Local scour characteristics around piles with different cross-sections under reversing tidal currents: experimental and numerical investigation

This study investigates local scour around circular, square, and rectangular piles subjected to reversing currents through flume experiments and RANS numerical simulations. Experiments covered flow intensity ratios Ur = 0.70–1.01 and dimensionless tidal periods NT = 2280–6840. Results show that all three cross-sections follow an exponential-approach scour development featuring step-like responses at each reversal. Equilibrium scour depths rank as square (Seq/D = 0.96) > rectangular (Seq/D = 0.87) > circular (Seq/D = 0.76). Numerical analysis reveals that forced separation at the square pile's corners generates the strongest horseshoe vortex, with peak bed shear stress 1.35–1.45 times that of the circular. The rectangular pile exhibits the highest scour-hole asymmetry (As = 0.16–0.23) due to unequal path lengths during flood and ebb. Both Urand NTexert positive effects on equilibrium scour depth, with Seq/Dapproaching an asymptotic limit at high NT. These findings provide a quantitative basis for scour prediction and design of non-circular pile foundations in tidal environments.