INTERACTION OF FLOWS BEHIND 2 CIRCULAR-CYLINDERS OF DIFFERENT DIAMETERS IN SIDE-BY-SIDE ARRANGEMENT

Experiments were performed to study the fluid dynamics of flow past tw o cylinders of diameter ratio 1:2 in a side-by-side arrangement with a gap spacing of TID = 1.5. Based on hot-wire measurements and flow vis ualization results, the most frequent mode of large-scale flow structu res in the wake consists of two vortex streets developed from the two cylinders. Behind the big cylinder the ''first'' (outer) and ''second' ' (inner) streets are isolated. The former has a higher convection vel ocity, which is the same as that of the small cylinder's vortices, whi le the latter convects with a lower velocity. The big and small vortex streets interact in two stages, resulting in lateral transport of flu id across the entire widths of the two wake regions. A locked repetiti ve pattern of four big vortices with 10 small vortices is observed. A third spectral component behind the gap portion of the small cylinder' s wake region is the consequence of the first-stage interaction. The l ess frequent mode does not suggest interaction of the big and small vo rtices.