System and method for reducing bucket tip losses

1. A system for reducing bucket tip losses comprising an airfoil portion of an unshrouded turbine bucket, the airfoil portion comprising:

a pressure-side surface and a suction-side surface each extending from a root surface to a tip surface and joined at a leading edge and a trailing edge, the pressure-side surface having a generally concave shape, the suction-side surface having a generally convex shape;

the airfoil portion having an increasing stagger angle in a span-wise direction from the root surface to the tip surface and an increasingly loaded suction-side surface as the suction-side surface approaches the tip surface and the tip surface approaches the leading edge, the airfoil portion having a resultant lean in a direction of the suction-side surface as the leading edge approaches the tip surface, and the pressure-side surface and the suction-side surface each having a locally reduced or reversed curvature in a direction of the pressure-side surface at their intersection with the tip surface.

2. The system of claim 1 , wherein the airfoil portion comprises a chord-wise loaded, stacked distribution of sections.

3. The system of claim 1 , further comprising a root portion connected to the airfoil portion at the root surface.

4. The system of claim 3 , wherein the root portion is connected to a rotor of a turbine.

5. The system of claim 1 , wherein the airfoil portion further has an increasingly loaded suction-side surface as the suction-side surface approaches the tip surface and the tip surface approaches the trailing edge, the airfoil portion further having a resultant lean in the direction of the suction-side surface as the trailing edge approaches the tip surface.

6. The system of claim 5 , wherein the pressure-side surface and the suction-side surface have a flare in a direction of the pressure-side surface at their intersection with the tip surface.

7. The system of claim 5 , wherein the airfoil portion comprises a chord-wise loaded, stacked distribution of sections.

8. The system of claim 5 , further comprising a root portion connected to the airfoil portion at the root surface.

9. The system of claim 8 , wherein the root portion is connected to a rotor of a turbine.

10. A method for reducing bucket tip losses comprising providing an airfoil portion of an unshrouded turbine bucket, the airfoil portion comprising:

a pressure-side surface and a suction-side surface each extending from a root surface to a tip surface and joined at a leading edge and a trailing edge, the pressure-side surface having a generally concave shape and the suction-side surface having a generally convex shape;

the airfoil portion having an increasing stagger angle in a span-wise direction from the root surface to the tip surface and an increasingly loaded suction-side surface as the suction-side surface approaches the tip surface and the tip surface approaches the leading edge, the airfoil portion having a resultant lean in a direction of the suction-side surface as the leading edge approaches the tip surface, and the pressure-side surface and the suction-side surface each having a locally reduced or reversed curvature in a direction of the pressure-side surface at their intersection with the tip surface.

11. The method of claim 10 , wherein the airfoil portion comprises a chord-wise loaded, stacked distribution of sections.

12. The method of claim 10 , further comprising connecting a root portion to the airfoil portion at the root surface.

13. The method of claim 12 , further comprising connecting the root portion to a rotor of a turbine.

14. The method of claim 10 , wherein the airfoil portion further has an increasingly loaded suction-side surface as the suction-side surface approaches the tip surface and the tip surface approaches the trailing edge, the airfoil portion further having a resultant lean in the direction of the suction-side surface as the trailing edge approaches the tip surface.

15. The method of claim 14 , wherein the pressure-side surface and the suction-side surface have a flare in a direction of the pressure-side surface at their intersection with the tip surface.

16. The method of claim 14 , wherein the airfoil portion comprises a chord-wise loaded, stacked distribution of sections.

17. The method of claim 14 , further comprising connecting a root portion to the airfoil portion at the root surface.

18. The method of claim 17 , further comprising connecting the root portion to a rotor of a turbine.

19. A system for reducing bucket tip losses comprising an airfoil portion of an unshrouded turbine bucket, the airfoil portion comprising:

a pressure-side surface and a suction-side surface each extending from a root surface to a tip surface and joined at a leading edge and a trailing edge, the pressure-side surface having a generally concave shape, the suction-side surface having a generally convex shape;

the airfoil portion having an increasing stagger angle in a span-wise direction from the root surface to the tip surface and an increasingly loaded suction-side surface as the suction-side surface approaches the tip surface and the tip surface approaches the leading edge, the airfoil portion having a resultant lean in a direction of the suction-side surface as the leading edge approaches the tip surface, and the pressure-side surface and the suction-side surface each having a locally reduced or reversed curvature in a direction of the pressure-side surface at their intersection with the tip surface,

wherein the leading edge has a lean distribution which is disposed on a suction side of a radial plane of the airfoil portion from the root surface to the tip surface.