Gas turbine engine having a multi-variable closed loop controller for regulating tip clearance

A gas turbine engine having, in flow series, a compressor section, a combustor, and a turbine section, and further having a system (i) for cooling the turbine section and (ii) for providing tip clearance control between turbine blades of the turbine section and circumferentially distributed segments which form an annular shroud surrounding outer tips of the turbine blades, the system including:

• a turbine section cooling sub-system which diverts a first cooling air flow received from the compressor section to a heat exchanger and then to the turbine section to cool components thereof, the first cooling air flow by-passing the combustor and being cooled in the heat exchanger, and the turbine section cooling sub-system having a first valve arrangement which regulates the first cooling air flow;
• a tip clearance control sub-system which supplies a second cooling air flow to an engine case to which the circumferentially distributed segments are mounted, the second cooling air flow regulating thermal expansion of the engine case and thereby controlling a tip clearance between the circumferentially distributed segments and the outer tips of the turbine blades, and the tip clearance control sub-system having a second valve arrangement which regulates the second cooling air flow;
• and a closed-loop controller configured to issue first and second demand signals to respectively the first and the second valve arrangements, each of the first and second demand signals being determined on the basis of:
• (i) a value of the first demand signal at at least one previous time step, and a measurement or estimate of a turbine section component temperature, and (ii) a value of the second demand signal at at least one previous time step, and a measurement or estimate of tip clearance.