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Numerical investigation on distribution characteristics of velocities at equal-width open-channel confluences
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摘要: 明渠水流的交汇现象在涉水工程中十分常见，其中交汇口流速的分布特性复杂，对渠道的设计与维护有着直接的影响。针对明渠交汇流的流速分布特性，基于雷诺方程模型（RSM）与体积函数法（VOF）建立等宽明渠交汇流三维数值模型，结合物理试验数据进行模型验证，对不同交汇角与流量比组合工况进行模拟研究，对交汇口水流流速的分布特性进行分析。计算结果表明，交汇口流速存在分区特征，交汇口内流线弯曲流速偏转，下游会出现回流结构与断面环流现象。当交汇角增大时，水流的偏转幅度更大，回流结构与环流现象增强，分区特征更明显，渠道边壁受到的水体冲击更大；当流量比增大时，主渠水体受到的挤压效应减弱，流速分区特征受到抑制，水流交汇更平顺，边壁受到的冲刷更少。Abstract: The confluence of open channel flows is a common phenomenon in water-related projects. The distribution characteristics of flow velocities at the junction are complex and have a direct impact on the design and maintenance of channels. For the velocity distribution characteristics of combining flows, a three-dimensional numerical model of the equal-width open channel confluence was developed with RSM and the VOF method. Based on the measured results of experiment, the model was verified to study the velocity distribution with different combined scenarios in the junction area. The results reveal that: the flow velocity distribution is zone-featured; at the junction, the streamlines blend and the velocity deflects, and a recirculation structure and secondary flow are located downstream. A greater junction angle leads to larger deflection, stronger recirculation structure and stronger secondary flow, which strengthens the characteristic of velocity distribution and brings a greater impact on the walls of channel. A greater discharge ratio leads to a smaller squeezing effect on the water in the main channel and impacts the zone-featured distribution of velocities, which makes the confluence of water smoother and reduces scour on the walls.
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图 3 水面线计算结果对比（点：物理实测值；线：模型计算结果）
Figure 3. Comparison of free surface profiles (Point: physical measured results; Line: RSM results)
图 4 交汇口下游测点流速剖面对比（点：物理实测值；线：模型计算结果）
Figure 4. Comparison of streamwise velocity profiles (Point: physical measured results; Line: RSM results)
图 5 水平截面中U *与流线分布
Figure 5. Streamlines and U * velocity contour in two horizontal sections
图 7 竖直截面X *=−2中的速度矢量分布
Figure 7. Vector fields of velocity in vertical section (X *=−2)
图 8 q=0.250时不同交汇角度下截面Z *=0.278内U *与流线分布
Figure 8. Streamlines and U * velocity contour in section Z *=0.278 for different junction angles (q=0.250)
图 9 q=0.250时不同交汇角度下截面X *=−2内U *与速度矢量分布
Figure 9. U * velocity contour and vector fields in section X *=−2 for different junction angles (q=0.250)
图 10 θ=90°时不同流量比工况下截面Z *=0.278内U *与流线分布
Figure 10. Streamlines and U * velocity contour in section Z *=0.278 for different discharge ratios (θ=90°)
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