Radial seal pin   

TECHNICAL FIELD

The present application relates generally to gas turbine engines and more particularly relates to a radial seal pin design for preventing leakage between gas turbine buckets.

BACKGROUND OF THE INVENTION

Gas turbines generally include a rotor with a number of circumferentially spaced blades or buckets. As is known, the buckets generally include an airfoil, a platform, a shank, a dovetail, and other elements. The dovetail may be positioned about a rotor and secured therein. The airfoils project into a hot combustion gas path produced by a combustor so as to convert the kinetic energy of the gas into rotational mechanical energy.

A radial seal pin may be used between the shanks of adjacent buckets so as to seal against cross-shank leakage with respect to gas turbines using long shank bucket designs. Generally described, the pin contacts a seal slot face angle under centrifugal load due to rotation and slides towards the side seal rails. The slot face angle forces the pin towards the adjacent bucket so as to prevent cross-shank leakage between two bucket shank cavities.

Current issues with such radial seal pins include mushrooming or flattened ends due to the use of low creep resistant material, buckling due to inadequate head space, pin binding, pin lockup, and simple pin wear. Moreover, leakage is still an issue even with properly functioning pins. Leakage areas include the shank inside diameter and outside diameter regions. The cross-shank leakage may lower the purge pressure in the bucket shank cavity. Such lower purge pressure may lead to possible hot gas ingestion and subsequent hardware distress.

There is thus a desire for improved radial seal pin designs for gas turbines. The improved radial seal pin design should adequately prevent or limit cross-shank leakage while being durable and reliable. Such improved sealing should provide improved cooling, increased bucket life, and overall increased system performance and efficiency.

SUMMARY

The present application thus provides a turbine bucket. The turbine bucket may include a shank, a radial seal pin slot positioned on the shank, and a seal pin positioned within the radial seal pin slot. The seal pin may include a pair of shouldered ends.

The present application further provides a turbine bucket. The turbine bucket may include a shank, a pair of radial seal pin slots positioned on the shank, and a seal pin positioned within each of the radial seal pin slots. The seal pin may include a pair of shouldered ends with a rounded portion and a flat portion.

These and other features and improvements of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a gas turbine engine.

FIG. 2 is a side view of a known rotor bucket.

FIG. 3 is a perspective view of a seal pin positioned in the radial seal pin slot of a rotor bucket.

FIGS. 4A and 4B are side views of shank leakage areas using known seal pins.

FIG. 5 is a perspective view of a radial seal pin slot of a rotor bucket.

FIG. 6 is an expanded view of the radial seal pin slot with a sealing pin therein as is described herein.

FIG. 7 is a side plan view of the seal pin of FIG. 6.

FIG. 8 is an expanded view of an end of the seal pin of FIG. 6.

FIG. 9 is a perspective view of the radial seal pin slot of FIG. 6.

FIG. 10 is a further perspective view of the radial seal pin slot of FIG. 6.

FIGS. 11A and 11B are side views of shank leakage areas filled by the seal pin of FIG. 6.

DETAILED DESCRIPTION

Referring now to the drawings, in which like numbers refer to like elements throughout the several views, FIG. 1 shows a side cross-sectional view of a gas turbine engine 10. As is known, the gas turbine engine 10 may include a compressor 12 to compress an incoming flow of air. The compressor 12 delivers the compressed flow of air to a combustor 14. The combustor 14 mixes the compressed flow of air with a compressed flow of fuel and ignites the mixture. (Although only a single combustor 14 is shown, the gas turbine engine 10 may include any number of combustors 14.) The hot combustion gases are in turn delivered to a turbine 16. The hot combustion gases drive the turbine 16 so as to produce mechanical work. The mechanical work produced in the turbine 16 drives the compressor 12 and an external load such as an electrical generator and the like.

The gas turbine engine 10 may use natural gas, various other types of syngas, and other types of fuels. The gas turbine engine may be a 9FBA heavy duty gas turbine engine offered by General Electric Company of Schenectady, N.Y. The gas turbine engine 10 may have other configurations and may use other types of components. Other types of gas turbine engines may be used herein. Multiple gas turbine engines 10, other types of turbines, and other types of power generation equipment may be used herein together.

