Turbine blade tip clearance system

Abstract

A stage of gas turbine engine turbine blades ( 22 ) is surrounded by segments ( 26 ) that in turn, are suspended from a flexible casing ( 24 ). The inner surface of casing ( 24 ) is exposed to compressor flow. On engine thrust being increased, compressor output also increases and rapidly flexes casing ( 24 ) radially outwards, thus equally rapidly moving the segments ( 24 ) away from the tips of the turbine blades ( 22 ).

1 . A turbine blade tip clearance system comprising a rigid outer casing and an inner casing having induced flexing capability supported by the outer casing in radially spaced relationship therewith, so as to define an annular space therebetween, and wherein said inner casing supports a ring of arcuate segments within it in fixed radial relationship therewith, such that on placing the whole around a stage of disk mounted turbine blades in coaxial relationship therewith, said segments will lie in radial close spaced relationship with the tips of said turbine blades.  
   
   
       2 . A turbine blade tip clearance system as claimed in  claim 1  wherein said arcuate segments are suspended from said inner casing by screw threaded fastening means so as to enable radial positional adjustment of said arcuate segments with respect to a selected datum.  
   
   
       3 . A turbine blade tip clearance system as claimed in  claim 1  wherein said outer casing is manufactured from a temperature sensitive material.  
   
   
       4 . A turbine blade tip clearance system as claimed in  claim 3  wherein said material comprises nickel.  
   
   
       5 . A turbine blade tip clearance system as claimed in  claim 1  when installed in a gas turbine engine.  
   
   
       6 . A gas turbine engine including an installed turbine blade tip clearance system as claimed in  claim 5  and including ducting connecting a compressor of said gas turbine engine in flow series with the inner surface of said inner casing so as to cause said inner casing to flex outwardly of the axis of said gas turbine engine and thereby lift said segments away from said blade tips during an appropriate stage in the engine operating regime.  
   
   
       7 . A gas turbine engine as claimed in  claim 6  including ducting connecting a compressor of said gas turbine engine in flow series with said outer casing so as to heat said outer casing and cause it to expand and thereby slow the rate of return of said segments to their original positions, during an appropriate stage in the engine operating regime.