US3804551A

US3804551A - System for the introduction of coolant into open-circuit cooled turbine buckets

Info

Publication number: US3804551A
Application number: US00285633A
Authority: US
Inventors: J Moore
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-09-01
Filing date: 1972-09-01
Publication date: 1974-04-16
Anticipated expiration: 1991-04-16
Also published as: SU670237A3; NO143880C; GB1437618A; JPS4992413A; IT993116B; DE2336952C2; DE2336952A1; NO143880B; NL7311237A; JPS5644241B2; FR2198052B1; FR2198052A1

Abstract

An improved coolant distribution system is described for the introduction of liquid coolant into the open-circuit cooling channels of a turbine bucket. Liquid coolant is transported by centrifugal force from the gutter to a pool located at the underside of the platform, the liquid entering the pool beneath the surface thereof. At least one weir is formed in the pool periphery for controlled distribution of the coolant from the pool to cooling channels in one or more turbine buckets.

Description

United States Patent 1191 Moore 15 1 SYSTEM FOR, THE mrnonucnou 0F COOLANT INTO OPEN-CIRCUIT COOLED TURBINE BUCKETS [75] Inventor:

[73] Assignee:

John Moore, Schenectady, NY.

General Electric Company, 1 Schenectady, NY.

1451 Apr. 16, 1974 Kydd 416/97 FOREIGN PATENTS OR APPLICATIONS 1,801,475 4/1970 Germany 416/96 Primary Examiner-Everette A. Powell Attorney, Agent, or Firm-Leo I. MaLossi; Joseph T; Cohen; Jerome C. Squillaro [5 7] ABSTRACT An improved coolant distribution system is described for the introduction of liquid coolant into the opencircuit cooling channels of a turbine buc'ket. Liquid coolant is transported by centrifugal force from the gutter to a pool located at the underside of the platform, the liquid entering the pool beneath the surface thereof. At least one weir is formed in the pool periphcry for controlled distribution of the coolant from the pool to cooling channels in one or more turbine buckets.

8 Claims, 4 Drawing Figures WENTEUAPR 16 19m SHEET 2 0f 3 SYSTEM FOR THE INTRODUCTION OF COOLANT INTO OPEN-CIRCUIT COOLED TURBINE BUCKETS I BACKGROUND OF THE INVENTION Structural arrangements for the open-circuit liquid cooling of gas turbine buckets are shown in U. S. Pat. Nos. 3,446,481 Kydd and 3,446,482 Kydd. An arrangement for the metering of liquid coolant to such buckets is shown in U. S. Pat. No. 3,658,439 Kydd. These patents are incorporated by reference.

Open-circuit liquid cooling capability is particularly important because it makes feasible increasing the turbine inlet temperature to an operating range of from 2,500 F to at least 3,500 F thereby obtaining an increase in power output ranging from about 100 to 200 percent and an increase in thermal efficiency ranging to as high as 50 percent. Such open-circuit liquid cooled turbine structures are referred to as ultra high temperature gas turbines.

Liquid coolant metering is complicated by the extremely high bucket tip'speeds employed resulting in centrifugal fields of the order of 250,000 G. Ideally, liquid fiow to each coolant passage would be correlated with the quantity of heat it is desired to transfer to that given passage. Since liquid coolant is distributed to the coolant passages by flow over a weir structure, improvements that could predictably and controllably distribute weir flow at least as an approximate function of FIG. 1 shows a unified bucket/rotor diskrim construction embodying the means of the instant invention for conducting liquid to the pool/weir structure and power augmentation means of the general type disclosed and claimed in the aforementioned Day application;

FIG. 2 is a section taken on line 22 of FIG. 1 (but notto the same scale) showing the interrelationship between the pool, the weir construction and the liquid coolant conducting means of this invention;

FIG. 3 is a section taken on line 34-3 of FIG. 2 and FIG. 4 isa section showing the application of the instant invention to dovetailed bucket construction.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turbine bucket 10 consists of metal skin 11 bonded to hollow core 12 having spanwise extending grooves 13a formed in the surfaces thereof. The rectangular cooling channels, or passages, 13 defined by skin 11 and grooves 13a conduct cooling liquid therethrough beneath skin 11. At the upper ends thereof the rectan-. gular cooling channels 13 on the pressure side of bucket 10 are in flow communication with, and terminate at, manifold 14 recessed into core 12. On the suction side of bucket 10 the rectangular cooling channels the gas side heat transfer coefficient would be highly desirable. 7

Reference is-also made herein to power augmenter construction described and claimed in U. S. Pat. application Ser. No. 285,631 Day, filed Sept. 1, 1972 and assigned to the assignee of the instant invention.

