Contra rotatable turbine system

Abstract

A three shaft ducted fan gas turbine engine ( 10 ) has a turbine system comprising a high pressure turbine rotor ( 32 ), an intermediate pressure turbine rotor ( 36 ) and first and second low pressure turbine rotors ( 42,44 ), that straddle intermediate pressure turbine rotor ( 36 ). Rotors ( 42,44 ) are mechanically connected by a casing ( 46 ) that bridges turbine rotor ( 36 ) so as to achieve transmission of torque from the first to the second thereof. Rotor ( 42 ) also delivers gas flow to the intermediate pressure rotor ( 36 ) at a much lower temperature than is experienced by conventional arrangements.

1 . A ducted fan gas turbine engine turbine system comprising, in flow series, a high pressure bladed turbine rotor, a fixed, bladed stator stage, a first low pressure bladed turbine rotor, an intermediate pressure bladed turbine rotor and a second low pressure bladed turbine rotor, the two low pressure bladed turbine rotors being mechanically connected for co-rotation in a direction contrary to that of the high pressure and intermediate pressure turbine rotors, said contra rotation being effected, at least in part, by appropriate shaping of the gas flow paths through said stage of stator blades.  
   
   
       2 . A ducted fan gas turbine engine turbine system as claimed in  claim 1  wherein said mechanical connection comprises a casing fixed on the outer tip extremities of the blades of each low pressure turbine rotor and bridging said intermediate pressure turbine rotor.  
   
   
       3 . A ducted fan gas turbine engine turbine system as claimed in  claim 1  wherein in situ in a ducted fan gas turbine engine, said high pressure turbine rotor is drivingly connected via a shaft to a high pressure compressor, said intermediate pressure turbine rotor is drivingly connected via another shaft to an intermediate pressure compressor immediately upstream of said high pressure compressor and said second low pressure turbine rotor is directly drivingly connected via a further shaft to a ducted fan at the upstream end of said engine.  
   
   
       4 . A ducted fan gas turbine engine turbine system as claimed in any of claims  1  wherein said intermediate pressure turbine rotor is effectively mechanically connected to said first low pressure turbine rotor so as to impart a rotary force thereon during operation in a said engine.  
   
   
       5 . A ducted fan gas turbine engine turbine system as claimed in  claim 4  wherein said mechanical connection comprises a geared connection between the intermediate turbine rotor shaft and said first low pressure turbine rotor.  
   
   
       6 . A ducted fan gas turbine engine turbine system as claimed in  claim 5  wherein said geared connection comprises a spur gear on said intermediate turbine rotor shaft that engages a plurality of planet gears supported from fixed structure and which in turn engage a spur gear on said first low pressure turbine rotor.  
   
   
       7 . A ducted fan gas turbine engine turbine system as claimed in  claim 4  wherein said mechanical connection comprises a geared connection between the upstream end of an intermediate compressor and a ducted fan when all are assembled.  
   
   
       8 . A ducted fan gas turbine engine turbine system as claimed in  claim 5  wherein said connection of said gears is made via planet gears supported from fixed structure.