Abstract:
A method of fabricating a test model of a gas turbine engine combustor dome, and the test model produced thereby. The method entails individually stamping a plurality of dome wall segments and first and second mounting band segments. Each wall segment comprises at least one cup between radially inward and outward edges of the wall segment, and an opening in the cup. At least one wall segment and its two corresponding mounting band segments are placed on a fixture that locates the opening of the wall segment, locates the first and second mounting band segments at the radially-inward and outward edges of the wall segment, and orients the wall segment to establish a dome angle of the fixtured dome assembly. The wall segment and mounting band segments are then joined while the fixtured dome assembly remains on the fixture to form at least a unitary sector of the test model.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to combustion systems of gas turbine engines. More particularly, this invention relates to a method of fabricating a gas turbine engine combustor dome suitable for use in the development and testing of a combustor.  
           [0003]    2. Description of the Related Art  
           [0004]    A conventional gas turbine engine of the type for aerospace and industrial applications has a combustor with an annular-shaped combustion chamber defined by inner and outer combustion liners. The upstream ends of the combustion liners are secured to a pair of mounting bands spaced radially from each other on an annular-shaped dome, which defines the upstream end of the combustion chamber. Between the mounting bands, the dome has an annular-shaped wall, typically disposed at some angle (“dome angle”) to a plane perpendicular to the axis shared by the dome and combustion chamber. A number of circumferentially-spaced contoured cups are formed in the dome wall, with each cup defining an opening in which one of a plurality of air/fuel mixers, or swirler assemblies, is individually mounted for introducing a fuel/air mixture into the combustion chamber. The dome is important to the desired performance and functionality of the combustor since the dome affects the shape of the combustion chamber and the size and locations of the openings in the dome locate and affect the performance of the swirler assemblies mounted within the openings. Consequently, domes have been manufactured as a one-piece stamping to provide accuracy and consistency in the location and shape of the dome, including its cups and mounting bands.  
           [0005]    During the development of a gas turbine engine, combustor mockups are often fabricated to perform a variety of tests, such as profile and pattern factor development, that assess the performance of a combustor and its individual components, including the aerodynamic, heat transfer and mechanical design requirements of the dome. One approach for fabricating a dome test model for development testing is to fabricate a production-type tool capable of forming the entire dome in a single stamping operation. However, a significant drawback with this approach is the large capital expense and lead times required to fabricate the tooling. Furthermore, this tooling is dedicated to a particular dome design that may be one of a number of designs evaluated before a suitable production design is identified. Another approach is to fabricate a number of individual components, such as cones, cylinder and flat plates, that can be assembled and welded together to form domes of various configurations. However, the suitability of this approach depends on the ability of the fabricator to consistently produce a relatively large number dimensionally accurate parts, which must then be carefully assembled to obtain the relative positions and orientations of the individual dome components.  
           [0006]    In view of the above, it would be desirable if an improved method were available for fabricating a dome that is suitable for developmental testing, wherein the dome can be designed and assembled with reduced costs and shorter lead times, yet meet the stringent dimensional requirements to accurately replicate the performance of the dome design being evaluated for production.  
         SUMMARY OF INVENTION  
         [0007]    The present invention provides a method of fabricating a test model of a dome for a gas turbine engine combustor, and the test model produced by the method. Dome test models of this invention can be consistently and accurately fabricated to have the configuration and dimensions of a dome desired for evaluation, yet can be designed and fabricated in far less time than if the dome were formed as a single stamping.  
           [0008]    The method of this invention generally entails stamping a plurality of dome wall segments, each dome wall segment comprising an arcuate radially-inward edge, an arcuate radially-outward edge, at least one cup between the radially inward and outward edges, and an opening in the cup for receiving a combustor swirler assembly. Also stamped are a plurality of individual arcuate-shaped first and second mounting band segments. At least one of the dome wall segments and at least one of each of the first and second mounting band segments are then placed on a fixture to form a fixtured dome assembly. The fixture comprises means for locating the opening(s) of the dome wall segment(s) on the fixture, means for locating the first mounting band segment(s) at the radially-inward edge of the dome wall segment(s), means for locating the second mounting band segment(s) at the radially-outward edge of the dome wall segment(s), and means for orienting the dome wall segment(s) to establish a dome angle of the fixtured dome assembly. The dome wall segment(s) and the first and second mounting band segments are then joined while the fixtured dome assembly remains on the fixture to form at least a unitary sector of a dome test model.  
