Analysis of plume infrared signatures of S-shaped nozzle configurations of aerial vehicle

The infrared susceptibility of the propulsion system of an aircraft is significantly affected by nozzle shapes and atmospheric conditions. Toexamine the effects of nozzle shapes and atmospheric conditions, various nozzle shapes were selected by considering arepresentative low-observable unmanned aerial vehicle and its propulsion system. Then, using thedensity-basedNavier-Stokes-Fouriercomputational-fluid-dynamicscode,the thermal flowfield andthe distribution of chemical species within a plume, which are essential for the analysis of infrared signatures, were calculated. From the analysis of plume infrared signatures for noncircular nozzles, it was found that infrared signature levels were reduced significantly in the axial direction. However, relatively higher signature levels were observed on the left and right sides and below the nozzle due to increase in the aspect ratio of the nozzle outlet as well as curvature, which led to a wider distribution of the plumes along a downward slope. Further, to take into account atmospheric effects, the atmospheric transmissivity according to changes of season and observational distance was analyzed in detail. Finally, the lock-on range was calculated for different nozzle configurations and was compared with the basic circular shape.