Unified Numerical Analysis of Galileo Probe Entry Flight Flowfield with Radiation and Ablation

1995年，美国宇航局发射的伽利略号探测器以49公里/秒的速度进入木星大气层。探测飞行器采用烧蚀隔热板进行热保护。根据实际飞行数据，发现滞止点处的隔热板衰退量比飞行前预测的减少了一半，锥台区域的衰退量增加了一倍。在本研究中，利用新开发的计算机程序对伽利略探测器上的强辐射流场进行了数值计算，其中我们假设热化学平衡流场和隔热板的稳定烧蚀。我们首次成功地再现了截锥体区域的隔热层衰退量。我们还确定了在截锥区域发生的增强辐射加热的原因。然而，研究表明，在停滞区，隔热层的衰退量仍然被高估了。这可能是由激波层的非平衡效应引起的，本研究未考虑到这一点。虽然非平衡效应本身降低了滞止区辐射受热量，但在未来的探测飞行器设计中，为了减轻隔热板重量，实现载荷最大化，必然需要更精确的预测方法。作为第一步，我们优化了氢氦混合物的多波段辐射模型。在较高的温度下，氢原子的辐射特性受到电子数密度的严重影响。因此，新建立的多波段模型不仅考虑了气体的平移温度，同时也考虑了电子数密度。对模型的准确性进行了严格的评估。所建立的辐射模型将用于各种激波管实验中观测到的氢的非平衡电离的计算机模拟。

In 1995, the Galileo probe vehicle launched by NASA entered into the Jovian atmosphere at a velocity of 49 km/s. The probe vehicle was thermally protected by ablative heatshield. According to the actual flight data, the amount of heatshield recession at the stagnation point was found to be halved and that at the frustum region was doubled than those given by the preflight prediction.In this study, the strongly radiating flowfield over the Galileo probe vehicle is numerically obtained using the newly developed computer code, in which we assume the thermochemical equilibrium flowfield and also the steady ablation of the heatshield. For the first time, we have successfully reproduced the amount of heatshield recession at the frustum region. We have also identified the cause of enhanced radiative heating occurred at the frustum region. It is however indicated that the amount of heatshield recession at the stagnation region is still overestimated. This is probably caused by nonequilibrium effect in the shock layer that is not accounted for in this study. Although the nonequilibrium effect itself reduces the amount of radiative heating at the stagnation region, a more accurate prediction method is certainly needed to reduce the weight of heatshield and maximize payload in the design of future probe vehicles.As a preliminary step, we have optimized the multiband radiation model for the mixture of hydrogen and helium. At higher temperatures, the radiative property of atomic hydrogen is critically influenced by the number density of electron. Therefore, the newly developed multiband model accounts not only for the translational temperature of the gas but also for the number density of electron, simultaneously. The accuracy of the model is critically assessed. The developed radiation model will be employed in the computer simulation of nonequilibrium ionization of hydrogen observed in various shock tube experiments.