PIV experimental study on the flow field characteristics of pile groups under hydraulic action

Particle Image Velocimetry (PIV) technology-based physical model experiments were conducted to investigate the local flow field characteristics of 3×3 rectangularly arrayed circular pile groups. The study focused on conditions with Reynolds numbers (Re) of 2,400, 6,000, and 12,000, longitudinal pile center distance ratios of 5, and lateral pile center distance ratios of 4. The results indicate significant variations in the flow field characteristics between the mid-downstream and upstream-midstream pile intervals, highlighting the substantial impact of Reynolds numbers on inter-pile flow field changes. At Re of 2,400 and 6,000, the length of the vortex wake and the recirculation zone length behind the upstream central pile were considerably larger than those beside the lateral piles, with the phenomenon more pronounced at Re of 6,000. However, this discrepancy dissipated as Re increased to 12,000. Due to the shielding effect of upstream piles, the intensity of the vortex wake behind the midstream piles was notably weaker than that behind the front row piles, leading to a reduced recirculation area. With the increase in Reynolds numbers, the vortex wake length and the scale of the recirculation zone behind the upstream piles gradually decreased. Additionally, the study analyzed the distribution changes of turbulence intensity and Reynolds shear stress within the intragroup plane. This research, based on the prototype of high-pile wharf pile foundations, explored the variabilities in the internal flow field characteristics of pile groups. The findings aim to advance the research on the mechanisms of sediment scouring and deposition changes at high-pile wharves, thereby enhancing the safety assessment capabilities of high-pile wharves.