后台阶下游床面冲刷过程数值模拟研究

以床面瞬时剪应力作为泥沙起动及输运的水动力机制,建立了结构物周围复杂流场下床面局部冲刷的数学模型。并应用大涡模拟方法对后台阶下游三维湍流流动进行数值模拟,得到台阶下游床面瞬时剪应力的分布规律。为了确定床面瞬时剪应力与泥沙上扬通量的关系,先应用数学模型对不同模型参数下,冲刷开始后5分钟时台阶下游床面形状进行试算。通过试算与实验结果的比较,确定床面瞬时剪应力与泥沙上扬通量关系中需要的模型参数。进一步对冲刷开始后30分钟内台阶下游床面演化规律进行模拟,模拟结果与实验结果相符合。

Numerical Investigation on the local scour at the downstream of the backward-facing step flow

Assuming that the instantaneous bed shear stress is the hydrodynamic mechanism of sediment incipience and transportation,the numerical model of the local scour under the complex flows around the structures is presented.The method of large eddy simulation is employed to simulate the three dimensional turbulence at the downstream of the backward-facing step flow,and the distribution of the instantaneous bed shear stress at the downstream of the step is obtained.In order to determine the relation between the pick-up flux and the instantaneous bed shear stress,the formations of the bed at the downstream of the step at 5 minutes after the beginning of the scour are simulated according to different model parameters.The model parameters needed to calculate the pick-up flux are determined by comparing the results of numerical simulation and experiment.The process of the scour at the downstream of the step during 30 minutes after the beginning of the scour is simulated,and the results of the simulation and the experiment agree well.