By analyzing the structure and aerothermodynamics processes of the typical auxiliary power unit (APU)

this paper used object-oriented technology and C++ program to design the classes of APU components.In order to simulate a 150-class civil aircraft APU model

instances of the component classes were assembled.According to the APU operating conditions

the thermodynamic and off-design performance calculations were completed

the design state performance and operating envelope about aircraft environment control and main engine start models

as well as altitude-speed

temperature and load characteristics

were obtained accordingly.