顺直微弯型分汊河道水流的紊动特性试验研究

Experimental study on turbulence characteristics of flow in straight or slightly curved braided rivers

对顺直微弯型分汊河道的水流紊动特性进行了试验研究,构建了分汊河道的物理模型试验系统,探究了在不同汊道宽度比和上游来流量条件下,水流在分汊河道沿程不同断面的紊动能分布特征.试验结果表明:在平面上,水流紊动最为剧烈的区域发生在支汊进口段凹岸的回流区与凸岸的高流速区之间的过渡地带,表、中、底3层的高紊动区的强度和范围以中层为最大,表层次之,底层最小;在横断面上,紊动强度在分汊前、中、后各有不同,支汊进口段断面的凹岸侧紊动强度最大,其高紊动区等值线由底至表呈现由凹岸倾向凸岸的规律,交汇断面对应岛屿尾尖的区域紊动也较为剧烈;上游来流增大明显增强断面紊动强度,但对紊动能等值线分布特征影响较小;不同支汊宽度比引起交汇断面高紊动能位置的变化,以及支汊进口断面紊动能的量值与位置也有所差异.

The physical model experiment system was developed to study the turbulence characteristics of flow in the straight or slightly curved braided rivers.The turbulent kinetic energy distributions of different cross-sections of braided rivers were studied under different anabranch widths and upstream flow rates.The experimental results show that the turbulent intensity peaks in the planes occur at the transition zone between the recirculation zone near the concave bank and the high-velocity flow zone near the convex bank in the entrance region of each anabranch.The intensity and range values of the high turbulence zone are large at the middle layer,medium at the surface layer,and small at the bottom layer.The turbulent intensities at the cross sections of bifurcation,branch and confluence are different.The turbulent intensity peaks at the cross sections occur near the concave bank of the cross section in the entrance region of each anabranch,and the high turbulence zone inclines towards the convex bank from the concave bank from the bottom to the surface.In addition,the region behind the tail tip of the braid bar at the confluence cross section also has high turbulent kinetic energy.The upstream flow rate causes the tubulent intensity to increase,but has little influence on the turbulent kinetic energy.The location of the high turbulence zone in the confluence cross section and the magnitude and location of the high turbulence zone at the entrance sections in each anabranch vary with the width ratio of two anabranches.