Cooling system for the trailing edges of turbine bucket airfoils
The cooling system includes a plurality of generally radially extending passages within the airfoil for convectively cooling the airfoil. A predetermined number of the passages exit through the airfoil tip. One or more of the remaining passages exit into a plenum adjacent the trailing edge and airfoil tip region of the airfoil and flow radially inwardly along one or more passageways adjacent the trailing edge region. The passageways exit in openings along the pressure side of the airfoil. In this manner, the trailing edge region is convectively cooled as well as film cooled by the film of air exiting the holes.
1. A cooling system for a turbine bucket comprising:
an airfoil, a base and a platform interfaced between the airfoil and base;
said airfoil having a plurality of passages extending generally radially therealong for communication with a supply of cooling medium at radial inner ends thereof and convectively cooling the airfoil as the cooling medium flows generally radially outwardly along the passages toward a tip of the airfoil;
a predetermined number of said passages having exit openings adjacent said airfoil tip for flowing spent cooling medium into a hot gas path of the turbine;
at least one remaining passage of said plurality of passages being in communication adjacent the tip of the airfoil with a cooling passageway extending generally inwardly along a trailing edge region of the airfoil for convectively cooling the trailing edge region,
said passageway terminating in an exit hole along one side and intermediate the length of the airfoil for film cooling the trailing edge along said one airfoil side.
2. A system according to claim 1 wherein said hole exits through the pressure side of the airfoil.
3. A system according to claim 2 wherein said hole has an elliptical profile along said pressure side.
4. A system according to claim 1 wherein said passageway extends along a path closer to the trailing edge than said one passage.
5. A system according to claim 1 wherein remaining passages of said plurality of passages lie in communication adjacent the tip of the airfoil with at least two passageways extending generally radially inwardly along the trailing edge region of the airfoil for convectively cooling the trailing edge region of the airfoil, said two passageways terminating in exit holes along said one side and intermediate the length of the airfoil for film cooling the trailing edge along said one airfoil side.
6. A system according to claim 5 wherein said exit holes lie at different radial locations along the length of said airfoil.
7. A system according to claim 1 wherein said airfoil includes a crossover plenum adjacent said airfoil tip in communication with an outlet of said one remaining passage and an inlet to said passageway.
8. A system according to claim 7 wherein said plenum opens through the tip of the airfoil and a cover closes the plenum at the tip of the airfoil.
9. A system according to claim 8 wherein said plenum has a base spaced radially inwardly of the airfoil tip.
10. A system according to claim 8 wherein said base is inclined radially inwardly in a direction toward said trailing edge.
11. A system according to claim 1 wherein remaining passages of said plurality of passages lie in communication adjacent the tip of the airfoil with at least two passageways extending generally radially inwardly along the trailing edge region of the airfoil for convectively cooling the trailing edge region of the airfoil, said two passageways terminating in exit holes along said one side and intermediate the length of the airfoil for film cooling the trailing edge along said one airfoil side, said plenum including a crossover plenum adjacent said airfoil tip in communication with outlets of said remaining passages and inlets to said two passageways.
12. A system according to claim 11 wherein said plenum opens through the tip of the airfoil and a cover closes the plenum at the tip of the airfoil.
13. A system according to claim 12 wherein said plenum has a base spaced radially inwardly of the airfoil tip and inclined in a radial inward direction toward said trailing edge.
14. A system according to claim 13 wherein said exit holes of said passageways lie at different radial locations along the length of said airfoil.
15. A method of cooling a trailing edge region of an airfoil forming part of a turbine bucket having a base and a platform interfaced between the airfoil and base comprising the steps of:
providing said airfoil with a plurality of passages extending generally radially therealong toward a tip of the airfoil;
flowing a cooling medium generally radially outwardly along said passages toward the airfoil tip for convectively cooling the airfoil;
providing exit openings adjacent said airfoil tip for a predetermined number of said passages enabling flow of spent cooling medium into a hot gas path of the turbine;
communicating the cooling medium at a location adjacent the tip of the airfoil from at least one of remaining passages of said plurality of passages with a cooling passageway extending generally radially inwardly along a trailing edge region of the airfoil for convectively cooling the trailing edge region; and
terminating the passageway in an exit hole along one side of the airfoil intermediate the length of the airfoil for film cooling the trailing edge along said one airfoil side.
16. A method according to claim 15 including providing a crossover plenum adjacent the tip of the airfoil for flowing cooling medium from an outlet of said one remaining passage into an inlet of said passageway.
17. A method according to claim 16 including securing a cover plate to the tip of the airfoil to close said plenum.