Airfoil for a turbine of a gas turbine engine

1. An airfoil for a turbine of a gas turbine engine comprising:

a main body comprising a wall structure defining an inner cavity adapted to receive cooling air, said wall structure including a plurality of first diffusion regions, at least one first metering opening extending from said inner cavity to each of said first diffusion regions so as to deliver cooling air from said inner cavity into each said first diffusion region, said wall structure further comprising at least one cooling circuit associated with each said first diffusion region, said cooling circuits each comprising:

a second diffusion region; and

at least one second metering opening extending from said respective first diffusion region to said second diffusion region so as to deliver cooling air from said respective first diffusion region into said second diffusion region, said at least one second metering opening including a length in a flow direction and first and second dimensions transverse to one another and to said length such that a first ratio of said length to said first dimension is equal to or greater than about 1.5:1 and a second ratio of said length to said second dimension is equal to or greater than about 1.5:1.

2. The airfoil as set out in claim 1 , wherein said first and second dimensions of said at least one second metering opening of each said cooling circuit are defined by a diameter of said at least one second metering opening.

3. The airfoil of claim 1 , wherein each said cooling circuit further comprises at least one third metering opening and at least one third diffusion region, said at least one third metering opening extending from a respective one of said second diffusion regions to said at least one third diffusion region so as to deliver cooling air from said respective second diffusion region into said at least one third diffusion region.

4. The airfoil of claim 3 , wherein said at least one third metering opening of each said cooling circuit having a length in a flow direction and first and second dimensions transverse to one another and to said length such that a first ratio of said length of said at least one third metering opening to said first dimension of said at least one third metering opening is equal to or greater than about 1.5:1 and a second ratio of said length of said at least one third metering opening to said second dimension of said at least one third metering opening is equal to or greater than about 1.5:1.

5. The airfoil of claim 3 , wherein said at least one third diffusion region of each said cooling circuit comprises a plurality of third diffusion regions and said at least one third metering opening comprises a plurality of third metering openings, each of said plurality of third metering openings extending from said respective second diffusion region to a corresponding one of said plurality of third diffusion regions.

6. The airfoil of claim 5 , wherein said wall structure comprises inner and outer wall sections, first, second and third intermediate wall sections extending between said inner and outer wall sections, and a plurality of ribs extending between said inner and outer wall sections, said plurality of third metering openings and said plurality of third diffusion regions of each said cooling circuit being defined by corresponding portions of said inner and outer wall sections, corresponding portions of said first and third intermediate wall sections and said plurality of ribs.

7. The airfoil of claim 6 , wherein said at least one second metering opening of each said cooling circuit comprises a plurality of second metering openings, and each of said plurality of ribs being substantially in-line with a corresponding one of said second metering openings such that cooling air exiting each of said plurality of second metering openings impinges upon a corresponding one of said ribs.

8. The airfoil of claim 7 , wherein each said second diffusion region is defined by corresponding portions of said inner and outer wall sections and corresponding portions of said first, second and third intermediate wall sections, and a summation of a volume of each of said plurality of second metering openings define a second metering opening summation volume and a ratio of a volume of said second diffusion region relative to the second metering opening summation volume is greater than about 20:1.

9. The airfoil of claim 5 , wherein at least one of said cooling circuits further comprises a fourth diffusion region communicating with each of said plurality of third diffusion regions and terminating at an exit opening defined by curvilinear wall portions of said wall structure, said exit opening having an area equal to or greater than about 10 times an area of said third metering openings.

10. The airfoil of claim 1 , wherein at least one of said cooling circuits is located in a trailing edge of said main body such that a longitudinal axis of said at least one first metering opening is generally parallel with a longitudinal axis of said at least one second metering opening.

11. A vane for a turbine of a gas turbine engine comprising:

first and second endwalls; and

an airfoil comprising a main body located between said first and second endwalls, said main body including a wall structure having a first end adjacent said first endwall and a second end adjacent said second endwall, said wall structure defining an inner cavity adapted to receive cooling air and comprising a plurality of first diffusion regions extending from said first end of said wall structure to said second end of said wall structure and at least one first metering opening extending from said inner cavity to each of said first diffusion regions so as to deliver cooling air from said inner cavity into each said first diffusion region, said wall structure further comprising first and second cooling circuits associated with each said first diffusion region, each of said first and second cooling circuits comprising:

a second diffusion region; and

at least one second metering opening extending from said respective first diffusion region to said second diffusion region so as to deliver cooling air from said respective first diffusion region to said second diffusion region.

12. The vane of claim 11 , wherein said at least one second metering opening in each of said first and second cooling circuits includes a length in a flow direction and first and second dimensions transverse to one another and to said length such that a first ratio of said length to said first dimension is equal to or greater than about 1.5:1 and a second ratio of said length to said second dimension is equal to or greater than about 1.5:1.

13. The vane of claim 11 , wherein each of said first and second cooling circuits further comprises at least one third metering opening and at least one third diffusion region.

14. The vane of claim 13 , wherein said at least one third diffusion region in each of said first and second cooling circuits comprises a plurality of third diffusion regions.

15. The vane of claim 14 , wherein said at least one third metering opening in each of said first and second cooling circuits comprises a plurality of third metering openings, each of said third metering openings of each said first cooling circuit extending from said second diffusion region of said respective first cooling circuit to a corresponding one of said third diffusion regions of said first cooling circuit so as to deliver cooling air from said second diffusion region of said respective first cooling circuit into said third diffusion regions of said respective first cooling circuit and each of said third metering openings of each said second cooling circuit extending from said second diffusion region of said respective second cooling circuit to a corresponding one of said third diffusion regions of said second cooling circuit so as to deliver cooling air from said second diffusion region of said respective second cooling circuit into said third diffusion regions of said respective second cooling circuit.

16. The vane of claim 15 , wherein said wall structure comprises first, second and third intermediate wall sections, a plurality of first ribs, and inner and outer wall sections, said plurality of third diffusion regions of each said first cooling circuit being defined by corresponding portions of said inner and outer wall sections, corresponding portions of said first and third intermediate wall sections and said plurality of first ribs.

17. The vane of claim 16 , wherein said at least one second metering opening in each said first cooling circuit comprises a plurality of second metering openings, and each of said plurality of first ribs in each said first cooling circuit being substantially in-line with a corresponding one of said second metering openings in said corresponding first cooling circuit such that cooling air exiting each of said plurality of second metering openings in said corresponding first cooling circuit impinges upon a corresponding one of said first ribs in said corresponding first cooling circuit.

18. The vane of claim 14 , wherein at least one of said first cooling circuits further comprises a fourth diffusion region communicating with each of said plurality of third diffusion regions of said corresponding first cooling circuit and a first exit opening defined by corresponding curvilinear wall portions of said wall structure and at least one of said second cooling circuits further comprises a fourth diffusion region communicating with each of said plurality of third diffusion regions of said corresponding second cooling circuit and a second exit opening defined by corresponding curvilinear wall portions of said wall structure.

19. The vane of claim 18 , wherein at least one of said first cooling circuits is located in a trailing edge of said main body such that a longitudinal axis of said corresponding at least one first metering opening is generally parallel with a longitudinal axis of said at least one second metering opening of said corresponding first cooling circuit.