Flow feature of a pair of in-line forced oscillating 45 degrees staggered arranged circular cylinders

In order to understand the aspect of the mutual interference flow from two circular cylinders, the visual observation experiments was performed. The staggered arrangement angle was made into 45 degrees and the cylinder setting conditions were three kinds of distance ratios (L/d = 1.5, 2.5 and 5.5). The oscillating conditions were four kinds of amplitude ratios (2a/d = 0.25, 0.5, 0.75 and 1.0), and the oscillation frequency ratio f/fK in 28 steps. The Reynolds number was about 640. As the result of experiment, also in the case of staggered arrangement oscillating two circular cylinders, the lock-in phenomenon was observed. Four characteristic flow patterns at the time of lock-in were obtained by having oscillated two circular cylinders of staggered arrangement in the direction of the flow. Even if the mutual interference of two circular cylinders was in the state of appearing strongly, when the circular cylinder was oscillated, the lock-in phenomenon was observed. In a single circular cylinder and two circular cylinders of staggered arrangement, the distribution of the range and a flow pattern which carries out a lock-in differs. Distribution of the flow pattern of the 1st circular cylinder and distribution of the flow pattern of the 2nd circular cylinder change with distance ratios.