US3781125A - Gas turbine nozzle vane structure - Google Patents

Abstract

A nozzle vane structure for a gas turbine having a cavity in the outer shroud structure acting as a plenum chamber that provides pressurized coolant fluid to the vanes, and in which the internal stress effect due to large temperature gradients is minimized by a key-hole shaped slotted portion in the outer shroud having a thin walled sleeve split as its periphery and attached thereto and receiving a threaded sealing member therein to restrict coolant flow therepast during deformation incident to operation.

Description

United States Patent 1191 Rahaim et a1.

[ Dec. 25, 1973 [54] GAS TURBINE NOZZLE VANE STRUCTURE 3,427,000 2/1969 Scalzo 415 115 [75] Inventors: Thomas J Rahaim, Caymoht; 3,689,174 9/1972 Rahalm et a1 415/116 Leslie G. Kish, Wilmington, both of FOREIGN PATENTS OR APPLICATIONS v 1961- 865,198 4/1961 Great Britain 4151217 [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa. Primary Examiner-C. J. Husar [22] Filed: Apr. 7, 1972 Attorney-A. T. Stratton et a1.

[21] Appl. No.: 241,943 ABSTRACT [52] U S Cl 5/115 415,178 HS/217 A nozzle vane structure for a gas turbine having a cav- 415/136 ity in the outer shroud structure acting as a plenum [51] Int Cl F01 d 5/14 chamber that provides pressurized coolant fluid to the 58 Field of Search..... 41s/115-117, 178, 216-218 r and wh'ch l .i effect due arge temperature gradients 1s mimmized by a keyhole shaped slotted portion in the outer shroud having [56] References Cited a thin walled sleeve split as its periphery and attached thereto and receiving a threaded sealing member UNITED STATES PATENTS therein to restrict coolant flow therepast during defor- 2,823,890 2/1958 Oechslin 415/136 mation incident to operation. 3,301,527 1/1967 Kercher 415/115 3,520,635 7/1970 Killmann et a1. 415/217 10 Claims, 4 Drawing Figures 54 5 54 54 I 54 i I 54 35 e0 62 58 57 65 e5 5? 57 60 3| 57 I 37 44 3| 3| 37 54 54 ii 54 i X. 62 62 62 I 62 62 6 ez x l2 l9 22 GAS TURBINE NOZZLE VANE STRUCTURE BACKGROUND OF THE INVENTION In gas turbines operated with hot combustion gases at temperatures higher than the stationary nozzle vanes and rotor blades can safely withstand, coolant fluid such as compressed air is fed to these components to prevent dangerous overheating. One of the presently employed arrangements employs an annular nozzle vane structure formed in arcuate groups with a plenum chamber in the outer shroud structure to which pressurized cooling air is admitted. The air is then directed to each of a plurality of hollow nozzle vanes in the group to prevent overheating thereof by the hot motive gases flowing therepast in operation. This arrangement is more fully shown and described in A. J. Scalzo and A. Zabrodsky US. Pat. No. 3,529,903, issued Sept. 22, 1970, and assigned to the same assignee as this invention.

The above arrangement is highly successful and has permitted operation of the gas turbine at considerably higher temperatures than heretofore, with attendant advantages in thermal efficiency of the machine. However, it has been noted that the outer shroud attains an equilibrium temperature that is several hundred degrees lower than that of the inner shroud, due to the highly effective cooling effect of the pressurized coolant air in the plenum chamber therein.

This temperature difference creates large temperature gradients in the forward and rearward edge walls of the outer shroud structure that can cause stress cracks to occur therein with attendant leakage of coolant air from the plenum chamber directly into the motive gas stream with loss of cooling effect on the nozzle vane structure.

It is an object of this invention to provide a nozzle vane structure of the above type arranged in such a manner that the temperature gradients are permitted to occur without build-up of appreciable internal stresses, thereby to obviate the possibility of stress cracks in the outer shroud, and having sealing means to prevent leakage of coolant air from the plenum chamber directly into the motive gas stream during distortion incident to operation.

BRIEF SUMMARY OF THE INVENTION In accordance with the invention, a pair of openended key-hole shpaed slots are provided in the outer shroud for each vane in the arcuate nozzle vane structure. One of these slots is formed in the forward arcuate wall and the other is formed in the rearward arcuate wall of the shroud to pennit thermal growth to occur without thermal internal stresses of a damaging nature.

