Investigation of the influence of cylinder span length on vortex shedding from an in-line oscillating circular cylinder

Abstract

In order to investigate the dependability of the circular cylinder span length of a lock-in phenomenon, closed circuit water channel experimental apparatus was used, and the visualization experiment was performed. In the visualization experiment, the aspect of the vortex shedding from the circular cylinder which is carrying out the in-line forced oscillation was observed by varying the water level of a test section. In the experiment, adjustment was carried out so that flow velocity might constitute about 0.06 m/s every water level. Main experiment parameters are a circular cylinder diameter (6 mm, 10 mm and 16 mm), amplitude ratio (2a/d=0.5 and 1.0),oscillation frequency ratio (range of f/fK is from 0 to 6), and circular cylinder span length (200 mm, 150 mm and 100 mm). As a result, although changes of the configuration of the lock-in corresponding to the variation of circular cylinder oscillating frequency were the same, it was found that the appearance ranges differ. Distribution of the lock-in range was classified into three groups by the aspect ratio. In the closed circuit water channel experiment, sunken span length was required 150 mm or more, and the aspect ratio L/d obtained the indicator in which the circular cylinder diameter which becomes 15 or more was selected.