电弧风洞CO_2介质运行分析

Evaluation of arc-heated wind-tunnel operation in CO_2 atmosphere

为开展金星和火星探测器地面防热试验研究,通过对CO2气体平衡成分分析、喷管流场计算和风洞运行能力分析,评估了电弧风洞模拟探测器进入CO2大气环境时的防热试验能力。首先采用平衡常数法计算分析CO2气体在不同温度和压力下的平衡成分,接着利用一维等熵理想气体模型分析喷管内平衡流和冻结流2种流态下的流场参数,最后计算CO2介质运行时喷管出口的驻点参数,评估驻点压力和驻点热流的包络性能。结果表明:电弧风洞CO2介质运行时气流在加热器内含碳量高达30%,并可能在水冷壁上沉积,降低设备绝缘性能和换热效率,给设备安全运行带来隐患;在平衡流和冻结流2种流态下,喷管出口气流中均含有CO和O2,且CO含量高达50%,为保护下游的真空设备和人员安全,防止反应生成的CO浓度达到爆炸极限,给出了在扩压器补充惰性气体钝化的初步方案。

The main interest of this study is to investigate the performance of the arc-heated wind tunnel using CO2 as the test gas in order to develop heat shield materials for entering Venus and Mars atmospheres which are mainly composed of CO2.Firstly,the mixture composition equilibrium of the CO2 atmospheres for a range of temperatures and pressures has been studied via the equilibrium constant method.Then,numerical simulations of the flow along the facility nozzle have been performed using a one-dimensional isentropic method with and without freezing.The stagnation point parameters at the exit of the nozzle and theoretical performance map of the archeated wind tunnel with CO2 atmospheres have been calculated with one-dimensional method at the equilibrium with and without freezing,based on air envelope and neglecting the effect of archeater efficiency.It indicates that since the mole fraction of carbon in the arc-heated flow is as high as 30%,a large amount of carbon can be deposited onto the inside of the arc-heated wind tunnel,which can reduce the performance of insulation and heat conduction.There is a large amount of explosive gas CO at the exit of the nozzle no matter whether the flow is freezing or not,whose mole fraction can be as high as 50%.Therefore,it is suggested that all tests in the archeated wind tunnel for the simulation of CO2 atmospheres should be carried out using an additional injection gas such of N2 in the diffuser to deactivate the produced CO in order to protect the vacuum pump system and ensure the safety of people.