Performance Advantage Evaluation of Air-Oil Heat Exchanger Based on Variable Cycle Engine in Flight Mission

Abstract

Adding an air-oil heat exchanger to the aero-engine is beneficial to improve the cooling quality of turbine cooling air, while its influence mechanism during the whole flight envelope is still ambiguous. This paper evaluates the performance advantages of the air-oil heat exchanger by building a comprehensive performance simulation model integrating variable cycle engine (VCE), air-oil heat exchanger, and blade temperature evaluation model. The results show, based on typical flight tasks: adding a heat exchanger without changing the cycle parameters reduces the engine’s overall performance, but the blade thermal environment improves, and the temperature drop of the cooling air can reach 45–214K under various operating conditions. Adding a heat exchanger and adjusting bleed air ratio or turbine inlet temperature can increase thrust obviously. For these two parameters, adjusting turbine inlet temperature can gain more enhancement in aeroengine performance. The increase in thrust is no less than 15% in take-off, climbing, and air combat conditions when high thrust is needed, effectively improving the climbing rate, service limit, and maneuverability of the assembled aircraft. Based on the flight envelope: the influence of flight environment on the two modes of VCE is consistent, the cooling air temperature and blade surface temperature are higher in the high-Ma region. Moreover, from the perspective of the engine’s internal thermal environment, double bypass mode is more suitable in low-altitude and low-speed regions, while single bypass mode is more fit in high-altitude and high-speed regions. Furthermore, the heat exchanger can effectively improve the thermal environment of hot-end components in the high-Ma region, ensuring the engine runs in safe conditions. In conclusion, this study points out the performance advantages of air-oil heat exchangers on VCE, which could help solve thermal problems in future advanced engines.