Each of the slots has a tubular thin walled split sleeve received in the circular portion of the slot and attached to the shroud wall by a peripheral weld. The sleeve is threaded internally and disposed with the cut in its periphery in registry with the slot. A threaded male member having a head at one end, such as a short bolt, is threadedly received therein.

Since the split sleeve is thin and of C-shaped crosssection, ithas little, if any, stiffening effect'on the slotted shroudwall, thereby allowing thermal growth and the accommodating change inshape to take place during operation, and preventing excessive internal thermal stresses to occur. During such thermal deformation, the mating thread portions act as a labyrinthian seal to minimize leakage of coolant air therethrough. The main sealing action, however, occurs between the bolt head and the shroud wall, since the sealing face of the bolt is in a plane parallel to that in which any deformation will occur.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial sectional view of a portion of an axial flow gas turbine having a stationary annular nozzle vane structure formed in accordance with the invention;

FIG. 2 is an enlarged front elevational view showing one of the arcuate nozzle vane group structures;

FIG. 3 is a fragmentary sectional view of the outer shroud showing one of the sealing structures therein; and

FIG. 4 is a perspective view of one of the nozzle vane group structures with the corner plate rewound to show internal details.

PREFERRED EMBODIMENT Referring to the drawings in detail, in FIG. I there is shown a portion of an axial flow gas turbine 10. Only the upper radial half of the turbine is shown, since the lower half is substantially identical to the upper half. The turbine 10 comprises an outer casing 11 of generally tubular or annular shape, an inner casing 12 of annular shape encompassed by the outer casing 11, and a rotor 14 rotatably supported within the inner casing 12 in any suitable manner and having at least one annular row of blades 16. Cooperatively associated with the rotor blades 16 to form a motive fluid expansion stage is an annular row of stationary nozzle vanes 18 supported within the inner casing 12.

The stationary nozzle vanes 18 are provided with a radially inwardly extending air foil shaped vane portion 19, an inner arcuate shroud portion 20 and an outer shroud portion 22 received in an annular groove 24 formed in'the inner casing 12.

The inner casing 12 is suitably secured to the outer casing 11 by an annular radially extending flange 26 and jointly therewith forms an annular air space 27 that surrounds the inner casing.

The stationary nozzle vanes 18 are of hollow form, with the outer shroud portion 22 of box-like form and defining an arcuately shaped plenum chamber 28. The vane portions 19 are provided with passages 31 and a radial series of outlet orifices 32 in their trailing portions. The passages 31 provide a fluid communication between the plenum chamber 28 and the orifices 31.

The nozzle vanes 18 are preferably formed in arcuate groups 34 (as best shown in FIGS. 2 and 4) with a plurality of the vane portions 19 connected in parallel fluid flow communication with the common outer plenum chamber 28. As illustrated, the arcuate vane group 34 extends through a central angle of 45,with the inner and outer shrouds 20 and 22 integrally formed with four of the vanes 19, as by casting. Since each arcuate nozzle vane group 34 subtends a central angle of 45 the annular row of nozzle vanes would include eight such groups disposed in end-to-end relation, as well known in the art (example: 8 X 45 360).

The outer shroud portion 22 is provided with a forward end wall 35 and a rearward end wall 36 (both of arcuate shape and subtending the 45 central angle, as described above) and a pair of opposed side walls 37 to impart the box-like shape to an open cavity 38 (FIG. 4) that is employed as the plenum chamber 28.

An outside cover plate 40 with its peripheral portions held in a grooved rail structure 41, 42 is nested in a suitable peripheral flanged portion 44 to complete the enclosure for the plenum chamber 28.

The nozzle vane groups 34 are keyed in the casing groove 24 and are retained therein by a tubular fitting 46 threadedly received in the inner casing 12 and having a cylindrical portion 47 extending through a mating opening 48 in the cover plate 40. The fitting 46 has a central bore 50 extending therethrough to provide a fluid communication between the intercasing space 27 and the plenum chamber 28. A tube or pipe 51 received in the outer casing 11 provides pressurized coolant fluid, such as pressurized air from any suitable source (not shown) to the space 27 during operation.

