Retaining ring for a turbine nozzle with improved thermal isolation   

FIELD OF THE INVENTION

This invention relates generally to a retaining ring for supporting a turbine nozzle of a gas turbine and more specifically to a retaining ring with improved thermal isolation so as to prevent retaining ring out of roundness.

BACKGROUND OF THE INVENTION

In a gas turbine, hot gases of combustion flow from an annular array of combustors through a transition piece for flow along an annular hot gas path. In particular, turbine stages are disposed along the hot gas path such that the hot gases of combustion flow from the transition piece through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The first-stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each first-stage nozzle segment also includes inner and outer sidewall portions spaced radially from one another. Upon assembly of the nozzle segments, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer sidewalls. A nozzle retaining ring connected to the turbine casing is coupled to the outer sidewall of the first-stage nozzles and supports the first-stage nozzles in the gas flow path of the turbine. An annular nozzle support ring, preferably split at a horizontal midline, is engaged by the inner sidewall and may support the first-stage nozzles against axial movement.

Side seals may seal the annular array of nozzle segments one to the other along adjoining circumferential edges. The side seals may seal between a high pressure region radially inwardly of the inner sidewall and radially outward of the outer sidewall (i.e. compressor discharge air at high pressure) and the hot gases of combustion in the hot gas flow path which are at a lower pressure. Chordal hinge seals are used to seal between the inner sidewall of the first-stage nozzles and an axially facing surface of the nozzle support ring and between the outer sidewall and a shroud of the first bucket. As such, the chordal hinge seals may also seal against leakage from the high pressure region into the lower pressure region of the hot gas path.

FIG. 1 illustrates a prior art sidewall retention system 100 for a first stage nozzle 110 of a gas turbine. The first stage nozzle 110 includes an outer sidewall 115, an inner sidewall 120 and an airfoil 125 positioned between a nozzle retaining ring 130 and a nozzle support ring 135. The nozzle retaining ring 130 and the support ring 135 are attached to the casing of the turbine (not shown). The nozzle retaining ring 130 is also coupled to the outer sidewall 115 and secures the first-stage nozzle 110. The nozzle support ring 135 is disposed radially inwardly of the inner sidewall 120 and engages the inner sidewall 120. The first stage nozzle 110 also includes chordal hinge rails for the inner sidewall 120 and the outer sidewall 115. The chordal hinge rail 145 on the inner sidewall 120 provides axial support for the nozzle 110 against the support ring 135 and the chordal hinge rail 150 on the outer sidewall 115 provides axial support for the nozzle 110 against the shroud 160 of the first stage bucket 170. The inner chordal hinge rail 145 and outer chordal hinge rail 150 further provide chordal hinge seals 147, 152 to seal against leakage from the high pressure compressor discharge region into the lower pressure region of the hot gas path

The chordal hinge rail 150 on the outer sidewall 115 of the nozzle 110 projects outward radially from the outer sidewall 115. The chordal hinge rail 150 incorporates a forward-facing annular retaining land 175 at its outermost radial projection. The retaining land 175 mates with an aft-facing annular groove 180 defined by an aft-facing retaining hook 185 on the retaining ring 130. The retaining land 175 of the chordal hinge rail 150 acting on the retaining hook 185 of the retaining ring 130 provides radial support for the nozzle 110. The annular retaining hook 185 may be divided into segments (not shown). Circumferential support may be provided by an anti-rotation pin (not shown) that passes through the retaining ring 130 and the retaining land 175.

Power generation gas turbines traditionally use some type of hook retention scheme. Improvements have been made on the traditional hook retention scheme by changing from a continuous hook arrangement to a segmented hook arrangement. This change resulted in more determinate nozzle loading and better nozzle sealing but also resulted in less than optimal thermal isolation of the retaining ring and, thus, exposure of the retaining ring to high thermal gradients. The resulting thermal stresses from such exposure can exceed the yield strength of the retaining ring material, which may cause the retaining ring to warp or go out of round. This can be a significant problem, as ring out of roundness typically increases repair and maintenance costs associated with the retaining ring and the stage one nozzle assembly. Additionally, retaining ring out of roundness may cause deflection of the stage one nozzle assembly, which can result in contact of the nozzle angel wing and the stage one bucket platform and can eventually damage the bucket.

