Flow And Sediment Transport In A Channel Bend With A Barb Spur Dike

The water flow in the bend is affected by gravity and centrifugal force,forming spiral flow in the bend,causing concave bank scouring and convex bank silting,causing the river shape change,and even leading to the straightening of the cut bend,which is not conducive to the long-term planning of national construction.As the most extensive river management structure,spur dikes can improve the bend flow regime and maintain the stability of river facies.Barb spur dike is a kind of semi-submerged spur dike with an angle to the upstream,which requires less material.It has been used in a few countries,but the understanding of its action mechanism on the flow characteristics and sediment transport in a channel bend is still very poor.Based on the barb type as the research object,along with the flume experiment and 3D numerical simulation,the method of combining the barb type spur dike is studied on the effect of flow and sediment transport and its influence,analyzed the curve along the water level,flow velocity,vorticity,the change of the flow structure and sediment characteristics,the swirling strength of sediment deposition in relationships.The main contents and research results are as follows:(1)The water level of the flume flow field along the fixed bed bend is measured.Combined with the numerical results,the variation characteristics of the liquid level are analyzed.In the streamwise direction,the barb-shape spur dike and rectangular spur dike both have three stages of changes: namely,the elevation in front of the groin the fall behind the dam,and the fluctuation out of the bend.In the transverse direction,the flow field of barb spur bend always maintains a lower horizontal drop than that of the original bend,which is lower than that of the external high and internal low.Although there is a V-shape surface line,the down cut is lighter.(2)The measurement results of particle image velocimetry technology and numerical simulation results were used to analyze the characteristics of bends with different groin conditions.The barbed spur dike can enhance the lateral mixing of the water flow behind the dam and effectively restrain the main stream close to the concave bank.(3)Based on the velocity,vorticity and the variation of sediment scouring and silting characteristics,the secondary flow and its influence on sediment transport are analyzed.The secondary flow caused by the barbed spur can counteract the spiral flow in the bend and cause scour in the middle area of the downstream flow surface of the spur.(5)Swirling strength was used to analyze the variation of sediment scouring and silting in the bend.On the bed surface,taking the scouring and silting balance line as the boundary.On the convex side,the swirling strength is negatively correlated with the sediment height.In the concave side,the swirling strength is positive correlation with sediment scouring and deposition.The swirling strength on both sides of the barbed spur band is less than 0.5 times that of the condition without the spur,which promotes silting on both sides and helps to maintain the stability of the river course.