SUMMARY or THE INVENTION The improved system of this invention for the introduction of liquid coolant into opencircuit liquid cooled turbine buckets is a very substantial answer to the need set forth hereinabove. In addition to satisfying this need the instant invention reduces the amount of coolant flow required, eliminates the flow of vapor in thesystem in a direction opposing thejcoolant flow,

provides greater selectivity of bucket: operating tem- 'a pool of coolant maintained adjacent the weir construction and means for directing the incoming liquid flow to the pool. With this construction the How of liquid coolant passing over the'weir construction at various stations therealong may be roughly correlated with the given demands for cooling capacity in those coolant passages serving particular portions of the turbine bucket.

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:

13 are in flow communication with and terminate at a similar manifold (not shown) recessed into corel2; near the trailing edge of bucket 10, a crossover conduit connects the manifold on the suction side with manifold 14 via opening 15. i

The open-circuit coolant discharge from manifold 14 (and, thereby, from the manifold on the suction side) is accomplished via convergent-divergent nozzle 16 described in the aforementioned Day application. Annular collection slot 17 formed in casing 18 receives the liquid component of the coolantfiowdischarge from power augmenter nozzle 16 e.;g. for recirculation thereof. i

The root end of core 11 consists of a number of finger-like projections, or tines, 19 ,of varying length. These projections 19 may presenta generally rectangular profile as shown or each tine maybe tapered toward the distal-end thereof to present a generally triangular profile. Rim 21 of turbine disk 22 has grooves 23 ma- 'chined thereinv extending to variousdepths separated by ribs 24, the depths and widths of grooves 23 matching the different lengths and widths of bucket tines 19 such that tines 19 will fit snugly therein in an interlocking relationship.

Once the proper fit has been obtained, the appropriate amount of brazing alloy is placed in each groove 23 and the buckets are inserted and held in fixed position by a fixture. The fixture is biased to maintain a tight fit between tines 19 and grooves 23 regardless of thermal expansion. Conventional brazing alloys having melting points ranging from 700 to 1,100" C may be used.

Thereafter, the assembly (rim with all the buckets properly located) is furnace-brazed to provide an integral structure.

Steel alloys may be used for the skin and core, preferably those containing at least 12 percent by weight of chromium for corrosion resistance and heat treatable to achieve high strength. i

The cutting of grooves 23 into rim 21 not only provides the requisite configuration for fastening the bucket root and lessens the weight of the rim, but in addition, the ribs 24 between grooves 23 provide areas on the upper surface thereof for attachment thereto of the investment cast platform elements 26, which have concave undersides to accommodate pools 27 of liquid coolant. Support segments 28 are dimensioned and located so that the widths thereof coincide with the widths of ribs 24, when placed in juxtaposition.

The weir structures 29 for metering of the liquid coolant are formed along walls, which extend along the sides of pools 27 and are accurately ground to some preselected radius, e.g..the radius of the initial radius of the ribs 24. Thus, each weir 29 provides a cylindrical surface (the elements of which extend in the axial direction) following the trace of bucket (FIG. 3) on each side thereof separating a pool 27 from adjacent cooling channels 13.

Platform elements 26 are affixed to the rotor rim 21 by the electron beam welding of platform edges 26a and supports 28 to ribs 24 after previously grinding the radially inwardly faces of edges 26a and supports 28 to a radius common to the initial radius of ribs 24.

