Patent Grant
6931728
1. Field of the Invention
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.
2. Description of the Related Art
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.
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.
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.
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.
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.
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.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
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.
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
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
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.
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
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.
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