Numerical Simulation Study On The Influence Of Permeable Spur Dike On The Characteristics Of Bend Flow And Riverbed Erosion And Sedimentation

Permeable spur dike is a new type of water conservancy project structure.The permeable hole of the dam body can let part of the water flow through,which can reduce the water level.slow down the water flow speed,and reduce erosion.Compared with traditional spur dikes,permeable spur dikes have the advantages of light structure,convenient construction,and low material cost,which can produce significant economic and ecological benefits.It is of areat theoretical significance to study the layout of permeable spur dikes in curved channels and analyze the influence of permeable spur dikes on the flow and riverbed erosion and deposition characteristics of curved channels.In this paper,FLOW-3D numerical simulation software is used to simulate the layout of solid spur dikes in 90° bends and separate permeable spur dikes with different positions and different angles and spur dike groups with different spacing.The simulation results are analyzed from the aspects of flow velocity,water surface morphology,and riverbed erosion and deposition.The main results are as follows:(1)The permeable spur dike can make the flow in the bend no longer directly rush the concave bank.Compared with the non-spur dike,the flow velocity on the concave bank side of the bend decreases,the water level decreases,the flow velocity on the convex bank side increases,the water level increases,and the transverse gradient along the bend decreases.Compared with the solid spur dike,the downstream flow velocity of the permeable spur dike is 22.4%lower than that of the solid spur dike,and the vortex intensity behind the darm is weaker.The width of the concave bank erosion pit formed at the end of the bend is 59.6%of that of the solid spur dike,and it is farther away from the concave bank.(2)When the permeable spur dike is arranged at 45° of the bend,in the case of a large length of the recirculation zone,the range of the high-velocity zone at the dam head is only 49.1%of the other positions,and the improvement effect on the water surface of the bend is the best.At this time,the width of the scour pit formed at the end of the bend is smaller,the distance from the concave bank is farther,and the effect of protecting the concave bank behind the dam is better.An obvious scour pit will be formed at the head of the permeable spur dike with different flip angles.With the decrease of the flip angle,the scour depth of the dam head will gradually decrease,and the corresponding scour pit range will gradually decrease.The downstream scour pit behind the spur dike is smaller,and the main scour position is closer to the mainstream area.(3)The change of spacing between permeable spur dikes has little effect on the size of mainstream velocity.The layout of permeable spur dikes makes the frequency of transverse gradient change more and the amplitude of change decrease.When the spacing of the permeable spur dike group is five times the spur dike length of 5L,the average transverse gradient along the bend is the smallest,the average water level difference before and after the dam is the smallest,and the improvement effect on the water surface of the bend is the best.At this time,the first spur dike has a certain shielding effect on the subsequent spur dike and forms a continuous protection range,which can achieve the purpose of effectively protecting the concave bank.Compared with the siltation of the convex bank of the bend without spur dike,the whole permeable spur dike group has the best effect on the improvement of the siltation of the convex bank.