Numerical Investigation On Hydraulic Characteristics Of Flow Of Stepped Spillway

An overall three-dimensional(3-D) flow field numerical simulation is made in order to fully research the hydraulic characteristics of flow of a stepped spillway, in which the calculation region is established in CAD and meshed by structured grids with ANSYS ICEM CFD. The κ-ε model is used to simulate turbulence and the VOF method to track the free surface with FLUENT. The calculations of water surface elevation, bottom pressure, section velocity and energy dissipation rate are in good agreement with model test data after comparison and analysis. In order to avoid cavitation, erosion damage and ensure full dissipation, a joint dissipater of steps, stilling basin and baffle pier have been formed. Studies have shown that 3-D numerical simulation region and method can reflect the stepped spillway water flow field characteristics accurately, and provide smoother and completer flow field information rapidly. Besides, it provide a reliable basis for the optimum design of its structure.The main research results are:(1)About flow regime. They are skimming flow. Eddies rotated clockwise. There is a gentle slope of 15.9° on the stepped spillway. Wake of the step above interfers the next one, where a three dimensional unsteady flow is formed. This kind of skimming flow is called "wake-step interference".(2)About pressures. The pressure of every is evenly distributed and the pressure distribution rules is same. When there is a rolling flow on the step, there is the maximum positive pressure on the horizontal plane because of the flow’s impact, and there is negative pressure on the vertical plane because of the flow’s out of wall. When there no rolling flow, there is a slight or no negative pressure on the vertical plane of steps.(3)About velocity. The velocity distribution along vertical depth of a typical cross-section is on the wall’s velocity is zero, the greater the velocity close to the surface until the water surface is the maximum. There is eddies at the concave corners. The velocity is close to zero at the eddies’ center, the velocity increases gradually from the center of eddies to the flow surface.(4)About energy dissipation rate. The energy dissipation rate at the end of steps has reached more than 80%, indicating that the stepped effect is significant. However, with the increase of the upstream head, the proportion of collision energy consumption between water and steps decreases, resulting in lower energy dissipation rate. The joint energy dissipation stepped spillway’s energy dissipation rate increases to 95% or more, whose result is satisfactory. The velocity behind the baffle pier is small and the flow regime is steady, therefore, a new measure can be made to solve the energy dissipation in practical projects.