FIG. 2 shows an example of a known rotor bucket 18. As is known, the rotor bucket 18 may include an airfoil 20 extending from a platform 22, a shank 24, and a dovetail 26. As described above, the dovetail 26 may be positioned about a rotor (not shown) and secured therein for rotation. The shank 24 may include a leading edge radial seal pin slot 28 and a trailing edge radial seal pin slot 30. Other rotor bucket designs may be used herein.

FIG. 3 shows the trailing edge radial seal pin slot 30 with a known seal pin 32 positioned therein. As is shown, the seal pin 32 generally has rounded ends 33. In this diagram, α is the bucket angle, i.e., the angle of a bucket cover plate 34; β is the seal pin angle, i.e., the angle of a seal pocket top face 35; Fc is the centrifugal force due to bucket rotation; Fp is the force normal to the seal pocket top face; Fs is the force along the seal pocket top; and Fr is the resultant frictional force. For effective sealing, Fs should be greater than Fr. Although not shown here, γ is the angle of a seal pocket corner 36. Generally described, the bucket angle α and the seal pocket face angle β accomplish the sideways loading of the pin 32. Specifically, centrifugal force will force the pin 32 against the seal pocket face 35. The angle γ of the seal pocket corner 36 then will force the pin 32 tangentially towards an adjacent bucket 37 so as to fill a gap 39 therebetween.

FIGS. 4A and 4B show the seal pin 32 positioned between the rotor bucket 18 and the adjacent bucket 37. FIG. 4A shows an outer diameter leakage gap 38. The outer diameter leakage gap 38 may be about equal to the ligament thickness of the top of the seal slots 28, 30. The ligament thickness generally relates to structural strength limitations. FIG. 4B shows an inner diameter leakage gap 40. The inner diameter leakage gap 40 may be about equal to the amount of binding tolerance on the seal pin 32. The binding tolerance generally accounts for different coefficients of thermal expansion between the seal material and the bucket material as well as transient operating conditions.

FIGS. 5 and 6 show a rotor bucket 100 as is described herein. As described above, the rotor bucket 100 may include an airfoil 110, a platform 120, a shank 130, and a dovetail 140. The shank 130 includes a pair of radial seal pin slots 150. Although only one radial seal pin slot 150 is shown, the shank 130 will include a leading edge and a trailing edge radial seal pin slot.

FIGS. 6 through 8 show a seal pin 160 as may be described herein. The seal pin 160 may have a first shouldered end 170 and a second shouldered end 180. As is shown, the shouldered ends 170 have a rounded portion 190 and a flat portion 200. The ends 170, 180 may be largely identical. The pin 160 may be slightly shorter than the seal pin slot 150 so as to provide for thermal growth and avoid pin binding.

The seal pin 160 may be made out of an Inconel 738 material (a nickel-chromium superalloy) or similar types of material with sufficient bulk creep strength. The pin 160 may be positioned within the slots 150 in any orientation. The pin 160 may be used in any stage of the turbine 16 or elsewhere.

As is shown in FIGS. 9 and 10, the shank 130 includes the bucket angle α. The seal pin slot 150 includes a seal pocket top face 210 with the angle β. The combination of angles α and β make the seal pin 160 move forward under centrifugal force. Likewise, the radial pin slot 150 includes an angled corner 250 with the angle γ. The angle γ makes the seal pin 160 move towards the shank 130 of the next bucket when the pin 160 moves sideways. Likewise, as shown in FIGS. 11A and 11B, the use of the shoulders 170, 180 fills the outer diameter gap 38 and the inner diameter gap 40 described above for improved performance.

Generally described, for determinate sealing:

Fs≧Fr

Fc sin(α+β)≧μFp

Fc sin(α+β)≧μFc cos(α+β)

tan(α+β)≧μ

μ=0.35

α+β≧19.3°

Likewise, angle γ should be greater than the frictional angle between the bucket material and the pin material to prevent pin lock up due to thermal growth during transient conditions:

Fs≧Fr

F sin(γ)≧μFp

F sin(γ)≧μF cos(γ)

tan(γ)≧μ

μ=0.35

γ≧19.3°

The present application thus provides better sealing between turbine stage buckets. Specifically, the leakage areas about the radial seal pins may be substantially reduced. Improved sealing provides improved efficiency due to low leakage and also may reduce hot gas ingestion and improve component reliability.

It should be apparent that the foregoing relates only to certain embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.