Rotor assembly having a closure group of rotor blades with fixturing and alignment features

1 . A rotor assembly comprising:

a rotor defining an annular slot that includes a main portion and a gate portion;

a plurality of rotor blades positioned in the annular slot, the plurality of rotor blades including a standard group of rotor blades and a closure group of rotor blades, the standard group of rotor blades positioned in the main portion of the annular slot, and wherein the closure group of rotor blades comprises:

a first auxiliary rotor blade having a first auxiliary mounting portion that includes a first fixturing tab, and wherein the first auxiliary mounting portion partially defines a first pin hole;

a second auxiliary rotor blade having a second auxiliary mounting portion that includes a second fixturing tab, and wherein the second auxiliary mounting portion partially defines a second pin hole; and

a closure rotor blade positioned in the gate portion of the annular slot between the first auxiliary rotor blade and the second auxiliary rotor blade, the closure rotor blade having a closure mounting portion defining a radially innermost surface, the radially innermost surface being in contact with the first fixturing tab and the second fixturing tab, and wherein the closure rotor blade partially defines the first pin hole and the second pin hole.

2 . The rotor assembly as in claim 1 , wherein the first auxiliary mounting portion comprises a first auxiliary platform, a first auxiliary dovetail, and a first auxiliary neck extending between the first auxiliary platform and the first auxiliary dovetail.

3 . The rotor assembly as in claim 2 , wherein the first fixturing tab extends from the first auxiliary neck.

4 . The rotor assembly as in claim 2 , wherein the first pin hole is partially defined by the first auxiliary platform.

5 . The rotor assembly as in claim 2 , wherein a first recess is defined in the first auxiliary neck portion radially outwardly of the first fixturing tab.

6 . The rotor assembly as in claim 1 , wherein the second auxiliary mounting portion comprises a second auxiliary platform, a second auxiliary dovetail, and a second auxiliary neck extending between the second auxiliary platform and the second auxiliary dovetail.

7 . The rotor assembly as in claim 6 , wherein the second fixturing tab extends from the second auxiliary neck.

8 . The rotor assembly as in claim 6 , wherein a second recess is defined in the second auxiliary neck portion radially outwardly of the second fixturing tab.

9 . The rotor assembly as in claim 6 , wherein the second pin hole is partially defined by the second auxiliary platform.

10 . The rotor assembly as in claim 1 , wherein the closure mounting portion comprises a closure platform, a closure dovetail, and a closure neck extending between the closure platform and the closure dovetail.

11 . The rotor assembly as in claim 10 , wherein the closure platform partially defines the first pin hole and the second pin hole.

12 . The rotor assembly as in claim 1 , wherein a first pin is disposed in the first pin hole, and wherein a second pin is disposed in the second pin hole.

13 . A steam turbine comprising:

a casing; and

a rotor assembly disposed in the casing, the rotor assembly comprising:

a rotor defining an annular slot that includes a main portion and a gate portion;

a plurality of rotor blades positioned in the annular slot, the plurality of rotor blades including a standard group of rotor blades and a closure group of rotor blades, the standard group of rotor blades positioned in the main portion of the annular slot, and wherein the closure group of rotor blades comprises:

a first auxiliary rotor blade having a first auxiliary mounting portion that includes a first fixturing tab, and wherein the first auxiliary mounting portion partially defines a first pin hole;

a second auxiliary rotor blade having a second auxiliary mounting portion that includes a second fixturing tab, and wherein the second auxiliary mounting portion partially defines a second pin hole; and

a closure rotor blade positioned in the gate portion of the annular slot between the first auxiliary rotor blade and the second auxiliary rotor blade, the closure rotor blade having a closure mounting portion defining a radially innermost surface, the radially innermost surface being in contact with the first fixturing tab and the second fixturing tab, and wherein the closure rotor blade partially defines the first pin hole and the second pin hole.

14 . The steam turbine as in claim 13 , wherein a first pin is disposed in the first pin hole, and wherein a second pin is disposed in the second pin hole.

15 . The steam turbine as in claim 13 , wherein the first auxiliary mounting portion comprises a first auxiliary platform, a first auxiliary dovetail, and a first auxiliary neck extending between the first auxiliary platform and the first auxiliary dovetail, wherein the first fixturing tab extends from the first auxiliary neck.

16 . The steam turbine as in claim 13 , wherein the second auxiliary mounting portion comprises a second auxiliary platform, a second auxiliary dovetail, and a second auxiliary neck extending between the second auxiliary platform and the second auxiliary dovetail, wherein the second fixturing tab extends from the second auxiliary neck.

17 . A method of installing a plurality of rotor blades in a rotor, the plurality of rotor blades including a standard group of rotor blades and a closure group of rotor blades, the method comprising:

inserting each standard rotor blade in the group of standard rotor blades through a gate portion of an annular slot and into a main portion of the annular slot;

inserting a first auxiliary rotor blade through the gate portion of the annular slot and into the main portion of the annular slot, the first auxiliary rotor blade having a first auxiliary mounting portion that includes a first fixturing tab, and wherein the first auxiliary mounting portion partially defines a first pin hole;

inserting a second auxiliary rotor blade through the gate portion of the annular slot and into the main portion of the annular slot, the second auxiliary rotor blade having a second auxiliary mounting portion that includes a second fixturing tab, and where in the second auxiliary mounting portion partially defines a second pin hole; and

inserting a closure rotor blade through the gate portion until a radially inner most surface of a closure mounting portion of the closure rotor blade contacts the first fixturing tab and the second fixturing tab, wherein the closure rotor blade partially defines the first pin hole and the second pin hole.

18 . The method as in claim 17 , wherein inserting each of the standard rotor blades, the first auxiliary rotor blade, and the second auxiliary rotor blade comprises:

inserting one of the standard rotor blades, the first auxiliary rotor blade, or the second auxiliary rotor blade through the gate;

rotating the one of the standard rotor blades, the first auxiliary rotor blade, or the second auxiliary rotor blade through the gate; and

moving the one of the standard rotor blades, the first auxiliary rotor blade, or the second auxiliary rotor blade through the gate from the gate portion to the main portion after the rotating step.

19 . The method as in claim 17 , further comprising:

installing the closure group in a fixture by:

positioning an inner surface of the first auxiliary rotor blade and an inner surface of the second auxiliary rotor blade on the fixture, wherein the inner surface of the first auxiliary rotor blade and the inner surface of the second auxiliary rotor blade are parallel; and

positioning the closure blade between the first auxiliary rotor blade and the second auxiliary rotor blade such that the closure blade contacts the first fixturing tab and the second fixturing tab; and

machining the first pin hole and the second pin hole.

20 . The rotor assembly as in claim 1 , wherein a first radial gap is defined between a floor of the rotor and a first inner surface of the first auxiliary mounting portion, wherein a second radial gap is defined between the floor and the inner surface of the closure mounting portion, and wherein the second radial gap is larger than the first radial gap.