电弧风洞中基于TDLAS的气体温度和氧原子浓度测试

电弧风洞是对防热材料/结构进行地面考核的关键设备,其流场参数是评估设备性能和品质的关键数据。由于高温气流的恶劣环境,尚无有效诊断手段。本文使用可调谐二极管吸收光谱技术(TDLAS),针对气流中氧原子,选用氧原子特征吸收谱线(λ=777.2nm),测量了电弧风洞中水冷平头圆柱体模型脱体激波后的气体温度和氧原子数密度,试验测量与工程计算结果较为一致。试验显示出TDLAS具有高温电弧风洞应用的潜在优势。

Measurements of gas temperature and atomic oxygen density in the arc-heated wind tunnel based on TDLAS

Large-scale,high-enthalpy arc heated wind tunnels are the most reliable ground test facilities to test thermal protection materials and heat shield structures for space vehicles. Flow conditions in the facility need to be monitored.Currently,the facility conditions are defined using either the anticipated surface temperature with an assuming emissivity or the expected heat flux level.While this is useful to evaluate relative performance of the facility,it is not sufficient for quantitative measurement of the flow conditions.Temperature is one of the most important thermodynamic quantities in determining arc heated wind tunnel because it is a key parameter in determining arc-heater operating status and chemical reactions.Therefore,the development of accurate quantitative diagnostic techniques is necessary for better understanding the complex physics involved in the arc heated wind tunnel.The design of a tunable diode laser absorption spectroscopy (TDLAS)system to probe gas parameters during a bow shock wave ahead of a wa-ter cooled copper cylinder is presented in this paper.TDLAS is an effective method for measuring gas temperature and concentration in many fields due to its advantage of non-intrusive,high sensitivity, gas-specific and quick response.In our studies,an atomic oxygen absorption line near 777.2nm is utilized for detecting the arc-heated plasma using scanned-wavelength direct absorption mode with 100Hz repetition rate.The value of temperature is inferred directly from the Doppler broadening component of the absorption lineshape.Moreover,the number density of atomic oxygen is also determined through the integrated absorbance assuming local thermal equilibrium conditions. The agreement of the experimental observations and theoretical calculations shows that the ther-mal equilibrium assumption is valid.The current experimental results of this study illustrate the high potential of TDLAS measurements for routine and economical monitoring of arc heated wind tunnel operating status (gas temperature)as well as the time-resolved flow conditions in front of the model.