Currently, one solution for preventing ring out of roundness is to change the type of material used to make a retaining ring. For example, the ring material may be changed to a higher strength alloy so as to permit the retaining ring to withstand the increased stress caused by a lack of thermal isolation. However, the use of such higher strength alloys significantly increases the cost of a retaining ring and the overall cost of producing a gas turbine.

Accordingly, improved thermal isolation of a retaining ring in order to reduce the thermal stresses acting on the retaining ring and, thereby, prevent retaining ring out of roundness would be accepted in the technology.

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

In one aspect, the present subject matter provides a retaining ring for a turbine nozzle of a gas turbine. The retaining ring includes a main body and a pair of circumferential retaining lands projecting inward radially from the main body. The pair of circumferential retaining lands may be configured to be attached to a nozzle. Additionally, each retaining land of the pair of circumferential retaining lands may be segmented along its circumferential length.

In another aspect, the present subject matter provides an outer sidewall retention scheme for a turbine nozzle of a gas turbine. The outer sidewall retention scheme may include a retaining ring and at least one nozzle. The retaining ring may include a main body and a pair of circumferential retaining lands extending from the main body. The nozzle may include an inner sidewall and an outer sidewall. The pair of circumferential retaining lands may be segmented along their circumferential length and may be configured to be attached to the outer sidewall of the nozzle so as to support the nozzle.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 illustrates a typical hook retention scheme for an outer sidewall of a first stage nozzle;

FIG. 2 illustrates an isometric cross section of an embodiment of a retaining ring from an aft perspective in accordance with an aspect of the present subject matter;

FIG. 3 illustrates an isometric cross section of an embodiment of a retaining ring from a forward perspective in accordance with an aspect of the present subject matter;

FIG. 4 illustrates an isometric view of a portion of an embodiment of the inner circumference of a retaining ring in accordance with an aspect of the present subject matter;

FIG. 5 illustrates a side view of an embodiment of a nozzle in accordance with an aspect of the present subject matter;

FIG. 6 illustrates an isometric view of an embodiment of an outer surface of an outer sidewall of a nozzle in accordance with an aspect of the present subject matter;

FIG. 7 illustrates a top view of an embodiment of an outer surface of an outer sidewall of a nozzle in accordance with an aspect of the present subject matter; and

FIG. 8 illustrates a schematic side view of one embodiment of an outer sidewall retention scheme in accordance with an aspect of the present subject matter.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

As indicated above, a retaining ring in a gas turbine may often be subject to high thermal gradients. This is generally due to the operating environment within the gas turbine, along with a lack of sufficient thermal isolation of the retaining ring. For example, the locations at which turbine nozzles attach to a retaining ring may be exposed to high temperatures due to heat transferred from and through the outer sidewalls of the nozzles as hot gases of combustion flow along the hot gas path. However, at locations on a retaining ring further away from such attachment points, the temperature is relatively cooler. This temperature differential can result in increased thermal stresses acting on the retaining ring. In particular, at times when the retaining ring is exposed to significantly increased thermal gradients, such as during transient operation (e.g. startup/shutdown of the gas turbine), the resulting thermal stresses may exceed the yield strength of the ring material, thereby causing the retaining ring to go out of round.

In accordance with an aspect of the present subject matter, FIGS. 2, 3 and 4 illustrate an embodiment of a retaining ring 300 configured to be attached to and support a turbine nozzle of a gas turbine. In addition, the retaining ring 300 may be configured so as to reduce the thermal gradients seen in the ring 300 by permitting high temperature regions of the retaining ring 300 to be thermally isolated from lower temperature regions. As such, the resulting thermal stresses acting on the retaining ring 300 can be reduced and, thereby, prevent or reduce the likelihood of retaining ring out of roundness due to ring yielding.

