Abstract: 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.

Key words: reentry missile, asymmetric body, thermal protection, aerothermal, ablation, carbon/carbon material, loosely coupled simulation