水利水电技术（中英文）

丹江口及三峡水库运用后,坝下游急弯河段普遍出现了不同程度的切滩撇弯现象,以往研究表明弯曲河道的切滩撇弯是由于水流弯曲半径与河道曲率半径的不相适应所致,水流动力轴线摆动是发生切滩撇弯的基本原因之一,水流动力轴线摆动是水流动力因素与边界条件共同作用的结果。以往研究主要集中于水流动力因素变化对水流动力轴线摆动的影响,然而围绕水流动力因素与边界条件共同作用对水流动力轴线摆动幅度的影响研究较少。以三峡水库下游荆江典型弯曲河段调关-莱家铺河段为例,采用二维水流数学模型模拟了不同流量级条件下本河段的流场分布,绘制了6种流量级条件下的水流动力轴线,选取了多个不同曲率的典型断面,对比各个断面在不同流量级下水流动力轴线的摆动幅度,分析了河道曲率变化对水流动力轴线摆动幅度的影响。结果表明:水流条件的改变是导致水流动力轴线摆动的主要因素,随着流量的增大,水流动力轴线的摆幅逐渐增大,顶冲点位置向下移动,河道的曲率大小影响水流动力轴线摆动对流量改变的响应,河段的曲率越大,这种响应越快,向凸岸侧产生的摆动幅度越大。结合数值模拟结果可以看出,在小流量作用下,水流动力轴线与深泓线基本一致,大流量作用下,水流动力轴线在弯曲河段大曲率处靠近凸岸,与实际发生的冲淤情况一致,这会导致弯曲河段大曲率处容易出现撇弯切滩现象。本次研究可为进一步深入研究三峡水库下游弯曲河道的演变规律提供参考。

After initiating the operations of Danjiangkou Reservoir and the Three Gorges Reservoir, the phenomena of bend bypassing and shoal cutting occur at the downstream sharp bending river reaches of both the dams, for which the previous studies show that the phenomena of bend bypassing and shoal cutting of the bending river channels are the results of the mutual unadaptability between the bending radius of water flow and the radius of river channel curvature, while the swing of flow dynamic axis is one of the basic causations and the axis swing is the result from the common effects from both the flow dynamic factors and the relevant boundary conditions. The previous studies mainly focus on the impacts from the flow dynamic factors on the swing amplitude of flow dynamic axis, but only few studies are made around the impacts from the common effects from both the flow dynamic factors and the relevant boundary conditions on the swing amplitude of flow dynamic axis. By taking the downstream typical bending river reach(Tiaoguan--Laijiapu River Section) of the Three Gorges Reservoir as the study case, the flow field distributions of this river reach under the conditions of different levels of flow rate are simulated with a 2-D flow mathematical model, and then the flow dynamic axes under six levels of flow rate are drawn, while several typical sections with different curvatures are selected for comparing the swing amplitudes of the flow dynamic axis under different levels of flow rate of all the sections and analyzing the impact from the change of the river channel curvature on the swing amplitude of the flow dynamic axis. The study result shows that the change of the flow condition is the main factor to cause the swing of the flow dynamic axis, and then the swing amplitude of the flow dynamic axis gradually increases along with the increase of the flow rate with the downward movement of the location of the top rushing point, while the river channel curvature impacts the response from the swing of flow dynamic axis on the change of flow rate, for which the larger the curvature of the river reach is, the faster the response is to be and the larger the amplitude of the swing toward the side of convex bank is to be as well. In combination with the numerical simulation result, it is can be seen that the flow dynamic axis is basically consistent with the thalweg under the effect of a small flow rate, while the flow dynamic axis is close to convex bank at the location of a large curvature of the bending river reach under the effect of large flow rate, which is coincided with the actual scouring and depositing status, thus can lead to the occurrence of the phenomenon of bend bypassing and shoal cutting at the location of the large curvature of the bending river reach. The study can provide references for the further deep study of the evolution law of the downstream bending river channel of the Three Gorges Reservoir.