FIELD OF THE INVENTION
The invention relates to apparatus and assembly methods for a gas turbine exhaust section, and particularly to apparatus and methods for alignment of upper and lower halves of an exhaust diffuser outer shroud during transportation or during on site assembly and re-assembly.
BACKGROUND OF THE INVENTION
A gas turbine (GT) exhaust diffuser is a divergent annular flow path between inner and outer annular diffuser shells through which the exhaust gas passes. The cross-sectional area of the duct progressively increases in the flow direction to reduce the speed of the exhaust flow and increase its pressure. The exhaust diffuser is commonly fabricated in an upper and lower halves joined along horizontal joints between the inner and outer shells. The diffuser halves require complex fabrication, including complex machining profiles along the horizontal joints. There is potential for misalignment between the upper and lower halves, especially radial misalignment, which can make alignment of bolt holes for joining difficult.
The diffuser may operate at temperatures of 500-700° C. or more, and experiences thermal and mechanical stresses due to operational gradients and GT start/shutdown cycles. This results in material distortions that make it difficult to realign the halves of the diffuser after manufacturing, transport, and disassembly for servicing purposes.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained in the following description in view of the drawings that show:
FIG. 1 is an axial sectional view of an exhaust section of a prior art gas turbine taken along line 1-1 of FIG. 2.
FIG. 2 is a transverse sectional view of the exhaust section of FIG. 1 taken along line 2-2.
FIG. 3 is a perspective view of a prior art bolt flange joint between upper and lower halves of the outer diffuser shell.
FIG. 4 is a sectional view of the bolt flange joint of FIG. 3 taken along line 4-4 of FIG. 3.
FIG. 5 is a sectional view of the bolt flange joint of FIG. 3 connected to the surrounding casing of the exhaust section by turnbuckles.
FIG. 6 is a top sectional view of one side of the upper half of an exhaust diffuser outer shell with a series of turnbuckles spanning between an upper bolt flange and the exhaust section casing.
FIG. 7 is a perspective view of a threaded clevis fitting and clevis bolt.
FIG. 8 is a perspective view of a non-threaded clevis fitting and clevis pin.
FIG. 9 is a top view of a turnbuckle with eye bolts.
FIG. 10 is a top view of a turnbuckle with clevis-ends.
FIG. 11 is a partial sectional view an arrangement of upper/lower clevis fittings.
FIG. 12 is a front sectional view of an eye fitting that retains a hook end of a turnbuckle in moderate compression and tension.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates an exhaust section 20 behind a last row of rotating blades 22 of a gas turbine engine. A bearing hub 24 may extend into the exhaust section and enclose an aft bearing 26 that supports the turbine shaft 28 for rotation about an axis 30. A diffuser 40 defines a divergent annular flow path for the exhaust gas 48. The diffuser may be fabricated as upper 38A and lower 38B inner shells and upper 40A and lower 40B outer shells. A horizontal joint 49 exists between the upper and lower inner shells 38A-B. A horizontal joint 50 (later shown) exists between the upper and lower outer shells 40A-B. Struts 32 may span between the hub and a casing 34 in a circular array. For conceptual clarity, in FIG. 1 the struts may be oriented radially, or they may be oriented tangentially to the hub as shown in FIG. 2. Each strut may be surrounded by a heat shield 36 connected between the inner 38A-B and outer 40A-B diffuser shells. Each shield is a tube that surrounds the strut and may provide space 42 for coolant flow along the strut. An inner collar 44 and an outer collar 46 on each shield 36 attach the shield to the respective diffuser shell 38A-B, 40A-B. Stress concentrations in these collars may contribute to distortions in the shells.
FIG. 2 is a transverse sectional view of the GT exhaust section 20 of FIG. 1. A hub 24 encloses an aft bearing 26 that supports the turbine shaft 28. A circular array of struts 32 connects the hub to the casing 34 for mutual support and positioning. The casing 34 is formed in halves and is bolted together at joint 51. The struts may be oriented radially or tangentially to the hub as shown to accommodate differential thermal expansion between the hub, struts, and case. Each strut is surrounded by a heat shield 36 connected between the inner 38A-B and outer 40A-B diffuser shells. An inner collar 44 and an outer 46 collar attach each heat shield to the respective diffuser shell 38A-B, 40A-B. The inner diffuser shell is formed in upper 38A and lower 38B halves. The outer diffuser shell is formed in upper 40A and lower 40B halves, which are joined along a horizontal joint 50 by respective bolt flanges 41A, 41B.
FIG. 3 is a perspective view of a joint 50 between the upper 40A and lower 40B halves of the outer diffuser shell. Upper 41A and lower 41B bolt flanges may each have a respective series of upper and lower bolt bosses 43A, 43B that must be aligned so that bolts can be inserted through them.
FIG. 4 is a front sectional view of the joint 50 between the upper 40A and lower 40B halves of the outer diffuser shell. The upper 43A and lower 43B bolt bosses must be aligned so that bolts can be inserted through respective aligned bolt holes 52A, 52B. Therefore, radial misalignment as shown must be corrected before this joint can be assembled. “Radial” herein is with respect the turbine axis 30 (FIGS. 1, 2)
FIG. 5 is a front sectional view of the joint 50 between the upper 40A and lower 40B halves of the outer diffuser shell disposed inside the exhaust section casing 34. Turnbuckles 56, 57 span between each respective bolt flange 41A, 41B and the casing 34 on respective sides of casing joint 51. These turnbuckles provide radial adjustment of one or both flanges as needed for alignment. Each turnbuckle is capable of providing at least tensile force 58, and may also be capable of providing compressive force 59. For example, the ends of the turnbuckles may be welded 60 to the flanges and the casing as shown. This makes each turnbuckle capable of provide both tension or compression as needed for alignment, so that bolts 54 can be inserted through the upper 43A and lower 43B bolt bosses.
