Patent Application
20150107264
The invention relates to a mounting arrangement for a can-annular combustion system of a gas turbine engine. Specifically, the arrangement permits relative radial motion yet prevents relative axial motion between an annular chamber of the combustion system and the turbine vane carrier to which the annular chamber is secured.
Conventional can-annular gas turbine engines include a plurality of individual combustor cans, where each can is secured to a respective transition duct that directs combustion gases from the combustor can, and through inlet guide vanes to a respective portion of a turbine inlet annulus. Each flow of combustion gas remains discrete from the combustor until exiting the respective transition duct. In contrast, in certain emerging gas turbine engines that use can combustors, the array of transition ducts are replaced with a duct arrangement that receives the discrete combustion gas flows from repositioned combustor cans, accelerates them to a speed appropriate for delivery onto the first row of turbine blades, and directs them into a common duct structure that may include an annular chamber where the combustion gas flows are no longer segregated from each other. The annular chamber exhausts directly into the turbine inlet. (Other configurations exist where the individual flows remain discrete even within the common duct structure.) The proper orientation and speed created by the arrangement eliminates the need for a first row of inlet guide vanes present in the conventional arrangements. An example of this configuraton may be seen in US Patent Application Publication Number 2011/0203282 to Charron et al., published Aug. 25, 2011, which is incorporated by reference in its entirety herein.
In conventional gas turbine engine combustor arrangements, since the combustion gas flows are not accelerated a substantial amount in the transition ducts there is a relatively small static pressure difference between compressed air in the plenum surrounding the transition duct and a static pressure of the combustion gas flows within the transition. Consequently, there is a relatively small force pressing inward on the exterior surface of the transition ducts.
In contrast, in the emerging technology ducting arrangement the combustion gas flows are traveling at significantly greater speeds. This results in significantly greater pressure differences (up to six atmospheres) and resulting forces acting on the exterior surface of the ducting arrangement. In configurations with an accelerating geometry that accelerates the combustion gas flows to the proper speed for delivery onto the first row of turbine blades, such as the configuration with the annular chamber, the annular chamber experiences the greatest of these forces because the combustion gas flows are fully accelerated when in the annular chamber. These forces act to deform the ducting arrangement, in particular the annular chamber, and there is room in the art for improvements that resist this deformation.
The invention is explained in the following description in view of the drawings that show:
The present inventors have devised an innovative mounting arrangement that resists deformation of ducting associated with emerging technology can annular combustion arrangements. The mounting arrangement permits relative radial movement while preventing relative axial movement of the ducting with respect to the turbine vane carrier to which the ducting is mounted. In addition, the mounting arrangement provides a bracing function that helps the ducting retain its shape/profile despite pressure induced forces acting to deform the ducting.
When engaged the outer diameter mounting arrangement 34 permits the outer diameter 52 of the annular chamber 14 to move radially with respect to the turbine vane carrier 20. This is very important because during transient events the two might heat and cool at different rates and this may cause relative thermal growth in a radial direction that requires relative radial movement to avoid thermal stresses between the two. Furthermore, vibration during operation may require the freedom of radial movement. However, relative axial movement must be prevented in order to keep the annular chamber 14 from reaching the first row of turbine blades.
The inner diameter mounting arrangement 36 refers to the arrangement required to secure an inner diameter 60 of the annular chamber 14. The inner diameter mounting arrangement 36 is configured to permit relative radial movement and prevent relative axial movement and may include: an inner diameter flange 62 associated with the inner diameter 60 of the annular chamber 14, a bracket 64, and a radially oriented inner mount groove 66 fixed with respect to the turbine vane carrier 20. The bracket 64 includes a vane carrier end 68 and an annular chamber end 70. The vane carrier end 68 may include a bracket radially oriented flange 72 configured to fit within the radially oriented inner mount groove 66. The annular chamber end 70 may fixedly secure to the inner diameter flange 62. By fixedly secured it is meant that relative movement is not permitted at the location.
In this configuration it can be seen that the inner diameter 60 of the annular chamber 14 is secured, via the inner diameter flange 62, the bracket 64, the bracket radially oriented flange 72, and the radially oriented inner mount groove 66, to the turbine vane carrier 20 in a manner that permits relative radial movement and prevents relative axial movement between the inner diameter 60 and the turbine vane carrier 20. The bracket 64 will float with any radial movement of the inner diameter 60, and hence will float within the radially oriented inner mount groove 66. However axial movement will be prevented because the vane carrier end 68 of the bracket is prevented from axial movement by a fore surface 80 of the turbine vane carrier 20. An inherent rigidity of the bracket 64 will prevent the annular chamber end 70 from moving axially. The bracket 64 will be able to maintain its orientation via an interaction of the bracket radially oriented flange 72 and the radially oriented inner mount groove 66.
The mounting arrangement 32 may optionally include a supplemental support arrangement 90 that provides supplemental support for an additional location 92 of the ducting arrangement 10 at a supplemental support point 94 of the bracket 64 between the vane carrier end 68 and the annular chamber end 70. This may be accomplished via a sliding relationship of an additional tab 96 and the supplemental support point 94 that allows for thermal growth mismatch but still provides the necessary support for the inner diameter 60.
