Vortex Shedding and Vortex Formation from a Pair of In-Line Forced Oscillating Parallel Arranged Two Circular Cylinders (In the Case of Unequal Diameter)

Abstract

In this study, the flow features of vortex shedding from a pair of parallel arranged circular cylinders of unequal diameter oscillating along the direction of the flow were observed by visualizing water flow experiment at the ranges of the frequency ratio f/fK=0∼7, amplitude ratio 2a/d=0.125, 0.25, 0.5 and 0.75, gap ratio G/d=0.25, 0.75 and 1.75, diameter ratio d'/d=0.25 and 0.5 and Reynolds number Re=500. The variations of mean vortex shedding frequency from oscillating cylinder were investigated. As a result of the experiments, the occurrence of the lock-in phenomenon and its range were shown. It was obtained that the states of the interference flow at the time of lock-in by the cylinder oscillation. Some representative flow patterns were obtained. It was shown that the stage number of flow pattern was depended on the gap ratio G/d.