Flow patterns of cross-flow around a varicose cylinder

The near wake of a varicose cylinder has been experimentally investigated using Laser Induced Fluorescence (LIF) and Digital Particle Imaging Velocimetry (DPIV). The work aims to provide understanding to the mechanism of the cross flow around varicose cylinder as well as to comprehend why the introduction of relatively small degrees of spanwise waviness can have a significant effect on drag reduction and suppression of the cylinder vibration. The evolution of the flow patterns and the corresponding vortex interactions are obtained. The experimental results indicated that the wake width and the formation length vary along the span of the varicose cylinder. A wider wake and a longer formation length were observed in the saddle plane. In addition, an interpretation of the three-dimensional wake structures is postulated and conceptually shown. The numerical simulation by 3-D finite volume method is successful in predicting the flow features found by the experiments.