Active tip clearance control system for aircraft engine

A system for controlling a clearance between tips of turbine blades and a shroud supported by a turbine casing in an aircraft engine, the system comprising:

• a first source of cooling air operating at a first temperature;
• a second source of cooling air operating at a second temperature greater than the first temperature;
• a conduit fluidly coupling the first source of cooling air and the second source of cooling air to the turbine casing;
• a sensor configured to measure the clearance between the tips of the turbine blades and the shroud;
• a valve in the conduit, the valve having a first inlet fluidly connected to the first source of cooling air, a second inlet fluidly connected to the second source of cooling air, and an outlet selectively connectible to the first inlet and to the second inlet, the outlet fluidly connected to the turbine casing to selectively direct a flow of cooling air from the first source of cooling air or the second source of cooling air to the turbine casing;
• and
• a controller operatively connected to the sensor for receiving a signal from the sensor indicative of a measured clearance, the valve controlled by the controller to fluidly couple the first source of cooling air to the turbine casing upon the measured clearance being above a predetermined value and to fluidly couple the second source of cooling air to the turbine casing upon the measured clearance being below the predetermined value.

A method for controlling a clearance between turbine blades and a shroud of a turbine casing in an aircraft engine, comprising:

• receiving an indication from a sensor that the clearance is above or below a predetermined value;
• when the clearance is above the predetermined value, controlling a valve to flow a first flow of cooling air operating at a first temperature to the turbine casing;
• and
• when the clearance is below the predetermined value, controlling the valve to block the first flow of cooling air and to flow a second flow of cooling air operating at a second temperature, the second temperature greater than the first temperature, to the turbine casing.