桥墩局部冲刷动态模拟及不同截面的冲刷特性

Dynamic simulation of local scour around bridge piers and scouring characteristics of piers with different cross sections

为了获得桥墩局部冲刷随时间的演变过程,探讨不同截面桥墩的冲刷特性,采用计算流体动力学软件FLUENT的自定义函数功能和动网格更新技术,考虑湍流涡增强效应的床面剪应力和坡度影响的临界剪应力,得到床面的输沙率,通过输沙率与床面高程的变化关系实现床面地形随时间的动态变化,并利用泥沙坍塌的调整来克服床面坡度超过泥沙休止角造成的模拟失真及数值不稳定。结果表明:局部冲刷最大深度、冲坑形态及流场结构的模拟结果与试验结果较为吻合;在最大墩宽一致的情况下,流线形桥墩的冲坑深度比圆柱形桥墩降低约45%,比尖角形桥墩降低约40%,冲坑范围也有所下降。

To obtain the time evolution of the local scour of bridge piers and to explore the scouring characteristics of piers with different cross sections,the user-defined function and the dynamic mesh updating technique of the computational fluid dynamics software FLUENT were used. The bed shear stress considering the enhancement effect of turbulence vortex and the critical shear stress considering the influence of the bed slope were calculated to obtain the sediment transport rate. The dynamic variation of bed topography with time was achieved by the relationship between sediment transport rate and bed elevation. Simulation distortion and numerical instability caused in the condition that the bed slope is greater than the sediment repose angle can be overcome through the adjustment of sediment collapse. It shows that the maximum scour depth,the shape of the scour hole and the flow structures by numerical simulation are in good agreement with the experimental results. With the same maximum pier width,the scour depth of the streamlined piers is about 45% and 40%lower than that of the round-ended piers and the sharp-nosed piers respectively,and the range of the scour hole is also reduced.