As thus far described, the structure has been previously proposed and more fully described in A. J. Scalzo U.S. Pat. No. 3,427,000 and A. J. Scalzo and A. Zabrodsky U.S. Pat. No. 3,529,903, both assigned to the same assignee as this invention. As explained therein, in operation, hot motive fluid, such as pressurized combustion gas generated in a suitable fuel combustion chamber (not shown), is directed through an inlet passageway 52 past the stationary nozzle vanes 18 and the rotor blades 16, in the direction indicated by the arrows 53 with resulting expansion of the motive fluid to rotate the rotor 14.

The motive gases directed past the nozzle vanes 18 are hottor than the vanes can withstand safely, accordingly pressurized coolant air is continuously provided to the nozzle vanes 18, as previously described, to maintain them within safe temperative limits and is then ejected through the outlet orifices 32 into the stream of hot motive fluid.

In accordance with the invention, the forward end wall 35 of the outer shroud 22 is provided with a plurality of spaced open-ended slots 54 extending radially inwardly and terminating in circular shaped bottom portions 55. Hence, for ease of further description the slots 54 may be considered to be of key-hole shape.

As best seen in- FIG. 2, the key-hole slots 54 are identical and each slot extends substantially the entire radial width of the shroud wall 35 to lend curvature flexibility to the shroud 22. As best seen in FIG. 3, a thin walled tubular sleeve member 57 has an annular end portion 58 of reduced diameter received in mating engagement with the circular portion 55 of the slot 54 and is split by a slit 60 into a C-shaped (see FIG. 4). The thus formed C-shaped sleeve 57 is secured to the wall 35, such as by welding W along its entire periphery, with its slit 60 in registry with the associated slot 54.

The sleeve 57 is threaded internally and a bolt-like threaded, male sealing member 62 having a circular head 63 at one end and a screwdriver groove 65 in the other end is threadedly received therein. As best seen in FIG. 4 the head 63 is of cylindrical shape and of the same diameter as the circular slot portion 55 and has an inner planar face 65.

In FIG. 3 the bolt heads 63 are shown in their final machined state in solid lines, but are shown in their original contour by the dot-dash lines, and the portion P is cut away between the dot-dash lines and the final contour after installation in the outer shroud. This contour provides a flush assembly with the forward shroud wall 35 and permits a close fitting in the inner casing groove 24.

It will be noted, by referring to FIG. 2 that four pairs of slots 54 are provided in each nozzle vane group 34, one pair for each vane 19, and that the slots are substantially equally spaced along the outer periphery of the shroud wall 35.

The rear wall 36 of the outer shroud 22 (FIG. 4) is substantially similar to the forward wall 35 and is provided with a plurality of (in this example, seven) slots 54, each fitted with a split sleeve 57 and an associated male threaded bolt-like member 62. In th illustration shown in FIG. 4, six of the heads 63 are shown in the original contour before final machining to a flush finish with the surface of the shroud wall 36 and one of the heads 63 (at the right end of the nozzle group 34) is illustrated in the final contoured shape. Here again, the bolt heads 63 are machined to a flush fit to permit a good fit with the groove 24 in the inner casing 12 (FIG. 1).

To prevent leakage of coolant air from the plenum chamber 28 through the upper or narrow end portion of the slots 54, the side walls 70, 71 of the casing groove 24 are extended radially inwardly to overlap this portion of the slots (see FIG. 1).

During operation, as the stationary nozzle vane structure 18 becomes heated by the motive gases 53, coolant air flowing into the plenum chamber to the vanes 19 (to cool the latter) tends to keep the outer shroud structure 35 somewhat cooler than the inner shroud 20. Accordingly, a radial temperature gradient exists and the outer shroud 35 behaves as a curved bar, i.e., it will tend to increase its radius of curvature. In doing this, the vanes 19 exert a strong radial force at the junction of the outer shroud and the vanes. However, since the forward and rearward walls 35 and 36 are slotted and thus rendered flexible, they permit the shroud to undergo an accommodating change of shape without creating high local internal stresses Since the outer shroud tends to increase its radius of curvature, due to thermal growth the slots 54 tend to deform in shape and this deformation is freely permitted by the split sleeves 57, while still acting to prevent leakage therepast from the plenum chamber 28, as previously described.

