基于CEM方法的直升机RCS计算及参数分析

Helicopter RCS Calculation and Parameter Analysis Based on CEM Method

为提高直升机雷达散射特性预估的准确性,建立了目标雷达散射特性分析的计算电磁学方法(Computational electromagnetics method,CEM),并开展了结构参数对雷达散射截面(Radar cross section,RCS)特性影响的研究。以微分形式的Maxwell方程作为电磁特性求解的控制方程,电磁计算网格采用Yee元胞的技术生成,对控制方程进行时间和空间的中心差分格式离散。应用完全匹配层(Perfect matching layer,PML)技术作为吸收边界条件,并与基于等效原理的近远场外推法相结合,建立了直升机RCS的高精度数值方法。分别采用二维无限长导体圆柱和三维金属立方体作为验证算例,结果表明CEM方法比高频方法具有明显的高精度特点。在此基础上,研究翼型厚度、弯度、桨叶片数对旋翼雷达散射特征的影响机理和变化规律,同时计算机身不同结构布局参数下的RCS特性,分析短翼和平尾对机身强散射特征的影响规律。研究表明:桨尖是旋翼的重要散射源之一,采用薄翼型桨叶能有效改善旋翼的雷达散射性能,短翼和平尾会在不同角域内增加机身的雷达散射截面,在直升机隐身设计中需要重点考虑。

In order to increase the prediction accuracy on helicopter radar scattering characteristics, the computational electromagnetics method （CEM） is established to analyze radar scattering characteristics, and the influence of structure parameters on radar cross section （RCS） characteristics is studied. The differential forms of Maxwell＇s equations are taken as the governing equations for solving electromagnet- ic property, computational electromagnetic grids are generated by adopting the Yee grid technology, and the governing equations are solved by temporal and spatial discretization with central difference scheme. The perfect matching layer （PML） technique is employed as the absorbing boundary conditions, and the numerical method with high precision for helicopter RCS is established by combined with the equivalence principle of near-far field extrapolation. Two-dimensional conductor cylinder with infinite length and three-dimensional metal cube are taken as numerical examples respectively. The results show that CEM has higher precision than the high frequency method obviously. On this basis, researches on the influ- ence mechanism and variation characters of airfoil thickness, airfoil camber and the number of blades on rotor radar scattering characteristics are carried out, and RCS characteristics of fuselage with different structure parameters are computed, then the influence mechanism of short wings and horizontal tails on fuselage strong scattering characteristics is analyzed. It is demonstrated that blade tip is one of the sig- nificant scattering sources of rotor, rotor with thin airfoil can improve the radar scattering performance effectively, and short wings and horizontal tails can increase the RCS of fuselage in different angles, which should be taken into key consideration in stealth design of helicopter.