Boosting gas turbine engine power with fluid motor

1. A method of operation, comprising:

driving rotation of a rotating assembly during a mode of engine operation by converting fluid power of combustion products flowing through a flowpath within a turbine section into mechanical power using a turbine rotor, wherein a powerplant includes a gas turbine engine, a drivetrain and a fluid motor, wherein the gas turbine engine includes the rotating assembly, a compressor section, a combustor section, the turbine section and the flowpath, wherein the flowpath extends through the compressor section, the combustor section and the turbine section, wherein the rotating assembly includes the turbine rotor in the turbine section, and wherein the mode of engine operation is different than startup of the gas turbine engine;

driving rotation of a thrust rotor using the powerplant during the mode of engine operation; and

boosting the mechanical power for driving the rotation of the rotating assembly during the mode of engine operation using the fluid motor, wherein the drivetrain rotatably couples the fluid motor to the rotating assembly.

2. The method of claim 1 , wherein the mode of engine operation is a transient mode of engine operation.

3. The method of claim 1 , further comprising rotating the rotating assembly during the startup of the gas turbine engine using the fluid motor.

4. The method of claim 1 , wherein the fluid motor comprises a hydraulic motor.

5. The method of claim 1 , wherein the fluid motor comprises a pneumatic motor.

6. The method of claim 1 , wherein the powerplant further includes an electric pump fluidly coupled with the fluid motor, and the electric pump is configured to pump fluid to the fluid motor to power operation of the fluid motor.

7. The method of claim 1 , wherein the powerplant further includes a mechanical pump fluidly coupled with the fluid motor, the mechanical pump is configured to pump fluid to the fluid motor to power operation of the fluid motor.

8. The method of claim 7 , wherein the powerplant further includes a second gas turbine engine rotatably coupled with and configured to drive the mechanical pump.

9. The method of claim 1 , wherein the powerplant further includes a pressure tank fluidly coupled with the fluid motor, and the pressure tank is configured to direct fluid to the fluid motor to power operation of the fluid motor.

10. The method of claim 1 , wherein the drivetrain comprises a clutch.

11. The method of claim 1 , wherein the drivetrain is configured to

rotatably couple the fluid motor to the rotating assembly during the mode of engine operation; and

decouple the fluid motor from the rotating assembly during a second mode of engine operation.

12. The method of claim 1 , wherein the rotating assembly further includes a compressor rotor in the compressor section.

13. The method of claim 12 , wherein the gas turbine engine further includes a second rotating assembly coupled to and configured to drive the rotation of the thrust rotor, and the second rotating assembly includes a second turbine rotor in the turbine section.

14. The method of claim 1 , wherein the rotating assembly is coupled to and configured to drive the rotation of the thrust rotor.

15. The method of claim 1 , wherein

the turbine rotor is further configured to convert the fluid power of the combustion products flowing through the flowpath within the turbine section into the mechanical power for driving the rotation of the rotating assembly during a second mode of engine operation; and

the fluid motor is non-operational during the second mode of engine operation.

16. The method of claim 1 , wherein the thrust rotor comprises a propeller rotor.

17. The method of claim 1 , wherein the thrust rotor comprises a rotorcraft rotor.

18. A method of operation, comprising:

driving rotation of a rotating assembly during a mode of engine operation by converting fluid power of combustion products flowing through a flowpath within a turbine section into mechanical power using a turbine rotor, wherein a powerplant includes a gas turbine engine, a drivetrain and a fluid motor, the gas turbine engine includes the rotating assembly, a compressor section, a combustor section, the turbine section and the flowpath, the flowpath extends through the compressor section, the combustor section and the turbine section, the rotating assembly includes the turbine rotor in the turbine section, and the mode of engine operation is a non-transient mode of engine operation;

driving rotation of a thrust rotor using the powerplant during the mode of engine operation; and

boosting the mechanical power for driving the rotation of the rotating assembly during the mode of engine operation using the fluid motor, wherein the drivetrain rotatably couples the fluid motor to the rotating assembly.

19. A method of operation, comprising:

driving rotation of a rotating assembly during a mode of engine operation by converting fluid power of combustion products flowing through a flowpath within a turbine section into mechanical power using a turbine rotor, wherein a powerplant includes a gas turbine engine, a drivetrain and a fluid motor, the gas turbine engine includes the rotating assembly, a compressor section, a combustor section, the turbine section and the flowpath, the flowpath extends through the compressor section, the combustor section and the turbine section, the rotating assembly includes the turbine rotor in the turbine section, and the mode of engine operation is an emergency mode of engine operation;

driving rotation of a thrust rotor using the powerplant during the mode of engine operation; and

boosting the mechanical power for driving the rotation of the rotating assembly during the mode of engine operation using the fluid motor, wherein the drivetrain rotatably couples the fluid motor to the rotating assembly.