远程战略导弹再入大气层，热环境十分严酷，烧蚀量很大，外形呈现非对称性。烧蚀变形、质量引射和表面烧蚀花纹反作用于气动力、气动热及表面温度场。它们之间的相互作用十分复杂，影响落点精度。依据等效转换，将有迎角、侧滑角的绕流转换成总迎角绕流。对于不同子午面，将其变换到纵向坐标轴沿等效流动方向的气流坐标系，通过等效迎角化为零迎角绕流。采用Monte-Carlo统计方法，生成伪随机数，对弹头表面粗糙度随机抽样，表征不同子午线上转捩初始位置的随机分布。改进了零迎角烧蚀外形计算方法，拓展了其应用范围，并通过与能反映转捩点移动方向的松耦合计算策略相结合，采用数值求解烧蚀外形方程，成功模拟了小倾角再入过程中端头非对称烧蚀外形。
Strategic missiles are heated by hypersonic gas while they are reenter into the earth's atmosphere at small attitude angles. The thermal environment is so harsh that the loss of surface material from spacecraft through evaporation or melting caused by friction with the atmosphere is a considerable amount of ablation, thereby forming a visible asymmetric shape. Shape change, matter inject to boundary layer and a number of different types of patterns by ablation will affect the aerodynamics, aerothermodynamics and temperature distribution in the matters. Thermal environment, ablation, and the shape are the cause and effect for each other, and therefore make the impact scatter to spread out. According to equivalent transform analysis, the flow field relative to the vehicle at some angles of attack and sideslip can be equal to that at a total angle of incidence. The vertical axis at a meridian plane is transformed to the flow direction, wherefore the flow flied is at the zero angle of attack. Random sampling of surface roughs is conducted with Monte-Carlo statistical measure to simulate the random distribution of the transition regions at different circumferential positions. The rough sizes are created by the randomizer. The calculation procedure has been improved with these techniques, and the loosely coupled simulation that can exhibit the movement of the transition point towards the vertex of the nosetip is also employed. The numerical calculation method is also used to sole the nonlinear partial differential equation for the ablative shape. The irregular shape of the nosetip of ballistic missiles at small incidence angle in reentry into the earth's atmosphere can be successfully simulated with the methods applied proposed.
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