Numerical investigation was performed on the infrared suppress characteristics of the nozzles with and without cone cooled.In the former,cone and blade were cooled by secondary channel gas,and the temperatures of blade and cone walls were effectively decreased by 21.1% and 46.2% respectively,using only 1.6% of the secondary gas.The radiation of nozzle cavity in 3-5 μm was suppressed effectively,the radiation in the small view angle range from behind the nozzle decreased obviously,and the radiation decreased by 30% from straight behind the nozzle compared to the nozzle without cone cooling.
Background radiation characteristic is an important part of the target infrared radiation.For the typical stealth UAV,the effect of the background radiation on target infrared radiation was theoretically analyzed,and the mathematical model of the target infrared radiation was established.Using the numerical simulation method,the target infrared radiation characteristic under the background radiation was calculated,and the effect of background radiation on the target infrared radiation characteristics was analyzed.The results provide a reference for the aircraft infrared detection and infrared stealth design.
A numerical study was conducted on infrared radiation characteristics in the waveband of 3～5 μm for exhaust system of an unmanned aerial vehicle(UAV) with engine installed on the back of its fuselage.The flow field of the exhaust jet was calculated with commercial software FLUENT.The infrared radiation characteristics were calculated by using the software developed by the authors based on discrete transfer method.In the computation,multiple effects were considered,which included the emission and reflection of the nozzle wall,the absorption and emission of species of combustion gas,e.g.CO2,H2O and CO,the shelter of fuselage,and the absorption of atmosphere.The results show that by installing the engine on the back of the fuselage,sheltering the nozzle from its underside and forward shifting the nozzle exit relative to the aft-fuselage,the infrared radiation of the exhaust system to under hemisphere is reduced evidently,but on the other side the infrared radiation to the top hemisphere is increased;and the absorption effect of atmosphere on infrared radiation for the front hemisphere is stronger than that for the aft hemisphere.
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