| Discharge and energy dissipation of stilling basin with low Froude number is one of the most difficult problems in hydraulic engineering,which is characterized by unstable hydraulic jump in the basin,low energy dissipation rate and severe scouring downstream.In order to overcome the problems of unstable hydraulic jump and low energy dissipation rate in stilling basin with low Froude number,it is proposed to arrange the joint auxiliary energy dissipator of the diversion pier-suspended grid in stilling basin.By combining model test with numerical simulation,the hydraulic characteristics of the diversion pier and the diversion pier-suspended grid energy dissipator in stilling basin are respectively analyzed under the condition of 2<Fr<4.5,and the joint arrangement parameters of diversion pier-suspended grid are optimized on this basis.The main conclusions are:(1)The diversion pier added at the end of steep slope of stilling basin changes the inflow structure of the basin,makes the water behind the pier have three-dimensional flow characteristics,and enhances turbulent shear between the water bodies;it also reduces the maximum time-averaged dynamic water pressure at the bottom of the basin,decreases the flow rate near the bottom,and decreases the maximum flow rate near the bottom at the center axis and 1/3 axis by 28%and 23%respectively;under three working conditions,the length of hydraulic jump is shortened by 20.05%,21.09%and 15.03%respectively,and the energy dissipation rate is increased by 8.23%,6.55%and 7.14%respectively.(2)Two parameters of height ratio C and contraction ratio the diversion pier stilling basin,with C of 0.7,0.75,0.8 and concluded through experimental study that when C is 0.75 and of the diversion pier are constructed in of 0.5,0.6 and 0.692 respectively.It is of 0.6,the flow regime in the basin is stable and the flow velocity gradient changes significantly;under three conditions,the maximum time-averaged dynamic water pressure of the basin bottom is 719.81 pa,895.77 pa and 919.788 pa respectively,which is far less than that of other diversion pier layout parameters,and the energy dissipation rate is increased by 12.43%,10.55%and 11.24%respectively compared with the traditional stilling pool.(3)Compared with the diversion pier stilling basin,the water depth in front section of the diversion pier-suspended grid stilling basin increases,the position of the section before the jump moves forward,the hydraulic jump state is further improved,and the turbulent shear of water body is enhanced.Collision and friction occur between the flow through the grid and the side wall of the grid;at the same time,counter-clockwise vortex is formed behind the grid,which increases the energy dissipation around the suspended grid along the way in the basin.Under the three conditions,the energy dissipation rates are increased by 4.05%,3.33%and 4.5%respectively,with remarkable energy dissipation effect.(4)Aiming at the height and spacing of suspended grid arrangement in diversion pier-suspended grid joint energy dissipator,two parameters,namely,relative arrangement height of suspended gridξ_hand arrangement clearance ratioξ_l,are established.Takingξ_has 0.82,0.91,1,1.1 and 1.12 respectively,and takingξ_las 0.12,0.15 and 0.2 respectively,it is concluded through experimental study that when the height ratio of diversion pier in joint energy dissipator is 0.75,the contraction ratio is 0.6,the relative arrangement height of suspended grid is 0.91,and the clearance ratio is 0.15,the water flow on the hydraulic jump surface swirls violently,stable vortices are generated between adjacent girds,the turbulent energy and vorticity intensity of water body behind the girds are increased,and the energy dissipation in the pool is aggravated.Compared with the traditional stilling basin without energy dissipators,the energy dissipation rates under the three working conditions are respectively increased by 17.61%,16.13%and 16.93%,which effectively eliminates the unstable state of hydraulic jump in the stilling basin with low Froude number and solves the problem of serious downstream scouring. |
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