Investigation on Influence Mechanism of Wall Coating on Infrared Radiation Signature of Serpentine Nozzle

Stealth performance is one of the important factors to evaluate the technical level of the modern battleplane. With the development of radar stealth technology, The opportunity for aircraft to break through the radar blockade and penetrate deep into the war zone increases, which increases the threat of infrared guidance missiles to aircraft. Reducing the infrared radiation feature and enhancing the infrared stealth capability are very important to improve the survivability and combat capability of aircraft in the battlefield. The exhaust system is the main infrared radiation source of the aircraft. Reducing the infrared radiation feature of exhaust system is the chief problem to be solved in order to realize the infrared stealth of the aircraft. The serpentine nozzle can block the direct radiation transmission path between the high-temperature components in the engine and the infrared detector, thus inhibiting the infrared radiation feature. However, due to the reflection characteristics of the nozzle wall, this method can also cause the indirect transmission of the infrared radiation through the wall reflection to form a local high radiation area. Coating technology controls the emissivity of the wall surface by covering the coating on the original high-temperature components to suppress the infrared radiation from the high-temperature wall surface. However, this method also has the disadvantages of weight gain, difficult maintenance after ablation and high cost.

In order to solve these problems, this paper combines two methods, Aiming at the situation of turbofan engine using serpentine nozzle, the influence mechanism of coating position and emissivity of serpentine nozzle on infrared radiation feature is calculated and analyzed based on discrete transfer method, the control scheme of coating emissivity which has the least coating area and can effectively suppress the indirect infrared radiation transmission is also studied. Due to the special geometry of the serpentine nozzle, the radiation emission and reflection of its wall surface are relatively complicated. Therefore, in this paper the wall surface of serpentine nozzle was divided into 6 regions along the center line according to the geometric characteristics to analyze the influence mechanism of coating position on infrared radiation feature, and the wall emissivity of each region was adjusted to 0.1, 0.5, 0.9 and 0.99 separately to analyze the influence of coating emissivity on infrared radiation feature. The comparison of infrared radiation feature of numerical examples with different coating emissivity adjustment and different coating positions can reflect the radiation reflection mechanism between the walls and the influence law of wall coating on infrared radiation feature of serpentine nozzle. The results show that reducing the wall emissivity will increase the reflectivity, and then strengthen the indirect transmission of infrared radiation, causing the increase of the exhaust system infrared radiation intensity, while increase the wall emissivity will reduce the wall reflectivity, the local high radiation area caused by indirect radiation transmission can be effectively prevented. The infrared radiation feature of exhaust system will be affected only when the emissivity of serpentine nozzle wall is adjusted, which can be detected directly by infrared detector. After adopting the optimized wall emissivity coating scheme, the infrared radiation intensity of serpentine nozzle for turbofan can be reduced by 51.3% on the original basis, which effectively solves the problem of high radiation area caused by wall reflection.