三维钝体的绕流问题是流体力学研究的一个重要方向。相比于二维情况，三维钝体尾迹中的流动结构更加丰富和复杂，而对于三维钝体绕流流动控制的研究也要少得多。本申请项目将运用层析粒子图像测速（PIV）和小波分析等先进的实验测量和数据分析方法，研究放置于平板上的有限高方柱体的三维绕流流场，并且提出在柱体上开孔的三维绕流被动流动控制新方法。采用层析PIV技术可以测得三维流场并观测三维流动结构，而发展三维离散正交小波分析技术可以将测得的流场分解为不同的小波成分，从而提取出不同尺度的流动结构并研究它们的演化和相互作用规律。在柱体上开连通孔是一种很有潜力的三维钝体绕流控制方法，本项研究将系统地研究方柱高径比，开孔位置、大小和角度等参数的影响，找到最优控制参数，并且结合三维流动测量和小波分析技术，研究最优控制情况下开孔对不同尺度流动结构的影响规律并揭示其流动控制机理。

The flow around a three-dimensional bluff body is an important aspect in the field of fluid mechanics. Compared to the two-dimensional case, the wake of a three-dimensional bluff body contains more abundant and complex flow structures, while investigations on the control of flow around the three-dimensional bluff body are much less. This research proposal will use advanced measuring and analyzing techniques, such as tomographic particle image velocimetry (PIV) and wavelet analysis, to investigate the flow around a finite-height cylinder mounted on a flat plate, and a new passive control method using bleeding holes in the square cylinder is proposed. Tomographic PIV will be used to measure the three-dimensional flow field. Three-dimensional discrete orthogonal wavelet analysis will be developed to decompose the flow into different wavelet components, from which coherent structures of different scales can be extracted and their evolutions and interactions can be examined. Bleeding through a hole is a passive control method that has a lot of potential in controlling three-dimensional flow around the wall-mounted cylinder. In this research proposal, the influences of locations, sizes and angles of the bleeding hole will be investigated, and the parameters that has the best performance will be determined. The influence of the bleeding hole with the optimal parameters on the flow structures of different scales will be investigated, in an attempt to reveal the mechanism of flow control.