           [0009]    In view of the above, the present invention provides a unitary test model of a combustor dome, in which the test model generally comprises a plurality of individually-stamped dome wall segments and individually-stamped first and second mounting band segments. Each of the first and second mounting band segments is joined to the radially-inward or radially-outward edge, respectively, of a corresponding one of the dome wall segments. The test model can be viewed as comprising a plurality of unitary sectors, with each sector comprising one or more dome wall segments and the corresponding first and second mounting band segments joined to the dome wall segment(s). This construction enables the individual components of the dome, particularly the openings for the swirler assemblies, to be accurately shaped and sized by a stamping operation, yet at the same time can make use of stamping tooling that requires far less time to design and fabricate. The relative locations of the openings of the test model are then established by the fixturing, as are the dome angle and the orientation of the mounting band segments. As such, the resulting dome test model of this invention is capable of accurately replicating the performance of a dome formed of a unitary stamping, but the lead time and costs associated with fabricating the test model are significantly less than what would be required to fabricate a unitary stamped dome, while also being less dependent on the skill of the fabricator.  
           [0010]    Other objects and advantages of this invention will be better appreciated from the following detailed description. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]    [0011]FIGS. 1 and 2 are fragmentary perspective and end views of a dome sector and a fixture on which the sector has been fabricated in accordance with this invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]    [0012]FIGS. 1 and 2 depict a unitary dome sector  10  that, when assembled with other sectors  10 , forms a unitary test model of a dome for a gas turbine engine combustor. As shown, the sector  10  comprises a number of individually-stamped dome wall segments  12 , with each dome wall segment  12  comprising arcuate radially-inward and outward flanges  14  and  16 , a single cup  18  between the inward and outward flanges  14  and  16 , and an opening  20  in the cup  18 . As shown, the wall of each cup  18  is arcuate, rising above the surrounding surface of its wall segment  12  and terminating in the opening  20  that lies in a plane substantially parallel to the surrounding surface of the wall segment  12 . The sector  10  further comprises a number of individually-stamped arcuate-shaped mounting band segments  22  and  24  joined to the inward and outward flanges  14  and  16 , respectively, of the dome wall segments  12 . For this purpose, the mounting band segments  22  and  24  are represented as having flanges  28  and  29  joined to the wall segment flanges  14  and  16 , though other configurations are possible.  
         [0013]    Together, a single dome wall segment  12  and its corresponding inner and outer mounting band segments  22  and  24  can be described as forming a single dome segment  26 . In a preferred embodiment, each dome segment  26  comprises mounting band segments  22  and  24  brazed to a dome wall segment  12 , while adjacent dome segments  26  are joined by welding together their adjacent dome wall segments  12 , inner mounting band segments  22 , and outer mounting band segments  24 . The dome wall segments  12  and the mounting band segments  22  and  24  are all preferably formed of the same superalloy. An example of a suitable superalloy is a cobalt-based superalloy commercially available under the name HS188 and having a nominal composition of, by weight, Co-22Ni-22Cr-14W-0.35Si 0.10C-0.03La-3Fe(max)-1.25Mn(max). However, the benefits of this invention are applicable to combustor domes that may be formed of various high temperature materials, including nickel-based and iron-based superalloys.  
         [0014]    Each of the dome wall segments  12  is represented as defining a single cup  18  and opening  20 , which promotes the dimensional accuracy and shape of the cup  18  and opening  20  possible with a stamping operation. In contrast, the circumferential spacing of the cups  18  and openings  20  along the length of the sector  10  is determined by the manner in which the dome wall segments  12  are supported and positioned relative to each other with a fixture  30  shown in FIGS. 1 and 2. The fixture  30  is represented as comprising a baseplate  32  and a number of cylindrical members  34  that are individually received in the wall segment openings  20 , each of which serves as a datum point for locating the wall segments  12  on the fixture  30 . Each cylindrical member  34  is attached and oriented relative to the backplate surface  38  at an angle corresponding to the dome angle of the dome being modeled. As shown, the dome angle is other than zero, resulting in a “tipped” dome, though a dome angle of zero, resulting in a “flat” dome, is also within the scope of this invention. A number of riser blocks  36  are also shown as being attached to the surface  38  of the baseplate  32  and support the outer joint defined by each wall segment  12  and its outer mounting band segment  24 . The inner joint defined by each wall segment  12  and its inner mounting band segment  22  is represented as being supported directly by the baseplate  32 . The use and location of the riser blocks  36  will depend on the dome angle required by the dome being modeled. Therefore, it is foreseeable that riser blocks  36  or other suitable features could be provided that support the inner joint in addition to, or instead of, supporting the outer joint. As seen in FIG. 2, triangular-shaped gussets  40  are preferably attached to the baseplate  32  to ensure that the mounting band segments  22  and  24  are properly positioned and held against the flanges  14  and  16  of their respective wall segments  12 . Following fixturing, the wall segments  12  are preferably tack-welded to their respective cylindrical members  34  and the mounting band segments  22  and  24  are preferably tack-welded to their respective riser blocks  36  and gussets  40 , and these tack welds remain during the welding of the dome segments  26  and brazing of the mounting band segments  22  and  24  to the dome wall segment  12 , as well as during a stress relief treatment that preferably follows the welding operation.  
