The Numerical Simulation Of Water And Sediment Two Phase Flow In Fen He Reservoir

Water is the source of life and a strategic resource.Solving water bottlenecks and providing water security are major strategic issues.Large coal mine reserves but water shortages are one of the issues that Shanxi cannot ignore at present.Without solving the water problems,Shanxi Province has strategic problems.In the context of Shanxi Province's comprehensive promotion of the"Five Waters Comprehensive Reform",as the largest reservoir in the Fenhe River Basin,Fenhe Reservoir has played an important role in the economic and social development of Shanxi.However,a large amount of sediment was deposited in the reservoir in the early stage of operation,which resulted in a significant reduction in effective storage capacity,seriously affected the benign performance of the reservoir's comprehensive benefits,and significantly increased the threat to the safety of the life and property of the people downstream of the reservoir.Therefore,in this paper,a two-dimensional water and sediment transport model is established to study the reservoir sediment transport law under different influencing factors,and the influence of runoff factors is the largest.Then,a three-dimensional hydrodynamic model is built to conduct a numerical simulation analysis of the three-dimensional movement law of the flood into the reservoir.This paper proposes a reasonable sediment management plan,which can provide a scientific basis for the operation management and reservoir scheduling of Fenhe Reservoir.The main research contents and results are as follows:(1)In this paper,the Fenhe Reservoir is used as a research vehicle,based on the electronic chart of the reservoir area,combined with the surrounding water and land environment to determine the simulation range,establish an unstructured triangular grid,and obtain the water depth numerical terrain file.Through the setting of various parameters such as roughness,source and sink terms,two-dimensional mathematical models of water and sand and three-dimensional flow are constructed respectively.This paper verifies the accuracy and rationality of the model based on the measured data.The verification results show that the root mean square error is within the allowable range of error.The simulated approximation of the established model meets the requirements and can be used in the numerical simulation of the reservoir;(2)Based on the existing hydrological data,comprehensively considering the various factors that affect the erosion and deposition changes in the reservoir area,combined with the sediment transport module,a two-dimensional hydrodynamic sediment transport coupling model was established.In this paper,three factors affecting the total amount of runoff,rainfall in the reservoir area,and different sources of water and sediment were designed to conduct single-factor control experiments.The Engelund-Hansen full-sand formula was used to evaluate the sediment transport and siltation status of the Fenhe Reservoir in the 2018 flood season.The evolution process of underwater landforms was simulated and analyzed.Two-dimensional water and sediment simulation results show that:1)After the water enters the reservoir area,the suspended sediment concentration and sediment transport rate gradually decrease as the sediment carrying capacity of the water decreases along the way.Contrary to the fact that the bed elevation of the Fenhe Reservoir area decreases along the way,the longitudinal sedimentation of the reservoir gradually increases along the way.The largest amount of siltation in front of the dam will affect the opening of the floodgate gate in the long run.2)Fenhe Reservoir includes two sources of water and sand:Fenhe River and Jianhe River.The vertical and horizontal erosion and siltation of the reservoir are mainly affected by the inflow and sediment of the Fenhe River.The inflow and sediment of the Jianhe river mainly affects the erosion and siltation of the 2#section,which has little impact on the upper part of the reservoir and the middle and lower parts of the reservoir It is also much smaller than the main stream of Fen River.The runoff into the reservoir during the flood season is an important factor that affects the vertical and horizontal siltation of the reservoir and the change of the concentration distribution of suspended sediment.Under the same conditions,the influence of the rainfall factor in the reservoir area can basically be ignored.Therefore,the study of the flow field distribution of the inflow in the flood season has a strong guiding role in the analysis of water and sediment transport laws.3)As of 2018,based on Surfer software calculation,the silt storage capacity of Fenhe Reservoir was 39.953 million m3,which exceeded the designed silt storage capacity of the reservoir by 54.53 million m~3,Sedimentation has occupied14.9%of the storage capacity that can exert comprehensive benefits,which had seriously affected the comprehensive benefits of the reservoir.(3)According to the complex geographic and boundary conditions of the reservoir,based on the three-dimensional hydrodynamic model and the flood data of the Fenhe Reservoir,this paper simulated and analyzed the Fenhe Reservoir at p=0.5%,1%,5%,20%,a total of 4 different frequencies During the flooding process,the three-dimensional flow field of the surface,middle and bottom layers of the reservoir area,as well as the changes in the water level and capacity of the reservoir with time and their relationship with each other.Intuitively shows the complex vertical and horizontal movement of the flood in the reservoir area.The simulation results of the three-dimensional flow model show that:1)Under different frequency flood conditions,the flow velocity law of the reservoir area is consistent:in the longitudinal direction,the flow velocity from the inlet to the front of the dam decreases significantly.In the vertical direction,the flow velocities in all parts of the reservoir area are in accordance with the law of decreasing gradually from the surface to the bottom.The flow velocity of each part of the reservoir area increases with the decrease of the flood frequency.Attention should be paid to protecting the bank slope of the reservoir to avoid the bank collapse caused by the severe erosion of the flood.The peak value and the average water level value both increase with the decrease of the flood frequency,and the difference between the two increases with the decrease of the flood frequency.The magnitude of the water level change is large,and the frequency of dynamic water pressure experienced by the dam is large.The risk has increased significantly.2)The flow velocity of each layer decreases significantly with the increase of the flood frequency,and the difference in flow velocity between the layers gradually decreases,indicating that as the flood frequency continues to increase,the water velocity gradually becomes uniform in the vertical direction.When the flood frequency P?20%,it can be generalized to two-dimensional flow for research.3)The appearance time of the peak water level lags behind the appearance time of the flood peak,and the lag time difference increases continuously with the decrease of the flood frequency.4)Due to the influence of the topography of the reservoir,the sensitivity of the reservoir capacity change affected by the water level gradually increases,and the unit change value of the reservoir capacity with the increase of the water level gradually increases.In this paper,the relationship curve between water level and storage capacity is obtained based on the least square method,which can provide a certain basis for the operation and management of the reservoir.(4)This article systematically studied the hydrodynamic conditions and the distribution rule of sediment erosion and silt in Fenhe Reservoir in flood season,and proposed the following silt reduction measures in view of the current sediment control measures of the upper and lower discharge of Fenhe Reservoir:Sediment:including emptying the reservoir to discharge sand and discharge the sediment through gravity flow;2)setting up submerged dams;conducive to the centralized cleaning of the sediment after the end of the flood season;3)doing a good job of water and soil conservation in the Fenhe River basin upstream of the reservoir To reduce the amount of sediment entering the reservoir from the source.The research in this paper can provide a strong theoretical basis and technical support for alleviating the sedimentation problem of the reservoir,prolonging the service life of the reservoir,and giving full play to the comprehensive benefits of the reservoir.