Numerical Simulation Of Local Scour In Pick Flow

The energy dissipation of high head hydraulic structure is commonly used to discharge flood energy,but the energy dissipation of high head hydraulic structure will form a large local scour pit in the downstream,which poses a threat to the normal operation of the project.In order to predict the scope of the scour pit in advance,this paper takes the starting shear stress of sediment as the deformation condition of the riverbed.By applying the riverbed deformation equation and dynamic grid technology,the three-dimensional numerical simulation of the local scour process of the downstream riverbed is realized with the help of Fluent platform.The relevant hydraulic parameters in the scour process of the scour pit and the change process of the scour pit shape are explored,and the local scour law of the overrun flow is summarized.The main research contents and achievements are as follows:(1)According to the physical model test data,the three-dimensional numerical global model of the high head flood discharge and sand erosion tunnel is established;By numerical simulation of the three-dimensional flow field of the whole model,the data such as discharge rate and water tongue parameters are obtained.The results are basically consistent with the physical model test data,indicating that the model established in this paper is more accurate.(2)The custom function program which takes the shear stress of the bed surface as the deformation condition of the river bed is improved,and the improved program is combined with the steady-state calculation results to carry out the three-dimensional transient numerical simulation calculation of the differential canes in the checking condition.The simulation results show that the relative error between the calculated scour depth and the experimental value is 3.5%,and the calculated results are in good agreement with the physical model test.The 3D numerical simulation of local scour of pick current is realized.The improved numerical simulation speed is about four times of that before the improvement,and the calculation efficiency is improved.(3)Based on the three-dimensional numerical model of the high head flood discharge and sand erosion tunnel,based on the two types of nose bumps proposed in the physical model test,the water tongue flow pattern and scour pit shape of the two types of nose bumps were simulated,and the differences of related parameters of the two types of nose bumps and the reasons for the differences were analyzed.The results show that compared with the differential nose check,the tongue can increase the transverse diffusion of the tongue,reduce the single width flow rate of the tongue into the water,significantly reduce the depth of the deepest point of the scour pit,reduce the longitudinal range of the scour pit,and slow down the slope near the deepest point of the scour pit.(4)Explore and analyze the scouring process of pick flow,and summarize the local scouring law of pick flow: with the progress of scouring,the flow velocity within the scouring pit gradually decreases;The shear stress of the bed surface changes greatly in different scour periods.With the scour of the river bed,the shear stress of the bed surface decreases continuously,and the high shear stress area shrinks.At the end of scour,the high shear stress area basically disappears.The scour pit formed a basic form in the early scour stage,and the subsequent scour pit expanded slightly in plane scope and deepened in depth.In the early stage of erosion,the height of the deepest point of the scour pit dropped quickly and the scour rate was fast.In the later stage,the height of the deepest point of the scour pit dropped slowly and the scour rate was slow.