| The stepped spillway is a new energy dissipation which sets steps on the flow surface to dissipate energy. Compare with slippery spillway, its energy dissipation is not only obvious, but also make the energy dissipation structure simpler and save the cost, hence it has been studied and applicated widely. In order to discuss numerical simulation study of turbulence flow in the stepped spillway and analysis on influencing factors of dissipation, the paper discussed the effect of the step height, the slope, the step shape on the hydraulic characteristics and energy dissipation with numerical simulation, simulated the flow of the flexible protected stepped spillway initially, at the same time, discussed and evaluated the formula of the energy dissipation ratio and the air entrainment coefficient of the velocity formula.Combined with the method of VOF (Volume of fluid), the paper used the three models of standard k-ε, RNG k-εand Realizable k-εto simulate the stepped spillway and compared with the experimental result, the results indicate that RNG k-εmodel can be better performed in the simulation and the calculation efficiency, and it is feasible and reasonable.In order to analysis and discuss the factors of effecting the related energy dissipation in the stepped spillway, the paper designed several different simulated experiments about the step height, the slope and the step shape. Through the simulation, it is found that when the slope and dam height are the same, the step height will affect the related energy dissipation ratio obviously in a smaller flux, but will not affect the related energy dissipation ratio basically in a greater flux. In the experimental range, when the angle of slope between 5.71°and 33.69°, there exists a some step height will make the related energy dissipation ratio reach the maximum value. When the step height, flux and dam height are the same, the result shows that the gentler the slope, the greater the related related energy dissipation ratio, but the increased extent is very slow, it indicates that the slope will affect the related energy dissipation a little. When the slope,the flux and the dam height are the same, there is a more difference among the different step shape(or the placed way of steps)on related energy dissipation ratio, it indicates that the step shape will affect the related energy dissipation ratio in a certainn extent.Among them,the related energy dissipation ratio of the V-shape step,the transitional step,the bulgy step and the right angle step are more bigger, the related energy dissipation ratios(η) of the different step shape can be arranged in an order as follow:ηv-shape>ηtransition≈ηbulgy step>ηright angle>ηcuneal >ηchop angle >ηmodified round.For the flexible protected stepped spillway which used the geomembrane bags to make up of steps to dissipate energy, the paper combined with the RNG k-εmodel and the VOF method, the paper simulated the flow in this stepped spillway, and compared with the simulated result and the practical result, it was found that they were close. It indicated that the method above was feasible in simulating and analyzing the hydraulic characteristics of the flexible stepped protected spillway. When the flux and slope are the same, through the contrast of the numerical simulation results between the two placed ways of the bags, the paper found that the way of the inclined placed geomembrane bags could be better performed in the related energy dissipation ratio than the way of horizontal placed geomembrane bags.Based on the data of experiment, the paper discussed and evaluated the property of the energy dissipation ratio formula, modified the energy dissipation ratio formula of Tang Shengcai, put forward the modified formula. The modified result is close to the practical energy dissipation ratio. At the same time, the paper discussed the air entrainment coefficient-K in the formula of Luo Qibei. The paper fitted the curve with the experiment data, gave the approximate estimate formula of K in the condition of 30°<θ<60°, 0.72 |
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