Experimental Study On Influence Of Double Spur Dikes On Flow Characteristics In Bending Reach

Flume test is used to study the variation of flow characteristics near spur dikes and in bending reach when spur dike is placed before the entrance of the bend with different widths,different distance from the bend and different types of double spur dikes(non-submerged and stair-stepping),meanwhile,the comparative experimental group without spur dike and with single spur is added because the influence of double spur dikes on flow characteristics in bends is complex.Velocity and water level near spur dike and in bending reach were measured by velocity and automatic water level measurement system,and using measurement results to study law of velocity distribution,turbulence intensity change,length of backflow zone and water level,transverse gradient in the longitudinal direction,the test results show that:?.No spur dike(1)Larger water discharge,larger velocity and turbulence intensity.The high velocity region is close to the convex bank,while the high turbulence intensity region mainly appears in the middle of the flume and the side near the concave bank.(2)The water level of concave bank in bend is higher than that of convex bank.,and water surface along concave bank is convex and convex bank is concave.Larger water discharges,higher water level along the bending,yet smaller the transverse gradient,and the position of the maximum transverse gradient moves backward.?.Single spur dike(1)When the spur dike is narrower or closer to the inlet of the bend,the recirculation zone length is longer,region of high turbulence intensity and turbulence intensity are smaller,water level concave bank is lower.(2)Length of recirculation zone is proportional to width.(3)Spur dike changes longitudinal surface pattern,Specially,the water level around the apex in concave bank transforms from high to low.(4)When the spur dike is narrower or farther to the inlet of the bend,water surface transverse gradient is lower,reducing transverse circulation in bending reach,and hydrodynamic axes are near the convex bank,protecting concave bank.?.Double spur dikes(1)non-submerged double spur dikes(1)When non-submerged double spur dikes are farther from the bend or water discharge is larger or photographic plane is higher,the velocity is faster and region of high turbulence intensity is larger and its turbulence intensity is higher.(2)The larger width of the non-submerged double spur dikes,the slower the velocity near the spur dikes,and the higher velocity area moves from the middle of the flume to the opposite side of spur dike.(3)In the non-submerged double spur dikes,the recirculation zone length of the latter spur dike B is shorter than that of the former spur dike A,and there is no clear correspondence between recirculation zone length and the distance from the double spur dikes to the bend or flow rate.(4)When non-submerged double spur dikes are farther from the bend,water level of both sides are higher,but the transverse gradient are lower;When water discharge is larger,water level or transverse gradient are all higher.(2)stair-stepping double spur dikes(1)When stair-stepping double spur dikes are farther from the bend or water discharge is larger or photographic plane is higher,the velocity is faster and region of high turbulence intensity is larger and its turbulence intensity is higher.(2)The larger width of the stair-stepping double spur dikes,the slower the velocity near the spur dikes,and the higher velocity area moves from the middle of the flume to the opposite side of spur dike.(3)On the lower plane,the recirculation zone length of spur dike B is shorter than that of spur dike A;On the higher plane,the recirculation zone length of spur dike A is longer,but no recirculation zone appears behind spur dike B,shows that there is no clear correspondence between recirculation zone length and the distance from the stair-stepping double spur dikes to the bend or flow rate.(4)When stair-stepping double spur dikes are farther from the bend or water discharge is larger,the water level or transverse gradient are lower;When water discharge is larger,water level or transverse gradient are all higher.Compared with stair-stepping double spur dikes,maximum velocity,high turbulence intensity region and turbulence intensity of non-submerged double spur dikesall higher and larger,and the transverse gradient are higher.This paper reveals the variation law of flow characteristics near spur dikes and in bending reach when spur dike under different distance from the bend,different widths and different types of double spur dikes(non-submerged and stair-stepping).Filling in the blank of previous studies on spur dikes width and stair-stepping double spur dikes,so the results are innovative.