Active tip clearance control system for aircraft engine

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

• a first cooling air source operating at a first temperature;
• a second cooling air source operating at a second temperature greater than the first temperature;
• a conduit fluidly coupling the first cooling air source and the second cooling air source to the turbine casing;
• a valve in the conduit, the valve having a first inlet fluidly connected to the first cooling air source, a second inlet fluidly connected to the second cooling air source, and an outlet selectively connectible to the first inlet and to the second inlet, the outlet fluidly connected to the turbine casing such that the valve is configured to selectively direct a flow of cooling air from the first cooling air source or the second cooling air source to the turbine casing;
• and
• a controller configured to direct the valve to open to the first cooling air source upon receipt of an indication of the aircraft engine operating in a first engine operating condition, the controller further configured to direct the valve to open to the second cooling air source upon receipt of an indication of the aircraft engine operating in a second engine operating condition;
• wherein the turbine casing is a high pressure turbine casing, the system further comprising an additional conduit fluidly coupling the high pressure turbine casing to a shroud of a low pressure turbine downstream of the high pressure turbine, a first aperture through the high pressure turbine casing fluidly coupling a cavity surrounding the high pressure turbine casing to an additional cavity surrounding the low pressure shroud, a second aperture through the low pressure shroud fluidly coupling the additional cavity to an engine gas path at the low pressure turbine.