A computation model for auxiliary power unit air bleeding performance based on flat rating

To overcome the disadvantages of the computation model for auxiliary power unit (APU) air bleeding performance in engineering, the structure characteristics and working principle of APU with load compressor were researched. A model based on the matching principle between APU and air start turbine and an interpolation model of variable geometry characteristics of load compressor were presented. On this basis, the regulation law based on APU flat rating was researched, and the relationship among the shaft power load, the APU turbine inlet temperature, the exhaust gas temperature and the inlet guide vane angle of load compressor was determined, consequently the APU bleeding performance was computed at various states in flight envelope. The model was validated with GTCP131-9A’s test data. Results showed that, the deviation of air bleeding mass flow was within 3%, while the deviation of air bleeding pressure was within 4%; in addition, the turbine inlet temperature limit at different altitudes was only related to the shaft power load, but not to the inlet temperature. The model provides a good reference for performance simulation and regulating law design of APU with load compressor.