Wavelet vector analysis of turbulent structures in the near-wake of a cylinder

Abstract

The vector wavelet multi-resolution decomposition technique based on a two-dimensional orthogonal wavelet transform is used to analyze the velocity data that were simultaneously obtained by sixteen X-wires in the turbulent near-wake of a circular cylinder. This investigation aims to identify and separate turbulence structures of various scales and focuses on the behaviors of the intermediate-scale and relatively small-scale structures. The instantaneous velocity vector field is decomposed into the multi-scale structures. The large-scale structures in the plane of mean shear are consistent with the well-known Karman vortices. Both intermediate-scale and smallscale structures exhibit a strong three dimensionality. The structures that correspond to the saddle region between Karman vortices are identified with the riblike structures. The topologies of normal and shear stresses, RMS vorticity and flatness factor at each scale associated with the multi-scale structures are discussed.