Sedimentation Efficiency Analysis Of Desilting Basin Under Different Inlet Boundary Conditions

The desilting basin at the head of the channel is one of the main measures for sediment treatment in muddy water irrigation area.As a channel system building connecting the outlet basin of the pumping station and the desilting basin,the channel at the transition section on the one hand makes the outlet flow rate of the pumping station slow enough to be gentle and stable,so that the flow velocity head entering the desilting basin does not affect the desilting efficiency.On the other hand,the sediment carrying capacity of the flow in the transition section must meet the various working conditions.The channel can not produce cumulative sedimentation.Due to the temporal and spatial changes of natural river water and sediment conditions and pumping station operating conditions,the flow and sediment conditions at the inlet of the settling basin(the end of the transition section channel)are also changing.Ideally,the flow elements of the transition section always change along the way,and tend to be uniform flow state at the end of the transition section channel.The sediment carrying state of the muddy water flow in the transition section should also be sub-saturated or at least balanced.However,the actual situation is that many large-scale irrigation areas in China have different degrees of sediment deposition in the transition section.The changes of sediment elements in the muddy water flow along the transition section are more complicated.In production practice,the quantitative and accurate level of sediment non-deposition design in this section needs to be improved urgently.It is of great practical significance to study the variation law of flow and sediment elements in the transition section of the outlet pool of the pumping station,to discuss and solve the relevant technical problems in the design of sediment non-deposition in the transition section,and to carry out the analysis and research on the influence of different flow and sediment boundary conditions at the inlet of the settling basin(the end of the transition section)on the settling efficiency of the settling basin,which is of great practical significance to the precise regulation of water and sediment in the muddy water canal irrigation area.The main contents and conclusions of this research work are :Firstly,based on the Geometry and Mesh modules in ANASYS-CFD,the geometric model is established and the grid is divided.Then,the RNG k-ε model and VOF model in Fluent software are used to establish a three-dimensional water flow model.The finite volume method is used to discretize the control equations,and the SIMPLE algorithm is used to couple the flow field and pressure field.The numerical simulation analysis of water flow in the outlet pool and transition section of the pumping station is carried out,and the analysis and determination method that can quantitatively describe the water flow movement elements in the transition section is obtained.Secondly,based on the results of the numerical simulation analysis of the flow in the transition section,based on the one-dimensional non-uniform suspended sediment unbalanced sediment transport control equation and other related basic theories of sediment movement,an analysis and calculation model that can quantitatively describe the variation characteristics of sediment particles with different particle sizes in the transition section channel is constructed.Then,aiming at the key problem of how to determine the recovery saturation coefficient when the unbalanced sediment transport theory of one-dimensional suspended non-uniform sediment is applied to the quantitative analysis of sediment movement characteristics in the transition section,the theoretical analysis and research are carried out.Based on the theoretical formula of the recovery saturation coefficient of academician Han Qiwei,the analysis and calculation method of the reasonable value of the recovery saturation coefficient in the transition section is given.Finally,based on the above-mentioned analysis and determination method of flow elements in the transition section,the analysis and calculation model of the motion characteristics of suspended non-uniform sediment in the transition section,and the in-depth study of the method for determining the value of the saturation recovery coefficient in the transition section,a calculation model and method for quantitatively analyzing and determining the characteristic values of flow and sediment elements at the end of the transition section(the inlet of the sedimentation tank)are constructed.Based on this,the calculation model and method are used as the basis for determining the change of water and sediment conditions at the inlet of the sedimentation tank,and the analysis and research on the sedimentation efficiency of the sedimentation tank under different inlet boundary conditions are carried out.This paper mainly takes the main working condition parameters of the first-stage pumping station at the head of the canal in Zuncun Irrigation District of Shanxi Province as the reference basis,constructs the research object through generalized analysis and carries out the research work.The analysis and calculation process and calculation model provided in this paper can provide reference for the accurate quantitative analysis of sediment transport in the transition section of similar projects,and also provide a method for the analysis and comparison of the relevant hydraulic geometric constraints based on the non-silting design of the transition section channel.Based on the quantitative analysis of the variation characteristics of flow and sediment elements along the transition section,the sediment deposition efficiency of the sediment basin under different inlet water and sediment conditions is accurately analyzed and determined,which can also provide a basis for the reasonable determination of the operation and management scheme of the sediment basin in the muddy water irrigation area.