Wavelet multi-resolution analysis of the three-dimensional vorticity in a circular cylinder wake

Simultaneous measurements of the three-component vorticity fluctuations were conducted in the intermediate wake (x/d = 10, where d is the diameter of the cylinder) of a circular cylinder in a low turbulence wind tunnel using an eight-hot-wire vorticity probe. The characteristics of vorticity were investigated using a wavelet multi-resolution technique. The contributions from the wavelet components to the time-averaged vorticity were calculated. The large-scale structures (with a frequency equals to that of the vortex shedding) make a significant contribution (37%) to the spanwise vorticity component for y/d < 0.5. While the relatively small-scale turbulent structures contribute about 60% to the spanwise vorticity, they contribute most (80%) to the longitudinal and transverse vorticity components.