串列双圆柱桥墩局部冲刷精细化模拟

Refined Simulation for Local Scour Around Cylinder Piers in Tandem

为研究不同墩心距下沿流向串列布置的双圆柱桥墩局部冲刷坑形态的变化规律,提出1种平衡湍流边界层模型以获得稳定的湍流来流边界条件;利用雷诺时均N-S方程和标准k-ε湍流模型求解河床上双圆柱桥墩周围的复杂绕流场;基于能考虑河床面任意斜坡和泥沙坍塌效应的泥沙输运模型和动网格技术模拟双圆柱桥墩局部冲刷的动态演化过程,得到平衡冲刷坑形态,揭示冲刷发展过程的流动特征和冲刷机理。模拟结果与中美规范局部冲刷预测结果比较表明:串列双圆柱桥墩之间存在干扰效应;受下游桥墩施扰,最大冲刷都发生在上游桥墩,冲刷深度比单圆柱桥墩大,当墩心距L与桥墩直径D之比L/D=4时,达到最大值;而下游桥墩受上游桥墩遮挡的影响,最大冲刷深度在L/D=2时达到最小值,随着墩心距的增大,下游冲刷深度增大;当墩心距大于5倍桥墩直径后,下游桥墩可不考虑遮挡效应;获得的串列双圆柱桥墩最大冲刷深度值与美国规范预测值较为接近,而中国规范公式预测值偏小,提出的下游桥墩冲刷深度遮挡因子可为桥梁抗冲刷设计提供参考。

To study trends in the changes of scour hole dimensions around cylinder piers in tandem under different pier spacing scenarios, an equilibrium turbulence boundary layer(ETBL) was presented to obtain the steady turbulence inflow conditions. Reynolds averaged Navier-Stokes equations and standard turbulence models were employed to solve the complex flow field around the cylinder piers in tandem. The dynamic evolution processes of local scour around the tandem cylinder piers were simulated to obtain the equilibrium dimensions of the scour hole based on the sediment transport model considering the effects of the slope of the bed and collapse of sediment, and dynamic mesh technique, which could help to reveal the flow characteristics and scour mechanisms. By comparing the simulation results and prediction results with respect to the Chinese and US standards, the results show that there is interference between the cylinder piers in tandem. The maximum scour depth of the cylinder piers in tandem forms in the upstream pier and is larger than that of the single cylinder pier. When L/D(the ratio of pier spacing to pier diameter) is 4, the depth of scour is maximum. The depth of scour around the downstream pier, which is shielded by the upstream pier, is minimum for L/D=2. The depth of scour around the downstream pier increases with pier spacing, and a magnitude of 5 times the pier diameter is the critical value of the shielding effect. Meanwhile, the simulated results are closer to the predicted results for the US code, and the predicted results for the Chinese code are too small. The shielding factor presented here can be used to provide reference for scour design in the future applications.