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Three-dimensional numerical simulation of the influence of advancement patterns on local scour around dike
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摘要: 在实施土石堤坝溃口快速封堵、河道截流等水利和防洪减灾工程时，口门或龙口处存在较强的局部冲刷。基于已有的经圆柱、丁坝局部冲刷试验结果验证的三维数值模型，模拟了单向、双向进占方式下龙口宽度B/H = 4.3、5.8时堤头和河床的局部冲刷发展。根据水流特性与冲刷发展的关系，分析了加剧局部冲刷的水流结构和进占方式对局部冲刷发展的影响规律。研究结果表明：单向进占时，戗堤对水流和冲刷发展存在偏移效应；冲刷在初始阶段均表现为沿堤头上游、裹头下游形成的斜向轴线冲刷趋势，堤头上游绕流后的边界冲刷在整个冲刷过程中始终剧烈；进占长度对水流冲刷偏移效应产生影响，在B/H = 5.8时剧烈淘刷区位于戗堤堤头上游的底部堤脚，但是在B/H = 4.3时则位于裹头下游。双向进占时，水流沿龙口轴线对称分布；进占长度影响戗堤局部冲刷的剧烈程度。下潜水流和涡旋是造成戗堤局部冲刷的主要原因。Abstract: During the implementation of water conservancy and flood control and disaster mitigation, such as river closure and quick closuring earth-rock dike breaches, a strong local scour occurs at the gap or mouth. A 3D numerical model of local scour was verified by the experiments of previous studies, and this model was applied to simulate the local scour around the dike and the Riverbed under the one-way and two-way advancement patterns at the gap width B/H = 4.3 and 5.8. The influence of advancement patterns on the development of local scour around dike was analyzed. The results show that in the case of one-way advancement pattern, the gap flow was deflected by the dike to the other side. The local scour of the upstream dike head is always intense in the whole process. Due to the deflection of the dike, the locations of intense scouring downstream are different. The intense scouring area is located at the bottom of the upstream end of the dike at B/H=5.8, and this area was located at the wrapping head downstream at B/H = 4.3. In the case of two-way advancement pattern, the flow is distributed symmetrically along the gap axis. The gap width only affects the intensity of local scouring on the dike. The diving flow and eddy are the main reasons for local scour around the dike.
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Key words:
- river closure /
- advancement patterns /
- local scour /
- flow fields /
- 3D numerical simulation
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图 1 截流戗堤数值计算区域和进占分区A-A剖面示意（单位：mm）
Figure 1. Numerical domain of river closure dike and A-A sectional view for the dike (unit: mm)
图 2 单向和双向进占方式下整体流场(单位：m/s)（纵横坐标的端点不能随意，应有数值。全文所有图都一样）
Figure 2. The flow field with different gap length in one-way or two-way advancement (unit: m/s)
图 3 单向、双向进占方式下龙口三维流场(单位：m/s)
Figure 3. The 3D flow field with different gap width in one-way or two-way advancement (unit: m/s)
图 4 龙口B/H = 4.3河局部冲刷发展(单位：mm )
Figure 4. The local scour development of riverbed at the gap when B/H = 4.3 (unit: mm )
图 5 龙口B/H = 5.8底床冲刷发展(单位：mm )
Figure 5. The local scour development of riverbed at the gap when B/H = 5.8 (unit:mm )
图 6 龙口B/H = 4.3底床冲刷发展(单位：mm )
Figure 6. The local scour development of riverbed at the gap when B/H = 4.3 (unit: mm )
图 7 龙口宽度B/H = 5.8底床冲刷发展(单位：mm)
Figure 7. The local scour development of riverbed at the gap width B/H = 5.8 (unit: mm)
图 8 龙口B/H = 5.8时戗堤近岸边流线
Figure 8. The streamlines near the bank at the gap when B/H = 5.8
表 1 计算工况
Table 1. Numerical conditions
工况 进占长度/m 流量/（m3·s−1） 流速/（m·s−1） 水深/m 龙口宽度/m 龙口落差/mm 原型 模型 单向进占 I区 0.75 2 800 0.158 0.32 0.20 1.16 18.0 II区 1.05 2 800 0.158 0.32 0.20 0.86 18.5 双向进占 I区 0.62 2 800 0.158 0.32 0.20 1.16 18.0 II区 0.77 2 800 0.158 0.32 0.20 0.86 18.5 
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