FIGS. 2 and 3 illustrate an isometric cross section of an embodiment of the retaining ring 300 from an aft and a forward perspective, respectively. FIG. 4 illustrates an isometric view of a portion of an embodiment of the inner circumference of the retaining ring 300.

Referring to FIGS. 2, 3 and 4, the retaining ring 300 includes a main body 310 of a generally cylindrical shape that may be supported by the casing of the turbine by methods generally known in the art. Although not shown, the retaining ring 300 may be preferentially divided into two semi-circular rings to facilitate assembly. The main body 310 may include a pair of circumferential retaining lands 315 projecting inward radially from the main body 310. The pair of circumferential lands 315 may be generally located on the aft side of the retaining ring 300, each land being separated from each other axially by a predetermined width w. The projection d from the main body 310 and the predetermined width w between the pair of circumferential lands 315 define a circumferential annular groove 320. Generally, the pair of circumferential retaining lands 315 may include an aft retaining land 325 and a forward retaining land 330. The aft retaining land 325 may include an aft circumferential face 326 and a forward circumferential face 328 and the forward retaining land 330 may include a forward circumferential face 331 and an aft circumferential face 333.

A plurality of axial-oriented through-holes 345 may be provided between the aft circumferential face 326 and the forward circumferential face 328 of the aft retaining land 325. A plurality of axial-oriented closed-end bore holes 350 may be provided through the aft face 333 of forward retaining land 330. Generally, the plurality of axial-oriented through-holes 345 in the aft retaining land 325 and the plurality of axial-oriented closed-end bore holes 350 in the forward retaining land 330 may be radially and circumferentially organized coaxially to accept a retaining pin (not shown) axially through the aft retaining land 325 and into the bore hole 350 of the forward retaining land 330. The coaxially oriented holes with centerlines 358 may be further arranged circumferentially in pairs, equally spaced around the retaining lands 315. It should be appreciated that the diameters of the paired holes 360 may be sized to accept retaining pins for retaining the nozzle.

The retaining ring 300 may also include a plurality of radially oriented cooling holes 340 formed in the main body 310. Generally, the cooling holes 340 may be formed in the main body 310 so that the holes 340 interrupt the forward retaining land 330 along its circumferential length and, thereby, create a plurality of circumferential segments 334 in the forward retaining land 330. More specifically, as illustrated in FIGS. 3 and 4, the cooling holes 340 may be formed such that a centerline 370 of each of the cooling holes 340 is substantially aligned with a circumferential centerline 375 of the forward retaining land 330.

Due to the segmenting of the forward retaining land 330 and the alignment of the cooling holes 340, the amount of stress acting on the forward retaining land 330, particularly during transient operation of the gas turbine, may be reduced below the retaining ring material yield strength. For example, the alignment of the cooling holes 340 with the circumferential centerline 375 of the forward retaining land 330 may reduce the amount the mechanical stress acting on the retaining land 330 by reducing the geometrical discontinuities created at the ends 380 of each of the circumferential segments 334. Specifically, such an alignment can avoid the creation of sharp edges or corners at the ends 380 that may otherwise form areas of high stress concentration on the forward retaining land 330.

Moreover, as the cooling holes 340 may be formed so as to interrupt or segment the forward retaining land 330 along its circumferential length, the hottest regions of the retaining land 330 may be isolated from the cooler regions. Particularly, the circumferential segments 334 of the forward retaining land 330 may define the locations at which the closed end boreholes 350 may receive retaining pins 490, 495 (FIG. 7) so as to permit a nozzle to be attached to the retaining ring 300. Accordingly, the circumferential segments 334 may generally define the hottest regions on the forward retaining land 330, as heat is transferred from the nozzle during operation of a gas turbine. Thus, isolating the circumferential segments 334 from the relatively cooler regions of the forward retaining land 330 can reduce the thermal gradients seen in the forward retaining land 330 and, thereby, reduce the thermal stresses acting on such land.

