Measurement of Three Dimensional Velocity Vectors in a Flow Field Based on a Spatio-Temporal Correlation Method

三维速度矢量测量系统是分析高度复杂流场的基础，本文提出了一种基于时空相关法的流场三维速度矢量测量方法。相关法是一种先进的二维速度矢量测量方法。该方法需要在流动方向上的短距离处观察到两个行进粒子图像。两幅图像中的每一幅都由帧时间序列组成。利用空间相关可以得到三维速度矢量上的二维信息。此外，时间相关性给出了关于第三维的信息。通过计算两幅图像之间的时空相关性，从而获得三维速度矢量。该系统实际应用于简单的2-D流动和3-D流动与反向流动，以确认该技术的适当性，并评估其测量不确定度。与传统的立体测量方法相比，其中每个示踪剂在3-D空间中跟踪，明确了以下优点：（1）该方法具有广泛的应用，可视化流动图像，因为示踪粒子的图像被观察到的空间模式。3）该方法原则上不需要已知流动特性的任何信息，但缺点是只能得到狭缝平面上的速度矢量分布。为了解决这个问题，必须设计一种改进的光学系统，包括狭缝，以获得整个三维流场的许多三维速度矢量。

A measurement system of 3-D velocity vectors is essential in analyzing a highly complex flow field.In this study, a new measurement method of 3-D velocity vectors in a flow field using spatio-temporal correlation method was developed. It is an advanced method for 2-D velocity vector measurement using correlation. The method needs two travel particle images observed at a short distance in the flow direction. Each of the two images consists of frame time series. The 2-D information on a 3-D velocity vector can be obtained using spatial correlation. In addition, the temporal correlation gives information on the third dimension. A 3-D velocity vector is consequently obtained by calculating the spatio-temporal correlation between the two images. This system was actually applied to a simple 2-D flow and a 3-D flow with reverse flow to confirm the appropriateness of this technique and its measurement uncertainty was evaluated.In comparison with a conventional stereoscopic measurement method, in which each tracer is tracked in a 3-D space, the following advantages were clarified.1) The method has wide applications to visualized flow images because the images of tracer particles are observed as a spatial pattern.2) A spatially high-density vector distribution is obtained in a flow cross section.3) In principle, the method does not need any known information on the flow characteristics.The disadvantage, however, is that only a velocity vector distribution on a slit plane is obtained. To solve the problem, an improved optical system including slits will have to be devised to obtain many 3-D velocity vectors over the entire 3-D flow field.