Wear monitor for a gas turbine engine

Abstract

An abradable liner for a gas turbine engine compressor stage, comprising: an abradable body having a radially inner surface over which an aerofoil tip passes in use; a plurality abradable depth indicators extending into the body from the surface; each depth indicator may be filled with a visual indicator. The depth indicator can be observed by a boroscope to provide a simple mechanical visual indication which can be used to provide quick and reliable information as to the extent and pattern of wear in an attrition liner.

1 . An abradable liner for a gas turbine engine compressor stage, the liner extending about an axis and comprising:
 an abradable body having a radially inner surface over which an aerofoil tip passes in use;   a plurality depth indicators extending into the body from the surface;   wherein, the depth indicators are arranged in two or more groups each group being circumferentially spaced on the surface from another group; wherein each group has a first subgroup of depth indicators that are circumferentially offset from other depth indicators in the first subgroup, the depth indicators also being axially offset from other depth indicators in the first subgroup;   each group further having a second subgroup of depth indicators circumferentially offset from the first subgroup, the depth indicators in the second subgroup being circumferentially aligned with other depth indicators in the second subgroup.   
     
     
         2 . An abradable liner according to  claim 1 , wherein at least one depth indicator extends into the body a greater distance than at least one other depth indicator. 
     
     
         3 . An abradable liner according to  claim 1 , wherein each depth indicator is a blind aperture. 
     
     
         4 . An abradable liner according to  claim 3 , wherein each blind aperture presents a circular or elliptical cross-section to the surface. 
     
     
         5 . An abradable liner according to  claim 4 , wherein the maximum length of the longest axis of the cross-section is between 4 to 5 mm 
     
     
         6 . An abradable liner according to  claim 3 , wherein each depth indicator tapers as it extends into the abradable liner. 
     
     
         7 . An abradable liner according to  claim 1 , wherein each depth indicator is filled with a visual indicator of a coloured material. 
     
     
         8 . An abradable liner according to  claim 7  wherein the coloured material is provided as two or more discrete layers. 
     
     
         9 . A gas turbine engine compressor unit having a row of blades which rotate about an axis, and a liner extending about the axis;
 the liner having an abradable body with a radially inner surface over which an blade tip passes in use;   a plurality of abradable depth indicators extending into the body from the surface;   wherein, the depth indicators are arranged in two or more groups each group being circumferentially spaced on the surface from another group;   each group having a plurality of axially spaced depth indicators aligned to respectively correspond with a leading edge, a trailing edge and a mid-chord of the blade tip.   
     
     
         10 . A gas turbine engine compressor unit according to  claim 9 , wherein the groups extend in at least one array extending circumferentially along the inner wall. 
     
     
         11 . A gas turbine engine compressor unit according to  claim 10 , wherein two or more arrays are provided with each array being axially spaced from another of the arrays. 
     
     
         12 . A gas turbine engine compressor unit according to  claim 9 , wherein each group has a first subgroup of depth indicators that are circumferentially offset from each depth indicator in the first subgroup and one depth indicator is axially aligned to correspond with the leading edge, a second depth indicator is axially aligned to correspond with a trailing edge and third depth indicator is axially aligned to correspond with a mid-chord of the aerofoil tip; each group further having a second subgroup of depth indicators circumferentially offset from the first subgroup, the depth indicators in the second subgroup being circumferentially aligned with each other. 
     
     
         13 . A gas turbine engine compressor unit according to  claim 9 , wherein each depth indicator in the second subgroup extend into the body the same distance as the one depth indicators in the second subgroup. 
     
     
         14 . A gas turbine engine compressor unit according to  claim 9 , wherein each depth indicator in the first subgroup extend into the body to a different distance as the other depth indicators in the first subgroup. 
     
     
         15 . A gas turbine engine compressor unit according to  claim 9 , wherein each depth indicator is filled with a visual indicator of a coloured material. 
     
     
         16 . An abradable liner for a gas turbine engine compressor stage, comprising: an abradable body having a radially inner surface over which an aerofoil tip passes in use; and
 a plurality abradable depth indicators extending into the body from the surface; wherein each abradable depth indicator comprises an aperture filled with a coloured visual indicator.   
     
     
         17 . An abradable liner according to  claim 16 , wherein each blind aperture presents a circular or elliptical cross-section to the surface. 
     
     
         18 . An abradable liner according to  claim 17 , wherein the maximum length of the longest axis of the cross-section is between 4 to 5 mm 
     
     
         19 . An abradable liner according to  claim 16 , wherein each depth indicator tapers as it extends into the abradable liner.