Effects of initial conditions on wavelet-decomposed structures in a turbulent far-wake

The effect of initial conditions on a self-preserving plane wake has been investigated for two wake generators, i.e. a circular cylinder and a screen of 50% solidity. Measurements were made at x/θ (x is the streamwise distance downstream of the cylinder and θ is the momentum thickness of the wake) = 580 for the circular cylinder and 830 for the screen using 8 X-wires in the plane of mean shear. A vector wavelet multi-resolution technique is applied for analysis of the hot-wire data. This technique decomposes turbulent structures into a number of components based on their central frequencies, which are linked with the turbulence scales. Sectional streamlines, vorticity contours and probability density functions of the fluctuating velocities at the same central frequency, i.e. the comparable scales of turbulent structures, are examined and compared between the two generators. Discernible differences are observed in the turbulent structures of large-down to intermediate-scales. The differences are further quantified in terms of contributions from the turbulent structures of different scales to the Reynolds stresses and vorticity variance. The vorticity behavior of the screen wake is different from that of the circular cylinder. The difference exhibits an extraordinary similarity to that in the near wake.