Spring seal for turbine dovetail

A spring seal system for a turbine dovetail tab. The spring seal system may include a sealing slot positioned about the tab and a spring seal positioned within the sealing slot. The spring seal may include a substantial “U” shape.

TECHNICAL FIELD

The present application relates generally to any type of turbine and more particularly relates to systems and methods for sealing a gap formed between a turbine bucket dovetail and a turbine rotor via a spring seal.

BACKGROUND OF THE INVENTION

Gas turbines generally include a turbine rotor (wheel) with a number of circumferentially spaced buckets (blades). The buckets generally may include an airfoil, a platform, a shank, a dovetail, and other elements. The dovetail of each bucket is positioned within the turbine rotor and secured therein. The airfoils project into the hot gas path so as to convert the kinetic energy of the gas into rotational mechanical energy. A number of cooling medium passages may extend radially through the bucket to direct an inward and/or an outward flow of the cooling medium therethrough.

Leaks may develop in the coolant supply circuit based upon a gap between the tabs of the dovetails and the surface of the rotor due to increases in thermal and/or centrifugal loads. Air losses from the bucket supply circuit into the wheel space may be significant with respect to blade cooling medium flow requirements. Moreover, the air may be extracted from later compressor stages such that the penalty on energy output and overall efficiency may be significant during engine operation.

Efforts have been made to limit this leak. For example, one method involves depositing aluminum on a dovetail tab so as to fill the gap at least partially. Specifically, a circular ring may be pressed against the forward side of the dovetail face. Although this design seals well and is durable, the design cannot be easily disassembled and replaced in the field. Rather, these rings may only be disassembled when the entire rotor is disassembled.

There is thus a desire for improved dovetail tab sealing systems and methods. Such systems and methods should adequately prevent leakage therethrough so as to increase overall system efficiency while being installable and/or repairable in the field.

SUMMARY OF THE INVENTION

The present application thus provides a spring seal system for a turbine dovetail tab. The spring seal system may include a sealing slot positioned about the tab and a spring seal positioned within the sealing slot. The spring seal may include a substantial “U” shape.

The present application further provides a spring seal system for a turbine dovetail tab. The spring seal system may include a sealing slot positioned about the tab and a spring seal positioned within the sealing slot. The sealing slot may define a first leg and a second leg. The spring seal may include an opening facing the second leg.

The present application further provides a method of sealing a gap between a dovetail tab and a rotor of a turbine. The method includes the steps of positioning a spring seal within a sealing slot of the dovetail tab, operating the turbine, and expanding the spring seal into the gap.

These and other features 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.

DETAILED DESCRIPTION

Referring now to the drawings, in which like numerals refer to like elements throughout the several views,FIG. 1Ashows a bucket10as may be used herein. The bucket10may be a first or a second stage bucket as used in a 7FA+e gas turbine sold by General Electric Company of Schenectady, N.Y. Any other type of bucket or stage also may be used herein. The bucket10may be used with a rotor20as is shown inFIG. 2.

As is known, the bucket10may include an airfoil30, a platform40, a shank50, a dovetail60, and other elements. It will be appreciated that the bucket10is one of a number of circumferentially spaced buckets10secured to and about the rotor20of the turbine. The bucket10ofFIG. 1Ahas a shroud65on one end of the airfoil30. A bucket11ofFIG. 1Blacks the shroud. Any other type of bucket design may be used herein.

As described above, the rotor20may have a number of slots25for receiving the dovetails60of the buckets10,11. Likewise, the airfoils30of the buckets10,11project into the hot gas stream so as to enable the kinetic energy of the stream to be converted into mechanical energy through the rotation of the rotor20. The dovetail60may include a first tang or tab70and a second tab80extending therefrom. Similar designs may be used herein. A gap90may be formed between the ends of the tabs70,80of the dovetail60and the rotor20. A high pressure cooling flow may escape via the gap90unless a sealing system of some type is employed.

FIGS. 3-6show a spring seal100as is described herein. As is shown, the spring seal has an axial opening110along one side thereof. In other words, the spring seal100is largely tube like in shape with a portion removed so as to form a substantial “C” shape along its cross-section. The spring seal100also may be in the form a substantial “U” shape so as to fit within the dovetail tab70,80. Other shapes and configurations may be used herein.

The spring seal100may be made out of a high temperature resistant material with elastic characteristics. Examples include alloys of nickel, iron, or cobalt, various types of stainless steels, and other types of materials. An alloy may be a cobalt based super alloy such as Inconnel X-750, A-286, and similar materials. The spring seal100may be a single element or several sections may be joined together. The spring seal100may be made by rolling a sheet of material into a “C” shape and then forming the “C” shape into the final design such as the “U” shape shown. Alternatively, the spring seal100may be formed as a continuous ring which then may be milled to create the “C” cross-section and then cut in half to yield two (2) “U” shaped seals. The use of the “U” shape allows the spring seal100to be used with the tabs70,80as will be described in more detail below.

FIGS. 7 and 8show a spring seal system120as is described herein. The spring seal system120may be positioned about and within the first tab70of the dovetail60of the bucket10. The spring seal system120may include a sealing slot130positioned within the first tab70. The sealing slot130may extend about the parameter of the first tab70in whole or in-part. The dimensions and shape of the sealing slot130may vary. The sealing slot130may be formed with conventional machining techniques or other types of manufacturing technique. The spring seal system120also may be used with the second tab80and elsewhere.

The sealing slot130defines a first leg140and a second leg150within the tab70and with the sealing slot130therebetween. The first leg140may be positioned adjacent to a high pressure side160of the dovetail60. The high pressure side160may provide the bucket cooling air supply. The second leg150may be positioned about a low pressure side170, i.e., the wheel space.

The spring seal100may be positioned within the sealing slot130of the spring seal system120. The axial opening110may face the second leg150and the low pressure side170. Other orientations and configurations of the spring seal100may be used herein. Upon operation of the bucket10, the spring seal100expands into the gap90so as to block or reduce the loss of cooling fluid. Specifically, the spring seal100compresses upon assembly and expands upon turbine operation due to its inherent elastic characteristics.

FIG. 9shows an alternative embodiment of a spring seal180. The spring seal180is similar to the spring seal100above but with a radial opening190along one side thereof. Specifically, a portion of the diameter is removed or is missing so as to form the radial opening190. The spring seal180may be positioned within the sealing slot130in a manner similar to that described above.

The spring seal100,180may come in any shape or orientation including those in a substantial “E”, “W”, “V”, “O”, or other common seal shapes. The opening, such as the axial opening110, the radial opening190, and the like, may be positioned either parallel to the leakage path or perpendicular to it. Other configurations also may be used herein.

Use of the sealing system100thus reduces leakage through the gap90. Sealing efficiency similar to that of the commonly used aluminum coating thus may be found and improved upon without the use of the aluminum material. The reduction of cooling flow leakage improves overall system efficiency. The spring seal system120may be used with other sealing systems and methods.