尾喷管作为飞行器后向强散射源之一，可通过特殊结构设计和介质涂覆缩减其雷达散射截面(RCS).本文采用迭代物理光学法和阻抗边界条件的混合计算模型，研究了6种涂覆方案和不涂覆时双S弯排气系统的电磁散射特性，采用所提出的射线行程追踪方法提高了几何消隐计算效率，利用前后向迭代方法加速收敛并采用openMP和MPI并行技术缩短计算时间，获得了在X波段下7种模型的RCS随探测角度的变化规律.研究结果表明，介质涂覆能够有效抑制双S弯排气系统的RCS；合理的介质涂覆方案不仅具有明显的抑制效果，同时又具有经济性好、重量轻及涂覆方便等优势；相比全涂覆方案，仅在喷管出口附近涂覆的方案，可减少73.6%的涂覆材料，且其RCS的最大增幅不超过15.6%，相比未涂覆方案， RCS至少降低18.5%.同时所开发的计算程序可用于任意腔体电磁散射特性的计算，可为带介质涂覆腔体试验提供技术支撑.%As one of the strong electromagnetic scattering source of the aircraft, the radar cross section (RCS) of the nozzle can be reduced by the special geometry and coating microwave absorbing material at the backward direction of the aircraft. In order to simulate the radar scattering characteristics of six coating models and one metal surface model of double S-shape nozzle, the mode combining impedance boundary condition with iterative physical optics (IPO) method is built. Forward and back-forward IPO method and open MP, MPI parallel computing technology are added to accelerate the convergence and reduce computational time. Besides, the ray tracing method is also adopted to improve the efficiency of geometric blanking judgment. The RCS variation regulations of 7 models under X waveband are obtained. The results indicate that coating medium can effectively diminish the RCS of double S-shape exhaust system. Proper coating method can not only reduce the RCS of exhaust system significantly, but also be economical, easy to coat and light-weight. Compared with all parts coating medium model, the model which is only coated at nozzle outlet can reduce microwave absorbing material cost by 73.6% and ensure that the maximal increment of RCS is less than 15.6%. Comparing with the metal model case, The RCS will decrease by at least 18.5%. The improved IPO method can be applied to the RCS evaluation of cavity and the study of coating absorbing material method, and provide technical support for the coating medium model experiment.
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