Turbine airfoil with local wall thickness control

1. A turbine airfoil for a gas turbine engine, the turbine airfoil comprising:

a root;

a tip;

an outer peripheral wall comprising:

an external surface, the outer peripheral wall enclosing an interior space; and

a concave pressure sidewall and a convex suction sidewall joined together at a leading edge and at a trailing edge,

wherein the outer peripheral wall has a varying wall thickness which incorporates a locally-thickened wall portion and the outer peripheral wall tapers in thickness from a maximum value at the root to a minimum value at the tip; and

a film cooling hole comprising a shaped diffuser exit passing through the outer peripheral wall within the locally-thickened wall portion.

2. The turbine airfoil of claim 1 , wherein the film cooling hole further comprises an upstream metering portion which communicates with the interior space of the airfoil and a divergent downstream portion which communicates with the external surface of the turbine airfoil.

3. The turbine airfoil of claim 1 , wherein the locally-thickened wall portion is defined by a discrete element protruding from an inner surface of the outer peripheral wall.

4. The turbine airfoil of claim 1 , wherein the outer peripheral wall comprises a tapered portion incorporating both a relatively smaller thickness and a relatively larger thickness, and the locally-thickened wall portion is defined by the relatively larger thickness.

5. The turbine airfoil of claim 1 , wherein the locally-thickened wall portion is defined by one of the sidewalls which is thicker than the other of the sidewalls.

6. The turbine airfoil of claim 1 , further comprising a rib extending between the pressure sidewall and the suction sidewall, wherein the rib and portions of the sidewalls adjacent to the rib cooperate to define two or more cavities within the interior space, and wherein one of the portions of the sidewalls defines the locally-thickened wall portion.

7. The turbine airfoil of claim 1 , wherein the airfoil is part of a turbine vane and extends between an arcuate outer band and an arcuate inner band.

8. The turbine airfoil of claim 1 , wherein the airfoil is part of a turbine blade.

9. The turbine airfoil of claim 8 , wherein the outer peripheral wall comprises a first locally-thickened portion at the root and a second locally-thickened portion at the tip, wherein the first and second locally-thickened portions have equal thickness.

10. A turbine blade for a gas turbine engine, the turbine blade comprising:

an airfoil comprising a root and a tip, the airfoil defined by an outer peripheral wall comprising:

an external surface, the outer peripheral wall enclosing an interior space; and

a concave pressure sidewall and a convex suction sidewall joined together at a leading edge and at a trailing edge,

wherein the outer peripheral wall tapers in thickness from a maximum value at the root to a minimum value at the tip,

wherein the outer peripheral wall further comprises a first locally-thickened portion at the root and a second locally-thickened portion at the tip, the first and second locally-thickened portions having equal thickness; and

first and second film cooling holes each comprising a shaped diffuser exit, the first film cooling hole passing through the outer peripheral wall within the first locally-thickened portion and the second film cooling hole passing through the outer peripheral wall within the second locally-thickened portion.

11. The turbine blade of claim 10 , wherein one of the first film cooling hole and the second film cooling hole comprises an upstream metering portion which communicates with the interior space of the turbine blade and a divergent downstream portion which communicates with the external surface of the turbine blade.

12. The turbine blade of claim 10 , wherein the outer peripheral wall further comprises a tapered portion incorporating both a relatively smaller thickness and a relatively larger thickness, and the locally-thickened wall portion is defined by the relatively larger thickness.

13. The turbine blade of claim 10 , wherein the locally-thickened wall portion is defined by one of the sidewalls which is thicker than the other of the sidewalls.

14. The turbine blade of claim 10 , further comprising a rib extending between the concave pressure sidewall and the convex suction sidewall, wherein the rib and portions of the sidewalls adjacent to the rib cooperate to define two or more cavities within the interior space, and wherein one of the portions of the sidewalls defines the locally-thickened wall portion.