Bleed flow structure in the wake region of finite array of cylinders acting as an alternative supporting structure for foundation

Hexagonal arrays of circular cylinders (HACCs) can be preferred over mono-piles in the design of marine and hydraulic structures due to certain reasons, e.g. efficiency in scour reduction, decreased stagnation and drag, easier applicability, cost-efficiency. In this study, the influence of the HACC on the flow domain was experimentally investigated and compared to that of a solid cylinder using flume experiments. The primary objective of the experiments was to understand the role of orientation and density of array on bleed flow characteristics, which can be regarded as the major origin of the coherent flow structures generated around the HACC. Mean and turbulent flow quantities were mapped behind the obstacles in each experimental test, collecting high-frequency velocity measurements over a spatially dense grid. A key outcome of the study is the identification of the solid volume fraction (SVF) above which the array behaves like a solid cylinder. Furthermore, the results show that the angle of attack, or HACC orientation, influences only the flow structure for intermediate SVFs. Above and below this intermediate range, the flow structure is insensitive to HACC orientation. It was also witnessed that while the highest resistance to flow was generated by staggered configuration, the highest lateral velocity gradient values occurred in the angled cases.