上游堰坡对淹没式矮堰浑水冲刷深度振荡频率的影响研究

Impacts of Upstream Weir Slope on Fluctuating Frequency of Live Bed Scour Depth around Submerged Weirs

淹没式矮堰是一种常见的河道整治建筑物,常用于改善通航条件和防止河道下切。淹没式矮堰的存在会改变其周围的水流结构,产生基础冲刷,威胁其结构安全。在浑水冲刷条件下,即水流强度大于泥沙临界启动条件时,矮堰上游的泥沙会以沙波形式向下游运动,与水流产生的冲刷坑交互影响,使冲刷过程变得更为复杂。该文在一条长12 m,宽0.44 m,深0.58 m的水沙自循环水槽里开展了平衡输沙条件下的淹没式矮堰浑水冲刷实验,测量了淹没式矮堰上游和下游瞬时冲刷深度以及上游瞬时床面高度的变化过程,分析了上游沙波频率与淹没式矮堰浑水冲刷深度振荡频率之间的响应关系。通过对比矩形淹没式矮堰和带上游堰坡的淹没式矮堰实验结果,分析了上游堰坡对"沙波频率—浑水冲刷深度振荡频率"关系的影响。实验结果显示上游堰坡虽然能有效减少矮堰上游浑水冲刷深度,但不影响上游浑水冲刷深度的振荡频率;上游堰坡能增加下游浑水冲刷深度的振荡频率。

Submerged weirs are river training structures, which span the full width of the channel, for raising upstream water level, maintaining navigation water depth, and limiting excessive bed degradation. However, the flow over such structures can lead to local scour, causing structure damage or ultimately failure. The fast evolution of underwater mobile topographies and propagating bedforms increase the complexities of the scour process at the submerged weir under live-bed scour conditions.Experiments were carried out in a 12-m-long, 0.38-m-deep, 0.44-m-wide glass-walled recirculating flume with adjustable slope,and topographic time-series data were measured. This study aims to investigate the relationships between fluctuating frequencies of the approaching bedforms and live bed scour depths around the submerged weir. By comparing the test results of rectangular submerged weir with different upstream weir slope, the influence of upstream weir slope on the relationship between fluctuating frequencies of the approaching bedforms and live bed scour depths is analyzed. The results show that upstream weir slope can effectively reduce the upstream scour depth, but it does not affect the fluctuating frequencies of the upstream scour depth in live-bed scour condition. The upstream weir slope can considerably increase the fluctuating frequencies of the scouring depth of the downstream.