It should be appreciated that the size and shape of the cooling holes 340 may generally vary depending on the size and configuration of the retaining ring 300. In general, the cooling holes 340 may be sized such that the forward retaining land 330 is sufficiently segmented along its circumferential length. In one embodiment, the cooling holes 340 may be circular and have a diameter ranging from about 5 cm to about 6.5 cm, such as from about 5.5 cm to about 6.4 cm or from about 5.8 cm to about 6.1 cm and all other subranges therebetween. Further, it should be appreciated that the cooling holes 340 may also provide a path for cooling compressor discharge air to flow through the main body 310 of the retaining ring 300 to cool various components of a turbine nozzle. For example, the cooling holes 340 may mesh with an internal channel (not illustrated) of a nozzle airfoil to facilitate nozzle cooling.

The retaining ring 300 may also include a plurality of openings 385 formed in the aft retaining land 325. Generally, the openings 385 may be formed in the aft retaining land 325 so that the retaining land 325 is interrupted or segmented along its circumferential length. As such, the openings 385 may create a plurality of circumferential segments 390 in the aft retaining land 325. Similar to circumferential segments 334 of the forward retaining land 330 described above, the circumferential segments 390 of the aft retaining land 325 may generally define the hottest regions on the retaining land 325 due to heat transferred from the nozzle. Specifically, the circumferential segments 390 may define the locations at which the through holes 345 may receive retaining pins 490, 495 (FIG. 7) so as to permit a nozzle to be attached to the retaining ring 300. Accordingly, this segmenting can serve to isolate the hottest regions of the aft retaining land 325 from the relatively cooler regions, thereby reducing the thermal gradients and the resulting thermal stresses seen in the aft retaining land 325. In particular, the segmenting can maintain the stress seen on the retaining ring 300 below the yield strength of the retaining ring material and reduce the likelihood of ring out of roundness occurring over the operating life of the retaining ring 300.

As illustrated, the openings 385 may be famed in the aft retaining land 325 as arcuate shaped openings, thereby defining scallops along the circumferential length of the retaining land 325. It should be appreciated, however, that the openings 385 may generally have any shape that permits segmenting of the aft retaining land 325. Similarly, the openings 385 may generally be of any size that sufficiently isolates the hottest regions of the aft retaining land 325 from the cooler regions. As such, in one embodiment, each opening 385 may have a radius of about 2.5 cm so that each circumferential segment 390 of the aft retaining land 325 is completely isolated from the other. However, the required radius, width or size of the openings 385 will generally vary depending on the size and configuration of the retaining ring 300 and, in particular, the aft retaining land 325.

Additionally, the amount of cooling holes 340 formed through the forward retaining land 330 and the amount of openings 385 formed in the aft retaining land 325 may be equal to the total number of turbine nozzles attached to and supported by the retaining ring 300. Thus, for every turbine nozzle attached to the retaining ring 300, a corresponding cooling hole 340 and opening 385 may be formed in the ring 300 to segment the forward and aft retaining lands 330, 325 and, thereby, thermally isolate the hottest regions of the lands 330, 325. However, it should be appreciated that, in alternative embodiments, the amount of cooling holes 340 and openings 385 formed in the retaining ring 300 may be more or less than the total number of nozzles to attached to a particular retaining ring 300. Further, it should be appreciated that the locations at which the openings 385 and the cooling holes 340 are formed in the retaining ring 300 may generally vary depending on the configuration of the retaining ring 300. For example, in an alternative embodiment, the openings 385 may be formed in the forward retaining land 330 so as to interrupt the retaining land 330 along its circumferential length and create a plurality of circumferential segments. In such an embodiment, the cooling holes 340 may be formed in the main body 310 such that the holes 340 interrupt the aft retaining land 325 along its circumferential length and create a plurality of circumferential segments in the aft retaining land 325.

