Research On The Influence Of Permeable Spur Dams’ Hole Types And Layout On The Hydrodynamic Characteristics Near The Dam Body

As the ’ main force ’ of river regulation project,the flow structure near the spur dike is extremely complex.The traditional solid spur dike is prone to local water damage due to its impermeable dam body,which has drawbacks.The permeable spur dike body is permeable,the structure is stable,the operation is safe,and the development prospect is.However,due to the permeable characteristics of the dam body,the water flow structure near the spur dike is greatly affected by its permeable orifice and its arrangement.The flow structure and turbulence characteristics near the spur dike have always been the focus of academic and engineering circles.It is of great significance to study the influence of different permeable holes and their arrangement on the flow structure and turbulence characteristics of the river channel for the rational design of the permeable holes of the permeable spur dike and the improvement of the flow field structure near the spur dike.In this paper,through indoor flume test and theoretical analysis,the flow velocity and turbulence intensity near permeable spur dikes under different permeable orifices and their arrangement modes are analyzed.On this basis,the cumulative effect of composite spur dikes combined with solid spur dikes and permeable spur dikes is studied.The main conclusions are as follows:(1)The type and arrangement of permeable holes have little impact on the flow velocity of the section in front of the spur dike.The flow velocity in the reflux zone behind the permeable groin fluctuates significantly,and the flow velocity in the transition zone rapidly increases to its maximum value.The flow velocity in the mainstream zone is relatively large but relatively stable.The permeable pore type has a significant impact on the flow velocity in the backflow area behind the dam.The average flow velocity of different permeable pore types in this area is in descending order: elliptical,square circular,and rectangular;The influence of permeable pore type on the flow velocity in the transition zone and mainstream zone is relatively small.As the distance from the permeable groin increases,the backflow phenomenon behind the dam gradually weakens,and the fluctuation of flow velocity also weakens.(2)The turbulence intensity of the downstream flow of the dam body with rectangular,square circular,and elliptical permeable holes increases sequentially.When the permeable holes are arranged in a plum blossom shape,the turbulence intensity of the water flow around the permeable groin is the highest,while the turbulence intensity is the lowest under the grid type arrangement.(3)The cross section velocity distribution behind the No.1 spur dike is mainly influenced by the layout of the first spur dike,the cross section velocity distribution behind the No.2 spur dike is mainly influenced by the layout of the first two spur dike,and the cross section velocity distribution behind the No.3 spur dike is influenced by the layout of the first three spur dike groups.(4)The arrangement of the first spur dike of the composite spur dike group is very important to the overall slow flow effect of the spur dike group.When the first spur dike is a solid spur dike,the flip flow effect is strong and the water blocking effect is large,but the dam head is seriously scoured and the stability is poor.The first spur dike of the composite spur dike group should be arranged as a permeable spur dike,and the arrangement method is permeable,solid,and permeable.(5)Under the optimal arrangement of the composite spur dike group,the influence of the length of different solid spur dikes on the velocity distribution of the upstream and downstream cross sections of the composite spur dike group is analyzed.It is concluded that when the effective dam length of the composite spur dike group is about 83 % of the permeable spur dike,the slow flow effect of the spur dike group is the best,and the revetment effect is the best.