Development and Validation of Two-Dimensional Velocity Measurement by Laser-induced Fluorescence Images

利用双脉冲激光光学系统和互相关技术，对一对激光诱导荧光图像(FIV)的速度矢量轮廓测量进行了改进和验证。一对波长与入射激光不同的激光诱导荧光图像可以将其与米氏散射区分开来。以双乙酰蒸气为荧光气，与示踪剂颗粒混合到主流道上。通过一对双乙酰-LIF图像之间的互相关来测量速度。通过示踪粒子的双曝光Mie散射图像，比较了FIV测量的速度矢量和PTV测量的速度矢量。结果表明，由FIV得到的速度矢量与由PTV得到的速度矢量具有很好的一致性。为了研究标量图像测速技术的性能，通过数值模拟和互相关技术，将流体速度与具有大尺度涡旋的非定常非反应射流中的非均匀浓度或颗粒分布的位移速度进行了比较。得到的结果如下。(1)当非均匀浓度分布的尺寸小于旋涡的尺寸时，采用与颗粒浓度分布相似的参考尺寸，驱替速度与流体速度一致。(2)在浓度分布随时间合并消散或被旋涡扭曲的情况下，驱替速度与流体速度相对不一致。(3)由于颗粒分布的尺寸可能比浓度分布的尺寸小，流体速度与颗粒分布的位移速度与浓度分布的位移速度基本一致。

The development and validation of velocity-vector profile measurement, which was derived from a pair of Laser-induced fluorescence images (FIV: Fluorescence Image Velocimetry) was carried out by a double-pulse laser optical system and the cross correlation technique. A pair of LIF images that has the different wavelength from the incident laser can distinguish that from Mie scattering. Vapor of biacetyl was used as a fluorescent gas and it was mixed to the main flow with tracer particles. Velocities were measured by cross correlation between a pair of biacetyl-LIF images. The velocity vectors by FIV were compared with the velocity vectors derived from the PTV by the double-exposed Mie scattering image of tracer particles. The result shows that velocity vectors derived from FIV agree well with those derived from PTV. The agreement was improved by changing the size of the reference matrix.The fluid velocity were compared with the displacement velocity of inhomogeneous concentration or particles distribution in an unsteady non-reacted jet with a large-scale vortex by the numerical simulation and cross correlation techniques in order to investigate performance of Scalar Image Velocimetry. The obtained results are as follows. (1) When the smaller size of inhomogeneous concentration distribution than that of the vortex is given, the displacement velocity agrees with the fluid velocity by using the similar reference size to the species concentration distribution. (2) The displacement velocity relatively does not agree with the fluid velocity in the case that the concentration distribution merges and dissipates with time, or it is distorted by the vortex. (3) The fluid velocity fairly agrees with the displacement velocity of the particle distribution as compared with that of the concentration distribution because the size of the particle distribution might be smaller than that of the concentration distribution.