If the radius of those portions of ribs 24 located under platform elements 26, but not actually affixed to supports 28, remains unchanged, they can interfere with the free movement of liquid coolant in pools 27. Thus, to avoid disturbing the pool surfaces, the ribs 24 are cut back as shown in FIG. 2 in comparing are 30 (the initial outer surface of rims 24) and arc 30a (the cut-back portions of rims 24).

Although the platform construction shown herein consists of individual platform elements other constructions are equally feasible. For example, the platform components may be made integral with each bucket. In each case the weir surfaces distributing coolant to buckets 10 will be formed as part of the platform construction located adjacent each side of each bucket 10.

As is described in the aforementioned Kydd patents, cooling liquid (usually water) is sprayed at low pressure in a generally radially outward direction from nozzles (not shown, but preferably located on each side of disk 22) and impinges on disk 22. The coolant thereupon moves into

gutters

32, 32a defined in part by downwardly extending lip portions 33, 33a. The cooling liquid is retained in the gutters until this liquid has accelerated to the prevailing disk rim velocity.

After the cooling liquid in

gutters

32, 32a has been so accelerated, this liquid continually drains from gutters'32, 32a passing radially outward via pool supply tubes 34, each pool 27 (one for each platform element 26) receiving liquid coolant from at least two tubes 34.

. An alternate arrangement (not shown) for conducting

liquid coolantfrom gutters

32, 32a to pools 27 would consist of providing internal passageways, which run in the general radial direction, through the outer walls of rim 21 and platform edges 26a, each passageway being in flow communication with a gutter and a pool. Entry to the pool would be made radially outward of the weir surface 29.

As the coolant in each pool 27 passes over the surfaces of the platform elements 26, these elements are kept cool. Thereafter, the coolant passes over weirs 29 and then into the radially inner end of cooling channels 13 (via grooves 130) in adjacent buckets l0.

As the cooling liquid moves radially outward through cooling channels 13 of any given bucket 10, then depending upon (a) the rate at which coolant is supplied, (b) the desired operating temperature of the bucket, (c) the area of the throat of nozzle 16 and (d) the extent of frictional heating of the coolant within the distribution circuit, some portion of the liquid coolant is converted to the gaseous or vapor state as it absorbs heat from the skin 11 and core 12 of the bucket. At the outer ends of cooling channels 13 the vapor or gas and any remaining liquid coolant pass into manifold 14 and the manifold on the suction face. Thereafter, the flow from the suction face manifold is merged with the flow in manifold 14 (via opening 15) and these combined flows exit therefrom through power augmenter nozzle 16. As is described in the aforementioned Day application, incorporated herein by reference, this exit flow is relied upon for the recovery of reaction energy and is particularly effective when the exit flow is made supersonic.

Investigations have shown that the characteristics of flow in pools 27 and the'condition of the surface of each of these pools strongly influence the accuracy with which metering of the liquid coolant flow to grooves 13a may be accomplished. The pool flow characteristics and pool surface condition are, of course, strongly affected by the rate of entry of liquid coolant into the pool, the direction and velocity of the entering liquid and the manner of entry thereof.

Thus, the flow of liquid entering pool 27 should distribute itself therein at a uniform constant low velocity so as not to disturb the surface 36 of pool 27 and performance of the metering function is found to be greatly improved by introducing the liquid coolant beneath the pool surface 36. This entry is accomplished by locating the discharge end 37 of each supply tube 34 radially outward of surface 36, end 37 being spaced away from the underside of platform element 26 by means of tip 38 e.g. a projecting portion of the wall of tube 34 in contact with the base of the concavity containing pool 27. Since the distance from the underside of platform 26 to surface 36 must exceed the distance from the underside of platform 26 to the weir surface 29 by a finite amount (e.g. about 000075 inch) in order for liquid flow to pass over weir 29, end 37 may be radially disposed at the same level as the surface of weir 29 or'at some optimum position radially outward therefrom.

By introducing liquid coolant via supply tube 34 located in the manner shown, this entering liquid does not splash into pool 27, but enters smoothly without disturbing surface 36. Any tendency of the

liquid leaving gutters

32, 32a to form waves or to splash on its way to pool 27 is confined to the inside of the inlet tubes 34. In fact it is of advantage to provide irregularities over the inner surface of each tube 34-(e.g. a threaded surface) to offset the effects of radial acceleration tending to dispose the liquid coolant over the trailing wall of tube 34 as it passes to pool 27.

