Domed tip cap and related method
A bucket for a turbine includes a dovetail mounting portion, a shank portion defined at a radially outer end thereof by a platform, and an airfoil portion extending radially outward of the platform. The airfoil portion has a radially outer end closed by a tip cap having a non-planar shape that reduces stress in the tip cap during use. A related method of reducing stress in a tip cap of a turbine bucket includes providing an airfoil portion of the turbine bucket with a radially outer end; and closing the radially outer end with a tip cap having a non-planar shape that reduces stress in the tip cap during use.
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This invention relates to turbine technology and, more specifically, to cap constructions for turbine buckets or blades. Traditionally, tip caps have been used to cover the tips of airfoil portions of turbine buckets that have internal serpentine cooling circuits. These tip caps are manufactured from flat plate stock and are typically either welded to the radially outer end of the airfoil portion of the bucket, or cast in with the airfoil portion. In either case, the flat tip caps are subject to high stresses during operation.
BRIEF SUMMARY OF THE INVENTIONIn one exemplary but non-limiting embodiment, a tip cap insert is adapted to be welded to the radially outer end of a bucket airfoil portion. In accordance with this embodiment, the tip cap is in the shape of an inverted dome, i.e., it is substantially concave in a radially inward direction (as seen from the exterior of the bucket).
The tip cap is also formed with a peripheral flange adapted to seat on an internal shoulder within the airfoil portion to which the tip cap is welded.
In another exemplary but non-limiting embodiment, the domed tip cap is cast integrally with the airfoil portion and other airfoil features of the bucket.
Accordingly, in one aspect, there is provided a bucket for a turbine comprising a dovetail mounting portion, a shank portion defined at a radially outer end thereof by a platform, and an airfoil portion extending radially outward of the platform, the airfoil portion having a radially outer end closed by a tip cap wherein one or both of an interior and exterior surface of the tip cap is formed of a non-planar shape that reduces stress in the tip cap during use.
In another aspect, there is provided a bucket for a turbine comprising a dovetail mounting portion, a shank portion defined at a radially outer end thereof by a platform, and an airfoil portion extending radially outward of the platform, the airfoil portion having a radially outer end closed by a tip cap wherein at least an interior surface of the tip cap is domed in a radially inward direction; and wherein the tip cap is formed with one or more internal ribs.
In still another aspect, there is provided a method of reducing stress in a tip cap of a turbine bucket comprising an airfoil portion of the turbine bucket with a radially outer end; and closing the radially outer end with a tip cap having a non-planar shape that reduces stress in the tip cap during use.
A more detailed description will now be provided in connection with the drawings identified below.
With reference to
Turning now to
In another exemplary but non-limiting embodiment illustrated in
By imparting an inverted dome shape to the (i.e., planar) tip cap, bending stresses typically associated with flat tip caps can be reduced. In some cases, the stress-reducing benefit of the dome cap may be sufficient to justify elimination of rib welds that are traditionally used to secure the tip caps to their respective airfoils. It will be appreciated that the curvature of the tip cap dome is optimized to provide stress reduction to all regions of the tip cap, regardless of the span being covered. In addition, the domed tip cap may be provided with known surface features (such as turbulators) to enhance convection (see, for example, internal ribs 122 in
The dome shape of the tip cap also enables a reduction in required material capability and/or material thickness, and increased operating temperatures of the tip cap may be possible without altering the material composition. In addition, wider openings can be covered than with flat designs of the same material and thickness.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims
1. A bucket for a turbine comprising a dovetail mounting portion, a shank portion defined at a radially outer end thereof by a platform, and an airfoil portion extending radially outward of said platform, said airfoil portion having a radially outer end closed by a tip cap wherein one or both of an interior and exterior surface of the tip cap is formed of a non-planar shape that reduces stress in the tip cap during use.
2. The bucket of claim 1 wherein said non-planar shape is domed in a radially inward direction.
3. The bucket of claim 2 wherein said tip cap is cast-in with said airfoil portion.
4. The bucket of claim 1 wherein said tip cap is welded to said airfoil portion.
5. The bucket of claim 4 wherein said tip cap is formed with a peripheral flange seated on a shoulder formed in said airfoil portion.
6. The bucket of claim 1 wherein said tip cap is formed with one or more internal ribs.
7. A bucket for a turbine comprising a dovetail mounting portion, a shank portion defined at a radially outer end thereof by a platform, and an airfoil portion extending radially outward of said platform, said airfoil portion having a radially outer end closed by a tip cap;
- wherein at least an exterior surface of said tip cap is domed in a radially inward direction; and
- wherein said tip cap is formed with one or more internal ribs.
8. The bucket of claim 7 wherein said tip cap is cast-in with said airfoil portion.
9. The bucket of claim 7 wherein said tip cap is welded to said airfoil portion.
10. The bucket of claim 9 wherein said tip cap is formed with a peripheral flange seated on a shoulder formed in said airfoil portion.
11. A method of reducing stress in a tip cap of a turbine bucket comprising providing an airfoil portion of the turbine bucket with a radially outer end; and
- closing the radially outer end with a tip cap having a non-planar shape that reduces stress in the tip cap during use.
12. The method of claim 11 including welding the tip cap to the airfoil portion.
13. The method of claim 12 wherein the tip cap is seated on an internal flange in the airfoil portion.
14. The method of claim 11 wherein the tip cap is cast in with the airfoil portion.
15. The method of claim 11 wherein said tip cap is formed with one or more internal ribs.
16. The method of claim 11 wherein interior and exterior surfaces of said tip cap are domed in a radially inward direction.
17. The method of claim 11 wherein an exterior surface of said tip cap is domed in a radially inward direction.
Type: Application
Filed: Jun 25, 2007
Publication Date: Dec 25, 2008
Applicant: General Electric Company (Schenectaday, NY)
Inventors: Louis Veltre (Simpsonville, SC), William S. Zemitis (Simpsonville, SC), Gary C. Liotta (Simpsonville, SC)
Application Number: 11/819,030
International Classification: F01D 5/18 (20060101);