| Spur dam,as a relatively common bank protection structure in water conservancy projects,can protect the river bank by changing the structure of water flow by using its water-carrying function.In this paper,two spur dikes with different geometric shapes,straight spur and T-shaped spur dikes,are arranged in the bends of the flume to study the influence of the spur dikes on the flow characteristics of the 180-degree open channel bends.The experiment includes two parts:physical model and mathematical model,to study the influence of different spur dikes in the bend on the flow characteristics.In the physical model part,an automatic water level measurement system combined with a manual measurement method and a flow rate measurement system is used.Two spurs with different geometric shapes are placed at the 30-degree,60-degree and 90-degree positions of the U-shaped flume curve.The research is the T-shaped spur dike.When a spur dam is placed in a bend,the water flow characteristics have undergone major changes,and its rules are summarized based on the experimental results.In the mathematical model part,numerical simulation is carried out through the ANSYS CFD module,the Geometry software is used to establish a three-dimensional numerical model with the same size as the physical model,and the Fluent software is used to set the solution conditions for solution calculation,and the data results are compared with the data obtained from the sink physical model.After that,the spur dike was placed at the 60° position of the bend.By changing the position,length,angle,and head length of the T-shaped spur dike,the flow velocity in the bend and the back of the dam were compared and analyzed by changing the position,length,angle,and head length of the T-shaped spur dike.The scale of the recirculation zone,the distribution and change of turbulent kinetic energy The main research results and conclusions are as follows:(1)The layout of the spur dam at the bend has obvious changes in the water flow characteristics.The most important thing is that the water level before and after the dam has a large drop.The water level change in the straight road is not very obvious,but in the straight road.The water level of the concave bank in the bend is slightly larger than the water level of the convex bank,and the water level shows ups and downs.(2)The closer the spur dike is to the top of the bend,the more obvious the effect of water level reduction.By comparing the straight spur dike and T-shaped spur dike in the bend,the water level changes along the bend at different locations,it can be seen that the straight spur and the T-shaped spur dike are placed at different positions of the bend.The water level in front of the T-shaped spur dam has the same degree of obstruction,and the water level before and after the T-shaped spur dam has a greater range of changes,and the water level has dropped significantly.(3)The arrangement of spur dams makes the horizontal drop of water surface rise significantly.When spur dams of different shapes are arranged at 30 degrees of bends,straight spur dams have less influence on the horizontal drop of water.When spurs are placed at 60 degrees of bends,The T-shaped spur dike has little effect on the lateral gradient of the water surface,and has a certain effect on reducing the lateral circulation of the bend and the spiral flow of the bend.It can be beneficial to the adjustment of the longitudinal gradient of the water and stabilize the flow pattern of the water in the bend.(4)The flow velocity analysis of straight spur dams at different locations shows that the closer the spur dam is to the bend entrance,the lower the flow velocity in front of the dam and the greater the flow velocity at the dam head;when the T-shaped spur dam is placed at 90 degrees,the flow velocity in front of the dam is the smallest.,And the flow velocity at the head of the dam is also the largest.Comparing the straight spur dam and the T-shaped spur dam,it can be seen that the T-shaped spur spur dam is more obvious.(5)Under the action of the spur dike,the cross-section of the river near the spur dike shrinks,and the main flow tends to the convex bank,forming a high-velocity area around the dam head,extending a larger range of influence near the spur dike,and increasing the flow velocity near the convex bank Obviously,there may be some erosion on the convex bank.The water flow before and after the concave bank of the spur dam is blocked by the spur dike,especially in the area behind the dam,the flow velocity of the water flow is very obvious,which has played a significant role in protecting the concave bank within a certain range.(6)Arrange spur dams at 60 degrees of bends.The length of spur dams is within a certain range.As the length of spur dams increases,the length of the return zone increases accordingly.Therefore,short spur dams can better protect the river bank.(7)When the spur spur angle is 75 degrees and 120 degrees,the length of the backflow zone behind the dam decreases with the increase of the spur spur angle within a certain range.The 75-degree spur spur backflow zone has a longer range of action,which is beneficial to Reduce the erosion of the river bank by the current.(8)Changing the length of the head of the T-shaped spur dike,the length of the backflow zone at the back of the dam increases with the increase of the head of the T-shaped spur within a certain range.Appropriately increasing the length of the head of the T-shaped spur dike can well increase the length of the backflow zone.The length can reduce the erosion of the concave bank by the water flow.Considering the influence of the flow rate recirculation zone,choosing the appropriate length of the T-shaped spur dike head can better protect the river bank.(9)The impact of the spur dike on the turbulent kinetic energy is concentrated on the head of the spur,the attachment area behind the dam and the downstream middle position of the dam.After the water flows out of the bend,the turbulent kinetic energy gradually returns to balance.Within a certain range,the maximum value of turbulent kinetic energy increases with the increase of the pick angle,and the maximum value of turbulent kinetic energy decreases with the increase of the head of the T-shaped spur dike. |
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