The promotion of smooth flow in the liquid moving laterally from discharge end 37 toward the central region of pool 27 is accomplished both by properly directing the entering liquid and by minimizing obstruction to this lateral flow. These improved conditions are accomplished by proper selection of the size and shape of inlet tube tips 38, by locating each tip 38 around the central axis of tube 34 in an optimum position, and by employing the minimum number of support ribs 28, each rib 28 being of minimum length. These support ribs 28 provide interconnection between each platform element 26 and ribs 24 aligned therewith.

Instead of employing separate support projections 28 to align with certain ribs 24, each platform element 26 may be made with a single support projection formed on the underside thereof extending generally transverse of ribs 24 for attachment thereto. By proper selection of the shape of this projection an optimum pool geometry for weir flow distribution can be achieved.

The disposition of tips 38 (illustrated in FIG. 3) around the central axes of the tubes 34 to which they are connected is such as to direct the entering liquid so as to cause preferential flow in a controlled manner, i.e. at certain weir stations. Thus, in the placement shown the lateral flow of liquid entering at low velocity is encouraged to provide the desired pool depth profile over the extent of pool 27. With the combination shown, flow at specific weir stations e.g. adjacent the pressure side leading edge and adjacent the pressure side trailing edge of buckets is increased to compensate for the larger cooling capacity required over these specificturbine bucket surface areas. l

Preferably supply tubes 34 are located with the axes thereof extending in a radial direction so that the initial velocity of the incoming coolant flow is perpendicular to the bottom of the pool. However, if additional directional effect is required, it may be obtained by introducing a slight (as much as about inclination of the axes of tubes 34 to theradial direction. Tip support 34 need not be made as a single piece as shown, but may, if desired, be in the form of a plurality of spaced tip extensions.

The power required to pump the coolant through the cooling circuit may be reduced in part by reducing the mass flow of liquid coolant employed. This in turn results in the vaporization of some or all of the liquid coolant. Generally, the volume of the vapor so generated is orders of magnitude larger than the volume of the liquid actually in the cooling channels and the vapor velocities in the cooling channels is very high. Unfortunately, these vapor flows can deleteriously influence the coolant liquid flows. In particular, any flow of vapor in a direction opposite to the direction of distribution of the liquid flow will slow down the required transit of the liquid coolant. If this occurs, the thickness of the liquid film-in the coolant passages is increased and the high convective heat transfer coefficient to the buckets is reduced. Another advantage of the instant invention in addition to the increased effectiveness of metering of the coolant flow is that by disposing each supply tube 34 with the end 37 thereof below the surface 36 of pool 27, flow of vapor in the upstream direction in the cooling circuit is prevented, while still preserving the downstream flow of coolant liquid.

The aforementioned vaporization of coolant increases the pressure in coolant passages 13 and this in turn increasesthe boiling point of the liquid coolant. The pressure in coolant passages 13 will rise in this manner until a balance is created between theproduction of coolant vapor and the escape of coolant vapor. Any upstream escape of the coolant vapor is prevented by the sealing off of the ends 37 of supply tubes 34 by the. liquid in pools 27 and the increase in pressure in coolant passages 13 becomes balanced by a rise in the to the

gutters

32, 32a, the transfer of heat to buckets l0 and the area of the throat of each nozzle 16, a condition of self-regulation is imposed whereby the distance H is maintained. The balance of the volume of each tube 34 (radially inward of the liquid level) consists essentially of air, hot gas and/or steam. Liquid coolant entering inlet tubes 34 in the rotating system disposes itself over the trailing wall of the tubes 34 as it traverses volume 39, except for portions of the flow, which may tend to splash away from the walls within the confines of tube 34, particularly if the inside surface thereof is roughened, until the coolant liquid reaches the liquid level.

