Study of local scour around multiple-arranged piles in unidirectional flow

Local scour around piles is a critical phenomenon in hydraulic engineering, affecting the stability of structures such as bridges, offshore wind turbines, and coastal docks. This study investigates the mechanisms of local scour around single- and multi-pile configurations under unidirectional flow conditions. Local scour around single-, parallel-, triangle-, and square-arranged piles was conducted in a flume with non-cohesive sediment at a flow intensity of 1.0, focusing on the temporal evolution of scour depth and the three-dimensional characteristics of scour holes and sediment deposition. Flow fields and kinetic energy were studied using OpenFOAM with the turbulent model of improved delayed detached-eddy simulation. Temporal scour depths in front of piles were monitored. Three-dimensional and two-dimensional bed elevation profiles were measured by a laser scanner. The results reveal that the maximum scour depths are at pile noses and can attain their equilibrium scour depths within two hours. The equilibrium scour depth is slightly influenced by the arrangement of piles with pile-to-pile space of five times the diameter of a single pile. The equilibrium scour depths at upstream piles are about 1.85 times of pile diameter and independent of downstream piles. The presence of upstream piles significantly affects the scour patterns around downstream piles, particularly in triangular and square arrangements. The study also highlights the role of horseshoe vortexes and wake vortexes in sediment transport and scour development. The findings provide valuable insights for the design and protection of pile foundations in engineering applications.