The mutual interference vortex flow from a pair of in-line forced oscillating staggered arranged circular cylinders

In order to understand the aspect of the mutual interference flow from two circular cylinders, the visual observation experiment was performed. The cylinder setting conditions were three kinds of distance ratios (L/d=1.5, 2.5 and 5.5), and seven kinds of arrangement angles (α=0, 15, 30, 45, 60, 75 and 90 degrees). 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 24 steps. The Reynolds number was about 640. As the result of experiment, even if the distance ratio was the same, the vortex shedding characteristics changed with arrangement angles. The mutual interference will become remarkable if the distance ratio is small. In the arrangement angle, 30 degrees and 45 degrees are carrying out mutual interference most. Even when a forced in-line oscillation was performed under the conditions in which two circular cylinders are carrying out mutual interference, it was found that a lock-in phenomenon occurs. The vortex shedding features were obtained and flow pattern distributions were shown. The lock-in characteristics were investigated and the lock-in ranges have been presented in each distance ratio. Four kinds of typical flow patterns at the time of the lock-in of staggered arrangement oscillating two circular cylinders were shown.