A high-resolution Tomographic particle image velocimetry (Tomo-PIV), which consists of four high-resolution double-exposure CCD cameras, was used to measured three-dimensional (3D) flow structures behind a wall-mounted short cylinder of an aspect ratio 1 at Reynolds number 10,720 in a water tunnel. Based on the measured instantaneous 3D velocity distribution, 3D velocity fields, the vorticity, the Q criterion, the rear separation region and the characteristic of arch type vortex and tip vortices are first discussed. In order to evaluate 3D multi-scale wake flow structures and energetic flow structures, the 3D orthogonal wavelet multi-resolution technique and proper orthogonal decomposition (POD) are applied to analyze instantaneous 3D velocity fields of Tomo-PIV. A 3D W-type arch vortex behind the short cylinder is found, which is originated by the interaction between upwash and downwash flows. The head shape of arch vortex structure is associated with the aspect ratio of the cylinder. By using the 3D orthogonal wavelet multi-resolution analysis, the instantaneous arch vortex and streamwise vortices are extracted in the large-scale structures of the wavelet level 1. It also found that the intermediate-scale upwash flows play an important role in originating the head of W-type arch vortex. Strong small-scale structures appeared in the shear layer and were contained in the intermediate-scale structures. The POD analysis indicates that the first two modes account for 13.3% of the total turbulent fluctuating energy, and the first four POD modes exhibit several large-scale streamwise vortices.

由四个高分辨率双曝光CCD相机组成的高分辨率断层摄影颗粒图像测速仪（Tomo-PIV）用于测量长宽比壁挂式短圆柱体后面的三维（3D）流动结构雷诺兹编号为10,720的1座水道。基于所测得的瞬时三维速度分布，三维速度场，涡度时，Q首先，讨论了后分离区域以及拱形涡旋和尖端涡旋的特征。为了评估3D多尺度尾流结构和高能流结构，将3D正交小波多分辨率技术和适当的正交分解（POD）用于分析Tomo-PIV的瞬时3D速度场。在短圆柱体后面发现了一个3D W型弧形涡旋，这是由上冲流和下冲流之间的相互作用引起的。拱形涡旋结构的头部形状与圆柱的长宽比有关。通过使用3D正交小波多分辨率分析，在小波级别1的大型结构中提取了瞬时拱涡和流涡。还发现，中等规模的上冲流在产生W型拱旋涡旋的头部方面起着重要作用。强的小尺度结构出现在剪切层中，并包含在中等尺度的结构中。POD分析表明，前两种模式占总湍流脉动能量的13.3％，而前四种POD模式表现出几个大规模的流向涡旋。