Comparison Between Triangular Cylinder and Screen Near-Wakes in the Orthogonal Wavelet Representation

Abstract

The near wake generated by a triangular cylinder and a screen, respectively, has been investigated with a view to provide information on the effect of initial conditions on turbulence structures of various scales based on the wavelet multi-resolution analysis. The velocity data were simultaneously obtained at x/h (x is the streamwise distance downstream of the wake generator and h is the height of the wake generator)=20 using a rake of eight X-wires aligned in the plane of mean shear. A vector wavelet multi-resolution technique was applied to decompose the velocity data into a number of wavelet components based on the central frequencies. The instantaneous sectional streamlines and vorticity field were used to reveal the turbulent structures at each wavelet component/central frequency. It was found that the behavior of large- and intermediate-scale structures depend on the initial conditions and the small-scale structures are independent of the initial conditions. The contributions from the wavelet components to the time-averaged Reynolds stresses and vorticity variance were estimated. Both the large-scale and intermediate longitudinal structures make the most significant contributions to Reynolds stresses in the triangular cylinder wake, but the contribution from the large-scale structures appears dominating in the screen wake. The relatively small-scale structures of the triangular cylinder wake contribute most to the total spanwise vorticity variance.