Abstract: The hydraulic characteristics of a double-expanded flip bucket are simulated using FLOW-3D based on 3D incompressible fluid k-ε turbulence model. By analyzing the flow velocity in downstream channel and whether the water tongue directly impacts riverbank, we expound the hydraulic characteristics and the effects of the original flip bucket and two optimized schemes. According to the computation results under different conditions, the optimum shape of the flip bucket which meets the requirements of energy dissipation and discharge is given. Results reveal that compared with the original scheme, the radius of back arc increases from 64 m to 128 m, the length of back arc section increases by 10 m; the diffusion width of side wall is narrowed by 0.4 m, and the angle of pick-up reduces from 43.3° to 22 °. In the optimized schemes, the impact of water tongue on channel bank is significantly alleviated under the condition of low water level and flow rate; the lift distance of water tongue expands from 91.2 m to 118.8 m, away from bank slope; the maximum flow velocities on the left and right banks of the river drop by 0.7 m/s and 1 m/s respectively, and the return flow decreases. The research findings provide reference for the improvement of flow pattern downstream of flip flow energy dissipation.

Key words: flip bucket, energy dissipation and scour prevention, 3D numerical simulation, flow rate, water tongue, shape optimization