Study about vortex shedding from a pair of in-line forced oscillating parallel arranged circular cylinders

Abstract

In this study, the flow features of vortex shedding from a pair of parallel arranged circular cylinders (same diameters and unequal diameters) oscillating along the direction of the flow were observed by visualizing water flow experiment at the ranges of the frequency ratio f/f K=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, and Reynolds numbers Re=470∼670. The variations of mean vortex shedding frequency from each oscillating cylinder were investigated. As a result of the experiments, typical flow patterns of lock-in or un-lock-in state were shown every gap ratio G/d. It was found that the stage number of flow pattern was depended on the gap ratio G/d. In the cases of gap ratio G/d=0.25, there were four states, in the case of gap ratio G/d=0.75, there were six states, and in the case of gap ratio G/d=1.75, there were seven states. It was found that the measurement result of vortex shedding frequency depended on the observation point because the rearrangement of vortex formation had changed the characteristics of the flow. When the cylinders were oscillated to the direction of flow, the flow pattern of bias gap flow became not seen. The map of lock-in state in the lock-in range was obtained. It was found that the lock-in range and the lock-in form were more different from the case of single oscillating cylinder. © 2011 The Japan Society of Mechanical Engineers.