Numerical Simulation Of Heat And Mass Transfer In Ablation Layers Of Re-Entry Space Vehicles

During the vehicle re-entry the Earth's atmosphere, its surface will sustain such a great mount of heat load with aerodynamic heating that the performance of the vehicle's interior material will probably be destroyed. So under such conditions, special thermal protection shields need to be taken to make assurance that the interior vehicle is at a normal temperature. Ablation shield has been widely adopted as a main heat protection method recently.In the ablating process, the material will be melted, pyrolyzed or sublimate in the heating environment. The pyrolysis gas will inject into the boundary layers of the surrounding gas, bringing away so much heat that the aerodynamic heat will be prevented partly from transferring into the interior material. According to different mechanics, the ablator material can be classified into three types: the melting type, the sublimating type and carbonizing type.The ablating process is accompanied by phase-change, so the ablating problem can be regarded as a heat conduction problem with phase-change. Phase-change problems have two special points: a moving-boundary or two-phase moving region exists between the two phases. Second, latent heat in ablation is absorbed or released at the interface. Accordingly, the key point of solving phase-change problems lies in how to deal with the moving-boundary. In this thesis, variable-time-step method is taken as a solution for the heat conduction equations.Assuming that the specific heat and the coefficient of heat conductivity is unchangeable with the changing of the temperature of the material, one dimensional quasi-steady ablation and one dimensional unsteady-state ablation problems are numerically calculated. Focused on five factors: aerodynamic heat amount, density, specific heat, the coefficient of heat conductivity and latent heat in ablation, it's analyzed that how these above factors affect the ablation velocity, heat-flux distribution of the wall and the temperature distribution of the interior material. By comparing the ablation performances of the four kinds of materials, terylene-phenolic, nylon-phenolic, DC-325 and AVCO-5029-39, it's concluded that a better ablator material should have these characteristics that the coefficient of heat conductivity is smaller, its density is lower and the latent heat of ablation is higher. This research has provided a reference for both material selection and thickness calculation in the design of thermal protection shields.