         [0015]    The method by which the sector  10  is fabricated begins with the stamping of the individual dome wall segments  12 , during which the radially-inward and outward flanges  14  and  16  of the segments  12 , the cups  18  and the openings  20  within the cups  18  are formed. Suitable stamping techniques and materials and methods for fabricating a die capable of forming the wall segment  12  are known to those skilled in the art, and therefore will not be discussed here in any detail. The mounting band segments  22  and  24  are also preferably fabricated with a stamping operation. The dome wall segments  12  and their corresponding mounting band segments  22  and  24  are then placed on the fixture  30 , as depicted in FIGS. 1 and 2, to yield what may be termed a fixtured dome assembly. When properly positioned on the fixture  30 , the openings  20  of the dome wall segments  12  are located on the fixture  30  with the cylindrical members  34 , and the riser blocks  36  and gussets  40  support and locate each inner and outer mounting band segment  24  at the corresponding inward and outward flange  14  and  16 , respectively, of its dome wall segment  12 . As noted above, the wall segment  12  and the band segments  22  and  24  are then preferably tack welded to the cylindrical members  34 , riser blocks  36  and gussets  40  to positively position the wall segments  12  and the band segments  22  and  24  on the fixture  30 . A suitable tack weld for this purpose is about 0.05 to 0.10 inch (about 1.3 to about 2.5 mm) in diameter. In the configuration shown in FIG. 2, the riser blocks  34  support the outer radial flanges  16  of the dome wall segments  12  out of the plane of the baseplate surface  38 , causing the dome wall segments  12  to be disposed at an angle to the baseplate surface  38  that will result in the sector  10  being disposed at the proper dome angle for the dome being modeled.  
         [0016]    After fixturing the components of the sector  10  in the above-described manner, adjacent dome wall segments  12  are welded together, adjacent inner mounting band segments  22  are welded together, and adjacent outer mounting band segments  24  are welded together. A suitable welding technique is electron beam or laser welding, with or without a filler material, though other welding techniques (e.g., tungsten inert gas, or TIG) could potentially be used. As noted above, the wall segments  12  and mounting band segments  22  and  24  are preferably stress relieved following welding by subjecting the entire fixtured assembly to a heat treatment appropriate for the materials used to form the wall and band segments  12 ,  22  and  24  as well as the welds that join these components. To avoid the potentially detrimental effect of different physical properties, particular different coefficients of thermal expansion (CTE), the baseplate  32 , cylindrical members  34 , riser blocks  36  and gussets  40  of the fixture  30  are all preferably formed of the same material as the wall and band segments  12 ,  22  and  24 .  
         [0017]    Following heat treatment, the welded mounting band segments  22  and  24  are then brazed as a unit to the welded dome wall segments  12 , with each band segment  22  and  24  being individually brazed to its respective dome wall segment  12  while the fixtured dome assembly remains on the fixture  30 , the result of which is the unitary sector  10 . Suitable braze alloys for use with this invention include various high-temperature nickel-based alloys that are commercially available. To prevent brazing of the wall and band segments  12 ,  22  and  24  to the fixture  30 , a suitable braze inhibitor paste such as STOPOFF®, commercially available from Pyramid Plastics, Inc., can be used. Thereafter, the sector  10  can be welded to an appropriate number of identically-fabricated sectors to form a unitary test model of a dome. In practice, the five-cup sector  10  represented in FIG. 1 is one of several identical sectors that can be welded together to form a unitary dome test model. Alternatively, the sector  10  could consist of a single dome segment  26  formed of a dome wall segment  12  and its two mounting band segments  22  and  24  joined thereto. Yet another alternative is that the entire unitary dome test model could be fabricated in the manner described above by manufacturing the fixture  30  to accommodate enough dome segments  26  to form the desired test model. In any case, the test model can then be used in a developmental test conducted to evaluate the dome design.  
         [0018]    While the invention has been described in terms of a preferred embodiment, it is apparent that other forms could be adopted by one skilled in the art. For example, the physical configuration of the dome test model and fixture  30  could differ from that shown. For example, while the Figures show a single annular combustor dome being modeled, the fixture could be adapted to model a multidome combustor having two or more concentric domes. Therefore, the scope of the invention is to be limited only by the following claims.