Numerical simulation of aerodynamic characteristics during rarefied atmospheric braking

Aerodynamic characteristics in rarefied atmospheric environments are one of the key factors influencing the high-altitude aerodynamic braking of orbiters. This paper presents a numerical simulation of ground-based low-density wind tunnel test conditions using the direct simulation Monte Carlo (DSMC) method, within the context of the Martian atmosphere. A six-component micro-force balance measurement system was employed to conduct aerodynamic force tests on an orbiter model in a low-density wind tunnel, and the experimental results were compared with numerical predictions. Furthermore, taking the Martian atmospheric environment as a case study, numerical simulations were performed to analyze the flow characteristics of the orbiter configuration under various degrees of rarefaction, thereby revealing the aerodynamic behavior governing the Martian rarefied environment. The results indicate that high-altitude rarefied gas effects significantly alter the flow field structure around the orbiter. Distinct compression-expansion features are observed at different altitudes, and the flow field contours tend to exhibit a more circular distribution under the influence of rarefaction effects. Under the specified computational conditions, the freestream dynamic pressure is substantially influenced by flight altitude, leading to notable variations in the overall axial force coefficient, normal force coefficient, and side force coefficient with changing altitude (i.e., degree of rarefaction). A comparison between the numerical and experimental results demonstrates that, within the investigated conditions, the average deviations of the axial force coefficient, normal force coefficient, and pitching moment coefficient are 1.38%, 6.03%, and 12.2%, respectively, thereby validating the effectiveness of the current numerical simulation method. This study provides technical support for the aerodynamic braking design of Martian orbiters.