Research On Hydrodynamic Loads Of Stilling Basin With Drop Sill

In recent years, with the great development of society and economy, as well asthe improvement of people’s awareness of environmental protection and therequirements of ecology and environment, the influence of hydraulic engineeringconstruction on ecological environment has become one of the engineering feasibilityconstraints. People’s awareness and concern for the construction of hydropowerprojects is no longer merely the huge economic benefits, but considering the impact ofconstruction projects on the ecological environment. On this basis, stilling basin withdrop sill was proposed as a new energy dissipator which can be used in high-head,large-unit discharge engineering. As an energy-dissipator of downstream bed, thestability of stilling basin with drop sill was of great significance to both the energydissipation and the overall safety of the hydraulic structures. In this paper, based onthe model tests, numerical simulation and theoretical analysis, the characteristics ofhydrodynamic load in stilling basin with drop sill were studied. The main results andconclusions are as follows:(1)Basedon momentum theory and energy equations, the first critical depthformula was derived in stilling basin with drop sill and sudden expansion. Other more,the first and second critical depth empirical formulas were brought forward accordingto the results of numerical simulation and the model tests in stilling basin with dropsill. The formulas could be used to assess the flow pattern of similar projects.(2)Basedon the model tests and numerical calculation, the underflow velocitydistribution and the maximum velocity distribution characteirstic were comparedbetween the stilling basin with drop sill and the routine stilling basin. The index thatthe stilling basin with drop sill can effectively reduce the underflow velocity wasobtained.The influence of drop sill height, inlet energy and inlet angels on themaximum underflow velocity was investigated. The maximum underflow velocityformula was obtained as drop sill height or inlet energy changed.(3)Based on the model tests, the index that the stilling basin with drop sill caneffectively reduce the fluctuating pressure significantly was obtained. The distributionlaw, the probability characteristics, the cross correlation characteirstics and thespectrum characteristics of fluctuating pressure acting on chute slab and stilling basin slab were analyzed. The empirical formula of the maximum fluctuating pressure was obtained as drop sill height changed.(4) Based on the model tests, the uplift on slab was investigated between the stilling basin with drop sill and the routine stilling basin. The influence of drop sill height, slab size and pervious coefficient on the uplift was analyzed. The forecast formula of the maximum uplift was obtained. The uplift on chute slab in the jump region and the influence of the irregularity height on it were researched. The index of the influence of the irregularity height on uplift was obtained.(5) A new type of stilling basin with drop sill was put up for Liyuan Hydropower Project through a series of hydrodynamic test on different stilling basins with drop sill,which reduced the various hydraulics indicators of stilling basin, such as the underflow velocity, the fluctuating pressure, uplift and so on.