航天器再入全过程轴对称烧蚀热防护数值仿真研究

对航天器再入全过程轴对称烧蚀热防护进行了全过程数值仿真研究.采用修正Lees驻点热流密度方法和参考焓方法计算再入热流密度.采用JANAF模型计算烧蚀率.利用有限元法计算钝锥体再入航天器烧蚀层在移动边界条件下的轴对称温度场.采用碳化层-热解面-原始材料的轴对称碳化烧蚀模型;推导了热解气体流量计算方法.针对再入飞行大热流密度条件下,用有限元方法求解瞬态温度场时会产生的时间和空间上解的振荡问题.通过分析温度振荡现象产生的原因,采用集中热容矩阵向后差分方法解决振荡问题.计算结果表明,在时间步长选择合适的情况下,求解集中热容矩阵能够很好地解决数值振荡问题,同时烧蚀率和温度场计算比较准确.

Numerical Simulation Research on Axis-Symmetrical Ablative Thermal Protection for Spacecraft in Whole Reentry

The axis-symmetrical implicit thermal response and ablation program for predicting carbon-carbon and carbon based materials and shape change of spacecraft in whole reentry is presented. A modified Lees method is used to calculate heat flux at a stagnation point, and a reference enthalpy method is used to heat flux in other parts. JANAF model is used to calculate chemical ablation rate. A FEM is used to calculate the axis-symmetrical temperature field of thermal protection layer on spacecraft under the condition of moving boundary. Charred layer-pyrolysis surface-original material layer model is applied and pyrolysis gas mass flux calculation formulas are presented. Because the boundary heat flux is very big in reentry, the problem of temporal and spatial numerical oscillation is found when the finite element method is used to compute transient temperature field. By analyzing the reason of the numerical oscillation phenomenon, it is found that the numerical oscillation can be restrained effectively when the lumped heat capacity matrix is solved by using backward difference scheme. It is demonstrated from calculation results that the numerical oscillation can be resolved well when the lumped heat capacity matrix is solved by use of appropriate time step and ablative rate and temperature field calculations are correct.Numerical experiment shows that the simulation program is correct and effective.