Tie shaft arrangement for turbomachine

1. A turbomachine comprising:

a tie shaft extending along an axis;

multiple rotors mounted on the tie shaft;

first and second clamping members secured to the tie shaft and exerting a clamping load between the rotors and clamping members at multiple interfaces, the clamping load at one of the interfaces including a radial clamping load of greater than 5% of a total design clamping load at the one interface; and

a friction modifier is provided at the interface, wherein the interface includes at least one of a rough surface finish, a grit blasted surface, a coating, a spray, a plasma, colloidal particles, adhesives, pastes and additives.

2. The turbomachine according to claim 1 , wherein the radial clamping load is up to 40% of the total design clamping load with a balance of the total clamping load comprising an axial clamping load.

3. The turbomachine according to claim 1 , wherein the tie shaft is a high pressure spool.

4. The turbomachine according to claim 3 , wherein the rotors are high pressure compressor rotors.

5. The turbomachine according to claim 1 , wherein one of the rotors includes first and second rotor surfaces respectively providing radially and axially extending surfaces, the radial clamping load exerted on the second rotor surface.

6. The turbomachine according to claim 5 , wherein the first rotor surface is arranged radially inward of the second rotor surface.

7. The turbomachine according to claim 5 , wherein one of the first and second clamping members is a hub providing first and second hub surfaces respectively engaging the first and second rotor surfaces to produce the total clamping load.

8. The turbomachine according to claim 7 , wherein the hub includes a first leg having opposing first and second ends, the second end providing the first and second hub surfaces, the first end providing a flange supported by the tie shaft.

9. The turbomachine according to claim 8 , wherein the tie shaft includes a threaded surface, and comprising a nut secured to the threaded surface and configured to apply the clamping load through the first end.

10. The turbomachine according to claim 8 , wherein the first leg is inclined between 15° and 75° relative to the axis and extending from the flange to the second end.

11. The turbomachine according to claim 8 , wherein the hub includes a second leg joined to the first leg, the hub arranged between compressor and turbine sections and configured respectively to provide compressor and turbine clamping loads to the compressor and turbine sections.

12. A tie shaft clamping member comprising:

a hub including a first leg extending between first and second opposing ends, the first end providing a flange configured to be supported by a tie shaft, and the second end including first and second hub surfaces respectively extending in radial and axial directions, the first leg inclined between 15° and 75° relative to the axial direction and extending from the flange to the second end; and

a friction modifier is provided on at least one of the first and second hub surfaces, wherein the at least one of the first and second hub surfaces includes at least one of a rough surface finish, a grit blasted surface, a coating, a spray, a plasma, colloidal particles, adhesives, pastes and additives.

13. The tie shaft clamping member according to claim 12 , wherein the hub includes a second leg integral with the first leg and extending generally in the axial direction from a joint arranged between the first and second ends to a third end.