Anumerical 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.