Contoured flowpath surface

1. A spacer assembly for a rotor assembly of a gas turbine engine, the assembly comprising:

an endwall segment having a non-axisymmetric flowpath surface and an underside surface opposite the non-axisymmetric flowpath surface, wherein a perimeter of the flowpath surface includes a forward edge, an aft edge, a suction side edge and a pressure side edge;

a first depression formed along the flowpath surface adjoining the suction side edge;

a second depression formed along the flowpath surface adjoining the pressure side edge; and

a stiffening rib formation located-on the underside surface, wherein the stiffening rib formation includes a central rib extending axially along the underside surface between the first and second depressions and a plurality of additional ribs extending laterally from the central rib and along the underside surface, and wherein each of the plurality of additional ribs form an acute angle with respect to the central rib.

2. The assembly of claim 1 , wherein the first depression is spaced from both the forward edge and the aft edge.

3. The assembly of claim 2 , wherein the second depression is spaced from both the forward edge and the aft edge.

4. The assembly of claim 1 , further comprising:

a first seal positioned along the suction side edge, wherein the first seal follows a shape of the first depression; and

a second seal positioned along the pressure side edge, wherein the second seal follows a shape of the second depression.

5. The assembly of claim 1 , wherein the first and second depressions are spaced apart in the circumferential direction.

6. The assembly of claim 1 , wherein a maximum depth of the first depression is approximately 6-8% of a length of the first depression.

7. The assembly of claim 1 , further comprising:

a protrusion formed along the flowpath surface, located in between the first and second depressions in a circumferential direction.

8. The spacer assembly of claim 1 , wherein at least one of the first and second depressions has a length that is approximately 93% to 94% of a root chord length of an airfoil adjacent to the spacer assembly.

9. The spacer assembly of claim 1 , wherein the plurality of additional ribs includes:

a pair of opposing aft ribs; and

a forward rib, wherein the aft ribs and the forward rib are spaced from the first and second depressions.

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

a rotor disk;

a plurality of airfoils matingly secured to the rotor disk, wherein each of the airfoils has a leading edge and a trailing edge; and

a plurality of spacers each positioned between an adjacent pair of airfoils of the plurality of airfoils, at least one of the plurality of spacers comprising:

an endwall segment with a non-axisymmentric flowpath surface, wherein a perimeter of the flowpath surface is defined by a forward edge, an aft edge, a suction side edge and a pressure side edge; and

a first depression formed along the flowpath surface adjoining one of the suction side edge and the pressure side edge; and

a second depression formed along the flowpath surface adjoining the other of the suction side edge and the pressure side edge, wherein both the first depression and the second depression are positioned aft of the leading edge and forward of the trailing edge of one of the pair of adjacent airfoils, and wherein at least one of the first and second depressions has a length that is approximately 93% to 94% of a root chord length of the one airfoil.

11. The assembly of claim 10 , wherein the first depression is spaced from both the forward edge and the aft edge of the flowpath surface.

12. The assembly of claim 10 , wherein the first depression is positioned aft of the leading edges of the airfoils and forward of the trailing edges of the airfoils.

13. The assembly of claim 10 , further comprising:

a mounting structure extending from the endwall segment opposite the flowpath surface; and

a fastener for securing the mounting structure to the rotor disk.

14. The assembly of claim 10 , further comprising:

a seal positioned along the endwall segment, wherein the seal follows a shape of the first depression.

15. The assembly of claim 10 , further comprising:

a stiffening structure located on an underside surface opposite the flowpath surface, the stiffening structure comprising:

a central rib; and

a plurality of additional ribs extending from the central rib and along the underside surface at acute angles with respect to the central rib.

16. The assembly of claim 10 , further comprising:

a first seal positioned along the endwall segment, wherein the first seal follows a shape of the first depression; and

a second seal positioned along the endwall segment opposite the first seal, wherein the second seal follows a shape of the second depression.

17. The assembly of claim 10 , wherein the first and second depressions are spaced apart in the circumferential direction.

18. The assembly of claim 10 , further comprising:

a protrusion formed along the flowpath surface, located in between the first and second depressions in a circumferential direction.

19. A spacer for a gas turbine engine, the spacer comprising:

an endwall segment having a flowpath surface and an underside surface located opposite the flowpath surface; and

a stiffening structure located on the underside surface, the stiffening structure comprising:

a single central rib extending axially along the underside surface; and

a plurality of additional ribs extending laterally from the single central rib and along the underside surface, wherein the respective axial extend of each additional rib is less than the axial extent of the single central rib, and wherein each of the additional ribs forms an acute angle with respect to the single central rib.

20. The spacer of claim 19 , wherein a perimeter of the flowpath surface includes a forward edge, an aft edge, a suction side edge and a pressure side edge, the spacer further comprising:

a first seal element positioned along the suction side edge; and

a second seal element positioned along the pressure side edge.