The Effects Of Body Type Of Flaring Gate Pier And Stepped Spillway On Aerated Characteristic Of Steps

Due to high rate energy dissipation and saving project investment, the new energy dissipater of flaring gate pier combined with stepped spillway and stilling basin has effectively applied in the dam building with high head and large single-wide flow. In the engineering applications, however, the flow will cause cavitation on the stepped spillway surface in large single-wide flow, which cause cavitation damage in stepped spillway. Some engineering practice shows that the optimized flaring pier size and morphology of the steps can ensure a smooth transition from the flaring gate pier to the stepped spillway, and increase the aerated concentration at the bottom of the step surface, which can effectively reduce the cavitation damage on the step surface and thus make this energy dissipator used in high head and large discharge conditions. Currently, most studies for the energy dissipater of flaring gate pier combined with stepped spillway and stilling basin tend to explore the overall energy dissipation and aerated effect, while for the pressure distribution and aeration concentration distribution on the single step of vertical and horizontal solid wall on the stepped spillway never had done many researches. When the size and morphology of flaring gate piers and steps designs not very smoothly, the flow pattern transition is not smooth, which will result in a low levels air concentration on the solid wall, and a great level negative surface, ultimately make a stepped surface prone appear cavitation damage. Based on the above issues and combined with the model of energy dissipater of flaring gate pier combined with stepped spillway and stilling basin of Ahai Hydropower station, applying RNG turbulence model and VOF model of water vapor two-phase, this paper numerically simulated the 3D flow field of the whole model, and the range from the upstream reservoir to downstream stilling basin. With aerated cavity length experiment, comparatively analyze the experimental and simulation results, which shows the numerical simulation has a certain rationality and reliability. According to the results of simulation, this paper systematically analyzes the influence of contraction ratio of symmetric and asymmetric flaring gate pier to the ladder aeration cavity length and pressure distribution and size, and the influence of symmetrical contraction ratio and the angle of table-board of the first steps to the aerated characteristics and energy dissipation characteristics, which will applied to design reference of stepped spillway with large per unit discharge as a shape optimization. The main findings are as follows:(1) The simulation shows that the aeration cavity length increase with the contraction ratio decreases, the maximum negative pressure decreased, but extensive distribution of negative pressure in stepped spillway Under the symmetrical contraction ratio. The average aeration concentration along decreasing trend with some fluctuations under the conditions of different contraction ratio, with the contraction ratio decreases, aeration range on steps is reduced. The first few levels stepped surface with full aerated, along the horizontal solid wall outward, the aeration concentration first decreases and then increases, while along the vertical solid wall downward, the aeration concentration first increases and then decreases, the average aeration concentration at the same section increases with contraction ratio decreases. At the end of the step surface, along the horizontal solid wall outward,the aeration concentration increases, while along the vertical solid wall downward, the aeration concentration decreases, the average aeration concentration at the same section decreases with contraction ratio decreases. Energy dissipation rate increased with decreased contraction ratio of flaring gate pier.(2) The simulation results show that, with asymmetric flaring pier contraction ratio decreases, step aeration cavity length increases, and the aerated cavitylength of lateral side with smaller converging angle is larger4 to 5 times than lateral side with larger contraction expanded. Negative pressure on steps is reduced with decreased contraction ratio, but the negative pressure distribution gradually The outer edge of the steps all levels have negative pressure, but the maximum negative pressure in the cavity on the perpendicular solid wall of first step.(3) The results showed that the energy dissipation effect is better when the step is up than fall down. The turbulent energy and energy dissipation rate on ogee turbulent section and stilling board were greater,the largest pressure on stilling bottom and temporary bottom velocity were relatively small.The results shows that when the single-wide flow rate of 160m3/s · m, the ladder overflow face negative pressure -10.24kPa to -46.38kPa, maximum vacuum appears on flaring gate piers and stepped spillway outlet connections as well as the heads of a solid wall perpendicular.