化学非平衡效应对返回舱气动特性的影响分析

航天器返回舱再入过程中,高马赫数造成激波层内气体温度急剧升高,由此导致的化学非平衡效应对返回舱气动特性将产生显著影响。而飞行高度和速度的变化影响着化学非平衡过程,进而改变对飞行器气动特性的影响程度。文章通过求解三维Navier-Stokes流体动力学方程,利用耦合化学反应动力学模型对返回舱再入开展数值研究与机理分析,获得量热完全气体模型和化学非平衡气体模型的气动力预测值,分析飞行条件变化时化学非平衡效应对气动特性的影响规律。根据Apollo返回舱的AS-202飞行试验数据验证了计算模型与数值方法。对返回舱的模拟结果表明,高度不变、马赫数增大时,完全气体模型的气动特性预测值不变,化学非平衡效应影响下的轴向力系数、法向力系数和俯仰力矩系数与完全气体预测值的偏差均增大,化学非平衡效应增强;马赫数不变、高度增大时,化学非平衡效应造成的气动力预测值偏差也增大,配平攻角差值略有增加,化学非平衡效应同样增强。机理分析发现,飞行条件变化所造成的化学非平衡流场和压力分布变化是影响气动力变化的主要原因。

The effect of chemical non-equilibrium on aerodynamic characteristics of reentry vehicles

The chemical non-equilibrium has a strong impact on the aerodynamic characteristics of re-entry vehicles flying at high Mach number, which leads to a high temperature shock layer. The altitude and velocity variations would affect the chemical non-equilibrium, and in turn would affect the aerodynamic changes. The numerical investigation and the mechanism analysis are carried out for the re-entry vehicles by solving a three dimensional Navier-Stokes hydrodynamics equation, to understand the effect of the chemical non-equilibrium on the aerodynamic characteristics, as compared to the perfect gas model. The good agreement between the calculated results and the reference data for AS-202 flight test validates the model and the numerical methods. The results show that the predictions of the perfect gas model remain the same and the differences of the aerodynamic forces between the perfect gas model and the chemical reaction gas model are increased with the increase of the Mach number under unchanged altitude. That is because the increase of the Mach number strengthens the chemical non-equilibrium effect. With the increase of the altitude under the same Mach number, the differences between these two gas models show the same trend, the aerodynamic force and the trim angle deviations increase slightly. That indicates the increase of the altitude also strengthens the chemical non-equilibrium effect. It is found that the change of the flow structure under the chemical non-equilibrium and the flucturation of pressure distribution under different flight conditions is the main reason of the aerodynamic variations.