Turbine engine tip clearance control utilizing electric machine

1 . An operating method, comprising:

receiving a command to increase thrust generated by a propulsor rotor from a first thrust level to a second thrust level, the propulsor rotor operatively coupled to an engine core and an electric machine, the engine core including a flowpath, a compressor section, a combustor section and a turbine section, and the flowpath extending through the compressor section, the combustor section and the turbine section from an inlet into the flowpath to an exhaust from the flowpath;

operating the engine core in a transient state to increase power output from the engine core to the propulsor rotor from a first power level to a second power level in response to the command;

operating the electric machine to boost the power output from the engine core to the propulsor rotor while the engine core is operating in the transient state; and

operating a clearance control system for the engine core based on the operation of the electric machine;

wherein the clearance control system is configured to adjust clearance between a first turbine rotor in the turbine section and a first shroud circumscribing the first turbine rotor, based on the operation of the electric machine;

wherein the engine core is operated in the transient state to maintain a rate of change in temperature of combustion products within the flowpath below a threshold level and reduce differential thermally induced movement between the first turbine rotor and the first shroud during transient operation of the engine core;

wherein during the operation of the engine core in the transient state and prior to the operation of the electric machine, the clearance control system maintains a first pinch point margin between the first turbine rotor and the first shroud; and

wherein during the operation of the electric machine, the clearance control system changes the first pinch point margin to a second pinch point margin, and the second pinch point margin is less than the first pinch point margin.

2 . The operating method of claim 1 , wherein power output from the electric machine to the propulsor rotor, which boosts the power output from the engine core to the propulsor rotor while the engine core is operating in the transient state, decreases as the power output from the engine core to the propulsor rotor increases from the first power level to the second power level.

3 . The operating method of claim 1 , wherein power output from the electric machine to the propulsor rotor when the engine core enters the transient state is equal to the power output from the electric machine to the propulsor rotor when the engine core exits the transient state.

4 . The operating method of claim 3 , wherein the power output from the electric machine to the propulsor rotor when the engine core enters the transient state is a zero power output.

5 . The operating method of claim 3 , wherein the power output from the electric machine to the propulsor rotor when the engine core enters the transient state is a non-zero power output.

6 . The operating method of claim 1 , wherein a first period of time for the thrust generated by the propulsor rotor to increase from the first thrust level to the second thrust level is less than a second period of time for the power output from the engine core to the propulsor rotor to increase from the first power level to the second power level.

7 . The operating method of claim 6 , wherein the first period of time is at least two times greater than the second period of time.

8 . The operating method of claim 1 , wherein

the engine core further includes a first rotating assembly and a second rotating assembly;

the first rotating assembly includes a first compressor rotor in the compressor section and the first turbine rotor in the turbine section; and

the second rotating assembly comprises a second turbine rotor in the turbine section, and the second rotating assembly is operatively coupled to the propulsor rotor.

9 . The operating method of claim 8 , wherein the clearance control system is further configured to adjust clearance between the second turbine rotor and a second shroud circumscribing the second turbine rotor.

10 . The operating method of claim 8 , wherein the electric machine is operatively coupled to the propulsor rotor through the second rotating assembly.

11 . The operating method of claim 8 , wherein the electric machine is operatively coupled to the propulsor rotor independent of the second rotating assembly.

12 . The operating method of claim 8 , wherein another electric machine is operatively coupled to the first rotating assembly and provides a zero power output to the first rotating assembly during the operation of the engine core in the transient state.

13 . The operating method of claim 1 , wherein the propulsor rotor comprises a ducted propulsor rotor.

14 . The operating method of claim 1 , wherein the propulsor rotor comprises an open propulsor rotor.

15 . The operating method of claim 1 , wherein

the clearance control system includes at least one actuator operatively coupled to the first shroud; and

the operation of the clearance control system includes using the at least one actuator to adjust a clearance gap between the first turbine rotor and the first shroud.