火星进入流场特性中红外吸收光谱诊断研究

Mid-IR Laser Absorption Diagnosis on Flow Characteristics for MarsEntry

火星探索项目是我国深空探测工程的重要组成部分,“天问一号”2021年成功着陆火星,是中国航天在火星探索研究迈出的一大步。火星大气的气氛主要以二氧化碳为主,表面气压远低于地球大气,由于大气成分和进入轨道的差异,火星进入器面临的热环境同地球返回器有很大不同,其进入过程为非空气介质的高速流动,将产生严重的气动防热问题。利用电弧风洞模拟火星进入器气动加热环境,是开展火星探测防热系统设计的关键。电弧风洞模拟火星进入高温过程,其主要过程是CO_(2)主导的离解反应,并且CO等高温离解组分与火星进入器防热材料相互作用,产生的催化效应会显著影响气动热环境。利用中红外量子级联激光吸收光谱测量技术,开展电弧加热火星进入流场特性的在线定量研究。电弧加热在线诊断研究利用CO在4.5μm附近中心波长为2212.625 cm^(-1)(v″=0,R(19))的谱线,实现了对火星地面流场的高信噪比测量,采用单线-直接吸收光谱诊断技术获得了自由流静温和关键组分CO摩尔浓度的实时测量结果。典型状态下,火星进入流场自由流静温和CO摩尔组分浓度在整个运行时间内保持稳定,显示出电弧加热流场良好的稳定性。六组重复试验显示自由流静温和CO摩尔组分浓度分别在(1757±69)K和(0.189±0.027)范围内,自由流温度波动≤3.9%,CO组分浓度波动≤14.3%,证明电弧风洞建立的火星地面流场具有非常好的重复性。基于该研究发展的电弧风洞中红外激光吸收光谱诊断技术,可以为研究火星进入器气动热环境和防热材料烧蚀-催化特性提供精细化测量能力。

The Mars exploration mission is important to the national deep space exploration project.The successful landing of“Tianwen”on Mars in 2021 is a big step forward in China's space exploration and research on Mars.The Martian atmosphere is mainly dominated by carbon dioxide,and the surface pressure is much lower than the Earth's.Due to the differences in atmospheric composition and entry orbit,the thermal environment of Mars entry vehicles is very different from that of Earth space vehicles.The entry process involves a non-air high-speed flow,leading to serious aerothermal heating problems.The arc-heated wind tunnels are used to simulate the aerothermal heating environment for Mars entry,which is a key step in validating the thermal protection system design for Mars exploration.The-high-temperature flow simulated by the arc-heated wind tunnel includes a dominated CO_(2)dissociation reaction,and dissociation species such as CO interact with the thermal materials of the Mars entry vehicles,which would cause a catalytic effect and significantly affect the aerothermal environment.In this paper,the mid-infrared quantum cascade laser absorption spectroscopy is carried out for in-situ and quantitative measurements of the flow characteristics of ground-based simulation for Mars entry in the arc-heated facility.The in-situ diagnosis in the arc-heated facility utilizes the spectral line of CO with a central wavelength of 2212.625 cm^(-1)(ν″=0,R(19))near 4.5μm,to achieve a high signal-to-noise ratio measurement of the ground-based flow field.A single-line direct absorption spectroscopy obtains the static temperature and CO mole fraction of free stream in the arc-heated wind tunnel.Under a typical condition for Mar entry,the static temperature and CO mole fraction of freestream remain stable throughout the operation,showing good stability in the arc-heated flow field.Six repeated experiments show that the static temperature and CO mole fraction are in the range of(1757±69)K and(0.189±0.027)respectively,with fluctuation of less than or equal to 3.9%in flow temperature and fluctuation of less than or equal to 14.3%in CO concentration,demonstrating great repeatability for the ground-based simulated flow field.The developed mid-infrared laser absorption spectroscopy diagnostic technology in the arc-heated wind tunnel can provide refined measurement capabilities for research of the aerothermal environment and ablation-catalytic properties of the thermal protection materials of the Mars entry vehicles.