大型桥梁沉井下沉过程中的水流力数值模拟

Numerical Analyses of Current Load of Large Bridge Caisson during its Sinking Process

跨江桥梁大型沉井在下沉定位过程中会受到复杂的水流力作用。采用雷诺时均Navier-Stokes方程(RANS)和RNG k-ε湍流模型,考虑开挖基坑的影响,在计算流体动力学(CFD)软件中建立某桥梁大型沉井在不同入水深度时的三维足尺数值模型,计算不同流速、不同入水深度时沉井周围及内部流场特性、湍流特征和沉井动水压强,分析沉井受到的水流力随入水深度的变化规律。研究表明:开挖基坑会增大边界层高度,同时降低断面平均流速;在沉井定位下沉过程中,水流最大流速位于沉井4个角点处;沉井外围近壁面底部和基坑表面形状变化处水流湍流强度较大;沉井会受到非均匀分布的动水压强,最大值出现在4个角点处,且动水压强随着沉井入水深度增加而增大;CFD数值计算得到的水流力随入水深度增加先增大后减小。

The large caissons for the river-crossing bridge are subjected to complex current loads during its sinking process.A three-dimensional full-scale numerical model of a large-scale open caisson for bridge in different water depths is established based on the Reynolds time averaged Navier Stokes equation(RANS)and RNG turbulence model,considering the influence of the pit excavation.The characteristics of the flow field and turbulence around and inside the caisson and the dynamic water pressure on the outer wall of the caisson are calculated at different flow velocities and water depths,and the variation law of the current force on the caisson with the depth of water inflow is analyzed.The results show that the pit excavation increases the height of boundary layer and hence decreases the average flow velocity.In the sinking process of the caisson,the maximum velocity of water flow appears at four corners of the caisson.The turbulence intensity tends to be larger near the bottom of the caisson wall surface and at the change of the pit surface.The distribution of hydrodynamic pressure on the caisson is non-uniform with the maximum value at four corners.The hydrodynamic pressure increases with the increase of the sinking depth of the caisson.The current loads calculated by CFD increases firstly and then decreases with the increase of the sinking depth.