横丹水电站下游冲刷坑二维数值模拟

2D Numerical Simulation on the Local Scour Pit Downstream of Hengdan Hydropower Station

采用二维数学模型,对横丹水电站泄水建筑物下游冲刷过程进行了二维数值模拟.以泥沙起动拖曳力作为泥沙起动判据,在二维流场计算的基础上,提取每个时间步后床面各节点水流剪切应力,通过比较水流剪切应力与泥沙起动拖曳力的大小来控制床面高程的变化;采用动网格模型、弹簧光顺模型和局部重构模型较好的完成了计算过程中网格的移动和动边界局部网格自动调整,实现了冲刷坑冲刷过程的二维数值模拟.结果表明,模拟计算的冲刷坑形态和深度与模型实测值吻合良好.在冲刷起始阶段,床面剪切应力下降较快,之后下降较慢.与冲刷坑起始冲刷较快,之后冲刷较慢具有良好的一致性.

A two-dimensional model was adopted to predict downstream scour pit of Hengdan Hydropower Station discharge structure with regard to its shape and maximum erosion depth.Based on flow field simulated,the flow shearing stress on pit bed during scour process was calculated using the developed code.By comparing the flow shear stress and the incipient motion drag force,it could be judged whether bed sediment was in incipient motion or staying on riverbed,and the riverbed surface form could also be predicted accurately.Herein,dynamic mesh was applied to adapt to shifty bed surface corresponding to updated flow condition.Simulation results indicate that the developed model could give good predictions to scour pit in terms of its morphology and depth,which were in line with the results obtained from physical model experiments.At the initial stage of scour,shear stress on pit bed decreasing rapidly,and then it dropped slowly.This is in accordance with the predicted scour speed tendency.