College of Mechanics and Engineering Science,Hohai University,Nanjing 211100,China; 2.Institute of Science and Technology Research,China Three Gorges Corporation,Beijing 101199,China) Abstract：To address the issues of unclear local scour mechanisms and insufficient design basis for pile group foundations caused by complex flow field interference between piles,a three-dimensional coupled numerical model of fluid-pile-erodible seabed is established.This model simulates the scour process around a monopile and four typical pile group arrangements under steady current conditions on a sandy seabed with different pile spacings,and discusses the effects of flow field interference between piles and bed shear stress on the scour process.The study shows that in a twin-pile tandem configuration,the scour depth at the rear pile is reduced by 34%-53% compared with a monopile pile,owing to the shielding effect of the front pile.For side-by-side twin piles with G/D=2(where G is the pile spacing and D is the pile diameter),the maximum scour depth increases by 33% due to the gap flow between the piles.Compared with the monopile,the maximum scour depths for the regular-triangle and inverted-triangle arrangements increase by 20%-30% and over 30%,respectively.Therefore,it is recommended in engineering practice to adopt a pile spacing of G/D=3-4 for tandem piles to balance the shielding effect and scour risk,to employ a spacing significantly exceeding G/D=4 for side-by-side piles to markedly mitigate mutual interference,and to avoid using the inverted-triangle configuration as much as possible in three-pile arrangements.