Liquid Cooled Turbine Bucket With Dovetailed Attachment

Abstract

A liquid-cooled turbine bucket construction is described in which the airfoil bucket core, platform (with metering means) and root with dovetail configuration are integrally formed. The pressure and suction sides of each bucket are each provided with a liquid reservoir defined in part by metering means (e.g., a weir), grooves in the upper surface of the platform and face of the airfoil core and holes interconnecting these grooves with the underside of the platform adjacent the metering means.

Description

BACKGROUND OF THE INVENTION

Structural arrangements for the liquid cooling of gas turbine buckets are shown in U.S. Pat. Nos. 3,446,481 - Kydd, 3,446,482 - Kydd and 3,658,439 - Kydd. These patents are incorporated by reference.

Systems for supplying coolant to the cooling channels of liquid-cooled turbine buckets are determined in part by the type of attachment used to secure the buckets to the rotor. The art is in need of such a distribution system particularly adapted to buckets having dovetailed bucket-to-rotor attachment and integral platform construction.

SUMMARY OF THE INVENTION

A liquid-cooled turbine bucket construction is described in which the airfoil bucket core, platform (with metering means) and root with dovetail configuration are integrally formed. The pressure and suction sides of each bucket are each provided with a liquid reservoir defined in part by metering means (e.g., a weir), grooves in the upper surface of the platform and face of the airfoil core and holes interconnecting these grooves with the underside of the platform adjacent the metering means.

BRIEF DESCRIPTION OF THE DRAWING

The exact nature of this invention as well as objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings in which:

FIG. 1 is a view partially in section showing the side view in elevation of part of the dovetailed root, platform and airfoil and liquid coolant feed means in register therewith;

FIG. 2 is a view partially in section with the retainer/feed ring and a cover plate cut away to show the integral formation in the platform of the reservoir, the longitudinally extending metering means, platform gutter, platform coolant channels and feed holes leading thereto and

FIG. 3 is a view taken on line 3--3 of FIG. 2 with the airfoil skin removed in part to show the location and interconnection of the airfoil channels, the platform channels and feed conduits leading to the platform channels from the underside of the platform.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turbine bucket 10 consists of skin 11, 11a (e.g., sheet metal) affixed, as by brazing, to the unitary root/platform/airfoil core 12. Root portion 13 is formed in the conventional dovetail configuration by which bucket 10 is retained in slot 14 of wheel rim 16. Each groove 17 recessed in the surface of platform 18 is connected to a similar groove 19 recessed in the surface of airfoil portion 21 of unit 12. The cooling channels (preferably rectangular in shape) defined by skin 11a and grooves 17 are thus in communication on a one-to-one basis with the cooling channels defined by skin 11 and grooves 19 and cooling liquid is conducted therethrough at a uniform distance from the exterior surface. At the radially outer ends thereof the rectangular cooling channels on the pressure side of bucket 10 are in flow communication with, and terminate at, manifold 22 recessed into airfoil portion 21. On the suction side of bucket 10 the cooling channels are in flow communication with, and terminate at, a similar manifold (not shown) recessed into airfoil portion 21. Near the trailing edge of bucket 10 a cross-over conduit (opening shown at 23) connects the manifold on the suction side with manifold 22.

Open-circuit cooling is accomplished by spraying cooling liquid (usually water) at low pressure in a generally radially outward direction from nozzles, such as nozzle 24 (one shown), mounted on each side of the rotor disk. The coolant is received in annular gutter 26 formed in ring member 27, one of which is mounted on each side of wheel rim 16. Ring member 27, in addition to conducting the function of coolant distribution to each bucket also retains the buckets 10 properly positioned in wheel rim 16 as more completely described in U.S. Pat. application Ser. No. 385,096 - Wojcik, filed Aug. 2, 1973 and assigned to the assignee of the instant invention. The Wojcik application is incorporated by reference.

Coolant received in gutters 26, is directed through feed holes 28, each of which is in flow communication with a reservoir 29 extending in a direction parallel to the axis of rotation of the turbine disk. The openings into the feed holes 28 from gutters 26 are equally spaced around the circumference of gutters 26 to insure equal distribution of coolant to the buckets via these feed holes.

While coolant is spread out as a thin film in gutters 26, it accumulates to fill each reservoir 29 (the ends thereof being closed by means of a pair of cover plates 31). As liquid coolant continues to reach each reservoir 29, the excess discharges over the crest of weir 32 along the length thereof and is thereby metered. Preferably the crest of weir 32 is arcuate (convex toward the axis of rotation) in cross-section and is a portion of a cylinder in configuration in order to accommodate slight differences in the disposition of the buckets 10 relative to each other. Although the distance of the crest of any given weir from the axis of rotation may vary slightly from that of another weir, the cylindrical configuration of the weir crest curving toward the root must be accurately machined so that each element of each such cylindrical surface extends parallel to the elements forming the cylindrical convex ridges of the dovetailed configuration. In this manner each element of the crest surface can be set parallel to the axis of rotation (the axis of the shaft on which the rotor is mounted). This machining accuracy is required in order to insure that liquid coolant passes uniformly over the full length of the weir crest.

Coolant that has traversed the weir crest 32 continues in the generally radial direction to enter longitudinally extending platform gutter 33 as a film-like distribution, passing thereafter through the cooling channel feed holes 34. Thus, one each of reservoir 29, weir 32 and gutter 33 constitute a set, one such set being formed in the underside of platform 18 on each side of root portion 13. Most of the channel feed holes 34 are in flow communication with grooves 17 on a one-to-one basis, although a few of these holes 34 connect directly with grooves 19. In any event, the coolant passes from holes 34 to manifold 22 (and the suction manifold, not shown) via bucket cooling channels.

