考虑悬移质效应的桥墩动床冲刷精细化分析方法

Bridge Scour Simulation in Live-bed Condition with Suspended Load

基于欧拉流固两相流理论并考虑悬移质效应进行桥墩动床冲刷精细化分析.针对动床冲刷与清水冲刷的主要区别,采用不平衡输沙法建立床面变形方程,考虑悬移质与推移质质量交换从而间接影响床面变形.通过对计算流体力学(CFD)软件ANSYS Fluent二次开发,利用床底切应力以及底面网格泥沙浓度分别计算推移质输沙率以及悬移质与推移质的交换通量,由此得到床底网格瞬时变化值,从而实现边界网格的动态更新,以此进行桥墩周围河床动床冲刷过程的动态模拟.通过将数值计算结果与经典理论分析及部分试验结果进行对比,在悬移质分布、局部冲刷深度以及冲刷坑形态等方面充分验证所提出动床冲刷计算方法的合理性与准确性.最后通过参数分析证明了悬移质浓度会明显影响动床冲刷的深度与形态,得出了选择动床冲刷模型并采用流固两相流进行桥墩冲刷精细化分析具有显著必要性的结论.

Based on the Eulerian-Eulerian two-phase flow theory, the live-bed pier scour was carefully simulated with the consideration of suspended load. The riverbed variations were obtained using the non-e- quilibrium sediment transport model by calculating the mass exchange between the suspended load and traction load. By redeveloping a Computational Fluid Dynamics （CFD） software, i. e. , ANSYS Fluent, the sediment transport rates and exchange flux between the suspended load and traction load were calculat- ed using the shear stress of sediment and sediment concentration. By doing this, the riverbed boundary can be real-timely updated according to the calculated riverbed variations to conduct the live-bed scour simula- tion. The accuracy and rationality of the proposed simulation was fully verified by comparing with the clas sic theory and several experimental results from the viewpoints of the suspended load distribution, scour depth, and scour hole profile. The significant influence of the sediment concentration on the scour per- formance was finally proven by a parametric study. It can be concluded that using the live-bed scour mod- els based on the two-phase flow theory should be very necessary for an accurate simulation.