GB2082257A

GB2082257A - Liquid coolant distribution systems for gas turbines

Info

Publication number: GB2082257A
Application number: GB8119674A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1980-08-08
Filing date: 1981-06-25
Publication date: 1982-03-03
Also published as: NO812670L; NL8103719A; GB2082257B; IT8122933A0; IT1138056B; FR2488327A1; DE3129853A1; JPS5756629A; CA1159371A

Abstract

An improved cooling system utilizing flow resistant devices to distribute liquid coolant to air foil coolant channels formed in a bucket of a turbine is disclosed. A separate flow resistance device is associated with each of the air foil coolant channels so as to meter the flow of liquid coolant into the coolant channels. In the disclosed embodiments, the flow resistant devices alternately take the form of a tortuous passage, an orifice and a plurality of vortex flow chambers. <IMAGE>

Description

SPECIFICATION Liquid coolant distribution systems for gas turbines The present invention is directed towards an improved cooling system for a gas turbine. More particularly, the present invention is directed towards an improved cooling system which employs flow-resistance devices to meter coolant into a plurality of platform and air foil coolant channels located in the buckets of the gas turbine.

The cooling system of the present invention is utilized in connection with a gas turbine of the type including a turbine disk mounted on a shaft rotatably supported in a casing and a plurality of turbine buckets extending radially outward from the disk. Each of the buckets includes a root portion mounted in the disk, a shank portion extending radially outward from the root portion to a platform portion, and an air foil extending radially outward from the platform portion. During operation, the buckets receive a driving force from hot fluid moving in a direction generally parallel to the axis of the shaft and convert this driving force to rotational motion which is transmitted to the shaft via the turbine disk. As the result of the relatively high temperatures of the hot fluid, a significant amount of heat is transferred to the turbine buckets.In order to remove this heat from the bucket structure, the prior art has developed a large variety of open-liquid cooling systems.

Exemplary of such systems are U.S. Patent No.

3,658,439, issued to Kydd; U.S. Patent No.

3,804,551, issued to Moore; and U.S. Patent No.

4,017,210, issued to Darrow.

Open circuit liquid cooling systems are particularly important because they make it feasible to increase the turbine inlet temperature to an operating range of from 25000F to at least 35000F, thereby obtaining an increase in power output ranging from about 1 00%-200% and an increase in thermal efficiency ranging to as high as 50%. A primary requirement of open circuit liquid cooling systems is that the liquid coolant be evenly distributed to the several platform and air foil coolant channels formed in the bucket. Such a distribution is difficult to obtain as a result of the extremely high bucket tip speeds employed, resulting in centrifugal fields of the order of 25,000 G.

To obtain an even flow of coolant liquid throughout the several coolant channels, the prior art systems, as exemplified by U.S. Patents Nos.

3,804,551 and 4,017,210, supra, utilize weir structures which meter the amount of coolant liquid supplied to each individual channel from pools of coolant liquid formed in the platform portion of the bucket. Particularly, these systems introduced liquid coolant into each end of a trough formed in the platform portion of the bucket such that liquid coolant flows in a direction parallel to the axis of rotation of the turbine disk from each end of the trough. The liquid coolant flows over the top of an elongated weir which performs the metering for each channel.

In order to perform satisfactorily, it is critical that the top of these weirs is parallel to the axis of rotation of the turbine within a tolerance of several mils. If this relationship is not maintained, all of the coolant liquid will flow over the low end of the weir and, consequently, some of the coolant channels formed in the platform and air foil of the bucket will be starved for coolant.

In order to overcome the foregoing drawbacks of the prior art metering structures, the present invention utilizes resistance flow devices to meter water into each bucket cooling channel. Such devices are not dependent upon a stable, uniform water surface for accurate metering. Thus, while flow through a resistance flow device is typically proportional to the square root of the pressure head (i.e., H112), weir flow rates are at best about proportional to the pressure head and may be as sensitive as H5/2.

In accordance with the foregoing, the liquid coolant distribution system of the present invention includes: a plurality of shank coolant channels located in the shank portion of a turbine bucket and extending to platform cooling channels located in the platform portion of a turbine bucket that extend into foil cooling channels located in the air foil of the turbine bucket; and metering means for receiving coolant from a source of liquid coolant and for distributing the coolant evenly into each of the platform coolant supply channels, the metering means including a plurality of resistance flow devices.

For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that this invention is not limited to the precise arrangements and intrumentalities shown.

Figure 1 is a perspective view of a first embodiment of the improved cooling system of the present invention.

Figure 2 is a side plan view of a single turbine bucket and distribution channel formed in accordance with the present invention.

Figure 3 is an exploded view of a distribution channel forming part of the cooling system of Figure 1.

