with the channel  21  through radial bores  24 . As shown in FIGS. 6 and 8, the cooling air openings  23  are preferably disposed in an inward spirally directed cooling vent  25 .  
         [0036]    As best seen in FIGS. 7 and 8, preferably, the circumferentially extending band  17  is made of a number of arcuate segments  26 , each removably mounted to the interior surface of the combustor wall  13  with threaded studs  20 . The segments  26  of the circumferentially extending band  17  have combustor wall abutting edges  27  bounding the air flow channel  21 . Each segment  26  (shown in FIGS. 7 and 8) includes two combustor wall abutting end bulkheads  28  which circumferentially contained the compressed air within the channel  21  to flow out into the combustor through outlet openings  19  and through cooling air openings  23  via bores  24 .  
         [0037]    In the first embodiment (shown in FIGS.  3  to  8 ) the combustor wall  13  has a recessed groove. The combustor wall abutting edges  27  of the circumferential band  17  engage the recessed groove  29  in a generally close fitting manner in order to ensure that the bulk of compressed air progresses through inlet openings  18  and out through outlet openings  19  or through bore  24 . However as indicated in FIG. 4, a certain amount of leakage may escape through an air curtain gap defined between the interior surface of the combustor wall  13  and the combustor wall abutting edges  27  of the louver  17  to create a beneficial cooling air film or curtain. To simplify manufacture and assembly, as well as reduce stress concentration, the recessed groove has sloped side walls and a circumferential bottom wall into which the inlet openings  18  are provided (in FIG. 4).  
         [0038]    The remaining FIGS. 10 through 12 illustrate a second embodiment of the invention applied to replace the V-band louver  15  of a prior art reverse flow combustor  8  shown in FIG. 9. In the prior art arrangement illustrated in FIG. 9, the V-band groove  15  is disposed in the outer combustor wall  13  which is connected to the inner combustor wall with the dome  16 . The fuel nozzles and fuel supply tubes are omitted for clarity.  
         [0039]    [0039]FIG. 10 illustrates the replacement of the V-band louver  15  with a circumferentially extending band  17  mounted to the interior surface of the outer combustor wall  13  and covering inlet openings  18  in a manner similar to that described above in respect of the first embodiment. However, as best shown in FIGS. 11 and 12, the segments  26 , that are assembled into a circumferentially extending band  17 , are mounted flush with the internal surface of the combustor wall  13  (not in a groove  29  as the first embodiment). The flush mounting arrangement somewhat simplifies machining, assembly and manufacture, and its use is not dictated by the combustor configuration.  
         [0040]    As best seen in FIG. 11, the threaded studs  20  extend from the band  17  through the combustor wall  13  with removable nuts  30  externally fastened to the studs  20 . Vents  25  and laterally extending outlet openings  19  expel air jets as described above in relation to the first embodiment. As seen in FIG. 12 however, the bulkheads  28  also include at least one outlet opening  19  for cooling and purging hot gases from the area between abutting segments  26 .  
         [0041]    It will be appreciated from the above description and particularly FIGS. 7, 8 and  12 , that each segment  26  can be easily manufactured as a shallow arcuate metal casting which may require minimal machining to meet tolerances or form the outlet openings  19  for example. The studs  20  in FIG. 7 extend from a raised boss  31  within the channel  21 . The boss  31  reinforces the local area but does not significantly impede the free flow of compressed air through the channel  21 .  
         [0042]    Although the above description relates to a specific preferred embodiment as presently contemplated by the inventors, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein. It will also be understood that certain changes will also be apparent to those skilled in the art which may be made to the disclosed embodiments without departing from the invention described herein. For example, the invention may be applied to any combustor in which a V-band may beneficially produce a toroidial flow. The invention may be fastened to a combustor by any suitable means. Furthermore, the invention need not be cast but other suitable fabrication means may be employed. Still other changes will be apparent to those skilled in the art, and it is understood that such changes do not depart from the scope of claims below.