Supporting the ducting arrangement 10 and in particular the inner diameter 60 in this manner is important. The relatively high static pressure in the plenum 24 wants to bring the inner diameter 60 and the outer diameter 52 together. However, when the annular chamber is formed as a unified unit, this force is essentially accommodated by the ring shape of the annular chamber 14 itself. In the exemplary embodiment shown a unified unit includes an annular chamber 14 formed of multiple arc-sections that are secured together to form the annular chamber 14. There may be as many arc-sections as there are combustor cans. However, the number of sections need not be directly related to the number of combustor cans. For example, there could be six discrete sections instead of twelve, each section being associated with two adjacent combustor cans, or four discrete arc-sections each being associated with three combustor cans etc.
Edges of circumferentially adjacent sections may be, for example, bolted directly to each other. This reduces air leakage between adjacent sections and therefore increases engine efficiency. However, the pressure induced forces also push the inner diameter 60 aft, (to the right as shown) and without proper support the inner diameter 60 may tend to move aft. At the very least this will change a contour of the ducting arrangement 10. At the extreme end and under the proper conditions this could fatally buckle the ducting arrangement 10. The ducting arrangement 10 may be operated at higher temperatures that traditional transition ducts in order to reduce the amount of cooling air used, which in turn increases engine efficiency. The increased operating temperature brings the ducting arrangement closer to its operating limits and this reduces its structural strength. The above, plus the geometry of the annular chamber 14, net an arrangement where the thermal growth that occurs naturally during operation may be greater than the amount of strain it would take to cause the annular chamber 14 to yield. For all these reasons conventional brackets do not suffice in the new technology ducting arrangement 10.
Prior mounting arrangements have attempted to support the inner diameter by rigidly securing it to the turbine vane carrier 20, or by securing it to another part of the engine. Embodiments that rigidly secured the inner diameter 60 to the turbine vane carrier 20 were inadequate because the annular chamber 14 responds differently to thermal changes and hence there is relative thermal growth between the annular chamber 14 and the turbine vane carrier 20. The rigid connections resulted in an unacceptable thermal fight between the two. Embodiments that secured the inner diameter 60 to other locations often did not provide adequate support because the other locations added thermal growth differences of their own.
The present inventors recognized that it is necessary to give the annular chamber 14 the freedom to move radially with respect to the turbine vane carrier 20, and it is necessary to restrict its axial movement. The inventors further recognized that in order to provide the necessary radial movement freedom, both the inner diameter 60 and the outer diameter 52 needed to be radially free to move. They devised the current arrangement that effectively ties the inner diameter 60 and the outer diameter 52 to one component, the turbine vane carrier 20, and thus the thermal response of only the one component needed to be considered. The inventors further realized that when used in conjunction with a flange and groove arrangement for the outer diameter 52, a cantilever support with freedom of radial movement could satisfy both the need to provide radial movement freedom to the inner diameter 60 and the need to provide structural support/bracing (i.e. an exoskeleton-type function) for the ducting arrangement 10. Consequently, the bracket 64 may be secured in any number of ways to the ducting arrangement 10 so long as it achieves the goal of allowing relative radial movement and not relative axial movement with respect to the turbine vane carrier.
The bracket 64 may also be pre-stressed in a manner that is effective to counter pressure-induced forces on the inner diameter 60. For example, if movement in the axial direction 40 is to be countered, the bracket 64 could be pre-bent such that the supplemental support point 94 moves in a radially outward direction. When not under base load conditions the bracket 64 might tend to pull the inner diameter 60 to the left (fore), but the pull force at these lower pressure differentials would be within the structural capacity of the ducting arrangement 10. When under operation conditions the bracket 64 could be configured such that pressure differential pushes the inner diameter 60 to an operating position where there is reduced or no stress in the annular chamber 14. In this scenario most, if not all of the pressure-induced forces could be borne by the bracket 64 and radially oriented inner mount groove 66.
There may be any number of brackets 64 deemed necessary. For example, there may be one bracket 64 for each of the discrete arc-sections that constitute the annular chamber 14 in the exemplary embodiment shown. Alternately, there could be more or fewer brackets 64. For example, there could be two brackets 64 for each section. The annular chamber 14 exhibits a certain structural strength when bolted together, and thus there may be fewer than one bracket 64 per arc-section. The brackets may be evenly positioned about the circumference of the annular chamber 14, or their location may be selected based on localized needs, resulting in asymmetric positioning of the brackets 64 about the circumference.
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From the foregoing it can be seen that the inventors have devised an innovative solution to a unique problem associated with a new combustion arrangement design. The inventive mounting arrangement is an uncomplicated solution to a problem that was difficult to fully identify, and hence represents an improvement in the art.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
Development for this invention was supported in part by Contract No. DE-FC26-05NT42644, awarded by the United States Department of Energy. Accordingly, the United States Government may have certain rights in this invention.
