泄水建筑物下游冲刷坑二维数值模拟

对巨亭水电站泄水建筑物下游局部冲刷过程进行了二维数值模拟。采用RNG k-ε湍流模型封闭N-S方程、有限体积法在计算网格上离散求解、VOF方法追踪自由水面;采用C语言编写用户自定义函数,以泥沙起动切应力作为床面泥沙起动判别标准,通过分析比较水流剪切力与泥沙起动切应力大小,用以控制冲刷坑底部边界变化;采用局部重构模型和弹簧光顺模型更新计算区域和网格质量,藉以模拟和追踪局部冲刷坑边界变化。研究表明,模拟结果与实测资料符合良好。在冲刷坑的冲刷过程中,床面剪切应力随着冲刷的进程急剧减小,湍动能随着冲刷的进程减小缓慢;床面剪切应力和湍动能沿程变化均较为剧烈,床面剪切应力沿程先增大后减小,床面湍动能则沿程减小。冲刷坑的纵向平衡形态或床面泥沙起动主要决定于床面剪切应力,床面湍动能对泥沙起动也具有重要影响。

Two-dimensional numerical modelling on local scour pit downstream of flow release structure

A two-dimensional numerical model is established to simulate flow field and longitudinal profile of the scour pit downstream of Juting Hydropower Station,with RNG k-e turbulence model to close N-S equations.Finite volume method is used to discrete grid.VOF is used to track location of water surface.The wall shear stress was taken as the start criterion obtained using Ansys Fluent UDF program wrote with C program language to control the movement of the grid of the bottom boundary.Dynamic mesh model is used to achieve the reconstruction of the inter grid at erosion area.Simulation results show that the maximum scour depth and geometry of the river bed downstream of Juting Hydropower Station coincided well with those of physical model.The wall shear stress appears decreasing sharply in souring process,so it appears increasing at the front part and decreasing at the rear part along the way in the scour pit.The scope that the wall shear stress appears increasing along the way is expanded along with development of the scour pit,until the wall shear stress appears increasing along the way in the whole equilibrium scour pit.Turbulence kinetic energy appears gradually decreasing in souring process and it appears decreasing along the way in the scour pit.The equilibrium hydraulic geometry of scour pit or sediment incipient motion on the pit bed is mainly depended on flow shear stress,and turbulent kinetic energy on the pit bed has an important effect on sediment incipient motion.