激光诱导荧光技术在高焓空气氮原子测量中的应用  

Preliminary Study on Atom N in High-Enthalpy Flow Field

作　　者：罗杰[1] 马昊军[1] 王国林[1] 肖学仁 LUO Jie;MA Hao-jun;WANG Guo-lin;XIAO Xue-ren(Hypervelocity Aerodynamics Institute of China Aerodynamics Research and Development Center,Mianyang 621000,China)

机构地区：[1]中国空气动力研究与发展中心超高速空气动力研究所,四川绵阳621000

出　　处：《光谱学与光谱分析》2021年第7期2135-2141,共7页Spectroscopy and Spectral Analysis

基　　金：国家自然科学基金项目(11602289)资助。

摘　　要：高超声速飞行器再入大气层时,受到激波的压缩和激波层内粘性阻滞作用,周围绕流流场的空气温度在4000~15000 K之间,使空气中的氧、氮分子发生离解,从而出现高温气体效应,形成高焓化学非平衡流。飞行器表面防热材料基本都含有大量的碳元素,通常情况下主要是氧原子与碳发生反应,但在焓值大于18 MJ·kg^(-1)的情况下,氮原子与飞行器表面碳反应的无量纲烧蚀因子BC N>0.1725,此时碳在高焓空气介质中的无量纲质量烧蚀因子BC air>0.345,因此,碳的氮化烧蚀变得非常剧烈,和氧化烧蚀相当;同时离解的氮原子也会在飞行器表面发生催化复合反应放出大量的热,使飞行器表面承受更多的热载荷。因此,分析高焓化学非平衡流流场中的氮原子具有现实意义。在地面模拟设备中建立高焓化学非平衡流场,对氮原子进行测量技术,可以很好的对其进行研究。双光子吸收激光诱导荧光(TALIF)技术作为一种非接触测量,在不干扰流场环境的情况下,可以直接获得氮原子的浓度分布。对流场氮原子激发荧光,通过布置在风洞试验段外与流场和激光形成的平面呈垂直方向的ICCD获取到二维氮原子的荧光信号。为确保荧光图像的清晰及视场合适,选择了Nikon f=50 mm F/1.4镜头作为前级收光设备。实验成像采用50次曝光的累计结果,以消除气流扰动及激光能量抖动造成的不确定性。实验中,在理论激发波长附件进行测试,优化选择出206.717 nm作为正式实验中脉冲激光的最佳激发波长。在最佳激光波长条件下,从小到大调整激发能量,获得了该环境下的氮原子激发的非饱和线性区为1.8 mJ以下。正式实验过程中激光能量为1.6 mJ,处于线性区。对所获取的荧光图像进行处理,提取激光中心线上的荧光强度进行分析,发现无论是亚声速还是超声速,荧光强度沿径向都呈驼峰状分布,与之前氧原子测试结果比较When the hypersonic vehicle re-enters the atmosphere,it is subjected to the compression of the shock wave and the viscous blocking effect in the shock layer.The air temperature in the surrounding flow field is between 4000~15000 K,which causes oxygen and nitrogen molecules in the air to dissociate,resulting in high-temperature gas effect and the formation of high enthalpy chemical nonequilibrium flow.There are a large number of carbon elements in thermal protection materials on the surface of aircraft.Generally,the reaction between oxygen and carbon is the main reaction at high enthalpy.But when the enthalpy is greater than 18 mJ·kg^(-1),the dimensionless mass ablation factor for the reaction of nitrogen atoms with carbon on the aircraft surface is BC N>0.1725,and at the time,the dimensionless mass ablation factor of carbon in high enthalpy air is BC air>0.345;as a result,the nitriding ablation of carbon becomes very intense,which is equivalent to the oxidation ablation.Meanwhile,the dissociated nitrogen atoms also produce a large amount of heat in the catalytic reaction on the surface of the aircraft,which makes the aircraft surface withstand more thermodynamic impact.Therefore,the analysis of nitrogen atoms in high enthalpy chemical nonequilibrium flow field is of great practical significance.A high enthalpy chemical nonequilibrium flow field is established in ground simulation equipment,and nitrogen atoms can be well studied by measurement.Two-photon absorption laser-induced fluorescence(TALIF)technology,as a non-contact measurement,can directly obtain the concentration distribution without disturbing the flow field.Nitrogen atoms in the flow field are excited by a pulse laser,and two-dimensional nitrogen atom fluorescence signals are obtained through ICCD arranged outside a wind tunnel test section in a direction perpendicular to a plane formed by the flow field and the laser.In order to ensure the fluorescence image is clear and the field of view is appropriate,the Nikon f=50 mm F/1.4 lens is selected as th

关 键 词：高焓化学非平衡流 氮原子 激光诱导荧光 优化选择 

分 类 号：O657.3[理学—分析化学]