| As a revetment building widely used in water conservancy projects,spur dam is a very important waterway regulation building.The spur dam uses its stream-pumping function to keep the mainstream of the water flow away from the embankment,thereby protecting the embankment from erosion,maintaining the channel water depth,and maintaining the original form of the river channel.Natural river channels are mostly curved,and a large part of them are even large-curvature curves.Therefore,studying the influence of spurs on the flow characteristics of large-curvature curves is very important for the rational arrangement of spurs in large-curvature curves and improving the flow field near the spurs.significance.This thesis adopts a combination of model test and numerical simulation.The model test uses PIV system and wireless ultrasonic automatic water level measurement system to measure the flow velocity and water level of the typical section of the curve.The characteristics and changes of water surface line,water level horizontal drop and water level vertical drop along with the mean time velocity near the spur and the curve are analyzed.For numerical simulation,Ansys Icem was used to establish a three-dimensional mathematical model consistent with the dimensions of the physical test and solved with Fluent.Based on this,the distribution and change law of the curve velocity distribution,the size of the backflow area behind the dam,the turbulent kinetic energy,and turbulent viscosity were systematically analyzed The main research results and conclusions are as follows:(1)The layout of the spur dike caused the redistribution of the flow structure of the bend.The water in the upstream of the spur dam was obvious.After the water bypassed the dam head,there was a drop in the downstream.A vortex was formed behind the dam.The water level was significantly reduced.The water level of the shore is higher than that of the convex shore,and it stabilizes after a certain distance from the exit of the curve.(2)When the spur dike is installed at 45 degrees,the longer the spur dike is,the greater the maximum water level along the way will be,and the effect of backwater will be more obvious,and the position where the highest water level appears will be shifted towards the entrance.When the spur dam is installed at 90 degrees of the bend,the length of the dam will not affect the position of the highest water level;the longer the spur dam,the closer the lowest point of the water level along the bend to the inlet side.When the spur dam is placed at a 90-degree bend,the drop in water level before and after the dam at the 45-degree sag increases significantly,and the spur dam's water blocking effect is more obvious.(3)The closer the spur dam is to the bend entrance,the greater the highest and lowest points of the water level;the farther the concave bank is from the bend,the higher the front dam width,and the opposite is the convex shore.The highest water level along the 90-degree section of the spur dike is higher than that of the 45-degree section;the water level in front of the spur dam is similar at different positions in the bend,while the water level drop after the long spur dam is significantly greater than that of the short spur dam.(4)At 45 degrees of the bend,the placement of the spur dike causes the curve's lateral drop to rise significantly.The shorter the spur dike,the smaller the impact on the lateral drop.The maximum water surface superelevation value of the spur dam at 90 degrees of the bend is obviously larger,and the position of the minimum horizontal drop,that is,the position where the two banks reach the stability is also relatively backward,indicating that the placement of the spur dam at 90 degrees of the bend is relatively unfavorable for channel navigation.Safety.Compared with the long spur dike,the short spur dike is arranged at 45 degrees,and the change of lateral ratio drop is relatively gentle at 90 degrees.It has a certain effect on reducing the lateral circulation of the bend and the spiral flow of the bend.(5)The maximum vertical drop on both sides of the bend under the influence of the spur dike appears on section 3-4,indicating that the section is most significantly affected by the adjustment effect of the spur dike and the bend.Placed at 90 degrees.(6)The horizontal,vertical and vertical analysis of the time-averaged flow velocity under different working conditions in the bend is carried out.The results show that the closer the spur is placed to the bend entrance in the longitudinal direction,the smaller the flow velocity in front of the dam and the greater the flow velocity at the dam head;The longer the spur dam,the more obvious the effect of the water on the bend,and the greater the velocity at the convex bank;the layout of the spur dam can effectively weaken the erosion of the current on the concave bank,and the spur dam has a clear advantage at 45 degrees compared to 90 degrees.The analysis in the lateral direction shows that due to the water blocking effect of the spur dam,the water flow forms a split flow at the head of the dam,the main stream dives,and the spur dam is biased towards the convex bank,and the longer the spur dam,the greater the head velocity,the closer the main stream Convex bank and short dike are better than long dike.In terms of vertical direction,in general,the flow velocity is exponentially distributed along the water depth,and unevenness occurs in the local depth along the water depth.At 45 degrees,the effect of the Changding Dam on the vertical adjustment of the water flow is obvious,which can effectively reduce the flow velocity.Vertical unevenness.At 90 degrees,the adjustment effect of the short dike is better.(7)Due to the spur flow of the spur dam,the main flow deviates to the convex bank,forming a high flow velocity area at the dam head.The maximum flow velocity appears near the dam head and extends a certain range downstream.Within a certain range,the larger the spur dike angle,the larger the dam head and downstream high-velocity area,and the greater the maximum velocity.At the same time,the increase of the flow rate increases the overall flow velocity of the curve while also making the flow velocity gradient larger,which increases the speed non-uniformity.(8)The water blocking effect of the spur dam causes the water flow to bypass the spur dam,resulting in a violent separation flow at the head of the dam.Under the effect of inertia,the water flow is divided into two parts,one part continues to move forward,and the other part of the water flow is under the centrifugal force behind the dam The walls separate and form a counterclockwise vortex,creating a backflow zone behind the dam.Within a certain range,the larger the angle of spur dike,the greater the length of the backflow area behind the dam.The increase in flow will also expand the backflow area,but there is a critical value.When the backflow scale increases to a certain extent,it will no longer increase with the flow rate.(9)The area with larger turbulent kinetic energy is mainly distributed in the upstream of the spur dike on the concave bank,at the head of the dam,on the underside of the head of the dam,and in the attachment area after the dam.The flow velocity in the vortex area behind the dam is slow,and the turbulent kinetic energy is also relatively small.Scattered state.Within a certain range,the greater the picking angle,the greater the intensity of turbulent kinetic energy,and its scope of influence gradually expands.(10)The areas with large turbulent viscosity are mainly distributed in the upstream area of the spur dike and the backflow area behind the dam,and the law is similar to the turbulent kinetic energy. |
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