| The low Froude number hydraulic jump has become an important scientific problem to be solved urgently because of the large fluctuation of water surface and low energy dissipation rate.In this paper,combined with the actual project of the spillway tunnel of Wuyi Reservoir in Xinjiang,by means of model test and numerical simulation,taking the trapezoidal pier-suspension grid combined energy dissipator in the stilling basin with low Froude number as the research object,under the condition of low Froude number flow,the change law of hydraulic characteristics after adding trapezoidal piers and suspension grids in the stilling basin was compared and analyzed,the energy dissipation mechanism was clarified,and the layout parameters of trapezoidal piers and suspension grids were optimized.Finally,the main conclusions are as follows:(1)Under the flow condition of 2<Fr<4.5,the water depth in the stilling basin with trapezoidal pier-suspension grid combined energy dissipator is evenly distributed,the fluctuation range of pressure distribution gradient along stilling basin floor and time-averaged pressure distribution coefficientC_P is small,and the overall stability is better,and the kinetic energy correction coefficient is basically kept in the range of 1<α<2,which can effectively improve the velocity distribution of the inlet section.The energy dissipation rate increased from 52.25%,65.14%and 67.96%of the traditional stilling basin to 56.74%,74.88%and 77.75%.(2)The energy dissipation of trapezoidal pier-suspension grid combined energy dissipation structure is mainly composed of three parts:hydraulic jump energy dissipation,trapezoidal pier three-dimensional shear dissipation and suspension grid dissipation along the stilling basin.Trapezoidal piers and suspension grids are placed to change the hydraulic jump structure,and the bottom hydraulic jump zone is the main energy dissipation area;trapezoidal piers change the flow structure of the water flow into the pool,and a ternary diffusion jet is formed behind the piers,and the energy is dissipated again;the friction effect of the suspension grid flow area,the counterclockwise vortex behind the grids,and the further dissipation of mechanical energy along the stilling basin,the interaction of these three fully exerts the superimposed energy dissipation effect of the joint energy dissipator.(3)Constructing trapezoidal pier shape and layout parameters in trapezoidal pier-suspension grid stilling basin,comparing and analyzing the changing rules of the flow regime,velocity distribution and energy dissipation rate in the stilling basin under different body shape and layout parameters.It is concluded that when the trapezoidal pier in the stilling basin is arranged in double rows with a staggered manner,with pier height ratio C=0.436 and shrinkage ratioβ=0.4,layout relative positionξ_d=0.35,and row spacing ratioξ_r=0.16,the overall flow regime is relatively stable,and the vertical distribution gradient of flow velocity in the stilling basin increases.Under the three working conditions,the flow velocity at the end of the stilling basin decreases to 0.26m/s,0.44m/s and 0.48m/s respectively,and the energy dissipation effect is remarkable.(4)Based on the optimal layout of trapezoidal pier,constructing the layout parameters of suspension grid in trapezoidal pier-suspension grid stilling basin.The final result is:when the trapezoidal piers in the stilling basin are arranged in double rows with a staggered manner,the pier height ratio C=0.436,the shrinkage ratioβ=0.4,the relative arrangement positionξ_d=0.35,the row spacing ratioξ_r=0.16,and the suspension grid layout height ratioξ_h=1,layout spacing ratioξ_l=0.727,and the layout range ratioξ_a=0.637,the turbulent kinetic energy and distribution range of vorticity intensity in the hydraulic jump zone and the suspension grid area is expanded,and the energy dissipation is intensified,which is 4.75%,10.67%and 10.75%higher than that of the traditional stilling basin.The research results can provide reference for the study of underflow stilling basin. |
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