Atomic emission spectroscopy diagnostics for leak detection of cooling water in a low-enthalpy arc heater
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摘要: 电弧加热器试验中存在电极局部烧穿漏水导致电弧加热器严重烧损的风险，对漏水故障的快速诊断可大大提升电弧加热器的运行安全性。由于电弧加热器内高温气流的恶劣环境，漏水故障诊断技术匮乏。针对总焓范围2~12 MJ/kg的中低焓电弧加热器，提出一种基于原子发射光谱的漏水故障诊断技术。通过分析中低焓电弧加热器漏水故障条件和正常运行下高温流场的发射光谱特性，选择氧原子777.19 nm发射谱线为目标谱线，采用相对强度的处理方法，实时监测该中低焓电弧加热器是否发生漏水故障。试验获得了总焓H0分别为11.6和9.8 MJ/kg共2组工况下氧原子相对辐射强度的变化规律，结合电极烧蚀图像分析，证明该技术应用于中低焓电弧加热器漏水故障诊断具有较强的发展潜力。最后，提出该技术在单轨道-多焓值状态气动热试验条件下，每个状态均保证较高灵敏度的解决方案。Abstract: Arc-heated facilities play an important role in the development of thermal protection materials and heat shield structures for entry vehicles. Owing to the intensive heat fluxes generated by the arc root at the electrode surface, the erosion of the electrode is inevitable and there exists a risk of the cooling water leaking from the electrodes due to the accumulation erosion of the electrode material. It is well acknowledged that the arc heater can be severely damaged due to the late leak detection. Therefore, the development of fast response and accurately quantitative diagnostic techniques for leak detection of cooling water in an arc heater would be highly beneficial. Due to the harsh conditions inside the arc heater, especially for the low-enthalpy arc heater (total enthalpy range:2~12 MJ/kg), choices for the diagnostic methods are limited. Optical emission spectroscopy (OES) is a powerful tool to probe atoms and molecules which has been used in many areas such as chemical kinetics, non-equilibrium radiation, and so on. This paper presents an experimental investigation of the application of OES in the leak detection of cooling water for a low-enthalpy arc-heated wind tunnel (FD-04). According to the spectral characteristics of the high-temperature flow field in the FD-04 arc heater, the 777.19 nm emission spectral line of the atomic oxygen (O777.19) is utilized for monitoring the operating status and determining the leakage of the cooling water. A relative intensity determination method for the O777.19 emission is proposed and water leakage failures are successfully diagnosed under two test conditions at total enthalpy values of 11.6 and 9.8 MJ/kg. A solution is proposed that the diagnostic technology keeps high enough sensitivity for multiple total enthalpy conditions. This work demonstrates the potential of using the OES technique for leak detection of cooling-water in a low-enthalpy arc-heated facility.
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Key words:
- total enthalpy /
- arc heater /
- atomic oxygen /
- emission spectroscopy /
- leak detection
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图 1 FD-04电弧风洞及发射光谱测量系统布置示意图
Figure 1. Schematic of the experimental set-up of the FD-04 facility and the emission spectroscopy measurement system
图 3 氧原子777.19 nm特征光谱原始数据及相对强度
Figure 3. Raw emission spectrum and data processing for O777.19 emission intensity determination at 11.6 MJ/kg
图 4 总焓11.6 MJ/kg下氧原子谱线相对强度随时间的变化
Figure 4. Evolutions of O777.19 emission intensities at 11.6 MJ/kg
图 5 总焓9.8 MJ/kg下氧原子谱线相对强度随时间的变化
Figure 5. Evolutions of O777.19 emission intensities at 9.8 MJ/kg
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