The increase of pressure in the coolant circuit upstream of nozzle 16 can be made high enough so that the discharge of vapor through nozzle 16 is at supersonic velocity providing a very substantial force vector in a direction opposite to the direction of rotation of blades 10 effective to recoup at least in part thecoolant pumping losses.

of this invention to a dovetailed bucket made up of metal skin 51 and platform element 52 affixed to bucket core 53 having a dovetail root portion 54 integral therewith. i

Liquid is supplied from a coolant source (not shown) to

gutters

56, 56a via

passages

57, 57a extending through rotor 58.

Gutters

56, 56a are in flow communication with pools 59, 59a of liquid coolant via liquid coolant conducting tubes 61 having discharge ends 62 and positioning/deflection tips 62. Weirs 64, 64a are formed integral with platform elements 52, 52a. With the construction shown each bucket 50 is isolated from the rest of the turbine buckets and, furthermore, if desired, each side (pressure or suction side) can be isolated insofar as the coolant distribution function is concerned. Otherwise, operation of the coolant distribution system is the same as has been described hereinabove in that liquid coolant distributed over weir surfaces 64, 64a enters slots 66a (grooves in the airfoil surfaces) of bucket 53 for entry into coolant passages 66 defined by skin 51 and slots 66a. The arrangement of cooling channels 66, the collecting manifolds (not shown) and the ejection nozzle (not shown) would be the same as, or similar to the arrangement shown in FIG. 1.

Although use of the structures shown herein need not be limited in the following way, the grooved rim rotor with mating bucket root shown in FIGS. 1-3 appear to be more apt to be employed in the construction of small liquid cooled turbines while the dovetailed bucket construction shown in FIG. 4 appear to be more adaptable for use in larger liquid cooled turbine units.

This invention has been illustrated in connection with a liquid cooled gas turbine, but application, can be made thereof to any liquid cooled rotor system, e.g. a compressor, which would in essence comprise the general structure shown herein operated in reverse to work on a gas instead of having gaseous working fluid work on the rotor disk via the buckets.

What I claim as new and desire to secure by Letters Patent of the United States is v Y 1. 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 affixed to the outer rim thereof with platform structure disposed therebetween, said buckets receiving a driving force from hot motive fluid moving in a direction generally parallel to said axis of said shaft and the driving force being transmitted to said shaft via rotation of said turbine disk, means located radially inward of said platform structure for introducing liquid coolant within said turbine in a radially outward direction into openended coolant distribution circuits, each open-ended coolant distribution circuit comprising cooling channels extending beneath the airfoil surfaces of and in a generally radial direction along each of said buckets, metering means located beneath said platform structure in flow communication with said cooling channels and a manifold and discharge portion located in the .tip region of each of said buckets in flow communication with the radially outer ends of cooling channels of the given bucket whereby coolant passes to the underside of said platform structure, is metered into and proceeds through cooling channels and exits therefrom into said manifold and discharge portion, 7 the improvement comprising:

a. means located in each of said open-ended coolant distribution circuits for conducting coolant into a concavity formed in the underside of each of said platform structures,

b. at, least one metering surface formed along wall structure defining each concavity, said conducting means being located with the discharge end thereof disposed at a radial distance from said axis of said shaft at least as great as the radial distance of said at least one metering surface from said axis of said shaft. t

2. The improvement of claim 1 wherein each conducting means is a tube having at least one protrusion at the discharge end thereof, said at least one protrusion being in contact with the base of the concavity in the underside of the platform structure.

3. The improvement of claim 1 wherein each conducting means places an annular gutter in flow communication with the concavity in the underside of each platform structure, said annulargu'tter being located so as to receive liquid coolant from the means for introducing liquid coolant.

4. The improvement of claim 1 wherein a poweraugmenting nozzle comprises the discharge portion of each open-ended coolant distribution circuit.

5. In a liquid cooled rotor system wherein a rotor disk is mounted on a shaft rotatably supported in a casing, said rotor disk extending substantially perpendicular to the axis of said shaft and having buckets affixed to the outer rim thereof with platform structure disposed therebetween, means located radially inward of said platform structure for introducing liquid coolant within said rotor system in a radially outward direction into open-ended coolant distribution circuits, each openended coolant distribution circuit comprising subsurface cooling channels extending generally radially of each of said buckets and metering means located beneath said platform structure in flow communication with said cooling channels whereby coolant passes to the underside of said platform structure, is metering into and proceeds through said cooling channels and discharges from said cooling channels, the improvement comprising:

b. at least one metering surface formed along wall structuredefining each concavity, said conducting means being located with the discharge end thereof disposed at a radial distance from said axis of said shaft at least as great as the radial distance of said at least one metering surface from said'axis of said shaft.

