Numerical simulation of infrared radiation characteristics for exhaust system of an UAV with engine installed on the back of the fuselage

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.