Turbine-tip clearance control system offtake

Abstract

A turbine-tip clearance control system offtake for a gas turbine engine, comprising: an air input duct in fluid communication with a compressor bleed air outlet, the air input duct comprising an exit aperture, the exit aperture defining an exit flow path for at least a portion of the air flowing in the air input duct during use of the gas turbine engine. The direction of airflow through the exit aperture, during use of the gas turbine engine, has at least a component that is anti-parallel to the direction of airflow in the air input duct in a region of the air input duct adjacent to the exit aperture. A turbine-tip clearance control system, a gas turbine engine for an aircraft and a method of supplying airflow to a turbine-tip clearance control system in a gas turbine engine are also disclosed.

1 . A turbine-tip clearance control (TTCC) system offtake for a gas turbine engine, comprising:
 an air input duct in fluid communication with a compressor bleed air outlet,   the air input duct comprising an exit aperture, the exit aperture defining an exit flow path for at least a portion of the air flowing in the air input duct during use of the gas turbine engine,   wherein the direction of airflow through the exit aperture, during use of the gas turbine engine, has at least a component that is anti-parallel to the direction of airflow in the air input duct in a region of the air input duct adjacent to the exit aperture.   
     
     
         2 . The TTCC system offtake according to  claim 1 , wherein the exit aperture is formed in a wall of the air input duct. 
     
     
         3 . The TTCC system offtake according to  claim 2 , wherein the exit aperture is formed in a hollow protrusion formed in the wall of the air input duct. 
     
     
         4 . The TTCC system offtake according to  claim 3 , wherein the exit aperture is formed in a downstream portion of the hollow protrusion relative to the direction of airflow in the air input duct. 
     
     
         5 . The TTCC system offtake according to  claim 3 , wherein the hollow protrusion defines a region of lower pressure compared to the pressure in the region of the air input duct adjacent to the exit aperture. 
     
     
         6 . The TTCC system offtake according to  claim 1 , wherein the exit aperture lies in an aperture plane. 
     
     
         7 . The TTCC system offtake according to  claim 6 , wherein the exit aperture is formed in a wall of the air input duct, and wherein the aperture plane is angled relative to a plane parallel to at least part of a region of the wall of the input air duct surrounding the exit aperture. 
     
     
         8 . The TTCC system offtake according to  claim 7 , wherein the angle of the aperture plane is between 5 degrees and 135 degrees. 
     
     
         9 . The TTCC system offtake according to  claim 6 , wherein the exit aperture has an aperture axis extending through the exit aperture orthogonal to the aperture plane, and wherein the exit aperture is orientated such that a direction parallel to the aperture axis into the exit aperture has at least a component antiparallel to the direction of air flowing in the adjacent region of the air input duct. 
     
     
         10 . The TTCC system offtake according to  claim 9 , wherein the exit aperture is orientated such that a direction parallel to the aperture axis and pointing into the exit aperture has at least a component antiparallel to a longitudinal axis of the air input duct. 
     
     
         11 . The TTCC system offtake according to  claim 1 , wherein the exit aperture is in fluid communication with a TTCC system offtake duct, the turbine-tip clearance control system offtake further comprising a separator plate arranged between the TTCC offtake duct and the air input duct, the exit aperture being formed in the separator plate. 
     
     
         12 . The TTCC system offtake according to  claim 1 , wherein the compressor bleed air outlet is formed in a casing of the compressor, the casing defining a duct through which compression air flows through the compressor. 
     
     
         13 . The TTCC system offtake according to  claim 12 , wherein the compressor bleed air outlet is adapted to remove foreign objects from the airflow through the compressor. 
     
     
         14 . The TTCC system offtake according to  claim 13 , wherein the compressor bleed air outlet is disposed at or near a point at which a change in direction of the airflow through the compressor occurs. 
     
     
         15 . The TTCC system offtake according to  claim 12 , wherein the compressor comprises an annular duct defining the airflow path through the compressor, wherein the annular duct comprises a connecting region arranged to connect portions of the annular duct having a different outer radius to each other, and wherein the compressor bleed air outlet is disposed in or near the connecting region. 
     
     
         16 . The TTCC system offtake according to  claim 1 , wherein the air input duct is further arranged to provide a supply of pressurised air to a secondary system of the gas turbine engine in addition to the turbine-tip clearance control system. 
     
     
         17 . A TTCC system for a gas turbine engine, comprising:
 the TTCC system offtake according to  claim 1 ;   a valve fluidly coupled to the exit aperture of the TTCC system offtake to receive airflow from the air input duct;   a connection duct fluidly coupled to the valve;   a delivery system fluidly coupled to the connection duct, wherein the delivery system is arranged to deliver airflow from the TTCC system offtake to a casing of a turbine of the gas turbine engine.   
     
     
         18 . A gas turbine engine for an aircraft, comprising the TTCC system of  claim 17 . 
     
     
         19 . The gas turbine engine according to  claim 18 , further comprising:
 an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor;   a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and   a gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft,   wherein the compressor bleed air outlet is arranged to receive air from the compressor.   
     
     
         20 . A method of supplying airflow to a TTCC system in a gas turbine engine, comprising:
 providing an air input duct in fluid communication with a compressor bleed air outlet, the air input duct comprising an exit aperture, the exit aperture defining an exit flow path for at least a portion of the air flowing in the air input duct during use of the gas turbine engine; and   separating foreign objects from the airflow in the air input duct by directing airflow through the exit aperture, the airflow being directed such that the airflow has at least a component that is anti-parallel to the direction of airflow in the air input duct in a region of the input duct adjacent to the exit aperture.