Clearance control arrangement

Abstract

A clearance control arrangement ( 26 ) for a rotor ( 28 ), the arrangement comprising a rotor and a casing ( 32 ) radially outside the rotor. An annular array of segment assemblies ( 33 ) mounted to the casing and radially spaced from the rotor by a clearance ( 42 ). Each segment assembly comprising a heat transfer cavity ( 48 ) radially adjacent to the casing. A birdmouth cavity ( 66 ) towards the rear of the segment assembly. A bypass hole ( 68 ) configured to deliver air to the birdmouth cavity to reduce the amount of air which leaks from the heat transfer cavity to the birdmouth cavity.

1 . A clearance control arrangement for a rotor, the arrangement comprising:
 a rotor;   a casing radially outside the rotor;   an annular array of segment assemblies mounted to the casing and radially spaced from the rotor by a clearance; each segment assembly comprising:
 a heat transfer cavity radially adjacent to the casing; 
 a birdmouth cavity towards the rear of the segment assembly; 
 a bypass hole configured to deliver air to the birdmouth cavity to reduce the amount of air which leaks from the heat transfer cavity to the birdmouth cavity; and 
 a birdmouth seal defined at the radially outer extent of a rear segment carrier. 
   
     
     
         2 . An arrangement as claimed in  claim 1  wherein the birdmouth cavity is downstream of the birdmouth seal. 
     
     
         3 . An arrangement as claimed in  claim 2  further comprising a rear hook which supports the rear segment carrier, the birdmouth cavity formed between the rear hook and the rear segment carrier. 
     
     
         4 . An arrangement as claimed in  claim 1  wherein the birdmouth cavity is upstream of the birdmouth seal. 
     
     
         5 . An arrangement as claimed in  claim 4  wherein the birdmouth cavity is separated from the heat transfer cavity by a rib. 
     
     
         6 . An arrangement as claimed in  claim 1  further comprising a segment cooling cavity at the radially inner extent of the segment assembly. 
     
     
         7 . An arrangement as claimed in  claim 6  wherein the bypass hole is configured to receive air from the segment cooling cavity. 
     
     
         8 . An arrangement as claimed in  claim 7  further comprising a supply cavity radially between the heat transfer cavity and the segment cooling cavity. 
     
     
         9 . An arrangement as claimed in  claim 8  wherein the bypass hole is configured to receive air from the supply cavity 
     
     
         10 . An arrangement as claimed in  claim 6  further comprising a supply cavity radially between the heat transfer cavity and the segment cooling cavity. 
     
     
         11 . An arrangement as claimed in  claim 10  wherein the bypass hole is configured to receive air from the supply cavity. 
     
     
         12 . An arrangement as claimed in  claim 1  comprising an array of bypass holes. 
     
     
         13 . An arrangement as claimed in  claim 1  further comprising a first supply hole configured to allow ingress of air to the heat transfer cavity. 
     
     
         14 . An arrangement as claimed in  claim 1  further comprising a front hook which supports a front segment carrier, the front hook configured to allow ingress of air to the heat transfer cavity. 
     
     
         15 . An arrangement as claimed in  claim 1  further comprising an array of controlled entry holes configured to allow ingress of air to the heat transfer cavity. 
     
     
         16 . An arrangement as claimed in  claim 1  wherein the segment assembly includes cooling air delivery holes through its radially inner wall. 
     
     
         17 . A gas turbine engine comprising an arrangement as claimed in  claim 1 .