Affiliations: Department of Mechanical Engineering, Kagoshima
University, 1-21-40, Korimoto, Kagoshima 890-0065, Japan. | Department of Mechanical Engineering, The Hong Kong
Polytechnic University, Hung Hom, Kowloon, Hong Kong.
Abstract: The effects of initial conditions on turbulence structures of
various scales in a near wake have been investigated for two wake generators
with the same characteristic dimension, i.e., a circular cylinder and a screen
of 50% solidity, based on the wavelet multi-resolution analysis. The
experimental investigation used two orthogonal arrays of sixteen X-wires, eight
in the (x, y)-plane, and eight in the (x, z)-plane. Measurements were made at
x/h (x is the streamwise distance downstream of the cylinder and h is the
height of the wake generator) = 20. The wavelet multi-resolution technique was
applied to decomposing the velocity data, obtained in the wakes generated by
the two generators, into a number of wavelet components based on the central
frequencies. The instantaneous sectional streamlines and vorticity field were
thus 'visualized' for each wavelet component or 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 were estimated. Both the
large-scale and intermediate longitudinal structures make the most significant
contributions to Reynolds stresses in the circular cylinder wake, but the
contribution from the large-scale structures appears dominating in the screen
wake. The relatively small scale structures of the circular cylinder wake
contribute most to the total rms spanwise vorticity.
