Self-Aligning Static Seal for Gas Turbine Stator Vanes

1. Field of the Invention

This invention pertains to the art of providing a static seal between the inner shrouds of stator vane segments and a radially inner seal housing.

2. Description of the Prior Art

The most pertinent prior art of which we are aware is U.S. Pat. No. 3,529,906 of McLaurin et al and has been embodied substantially as illustrated in gas turbine machines which have been manufactured by the assignee of this application.

As we view it, that design employs a static seal loaded radially against the inner diameter of the first stator inner shroud. While the present invention also is a radially loaded arrangement, it is considered to be a superior arrangement to that shown with respect to several drawbacks of that prior art arrangement. These drawbacks include excessive leakage through the seal to the shroud "smile" clearance caused by mismatch between seal segments and shroud curvatures. Also one seal is required per vane segment thus leading to many joint leaks when single vane segments are used. Finally, each joint exposes a relatively large area to the high pressure fluid to be sealed against and requires a complex segment-to-segment linkage system to seal effectively.

It is the aim of this invention to provide an improved seal arrangement which does not suffer from the noted drawbacks of the prior art arrangement.

In accordance with the invention, the arrangement for sealing between the inner shrouds and the seal housing include outer seal means carried by the housing and comprising a first plurality of arcuate segments in end-to-end relation, with each segment being generally channel-shaped in cross-section throughout its length and being radially movably disposed in the radially outwardly open channel of the seal housing, and inner seal means radially movably disposed in the outer seal means channel and including a second plurality of arcuate segments which equal the number of the shrouds, and first resilient means biasing the outer seal means radially outwardly in the seal housing channel, and second resilient means independently biasing the inner seal means radially outwardly in the outer seal means channel.

Further particular details contemplated by the invention in its preferred form will be described hereinafter.

FIG. 1 is a partly broken and fragmentary face view of the seal arrangement according to the invention, this view looking in the direction of flow through the turbine;

FIG. 2 is a cross-sectional view corresponding to one taken along the line II--II of FIG. 1;

FIG. 3 is a cross-sectional view corresponding to one taken along the line III--III of FIG. 1; and

FIG. 4 is a fragmentary edge view of the seal arrangement of the invention at a joint between outer seal segments.

Referring to FIG. 1, that portion of a gas turbine including an annular array of individual stator vane segments includes a portion of blades or vanes 10 which, in conventional fashion, are secured between outer shrouds (not shown) and inner shrouds 12.

As noted before, the invention deals with an arrangement providing a static seal between the radially inner surfaces of the inner shrouds 12, and radially inner structure including the annular seal housing generally designated 14.

The portions of the seal housing 14 (FIGS. 2, 3) of interest in connection with the invention include an upstream wall 16, a downstream wall 18, and a radially inner, base wall 20 together forming a radially outwardly open channel 22 which extends circumferentially. Each of the walls 16 and 18 have inwardly projecting shoulders 16a and 18a, respectively, adjacent the radially outer opening of the channel.

Received within the channel 22 (FIGS. 2 and 3) are a plurality of outer seal segments generally designated 24, and each of which is arcuately shaped in a longitudinal direction and, as best seen in FIGS. 2 and 3, are generally channel-shaped in cross-section and include an upstream wall 26, a downstream wall 28, and a web or base wall 30. The base wall 30 has upstream projecting, and downstream projecting rails 30a and 30b, respectively, which, during assembly, prevent the disengagement of the outer seal segments from the channel 22 of the seal housing.

As an example, and for purposes of illustration and description only, one gas turbine of the assignee of this application has twenty-eight individual stator vane segments and correspondingly twenty-eight individual inner shrouds 12 against which a seal is to be maintained. Thus, with the twenty-eight inner shrouds in an annular array making a complete circle, each quadrant of the circle will have seven vane segments. For purposes of manufacture and assembly, a quadrant is provided with two outer seal members, one of which corresponds in length to provide sealing against the radially inner faces of three inner shrouds, while the other outer seal segment for the quadrant has a length to provide sealing against four inner faces of the inner shrouds. Thus, a total of eight outer seal segments in end-to-end relation provide a substantially complete circle.

