Numerical Calculation And Analyse On Flow Characteristics Around Fish-bone Type Dividing Dike

Fish-bone type dividing dike is one type of channel regulation project with complicated structure. Here the referred fish-bone type dividing dike is generalized, and flow characteristics are studied by 2D numerical model. Then several schemes with different spacing between fish bones are compared, by which the optimum spacing is obtained. The main achievements are as follows:(1) Near the dike, water level in the upper reach and around the fish back is raised; beside the dike, water level gets lower progressively, it changes greatly around the head and the top of the fish bones; for the backwater effect, water level in upstream face of the fish bones is much higher than that in the downstream face.Moreover, the longitudinal water surface profile decreases suddenly near the top of each fish bone and changes slowly between fish bones, it presents as a ladder; the further away from the dike, the few the longitudinal water surface profile changes. However, the horizontal water surface profile increases closing to the head of the fish bones, where horizontal slope emergences, and its variation amplitude decreases progressively towards to the bank. Crossing through the dike, the horizontal water surface profile gets smooth gradually.Changes of the water level on submerged and non-submerged condition are similar on the whole, and variation amplitude of water lever increases with the increasing discharge in both situation.(2) Close to the fish-bone type dividing dike, the flow is separated around the dike, the main current marches on alongside the dike due to the fish bones, and gets together gradually away from the dike. In the dike field, the flow pattern gets specially turbulent with low velocity, and circulating flow can be seen.Alongside the dike, the flow velocity gets larger, and it is on the contrary in the dike field. Near the head of the fish back and the fish bones, the velocity changes greatly with large velocity gradient. On condition of submerged and non-submerged, the velocity increases with larger discharge, given the same grade of discharge, velocity of submerged condition is larger than that of non-submerged condition.(3) When the value of spacing between fish bones is about 2.1 times of length of the upstream fish bone, water level in the upper reach and velocity alongside the dike both changes least compared with the other schemes, thus the very spacing between fish bones is the optimum one.