6. The improvement of claim S'Wherein each conducting means is a tube having at least one protrusion at the discharge end thereof, said at least one protrusion being in contact with the base of the concavity in the underside of the platform structure.

7. The improvement of claim 5 wherein a poweraugmenting nozzle forms part of each open-ended coolant distribution circuit and is in flow communication with the discharge ends of cooling channels in said circuit.

8. The improvement of claim 5 wherein each conducting means places an annular gutter in flow communication with the concavity in the underside of each platform structure, said annular gutter being located so as to receive liquid coolant from the means for introducing liquid coolant. I

Claims

1. 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 affixed to the outer rim thereof with platform structure disposed therebetween, said buckets receiving a driving force from hot motive fluid moving in a direction generally parallel to said axis of said shaft and the driving force being transmitted to said shaft via rotation of said turbine disk, means located radially inward of said platform structure for introducing liquid coolant within said turbine in a radially outward direction into open-ended coolant distribution circuits, each open-ended coolant distribution circuit comprising cooling channels extending beneath the airfoil surfaces of and in a generally radial direction along each of said buckets, metering means located beneath said platform structure in flow communication with said cooling channels and a manifold and discharge portion located in the tip region of each of said buckets in flow communication with the radially outer ends of cooling channels of the given bucket whereby coolant passes to the underside of said platform structure, is metered into and proceeds through cooling channels and exits therefrom into said manifold and discharge portion, the improvement comprising: a. means located in each of said open-ended coolant distribution circuits for conducting coolant into a concavity formed in the underside of each of said platform structures, b. at least one metering surface formed along wall structure defining each concavity, said conducting means being located with the discharge end thereof disposed at a radial distance from said axis of said shaft at least as great as the radial distance of said at least one metering surface from said axis of said shaft.

3. The improvement of claim 1 wherein each conducting means places an annular gutter in flow communication with the concavity in the underside of each platform structure, said annular gutter being located so as to receive liquid coolant from the means for introducing liquid coolant.

4. The improvement of claim 1 wherein a power-augmenting nozzle comprises the discharge portion of each open-ended coolant distribution circuit.

5. IN a liquid cooled rotor system wherein a rotor disk is mounted on a shaft rotatably supported in a casing, said rotor disk extending substantially perpendicular to the axis of said shaft and having buckets affixed to the outer rim thereof with platform structure disposed therebetween, means located radially inward of said platform structure for introducing liquid coolant within said rotor system in a radially outward direction into open-ended coolant distribution circuits, each open-ended coolant distribution circuit comprising subsurface cooling channels extending generally radially of each of said buckets and metering means located beneath said platform structure in flow communication with said cooling channels whereby coolant passes to the underside of said platform structure, is metering into and proceeds through said cooling channels and discharges from said cooling channels, the improvement comprising: a. means located in each of said open-ended coolant distribution circuits for conducting coolant into a concavity formed in the underside of each of said platform structures, b. at least one metering surface formed along wall structure defining each concavity, said conducting means being located with the discharge end thereof disposed at a radial distance from said axis of said shaft at least as great as the radial distance of said at least one metering surface from said axis of said shaft.

6. The improvement of claim 5 wherein each conducting means is a tube having at least one protrusion at the discharge end thereof, said at least one protrusion being in contact with the base of the concavity in the underside of the platform structure.

7. The improvement of claim 5 wherein a power-augmenting nozzle forms part of each open-ended coolant distribution circuit and is in flow communication with the discharge ends of cooling channels in said circuit.

8. The improvement of claim 5 wherein each conducting means places an annular gutter in flow communication with the concavity in the underside of each platform structure, said annular gutter being located so as to receive liquid coolant from the means for introducing liquid coolant.