Numerical Simulation Study Of Water-sand Characteristics Of Sand Drainage Funnel Based On DPM Model

The sand drainage funnel is a secondary sediment treatment facility in China with certain improvements and innovations,which opens up a new way for water-sand separation.However,due to the complexity of the three-dimensional spiral flow field of the sand drainage funnel,it is difficult to solve numerical solutions,and there are few numerical simulations of the water-sand transport characteristics of the sand drainage funnel,which are simulations of the clear water flow field.In this paper,we use the 1:8 physical model test of the Donglei yellow drainage funnel as the research object and use the computational fluid software Fluent to conduct numerical simulation research on the three-dimensional flow field and sediment movement characteristics inside the drainage funnel.The main contents and results of this paper are as follows:(1)A 1:8 physical model test of the Donglei yellow pumping sand drainage funnel is used as the research object,and the Reynolds stress turbulence(RSM)model and VOF method are applied to construct a three-dimensional flow field mathematical model of the sand drainage funnel.The simulation results show that the simulated values of tangential flow velocity and water consumption rate in the sand drainage funnel match with the measured values in the model test,which ensures the reliability of the calculation results.(2)By comparing the simulation results of the sand drainage funnel at the design flow rate(Q=13.9L/s)and the small flow rate(Q=0.05L/s),the reasons for the low water consumption rate of the sand drainage funnel were analyzed.When the inlet flow of the sand funnel reaches the design flow rate,the water consumption rate is 9.2%and a penetrating air vortex appears in the funnel chamber;while the water consumption rate of the sand funnel operating at a low flow rate is as high as 32%,which is because the penetrating air vortex reduces the overflow area of the bottom hole and lowers the water consumption rate of the sand funnel.(3)The hydrodynamic mechanism of the low water consumption and high sand interception rate of the sand funnel was elucidated based on the flow field results of the sand funnel at the design flow rate.The tangential flow velocity inside the funnel is larger than the radial and axial flow velocities,indicating that the tangential flow velocity is the main flow,the radial and axial flow velocities are the secondary flow,and the coupled three-dimensional spiral flow ensures the low water consumption rate of the sand drainage funnel.(4)Based on the aforementioned three-dimensional flow field mathematical model of the sand drainage funnel,a discrete phase(DPM)model is used to construct a sediment transport calculation model for the sand drainage funnel.The results show that the sediment particles of 0.05mm,0.075mm,and 0.01mm are mostly concentrated near the bottom hole of the sand discharge,and the sand content shows a distribution pattern of "small at the top and large at the bottom".This indicates that the sand funnel can effectively handle suspended sediment with particle sizes larger than 0.05mm.(5)The discrete phase model was used to capture the number of particles reaching the bottom hole of the sand discharge,and the sand interception rate of the sand discharge funnel was calculated for the 12 conditions mentioned above.It was concluded that the sand interception rate of the sand drainage hopper was the first to increase and then decrease with the increase of the sand transport rate of large-size particles(0.075mm and 0.1mm),while the sand interception rate of the sand drainage hopper was almost constant with the increase of the sand transport rate of smallsize particles(0.025mm and 0.5mm).