Figure 4 illustrates the interrelationship between the distribution channel inner member of Figure 3 and certain coolant channels formed in the distribution channel outer housing of Figure 2.

Figure 5 is a cross-sectional view taken along line 6-6 of Figure 4 illustrating a first embodiment of a flow resistance device which may be used in accordance with the principles of the present invention.

Figure 6 is a cross-sectional view taken along line 6-6 of Figure 4 illustrating a second flow resistance device which may be used in accordance with the principles of the present invention.

Figure 7 is a cross-sectional view taken along line 6-6 of Figure 4 illustrating a third flow resistance device which may be used in accordance with the principles of the present invention.

Figure 8 is a cross-sectional view taken along line 8-8 of Figure 7.

Figure 9 is a cross-sectional view illustrating internal passages of the flow resistance device of Figure 7.

Figure 10 is a cross-sectional view taken along line 10-10 of Figure 7.

Referring now to the drawings, wherein like numerals indicate like elements, there is shown in Figure 1 a turbine bucket constructed in accordance with the principles of the present invention and designated generally as 10. Bucket 10 includes a root portion 12, a shank portion 14, a platform portion 16 and an air foil 18. Root portion 12 is embedded in a turbine rotor disk 20 which is mounted on a shaft (not shown) rotatably supported in a casing (not shown). As will be recognized by those skilled in the art, an actual turbine will include a plurality of buckets 10 located about the entire periphery of the rotor disk 20.

As noted above, the present invention is directed towards an improved cooling system for use with gas turbines of the general type illustrated in Figure 1. Passage 94 directs the coolant liquid to stand pipe 96, which is integral with distribution channel 28 located beneath the root portion 12 of bucket 10. The structure of distribution channel 28 is illustrated in Figures 2-10 and is described in detail below. The coolant liquid supplied by passage 94 collects in stand pipe 96 of distribution channel 28 and is thereafter metered into a plurality of shank coolant channels 78 formed in the shank 14.

As best shown in Figure 4, a plurality of trap seals 98 are interposed in shank coolant channels 78 (preferably at the bottom thereof) to permit the passage of liquid coolant from distribution channel 28 to coolant channels 78 but prevent the passage of coolant vapor from coolant channel 78 to distribution channel 28.

As best illustrated in Figure 1, shank coolant channels 78 extend from distribution channel 28 to a plurality of platform coolant channels 30 (only two of which are shown) formed in platform 16 that in turn lead to foil coolant channels 32 formed in the foil 1 8. The foil coolant channels 32 extend in a generally radial direction throughout the outer perimeter of air foil 1 8 and serve to cool the foil.

As shown in Figure 1, the distribution channel 28 has a flattened top 22 which mates with a flattened bottom 62 of the turbine bucket 10 when the bucket and distribution channel are placed in the dovetail opening formed in rotor disk 20. Both surfaces 62, 22 are machined flat and parallel with the convolutions of the dovetail slot so that the centrifugal force applied to distribution channel 28 when the turbine is rotating ensures parallelism between these surfaces and the dovetail slots.

The detailed structure of distribution channel 28 will now be described with reference to Figures 2-10.

As shown in Figure 3, distribution channel 28 comprises two parts: an outer casing 68, and a cylindrical member 48. Outer casing 68 fits under the bottommost convolution of the dovetail slot in; rotor disk 20. A cylindrical bore 74 is formed in outer casing 68 and receives member 48 in interference fit therewith. A plurality of coolant channels 76 are formed in the top of casing 68 and each extends from bore 74 to flat upper surface 22. Coolant channels 76 are equal in number to the number of platform cooling channels 30 and are each connected to a respective platform coolant channel 30 by one of the shank coolant channels 78.

Member 48 has a hollow cylindrical central section 80, a threaded extension section 82, a coolant supply receiving section 84 and a side cover 50 which may, if desired, be formed integrally with member 48. The outer diameter of central section 80 is substantially identical to the inner diameter of bore 74 to ensure an interference fit when central section 80 is placed in bore 74. The length of central section 80 is equal to the length of bore 74 such that sections 82 and 84 extend beyond opposite ends of outer casing 68.

When distribution channel 28 has been placed in its position within the dovetail slot formed in rotor disk 20 (see Figure 1), threaded extension section 82 extends through an opening 90 in ring 34. In the preferred embodiment, the external threads on extension section 82 engage a retaining nut 92 which serves to lock ring 34 to rotor disk 20.

Coolant supply receiving section 84 of member 48 extends out the opposite side of casing 68.

Coolant fluid enters plenum 64 through stand pipe 96 which communicates with passage 94 formed in section 34.

