Abstract: To meet the requirements of future combat aircraft for long range and enhanced stealth capability, the effects of operating modes and third-stream flow rate on the aerodynamic and infrared radiation characteristics of an adaptive cycle engine exhaust system under cruise conditions are investigated, and a method for reducing engine infrared signatures by adjusting the third-stream flow rate is proposed. First, a three-dimensional exhaust system model is established based on the key performance parameters obtained from a zero-dimensional component-level engine model, and aerodynamic simulations are conducted. Then, the total pressure recovery coefficients at key cross-sections obtained from the simulations are used to iteratively correct the zero-dimensional model, thereby constructing a hybrid-dimensional model coupling the three-dimensional exhaust system with the zero-dimensional engine model. Based on this model, the effects of different operating modes and third-stream flow rates on engine performance and infrared characteristics under subsonic and supersonic cruise conditions are analyzed. The results show that the high-bypass-ratio mode exhibits better fuel economy and superior infrared stealth performance at large observation angles, making it suitable for subsonic cruise conditions. For the low-bypass-ratio mode, increasing the third-stream flow rate can effectively reduce the infrared signature of the exhaust plume at a 90° observation angle under both supersonic and subsonic cruise conditions by approximately 15.2% and 11.6%, respectively. Therefore, under the premise of satisfying thrust requirements, appropriately increasing the third-stream flow rate can improve both fuel economy and infrared stealth performance to a certain extent.

Key words: Adaptive Cycle Engine, Hybrid-dimension Model, Third Stream, Exhaust System, Infrared Radiation Characteristics