非恒定流下桩群绕流局部冲刷试验

水流经过桩群时，桩前会出现下降水流和马蹄形漩涡，显著增加水流的挟沙能力与输移能力。本文基于非恒定流桩群绕流局部冲刷水槽试验，研究非恒定流下桩群绕流的局部冲刷分布以及最大冲刷深度；通过计算流体力学软件Flow 3D对水槽试验进行模拟计算仿真，研究非恒定流下桩群绕流局部冲刷发展过程。研究表明：上游单桩的冲刷范围为桩前2D（桩径）至桩后1D，桩外侧2.5D至桩内侧1D；下游单桩的冲刷范围为桩前1D至桩后1D，桩外侧1.5D至桩内侧1D，且桩群各个区域的横向冲刷断面也有差异；最大冲刷深度和冲刷体积随时间呈对数形式增加，直至达到冲刷平衡状态，且20%的时间局部冲刷可完成冲刷平衡时的50%，50%的时间可达到冲刷平衡的80%。

Local scour experiment of flow around pile group under unsteady flow

When water flows past the pile group,there will be a descending water flow and a horseshoe shaped vortex in front of the pile,which significantly strengthens the sediment carrying capacity and transport capacity of the water flow.Based on the local scour flume experiment of unsteady flow pile group,this paper studies the local scour distribution and maximum scour depth of pile group under unsteady flow.By using computational fluid dynamics software Flow 3D to simulate and calculate the flume experiment,and investigate the development process of local scouring around the pile group under unsteady flow.The research shows that the scouring range of upstream single piles is from 2D in front of the pile(Pile diameter) to 1D behind the pile,and from 2.5D on the outside of the pile to 1D on the inside of the pile.The scouring range of downstream single piles is from 1D in front of the pile to 1D behind the pile,and from 1.5D on the outside of the pile to 1D on the inside of the pile.Additionally,there are differences in the transverse scouring sections in various areas of the pile group.The maximum scouring depth and scouring volume increase logarithmically with time until the scour equilibrium is reached.Moreover,20% of the time for local erosion can achieve 50% of the scouring equilibrium state,and 50% of the time can reach 80% of the scouring equilibrium state.