A plurality of grooves 56 are formed around the outer perimeter of central section 80 at spaced intervals corresponding to the spacing of coolant channels 76 formed in outer casing 68 such that each groove 56 cooperates with a different shank coolant channel 78. Liquid coolant supplied to supply plenum 64 exits member 48 via individual exit openings 58 formed in each of the grooves 56. A respective flow resistance device 66 (see Figures 5-1 0) is located between supply plenum 64 and each exit opening 58 and meters the flow of liquid coolant into its respective opening 58.

The manner in which liquid coolant is supplied to coolant channels 76 by distribution channel 28 can best be understood with reference to Figure 4.

Figure 4 depicts the right-hand portion of distribution channel 28 after it has been placed ini position within the dovetail slot formed in rotor 20, beneath root portion 1 2 of bucket 10. As the bucket rotates about the central axis of the turbine, the coolant fluid is forced in a radial outward direction by centrifugal force. As such, the coolant flows through stand pipe 96 into the supply plenum 64 where it collects on the radially outward wall of plenum 64. The coolant distributes throughout the distribution channel 28 and builds up in height until it passes through the flow resistance device 66 and flows through the opening 58 and into the groove 56.The sometered coolant flows into its associated outer casing cooling channel 76 and thereafter to a corresponding shank coolant channel 78, platform coolant channel 30 and foil coolant channel 32.

Three separate embodiments of flow resistance devices which may be utilized in connection with the present invention are illustrated in Figures 5-10. While these structures represent the preferred flow resistance devices, it should be recognized that a large number of different flow resistance devices can be used without departing from the spirit and scope of the present invention as long as such devices meter a liquid coolant into the individual coolant channels 76 in such a manner that the flow of coolant through such devices does not depend upon a stable, uniform water surface fo accurate metering.

Referring now to Figure 5, a first embodiment of a flow resistance device 66 is illustrated. In this embodiment, the flow resistance device 66 comprises a tortuous path 88 comprising a series of bends. In order to operate properly, it is essential that these passages be filled with liquid in order to generate the requisite losses. This is ensured when the liquid coolant flows radially inward against the "G" field, as shown. Head losses at each bend contribute to the total resistance of the passage. Passages of relatively large size are possible. For example, passages having a minimum cross-section dimension of 0.025 inches have been found to operate satisfactorily.

The relationship between flow and pressure drop as a function of the size and shape of constituent bend elements of the tortuous path may be found in the "Handbook of Hydraulic Resistance" authored by I. E. Idel'Chik. Since the particular size and shape of the tortuous path does not make up part of the present invention, a further discussion of the manner in which these parameters affect flow characteristics will not be set forth herein.

While the tortuous path 88 may be formed in any desired manner, one simple process is to form the path by laminating a plurality of wafer-like plates 70 each of which has been formed with an opening at the location corresponding to the tortuous path 88. These openings may be formed, for example, by using known photo-etching technology similar to that used in producing fluidic devices.

The operation of flow resistance device 66, as illustrated in Figure 5, is as follows. As the buckets 10 are rotated about the axis of rotor disk 20, the artificially generated "G" field causes the liquid coolant to flow through supply plenum 64 pressing against the radially outward wall thereof.

The height of the liquid coolant builds up and passes through a "last chance" strainer 72 locatec adjacent plenum 64. A separate strainer 72 is provided for each flow resistance device 66. The height of the liquid coolant continues to flow through the tortuous path 88 until it flows out the opening 58 into the groove 56 formed in the distribution channel 28. This liquid then flows into the coolant channel 76 and through its associated bucket coolant channel.

In operation, debris which is heavier than the liquid coolant is centrifuged away from strainer 72 to the bottom 54 of plenum 64. As a result, the openings formed in strainer 72 need only be smaller in diameter than the minimum dimension of tortuous path 88. In the preferred embodiment, strainer 72 is a metallic plate having a plurality of openings formed therein.

A second flow resistance device 66 which may be used in connection with the present invention is illustrated in Figure 6. In this embodiment, an orifice 46 is used to create the desired head losses. While a single orifice 46 is illustrated, a plurality of orifices may be used. As in the embodiment of Figure 6, the flow resistance device of Figure 6 includes a strainer 72 adapted to prevent small debris from fiowing into, and thereby clogging, orifice 46. In comparative tests, it has been found that bucket channel flow will vary as a function of the square root of the water head H (see Figure 4) when using an orifice such as that illustrated in Figure 6. In comparison, the channel flow varies as a function of H5'2 using a "V" shaped notched weir such as that described in U.S.Application Serial No. 044,660. In the illustrated embodiment, orifice 46 is formed as a projection in a cylindrical flow path 58. Other orifices may, however, be used.

