| T-shape spur dike can effectively relieve the erosion damage to bank, meanwhile the negative influences caused by T-shape spur dike are far less than those by the traditional type. The wing of T-shape spur dike can not only avoid the local scour near the head of groyne by Longitudinal blocking the flow, but also reduce lots of scour by both area and depth to the bed. At present, there is not much research about T-shape spur dike, and most current research mainly focuses on effects of Parameters on the volume of scour hole and the bed share stress, such as fraud number, length of spur dike, and wing length of spur dike. While the effects of the angle between wing and body, dam axis angle on hydraulic characteristics such as backflow area, water level gradient, lateral circulation, and velocity distribution have not been involved. This thesis analyze flow hydraulic characteristics in the 90°bend with three conditions about no spur dike, straight rectangle spur dike and T-shape spur dike, After getting the superiority and advantages of T-shape spur dike, this Paper significantly researches on the effects of hydraulic characteristics in the 90°bend from the Parameters of the angle between wing and body and dam axis angle. There are some conclusions as follows:(1) Like traditional spur dikes, T-shape spur dike sharpened corner flow seParation phenomenon, formed backflow zone both in the front of and behind. the dam However, the T-shape spur dike may be preferred as comPared to straight spur dike as far as the area of backflow is considered. As a result the size of the water level gradient, lateral circulation and bed share stress, the T-shape spur dike is better than straight spur dike too. The effect of the angle between wing and body on the width of backflow is large, which increases gradually with the decrease of θ. While the effect of the dam axis angle on length of backflow is large, which decreases gradually with the decreasing of a. When a is 30°, the length of backflow reduced by 49%, comParing with the one of rectangle spur dike.(2) Spur dikes would exacerbate the lateral circulation. ComPared with the rectangle spur dike, T-shape spur dikes can direct the lateral circulation to channel center, and its intensity is decreased. So it becomes easier to protect the bank from upstream inflow erosion. The Circulation intensity decreases with the decreasing of dam axis angle, and advanced disappears under the mutual influence of downstream backflow.(3) The effect of T-shape spur dike on velocity is also great. With the decreasing of 6, mainstream velocity will reduce gradually, but when θ decreases to a certain value(about 60°), velocity will however reversely increase. And the influence of dam site on velocity is not significant. With a decreasing, the velocity near spur dike will decrease slightly.(4) The extension of the high shear stress zone is smaller in T-shape spur dike, and its intensity decays much faster towards downstream. Bed shear stress increases with increasing fraud number, and it shows a trend that the shear stress will decline first and then increase with the decreasing of the angle between wing and body, besides its intensity decays shows a trend that is from increase to reverse decline. By comprehensive contrast, when 0 is 75°, the bed share stress is smallest. In addition, with a decreasing, the bed shear stress near spur dike will decrease slightly, in other words, the force from flow to the formation of the river bed scouring is decreased with the T-shape spur dike position nearing the bend inlet. In view of bend flow characteristics, it is better for bed form development when the T-shape spur dike lays on a bed where the central angle of cross section is 30°.(5) After the comprehensive comparison of backflow size, velocity, bed shear stress three aspects, it is the optimal one when the angle between wing and body of T-shape spur dike is 75°. And it will the best to exert advantage when T spur dike is placed near the bed where the central angle of cross section is 30°. |
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