火星登陆器隔热层间气体非平衡渗流机理与热量耦合传递特性研究

The thermal protection of cryogenic tanks in complex Mars environment is the key unsolved technology for the development of deep space exploration in China. In this project, aiming at the unique phenomenon of rarefied CO2 inflation process in the multilayer insulation (MLI) during reentry into the Martian atmosphere, by using kinetic theory of gases, lattice Boltzmann method and experimental investigation, the dynamic behaviors of percolation, collision and migration of low pressure CO2 and heat transfer characteristics under non-equilibrium conditions in MLI would be investigated. The contents include: 1) transient percolation mechanism of rarefied gas covering various flow regimes in MLI; 2) rarefied gas diffusion and carrying heat coupling transfer mechanism in MLI; 3) the influences of multi-parameters on the heat and mass transfer in MLI. Based on the above research, unsteady percolation migration mechanism and coupled heat transfer mechanism for rarefied CO2 covering various flow regimes in multilayer microporous structure would be clearly revealed, the change of inflation rate and the transient pressure distribution between layers would be obtained, and the relaxation time reached to the equilibrium state would be determined. Furthermore, the key factors of interlayer transient heat and mass transfer characteristics and its effect would be achieved. Finally, the best match of energy and mass transfer in multi-layered structure would be proposed by different control methods, in order to achieve the optimization of the directional transfer weakening of heat during the reentry process of Mars landers.

复杂火星环境下低温贮箱热防护是我国深空探测发展中的核心关键技术。本项目针对多层隔热材料（MLI）再入火星大气层时稀薄CO2充气过程的特有现象，采用气体动理学理论、格子Boltzmann方法与实验研究相结合的手段，对低压CO2在MLI内非平衡条件下渗流、碰撞、迁移的动力学行为和热量传递特性展开研究。内容包括：1）MLI内稀薄气体跨流域瞬态渗流机理；2）MLI内稀薄气体扩散与携带热量耦合传递机制；3）多参数对MLI内热质传递特性的影响规律。通过研究，揭示稀薄CO2在多层微孔结构内非稳态跨流域渗流迁移机理和热量协调传递机制，掌握充气速率变化及MLI层间瞬态压力分布规律，确定达到平衡态时的弛豫时间，明确层间瞬态热质传递特性的关键因素及其影响规律。在此基础上，研究采用不同调控手段实现多层结构内能质传递的最佳匹配，实现火星登陆器再入过程中MLI热侵定向传递减弱的优化目的。

火星登陆器低温燃料贮箱热防护设计是我国未来登陆火星过程中关键技术之一。围绕火星登陆器全周期任务剖面升空/在轨阶段放气与再入/火星表面停放阶段吸气的特有现象，采用理论方法、数值计算与实验测量相结合的手段，对低温燃料贮箱复合绝热结构内气体瞬态渗流与耦合传热特性开展研究。内容包括：1）火星登陆器低温燃料贮箱复合绝热结构性能研究；2）低温燃料贮箱MLI瞬态放气特性与绝热性能优化研究；3）仿火星环境多层隔热材料瞬态吸/放气实验研究；4）液氢容器高真空多层隔热材料绝热性能及气冷屏优化研究。通过研究，建立了气体瞬态渗流与耦合传热的数学模型，获得了火星登陆器再入过程多层隔热材料间的瞬态压力分布特征，掌握了CO2凝结对绝热性能的影响；构建了描述MLI非稳态放气特性的压力节点算法，掌握了MLI瞬态放气过程中层间压力分布规律，提出了组合缝隙率和组合变密度结构的优化方案；搭建了仿火星环境MLI瞬态渗流与传热性能测试实验平台，测出了层间压力非稳态放气/吸气分布规律，填补了层间压力瞬态变化的重要实验数据；发现了一种放气性能良好的新型间隔物(蜂窝网)；获得了采用单一气体冲洗MLI对其层间残余气体释放的影响规律；掌握了反射屏开孔方式和层数对MLI层间放气特性的影响规律；发现MLI层间放气持续10个小时后，仍未达到平衡态，且层间压力较真空环境的压力高出约3-5个数量级；与放气工况比，吸气速率变得很快，第一次充气MLI达到吸气平衡态的弛豫时间约64秒。实验研究结果补充了气体在复杂MLI内瞬态渗流与分布特征的认知，为MLI在航天飞行器低温燃料贮箱绝热结构设计中提供了优化方向。同时，扩宽了研究内容，对氢浆制备与低温气液掺混冷凝进行了实验研究，氢浆是一种具有未来火星登陆器应用前景的低温燃料。国内首次采用热交变技术制备出了13.9K浆氢固液两相产品，可视化测量了氢浆的制备过程。本项目研究结果服务于火星探测任务，可有效降低火星登陆器低温燃料贮箱全周期任务的热侵，提升热防护保障。