Rotor damper

Abstract

A rotor stage ( 100 ) of a gas turbine engine ( 10 ) comprises a platform ( 120 ) from which rotor blades extend. The platform is provided with a circumferentially extending damper ring ( 200 ), the damper ring having an engagement surface ( 210 ) that engages with the platform. The damper ring has a cross-sectional shape perpendicular to the circumferential direction that has a depth (a) in the radial direction, and a neutral bending axis ( 250 ) that is spaced (b) from the engagement surface by more than half of the depth. Increasing the spacing between the engagement surface and the neutral bending axis increases the amount of slip at the interface between the damper ring and the platform, thereby increasing the amount of frictional damping.

We claim: 
     
         1 . A rotor stage of a gas turbine engine comprising a plurality of blades extending from a generally circumferentially extending platform, wherein:
 a circumferentially extending damper ring is provided on the platform, the damper ring having an engagement surface that engages with the platform; and   the damper ring has a cross-sectional shape perpendicular to the circumferential direction that has a depth (a) in the radial direction, and a neutral bending axis that is spaced (b) from the engagement surface by more than half of the depth.   
     
     
         2 . A rotor stage of a gas turbine engine according to  claim 1 , wherein:
 the platform has a radially inner surface;   the damper ring is provided on the radially inner surface of the platform; and   the damper ring has a neutral bending axis that is closer to its radially inner extent than to its radially outer extent.   
     
     
         3 . A rotor stage of a gas turbine engine according to  claim 1 , wherein the cross-sectional shape of the damper ring is a T-shape. 
     
     
         4 . A rotor stage of a gas turbine engine according to  claim 1 , wherein the cross-sectional shape of the damper ring comprises a portion that widens with increasing distance from the engagement surface. 
     
     
         5 . A rotor stage of a gas turbine engine according to  claim 1 , wherein the damper ring has a generally annular shape. 
     
     
         6 . A rotor stage of a gas turbine engine according to  claim 1 , wherein the neutral axis of the cross-sectional shape of the damper ring is spaced from the engagement surface by at least two thirds of the cross-sectional depth. 
     
     
         7 . A rotor stage of a gas turbine engine according to  claim 1 , wherein the radially outer extent of the damper ring is defined by the engagement surface that is in contact with the radially inner surface of the platform. 
     
     
         8 . A rotor stage of a gas turbine engine according to  claim 1 , wherein the platform is provided with a slot, and the damper ring is retained by the slot. 
     
     
         9 . A rotor stage of a gas turbine engine according to  claim 1 , wherein the rotor stage is a blisk, with the plurality of blades provided integrally with a disc as a unitary part to form the blisk. 
     
     
         10 . A rotor stage of a gas turbine engine according to  claim 9 , wherein the circumferentially extending platform is a blisk rim. 
     
     
         11 . A rotor stage of a gas turbine engine according to  claim 1 , wherein the damper ring comprises two different materials. 
     
     
         12 . A rotor stage of a gas turbine engine according to  claim 11 , wherein the damper ring has a body portion and an engagement portion, the engagement portion comprising the engagement surface; and
 the engagement portion is manufactured using a first material, and the body portion is manufactured using a second material.   
     
     
         13 . A rotor stage according to  claim 12 , wherein:
 the first material is metal.   
     
     
         14 . A rotor stage according to  claim 12 , wherein:
 the second material is a composite material.   
     
     
         15 . A rotor stage of a gas turbine engine comprising a plurality of blades extending from a generally circumferentially extending platform, wherein:
 a circumferentially extending damper ring is provided on the platform, the damper ring having a body portion and an engagement portion, the engagement portion having an engagement surface that is in contact with the platform; and   the engagement portion is manufactured using a first material, and the body portion is manufactured using a second material.   
     
     
         16 . A rotor stage according to  claim 15 , wherein:
 the first material is metal.   
     
     
         17 . A rotor stage according to  claim 15 , wherein:
 the second material is a composite material.   
     
     
         18 . A method of damping vibrations in a rotor stage of a gas turbine engine, wherein:
 the rotor stage is a rotor stage according to  claim 1 ;   the vibration comprises a travelling wave passing circumferentially around the circumferentially extending platform; and   the damping is frictional damping generated through slip (s) between the engagement surface of the circumferentially extending damper ring and the platform caused by the travelling wave.