Objective Adaptive Cycle Engines (ACE) have made revolutionary improvements in areas such as fuel efficiency, thrust, power, and thermal management that traditional propulsion systems cannot match. They enable the modernization of fighter jet engines, allowing fighters to achieve high thrust during supersonic penetration and low fuel consumption during subsonic cruise. The third bypass airflow of ACE can cool high-temperature components and high-temperature gas streams, thereby reducing infrared radiation from the exhaust system and meeting the super-stealth requirements of sixth-generation fighter jets. ACE is an important future direction for turbofan engine development. However, current research on ACE, both domestically and internationally, is mainly focused on overall design and aerodynamics, with configurations including separate exhaust and mixed exhaust. The infrared radiation characteristics of ACE under different configurations, as well as the impact of the third bypass airflow on infrared radiation characteristics, are not yet clear. Therefore, it is necessary to conduct research on the infrared radiation characteristics of ACE.

Methods Based on the overall design of an ACE, under the constraints of each flow rate and thrust of the exhaust system, the ACE separate exhaust (Fig.1), axisymmetric mixing exhaust (Fig.4) and two-dimensional mixing exhaust system (Fig.6) were designed. The flow field of the exhaust system was simulated by commercial software, and the infrared radiation characteristics were calculated by software independently developed according to the reverse Monte Carlo method, and the aerodynamic and infrared characteristics of the three ACE exhaust systems were numerically simulated.

Results and Discussions Based on the above methods, the calculation results of static pressure distribution

Conclusions Three different ACE exhaust systems were designed for the subsonic cruise mission phase (Ma=0.85, 11 km), and the infrared radiation characteristics of the different exhaust systems were compared under the condition of keeping the exhaust system thrust and each bypass flow unchanged. The results show that the spatial distribution trend of the infrared radiation characteristics of the three ACE exhaust systems is the same, and the solid wall surface is the main contributor at 0°-15°, while the plume is the main contributor at 15°-90°. Since the thermal mixing degrees of the ACE two-dimensional mixing exhaust system and the axisymmetric mixing exhaust system are 6.6 and 5.83, respectively, which are greater than the thermal mixing degree of the separate exhaust system at 3.73, the infrared integral radiation intensity of the tail plume at a 90° angle of the ACE two-demensional mixing exhaust system and the axisymmetric mixing exhaust system is reduced by 87% and 60%, respectively, compared to the separate exhaust system. The center cone and the connotation inlet are the main sources of infrared radiation for the solid parts of the ACE exhaust system, which can be further suppressed by means of cooling, low emissivity coating, shading and other suppression measures. Among the three exhaust systems, the two-dimensional mixing exhaust system has the best infrared performance, with the overall infrared radiation intensity, especially the infrared radiation of the tail plume, being the lowest.