高焓流场氧原子激光诱导荧光技术初步研究

Preliminary Study on Atom O in High-Enthalpy Flow Field

基于双光子吸收激光诱导荧光(TALIF)技术,在纯净的高焓流场环境中,将脉冲激光从垂直于流场方向射入流场,并通过布置在风洞试验段外与流场和激光形成的平面向垂直方向上的ICCD测量获取到了二维氧原子的荧光信号,该信号可以反映氧原子相对浓度。为保证实验中使用到的激发激光波长为最佳激发波长,分别对氧原子基态处在不同角量子数的情况进行了测试,最终确定J=2时,波长为225.584nm为最终实验激发波长,为了保证所获取的氧原子荧光信号在非饱和线性区,在同种状态下,将激发激光能量从小到大调整并进行荧光信号的测试,获取了激光能量在3.4mJ以下的线性区域。为确保获取清晰对比度最优的ICCD荧光图像,选择了Nikon f=105mm F/2.8镜头为实验测试镜头,同时将50次曝光的累计结果作为图像输出。对所获取的荧光图像进行分析,实验结果可以清晰地看到超声速流场中压缩波形成的距中心线约±50mm位置处左右各一个的小峰,亚声速流场中中心处氧原子浓度有一个约60mm宽的均匀区域,区域以外氧原子浓度急剧下降,这些结果符合实验风洞特性,此测试方法可以很好地运用到流场测量中。

With Two-photon absorption laser-induced fluorescence（TALIF）technology,leads pulse laser in pure high-enthply flow field from the direction of perpendicular to flow field,and obtains the two-dimension atom O fluorescent signal with ICCD setting outside of test section on the vertical direction of flat made with flow field and laser,this signal reflects the relative concentration of atom O.In paper,given the experimental environment and experimental equipment,to ensure that excitation laser wavelength in experiment is the best one,different angular quantum number on ground state of atom O are tested;finally,it is determined that J=2,wavelength 225.584 nm shall be experimental excitation laser wavelength.To make sure that the obtaining atom O fluorescent signal is in unsaturated linear region,in same condition,changing the excitation laser energy from small to large to test fluorescent signal,ultimately acquiring laser energy linear region is below 3.4mJ.To record ICCD fluorescent image clearly with optimum contrast,Nikon f=105mm F/2.8lens is chosen as experimental lens,and the results are got with an accumulation of 50 times exposure.By analyzing the experimental fluorescent signal,we can get two peak positions on left and right of central line about±50mm wide which are generated with compressional wave in supersonic flow field,and atom O concentration has 60 mm wide uniform area in central zone of subsonic flow field,the concentration decreases dramatically.This phenomenon is consistent with flow characteristics of wind tunnel,so the method can be applied to flow parameters measurement in the future.