Apparatus and Method for Supporting a Vane Segment in a Gas Turbine

1. Field of the Invention

The present invention relates to gas turbines. More specifically, the present invention relates to an apparatus and method for supporting the vane segments in the turbine section of a gas turbine.

A portion of the annular gas flow path in the turbine section of a gas turbine is formed by vane segments circumferentially arrayed around the rotor. Each vane segment is comprised of an inner and an outer shroud, which together form the boundaries of the gas flow path, and one or more vanes. In order to maintain aerodynamic efficiency, it is important that the inner and outer shrouds of adjacent vane segments be properly aligned relative to each other so that a smooth surface is provided over which the hot gas may flow. Moreover, even though the shrouds may be properly aligned at assembly, aerodynamic forces imposed on the vane segments may result in misalignment of the shrouds under operating conditions. Hence, it is important that the vane segments be adequately supported so as to resist the aerodynamic forces imposed on it.

2. Description of the Prior Art

According to one approach used in the prior art to align and support the vane segments, each vane segment is affixed at its outer shroud to a cylinder, referred to as a blade ring, which encloses the vane segments. In addition, each vane segment is aligned and supported at its inner shroud by an inner cylinder. The inner cylinder support is achieved as follows. A series of torque plates are affixed to the inner cylinder so as to enclose slotted portions of the inner shrouds. The torque plates contain a splined hole for each vane segment. A splined bushing, having an eccentric pin projecting from its face, is partially inserted into the splined hole in the torque plate so that the pin engages the slot formed in the inner shroud. However, the bushing is not inserted so far into the hole that the splines in the bushing engage the splines in the hole. A cover plate is then threaded behind the bushing to stabilize it. With the cover plate in place, a square drive on the face of the bushing opposite the pin is used to rotate the bushing so that the pin forces the vane segment into alignment. After the proper alignment is obtained, the eccentric bushing is locked in place by inserting the bushing further into the hole so that the splines are engaged. The cover plate prevents disengagement of the splines by restraining motion of the bushing in the axial direction. The cover plate is peened to the torque plate to prevent the cover plate from backing out of the hole. This scheme is disclosed in U.S. Pat. No. 4,890,978, assigned to the same assignee as the current invention.

The prior art method of aligning and supporting vane segments discussed above suffers from three drawbacks. First, alignment of the vane segments can only be done on an incremental basis since the number of positions in which the bushing can be installed is limited by the number of splines. Thus, some degree of vane segment misalignment results when, as is usually the case, the desired position of the bushing for alignment purposes does not permit engagement of the splines. Hence, it would be desirable to devise a scheme which allowed infinitely fine adjustment of the vane segment alignment.

Second, since the orientation of the pin when it enters the inner shroud slot in the correctly aligned position cannot be determined in advance, the body of the pin is round to allow engagement with the slot in any orientation. However, the round pin shape results in line contact between the pin and the slot. Line contact is undesirable because vibration of the turbine components causes minute relative motion between the pin and slot resulting in wear along the contact line, eventually the wear results in a loosening of the pin in the slot and a loss of the original alignment.

Third, once the eccentric bushing is partially installed in the hole, the assembler is not able to observe the slot in the inner shroud. Thus, rotation of the eccentric bushing and minute adjustment in the vane segment alignment to allow the pin to enter the slot must be done on a trial and error basis. As a result, assembly of the inner shroud support structure is often a time consuming and tedious procedure.

Accordingly, it would be desirable to provide an apparatus and method for aligning and supporting vane segments which (1) allows infinitely fine adjustment of the vane segment alignment; (2) provides surface contact between the load-bearing surfaces on the alignment device and the inner shroud slot; and (3) aids the assembler in his efforts to insert the pin into the slot without visual guidance.

It is the object of the current invention to provide a means for aligning and supporting a gas turbine vane segment.

It is a further object of the invention that such aligning and supporting means be capable of infinitely fine adjustment of the alignment of the vane segment.

It is still another object of the invention that the load-bearing surfaces of the alignment and support device not be subject to wear which would tend to upset the alignment.

These and other objects are accomplished in a gas turbine having an annular array of vane segments in its turbine section. Each vane segment is supported and aligned to an inner cylinder by attaching a torque plate, having threaded holes, to the inner cylinder and inserting a threaded plug into the hole in the torque plate. A pin is then inserted into an eccentric hole in the threaded plug and the plug and pin are rotated until the pin can be pushed into a slot in the inner shroud of the vane segment. The plug is then rotated so that a flat surface on the end of the pin is loaded against the side of the slot. A nut locks the threaded plug in place, preventing further rotation, and a cap retains the pin, preventing it from disengaging from the inner shroud slot.

