Wake interference of two identical oscillating cylinders in tandem: An experimental study

This study aims to assess the impact of the spacing between cylinders on their dynamic behaviour. Observations during this experiment have helped to identify the effect of spacing on excitation mechanism of each cylinder as well as establishing the relationship between cylinders response and the spacing between them. Arrays of cylindrical Structures in close proximity are common in variety of engineering structures, particularly in the offshore industry. If the cylinders are flexible, and are subject to excitation from fluid flow, then the dynamics is influenced by complex interactions between the cylinders, dependent on a variety of parameters. Two cylinders were flexibly mounted in tandem at different spacings from 20D to 3.5D and were towed at different Reynolds numbers ranging from 8.7 x 10(3) to 5.2 x 10(4). The gap between cylinders was set to 20, 15, 10, 8, 5, 4, 3.5D respectively; the responses of the cylinders were measured and the mutual interactions were compared. The two cylinders were identical and free to oscillate in both cross-flow and stream-wise directions. The validity of results was examined by comparing to available data in literature and results attained by testing cylinders independently in the towing tank. The interaction of two cylinders are studied through frequency analysis of both cylinders response motion to determine how upstream vortices impact the trailing cylinder response in stream-wise and cross-flow differently. It was observed that leading and trailing cylinders oscillate at different frequencies which is in contrast with results obtained from two fixed cylinders in tandem where both cylinders oscillate at the same frequency. Additionally, it is discussed how spacing controls the excitation mechanism.