Patent ID: 8820090

Claim:
A method for operating a gas turbine engine including a longitudinal axis defining an axial direction of the engine and a casing having an engine casing portion including a casing wall having a top wall section defining a top dead center, left and right side wall sections, and a bottom wall section defining a bottom dead center, the method comprising: during a first mode of engine operation: compressing air in a compressor section; mixing at least a portion of the compressed air with a fuel and burning the mixture in a combustion section to create hot combustion gases; expanding the hot combustion gases in a turbine section to extract energy from the combustion gases, wherein at least a portion of the extracted energy is used to rotate a turbine rotor; and maintaining a valve system in a closed position to substantially prevent air from passing through a piping system of a shell air recirculation system, the shell air recirculation system being associated with the engine casing portion, which is disposed about the combustion section, the shell air recirculation system comprising: at least one outlet port formed in the engine casing portion; at least one inlet port formed in the top wall section of the casing wall; the piping system, which provides fluid communication between the at least one outlet port and the at least one inlet port; a blower for extracting air from an interior volume of the engine casing portion through the at least one outlet port and for conveying the extracted air to the at least one inlet port; and the valve system, which selectively allows and prevents air from passing through the piping system; and upon initiation of a turn down operation, which is implemented to transition the engine to a second mode of engine operation that is less than full load operation; decreasing the amounts of air and fuel burned in the combustion section so as to decrease the amount of hot combustion gases created in the combustion section; expanding the decreased amount of hot combustion gases in the turbine section to extract energy from the decreased amount of combustion gases, wherein at least a portion of the extracted energy is used to rotate the turbine rotor; opening the valve system to allow air to pass through the piping system of the shell air recirculation system; and operating the blower to: extract air from the interior volume of the casing portion through the at least one outlet port; convey the extracted air to the at least one inlet port; and inject the air into the interior volume of the engine casing portion through the at least one inlet port to circulate air within the engine casing portion, wherein the at least one inlet port is configured such that the air injected thereby flows from the top wall section of the casing wall down the left and right side wall sections of the casing wall toward the bottom wall section of the casing wall.