AN EXPLORATION OF THE WAKE 3 DIMENSIONALITIES CAUSED BY A LOCAL DISCONTINUITY IN CYLINDER DIAMETER

The wake three-dimensionality caused by a local discontinuity in cylinder diameter (a stepped cylinder) was studied. Changes in vortex shedding frequency caused by the discontinuity took place in either a direct or an indirect mode, depending on the diameter ratio and the Reynolds number. The roles of oblique shedding and frequency modulation of vortex shedding were studied. The physical change in vortex shedding frequency occurred differently for each mode. A wavelet analysis is used to explore frequency modulations in the wake. The relationship between vortex linkages, frequency changes, secondary instability, and these two modes is discussed.