We claim:

1. A nozzle vane structure for a hot elastic fluid utilizing machine, comprising a plurality of vane portions of generally airfoil cross-section, an inner arcuate shroud segment integrally connected to one end of said vane portions, an outer arcuate shroud segment integrally connected to the opposite end of said vane portions, and outer shroud segment having a forward end wall and a rearward end wall of arcuate cross-section, means cooperating with said outer shroud segment to form a plenum chamber, means for admitting a pressurized coolant fluid to said plenum chamber, each of said vanes having a passage therein communicating with said plenum chamber for directing coolant fluid from said chamber through said vane portions to cool the latter, at least one of said end walls having an open-ended circular slot to pennit thermal growth during operation, an internally threaded sleeve member received in said slot and attached to said one end wall, and a threaded male member disposed in mating threaded coolant therepast during distortion of said sleeve during operation.

2. The structure recited in claim 1 in which said one end wall is the forward end wall.

3. The structure recited in claim l in which said one end wall is the rearward end wall, and said threaded male member has an enlarged head in sealing abutment with one end of said sleeve member.

4. The structure recited in claim 1 in which a plurality of said open-ended slots are provided and each of said slots is provided with one of said tubular sleeves and one of said mating male members.

5. The structure recited in claim 5 in which said slots are disposed in substantial radial registry with said vanes.

6. The structure recited in claim 1 in which said one end wall is the forward end wall and a second openended slot is also provided in the rear-ward end wall, and each of said slots are provided with a tubular sleeve and a mating male member.

7. The structure recited in claim 1 in which said threaded male member has an enlarged head portion disposed in abutment with an annular end wall of said sleeve member to act as an additional seal.

8. The structure recited in claim l in which the plurality of vane portions forming the vane structure are spaced angularly from each other in a central angle and integrally connected to the inner and outer shroud segment, the forward and rearward end walls of the outer shroud segment subtend the central angle within which the vanes lie, each of the vane portions having a passage communicating with the plenum chamber and the plenum chamber is coextensive with the outer shroud segment.

9. The structure recited in claim 8 in a second openended circular slot is formed in the other of said end walls, and said second slot is provided with a tubular sleeve and a mating male member.

10. The structure recited in claim 1 in which said sleeve member is split at its periphery and is disposed with the split ends in registry with the open-end of the slot in the shroud.

Claims (10)

1. A nozzle vane structure for a hot elastic fluid utilizing machine, comprising a plurality of vane portions of generally airfoil cross-section, an inner arcuate shroud segment integrally connected to one end of said vane portions, an outer arcuate shroud segment integrally connected to the opposite end of said vane portions, and outer shroud segment having a forward end wall and a rearward end wall of arcuate cross-section, means cooperating with said outer shroud segment to form a plenum chamber, means for admitting a pressurized coolant fluid to said plenum chamber, each of said vanes having a passage therein communicating with said plenum chamber for directing coolant fluid from said chamber through said vane portions to cool the latter, at least one of said end walls having an open-ended circular slot to permit thermal growth during operation, an internally threaded sleeve member received in said slot and attached to said one end wall, and a threaded male member disposed in mating threaded engagement with said sleeve to restrict leakage of pressurized coolant therepast during distortion of said sleeve during operation.

2. The structure recited in claim 1 in which said one end wall is the forward end wall.

3. The structure recited in claim 1 in which said one end wall is the rearward end wall, and said threaded male member has an enlarged head in sealing abutment with one end of said sleeve member.

4. The structure recited in claim 1 in which a plurality of said open-ended slots are provided and each of said slots is provided with one of said tubular sleeves and one of said mating male members.

5. The structure recited in claim 5 in which said slots are disposed in substantial radial registry with said vanes.

6. The structure recited in claim 1 in which said one end wall is the forward end wall and a second open-ended slot is also provided in the rear-ward end wall, and each of said slots are provided with a tubular sleeve and a mating male member.

7. The structure recited in claim 1 in which said threaded male member has an enlarged head portion disposed in abutment with an annular end wall of said sleeve member to act as an additional seal.

8. The structure recited in claim 1 in which the plurality of vane portions forming the vane structure are spaced angularly from each other in a central angle and integrally connected to the inner and outer shroud segment, the forward and rearward end walls of the outer shroud segment subtend the central angle within which the vanes lie, each of thE vane portions having a passage communicating with the plenum chamber and the plenum chamber is coextensive with the outer shroud segment.

9. The structure recited in claim 8 in a second open-ended circular slot is formed in the other of said end walls, and said second slot is provided with a tubular sleeve and a mating male member.

10. The structure recited in claim 1 in which said sleeve member is split at its periphery and is disposed with the split ends in registry with the open-end of the slot in the shroud.

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