民用大涵道比涡扇发动机性能分析

Performance Analysis of Civil Turbofan Engine with Large Bypass-ratio

为了更加深入地了解民用大涵道比涡扇发动机的非设计点性能和引起性能参数变化的原因,通过模型民用大涵道比涡扇发动机为载体,采用部件法对其建模,然后对该模型进行仿真计算,研究了大涵道比涡扇发动机在给定控制规律下的转速特性、温度特性、速度特性和高度特性。结果表明,保持其他条件不变,增加发动机低压转子转速,耗油率先减小后增加,先减小主要因为单位推力增加,后增加主要由于油气比增加和涵道比减小,推力则不断增大;保持其他飞行条件不变,增加大气温度,在海平面时尾喷管中的气体都能完全膨胀,由于单位推力变化量较小,内外涵道空气流量减少较多,因此推力减小;研究速度特性时发现,随着飞行马赫数增加,单位推力减小是使耗油率增大的主要原因,马赫数小于0.8时,单位推力减小主导了推力减小,马赫数大于0.8时,空气流量增加较大最终导致推力增加;研究高度特性,对采取低雷诺数修正的高度特性进行研究;在高度大于11 000 m后,耗油率增加主要是由于低雷诺数导致部件效率降低进而引起油气比的升高,就压气机而言,高压压气机效率的下降大于低压压气机。

In order to further understand the characteristics of civil turbofan which has a high bypass-ratio in off-design situations and the reasons for changes in performance parameters, a component-level simulation model of civil turbofan engine with a high bypass-ratio was established, then, the throttling characteristic, the temperature characteristic, the speed characteristic and the height characteristic were calculated under given control schemes. The results show that specific fuel consumption reduces at low rotational speed mainly due to the increase of specific thrust, it ascends at high rotational speed primarily because of the increase of fuel-air-ratio and the decrease of bypass-ratio, the thrust rises all the time while the rotational speed of low-pressure compressor goes up. Meanwhile, the gas in nozzle can be expanded completely at the height of 0, thrust descends mainly due to the reduction of air flow entering the engine when the atmospheric temperature increases. When flight speed becomes faster, specific thrust is the dominating reason for the increase of specific fuel consumption, while the flight Mach number is less than 0.8, thrust reduces mainly because of the decrease of specific thrust, when flight Mach number is greater than 0.8, the great rise of air flow causes the increase of thrust. Low Reynolds number correction was adopted in the last research, when the height surpasses 11 000 m, the decreasing efficiency of compressors caused by low Reynolds number is the primary reason why specific thrust descends, the efficiency decline of high-pressure compressor is greater than that of low-pressure compressor.