Analysis of Plume Infrared Signatures of S-Shaped Nozzle Configurations of Aerial Vehicle

Abstract

The infrared susceptibility of the propulsion system of an aircraft is significantly affected by nozzle shapes and atmospheric conditions. To examine the effects of nozzle shapes and atmospheric conditions, various nozzle shapes were selected by considering a representative low-observable unmanned aerial vehicle and its propulsion system. Then, using the density-based Navier-Stokes-Fourier computational-fluid-dynamics code, the thermal flowfield and the 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.Article in Advance / 1 JOURNAL OF AIRCRAFT Downloaded by RMIT BUNDOORA LIBRARY on June 23, 2016 | http://arc.aiaa.org |

Effects of Propulsion System Operation on Military Aircraft Survivability

“…The latter correspond to the rather old J79 turbojet engine but are representative of a generic fully-mixed circular exhaust jet which remains a common configuration among modern military turbofan engines which will be the subject of this study. Following that, axisymmetric shape functions were used to form three-dimensional velocity contours based on the estimated velocities on the jet centerline, as per an expansion of the method to take into account non-circular nozzle configurations (shown to enhance mixing and reduce aircraft IR signature [39]) was considered as part of future work on the project. To account for the effects of forward velocity on the shape of the exhaust jet, as suggested by the theory of turbulent jets [37], the jet expansion angle β was modified according to the formula:…”

Technology challenges of stealth unmanned combat aerial vehicles

“…Passive countermeasures include: masking hot engine parts through geometry or structure modification, mixing hot exhaust gases with freestream air, reducing the reflectivity of the skin through certain coatings and paints, and modifying the skin temperature distribution through physical or chemical means such as liquid evaporation cooling. For jet engines, nozzles with large aspect ratios, defined as nozzle exit width over height, show significant reductions in the IR signature when compared with circular nozzles due to pressure changes in the plume, as well as a more widespread plume, which increases the mixture with cold ambient air, decreasing the overall length of the plume (61) ; ultimately, this leads to an important decrease in lock-on range, as high as 55%. However, for large-aspect-ratio nozzles, penalties can be as high as a 10% reduction in available thrust.…”

Numerical evaluation of the exhaust-direction effects on plume flow and helicopter infrared radiation under hover and cruise statuses

“…The advanced infrared (IR) detection and tracking technology lead to a more and more serious threat to the survivability of aircraft (Antonakis et al , 2019). To improve the survivability of aircraft against the IR-guided weapons, vast efforts have been devoted to the infrared radiation suppression technology during the past decades, including the low-emission exhaust nozzle (An et al , 2016; Cheng et al , 2019), the efficient cooling and optical blocking of internal hot components (Baranwal and Mahulikar, 2019), the mixing enhancement of hot plume with surrounding cold air (Shan and Zhang, 2009; Paszko, 2017) and the use of low-emissivity coating and functional structure (Mahulikar et al , 2006; Andersson, 2017), etc. Nowadays, infrared radiation suppression technology is still an important issue, with an ultimate goal to approach its ideal art-of-state.…”