Abstract:Regarding the problem of the unclear influence of different tandem and side-by-side spacing ratios on the flow field characteristics in pile foundation structures,we use particle image velocimetry (PIV) technology to carry out a physical model test of the flow field of a nine-pile group structure arranged in a rectangle under subcritical Reynolds number conditions,and systematically study the variation laws of the flow field characteristics of the pile group under the arrangements of tandem spacing ratios (X*) and side-by-side spacing ratios (Y*) at 1.5,2.5,and 4.0.The results show that with the increase of the tandem spacing ratio,the attached vortices behind the piles gradually expand and tend to roll up and detach;while the increase of the side-by-side spacing ratio significantly reduces the number of vortices inside the pile group,and gradually weakens the interaction of the shear layers between rows.The flow pattern shows an evolution trend from the (R,R) type to the (R,J) type and then to the (J,J) type with the increase of the tandem spacing ratio,and the smaller side-by-side spacing delays the roll-up of the shear layer.There is an obvious backflow phenomenon in the near-pile area,and the small spacing ratio condition can effectively suppress the backflow length.In addition,the small spacing ratio can reduce the turbulence intensity of the flow field in the pile group structure and inhibit the momentum exchange of the fluid.