It should also be appreciated that the present subject matter further encompasses an outer sidewall retention scheme 500 (FIG. 8) for a turbine nozzle of a gas turbine. The retention scheme 500 may generally comprise at least one turbine nozzle including an inner sidewall and an outer sidewall and the retaining ring 300 described and illustrated above. In particular, the pair of retaining lands 315 of the retaining ring 300 may be configured to be attached to the outer sidewall of a turbine nozzle in order to support the nozzle in the gas flow path of a turbine. Further, one of ordinary skill in the art should be appreciate that, while the outer sidewall retention scheme 500 is described below in the context of supporting first stage nozzles 400, the retention scheme 500 may be utilized generally at any stage in a gas turbine in order to retain and support turbine nozzles.

FIGS. 5, 6 and 7 illustrate an embodiment of a turbine nozzle, particularly a first stage nozzle 400, which may be attached to and supported by the retaining ring 300 in one embodiment of the outer sidewall retention scheme 500. Specifically, FIG. 5 illustrates a side view of the first stage nozzle 400. FIG. 6 illustrates an isometric view of an outer surface of the outer sidewall of the first stage nozzle 400. FIG. 7 illustrates a top view of the outer surface of the outer sidewall of the first stage nozzle 400.

The first stage nozzle 400 may include an inner sidewall 410, an outer sidewall 420 and an airfoil 430 in-between. The airfoil 430 may include an internal cavity (not illustrated) for nozzle cooling having an entrance aligned generally in axial and circumferential alignment with the cooling holes 340 (FIGS. 2, 3 and 4) of the retaining ring 300. The outer sidewall 420 may generally include an outer face 422 and an inner face 424. With respect to orientation of the four sides of the nozzle sidewall, when in place on the retaining ring 300, an aft end 450 is the downstream side and a forward end 452 is the upstream side with respect to flow through the turbine. Further, the pressure side is the clockwise side and the suction side is the counterclockwise side when looking down the flow path from the combustor end.

The outer face 422 of the outer sidewall 420 may include two retaining lugs. A first lug 440 and a second lug 445 may be positioned forward from the aft edge 450 of the sidewall by a predetermined distance s, the lugs being in axial alignment with respect to the aft end of the sidewall 420. The first lug 440 may be positioned on the pressure side 456 of the sidewall 420 and the second lug 445 may be positioned on the suction side 454 of the sidewall 420. Additionally, the first lug 440 and the second lug 445 may be circumferentially positioned in proximity to the edge of their respective edge of the outer sidewall 420. The first lug 440 and the second lug 445 may also include a width w1. W1 may be adapted to fit within the circumferential retaining groove 320 (FIG. 2) of the pair of retaining lands 315 when the nozzle 400 is mounted on the retaining ring 300.

Further, the first lug 440 may include an axial oriented open-ended slot 442 and the second lug 445 may include an axial-oriented closed pinhole 447. The closed pinhole 447 and the open-ended slot 442 may be centered to align radially and circumferentially with the centerline 358 (FIG. 2) of the axially oriented paired holes 360 (FIG. 2) in the retaining lands 315 when the nozzle 400 is mounted on the retaining ring 300. The closed pinhole 447 and the open slot 442 may also be sized to accept retaining pins 490, 495 for the nozzle 400. In general, nozzle stability may be enhanced by placement of the lugs as far forward as possible and as far apart as possible to generate longer moment arms for reacting out gas loads. Additionally, moving the support lugs away from the trailing edge reduces the stress input into the trailing edge.

