The Visual Observation of Vortex Shedding from an In-Line Forced Oscillating Circular Cylinder

Abstract

In this study, the flow features of vortex shedding from a circular cylinder forced-oscillating in the in-line direction were investigated by use of flow visualization technique at the Reynolds number Re=570,with four kinds of amplitude ratio (2a/d=0.25,0.5,0.75 and 1.0) and the range of oscillation frequency ratio f/f_k=0.18∿6.2. As a result of the experiments, it was found that when the oscillation amplitude ratio 2a/d becomes large, the lock-in range expands widely and even if the cylinder oscillation frequency is smaller than the natural Karman vortex shedding frequency, the lock-in phenomenon arises. The distribution of flow pattern in the lock-in range was shown. Two deferent flow patterns in the lock-in state of twin vortex shedding were observed. One of which was inside curl type and the other was outside curl type.