Cooling fan vane assembly for a resistor grid

1. A cooling fan vane assembly for a resistor grid, the vane assembly comprising:

a duct having a substantially round inlet opening, a substantially rectangular outlet opening, and a side wall extending between the inlet opening and the outlet opening shaped to transition from a substantially round shape to a substantially rectangular shape, the inlet opening having a cylindrical wall segment;

the cylindrical wall segment including a plurality of radially extending turning vanes; and

a frustoconical vane positioned in the duct adjacent and downstream of the plurality of radially extending turning vanes.

2. The vane assembly of claim 1 , wherein the frustoconical vane includes an annular side wall that tapers in diameter from an upstream end of the frustoconical vane to a downstream end of the frustoconical vane.

3. The vane assembly of claim 2 , wherein the frustoconical vane is shaped to extend into a transition region between the cylindrical wall segment and the substantially rectangular outlet opening.

4. The vane assembly of claim 1 , wherein the radially outer ends of the plurality of radially extending turning vanes are attached to the cylindrical wall segment.

5. The vane assembly of claim 4 , further comprising an inner stiffening ring attached to the radially inner ends of the plurality of radially extending turning vanes, such that the plurality of radially extending turning vanes extend radially outwardly from the inner stiffening ring to the cylindrical wall segment.

6. The vane assembly of claim 5 , wherein the inner stiffening ring corresponds in diameter to an outer diameter of a hub of an associated cooling fan.

7. The vane assembly of claim 6 , wherein the radially extending turning vanes have a length that is approximately equal to the length of blades of the associated cooling fan.

8. A method of cooling a dynamic braking grid, the method comprising:

providing a fan having a hub supporting a plurality of fan blades;

positioning a duct adjacent the fan, the duct having a substantially round inlet opening corresponding in diameter to an outer diameter of the plurality of fan blades and a cylindrical wall segment, a substantially rectangular outlet opening adjacent the dynamic braking grid, and a side wall extending between the inlet opening and the outlet opening shaped to transition from a substantially round shape to a substantially rectangular shape corresponding to a shape of the dynamic braking grid to guide cooling air blown by the fan to the dynamic braking grid;

attaching a plurality of radially extending turning vanes at outer ends thereof to the cylindrical wall segment and attaching inner ends of the plurality of radially extending turning vanes to an inner stiffening ring such that the plurality of radially extending turning vanes extend from the inner stiffening ring radially outwardly to the cylindrical wall segment;

shaping and angling the plurality of radially extending turning vanes to direct the cooling air in a substantially axial direction relative to the fan hub; and

providing a frustoconical vane positioned in the duct adjacent and downstream of the plurality of radially extending turning vanes, and shaping the frustoconical vane to distribute cooling air evenly across the dynamic braking grid.

9. A cooling fan vane assembly for a resistor grid, the vane assembly comprising:

a duct having a substantially round inlet opening, a substantially rectangular outlet opening, and a side wall extending between the inlet opening and the outlet opening shaped to transition from a substantially round shape to a substantially rectangular shape;

the inlet opening including a plurality of radially extending turning vanes;

a frustoconical vane positioned in the duct adjacent a downstream side of the plurality of radially extending turning vanes;

wherein the frustoconical vane includes a substantially annular side wall that tapers in diameter from an upstream end of the frustoconical vane to a downstream end of the frustoconical vane; and

wherein the frustoconical vane is shaped to extend into a transition region between the substantially round inlet opening and the substantially rectangular outlet opening.

10. The vane assembly of claim 9 , wherein the frustoconical vane has a taper angle of approximately 20° relative to a centerline of the duct.

11. The vane assembly of claim 10 , wherein the frustoconical vane has a length-to-diameter ratio at the upstream end of approximately 2:7.

12. A cooling fan vane assembly for a resistor grid, the vane assembly comprising:

a duct having a substantially round inlet opening, a substantially rectangular outlet opening, and a side wall extending between the inlet opening and the outlet opening shaped to transition from a substantially round shape to a substantially rectangular shape;

the inlet opening including a plurality of radially extending turning vanes;

a frustoconical vane positioned in the duct adjacent a downstream side of the plurality of radially extending turning vanes;

wherein the inlet opening includes a substantially cylindrical wall segment and radially outer ends of the plurality of radially extending turning vanes are attached to the cylindrical wall segment, the inlet opening including an inner stiffening ring attached to the radially inner ends of the plurality of radially extending turning vanes, the inner stiffening ring corresponding in diameter to an outer diameter of a hub of an associated cooling fan;

wherein the radially extending turning vanes have a length that is approximately equal to the length of blades of the associated cooling fan, are plate shaped, and are angled relative to a plane containing a centerline of the duct; and

wherein the frustoconical vane is mounted on one or more of the plurality of radially extending turning vanes.

13. The vane assembly of claim 12 , wherein the frustoconical vane is attached at the upstream end thereof to downstream edges of one or more of the plurality of radially extending turning vanes.

14. The vane assembly of claim 13 , wherein the upstream end of the frustoconical vane is positioned at approximately midpoints of the plurality of radially extending turning vanes, measured in a radial direction.

15. A cooling fan vane assembly for a resistor grid, the vane assembly comprising:

a duct having a substantially round inlet opening including a substantially cylindrical wall segment, a substantially rectangular outlet opening, and a side wall extending between the inlet opening and the outlet opening shaped to transition from a substantially round shape to a substantially rectangular shape;

the inlet opening including a plurality of radially extending turning vanes having a length approximately equal to the length of blades of the associated cooling fan, wherein radially outer ends of the plurality of radially extending turning vanes are attached to the cylindrical wall segment;

the inlet opening including an inner stiffening ring attached to radially inner ends of the plurality of radially extending turning vanes, wherein the inner stiffening ring corresponds in diameter to an outer diameter of a hub of an associated cooling fan; and

a frustoconical vane positioned in the duct adjacent and downstream of the plurality of radially extending turning vanes.

16. The vane assembly of claim 15 , wherein the radially extending turning vanes are plate shaped.

17. The vane assembly of claim 16 , wherein the radially extending turning vanes are angled relative to a plane containing a centerline of the duct.

18. The vane assembly of claim 17 , wherein the frustoconical vane is mounted on one or more of the plurality of radially extending turning vanes.