Abstract
Vortical structures were experimentally investigated in the wake of a sphere by multi-hotwire measurements and flow visualizations. Two kinds of the Strouhal numbers were observed in the range of Re=800〜7000: the low mode St number kept almost constant of St_L≒0.2 and the high mode St number increased discontinuously with increasing the Re number. A helical-type low mode structure composed of 2〜3 high mode vortices was observed for Re〓2000. A staggered-type I structure with 2〜6 high mode vortices existed for Re=1700〜3800. A staggered-type II structure containing of 4〜8 high mode vortices for Re=2400〜7000. For Re〓7000, the inside of the low mode structure became turbulent due to the interaction between the high mode vortices, then the low mode structure was basically staggered-type. Wavelet analyses showed that the whole number of the high mode vortices contained in the low mode structure increased with the Re number.
