Experimental and numerical investigation of infrared stealth measures on flow and infrared characteristics in turbofan exhaust systems

Infrared stealth performance has grown increasingly critical for modern aircraft. Low-observable exhaust systems can suppress infrared radiation (IR) by cooling high-temperature engine components and enhancing the mixing of exhaust plumes with ambient air, thereby improving the survivability of combat aircraft. This study designed infrared stealth measures for both axisymmetric and two-dimensional exhaust systems, including modifying the structure of the heatshield and trailing edge shaping. The modified exhaust systems were installed on a micro-turbojet engine for testing, where wall and exhaust plume parameters were measured. Fourier-transform infrared (FTIR) spectroscopy was employed to measure the infrared characteristic of the exhaust systems. In addition, numerical simulations were also employed to assist in analyzing the infrared suppression mechanism. The experiment results demonstrated the axisymmetric exhaust system achieved peak infrared reductions of 31.7 %. The two-dimensional exhaust system demonstrated enhanced performance, achieving peak significant infrared suppression of 57.6 % and 30.3 % in the vertical and horizontal plane. Successful infrared suppression in both configurations is due to the exit of the heatshield moving to the low-pressure area, which facilitated bypass flow entry into the heatshield channel, enhancing cooling of the divergent section walls. Because of the abrupt transitions in the two-dimensional nozzle, the stealth measures proved more effective in suppressing IR for the two-dimensional exhaust system. However, these measures incur a certain negative impact on thrust performance. The research advances the understanding of integrated thermal management and infrared stealth for next-generation combat aircraft.