Wavelet Analysis of Memory Effects on Turbulence Structures in a Far Wake

Initial condition effects in a self-preserving plane wake were investigated for two wake generators, i.e. a triangular cylinder and a screen of 50% solidity. Two orthogonal arrays of sixteen X-wires, eight in the (x, y)-plane, i.e. the plane of mean shear, and eight in the (x, z)-plane, which is parallel to both the cylinder axis and the streamwise direction, are used to simultaneously obtain velocity data in the experimental investigation. Measurements were made at x/h (x is the streamwise distance downstream of the cylinder and h is the height of the wake generator) = 330 for the triangular cylinder and 220 for the screen. A two-dimensional orthogonal wavelet transform is used to analyze the measured hot-wire data. This technique enables the turbulence structures of various scales to be separated and characterized. Discernible differences are observed between the two wake generators in the turbulence structures of large- down to intermediate-scales. The differences are quantified in terms of the Reynolds shear stress, kinetic energy and root mean square vorticity values.