FIG. 1 is an isometric view, partially cut away, of a gas turbine.

FIG. 2 is a cross-section of a portion of the turbine section of the gas turbine shown in FIG. 1 in the vicinity of the row 1 vane segment.

FIG. 3 is a detailed view of the portion of FIG. 2 denoted by the circle marked III, showing the vane segment inner shroud support apparatus.

FIG. 4 is a cross-section taken through line IV--IV shown in FIG. 3.

FIG. 5 is an enlarged view of the vane segment inner shroud support apparatus shown in FIG. 4.

FIG. 6 is a cross-section taken through VI--VI shown in FIG. 4.

There is shown in FIG. 1 a gas turbine. The major components of the gas turbine are the inlet section 32, through which air enters the gas turbine; a compressor section 33, in which the entering air is compressed; a combustion section 34 in which the compressed air from the compressor section is heated by burning fuel in combustors 38; a turbine section 35, in which the hot compressed gas from the combustion section is expanded, thereby producing shaft power; and an exhaust section 37, through which the expanded gas is expelled to atmosphere. A centrally disposed rotor 36 extends through the gas turbine.

The turbine section 35 of the gas turbine is comprised of alternating rows of stationary vanes and rotating blades. Each row of vanes is arranged in a circumferential array around the rotor 36. FIG. 2 shows a portion of the turbine section in the vicinity of the row 1 vane assembly. Typically, the vane assembly is comprised of a number of vane segments 1. Each vane segment 1 is comprised of a vane airfoil 43 having an inner shroud 2 formed on its inboard end and an outer shroud 15 formed on its outboard end. Alternatively, each vane segment may be formed by two or more vane air foils having common inner and outer shrouds.

As shown in FIG. 2, the vane segments 1 are encased by a cylinder 16, referred to as a blade ring. Also, the vane segments encircle an inner cylinder structure 48. The inner cylinder structure comprises a ring 7 affixed to a rear flange 38 of the inner cylinder. A row of rotating blades 18, affixed to a disk portion 17 of the rotor 36, is disposed downstream of the stationary vanes. A turbine outer cylinder 51 encloses the turbine section.

During operation, hot compressed gas 26 from the combustion section is directed to the turbine section by duct 53. The hot gas flows over the vanes, imposing aerodynamic loads in the form of bending moments and torque loads. If the vane segments were not fixed to the blade ring 16 or inner cylinder structure 48, the torque load would tend to rotate the vane segments about the center line of the rotor. The direction in which the torque is applied depends on the geometry of the vane segments, which, in turn, is a function of whether the rotor is designed to rotate in a clockwise or counterclockwise direction. The gas turbine described herein is designed for clockwise rotor rotation, when looking with the direction of flow. Thus, the torque load tends to rotate the vane segments in the counterclockwise direction, when looking with the direction of flow.

The vane segments are fixed to the blade ring 16 at their outer shroud 15 so that motion is restrained in the radial and circumferential directions. The radial restraint is provided by mating a slot 46 in the outer shroud 15 with a ring 44 affixed to the blade ring 16. The circumferential restraint is provided by a pin 45 which engages a keyway 47 in the outer shroud. The subject of the present invention concerns the support of the vane segments 1 by the inner cylinder structure 48. As shown in FIG. 4, a lug 3 protrudes radially inward from the inner surface of the inner shroud 2. A slot 39 is formed in each lug and serves as the point at which the inner shroud is supported to the inner cylinder structure 48. Radially oriented surfaces 13 and 14 form the sides of the slot 39. As explained further below, surface 13 forms a load-bearing surface for the slot.

During assembly, the vane segments are first attached to the blade ring 16 and are then correctly aligned with respect to each other. A support assembly comprised of torque plates 4 is then affixed to the upstream face of the ring 7. In the preferred embodiment, each torque plate 4 is an arcuate member as shown in FIG. 4. As installed, the torque plate has upstream 24 and downstream 23 axial faces, as shown in FIG. 3. Two holes 25, each having female threads are located in the upstream axial face 24. A recess 21 is formed in the downstream axial face 23. Each torque plate 4 is attached to the ring 7 by bolts 49 that extend through holes 19 in the torque plate and threaded holes 20 in the ring, as shown in FIG. 6. As shown in FIG. 3, after installation on the ring 7, the recess 21 in the torque plate forms a cavity 50 enclosing the lug 3. Thus, the torque plates 4 and the ring 7 provide upstream and downstream axial restraints, respectively, for the vane segments. These axial bending restraints enable the vane segments to resist the moments imposed on them.

