Flow Visualization & Measurement of Two-dimensional Temperature Field in the Rarefied Gas Flow Using LIF (Laser Induced Fluoresence)

发展了一种稀薄气流中温度的定量成像方法。用载气中碘分子的平面激光诱导荧光(PLIF)技术对流场进行了可视化。碘分子在可见光区有多条吸收线，并发出强烈的荧光。荧光强度与激光激发的能级中分子的数量成正比。根据这个数与温度的关系，可以由不同波长的激光照射得到的两个可视化图像的荧光强度之比来确定局部温度。这种方法可以利用激光薄片和高灵敏度摄像机对流场的二维温度分布进行成像。将该方法应用于温度变化较大的超音速自由射流流场的温度测量。结果表明，用P(16)/R(18)[514.720 nm]和P(26)/R(28)[514.942 nm]吸收线在B(v‘=43)X(v“=0)相变处测得的喷流温度分布与理论值吻合较好。

A method for quantitative imaging for temperature in the rarefied gas flow has been developed. The flow field is visualized by planar laser-induced fluorescence (PLIF) of iodine molecules seeded in carrier gas. Iodine molecules have many absorption lines in visible region and radiate intense fluorescence. The fluorescence intensity is proportional to the number of molecules in the energy level excited by the laser beam. From the dependence of this number on the temperature, the local temperature can be decided from the ratio of the fluorescence intensities of two visualized images which are obtained by irradiations of laser beams with different wave length. This method allows to image the two-dimensional temperature distribution of the flow field by means of a laser sheet and a high sensitive vidicon camera. This method is applied to the temperature measurement of the flow field of a su personic free jet in which temperature varies drastically. It is found that the temperature distribution of the jet measured by P(16)/R(18) [514.720 nm] and P(26)/R(28) [514.942 nm] absorption lines in the transition of B(v'=43) X(v"=0) agrees well the theoretical one.