再入飞行器尾迹流场及其雷达散射效应研究

对再入飞行器等离子体尾迹及其雷达散射特性进行了分析、研究和大量的计算。讨论了物形、流场各因素对尾迹雷达散射截面的影响。流场计算使用准一维粘性尾迹方程，以修正基尔方法（多值法）求解，用一阶Ｂｏｒｎ近似完成亚密雷达散射截面（ＲＣＳ）计算。计算中使用８组元混合空气、１４个非平衡化学反应模型，考虑５种不同尺度的小钝头锥形物体，沿再入轨道取６５至３４公里，共１３个高程的飞行条件。通过计算得到了再入体尾迹各流场参数、电子密度分布及湍流亚密尾迹的ＲＣＳ。结果说明再入钝锥细长体粘性尾迹的转捩特性对于等离子体的散射性质具有决定性的作用；再入弹头尾迹等离子体对地面单站雷达发射波的回波主要来源于尾迹湍流亚密的非相干散射；对确定的波长，当环境雷诺数达到临界值之后，可能出现ＲＣＳ的突增现象；不同物形及来流条件造成尾迹转捩位置的改变，从而影响ＲＣＳ的数值及其沿轨道的分布；改变尾迹颈部初值会引起ＲＣＳ值的明显变化。

Study of Wake Flowfield and Radar Cross Section of the Reentry Vehicle

In this paper,plasma wake flow of hypersonic reentry vehicle and radar scattering characteristics have been studied. The effects of body configurations and flow field properties on the radar cross section(RCS)have been analyzed.The flow field is calculated based on quasi-one-dimensional viscous equation proposed by the author, using modified Gill method.In computation, 8 components air mixture and 14 nonequilibrium chemical reactions are included.The RCS is calculated by first-order Born approximation,5 different small blunt cones at various flow conditions including 13 reentry altitudes from 65 to 34km are considered. Various flow field parameters, axial electron density and RCS of turbulent underdense wake of reenty vehicles are obtained. Results show that wake transition has a significant effect on the RCS. The echo wave energy of plasma wake received by a single station radar is mainly from the incoherent scattering in underdense region of turbulent wake. For a specific radar wave, the rapid rise in RCS occurs in a fully developed turbulent wake when environment Reynolds number exceeds transitional Reynolds number. Different body shapes and flow field parameters will change the location of wake transition and eventually the value and distribution of RCS. In addition, change of initial electron density at the wake neck causes obvious variation of RCS.