As shown in FIG. 3, a cylindrical plug 6 that has male threads formed on its external surface is screwed into hole 25 until shoulder 10, formed on each plug, bottoms in a counterbore 11 formed in the hole 25. Note that the length of the plug 6 downstream of the shoulder 10 and the depth of the recess 21 that forms cavity 50 are such that gap 41 is provided between the torque plate/plug and the lug 3 to allow for differential axial thermal expansion between the blade ring 16 and the inner cylinder support structure 48.

After installation of the plug 6, a cylindrical pin 5 is inserted into an axially oriented eccentric hole 40 in the plug so that the pin 5 is also axially oriented. As shown in FIG. 5, the common center line 30 of the hole 40 and the pin 5 is eccentric from the common center line 29 of the hole 25 in the torque plate and the plug 6--that is, centerline 30 is parallel to, but not coincident with, centerline 29. Thus, when the plug 6 is rotated relative to the torque plate by screwing the plug into or out of the hole 25, the center line 30 of the pin describes a circle 31 about the center line 29 of the hole 25 and plug 6. A key is formed on the pin by machining flat surfaces 12, which act as load-bearing surfaces, in the downstream end of the pin 5. As shown in FIG. 5, the distance from the center line 30 of the pin to either flat 12 is less than the distance 28 from the center line 29 of the hole 25 and plug 26 to radially oriented surface 13 of the slot 39, so that rotation of the plug causes flat 12 on the pin to come into contact with surface 13.

When the pin 5 is inserted into the plug 6, it initially bottoms against the upstream face of the lug 3. The plug 6 is then rotated counterclockwise, looking with the direction of flow, thereby screwing it out of the hole 25, until the pin 5 is aligned with the slot 39. In this regard, a chamfer 42 is formed in downstream end of the pin 5. By applying a downstream axial force on the pin while rotating the plug, the chamfer acts as a finder, allowing the installer to feel when the pin is aligned with the slot by sensing that the chamfer has dropped into the slot. Thus, the time required to assemble the inner shroud support is greatly reduced. Note that the width of the slot 39 is less than the diameter of the body of the pin but more than the width of the pin across the flats 12, so that the pin cannot be inserted into the slot unless the flats are aligned parallel with the radially oriented faces 13 and 14 of the slot. Thus, once the pin 5 and slot 39 are aligned, the pin is rotated in hole 40 until it can be inserted into the slot, indicating that the flats 12 are aligned with the slot faces 13 and 14.

As shown in FIG. 4, which is looking with flow, the torque load 22, resulting from the gas 26 flowing over the vane, is applied to the vane segments in a counterclockwise direction. To properly align the vane segments and assure the gas forces do not result in misalignment during operation, the vane segments must be secured against movement in the counterclockwise direction. Thus, after the pin is inserted into the slot, the plug 6 is rotated to insure that flat 12 bears against slot face 13 (rather than face 14), since face 13 faces the direction of torque load.

It is important to note that since the loading on the vane is transmitted through surface contact between the slot face 13 and the pin flat 12, rather than the merely line contact achieved by the prior art, the potential for wear of the pin and subsequent loss of alignment is greatly reduced.

Once the plug 6 has been rotated into its proper position, it is locked in place by nut 9, which is threaded onto the plug until the downstream face 27 of the nut is tightened against the upstream axial face 24 of the torque plate 4. Note that unlike the splined scheme used in the prior art, use of the threaded plug 6 and rotatable pin 5 of the present invention allows the plug to be rotated and locked into any position, thus allowing infinitely fine adjustment of the vane segment alignment.

Lastly, threaded cap 8 is screwed onto the plug and tightened against the upstream face 28 of the nut 9. The cap prevents disengagement of the pin 5 by restraining its motion in the axial direction.

Although the above description has been directed to a preferred embodiment of the invention, it is understood that other modifications and variations known to those skilled in the art may be made without departing from the spirit and scope of the invention as set forth in the appended claims.