Shape Optimization of Single Serpentine Nozzle to Minimize Observability of UCAV

Ensuring survivability of unmanned combat aerial vehicle (UCAV) is important to complete various missions in a battlefield environment. In particular, the infrared signal emitted from the exhaust gas plume of UCAV is tracked by infrared detectors, and it is one of the major threats to UCAV survivability. To solve this problem, a serpentine nozzle has been developed to reduce the observability of infrared signals. In this study, a shape design optimization of the single serpentine nozzle is performed to minimize the infrared signals. The design optimization framework proposed in this paper consists of three major parts: nozzle flow simulation, narrow-band model, and gradient-free optimization algorithm. Reynolds-averaged Navier-Stokes simulation is used to predict the propulsive performance and flow field around the single serpentine nozzle at the ground condition. Infrared signature characteristics are calculated using the narrow-band model. The Kriging surrogate model is used to construct the response surface that provides fast approximations of time-consuming function evaluation, and a genetic algorithm is used to find the optimal solution. The objective function is to minimize the infrared signal and six design factors are defined as the design variables that deform the shape of nozzle. As a result of shape optimization, 10.3% and 83.6% of the maximum infrared signal reduction are achieved in the azimuth and altitude angles, respectively, compared to the baseline nozzle.