| The oscillating water jump caused by low Froude number has always been a problem which is difficult to solve.In this paper,After carrying out the experiment research of the stilling basin with falling sill,the results showed that the low Froude number would cause the larger range of oscillation and fluctuation.Then setting the contraction pier at the end of the diffusion section,and the stilling basin with contraction bier combined with falling sill was proposed,the flow state and hydraulic characteristics under different flow,contraction ratios,heights of falling sill and downstream water levels were studied.Some main conclusions are drawn from the analysis as follows:(1)The stilling basin with falling sill could reduce the pressure of the pool bottom,and unstable vortexes at shear plane of the cushion and hydraulic jump,the water cushion provides an elastic boundary for the vortex,were the reason for the larger range of oscillation and fluctuation in the stilling basin with falling sill.Only relying on local shape optimization couldn’t eliminate the oscillatory flow pattern of the drop sill stilling basin though the experiments.(2)The water surface vertically diffused,and the two wings were converging,then colliding and mixing with each other after setting the contraction pier.Bottom flow was in a form of a jet diffused and leaped along the bottom of the stilling basin,and form the larger rolling at the surface,in this time the energy dissipation rate was larger,the diffusion jet damaged the unstable large-scale vortexes.The oscillatory flow pattern was disappeared.(3)There were three typical steady-state flow under different flow,contraction ratios,heights of falling sill and downstream water levels,which were submerged jet flow,slightly submerged jet flow and free jet flow.(4)According to the movement of the water in the pool,it can be divided into three regions:contraction jet region,interactive zone and energy dissipation by hydraulic jump region. |
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