An experimental study of ${\mathrm{CO}}_2$ flows subjected to expanding conditions relevant to Mars entry is presented. A condition with a nominal velocity of $4.0\mathrm{km}/\mathrm{s}$ was generated in the X2 expansion tunnel. Midwavelength infrared emission measurements of the 4.3 and $2.7\mu \mathrm{m}$ bands were made over both a two-dimensional wedge model and for the freestream. Consistent results in the characterization of the freestream were obtained from pressure and spectroscopic measurements. The rotational and vibrational temperatures estimated in the wedge flow using the $2.7\mu \mathrm{m}$ band were consistent with those estimated from the $4.3\mu \mathrm{m}$ band. The difference between the ${\mathrm{CO}}_2$ translational–rotational temperature and the ${\mathrm{CO}}_2$ vibrational temperature was shown to be small in the freestream and expanding flow over the wedge model: less than 10%. Using vibrational relaxation rates tuned for postshock conditions, computational fluid dynamics simulations significantly overestimated the thermal nonequilibrium in the expanding flow, but not in the postshock (compressive) flow. This observation is consistent with past results for ${\mathrm{N}}_2$ and CO, as well as ${\mathrm{CO}}_2$ at lower temperatures.

一项实验研究 ${\mathrm{二氧化碳}}_2$介绍了在与火星进入相关的扩展条件下的流动。名义速度为$4.0\mathrm{公里}/\mathrm{秒}$是在 X2 扩展隧道中生成的。4.3 和 4.3 的中波长红外发射测量$2.7\mu \mathrm{米}$波段是在二维楔形模型和自由流上制作的。从压力和光谱测量中获得了自由流表征的一致结果。楔形流中的旋转和振动温度估计使用$2.7\mu \mathrm{米}$ 频带与根据估计的那些一致 $4.3\mu \mathrm{米}$乐队。之间的区别${\mathrm{二氧化碳}}_2$ 平移-旋转温度和 ${\mathrm{二氧化碳}}_2$自由流和楔形模型上的膨胀流中的振动温度很小：小于 10%。使用针对震后条件调整的振动弛豫率，计算流体动力学模拟显着高估了膨胀流中的热非平衡，但没有高估了震后（压缩）流中的热非平衡。这一观察结果与过去的结果一致${\mathrm{N}}_2$ 和 CO，以及 ${\mathrm{二氧化碳}}_2$ 在较低温度下。