本研究以高逼真模型，針對戰機於巡航階段之主要熱源進行一系列數值模擬，其中因空氣動力效應而加熱之機體表面、引擎之高溫處以及噴流尾焰皆為本研究所考量。分析過程中，以計算流體力學依序執行流場模擬、熱傳模擬、表面間輻射模擬以及多波段模擬。由熱源所發出之兩主要特徵波段輻射經球面吸收並導出三視角之極化圖，用以分析各視角之紅外線訊跡特徵。結果顯示噴流尾焰及引擎高溫處之紅外線特徵於後半球面較為顯著，另外噴嘴外部延伸部件亦可於將內壁最高溫處之紅外線訊跡限制於特定角度範圍內。故各部件之幾何及溫度分布亦為紅外線分析之關鍵參數。另外，若欲模擬多種飛行條件、材料及引擎運作等環境，可以改變上述關鍵參數之方式達成，故本研究提供一深入分析紅外線訊跡及相關特徵之方法。

This paper investigated the main thermal sources from a cruising fighter by means of consecutive numerical methods in conjunction with a high-fidelity model. The fuselage surface heated aerodynamically, the hot part of the engine, and the jet flow plume were all considered in the simulation. In the analysis process, the CFD flow field simulation, heat transfer simulation, surface-to-surface (S2S), and multiband thermal radiation simulation were executed sequentially. The emitting radiative fluxes from the heat sources were collected by a spherical receiving wall through two main characteristic spectral bands, then the information was derived into polar plots in three section planes to analyze the IR characteristics. The effects of the exhaust plume and the heated engine surface could be mainly observed from the rear hemisphere. Also, the extended components on the nozzles were found to be effective for blocking strong IR-signature from the interior high-temperature wall over a limited range of angles. Hence, the aircraft geometry and the temperature distribution of the components were the key parameters of the IR-signature analysis. The mentioned parameters could also be modified according to different flight conditions, materials, or engine operations using this method. Therefore, this study provided an important opportunity to advance the understanding of IR-signature characteristics.

[1] Chong-Wei Chu, Joe Der Jr and Wyman Wun. "Simple two-dimensional-nozzle plume model for infrared analysis." Journal of Aircraft 18(12): 1038-1043, 1981
[2] SP Mahulikar, SK Sane, UN Gaitonde and AG Marathe. "Numerical studies of infrared signature levels of complete aircraft." The aeronautical journal 105(1046): 185-192, 2001
[3] SP Mahulikar, HR Sonawane and GA Rao. "Infrared signature studies of aerospace vehicles." Progress in aerospace sciences 43(7-8): 218-245, 2007
[4] Srinath S Heragu, KVL Rao and BN Raghunandan. "Generalized model for infrared perception from an engine exhaust." Journal of thermophysics and heat transfer 16(1): 68-76, 2002
[5] Wei Huang and Hong-Hu Ji. "Impact of Background Radiation on the Long Wave Infrared Radiation Characteristics of Aircraft at High Altitude." Defence Science Journal 66(1), 2016
[6] Tae-Hwan Kim, Hwan-Seong Lee, Ji-Yeul Bae, Tae-Il Kim, Jong-Hyun Cha, Dae-Yoon Jung and Hyung-Hee Cho. "Susceptibility of combat aircraft modeled as an anisotropic source of infrared radiation." IEEE Transactions on Aerospace and Electronic Systems 52(5): 2467-2476, 2016
[7] Ding-Guo Xu, Wei-Lin Feng and Jian-Hua Sang. "IR characteristics of aircraft aft fuselage skin." Infrared and Laser Engineering 42(1): 7-13, 2013
[8] W Sun and B Wang. Modeling and Simulation of Infrared Radiation from Aerial Combat Aircraft by Fluent. 2019 Proceedings of the Conference on Control and its Applications, SIAM. 2019
[9] Jian Wei Lu, Qiang Wang and Oh Joon Kwon. "Evaluating the effectiveness of infrared signature suppression of aircraft skin." Transactions of the Japan Society for Aeronautical and Space Sciences 55(4): 244-253, 2012
[10] Erwin Lindermeir and Markus Rütten. IR-signature of the MULDICON configuration determined by the IR-signature model MIRA. 2018 Applied Aerodynamics Conference. 2018
[11] Jian Liu, Hui Yue, Jia-Xuan Lin and Yuan Zhang. "A simulation method of aircraft infrared signature measurement with subscale models." Procedia Computer Science 147: 2-16, 2019
[12] Qing-Lin Niu, Zhi-Hong He and Shi-Kui Dong. "IR radiation characteristics of rocket exhaust plumes under varying motor operating conditions." Chinese Journal of Aeronautics 30(3): 1101-1114, 2017
[13] Siemens Industries Digital Software. Star CCM+ v 2019.2 User Manual. 2019
[14] Fazal Haq and Jun Huang. "Parametric design and IR signature study of exhaust plume from elliptical-shaped exhaust nozzles of a low flying UAV using CFD approach." Results in Engineering 13: 100320, 2022
[15] Chang-Da Wen and Issam Mudawar. "Emissivity characteristics of roughened aluminum alloy surfaces and assessment of multispectral radiation thermometry (MRT) emissivity models." International Journal of Heat and Mass Transfer 47(17-18): 3591-3605, 2004
[16] Michael Alberti, Roman Weber and Marco Mancini. "Gray gas emissivities for H2O-CO2-CO-N2 mixtures." Journal of Quantitative Spectroscopy and Radiative Transfer 219: 274-291, 2018
[17] Claes Nelsson, Patrik Hermansson, Thomas Winzell and Stefan Sjökvist. "Benchmarking and validation of IR signature programs: Sensorvision, Cameo-SIM and RadThermIR." Swedish Defence Research Agency Linkoeping, 2005