Three-Dimensional Orthogonal Wavelet Transform of Tomographic PIV Data

Three-dimensional (3D) flow structures around a wall-mounted short cylinder of an aspect ratio 1 were instantaneously measured by a high-resolution Tomographic particle image velocimetry (TPIV) in a water tunnel. Here both of the diameter D and height H of the cylinder is 70 mm. The 3D orthogonal wavelet multi-resolution technique is developed to analyze instantaneous 3D velocity fields of a high-resolution Tomographic PIV in order to clarify 3D multi-scale wake flow structures. This paper found a 3D W-type arch vortex behind the short cylinder, which is originated by the interaction between upwash and downwash flows. The head shape of arch vortex structure does not only depend on the aspect ratio of the cylinder, but also is associated with the cylinder diameter. By using the 3D orthogonal wavelet multi-resolution analysis, the instantaneous W-type arch vortex and streamwise vortices are extracted at the wavelet level 1. It also found that the intermediate-scale upwash vortices play an essential role in producing W-type head of arch vortex.