Thermal soak-back mitigation
A method of operating a gas turbine engine having a spool includes executing, by a controller, a shutdown procedure. The shutdown procedure includes: performing an idle rotation operation; determining a parameter associated with a thermal condition of the gas turbine engine while the idle rotation operation is performed; determining, based on the determined parameter, whether the gas turbine engine has met a pre-determined criterion corresponding to a thermally stabilised condition; and terminating the idle rotation operation in response to a determination that the gas turbine engine has met the pre-determined criterion.
1. A method of operating a gas turbine engine having a spool, the method comprising:
executing, by a controller, a shutdown procedure which includes:
performing an idle rotation operation;
determining a parameter associated with a first thermal condition of the gas turbine engine while the idle rotation operation is performed, the parameter being a monitored or predicted pressure at a location in the gas turbine engine;
determining, based on the determined parameter, whether the gas turbine engine has met a pre-determined criterion corresponding to a thermally stabilised condition, wherein the pre-determined criterion includes a thermal stabilization threshold that is a pre-determined value, and the pre-determined value corresponds to a pressure value threshold; and
terminating the idle rotation operation in response to a determination that the gas turbine engine has met the pre-determined criterion.
2. The method of claim 1 , wherein during performance of the idle rotation operation, a turbine of the gas turbine engine expands hot combustion products from a combustor to drive the spool to rotate.
3. The method of claim 1 , wherein the shutdown procedure is executed in response to:
receipt of a shutdown demand signal; or
a determination that a shutdown condition has been met.
4. The method of claim 1 , wherein executing the shutdown procedure further includes:
following termination of the idle rotation operation, performing a cranked rotation operation;
determining a parameter associated with a second thermal condition of the gas turbine engine while the cranked rotation operation is performed;
determining, based on the determined parameter of the second thermal condition, whether the gas turbine engine has met a further pre-determined criterion corresponding to a further thermally stabilised condition; and
terminating the cranked rotation operation in response to a determination that the gas turbine engine has met the further pre-determined criterion.
5. The method of claim 4 , wherein during performance of the cranked rotation operation:
an air turbine starter expands compressed air received from an external air source to drive the spool to rotate;
a mechanical coupling with an external power source drives the spool to rotate; or
an electric machine drives the spool to rotate.
6. The method of claim 1 , wherein the parameter associated with the thermal condition of the gas turbine engine is determined based on a signal received from a sensing arrangement.
7. The method of claim 1 , wherein the gas turbine engine is provided with a thermal management system, and wherein
executing the shutdown procedure further includes:
performing a heat removal operation comprising controlling the thermal management system to cause heat to be removed from the gas turbine engine; and/or
performing a heat redistribution operation comprising controlling the thermal management system to cause heat to be redistributed within the gas turbine engine.
8. The method of claim 7 , wherein the thermal management system includes a fluid pathway for circulating a coolant, wherein the fluid pathway is configured to prevent the coolant circulated therein from being discharged to ambient air.
9. The method of claim 7 , wherein the thermal management system includes a vapour-compression refrigeration circuit.
10. The method of claim 7 , wherein the thermal management system includes a thermal bus configured to transfer heat from a thermal source of the gas turbine engine to a process medium conveyed by the thermal bus.
11. The method of claim 10 , wherein the thermal bus is configured to reject heat from the process medium to an external medium.
12. The method of claim 10 , wherein the process medium is a fuel for combustion in a combustor of the gas turbine engine.
13. The method of claim 12 , wherein the thermal bus is configured to circulate the fuel between a heat transfer location for heat transfer with the thermal source and a fuel tank, wherein the heat transfer location is upstream of the fuel tank.
14. An apparatus including:
a gas turbine engine having a spool; and
a controller configured to carry out the method of claim 1 .
15. A non-transitory machine readable medium comprising instructions which, when executed by a controller of an apparatus comprising the controller and a gas turbine engine having a spool, cause the controller to carry out the method of claim 1 .