As the coolant traverses the surfaces of the platform and of the airfoil, these elements are kept cool. Some portion of the cooling liquid, depending upon the rate of flow, is converted to the gaseous or vapor state as it absorbs heat. The vapor or gas and any remaining liquid coolant exit from the manifold 22 via opening 36, preferably to enter a collection slot (not shown) formed in the casing for the eventual recirculation or disposal of the ejected fluid.

Although the cooling channels have been illustrated herein extending spanwise of the turbine bucket, the instant invention is equally applicable to bucket constructions in which the cooling channels are disposed in a convoluted or spiral configuration.

Claims

What we claim as new and desire to secure by by Letters Patent of the United States is:

1. Turbine bucket construction comprising in combination:

a. integrally formed airfoil-shaped core, platform and root portions, said root portion having a dovetailed configuration,

b. a first group of cooling grooves recessed into the upper surface of said platform portion,

c. a second group of cooling grooves recessed into the pressure and suction faces of the airfoil-shaped core, each of the cooling grooves in said first group being connected to a separate cooling groove in said second group,

d. skin material disposed over said upper surface of said platform portion and over said pressure and suction faces thereby covering said first and second groups of cooling grooves,

e. a pair of longitudinally-extending recesses formed in the underside of said platform portion one of said recesses extending along each side of, in the same direction as, and adjacent to said dovetailed configuration, a pair of longitudinally-extending gutters formed in the underside of said platform portion, one of said gutters extending parallel to and adjacent each of said recesses,

f. a pair of longitudinally-extending projections formed along the underside of said platform portion, each of said projections separating one recess and one gutter, each of said projections having a crest, said crest being arcuate in cross-section and presenting a convex cylindrical surface, the elements of the cylindrical surfaces of both crests being parallel to the elements of the cylindrical convex ridges of said dovetailed configuration and

g. a plurality of holes passing through said platform portion placing said first group of cooling grooves in flow communication with the underside of said platform portion adjacent each of said projections on the side thereof away from the recess adjacent thereto.

2. The turbine bucket as recited in claim 1 wherein the crest of the longitudinally extending projection is in the form of an arc of a circle in cross-section.

3. The turbine bucket as recited in claim 1 wherein the far ends of each of the recesses formed in the underside of the platform portion are closed off by a pair of plate-like members.

4. The turbine bucket as recited in claim 1 wherein the pair of recesses and the pair of projections are located between the pair of gutters.

5. The turbine bucket as recited in claim 1 wherein each groove of the second group of cooling grooves terminates in one of two interconnected manifolds located near the tip of said bucket.

6. In a gas turbine wherein a turbine disk is mounted on a shaft rotatably supported in a casing, said turbine disk extending substantially perpendicular to the axis of said shaft and having turbine buckets mounted on the outer rim thereof, means located radially inward of said bucket adjacent said turbine disk for supplying liquid coolant to said buckets to enter open-circuit distribution paths comprising cooling channels and a manifold system in each of said buckets, the improvement comprising:

a. each of said buckets having integrally formed airfoil-shaped core, platform and root portions, said root portion having a dovetailed configuration fitting into a matching slot in said outer rim,

b. the platform portion of each bucket having a pair of longitudinally-extending recesses formed in the underside thereof, one of said recesses extending along each side of, in the same direction as and adjacent said dovetailed configuration, a pair of longitudinally-extending gutters formed in the underside of said platform portion, one of said gutters extending parallel to and adjacent each of said recesses,

c. a pair of longitudinally extending projections formed along the underside of said platform portion, each of said projections separating one recess and one gutter, each of said projections having a crest, said crest being arcuate in cross-section and presenting a convex cylinder surface, the elements of the cylindrical surfaces of both crests being parallel to the elements of the cylindrical convex ridges of said dovetailed configuration and

d. in each of said buckets a plurality of first cooling grooves recessed into the upper surface of the platform portion, said cooling grooves being connected to a plurality of second cooling grooves recessed into the pressure and suction faces of the airfoil-shaped core, said second cooling grooves in turn being connected to a manifold system adapted to discharge coolant from said bucket,

e. skin material disposed over the upper surface of the platform portion and over the pressure and suction faces of each of said buckets thereby covering said first and second cooling grooves and said manifold system except for the exit therefrom,

f. a plurality of holes passing through said platform portion placing said first cooling grooves in flow communication with said pair of gutters and

g. said means for supplying liquid coolant being in flow communication with each of said longitudinally extending recesses,

whereby once any given recess has become full of coolant, as additional coolant enters said recess the excess coolant flows over the adjacent crest along the length thereof and passes through said holes, said first and second cooling grooves and said manifold for exit from said bucket.

7. The turbine bucket as recited in claim 6 wherein the pair of recesses and the pair of projections are located between the pair of gutters.

8. The improvement recited in claim 6 wherein the far ends of each of the recesses formed in the underside of the platform portion are closed off by a pair of plate-like members.

9. The improvement recited in claim 6 wherein in a given bucket the holes passing through the platform portion to the underside thereof are divided into two sets, one set in flow communication with cooling grooves on the pressure side of said bucket and the second set in flow communication with cooling grooves on the suction side of said bucket.