Visualization and Measuement of Rarefied Gas Flow using LIUFV

利用像增强器和CCD摄像机，利用氧分子的激光诱导紫外光荧光(LIUVF)技术，对稀薄气体流动的流场进行可视化。193 nm ArF准分子激光对应于Schumen-Runge X*B跃迁系统。氧分子通过照射这种激光束来辐射紫外光。将LIUVF方法应用于超音速自由喷流稀薄气流的流动显示。然而，由于荧光的微弱，利用氧分子的荧光不可能比利用碘分子的荧光更清楚地获得流场的图像。对于稀薄气流的温度测量，结果也表明精度不高。我们认为有必要改进荧光检测系统，并利用激光诱导碘荧光对稀薄气体流动进行流动可视化和温度测量。将流动显示技术应用于反向超音速自由射流的流场结构分析。发现了相互作用区内流场和不稳定流的特征结构。在温度测量方面，发展了双线PLIF方法。从理论上提出了选择两条吸收线最佳组合的方法，并通过实验验证了该方法的正确性和有效性。

Flow field of rarefied gas flow can be visualized by LIUVF(Laser-Induced Ultra Violet Fluorescence) of oxygen molecules using an image intensifier and a CCD camera. ArF excimer laser at 193 nm corresponds to the Schumen -Runge X*B system of transitions. Oxygen molecules radiate the UV fluorescence by irradiation of this laser beam. The LIUVF method is applied to the flow visualization of the rarefied gas flow; a supersonic free jet. Because of weakness of the fluorescence, however, an image of the flow field can not be obtained less clearly using the fluorescence of oxygen molecules than that of iodine molecules. For temperature measurement of the rarefied gas flow, the results also indicates low accuracy. We believe that it is necessary to improve a detection system of the fluorescence.Flow visualization and temperature measurement of the rarefied gas flow using laser-induced iodine fluorescence is also carried out. The flow visualization is applied to an analysis of the flow field structure of the opposed supersonic free jets. Characteristic structures of the flow field and an unstable flow in the interacting region is found. For temperature measurement, two lines PLIF method is developed. A method for selection of optimum combination of a two absorption lines is proposed theoretically and the propriety and effectiveness is verified by experiments