Influences of shield ratio on the infrared signature of serpentine nozzle

The criteria for designing the serpentine nozzle on the aspect of infrared suppression is undocumented currently. The aim of this paper is to investigate the influences of the shield ratio on the infrared signature of the serpentine nozzle. Firstly, a validation study was conducted to get the reliable computational method of the infrared signature. Then, the infrared signatures of the serpentine nozzles with variable shield ratios were investigated numerically, and the comparison between the serpentine nozzle and the circular nozzle was also conducted. Results show that 28.9% of the infrared radiation intensity, on average, can be reduced by the single serpentine nozzle, as compare with the circular nozzle. The shield ratio has little effect on the infrared signature of gas outside of the serpentine nozzle exit. And the completely shielded serpentine nozzle cannot bring the greatest benefit to the infrared stealth. The single serpentine nozzle with shield ratio of 0.75 and the double serpentine nozzle with shield ratio of 0.5 have better infrared stealth performance than the others. The visible area ratio can be used as an indicator to evaluate the infrared signature of the serpentine nozzle. In order to provide an effective infrared suppression, the visible area ratio of the single serpentine nozzle and the double serpentine nozzle should be restricted under 0.15 and 0.35, respectively.