For decades, the main structure of civil aircraft engine has not changed until the appearance of gear transmission technology. Gear transmission is the most widely used transmission form in mechanical transmission. Its transmission is more accurate, high efficiency, compact structure, reliable operation and long service life. With the development of gear transmission technology, it is also used in aircraft engines with higher transmission performance and accuracy requirements, which undoubtedly puts forward higher requirements for its structural design and material selection.
The thrust of the traditional turbine engine mainly comes from the high-pressure compressor, combustion chamber and high-pressure turbine of the engine. The air enters the compressor for compression and then enters the combustion chamber. After combustion with the fuel, the high-temperature gas will rush out of the exhaust nozzle. At the same time, because the compressor is coaxial with the turbine at the rear, the high-temperature gas works by expanding in the turbine and drives the compressor to rotate.
Since then, the turbofan engine works in the same way. Its biggest change is the “double duct”. Part of the air flow sucked in by the fan is sent to the compressor (inner duct), and the other part is directly discharged from the outside of the turbojet engine shell (outer duct). The ratio of the external culvert to the internal air flow is called the culvert road ratio. The performance of the turbofan engine is greatly influenced by the bypass ratio, which has a large bypass ratio and a low fuel consumption rate, but the windward area of the engine is large; when the bypass ratio is small, the windward area is small, but the fuel consumption rate is large.
However, in order to achieve this, the size of the intake fan (intake port) has to be increased. At the same time, the blades of the fan have to continue to grow, and the speed is also increasing. Any continuous increase in any aspect may lead to dangerous vibration. This increases the instability of the engine when it is running.