基于TDLAS的水蒸气非平衡凝结过程研究

Monitoring on the water vapour non-equilibrium condensation process based on TDLAS

目前国内开展的高超声速飞行器地面模拟试验,尤其是较大尺度的高焓试验,大部分在燃烧加热风洞中进行。气流在喷管的膨胀加速过程中温度快速降低,可能导致其中的水蒸气发生急剧凝结,这一过程会带来试验流场参数的改变。为了考察水蒸气的凝结过程,提出＂空间转化为时间＂思想,即将喷管中气流参数沿喷管流向的变化转换为膨胀过程中固定位置气流参数随时间的变化,设计搭建了一套模拟喷管凝结过程的试验装置,通过调节连接段最小截面积实现不同的时间尺度,采用片光技术实现凝结现象的观测,同时根据水蒸气和甲烷吸收光谱获得凝结过程中的温度变化以及水蒸气含量变化。结果表明：在试验段内通过片光可以观测到水蒸气的凝结现象;不同时间尺度下凝结过程中的温度变化趋势相近,均为先下降后上升,在温度趋势发生变化的时间点附近,水蒸气摩尔分数迅速下降,这一变化趋势与燃烧加热风洞喷管流动中参数变化的数值模拟结果具有较好的一致性;这种＂空间转化为时间＂的试验方案可以在一定程度上模拟喷管中水蒸气的凝结过程。

At present,domestic ground simulation experiment of hypersonic vehicle,especially most of larger scale high enthalpy experiments are carried out in combustion heated wind tunnel.The temperature rapidly decreases during the process of airflow expansion and acceleration in nozzle,which may cause rapid condensation of water vapour,particularly in combustion heated wind tunnel.This process will bring about the change of flow field parameters.In order to investigate the water vapor condensation process through nozzle,an idea that ＂space is transformed into time＂was put forward,that is the change of the airflow parameters along flow direction in nozzle is transformed into air flow parameters change with time at a fixed position in expansion process.For this purpose,a set of experimental device for simulating the condensation process in nozzle was designed and constructed.Different time scales are achieved by adjusting the minimum cross section area of connecting section,the phenomenon of condensation is observed by means of planar laser scattering imaging technique,at the same time,the temperature variation in condensation process and water vapor content change are obtained with TDLAS based on water vapor spectral lines and methane spectral line.Experimental results demonstrate that water vapour condensation phenomenon can be observed in experimental section by planar laser scattering imaging technique.At different time scales,temperature change trends in condensation process are similar,all fall first and then rise.Near the time point of temperature trend change,the mole fraction of water vapor drops rapidly.This trend is in good agreement with the numerical simulation results of parameter variation in nozzle of combustion heated wind tunnel.The experimental scheme of ＂space is transformed into time＂can simulate the condensation process of water vapor in nozzle to a certain extent.