FIG. 6 is a top sectional view of one side of the upper half 40A of the diffuser outer shell disposed within the exhaust section casing 34. Adjustable bracing in the form of turnbuckles 56A-D radially aligns the bolt flange 41A as previously described. In this embodiment, each turnbuckle is attached between two clevis fittings 62. This allows the turnbuckles to be easily removed after the horizontal joint 50 is aligned and bolted together. Each clevis fitting may have a clevis pin or bolt 63 as shown. The number of turnbuckles used may vary from unit to unit. The turnbuckles at each location may be of different lengths and/or thicknesses. The turnbuckle 56A nearest the forward end of the diffuser may be longer than the turnbuckle 56D nearest the aft end, and may also be thicker in cross sectional area to support the greater turnbuckle length and a higher rigidity of the forward end of the diffuser. Optionally, the bolt bosses 43A, 43B may be attached to the upper/lower shells 40A, 40B of the diffuser without a continuous flange 41A, and/or the turnbuckles may be attached directly to the upper/lower shells 40A/40B.
FIG. 7 shows a clevis fitting with parallel upper and lower plates 62A, 62B, at least one of which may be threaded to retain a threaded bolt 63A. The bolt hole in the upper plate 63A may be unthreaded and large enough to pass the bolt without interference. If the plates 62A, 62B are horizontal as shown, and only the lower plate is threaded as shown, the turnbuckle eye 66 (FIG. 9) can be inserted between the plates, and the bolt 63A can be dropped through the hole in the upper plate, where it is then retained by gravity until it is secured by turning it into the threads of the lower plate 62B. This makes attachment and detachment fast and reliable, and minimizes the number of parts. If a threaded bolt is used, and one or both plates 62A, 62B are threaded, then neither a cotter pin nor a nut is needed. FIG. 8 shows a clevis fitting 62 with a clevis pin 63B that may be retained in unthreaded plates 62A of the fitting by a cotter pin 64.
FIG. 9 shows a turnbuckle 56 with eye bolts 65 having eyes 66 that are inserted into the clevis fittings 62. The eyes may be formed by casting or other means. Cast eyes are especially capable of supporting both tension and compression modes of the turnbuckle, as are eyes formed as closed loops that are welded closed.
FIG. 10 shows an alternate turnbuckle design 67 with clevis-end bolts 68. Only simple eye fittings are required to retain this turnbuckle. A turnbuckle with open hooks can also be used on a simple eye fitting, especially if only the tension mode of the turnbuckles is sufficient for alignment.
FIG. 11 shows a partial sectional view an arrangement of upper/lower clevis fittings 70A, 70B that retains upper/lower turnbuckle eyes 66 and threaded clevis bolts 63A, 63C by gravity until the clevis bolts are secured by turning them into the threads. Each clevis fitting has parallel upper and lower plates 71, 72, at least one of which may be threaded, and a side plate 73 that blocks a lower end of the space between the parallel plates. The clevis fittings are angled from horizontal enough that insertion of the lower clevis bolt 63C into the lower clevis fitting 70B is not blocked by the upper clevis fitting 70A.
FIG. 12 is a front sectional view of an eye fitting 72 having a base 73 with a convex contact surface 74 that matches the end of the hook 76 to stably retain the hook end 76 of a turnbuckle bolt 77 in compression. This allows moderate tension and compression without a clevis attachment.
After the upper and lower halves of the diffuser are aligned and bolted together, the turnbuckles may be removed for engine operation by detachment from the fittings 62. If the turnbuckles are welded as in FIG. 5, they may be cut off.
The concepts of the present invention may be used during the transportation of a gas turbine engine wherein the exhaust section is typically shipped in two halves separated along the horizontal joint. Adjustable length braces such as the turnbuckles described above may be installed at the factory or other point of origin of a transportation route to secure the relative positions of the diffuser halves in relation to the respective casing halves so that the flanges and bolt holes of the two halves are not dislocated with respect to each other as a result of loads imposed during transportation. Upon arrival at the destination, some minor adjustment of the bolt hole locations may or may not be necessary and can be achieved by adjusting the length of the appropriate brace(s) in order to facilitate the assembly of the exhaust section.
The concepts of the present invention may also be used for assembly of a gas turbine engine. In one embodiment, an upper half of an exhaust diffuser is mounted on a lower half of the exhaust diffuser along a horizontal joint, and the diffuser is located within a casing of the exhaust section. A plurality of length adjustable braces are mounted on at least one and preferably both of the upper and lower halves of the exhaust diffuser along the horizontal joint to provide relative motion of the bolt holes and the surrounding casing. The lengths of the braces are then adjusted to align the bolt holes in the upper and lower halves of the diffuser flange, and the horizontal joint is then secured together with bolts through the bolt holes. The braces are then removed prior to operation of the gas turbine engine.
The concepts of the invention may also be used during a maintenance outage for a gas turbine engine. Adjustable length braces are attached between the diffuser halves and the surrounding casing halves prior to the separation at the horizontal joint. The braces serve to secure the relative positions of the bolt holes and the respective casing halves when the horizontal joint bolts are removed and the two halves are separated for service. Upon reassembly, the respective upper and lower bolt holes will align or may require minor adjustment of the length of the braces to achieve alignment.
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.
Patent Grant
9458737
