两步计算模式下的三门峡水库异重流模拟

Numerical Modeling of Turbidity Currents in the Sanmenxia Reservoir Using a Two-step Calculation Mode

针对传统的深度平均异重流模型在实际应用中获取上游边界条件的困难,提出了两步计算模式下的水库明流与异重流耦合模型。浑水明流段与异重流段交替运算,利用潜入点弗汝德数与体积比含沙量的关系作为判别条件确定异重流段的上游边界位置与相应水沙条件,在设置下游边界条件时使用极限吸出高度公式计算出流流量。采用该模型计算了三门峡水库两次异重流的形成、发展与消退全过程。模型预测的异重流潜入位置与观测结果一致,对库区内3个监测断面的异重流到达时间做出了较为准确的预测。计算的清浑水层交界面高程和含沙量过程与实测结果相符,模拟结果反映出浑水水库发生时异重流排沙效率降低的现象。因此该模型可用于水库异重流过程模拟和排沙方案设计。

To overcome the difficulty in providing upstream boundary conditions in traditional depth-averaged models for turbidity currents, a one-dimensional nmnerical model was proposed for predicting the coupled processes of open channel flow and turbidity current in reservoirs under a two-step calculation mode. The calculations of the open channel flow and the turbidity current alternated with each other, the relationship between the Froude number and the volumetric sediment concentration at the plunge point was used to determine the location of the upstream boundary for the turbidity current and to specify the corresponding boundary conditions, and the method for calculating the limiting height of aspiration was adopted to evaluate the outflow discharge of the current. The whole processes of two tur- bidity current events in the Sanmenxia Reservoir from formation to recession were simulated. The predicted plunge point Xocations were in agreement with the measurements, with the arrival times of the current front being satisfactorily predicted. The calculated sediment concentrations and elevations of interface between the clear-water layer and turbidity current layer agreed with the field measurements, and the simulation results indicated that the sediment delivery ratio was reduced considerably when a muddy reservoir was formed. The proposed model provided a viable tool for simulating turbidity current events and designing procedures for sediment routing.