Bowed rotor start mitigation in a gas turbine engine

1. A bowed rotor start mitigation system for a gas turbine engine, the bowed rotor start mitigation system comprising:

a controller operable to receive a vibration input indicative of an actual vibration level of the gas turbine engine and a speed input indicative of a rotor speed of the gas turbine engine, the controller generating a bowed rotor start mitigation request based on comparing the actual vibration level to a modeled vibration level at the rotor speed;

a motoring controller operable to determine whether to reduce a motoring time determined by a risk model based on a result of comparing the actual vibration level to the modelled vibration level at the rotor speed, wherein the risk model maps core temperature model data with time data and ambient temperature data to establish the motoring time as an estimated period of motoring to mitigate a bowed rotor of the gas turbine engine; and

a digital storage unit operable to store time and temperature data for the risk model, wherein the digital storage unit is operable to continue monitoring of temperature data while the gas turbine engine is shut down and the bowed rotor start mitigation system is operable to compare monitored temperature data with modelled temperature data to validate one or more temperature models of the gas turbine engine.

2. The bowed rotor start mitigation system as in claim 1 , wherein comparing the actual vibration level to the modeled vibration level at the rotor speed is triggered to be performed at a rotor speed threshold that is below a resonance speed of the gas turbine engine.

3. The bowed rotor start mitigation system as in claim 1 , wherein the controller is operable to perform the comparing of the actual vibration level to the modeled vibration level during a dry motoring mode of the gas turbine engine below a resonance speed of the rotor.

4. The bowed rotor start mitigation system as in claim 3 , wherein the controller drives motoring of the gas turbine engine to a bowed rotor mode determination speed that is less than a dry motoring mode speed to perform the comparing of the actual vibration level to the modeled vibration level at a range of rotor speeds up to the bowed rotor mode determination speed prior to reaching the dry motoring mode speed.

5. The bowed rotor start mitigation system as in claim 3 , wherein the controller periodically performs the comparing of the actual vibration level to the modeled vibration level in the dry motoring mode to determine whether bowed rotor mitigation has completed prior to reaching an engine starting time.

6. The bowed rotor start mitigation system as in claim 1 , wherein metrics of attempted bowed rotor mitigation are recorded based on determining that the attempted bowed rotor mitigation was unsuccessful or incomplete.

7. A gas turbine engine system comprising:

a motoring system operable to drive rotation of the gas turbine engine;

a vibration monitoring system operable to monitor actual vibration of the gas turbine engine;

an electronic engine control operable to receive a vibration input indicative of an actual vibration level from the vibration monitoring system and a speed input indicative of a rotor speed of the gas turbine engine, the electronic engine control generating a bowed rotor start mitigation request that drives the motoring system to perform bowed rotor mitigation based on comparing the actual vibration level to a modeled vibration level at the rotor speed; and

a motoring controller operable to determine whether to reduce a motoring time determined by a risk model based on a result of comparing the actual vibration level to the modelled vibration level at the rotor speed, wherein the risk model establishes the motoring time based on temperature data as an estimated period of motoring to mitigate a bowed rotor of the gas turbine engine.

8. The gas turbine engine as in claim 7 , wherein the actual vibration level is sampled below twenty-five percent of a resonance speed of the rotor to predict whether vibration amplitude of the rotor will be unacceptable for transiting the resonance speed.

9. The gas turbine engine as in claim 7 , wherein a maintenance request is triggered based on the actual vibration level exceeding a maintenance action threshold after completing an attempt of bowed rotor mitigation.

10. A method of bowed rotor start mitigation for a gas turbine engine, the method comprising:

receiving a vibration input indicative of an actual vibration level of the gas turbine engine;

receiving a speed input indicative of a rotor speed of the gas turbine engine;

generating, by a controller, a bowed rotor start mitigation request based on comparing the actual vibration level to a modeled vibration level at the rotor speed;

determining whether to reduce a motoring time determined by a risk model based on a result of comparing the actual vibration level to the modelled vibration level at the rotor speed, wherein the risk model maps core temperature model data with time data and ambient temperature data to establish the motoring time as an estimated period of motoring to mitigate a bowed rotor of the gas turbine engine;

continuing monitoring of temperature data while the gas turbine engine is shutdown; and

comparing monitored temperature data with modelled temperature data to validate one or more temperature models of the gas turbine engine.

11. The method as in claim 10 , further comprising:

triggering the comparing of the actual vibration level to the modeled vibration level at a rotor speed threshold that is below a resonance speed of the gas turbine engine.

12. The method as in claim 10 , wherein the comparing of the actual vibration level to the modeled vibration level is performed during a dry motoring mode of the gas turbine engine below a resonance speed of the rotor.

13. The method as in claim 12 , further comprising:

driving motoring of the gas turbine engine to a bowed rotor mode determination speed that is less than a dry motoring mode speed to perform the comparing of the actual vibration level to the modeled vibration level at a range of rotor speeds up to the bowed rotor mode determination speed prior to reaching the dry motoring mode speed.

14. The method as in claim 12 , further comprising:

periodically performing the comparing of the actual vibration level to the modeled vibration level in the dry motoring mode to determine whether bowed rotor mitigation has completed prior to reaching an engine starting time.

15. The method as in claim 10 , further comprising:

recording metrics of attempted bowed rotor mitigation based on determining that the attempted bowed rotor mitigation was unsuccessful or incomplete.

16. The method as in claim 10 , further comprising:

triggering a maintenance request based on determining that the actual vibration level exceeds a maintenance action threshold after completing an attempt of bowed rotor mitigation.