Turbine blade trailing edge cooling feed

1. A turbine blade comprising:

an attachment root having:

an inner diameter end;

a first axial end;

a second axial end, a rearward direction defined from the first axial end to the second axial end;

a first lateral side; and

a second lateral side, an end-to-end centerplane between and extending parallel to the first and second lateral sides;

an airfoil having:

a pressure side;

a suction side;

a leading edge; and

a trailing edge; and

a cooling passageway system comprising:

a plurality of trunks extending from respective inlets along the root inner diameter end from a leading trunk near the first axial end to a trailing trunk near the second axial end; and

a plurality of outlets along the airfoil including trailing edge outlets fed by the trailing trunk,

wherein viewed normal to the end-to-end centerplane:

the trailing trunk has a turn passing forward and then rearward;

an outside of the turn protrudes forward; and

the outside of the turn has a tighter curvature than an inside of the turn.

2. The turbine blade of claim 1 wherein:

the outside of the turn forms a first bump; and

the inside of the turn forms a second bump.

3. The turbine blade of claim 2 wherein:

a forward extreme of the second bump is radially outboard of a forward extreme of the first bump.

4. The turbine blade of claim 2 wherein viewed normal to the end-to-end centerplane:

the outside of the turn protrudes forward of an adjacent portion of the trunk by at least 10% of a span of the adjacent portion.

5. The turbine blade of claim 2 wherein viewed normal to the end-to-end centerplane:

a leading side of the turn including the outside of the turn has a transition from inwardly convex to inwardly concave to inwardly convex.

6. The turbine blade of claim 5 wherein:

along the inwardly concave portion of the leading side of the turn, the leading side turns by an angle θ 2 of 30° to 120°.

7. The turbine blade of claim 6 wherein:

along the inwardly convex portion of the leading side of the turn radially outboard of the inwardly concave portion, the leading side turns by an angle θ 3 of 30° to 55°.

8. The turbine blade of claim 2 wherein viewed normal to the end-to-end centerplane:

a trailing side of the turn has an inwardly concave portion turning by an angle θ 4 of 25° to 50° before an inwardly convex transition to a discharge slot.

9. The turbine blade of claim 2 wherein viewed normal to the end-to-end centerplane:

an angle θ 5 between a stacking line and a tangent at the inflection point where the leading side begins to turn back forward is at least 15°.

10. The turbine blade of claim 2 wherein:

the forward extreme of the first bump has a tighter curvature than the forward extreme of the second bump.

11. The turbine blade of claim 1 wherein viewed normal to the end-to-end centerplane:

the trailing trunk turn radially nests with a next forward one of the trunks.

12. The turbine blade of claim 11 wherein:

the next forward trunk feeds an uppass-downpass-uppass.

13. The turbine blade of claim 12 wherein viewed normal to the end-to-end centerplane:

the trailing trunk turn radially nests between the next forward one of the trunks and a turn from the downpass to the downstream uppass.

14. The turbine blade of claim 11 wherein:

the next forward trunk feeds an uppass with which the turn nests.

15. A method for using the turbine blade of claim 1 , the method comprising:

passing air in through the inlets and out the outlets, wherein:

air passing along the turn avoids separation.

16. The method of claim 15 wherein:

at a downstream end of the turn, the air fans out.

17. The method of claim 15 wherein:

at a downstream end of the turn, the air fans with a forward flowline turning by an angle of 15° to 60.

18. A turbine blade comprising:

an attachment root having:

an inner diameter end;

a first axial end;

a second axial end, a rearward direction defined from the first axial end to the second axial end;

a first lateral side; and

a second lateral side, an end-to-end centerplane between and extending parallel to the first and second lateral sides;

an airfoil having:

a pressure side;

a suction side;

a leading edge; and

a trailing edge; and

a cooling passageway system comprising:

a plurality of trunks extending from respective inlets along the root inner diameter end from a leading trunk near the first axial end to a trailing trunk near the second axial end; and

a plurality of outlets along the airfoil including trailing edge outlets fed by the trailing trunk,

wherein viewed normal to the end-to-end centerplane:

the trailing trunk has a turn passing forward and then rearward;

an outside of the turn protrudes forward

the outside of the turn forms a first bump;

the inside of the turn forms a second bump; and

a forward extreme of the second bump is radially outboard of a forward extreme of the first bump.

19. The turbine blade of claim 18 wherein viewed normal to the end-to-end centerplane:

an angle θ 5 between a stacking line and a tangent at the inflection point where the leading side begins to turn back forward is at least 15°.

20. The turbine blade of claim 18 wherein viewed normal to the end-to-end centerplane:

a trailing side of the turn has an inwardly concave portion turning by an angle θ 4 of 25° to 50° before an inwardly convex transition to a discharge slot.

21. A method for using the turbine blade of claim 18 , the method comprising:

passing air in through the inlets and out the outlets,

wherein:

air passing along the turn avoids separation;

at a downstream end of the turn, the air fans out; and

at a downstream end of the turn, the air fans with a forward flowline turning by an angle of 15° to 60.