当卡水电站下游局部冲刷三维数值模拟研究

为预测闸坝下游局部冲刷坑形态和发展,基于Fluent动网格技术对当卡水电站下游局部冲刷进行了三维数值模拟。采用VOF水-气界面追踪方法来处理闸坝下游冲刷坑内复杂的自由液面,将床面瞬时剪切应力作为泥沙起动及运输的水动力学条件,计算出不同方向上床底泥沙单宽体积输沙率,以此为基础得到河床高程坐标的瞬时变化;采用改进的泥沙起动临界剪切应力计算公式,有效地避免了床面坡度接近泥沙休止角时造成的输沙率数值计算的异常;采用弹簧光顺模型及局部网格重构模型实现了闸坝下游局部冲刷坑的三维演化过程。通过分析对比冲刷坑最终形态表明,数值模拟值与模型试验实测值吻合良好,说明数学模型计算准确,结果可信。

Three-dimensional Numerical Simulation on Local Scour in the Downstream of Dangka Hydropower Station

The local scour process in the downstream of Dangka hydropower station is simulated based on Fluent dynamic mesh to predict the development and topography of local scour in the downstream of dam and sluice.The VOF water-air interface tracking method is used to deal with the complex free surface in the local scour.With transient shear stress on river bed as a crucial hydrodynamic condition for sediment's incipient motion and transport,the volumetric transport rates per unit width of sediment on river bed in different directions are calculated,based on which the transient change of river bed elevation is obtained.Moreover,an improved formula of critical shear stress for sediment's incipient motion is employed to refrain from abnormal numerical values of sediment transport rate caused by bed slope gradient approaching sediment's angle of repose.Finally,the 3-D evolutionary process of local scour is acquired by adopting the spring-based method and remeshing method.The accuracy and reliability of the mathematical model are verified by comparing the simulated depth and topography of local scour with model test values.