This invention relates generally to gas turbine engines, and more specifically to gas turbine engine assemblies and methods of assembling the same.
At least some known gas turbine engines include a forward fan, a core engine, and a power turbine. The core engine includes at least one compressor, a combustor, a high-pressure turbine, and a low-pressure turbine coupled together in a serial flow relationship. More specifically, the compressor and high-pressure turbine are coupled through a shaft to define a high-pressure rotor assembly. Air entering the core engine is then mixed with fuel and ignited to form a high energy gas stream. The gas stream flows through the high-pressure turbine, rotatably driving it, such that the shaft that, in turn, rotatably drives the compressor.
The gas stream expands as it flows through the low-pressure turbine. The low-pressure turbine rotatably drives the fan through a low-pressure shaft such that a low-pressure rotor assembly is defined by the fan, the low-pressure shaft, and the low-pressure turbine. To facilitate increasing engine efficiency, at least one known gas turbine engine includes a counter-rotating low-pressure turbine that is coupled to a counter-rotating fan and/or a counter-rotating booster compressor.
To assemble a gas turbine engine including a counter-rotating low-pressure turbine, an outer rotating spool, a rotating frame, a mid-turbine frame, and two concentric shafts are installed within the gas turbine engine to facilitate supporting the counter-rotating turbine. The installation of the aforementioned components also enables a first fan assembly to be coupled to a first turbine and a second fan assembly to be coupled to a second turbine such that the first and second fan assemblies each rotate in the same rotational direction as the first and second turbines. Accordingly, the overall weight, design complexity, and/or manufacturing costs of such an engine are increased. Moreover, to facilitate supporting the fan assemblies, at least one of the fan assemblies is supported on a plurality of bearing assemblies. During operation of the engine, a fragment of a fan blade may become separated from the remainder of the blade. Accordingly, a substantial rotary unbalance load may be created within the damaged fan and carried substantially by the fan shaft bearings, the fan bearing supports, and the fan support frames.
To minimize the effects of potentially damaging abnormal imbalance loads, known engines include support components for the fan rotor support system that are sized to provide additional strength for the fan support system. However, increasing the strength of the support components may also increase an overall weight of the engine and decrease an overall efficiency of the engine when the engine is operated without substantial rotor imbalances.