The second or inner seal means generally designated 32 are disposed in the channel 33 of the first seal means and include a plurality of arcuate seal segments 34, equal in number to the number of inner shrouds of the stator vanes and, as disposed in end-to-end relation, substantially complete a circle.

The outer seal means 24 is biased radially outwardly in the seal housing channel 22, while the inner seal means is independently biased radially outwardly in the first seal means channel 33. In the preferred form of the invention, the outward biasing is accomplished by sets of compression springs 36 and 38 which, are concentrically arranged relative to each other. The arrangement includes a series of circumferentially spaced, radially outwardly open cups 40 supported from the base wall 20 of the seal housing and into which one compression spring 36 is received, with the opposite end of the spring bearing against the base wall 30 of the outer seal. At circumferentially correspondingly spaced locations along the length of the outer seal segments, openings 42 are provided in the base wall of the outer seal, and a thimble-shaped member 44 is received in each opening. The diametrically smaller compression spring 38 is received in the thimble 44. The bore of the inner spring 38 receives the shank 46 of a button 48 which has a base area greater than the area of the spring 38 so that the radially outer end of the spring 38 will bear against the button 48 to urge it in a radially outward direction. The faces of the buttons, and the opposing faces of the inner seal segments 34 are complementarily inclined relative to each other, as is readily seen in FIG. 2, so that the buttons 48 and segments 34 are urged in opposite axial directions (relative to the axis of the turbine) under the force of the spring 38 before start-up, and by the pressure differential holding segments 34 downstream when the unit runs. To the end of accomplishing this and to prevent binding, the axial dimensions of both the button and the inner seal segment 34 are less than the width of the channel 33 of the outer seals 24. Thus, this arrangement provides the necessary clearance to avoid binding under the temperature changes encountered, but still provides the sealing of the segments 34 against the facing downstream wall of the channel 33.

In the currently preferred embodiment, three compression spring sets are provided for each single inner seal segment 34 so, the shorter outer seal segment accommodating three of the inner seal segments will have a total of nine compression spring sets, while the longer outer seal segment accommodating four of the inner seal segments will have twelve compression spring sets.

At a number of circumferentially spaced locations, means are provided to prevent circumferential movement of the outer seals relative to the seal housing. As best seen in FIG. 3, this is accomplished by providing an upstream facing slot 50 in a lower portion of the upstream wall 26 of the outer seal means, and providing a retaining screw 52 inserted through a bore in the upstream wall 16 of the seal housing so that the end of the retaining screw is received in the slot.

In the currently preferred form of the invention, means is also provided to prevent circumferential movement of the inner seal segments 34 relative to the outer seal 24, while permitting limited radial movement of the inner seal 34 relative thereto. To this end, a radially extending slot 54 (FIGS. 1 and 2) is provided in the upstream wall 26 of the outer seal 24 at a location corresponding to the lengthwise center of each of the inner seals 34. Then a pin 56 is provided at that location of each inner seal segment 34 with its upstream end projecting into the slot 54.

Each of the outer seal means is also provided with a slot 58 (FIG. 1) at the upper end of the upstream wall 26 and adjacent each of its longitudinal ends to permit the insertion of a tool to retract the seals during disassembly and service.

The relation of the opposing ends of the outer seals to each other and of the inner seals to each other is best seen in FIG. 4. As there shown, the ends of the outer seals may, for example, have their ends squared off, while the inner seal segments 34 have their ends complementarily inclined as at 60.

The arrangement is considered to have a number of advantages. For example, the continuous channel 33 of the outer seal results in the outer seal part being relatively simple to manufacture. The outer seals span a number of inner shrouds and are loaded against the shrouds to provide a part of the seal. To the extent that individual inner shrouds are skewed or misaligned with respect to a perfect circle, the inner seal segments 34 individually span individual inner shrouds and enhance the sealing contact. The sealing force of the outer seal is partly from the outer spring 36, but is for the most part obtained through pressurization of the channel 22 by means of a series of circumferentially spaced openings 62 in the front wall 16 of the seal housing. This pressure loading of an outer seal is known in the prior art as evidenced in the noted patent. The inner seal segments 34 are independently loaded partly by the internal springs 38 but primarily by pressure forces to insure good sealing contact with the inner faces of the individual inner shrouds. PG,8