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Influence of the Mars atmosphere model on aerodynamics of an entry capsule

机译：火星大气模型对进入舱空气动力学的影响

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This study develops a dual purpose: i) evaluating the effects of two different Mars atmosphere models (NASA Glenn and GRAM-2001) on aerodynamics of a capsule (Pathfinder) entering the Mars atmosphere, ii) verifying the feasibility of evaluating the ambient density and pressure by means of the methods by McLaughlin and Cassanto, respectively and therefore to re-build the values provided by the models. The method by McLaughlin relies on the evaluation of the capsule drag coefficient, the method by Cassanto relies on the measurement of pressure at a point on the capsule surface in aerodynamic shadow. The study has been carried out computationally by means of: i) a code integrating the equations of dynamics of the capsule for the computation of the entry trajectory, ii) a DSMC code for the solution of the flow field around the capsule in the altitude interval 50-100 km. The models show consistent differences at altitudes higher than about 40 km. It seems that the GRAM-2001 model is more reliable than the NASA Glenn model. In fact, the NASA Glenn model produces, at high altitude, temperatures that seem to be too low compared with those from the GRAM-2001 model and correspondingly very different aerodynamic conditions in terms of Mach, Reynolds and Knudsen numbers. This produces pretty different capsule drag coefficients by the two models as well as pressure on its surface, making not feasible neither the method by McLaughlin nor that by Cassanto, until a single, reliable model of the Mars atmosphere is not established. The present study verified that the implementation of the Cassanto method in Mars atmosphere should rely (such as it is currently) on pressure obtained experimentally in ground facilities.
机译：这项研究具有双重目的：i）评估两种不同的火星大气模型（NASA Glenn和GRAM-2001）对进入火星大气的胶囊（探路者）空气动力学的影响，ii）验证评估环境密度的可行性和分别通过麦克劳克林（McLaughlin）和卡桑托（Cassanto）的方法进行压力测量，从而重建模型提供的值。麦克劳克林（McLaughlin）的方法依赖于胶囊阻力系数的评估，卡桑托（Cassanto）的方法依赖于气动阴影中胶囊表面某一点的压力测量。该研究是通过以下方式进行的：i）集成了舱室动力学方程的代码，用于计算进入轨迹； ii）DSMC代码，用于求解海拔区间中舱室周围流场的解50-100公里这些模型在高于约40 km的高度显示出一致的差异。看起来，GRAM-2001模型比NASA Glenn模型更可靠。实际上，与GRAM-2001模型相比，NASA Glenn模型在高海拔地区产生的温度似乎太低，并且在马赫数，雷诺数和克努森数方面相应地存在很大的空气动力学条件。这两个模型产生的胶囊阻力系数及其表面压力完全不同，直到没有建立一个可靠的火星大气模型之前，McLaughlin的方法和Cassanto的方法都不可行。本研究证实，在火星大气层中实施Cassanto方法应（如目前）依赖于地面设施实验获得的压力。

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