A third embodiment of a flow resistance device 66 constructed in accordance with the principles of the present invention is illustrated in Figures 7-10. In this embodiment, the flow resistance device takes the form of a plurality of vortex chambers 81, 83, 85 and 87. Liquid coolant located in supply plenum 64 passes through strainer 72 and flows into a first vortex chamber 81 wherein it is agitated in the known manner (see Figures 8, 9 and 10). The agitated coolant leaves vortex chamber 81 via a cylindrical opening 79 into a second vortex chamber 83.

As best illustrated in Figures 8, 9 and 10, liquid coolant in vortex chamber 83 passes into vortex chamber 85 via a linear passage 77. Liquid coolant leaves vortex chamber 85 via opening 75 and enters fourth vortex chamber 87 (see Figures 8, 9 and 10). Finally, the liquid coolant leaves vortex chamber 87 via passage 73 wherein it exits via opening 58 into groove 56.

Having described the structure and -Jr oration of the preferred flow resistance devices, the manner in which coolant flows from liquid coolant source through the entire bucket 10 will now be described. The buckets 10 receive a driving force from a hot fluid moving in a direction generally parallel to the axis of rotation of rotor disk 20. The driving force of the hot fluid is transmitted to the shaft about which the rotor disk 20 is mounted via the buckets 10 and rotor disk 20 causing the turbine to rotate about the axis of the shaft. The high rotational velocity of the rotor creates a substantial centrifugal force which urges the liquid coolant through the bucket in a' radially outward direction.As the liquid coolant enters coolant supply passage 94, it is forced in a radially outward direction into stand pipe 96 where it is collected in distribution channel 28. When the level of coolant in supply plenum 64 overflows, it passes through the individual flow resistance devices 66 into the respective platform cooling channels 76 and thereafter into the respective shank coolant channels 78. The coolant continues to advance in a generally radial direction to platform and foil cooling passages 30 and 32 to the tip of foil 18.

In the foregoing embodiment, distribution channel 28 is located in the wheel rim 20 below the bucket 10.

Although several preferred embodiments of this invention have been described, many variations and modifications will now be apparent to those skilled in the art, and it is therefore preferred that the instant invention be limited not by the specific disclosure herein, but only by the appending

Claims

claims. CLAIMS

1. An improved liquid coolant distribution system for a gas turbine of the type including a turbine disk mounted on a shaft rotatably supported in a casing, at least one turbine bucket extending radially outward from said disk, said bucket including a root portion mounted in said disk, a shank portion extending radially outward from said root portion to a platform portion, and an air foil portion extending radially outward from said platform portion, said distribution system comprising:: (a) a plurality of coolant channels located in said bucket and extending into said air foil portion; and (b) metering means for receiving coolant from a source of liquid coolant and for distributing said coolant evenly into each of said coolant channels, said metering means including a plurality of flow resistance devices, each of said flow resistance devices being associated with a respective one of said coolant channels and metering liquid coolant received by said metering means into its respective coolant channel.

2. The improved liquid coolant distribution system of Claim 1 , wherein said flow resistance devices each comprise a tortuous path formed of plurality of bends.

3. The improved liquid coolant distribution system of Claim 1, wherein said flow resistance devices each comprise a flow resistant orifice.

4. The improved liquid coolant distribution system of Claim 1, wherein said flow resistance devices each include a plurality of vortex flow chambers.

5. The improved liquid coolant distribution system of Claim 1, wherein said metering means comprises: (1) a hollow cylindrical tube having a plurality of grooves formed at spaced intervals about an outer periphery thereof; (2) a supply plenum formed in said cylindrical tube and extending past said plurality of grooves; (3) each of said flow resistance devices providing a flow path between said supply plenum and a respective one of said grooves, each of said grooves supplying liquid coolant to a respective one of said platform coolant channels.

6. The improved liquid coolant distribution system of Claim 5, wherein each of said flow resistance devices comprises a tortuous path formed of a plurality of bends.

7. The improved liquid coolant distribution system of Claim 5, wherein each of said flow resistance devices comprises a flow resistant orifice.

8. The improved liquid coolant distribution system of Claim 5, wherein each of said flow resistance devices comprises a plurality of vortex flow chambers.

9. The improved liquid coolant distribution system of any one of Claims 1, 5, 6, 7 or 8, further including a respective strainer located between said supply plenum and each of said flow resistance devices.

10. The improved liquid coolant distribution system of any one of Claims 1, 5, 6, 7, or 8, wherein said flow resistance devices are located radially inward of said supply plenum.

11. A liquid coolant distribution system for a gas turbine, substantially as described herein with reference to the accompanying drawings.