The outer sidewall 420 further includes a chordal hinge rail 460 on the aft edge 450. The chordal hinge rail 460 runs from the inner face of the sidewall 420 from the pressure side to the suction side and extends in a generally outward radial direction from the aft edge 450 of the sidewall 420. The chordal hinge rail 460 projects sufficiently outward radially to cover at least partially or fully the radial reach of the through-holes 345 (FIG. 2) in the aft face 326 of the aft retaining land 325. A chordal hinge seal 465 may be provided on the aft surface 468 of the chordal hinge rail 460 for providing a seating surface against the shroud for the first stage bucket. The chordal hinge seal 465 also provides axial support for the outer sidewall 420 against the shroud. The axial support by the shroud for the outer sidewall 420 complements the radial and circumferential support provided by the retaining lands 315 of the retaining ring 300.

Referring to FIG. 7, the top view of the outer sidewall illustrates that the sidewall 420 may have the shape of a parallelogram with a particular sidewall skew angle 485. In one embodiment, the sidewall skew angle 485 is approximately 23 degrees from the axial direction. The skewing results in the aft end 450 of the outer sidewall 420 (and hence the chordal hinge rail 460) being shifted circumferentially towards the pressure side 456 and away from the suction side 454 of the outer sidewall 420. With the first retaining pin 490 in place in the first retaining lug 440, axial insertion and removal along centerline line 492 of the first retaining pin 490 is thus blocked by chordal hinge rail 460. However, centerline 496 of second retaining pin 495 in the second retaining lug 445 falls circumferentially outside the chordal hinge rail 460.

The inner sidewall 410 further includes a chordal hinge rail 470 on an inner face 415 of the sidewall 410. The chordal hinge rail 470 runs across the inner face 415 from the pressure side to the suction side and extends in a generally inward radial direction from the inner face 415 of the inner sidewall 410. Additionally, the chordal hinge rail 470 may include the raised seating surface of a chordal hinge seal 475 that can seat with an inner support ring to provide axial support for the inner sidewall 410 of the nozzle 400. The chordal hinge seal 475 further blocks against passage of high-pressure air from the compressor between the inner sidewall 410 and the inner support ring.

FIG. 8 illustrates a schematic side elevational view of an embodiment of an outer sidewall retention scheme 500 for a turbine nozzle in accordance with an aspect of the present subject matter. As indicated above, the retention scheme 500 may generally include a turbine nozzle and a retaining ring for supporting the nozzle. Thus, as shown in FIG. 8, the retention scheme 500 may include a first stage nozzle 520 and a retaining ring 300, both of which may be configured as illustrated and described herein. Hot gases of combustion flow from a combustor (not shown) through transition piece 510. The hot gases enter the first stage nozzle 520, impinging on airfoil 430. The hot gases are directed by the airfoil 430 to the first stage bucket 540. The directing process performed by the nozzles accelerates the gas flow resulting in a static pressure reduction between inlet and outlet planes and high pressure loading of the nozzles. The retaining ring 300 includes a segmented forward circumferential land 330 and a segmented aft circumferential land 325, both of which may be configured to be attached to and support the nozzle 520. In particular, the retaining lugs 440, 445 (one shown) of the outer sidewall 420 for each first stage nozzle 400 may fit into the circumferential annular groove 320 of the retaining ring 300. The retaining pins 490, 495 (one shown) may fit through the axial holes 345 and 350 in the aft retaining land 325 and the forward retaining land 330, respectively. Additionally, the retaining pins 490, 495 may also be received into the open-ended slot 442 and closed pinhole 447 of the retaining lugs 440, 445, respectively. As such, the retaining pins 490, 495 may provide radial and circumferential support for the first stage nozzle 400 through retaining lugs 440, 445. Chordal hinge rail 460 on the outer sidewall 420 provides axial support for the nozzle 400 at the point of the chordal hinge seal 465 making contact with the shroud 550 for the first stage bucket 540. Chordal hinge rail 470 on the inner sidewall 410 provides axial support for the nozzle 400 at the point of chordal hinge seal 475 making contact with the support ring 580. Further, the retaining pins 490, 495 (one shown) are prevented from backing out from the retaining lugs 440, 445 by chordal hinge rail 460.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.